Download Chapter 14:The Brain and Cranial Nerves

Chapter 14
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The Brain and
Cranial Nerves
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Introduction
• The human brain is complex
• Brain function is associated with life
• This chapter is a study of brain and cranial nerves
directly connected to it
• Will provide insight into brain circuitry and function
14-2
Introduction
• Aristotle thought brain was “radiator” to cool blood
• Hippocrates was more accurate: “from the brain only,
arises our pleasures, joys, laughter, and jests, as well
as our sorrows, pains, griefs, and tears”
• Cessation of brain activity—clinical criterion of death
• Evolution of the central nervous system shows spinal
cord has changed very little while brain has changed a
great deal
– Greatest growth in areas of vision, memory, and motor
control of the prehensile hand
14-3
Overview of the Brain
• Expected Learning Outcomes
– Describe the major subdivisions and anatomical
landmarks of the brain.
– Describe the locations of its gray and white matter.
– Describe the embryonic development of the CNS and
relate this to adult brain anatomy.
14-4
Major Landmarks
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• Rostral—toward the
forehead
Rostral
Caudal
Central sulcus
• Caudal—toward the spinal
cord
• Brain weighs about 1,600 g
(3.5 lb) in men, and 1,450 g
in women
Gyri
Cerebrum
Lateral sulcus
Cerebellum
Temporal lobe
Brainstem
Spinal cord
(b) Lateral view
Figure 14.1b
14-5
Major Landmarks
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• Three major portions of the
brain
– Cerebrum is 83% of brain
volume; cerebral hemispheres,
gyri and sulci, longitudinal
fissure, corpus callosum
Rostral
Caudal
Central sulcus
Gyri
Cerebrum
Lateral sulcus
– Cerebellum contains 50% of the Temporal lobe
neurons; second largest brain
region, located in posterior
cranial fossa
Brainstem
– Brainstem is the portion of the
brain that remains if the
cerebrum and cerebellum are
removed; diencephalon,
midbrain, pons, and medulla
oblongata
Cerebellum
Spinal cord
(b) Lateral view
Figure 14.1b
14-6
Major Landmarks
• Longitudinal fissure—deep
groove that separates
cerebral hemispheres
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• Gyri—thick folds
Frontal lobe
• Sulci—shallow grooves
Cerebral
hemispheres
Central sulcus
Parietal lobe
• Corpus callosum—thick
nerve bundle at bottom of
longitudinal fissure that
connects hemispheres
Occipital lobe
Longitudinal fissure
(a) Superior view
Figure 14.1a
14-7
Major Landmarks
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• Occupies posterior
cranial fossa
Rostral
Caudal
Central sulcus
• Marked by gyri,
sulci, and fissures
Gyri
Cerebrum
Lateral sulcus
Cerebellum
Temporal lobe
• About 10% of brain
volume
Brainstem
Spinal cord
(b) Lateral view
• Contains over 50% of
brain neurons
Figure 14.1b
14-8
Major Landmarks
• Brainstem—what
remains of the brain
if the cerebrum and
cerebellum are
removed
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Rostral
Caudal
Central sulcus
Gyri
Cerebrum
Lateral sulcus
Cerebellum
Temporal lobe
• Major components
Brainstem
– Diencephalon
– Midbrain
– Pons
Spinal cord
(b) Lateral view
Figure 14.1b
– Medulla oblongata
14-9
Major Landmarks
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Central sulcus
Parietal lobe
Cingulate gyrus
Corpus callosum
Parieto–occipital sulcus
Frontal lobe
Occipital lobe
Thalamus
Anterior
commissure
Hypothalamus
Habenula
Pineal gland
Optic chiasm
Posterior commissure
Mammillary body
Epithalamus
Cerebral aqueduct
Pituitary gland
Fourth ventricle
Temporal lobe
Cerebellum
Midbrain
Pons
Medulla
oblongata
(a)
Figure 14.2a
14-10
Major Landmarks
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Cingulate gyrus
Lateral ventricle
Corpus callosum
Parieto–occipital
sulcus
Choroid plexus
Pineal gland
Thalamus
Hypothalamus
Occipital lobe
Midbrain
Posterior
commissure
Pons
Fourth ventricle
Cerebellum
Medulla
oblongata
(b)
b: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
Figure 14.2b
14-11
Gray and White Matter
• Gray matter—the seat of neuron cell bodies,
dendrites, and synapses
– Dull white color when fresh, due to little myelin
– Forms surface layer (cortex) over cerebrum and
cerebellum
– Forms nuclei deep within brain
• White matter—bundles of axons
– Lies deep to cortical gray matter, opposite relationship
in the spinal cord
– Pearly white color from myelin around nerve fibers
– Composed of tracts, or bundles of axons, that connect
one part of the brain to another, and to the spinal cord
14-12
Embryonic Development
• Nervous system develops from ectoderm
– Outermost tissue layer of the embryo
• Early in third week of development
– Neuroectoderm: dorsal streak appears along the length of
embryo
– Thickens to form neural plate
• Destined to give rise to most neurons and all glial cells except
microglia, which come from mesoderm
• As thickening progresses
– Neural plate sinks and its edges thicken
• Forming a neural groove with a raised neural fold on each
side
• Neural folds fuse along the midline
– Beginning in the cervical region and progressing rostrally and
caudally
14-13
Embryonic Development
• By fourth week, creates a hollow channel—neural
tube
– Neural tube separates from overlying ectoderm
– Sinks deeper
– Grows lateral processes that later will form motor nerve
fibers
– Lumen of neural tube becomes fluid-filled space
• Central canal in spinal cord
• Ventricles of the brain
14-14
Embryonic Development
Cont.
• Neural crest—formed from ectodermal cells that lay
along the margins of the groove and separate from the
rest forming a longitudinal column on each side
– Gives rise to the two inner meninges, most of the
peripheral nervous system, and other structures of the
skeletal, integumentary, and endocrine systems
• By fourth week, the neural tube exhibits three anterior
dilations (primary vesicles)
– Forebrain (prosencephalon)
– Midbrain (mesencephalon)
– Hindbrain (rhombencephalon)
14-15
Embryonic Development
• By fifth week, it subdivides into five secondary vesicles
– Forebrain divides into two of them
• Telencephalon—becomes cerebral hemispheres
• Diencephalon—has optic vesicles that become retina of the
eye
– Midbrain remains undivided
• Mesencephalon
– Hindbrain divides into two vesicles
• Metencephalon
• Myelencephalon
14-16
Embryonic Development
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Neural plate
Neural crest
Neural crest
Neural fold
Ectoderm
Neural groove
Notochord
(a) 19 days
(b) 20 days
Neural
crest
Neural
tube
Somites
(c) 22 days
(d) 26 days
Figure 14.3
14-17
Embryonic Development
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• Fourth week
Telencephalon
Prosencephalon
Diencephalon
– Forebrain
– Midbrain
– Hindbrain
• Fifth week
–
–
–
–
–
Optic vesicle
Mesencephalon
Metencephalon
Rhombencephalon
Myelencephalon
Spinal cord
(a) 4 weeks
(b) 5 weeks
Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon
Telencephalon
Forebrain
Diencephalon
Mesencephalon
Midbrain
Pons
Metencephalon
Cerebellum
Hindbrain
Myelencephalon
(medulla oblongata)
Spinal cord
(c) Fully developed
Figure 14.4
14-18
Meninges, Ventricles, Cerebrospinal
Fluid, and Blood Supply
• Expected Learning Outcomes
– Describe the meninges of the brain.
– Describe the fluid-filled chambers within the brain.
– Discuss the production, circulation, and function of
the cerebrospinal fluid that fills these chambers.
– Explain the significance of the brain barrier system.
14-19
Meninges
• Meninges—three connective tissue
membranes that envelop the brain
– Lies between the nervous tissue and bone
– As in spinal cord, they are the dura mater,
arachnoid mater, and the pia mater
– Protect the brain and provide structural framework
for its arteries and veins
14-20
Meninges
• Dura mater
– In cranial cavity; has two layers
• Outer periosteal—equivalent to periosteum of cranial bones
• Inner meningeal—continues into vertebral canal and forms
dural sac around spinal cord
– Cranial dura mater is pressed closely against cranial
bones
• No epidural space
• Not attached to bone except: around foramen magnum, sella
turcica, the crista galli, and sutures of the skull
• Layers separated by dural sinuses—collect blood circulating
through brain
14-21
Meninges
Cont.
– Folds inward to extend between parts of the brain
• Falx cerebri separates the two cerebral hemispheres
• Tentorium cerebelli separates cerebrum from cerebellum
• Falx cerebelli separates the right and left halves of
cerebellum
14-22
Meninges
• Arachnoid mater and pia mater are similar to those in the
spinal cord
• Arachnoid mater
– Transparent membrane over brain surface
– Subarachnoid space separates it from pia mater below
– Subdural space separates it from dura mater above in some
places
• Pia mater
– Very thin membrane that follows contours of brain, even dipping into
sulci
– Not usually visible without a microscope
14-23
Meninges
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Skull
Dura mater:
Periosteal layer
Meningeal layer
Subdural space
Subarachnoid
space
Arachnoid granulation
Arachnoid mater
Superior sagittal
sinus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Pia mater
Brain:
Gray matter
White matter
Figure 14.5
14-24
Meningitis
• Meningitis—inflammation of the meninges
– Serious disease of infancy and childhood
– Especially between 3 months and 2 years of age
• Caused by bacterial and virus invasion of the CNS by way
of the nose and throat
• Pia mater and arachnoid are most often affected
• Bacterial meningitis can cause swelling of the brain,
enlargment of the ventricles, and hemorrhage
• Signs include high fever, stiff neck, drowsiness, and
intense headache; may progress to coma then death within
hours of onset
• Diagnosed by examining the CSF for bacteria
– Lumbar puncture (spinal tap) draws fluid from subarachnoid
space between two lumbar vertebrae
14-25
Ventricles and Cerebrospinal Fluid
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Caudal
Rostral
Lateral ventricles
Cerebrum
Interventricular
foramen
Lateral ventricle
Interventricular
foramen
Third ventricle
Third ventricle
Cerebral
aqueduct
Fourth ventricle
Cerebral
aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Lateral aperture
Median aperture
Central canal
(b) Anterior view
(a) Lateral view
Figure 14.6a,b
14-26
Ventricles and Cerebrospinal Fluid
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Rostral (anterior)
Longitudinal
fissure
Frontal lobe
Gray matter
(cortex)
White matter
Corpus callosum
(anterior part)
Lateral ventricle
Caudate nucleus
Septum
pellucidum
emporal
lobe
T
Third ventricle
Sulcus
Gyrus
Lateral sulcus
Insula
Thalamus
Lateral ventricle
Choroid plexus
Corpus callosum
(posterior part)
Occipital lobe
Longitudinal
fissure
Figure 14.6c
(c)
Caudal (posterior)
c: © The McGraw-Hill Companies, Inc./Rebecca Gray,photographer/Don Kincaid, dissections
14-27
Ventricles and Cerebrospinal Fluid
• Ventricles—four internal chambers within the brain
– Two lateral ventricles: one in each cerebral hemisphere
• Interventricular foramen—a tiny pore that connects to third
ventricle
– Third ventricle: single narrow medial space beneath corpus
callosum
• Cerebral aqueduct runs through midbrain and connects third to
fourth ventricle
– Fourth ventricle: small triangular chamber between pons
and cerebellum
• Connects to central canal, runs down through spinal cord
14-28
Ventricles and Cerebrospinal Fluid
Cont.
• Choroid plexus—spongy mass of blood capillaries on the
floor of each ventricle
• Ependyma—neuroglia that lines the ventricles and covers
choroid plexus
– Produces cerebrospinal fluid
14-29
Ventricles and Cerebrospinal Fluid
• Cerebrospinal fluid (CSF)—clear, colorless liquid that fills
the ventricles and canals of CNS
– Bathes its external surface
• Brain produces and absorbs 500 mL/day
–
–
–
–
100 to 160 mL normally present at one time
40% formed in subarachnoid space external to brain
30% by the general ependymal lining of the brain ventricles
30% by the choroid plexuses
• Production begins with the filtration of blood plasma through
the capillaries of the brain
– Ependymal cells modify the filtrate, so CSF has more sodium and
chloride than plasma, but less potassium, calcium, glucose, and very
little protein
14-30
Ventricles and Cerebrospinal Fluid
• CSF continually flows through and around the CNS
– Driven by its own pressure, beating of ependymal cilia,
and pulsations of the brain produced by each heartbeat
• CSF secreted in lateral ventricles flows through
intervertebral foramina into third ventricle
• Then down the cerebral aqueduct into the fourth
ventricle
• Third and fourth ventricles add more CSF along the
way
14-31
Ventricles and Cerebrospinal Fluid
• Small amount of CSF fills the central canal of the spinal
cord
– All escapes through three pores
• Median aperture and two lateral apertures
• Leads into subarachnoid space of brain and spinal
cord surface
• CSF is reabsorbed by arachnoid villi
– Cauliflower-shaped extension of the arachnoid meninx
– Protrudes through dura mater
– Into superior sagittal sinus
– CSF penetrates the walls of the villi and mixes with the
blood in the sinus
14-32
Ventricles and Cerebrospinal Fluid
• Functions of CSF
– Buoyancy
• Allows brain to attain considerable size without being impaired by
its own weight
• If it rested heavily on floor of cranium, the pressure would kill the
nervous tissue
– Protection
• Protects the brain from striking the cranium when the head is
jolted
• Shaken child syndrome and concussions do occur from
severe jolting
– Chemical stability
• Flow of CSF rinses away metabolic wastes from nervous tissue
and homeostatically regulates its chemical environment
14-33
Ventricles and Cerebrospinal Fluid
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Arachnoid villus
8
Superior
sagittal
sinus
Arachnoid mater
1 CSF is secreted by
choroid plexus in
each lateral ventricle.
Subarachnoid
space
Dura mater
1
2 CSF flows through
interventricular foramina
into third ventricle.
2
Choroid plexus
Third ventricle
3
3 Choroid plexus in third
ventricle adds more CSF.
7
4
Cerebral
aqueduct
4 CSF flows down cerebral
aqueduct to fourth ventricle.
Lateral aperture
5 Choroid plexus in fourth
ventricle adds more CSF.
Fourth ventricle
6
5
6 CSF flows out two lateral apertures
and one median aperture.
Median aperture
7 CSF fills subarachnoid space and
bathes external surfaces of brain
and spinal cord.
7
8 At arachnoid villi, CSF is reabsorbed
into venous blood of dural
venous sinuses.
Central canal
of spinal cord
Subarachnoid
space of
spinal cord
Figure 14.7
14-34
Blood Supply and the Brain
Barrier System
• Brain is only 2% of the adult body weight, and receives 15%
of the blood
– 750 mL/min.
• Neurons have a high demand for ATP, and therefore,
oxygen and glucose, so a constant supply of blood is critical
to the nervous system
– A 10-second interruption of blood flow may cause loss of
consciousness
– A 1- to 2-minute interruption can cause significant impairment
of neural function
– Going 4 minutes without blood causes irreversible brain
damage
14-35
Blood Supply and the Brain
Barrier System
• Blood is also a source of antibodies, macrophages,
bacterial toxins, and other harmful agents
• Brain barrier system—strictly regulates what
substances can get from the bloodstream into the
tissue fluid of the brain
• Two points of entry must be guarded
– Blood capillaries throughout the brain tissue
– Capillaries of the choroid plexus
14-36
Blood Supply and the Brain
Barrier System
• Blood–brain barrier—protects blood capillaries
throughout brain tissue
– Consists of tight junctions between endothelial cells that
form the capillary walls
– Astrocytes reach out and contact capillaries with their
perivascular feet
– Induce the endothelial cells to form tight junctions that
completely seal off gaps between them
– Anything leaving the blood must pass through the cells,
and not between them
– Endothelial cells can exclude harmful substances from
passing to the brain tissue while allowing necessary ones
to pass
14-37
Blood Supply and the Brain
Barrier System
• Blood–CSF barrier—protects the brain at the choroid
plexus
– Forms tight junctions between the ependymal cells
– Tight junctions are absent from ependymal cells
elsewhere
• Important to allow exchange between brain tissue and CSF
• Blood barrier system is highly permeable to water,
glucose, and lipid-soluble substances such as oxygen,
carbon dioxide, alcohol, caffeine, nicotine, and
anesthetics
• Slightly permeable to sodium, potassium, chloride, and
the waste products urea and creatinine
14-38
Blood Supply and the Brain
Barrier System
• Obstacle for delivering medications such as antibiotics
and cancer drugs
• Trauma and inflammation can damage BBS and allow
pathogens to enter brain tissue
– Circumventricular organs (CVOs)—places in the third
and fourth ventricles where the barrier is absent
• Blood has direct access to the brain
• Enables the brain to monitor and respond to fluctuations in
blood glucose, pH, osmolarity, and other variables
• CVOs afford a route for invasion by the human
immunodeficiency virus (HIV)
14-39
The Hindbrain and Midbrain
• Expected Learning Outcomes
– List the components of the hindbrain and midbrain and
their functions.
– Describe the location and functions of the reticular
formation.
14-40
The Medulla Oblongata
• Embryonic myelencephalon
becomes medulla oblongata
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Central sulcus
Parietal lobe
Cingulate gyrus
Corpus callosum
• Begins at foramen magnum of
the skull
Parieto–occipital sulcus
Frontal lobe
Occipital lobe
Thalamus
Anterior
commissure
Hypothalamus
Habenula
Pineal gland
Optic chiasm
Posterior commissure
Mammillary body
Epithalamus
Cerebral aqueduct
Pituitary gland
• Extends for about 3 cm rostrally
and ends at a groove between
the medulla and pons
• Slightly wider than spinal cord
Fourth ventricle
Temporal lobe
Midbrain
Cerebellum
Pons
Medulla
oblongata
(a)
Figure 14.2a
• Pyramids—pair of external
ridges on anterior surface
– Resembles side-by-side
baseball bats
14-41
The Medulla Oblongata
• Olive—a prominent bulge
lateral to each pyramid
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Central sulcus
Parietal lobe
Cingulate gyrus
Corpus callosum
Parieto–occipital sulcus
Frontal lobe
• Posteriorly, gracile and
cuneate fasciculi of the
spinal cord continue as two
pair of ridges on the medulla
Occipital lobe
Thalamus
Anterior
commissure
Hypothalamus
Optic chiasm
Mammillary body
Pituitary gland
Temporal lobe
Habenula
Pineal gland
Epithalamus
Posterior commissure
Cerebral aqueduct
Fourth ventricle
Midbrain
Cerebellum
Pons
Medulla
oblongata
• All nerve fibers connecting
the brain to the spinal cord
pass through the medulla
(a)
Figure 14.2a
• Four pairs of cranial
nerves begin or end in
medulla—IX, X, XI, XII
14-42
The Medulla Oblongata
• Cardiac center
– Adjusts rate and force of heart
• Vasomotor center
– Adjusts blood vessel diameter
• Respiratory centers
– Control rate and depth of breathing
• Reflex centers
– For coughing, sneezing, gagging, swallowing, vomiting,
salivation, sweating, movements of tongue and head
14-43
The Medulla Oblongata
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(a) Midbrain
(b) Pons
(c) Medulla
Nucleus of
hypoglossal nerve
Gracile nucleus
Fourth ventricle
Cuneate nucleus
Nucleus of
vagus nerve
Dorsal spinocerebellar
tract
Trigeminal nerve:
Nucleus
Tract
Reticular formation
Tectospinal tract
Medial lemniscus
Inferior olivary
nucleus
Olive
Hypoglossal nerve
Pyramids of medulla
Corticospinal tract
(c) Medulla oblongata
Figure 14.9c
• Pyramids contain descending fibers called corticospinal tracts
– Carry motor signals to skeletal muscles
• Inferior olivary nucleus—relay center for signals to cerebellum
• Reticular formation—loose network of nuclei extending throughout
the medulla, pons, and midbrain
– Contains cardiac, vasomotor, and respiratory centers
14-44
The Medulla Oblongata
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Diencephalon:
Thalamus
Infundibulum
Optic tract
Mammillary body
Cranial nerves:
Midbrain:
Optic nerve (II)
Cerebral peduncle
Oculomotor nerve (III)
Trochlear nerve (IV)
Trigeminal nerve (V)
Abducens nerve (VI)
Pons
Facial nerve (VII)
Vestibulocochlear nerve (VIII)
Glossopharyngeal nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Medulla oblongata:
Pyramid
Hypoglossal nerve (XII)
Anterior median fissure
Regions of the brainstem
Diencephalon
Midbrain
Pyramidal decussation
Spinal nerves
Spinal cord
Pons
Medulla oblongata
(a) Ventral view
Figure 14.8a
14-45
The Pons
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Regions of the brainstem
Diencephalon
Midbrain
Pons
Medulla oblongata
Diencephalon:
Thalamus
Lateral geniculate body
Pineal gland
Medial geniculate body
Optic tract
Midbrain:
Superior colliculus
Inferior colliculus
Cerebral peduncle
Pons
Superior cerebellar
peduncle
Middle cerebellar
peduncle
Fourth ventricle
Inferior cerebellar
peduncle
Olive
Medulla
oblongata
Cuneate fasciculus
Gracile fasciculus
Spinal cord
(b) Dorsolateral view
Figure 14.8b
14-46
The Pons
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Central sulcus
Parietal lobe
Cingulate gyrus
Corpus callosum
Parieto–occipital sulcus
Frontal lobe
Occipital lobe
Thalamus
Anterior
commissure
Hypothalamus
Habenula
Pineal gland
Epithalamus
Posterior commissure
Optic chiasm
Mammillary body
Cerebral aqueduct
Pituitary gland
Fourth ventricle
Temporal lobe
Midbrain
Cerebellum
Pons
Medulla
oblongata
(a)
Figure 14.2a
• Metencephalon—develops into the pons and cerebellum
• Pons—anterior bulge in brainstem, rostral to medulla
• Cerebral peduncles—connect cerebellum to pons and midbrain
14-47
The Pons
• Ascending sensory tracts
• Descending motor tracts
• Pathways in and out of cerebellum
• Cranial nerves V, VI, VII, and VIII
– Sensory roles: hearing, equilibrium, taste, facial
sensations
– Motor roles: eye movement, facial expressions,
chewing, swallowing, urination, and secretion of saliva
and tears
• Reticular formation in pons contains additional
nuclei concerned with sleep, respiration, posture
14-48
The Pons
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(a) Midbrain
(b) Pons
(c) Medulla
Vermis of cerebellum
Fourth ventricle
Superior cerebellar
peduncle
Middle cerebellar
peduncle
Ventral
spinocerebellar tract
Tectospinal tract
Trigeminal nerve nuclei
Anterolateral system
Sensory root of
trigeminal nerve
Trigeminal nerve
Reticular formation
Transverse fascicles
Medial lemniscus
Longitudinal fascicles
(b) Pons
Figure 14.9b
14-49
The Midbrain
• Mesencephalon becomes one mature brain
structure, the midbrain
– Short segment of brainstem that connects the hindbrain
to the forebrain
– Contains cerebral aqueduct
– Contains continuations of the medial lemniscus and
reticular formation
– Contains the motor nuclei of two cranial nerves that
control eye movements: CN III (oculomotor) and CN IV
(trochlear)
14-50
The Midbrain
• Mesencephalon (cont.)
– Tectum: rooflike part of the midbrain posterior to
cerebral aqueduct
• Exhibits four bulges, the corpora quadrigemina
• Upper pair, the superior colliculi, function in visual
attention, tracking moving objects, and some reflexes
• Lower pair, the inferior colliculi, receives signals from
the inner ear
– Relays them to other parts of the brain, especially the
thalamus
14-51
The Midbrain
Cont.
– Cerebral peduncles: two stalks that anchor the
cerebrum to the brainstem anterior to the cerebral
aqueduct
• Cerebral peduncles—three main components
– Tegmentum
• Dominated by the red nucleus
• Pink color due to high density of blood vessels
• Connections go to and from cerebellum
• Collaborates with cerebellum for fine motor control
14-52
The Midbrain
– Substantia nigra
• Dark gray to black nucleus pigmented with melanin
• Motor center that relays inhibitory signals to thalamus and
basal nuclei preventing unwanted body movement
• Degeneration of neurons leads to tremors of Parkinson
disease
– Cerebral crus
• Bundle of nerve fibers that connect the cerebrum to the
pons
• Carries corticospinal tracts
14-53
The Midbrain
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Posterior
Superior colliculus
Tectum
Cerebral aqueduct
Medial geniculate nucleus
Reticular formation
Central gray matter
Cerebral peduncle:
Oculomotor nucleus
Medial lemniscus
Tegmentum
Red nucleus
Substantia nigra
(a) Midbrain
Cerebral crus
Oculomotor nerve (III)
(b) Pons
Anterior
(c) Medulla
(a) Midbrain
Figure 14.9a
14-54
The Reticular Formation
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Radiations to
cerebral cortex
Thalamus
Auditory input
Visual input
Reticular formation
Ascending general
sensory fibers
Descending motor
fibers to spinal cord
Figure 14.10
• Loosely organized web of
gray matter that runs
vertically through all levels of
the brainstem
• Clusters of gray matter
scattered throughout pons,
midbrain, and medulla
• Occupies space between
white fiber tracts and
brainstem nuclei
• Has connections with many
areas of cerebrum
– More than 100 small neural
networks without distinct
boundaries
14-55
The Reticular Formation
• Networks
– Somatic motor control
• Adjust muscle tension to maintain tone, balance, and
posture
• Especially during body movements
• Relays signals from eyes and ears to the cerebellum
• Integrates visual, auditory, and balance and motion
stimuli into motor coordination
• Gaze center—allows eyes to track and fixate on
objects
• Central pattern generators—neural pools that
produce rhythmic signals to the muscles of breathing
and swallowing
14-56
The Reticular Formation
Cont.
– Cardiovascular control
• Includes cardiac and vasomotor centers of medulla
oblongata
– Pain modulation
• One route by which pain signals from the lower body
reach the cerebral cortex
• Origin of descending analgesic pathways—fibers act
in the spinal cord to block transmission of pain signals
to the brain
14-57
The Reticular Formation
– Sleep and consciousness
• Plays central role in states of consciousness, such as
alertness and sleep
• Injury to reticular formation can result in irreversible
coma
– Habituation
• Process in which the brain learns to ignore repetitive,
inconsequential stimuli while remaining sensitive to
others
14-58
The Cerebellum
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Anterior
Vermis
Anterior lobe
Posterior lobe
Cerebellar
hemisphere
Folia
Posterior
Figure 14.11b
(b) Superior view
• The largest part of the hindbrain and the second largest part of the brain
as a whole
• Consists of right and left cerebellar hemispheres connected by vermis
• Cortex of gray matter with folds (folia) and four deep nuclei in each
hemisphere
• Contains more than half of all brain neurons—about 100 billion
– Granule cells and Purkinje cells synapse on deep nuclei
• White matter branching pattern is called arbor vitae
14-59
The Cerebellum
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Superior colliculus
Inferior colliculus
Pineal gland
Posterior commissure
Cerebral aqueduct
Mammillary body
Midbrain
White matter
(arbor vitae)
Gray matter
Oculomotor nerve
Fourth ventricle
Pons
Medulla oblongata
Figure 14.11a
(a) Median section
• Cerebellar peduncles—three pairs of stalks that connect the cerebellum
to the brainstem
– Inferior peduncles: connected to medulla oblongata
• Most spinal input enters the cerebellum through inferior peduncle
– Middle peduncles: connected to the pons
• Most input from the rest of the brain enters by way of middle peduncle
– Superior peduncles: connected to the midbrain
• Carries cerebellar output
• Consist of thick bundles of nerve fibers that carry signals to and from
the cerebellum
14-60
The Cerebellum
• Monitors muscle contractions and aids in motor coordination
• Evaluation of sensory input
– Comparing textures without looking at them
– Spatial perception and comprehension of different views of threedimensional objects belonging to the same object
• Timekeeping center
– Predicting movement of objects
– Helps predict how much the eyes must move in order to compensate
for head movements and remain fixed on an object
14-61
The Cerebellum
Cont.
• Hearing
– Distinguish pitch and similar-sounding words
• Planning and scheduling tasks
• Lesions may result in emotional overreactions and trouble
with impulse control
14-62
The Forebrain
• Expected Learning Outcomes
– Name the three major components of the diencephalon
and describe their locations and functions.
– Identify the five lobes of the cerebrum and their functions.
– Identify the three types of tracts in the cerebral white
matter.
– Describe the distinctive cell types and histological
arrangement of the cerebral cortex.
– Describe the location and functions of the basal nuclei
and limbic system.
14-63
The Forebrain
• Forebrain consists of two
parts
– Diencephalon
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• Encloses the third
ventricle
Telencephalon
Forebrain
• Most rostral part of the
brainstem
Diencephalon
Mesencephalon
Pons
Metencephalon
Cerebellum
• Has three major
embryonic derivatives
– Thalamus
– Hypothalamus
– Epithalamus
– Telencephalon
Midbrain
Hindbrain
Myelencephalon
(medulla oblongata)
Spinal cord
(c) Fully developed
Figure 14.4c
• Develops chiefly into the
cerebrum
14-64
The Diencephalon: Thalamus
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Thalamic Nuclei
Anterior group
Part of limbic system;
memory and emotion
Medial group
Emotional output to prefrontal
cortex; awareness of emotions
Ventral group
Somesthetic output to
postcentral gyrus; signals
from cerebellum and basal
nuclei to motor areas of cortex
Lateral group
Somesthetic output to
association areas of cortex;
contributes to emotional function
of limbic system
Posterior group
Relay of visual signals to
occipital lobe (via lateral
geniculate nucleus) and auditory
signals to temporal lobe (via
medial geniculate nucleus)
Lateral geniculate nucleus
Medial geniculate nucleus
(a) Thalamus
Figure 14.12a
• Thalamus—ovoid mass on each side of the brain perched at the
superior end of the brainstem beneath the cerebral hemispheres
– Constitutes about four-fifths of the diencephalon
– Two thalami are joined medially by a narrow intermediate mass
– Composed of at least 23 nuclei; to consider five major functional groups
14-65
The Diencephalon: Thalamus
Cont.
– “Gateway to the cerebral cortex”: nearly all input to the
cerebrum passes by way of synapses in the thalamic
nuclei, filters information on its way to cerebral cortex
– Plays key role in motor control by relaying signals from
cerebellum to cerebrum and providing feedback loops
between the cerebral cortex and the basal nuclei
– Involved in the memory and emotional functions of the
limbic system: a complex of structures that include some
cerebral cortex of the temporal and frontal lobes and some
of the anterior thalamic nuclei
14-66
The Diencephalon: Hypothalamus
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• Hypothalamus—forms part
of the walls and floor of the
third ventricle
• Extends anteriorly to optic
chiasm and posteriorly to
the paired mammillary
bodies
Central sulcus
Parietal lobe
Cingulate gyrus
Corpus callosum
Parieto–occipital sulcus
Frontal lobe
Occipital lobe
Thalamus
Anterior
commissure
Hypothalamus
Optic chiasm
Mammillary body
Pituitary gland
Temporal lobe
Habenula
Pineal gland
Epithalamus
Posterior commissure
Cerebral aqueduct
Fourth ventricle
Cerebellum
Midbrain
Pons
Medulla
oblongata
(a)
Figure 14.2a
• Each mammillary body
contains three or four
mammillary nuclei
– Relay signals from the
limbic system to the
thalamus
14-67
The Diencephalon: Hypothalamus
• Infundibulum—a stalk that attaches the pituitary gland to the
hypothalamus
• Major control center of autonomic nervous system and
endocrine system
– Plays essential role in homeostatic regulation of all body systems
• Functions of hypothalamic nuclei
– Hormone secretion
• Controls anterior pituitary
• Regulates growth, metabolism, reproduction, and stress responses
14-68
The Diencephalon: Hypothalamus
Cont.
– Hormone secretion
• Controls anterior pituitary
• Regulates growth, metabolism, reproduction, and stress responses
– Autonomic effects
• Major integrating center for autonomic nervous system
• Influences heart rate, blood pressure, gastrointestinal secretions,
motility, etc.
– Thermoregulation
• Hypothalamic thermostat monitors body temperature
• Activates heat-loss center when temp is too high
• Activates heat-promoting center when temp is too low
14-69
The Diencephalon: Hypothalamus
Cont.
– Food and water intake
• Hunger and satiety centers monitor blood glucose and amino
acid levels
– Produce sensations of hunger and satiety
• Thirst center monitors osmolarity of the blood
– Rhythm of sleep and waking
• Controls 24-hour (circadian) rhythm of activity
– Memory
• Mammillary nuclei receive signals from hippocampus
– Emotional behavior
• Anger, aggression, fear, pleasure, and contentment
14-70
The Diencephalon: Epithalamus
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Central sulcus
Parietal lobe
Cingulate gyrus
Corpus callosum
Parieto–occipital sulcus
Frontal lobe
Occipital lobe
Thalamus
Anterior
commissure
Hypothalamus
Habenula
Pineal gland
Epithalamus
Posterior commissure
Optic chiasm
Mammillary body
Cerebral aqueduct
Pituitary gland
Fourth ventricle
Temporal lobe
Midbrain
Cerebellum
Pons
Medulla
oblongata
(a)
Figure 14.2a
• Epithalamus—very small mass of tissue composed of:
– Pineal gland: endocrine gland
– Habenula: relay from the limbic system to the midbrain
– Thin roof over the third ventricle
14-71
The Telencephalon: Cerebrum
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Central sulcus
Parietal lobe
Cingulate gyrus
Corpus callosum
Parieto–occipital sulcus
Frontal lobe
Occipital lobe
Thalamus
Anterior
commissure
Hypothalamus
Habenula
Pineal gland
Epithalamus
Posterior commissure
Optic chiasm
Mammillary body
Cerebral aqueduct
Pituitary gland
Fourth ventricle
Temporal lobe
Midbrain
Cerebellum
Pons
Medulla
oblongata
Figure 14.2a
(a)
• Cerebrum—largest and most conspicuous part of the human
brain
– Seat of sensory perception, memory, thought, judgment, and
voluntary motor actions
14-72
The Cerebrum
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Cerebral
hemispheres
Rostral
Caudal
Central sulcus
Frontal lobe
Gyri
Cerebrum
Lateral sulcus
Central sulcus
Cerebellum
Temporal lobe
Parietal lobe
Brainstem
Occipital lobe
Longitudinal fissure
(a) Superior view
Figure 14.1a,b
Spinal cord
(b) Lateral view
• Two cerebral hemispheres divided by longitudinal fissure
–
–
–
–
Connected by white fibrous tract, the corpus callosum
Gyri and sulci: increase amount of cortex in the cranial cavity
Gyri increases surface area for information-processing capability
Some sulci divide each hemisphere into five lobes named for the
cranial bones overlying them
14-73
The Cerebrum
• Frontal lobe
– Voluntary motor functions
– Motivation, foresight,
planning, memory, mood,
emotion, social judgment,
and aggression
• Parietal lobe
– Receives and integrates
general sensory information,
taste, and some visual
Precentral
gyrus
processing
• Occipital lobe
– Primary visual center of Central
sulcus
brain
Insula
• Temporal lobe
– Areas for hearing, smell,
learning, memory, and
some aspects of vision and
emotion
• Insula (hidden by other
regions)
– Understanding spoken
language, taste and sensory
information from visceral
receptors
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Rostral
Caudal
Frontal lobe
Parietal lobe
Postcentral gyrus
Occipital lobe
Lateral sulcus
Temporal lobe
14-74
Tracts of Cerebral White Matter
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Association tracts
Projection tracts
Frontal lobe
Corpus callosum
Parietal lobe
Temporal lobe
Occipital lobe
(a) Sagittal section
Longitudinal fissure
Corpus callosum
Commissural tracts
Lateral ventricle
Thalamus
Basal nuclei
Third ventricle
Mammillary body
Cerebral peduncle
Pons
Projection tracts
Pyramid
Decussation in pyramids
Medulla oblongata
(b) Frontal section
Figure 14.14
14-75
The Cerebral White Matter
• Most of the volume of cerebrum is white matter
– Glia and myelinated nerve fibers transmitting
signals from one region of the cerebrum to another
and between cerebrum and lower brain centers
14-76
The Cerebral White Matter
• Three types of tracts
– Projection tracts
• Extends vertically between higher and lower brain and
spinal cord centers
• Carries information between cerebrum and rest of the body
– Commissural tracts
• Cross from one cerebral hemisphere through bridges called
commissures
– Most pass through corpus callosum
– Anterior and posterior commissures
– Enables the two sides of the cerebrum to communicate with
each other
14-77
The Cerebral White Matter
Cont.
– Association tracts
• Connect different regions within the same cerebral
hemisphere
• Long association fibers—connect different lobes of a
hemisphere to each other
• Short association fibers—connect different gyri within a
single lobe
14-78
The Cerebral Cortex
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Neural integration is
carried out in the gray
matter of the cerebrum
Figure 14.15
Cortical surface
• Cerebral gray matter
found in three places
– Cerebral cortex
– Basal nuclei
– Limbic system
I
Small pyramidal
cells
II
III
Stellate cells
IV
Large pyramidal
cells
V
VI
White
matter
14-79
The Cerebral Cortex
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Cerebral cortex—layer
covering the surface of
the hemispheres
– Only 2 to 3 mm thick
– Cortex constitutes about
40% of brain mass
– Contains 14 to 16 billion
neurons
Figure 14.15
Cortical surface
I
Small pyramidal
cells
II
III
Stellate cells
IV
Large pyramidal
cells
V
VI
White
matter
14-80
The Cerebral Cortex
• Contains two principal types of neurons
– Stellate cells
• Have spheroid somas with dendrites projecting in all
directions
• Receive sensory input and process information on a local
level
– Pyramidal cells
• Tall, and conical, with apex toward the brain surface
• A thick dendrite with many branches with small, knobby
dendritic spines
• Include the output neurons of the cerebrum
• Only neurons that leave the cortex and connect with other
parts of the CNS.
14-81
The Cerebral Cortex
• Neocortex—six-layered tissue that constitutes about
90% of the human cerebral cortex
– Relatively recent in evolutionary origin
14-82
The Basal Nuclei
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Cerebrum
Corpus callosum
Lateral ventricle
Thalamus
Internal capsule
Caudate nucleus
Insula
Putamen
Lentiform
nucleus
Third ventricle
Globus pallidus
Hypothalamus
Subthalamic nucleus
Optic tract
Pituitary gland
Corpus
striatum
Figure 14.16
• Basal nuclei—masses of cerebral gray matter buried deep
in the white matter, lateral to the thalamus
– Receives input from the substantia nigra of the midbrain and
the motor areas of the cortex
– Send signals back to both these locations
– Involved in motor control
14-83
The Basal Nuclei
• At least three brain centers form basal nuclei
– Caudate nucleus
– Putamen
– Globus pallidus
• Lentiform nucleus—putamen and globus pallidus collectively
• Corpus striatum—putamen and caudate nucleus collectively
14-84
The Limbic System
• Limbic system—important
center of emotion and
learning
• Most anatomically prominent
components are:
– Cingulate gyrus: arches
over the top of the corpus
callosum in the frontal and
parietal lobes
– Hippocampus: in the
medial temporal lobe;
memory
– Amygdala: immediately
rostral to the hippocampus;
emotion
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Medial
prefrontal
cortex
Corpus
callosum
Cingulate
gyrus
Fornix
Orbitofrontal
cortex
Mammillary
body
Hippocampus
Thalamic
nuclei
Basal nuclei
Amygdala
Temporal lobe
Figure 14.17
14-85
The Limbic System
• Limbic system components
are connected through a
complex loop of fiber tracts
allowing for somewhat
circular patterns of
feedback
• Limbic system structures
have centers for both
gratification and aversion
– Gratification: sensations
of pleasure or reward
– Aversion: sensations of
fear or sorrow
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Medial
prefrontal
cortex
Corpus
callosum
Cingulate
gyrus
Fornix
Orbitofrontal
cortex
Mammillary
body
Hippocampus
Thalamic
nuclei
Basal nuclei
Amygdala
Temporal lobe
Figure 14.17
14-86
Integrative Functions of the Brain
• Expected Learning Outcomes
– List the types of brain waves and discuss their
relationship to mental states.
– Describe the stages of sleep, their relationship to the
brain waves, and the neural mechanisms of sleep.
– Identify the brain regions concerned with consciousness
and thought, memory, emotion, sensation, motor control,
and language.
– Discuss the functional differences between the right and
left cerebral hemispheres.
14-87
Integrative Functions of the Brain
• Higher brain functions—sleep, memory, cognition,
emotion, sensation, motor control, and language
• Involve interactions between cerebral cortex and
basal nuclei, brainstem, and cerebellum
• Functions of the brain do not have easily defined
anatomical boundaries
• Integrative functions of the brain focus mainly on
the cerebrum, but involve combined action of
multiple brain levels
14-88
The Electroencephalogram
• Alpha waves 8 to 13 Hz
– Awake and resting with eyes closed and mind wandering
– Suppressed when eyes open or performing a mental task
• Beta waves 14 to 30 Hz
– Eyes open and performing mental tasks
– Accentuated during mental activity and sensory stimulation
• Theta waves 4 to 7 Hz
– Drowsy or sleeping adults
– If awake and under emotional stress
• Delta waves (high amplitude) <3.5 Hz
– Deep sleep in adults
14-89
The Electroencephalogram
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Alpha ()
Beta ()
Theta ()
Delta (δ)
Figure 14.18a
(b)
1 second
Figure 14.18b
• Electroencephalogram (EEG)—monitors surface electrical activity
of the brain waves
– Useful for studying normal brain functions as sleep and
consciousness
– In diagnosis of degenerative brain diseases, metabolic
abnormalities, brain tumors, etc.
14-90
The Electroencephalogram
Cont.
• Brain waves—rhythmic voltage changes resulting from
synchronized postsynaptic potentials at the superficial
layer of the cerebral cortex
– Four types distinguished by amplitude (mV) and
frequency (Hz)
• Persistent absence of brain waves is common clinical and
legal criterion of brain death
14-91
Sleep
• Sleep occurs in cycles called circadian rhythms
– Events that reoccur at intervals of about 24 hours
• Sleep—temporary state of unconsciousness from which one
can awaken when stimulated
– Characterized by stereotyped posture
• Lying down with eyes closed
– Sleep paralysis: inhibition of muscular activity
– Resembles unconsciousness but can be aroused by sensory
stimulation
– Coma or hibernation: states of prolonged unconsciousness where
individuals cannot be aroused by sensory stimulation
14-92
Sleep
Cont.
• Restorative effect
– Brain glycogen and ATP levels increase in non-REM sleep
– Memories strengthened in REM sleep
• Synaptic connections reinforced
• Four stages of sleep
– Stage 1
• Feel drowsy, close eyes, begin to relax
• Often feel drifting sensation, easily awakened if stimulated
• Alpha waves dominate EEG
14-93
Sleep
Cont.
– Stage 2
• Pass into light sleep
• EEG declines in frequency but increases in amplitude
• Exhibits sleep spindles—high spikes resulting from
interactions between neurons of the thalamus and cerebral
cortex
– Stage 3
•
•
•
•
Moderate to deep sleep
About 20 minutes after stage 1
Theta and delta waves appear
Muscles relax and vital signs fall (body temperature, blood
pressure, heart and respiratory rates)
14-94
Sleep
Cont.
– Stage 4
• Called slow-wave sleep (SWS)—EEG dominated by lowfrequency, high-amplitude delta waves
• Muscles now very relaxed, vital signs at their lowest, and
more difficult to awaken
• About five times a night, a sleeper backtracks from stage 3
or 4 to stage 2
– Exhibits bouts of rapid eye movement (REM) sleep, eyes
oscillate back and forth
– Also called paradoxical sleep, because EEG resembles the
waking state, but sleeper is harder to arouse than any other
stage
14-95
Sleep
Cont.
– Vital signs increase, brain uses more oxygen than when
awake
– Sleep paralysis stronger to prevent sleeper from acting out
dreams
• Dreams occur in both REM and non-REM sleep
– REM tends to be longer and more vivid
• Parasympathetic nervous system active during REM sleep
– Causing constriction of the pupils
– Erection of the penis and clitoris
14-96
Sleep
• Rhythm of sleep is controlled by a complex interaction
between the cerebral cortex, thalamus, hypothalamus,
and reticular formation
– Arousal induced in the upper reticular formation, near
junction of pons and midbrain
– Sleep induced by nuclei below pons, and in ventrolateral
preoptic nucleus in the hypothalamus
14-97
Sleep
• Suprachiasmatic nucleus (SCN)—another important
control center for sleep
– Above optic chiasma in anterior hypothalamus
– Input from eye allows SCN to synchronize multiple body
rhythms with external rhythms of night and day
• Sleep, body temperature, urine production, secretion, and
other functions
14-98
Sleep
• Sleep has a restorative effect, and sleep deprivation can be
fatal to experimental animals
– Bed rest alone does not have the restorative effect of sleep—
why must we lose consciousness?
– Sleep may be the time to replenish such energy sources as
glycogen and ATP
– REM sleep may consolidate and strengthen memories by
reinforcing some synapses, and eliminating others
14-99
Sleep Stages and Brain Activity
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Awake
Sleep spindles
REM
sleep
Stage
Stage 1
Drowsy
Stage 2
Light sleep
Stage 3
Moderate to
deep sleep
Stage 4
Deepest sleep
0
10
20
30
40
50
60
70
Time (min.)
(a) One sleep cycle
Awake
EEG stages
REM
REM
REM
REM
REM
Stage 1
Stage 2
Stage 3
Stage 4
0
1
(b) Typical 8-hour sleep period
2
3
4
5
6
7
8
Time (hours)
Figure 14.19
14-100
Cognition
• Cognition—the range of mental processes by
which we acquire and use knowledge
– Such as sensory perception, thought, reasoning,
judgment, memory, imagination, and intuition
• Association areas of cerebral cortex have
above functions
– Constitute about 75% of all brain tissue
14-101
Cognition
• Studies of patients with brain lesions, cancer, stroke,
and trauma yield information on cognition
– Parietal lobe association area: perceiving stimuli
• Contralateral neglect syndrome—unaware of objects
on opposite side of the body
– Temporal lobe association area: identifying stimuli
• Agnosia—inability to recognize, identify, and name
familiar objects
• Prosopagnosia—person cannot remember familiar faces
– Frontal lobe association area: planning our responses
and personality; inability to execute appropriate behavior
14-102
Memory
• Information management entails:
– Learning: acquiring new information
– Memory: information storage and retrieval
– Forgetting: eliminating trivial information; as important
as remembering
• Amnesia—defects in declarative memory: inability to
describe past events
• Procedural memory—ability to tie one’s shoes
– Anterograde amnesia: unable to store new information
– Retrograde amnesia: person cannot recall things
known before the injury
14-103
Memory
• Hippocampus—important memory-forming center
– Does not store memories
– Organizes sensory and cognitive information into a unified
long-term memory
– Memory consolidation: the process of “teaching the cerebral
cortex” until a long-term memory is established
– Long-term memories are stored in various areas of the
cerebral cortex
14-104
Memory
Cont.
– Vocabulary and memory of familiar faces stored in superior
temporal lobe
– Memories of one’s plans and social roles stored in the
prefrontal cortex
• Cerebellum—helps learn motor skills
• Amygdala—emotional memory
14-105
Accidental Lobotomy
• Phineas Gage—railroad
construction worker; severe
injury with metal rod
• Injury to the ventromedial
region of both frontal lobes
• Extreme personality change
– Fitful, irreverent, grossly profane
– Opposite of previous personality
• Prefrontal cortex functions
– Planning, moral judgment, and
emotional control
Figure 14.20
14-106
Emotion
• Emotional feelings and memories are interactions
between prefrontal cortex and diencephalon
• Prefrontal cortex—seat of judgment, intent, and
control over expression of emotions
• Feelings come from hypothalamus and amygdala
– Nuclei generate feelings of fear or love
14-107
Emotion
• Amygdala receives input from sensory systems
– Role in food intake, sexual behavior, and drawing
attention to novel stimuli
– One output goes to hypothalamus influencing somatic
and visceral motor systems
• Heart races, raises blood pressure, makes hair stand on
end, induces vomiting
– Other output to prefrontal cortex important in
controlling expression of emotions
• Ability to express love, control anger, or overcome fear
• Behavior shaped by learned associations between
stimuli, our responses to them, and the reward or
punishment that results
14-108
Sensation
• Primary sensory cortex—sites
where sensory input is first
received and one becomes
conscious of the stimulus
• Association areas nearby to
sensory areas that process and
interpret that sensory information
– Primary visual cortex is
bordered by visual association
area: interprets and makes
cognitive sense of visual stimuli
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Anterior
Precentral
gyrus
Frontal
lobe
Central
sulcus
Parietal
lobe
Postcentral
gyrus
– Multimodal association areas:
receive input from multiple
senses and integrate this into
an overall perception of our
surroundings
Occipital
lobe
Posterior
(a)
Figure 14.22a
14-109
The Special Senses
• Special senses—limited to the head and employ relatively
complex sense organs
• Primary cortices and association areas listed below
• Vision
– Visual primary cortex in far posterior region of occipital lobe
– Visual association area: anterior, and occupies all the
remaining occipital lobe
• Much of inferior temporal lobe deals with facial recognition and
other familiar objects
• Hearing
– Primary auditory cortex in the superior region of the
temporal lobe and insula
– Auditory association area: temporal lobe deep and inferior to
primary auditory cortex
• Recognizes spoken words, a familiar piece of music, or a
voice on the phone
14-110
The Special Senses
• Equilibrium
– Signals for balance and sense of motion project mainly to
the cerebellum and several brainstem nuclei concerned with
head and eye movements and visceral functions
– Association cortex in the roof of the lateral sulcus near the
lower end of the central sulcus
• Seat of consciousness of our body movements and orientation in
space
• Taste and smell
– Gustatory (taste) signals received by primary gustatory
cortex in inferior end of the postcentral gyrus of the parietal
lobe and anterior region of insula
– Olfactory (smell) signals received by the primary olfactory
cortex in the medial surface of the temporal lobe and inferior
surface of the frontal lobe
14-111
The General Senses
• General (somesthetic, somatosensory, or somatic)
senses—distributed over the entire body and employ
relatively simple receptors
– Senses of touch, pressure, stretch, movement, heat, cold, and
pain
• Several cranial nerves carry general sensations from head
• Ascending tracts bring general sensory information from the
rest of the body
– Thalamus processes the input
– Selectively relays signals to the postcentral gyrus
• Fold of the cerebrum that lies immediately caudal to the central
sulcus and forms the rostral border of the parietal lobe
– Primary somesthetic cortex is the cortex of the postcentral
gyrus
– Somesthetic association area: caudal to the gyrus and in the
roof of the lateral sulcus
14-112
The General Senses
• Awareness of stimulation occurs in primary somesthetic
cortex
• Making cognitive sense of the stimulation occurs in the
somesthetic association area
• Because of decussation, the right postcentral gyrus
receives input from the left side of the body and vice
versa
• Sensory homunculus—upside-down sensory map of the
contralateral side of the body
• Somatotopy—point-for-point correspondence between an
area of the body and an area of the CNS
14-113
The General Senses
• Sensory homunculus—
diagram of the primary
somesthetic cortex which
resembles an upside-down
sensory map of the
contralateral side of the body
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 14.22b
II III
I
IV V
II
V
IV
III
Toes
Genitalia
• Shows receptors in the lower
limbs projecting to the superior
and medial parts of the gyrus
Teeth, gums
Tongue
Abdominal
viscera
• Shows receptors from the face
projecting to the inferior and
lateral parts
Insula
Lateral
• Somatotopy—point-to-point
correspondence between an
area of the body and an area of
the CNS
Viscerosensory area
Lateral sulcus
Medial
(b)
14-114
Functional Regions of the Cerebral Cortex
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Primary somatosensory
cortex
Primary motor
cortex
Somatosensory
association area
Motor association
area
Primary gustatory
cortex
Wernicke area
Broca area
Visual association
area
Prefrontal
cortex
Primary
visual cortex
Olfactory
association
area
Primary
auditory cortex
Auditory
association area
Figure 14.21
14-115
Motor Control
• The intention to contract a muscle begins in motor
association (premotor) area of frontal lobes
– Where we plan our behavior
– Where neurons compile a program for degree and
sequence of muscle contraction required for an action
– Program transmitted to neurons of the precentral gyrus
(primary motor area)
• Most posterior gyrus of the frontal lobe
14-116
Motor Control
• Premotor area (cont.)
– Neurons send signals to the brainstem and spinal cord
– Ultimately resulting in muscle contraction
– Precentral gyrus also exhibits somatotopy
• Neurons for toe movement are deep in the longitudinal
fissure of the medial side of the gyrus
• The summit of the gyrus controls the trunk, shoulder, and
arm
• The inferolateral region controls the facial muscles
– Motor homunculus has a distorted look because the
amount of cortex devoted to a given body region is
proportional to the number of muscles and motor units in
that body region
14-117
Motor Control
• Pyramidal cells of the precentral gyrus are called upper
motor neurons
–
–
–
–
–
Their fibers project caudally
About 19 million fibers ending in nuclei of the brainstem
About 1 million forming the corticospinal tracts
Most fibers decussate in lower medulla oblongata
Form lateral corticospinal tracts on each side of the spinal
cord
• In the brainstem or spinal cord, the fibers from upper motor
neurons synapse with lower motor neurons whose axons
innervate the skeletal muscles
• Basal nuclei and cerebellum are also important in muscle
control
14-118
• Basal nuclei
Motor Control
– Determines the onset and cessation of intentional movements
• Repetitive hip and shoulder movements in walking
– Highly practiced, learned behaviors that one carries out with
little thought
• Writing, typing, driving a car
– Lies in a feedback circuit from the cerebrum, to the basal
nuclei, to the thalamus, and back to the cerebrum
– Dyskinesias: movement disorders caused by lesions in the
basal nuclei
• Cerebellum
–
–
–
–
–
–
–
Highly important in motor coordination
Aids in learning motor skills
Maintains muscle tone and posture
Smoothes muscle contraction
Coordinates eye and body movements
Coordinates the motions of different joints with each other
Ataxia: clumsy, awkward gait
14-119
Motor Homunculus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
V
IV
III
II
Toes
I
Vocalization
Salivation
Mastication
Swallowing
Lateral
Medial
Figure 14.23b
(b)
14-120
Motor Pathways Involving the Cerebellum
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a) Input to cerebellum
(b) Output from cerebellum
Motor cortex
Cerebrum
Cerebrum
Cerebellum
Reticular formation
Brainstem
Cerebellum
Brainstem
Eye
Inner ear
Spinocerebellar
tracts of spinal cord
Muscle and joint proprioceptors
Reticulospinal
and vestibulospinal
tracts of spinal cord
Figure 14.24
Limb and postural
muscles
14-121
Language
• Language include several abilities: reading, writing, speaking,
and understanding words assigned to different regions of the
cerebral cortex
• Wernicke area
– Permits recognition of spoken and written language and creates plan
of speech
– When we intend to speak, Wernicke area formulates phrases
according to learned rules of grammar
– Transmits plan of speech to Broca area
• Broca area
– Generates motor program for the muscles of the larynx, tongue,
cheeks, and lips
– Transmits program to primary motor cortex for commands to the lower
motor neurons that supply relevant muscles
• Affective language area lesions produce aprosody—flat
emotionless speech
14-122
Language Centers of the Left Hemisphere
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Anterior
Posterior
Precentral gyrus
Postcentral
gyrus
Speech center of
primary motor cortex
Angular
gyrus
Primary
auditory cortex
(in lateral sulcus)
Primary
visual cortex
Broca
area
Wernicke
area
Figure 14.25
14-123
Aphasia
• Aphasia—any language deficit from lesions in same
hemisphere (usually left) containing the Wernicke and Broca
areas
• Nonfluent (Broca) aphasia
– Lesion in Broca area
– Slow speech, difficulty in choosing words, using words that only
approximate the correct word
• Fluent (Wernicke) aphasia
– Lesion in Wernicke area
– Speech normal and excessive, but uses senseless jargon
– Cannot comprehend written and spoken words
• Anomic aphasia
– Can speak normally and understand speech, but cannot identify
written words or pictures
14-124
Cerebral Lateralization
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Left hemisphere
Right hemisphere
Olfaction, right nasal cavity
Olfaction, left nasal cavity
Anterior
Verbal memory
Memory for shapes
Speech
(Limited language
comprehension, mute)
Left hand motor control
Right hand
motor control
Feeling shapes with
left hand
Feeling shapes
with right hand
Hearing nonvocal sounds
(left ear advantage)
Hearing vocal sounds
(right ear advantage)
Musical ability
Rational, symbolic
thought
Intuitive, nonverbal thought
Superior language
comprehension
Superior recognition of
faces and spatial
relationships
Vision, right field
Posterior
Figure 14.26
Vision, left field
14-125
Cerebral Lateralization
• Cerebral lateralization—the difference in the structure and
function of the cerebral hemispheres
• Left hemisphere—categorical hemisphere
– Specialized for spoken and written language
– Sequential and analytical reasoning (math and science)
– Breaks information into fragments and analyzes it in a linear
way
• Right hemisphere—representational hemisphere
–
–
–
–
–
Perceives information in a more integrated holistic way
Seat of imagination and insight
Musical and artistic skill
Perception of patterns and spatial relationships
Comparison of sights, sounds, smells, and taste
14-126
Cerebral Lateralization
• Highly correlated with handedness
– Left hemisphere is the categorical one in 96% of right-handed
people
• Right hemisphere in 4%
– Left-handed people: right hemisphere is categorical in 15%
and left in 70%
• Lateralization develops with age
– Males exhibit more lateralization than females and suffer more
functional loss when one hemisphere is damaged
14-127
The Cranial Nerves
• Expected Learning Outcomes
– List the 12 cranial nerves by name and number.
– Identify where each cranial nerve originates and
terminates.
– State the functions of each cranial nerve.
14-128
The Cranial Nerves
• Brain must communicate with rest of body
– Most of the input and output travels by way of the spinal
cord
– 12 pairs of cranial nerves arise from the base of the
brain
– Exit the cranium through foramina
– Lead to muscles and sense organs located mainly in
the head and neck
14-129
Cranial Nerve Pathways
• Most motor fibers of the cranial nerves begin in
nuclei of brainstem and lead to glands and
muscles
• Sensory fibers begin in receptors located mainly
in head and neck and lead mainly to the
brainstem
– Sensory fibers for proprioception may travel to
brain in a different nerve from motor nerve
14-130
Cranial Nerve Pathways
• Most cranial nerves carry fibers between
brainstem and ipsilateral receptors and effectors
– Lesion in left brainstem causes sensory or motor
deficit on same side
• Exceptions: optic nerve where half the fibers
decussate, and trochlear nerve where all efferent
fibers lead to a muscle of the contralateral eye
14-131
Cranial Nerve Classification
• Some cranial nerves are classified as motor,
some sensory, others mixed
– Sensory (I, II, and VIII)
– Motor (III, IV, VI, XI, and XII)
• Stimulate muscle but also contain fibers of proprioception
– Mixed (V, VII, IX, X)
• Sensory functions may be quite unrelated to their motor
function
– Facial nerve (VII) has sensory role in taste and motor role in
facial expression
14-132
The Cranial Nerves
Figure 14.27a,b
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Frontal lobe
Frontal lobe
Longitudinal
fissure
Cranial nerves:
Olfactory bulb
(from olfactory nerve, I)
Olfactory tract
Olfactory tract
Optic chiasm
Optic nerve (II)
Temporal lobe
Temporal lobe
Oculomotor nerve (III)
Trochlear nerve (IV)
Infundibulum
Trigeminal nerve (V)
Optic chiasm
Pons
Abducens nerve (VI)
Facial nerve (VII)
Pons
Medulla
Vestibulocochlear nerve (VIII)
Glossopharyngeal nerve (IX)
Cerebellum
Vagus nerve (X)
Medulla
oblongata
Hypoglossal nerve (XII)
Accessory nerve (XI)
Cerebellum
Spinal cord
Spinal cord
(a)
(b)
b: © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer/DonKincaid, dissections
14-133
The Olfactory Nerve (I)
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Olfactory bulb
Olfactory tract
Cribriform plate of
ethmoid bone
Fascicles of
olfactory nerve (I)
Nasal mucosa
Figure 14.28
• Sense of smell
• Damage causes impaired sense of smell
14-134
The Optic Nerve (II)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Eyeball
Optic nerve (II)
Optic chiasm
Optic tract
Pituitary gland
Figure 14.29
• Provides vision
• Damage causes blindness in part or all of visual field
14-135
The Oculomotor Nerve (III)
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Oculomotor nerve (III):
Superior branch
Inferior branch
Ciliary ganglion
Superior orbital fissure
Figure 14.30
• Controls muscles that turn the eyeball up, down, and medially, as
well as controlling the iris, lens, and upper eyelid
• Damage causes drooping eyelid, dilated pupil, double vision,
difficulty focusing, and inability to move eye in certain directions
14-136
The Trochlear Nerve (IV)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Superior oblique muscle
Superior orbital fissure
Trochlear nerve (IV)
Figure 14.31
• Eye movement (superior oblique muscle)
• Damage causes double vision and inability to rotate eye
inferolaterally
14-137
The Trigeminal Nerve (V)
• Largest of the cranial
nerves
• Most important sensory
nerve of the face
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Superior orbital fissure
Ophthalmic division (V1)
Trigeminal ganglion
Trigeminal nerve (V)
Maxillary division (V2)
Foramen ovale
Mandibular division (V3)
Foramen rotundum
Infraorbital
nerve
Superior
alveolar nerves
Lingual nerve
• Forks into three divisions
Anterior trunk of V3 to
chewing muscles
Inferior
alveolar nerve
– Ophthalmic division
(V1): sensory
– Maxillary division
(V2): sensory
– Mandibular division
(V3): mixed
Temporalis muscle
Lateral pterygoid muscle
Medial pterygoid muscle
V1
Masseter muscle
V2
Anterior belly of
digastric muscle
V3
Motor branches of the
mandibular division (V3)
Distribution of sensory
fibers of each division
Figure 14.32
14-138
The Abducens Nerve (VI)
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Lateral rectus muscle
Superior orbital fissure
Abducens nerve (VI)
Figure 14.33
• Provides eye movement (lateral rectus m.)
• Damage results in inability to rotate eye laterally and at rest eye
rotates medially
14-139
The Facial Nerve (VII)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Facial nerve (VII)
Internal acoustic meatus
Geniculate ganglion
Pterygopalatine ganglion
Lacrimal (tear) gland
Chorda tympani
branch (taste and
salivation)
Submandibular ganglion
Sublingual gland
Parasympathetic fibers
Submandibular gland
Stylomastoid foramen
Motor branch
to muscles of
facial expression
Figure 14.34a
(a)
• Motor—major motor nerve of facial muscles: facial expressions;
salivary glands and tear, nasal, and palatine glands
• Sensory—taste on anterior two-thirds of tongue
• Damage produces sagging facial muscles and disturbed sense
of taste (no sweet and salty)
14-140
Five Branches of Facial Nerve
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Temporal
Zygomatic
Buccal
Buccal
Mandibular
Cervical
(b)
(c)
c: © The McGraw-Hill Companies, Inc./Joe DeGrandis, photographer
Figure 14.34b,c
Clinical test: test anterior two-thirds of tongue with substances such as sugar,
salt, vinegar, and quinine; test response of tear glands to ammonia fumes; test
motor functions by asking subject to close eyes, smile, whistle, frown, raise
eyebrows, etc.
14-141
The Vestibulocochlear Nerve (VIII)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Semicircular
ducts
Vestibular ganglia
Vestibular nerve
Cochlear nerve
Vestibulocochlear
nerve (VIII)
Internal
acoustic meatus
Cochlea
Vestibule
Figure 14.35
• Nerve of hearing and equilibrium
• Damage produces deafness, dizziness, nausea, loss of balance,
and nystagmus (involuntary rhythmic oscillation of the eyes from
side to side)
14-142
The Glossopharyngeal Nerve (IX)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Swallowing,
salivation, gagging,
control of BP and
respiration
Glossopharyngeal nerve (IX)
Jugular foramen
Superior ganglion
Inferior ganglion
Otic ganglion
Parotid salivary gland
• Sensations from
posterior one-third of
tongue
Carotid sinus
Pharyngeal muscles
• Damage results in
loss of bitter and sour
taste and impaired
swallowing
Figure 14.36
14-143
The Vagus Nerve (X)
• Most extensive distribution of
any cranial nerve
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Major role in the control of
cardiac, pulmonary, digestive,
and urinary function
Jugular foramen
Pharyngeal nerve
Laryngeal nerve
Carotid sinus
Vagus nerve (X)
• Swallowing, speech,
regulation of viscera
Lung
• Damage causes hoarseness
or loss of voice, impaired
swallowing, and fatal if both
are cut
Heart
Spleen
Liver
Kidney
Stomach
Colon
(proximal portion)
Small intestine
Figure 14.37
14-144
The Accessory Nerve (XI)
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Jugular
foramen
Vagus nerve
Accessory nerve (XI)
Foramen
magnum
Sternocleidomastoid
muscle
Spinal nerves
C3 and C4
Trapezius muscle
Posterior view
Figure 14.38
• Swallowing; head, neck, and shoulder movement
– Damage causes impaired head, neck, shoulder movement;
head turns toward injured side
14-145
The Hypoglossal Nerve (XII)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hypoglossal canal
Intrinsic muscles
of the tongue
Extrinsic muscles
of the tongue
Hypoglossal nerve (XII)
Figure 14.39
• Tongue movements for speech, food manipulation, and
swallowing
– If both are damaged: cannot protrude tongue
– If one side is damaged: tongue deviates toward injured
side; see ipsilateral atrophy
14-146
Cranial Nerve Disorders
• Trigeminal neuralgia (tic douloureux)
– Recurring episodes of intense stabbing pain in trigeminal
nerve area (near mouth or nose)
– Pain triggered by touch, drinking, washing face
– Treatment may require cutting nerve
• Bell palsy
– Degenerative disorder of facial nerve causes paralysis of
facial muscles on one side
– May appear abruptly with full recovery within 3 to 5 weeks
14-147
Images of the Mind
• Positron emission tomography (PET) and MRI
visualize increases in blood flow when brain areas are
active
– Injection of radioactively labeled glucose
• Busy areas of brain “light up”
• Functional magnetic resonance imaging (fMRI) looks
at increase in blood flow to an area (additional glucose is
needed in active area)—magnetic properties of
hemoglobin depend on how much oxygen is bound to it
(additional oxygen is there due to additional blood flow)
– Quick, safe, and accurate method to see brain function
14-148
Images of the Mind
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Rostral
Caudal
Primary auditory cortex
Visual cortex
1 The word car is seen in
the visual cortex.
Wernicke area
2 Wernicke area conceives
of the verb drive to go with it.
Premotor area
Primary motor cortex
Broca area
3 Broca area compiles a
motor program to speak
the word drive.
4 The primary motor cortex
executes the program and
the word is spoken.
Figure 14.40
14-149