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The Brain
Muse spring 2430
lecture 15
7/12/10
Embryonic Development
• Neural plate forms from ectoderm
• Neural plate invaginates to form a neural
groove and neural folds
Surface
ectoderm
Head
Neural
plate
Tail
1 The neural plate forms from surface ectoderm.
Figure 12.1, step 1
(a)
Neural
tube
Anterior
(rostral)
(b) Primary brain
vesicles
Prosencephalon
(forebrain)
Mesencephalon
(midbrain)
Rhombencephalon
(hindbrain)
Posterior
(caudal)
Figure 12.2a-b
(d) Adult brain
structures
(e) Adult
neural canal
regions
Telencephalon
Cerebrum: cerebral
hemispheres (cortex,
white matter, basal nuclei)
Lateral
ventricles
Diencephalon
Diencephalon
(thalamus, hypothalamus,
epithalamus), retina
Third ventricle
Mesencephalon
Brain stem: midbrain
Cerebral
aqueduct
Metencephalon
Brain stem: pons
(c) Secondary brain
vesicles
Cerebellum
Myelencephalon
Brain stem: medulla
oblongata
Spinal cord
Fourth
ventricle
Central canal
Figure 12.2c-e
Anterior (rostral)
Metencephalon
Mesencephalon
Diencephalon
Telencephalon
Myelencephalon
(a) Week 5
Posterior (caudal)
Midbrain
Cervical
Flexures
Spinal cord
Figure 12.3a
Cerebral hemisphere
Outline of diencephalon
Midbrain
Cerebellum
Pons
Medulla oblongata
(b) Week 13
Spinal cord
Figure 12.3b
(c) Week 26
Cerebral
hemisphere
Cerebellum
Pons
Medulla
oblongata
Spinal cord
Figure 12.3c
Cerebral
hemisphere
Diencephalon
(d) Birth
Cerebellum
Brain stem
• Midbrain
• Pons
• Medulla
oblongata
Figure 12.3d
Ventricles of the Brain
• Contain cerebrospinal fluid
• Two C-shaped lateral ventricles in the cerebral
hemispheres
• Third ventricle in the diencephalon
• Fourth ventricle in the hindbrain, dorsal to the
pons, develops from the lumen of the neural
tube
Lateral ventricle
Septum pellucidum
Anterior horn
Inferior
horn
Lateral
aperture
Interventricular
foramen
Third ventricle
Inferior horn
Cerebral aqueduct
Fourth ventricle
Central canal
(a) Anterior view
(b) Left lateral
Posterior
horn
Median
aperture
Lateral
aperture
view
Figure 12.5
Cerebral Hemispheres
• Surface markings
• Ridges (gyri), shallow grooves (sulci), and deep
grooves (fissures)
• Five lobes
• Frontal
• Parietal
• Temporal
• Occipital
• Insula
Cerebral Hemispheres
• Surface markings
• Central sulcus
• Separates the precentral gyrus of the frontal lobe
and the postcentral gyrus of the parietal lobe
• Longitudinal fissure
• Separates the two hemispheres
• Transverse cerebral fissure
• Separates the cerebrum and the cerebellum
PLAY
Animation: Rotatable brain
Precentral
gyrus
Frontal
lobe
Central
sulcus
Postcentral
gyrus
Parietal lobe
Parieto-occipital sulcus
(on medial surface
of hemisphere)
Lateral sulcus
Occipital lobe
Temporal lobe
Transverse cerebral fissure
Cerebellum
Pons
Medulla oblongata
Spinal cord
Fissure
(a deep
sulcus)
Gyrus
Cortex (gray matter)
Sulcus
White matter
(a)
Figure 12.6a
Frontal lobe
Central
sulcus
Gyri of insula
Temporal lobe
(pulled down)
(b)
Figure 12.6b
Anterior
Longitudinal
fissure
Frontal lobe
Cerebral veins
and arteries
covered by
arachnoid
mater
Parietal
lobe
Right cerebral
hemisphere
Occipital
lobe
Left cerebral
hemisphere
(c)
Posterior
Figure 12.6c
Left cerebral
hemisphere
Brain stem
Transverse
cerebral
fissure
Cerebellum
(d)
Figure 12.6d
Cerebral Cortex
• Thin (2–4 mm) superficial layer of gray matter
• 40% of the mass of the brain
• Site of conscious mind: awareness, sensory
perception, voluntary motor initiation, communication,
memory storage, understanding
• Each hemisphere connects to contralateral side of
the body
• There is lateralization of cortical function in the
hemispheres
Functional Areas of the Cerebral Cortex
• The three types of functional areas are:
• Motor areas—control voluntary movement
• Sensory areas—conscious awareness of
sensation
• Association areas—integrate diverse
information
• Conscious behavior involves the entire cortex
Motor Areas
• Primary (somatic) motor cortex
• Premotor cortex
• Broca’s area
• Frontal eye field
Motor areas
Central sulcus
Primary motor cortex
Premotor cortex
Frontal eye field
Broca’s area
(outlined by dashes)
Prefrontal cortex
Working memory
for spatial tasks
Executive area for
task management
Working memory for
object-recall tasks
Solving complex,
multitask problems
(a) Lateral view, left cerebral hemisphere
Sensory areas and related
association areas
Primary somatosensory
cortex
Somatic
Somatosensory
sensation
association cortex
Gustatory cortex
(in insula)
Taste
Wernicke’s area
(outlined by dashes)
Primary visual
cortex
Visual
association
area
Auditory
association area
Primary
auditory cortex
Vision
Hearing
Motor association cortex
Primary sensory cortex
Primary motor cortex
Sensory association cortex
Multimodal association cortex
Figure 12.8a
Primary Motor Cortex
• Large pyramidal cells of the precentral gyri
• Long axons  pyramidal (corticospinal) tracts
• Allows conscious control of precise, skilled,
voluntary movements
• Motor homunculi: upside-down caricatures
representing the motor innervation of body
regions
Posterior
Motor
Motor map in
precentral gyrus
Anterior
Toes
Jaw
Tongue
Swallowing
Primary motor
cortex
(precentral gyrus)
Figure 12.9
Premotor Cortex
• Anterior to the precentral gyrus
• Controls learned, repetitious, or patterned
motor skills
• Coordinates simultaneous or sequential
actions
• Involved in the planning of movements that
depend on sensory feedback
Broca’s Area
• Anterior to the inferior region of the premotor
area
• Present in one hemisphere (usually the left)
• A motor speech area that directs muscles of
the tongue
• Is active as one prepares to speak
Frontal Eye Field
• Anterior to the premotor cortex and superior to
Broca’s area
• Controls voluntary eye movements
Sensory Areas
• Primary somatosensory
cortex
• Somatosensory
association cortex
• Visual areas
• Auditory areas
• Olfactory cortex
• Gustatory cortex
• Visceral sensory area
• Vestibular cortex
Motor areas
Central sulcus
Primary motor cortex
Premotor cortex
Frontal eye field
Broca’s area
(outlined by dashes)
Prefrontal cortex
Working memory
for spatial tasks
Executive area for
task management
Working memory for
object-recall tasks
Solving complex,
multitask problems
(a) Lateral view, left cerebral hemisphere
Sensory areas and related
association areas
Primary somatosensory
cortex
Somatic
Somatosensory
sensation
association cortex
Gustatory cortex
(in insula)
Taste
Wernicke’s area
(outlined by dashes)
Primary visual
cortex
Visual
association
area
Auditory
association area
Primary
auditory cortex
Vision
Hearing
Motor association cortex
Primary sensory cortex
Primary motor cortex
Sensory association cortex
Multimodal association cortex
Figure 12.8a
Primary Somatosensory Cortex
• In the postcentral gyri
• Receives sensory information from the skin,
skeletal muscles, and joints
• Capable of spatial discrimination: identification
of body region being stimulated
Posterior
Sensory
Anterior
Sensory map in
postcentral gyrus
Genitals
Primary somatosensory cortex
(postcentral gyrus)
Intraabdominal
Figure 12.9
Somatosensory Association Cortex
• Posterior to the primary somatosensory cortex
• Integrates sensory input from primary
somatosensory cortex
• Determines size, texture, and relationship of
parts of objects being felt
Visual Areas
• Primary visual (striate) cortex
• Extreme posterior tip of the occipital lobe
• Most of it is buried in the calcarine sulcus
• Receives visual information from the retinas
Visual Areas
• Visual association area
• Surrounds the primary visual cortex
• Uses past visual experiences to interpret
visual stimuli (e.g., color, form, and movement)
• Complex processing involves entire posterior
half of the hemispheres
Auditory Areas
• Primary auditory cortex
• Superior margin of the temporal lobes
• Interprets information from inner ear as pitch,
loudness, and location
• Auditory association area
• Located posterior to the primary auditory
cortex
• Stores memories of sounds and permits
perception of sounds
OIfactory Cortex
• Medial aspect of temporal lobes (in piriform
lobes)
• Part of the primitive rhinencephalon, along
with the olfactory bulbs and tracts
• (Remainder of the rhinencephalon in humans
is part of the limbic system)
• Region of conscious awareness of odors
Gustatory Cortex
• In the insula
• Involved in the perception of taste
Visceral Sensory Area
• Posterior to gustatory cortex
• Conscious perception of visceral sensations,
e.g., upset stomach or full bladder
Vestibular Cortex
• Posterior part of the insula and adjacent
parietal cortex
• Responsible for conscious awareness of
balance (position of the head in space)
Motor areas
Central sulcus
Primary motor cortex
Premotor cortex
Frontal eye field
Broca’s area
(outlined by dashes)
Prefrontal cortex
Working memory
for spatial tasks
Executive area for
task management
Working memory for
object-recall tasks
Solving complex,
multitask problems
(a) Lateral view, left cerebral hemisphere
Sensory areas and related
association areas
Primary somatosensory
cortex
Somatic
Somatosensory
sensation
association cortex
Gustatory cortex
(in insula)
Taste
Wernicke’s area
(outlined by dashes)
Primary visual
cortex
Visual
association
area
Auditory
association area
Primary
auditory cortex
Vision
Hearing
Motor association cortex
Primary sensory cortex
Primary motor cortex
Sensory association cortex
Multimodal association cortex
Figure 12.8a
Premotor cortex
Corpus
callosum
Cingulate
gyrus
Primary
motor cortex
Frontal eye field
Prefrontal
cortex
Processes emotions
related to personal
and social interactions
Orbitofrontal
cortex
Olfactory bulb
Olfactory tract
Fornix
Temporal lobe
(b) Parasagittal view, right hemisphere
Uncus
Primary
olfactory cortex
Central sulcus
Primary somatosensory
cortex
Parietal lobe
Somatosensory
association cortex
Parieto-occipital
sulcus
Occipital
lobe
Visual
association
area
Primary
visual cortex
Calcarine sulcus
Parahippocampal
gyrus
Motor association cortex
Primary sensory cortex
Primary motor cortex
Sensory association cortex
Multimodal association cortex
Figure 12.8b
Multimodal Association Areas
• Receive inputs from multiple sensory areas
• Send outputs to multiple areas, including the
premotor cortex
• Allow us to give meaning to information
received, store it as memory, compare it to
previous experience, and decide on action to
take
Multimodal Association Areas
• Three parts
• Anterior association area (prefrontal cortex)
• Posterior association area
• Limbic association area
Anterior Association Area (Prefrontal
Cortex)
• Most complicated cortical region
• Involved with intellect, cognition, recall, and
personality
• Contains working memory needed for
judgment, reasoning, persistence, and
conscience
• Development depends on feedback from
social environment
Posterior Association Area
• Large region in temporal, parietal, and
occipital lobes
• Plays a role in recognizing patterns and faces
and localizing us in space
• Involved in understanding written and spoken
language (Wernicke’s area)
Limbic Association Area
• Part of the limbic system
• Provides emotional impact that helps
establish memories
Lateralization of Cortical Function
• Lateralization
• Division of labor between hemispheres
• Cerebral dominance
• Designates the hemisphere dominant for
language (left hemisphere in 90% of people)
Lateralization of Cortical Function
• Left hemisphere
• Controls language, math, and logic
• Right hemisphere
• Insight, visual-spatial skills, intuition, and
artistic skills
• Left and right hemispheres communicate via
fiber tracts in the cerebral white matter
Cerebral White Matter
• Myelinated fibers and their tracts
• Responsible for communication
• Commissures (in corpus callosum)—connect
gray matter of the two hemispheres
• Association fibers—connect different parts of
the same hemisphere
• Projection fibers—(corona radiata) connect the
hemispheres with lower brain or spinal cord
Longitudinal fissure
Lateral
ventricle
Superior
Commissural
fibers (corpus
callosum)
Association
fibers
Basal nuclei
• Caudate
• Putamen
• Globus
pallidus
Corona radiata
Thalamus
Internal
capsule
Fornix
Gray matter
Third
ventricle
White matter
Pons
Projection
fibers
Medulla oblongata
(a)
Decussation
of pyramids
Figure 12.10a
Basal Nuclei (Ganglia)
• Subcortical nuclei
• Consists of the corpus striatum
• Caudate nucleus
• Lentiform nucleus (putamen + globus pallidus)
• Functionally associated with the subthalamic
nuclei (diencephalon) and the substantia nigra
(midbrain)
Fibers of
corona radiata
Caudate
nucleus
Lentiform
Corpus
nucleus
striatum • Putamen
• Globus pallidus
(deep to putamen)
Projection fibers
run deep to
lentiform nucleus
(a)
Thalamus
Tail of
caudate
nucleus
Figure 12.11a
Anterior
(b)
Posterior
Cerebral cortex
Cerebral white matter
Corpus callosum
Anterior horn
of lateral ventricle
Caudate nucleus
Putamen
Lentiform
Globus
nucleus
pallidus
Thalamus
Tail of caudate nucleus
Third ventricle
Inferior horn
of lateral ventricle
Figure 12.11b (1 of 2)
Cerebral cortex
Cerebral white matter
Corpus callosum
Anterior horn
of lateral ventricle
Caudate nucleus
Lentiform nucleus
Thalamus
Third ventricle
Inferior horn
of lateral ventricle
(b)
Figure 12.11b (2 of 2)
Functions of Basal Nuclei
• Though somewhat elusive, the following are
thought to be functions of basal nuclei
• Influence muscular control
• Help regulate attention and cognition
• Regulate intensity of slow or stereotyped
movements
• Inhibit antagonistic and unnecessary
movements
Diencephalon
• Three paired structures
• Thalamus
• Hypothalamus
• Epithalamus
• Encloses the third ventricle
PLAY
Animation: Rotatable brain (sectioned)
Cerebral hemisphere
Septum pellucidum
Interthalamic
adhesion
(intermediate
mass of
thalamus)
Interventricular
foramen
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Corpus callosum
Fornix
Choroid plexus
Thalamus
(encloses third
ventricle)
Posterior commissure
Pineal gland
(part of epithalamus)
Corpora
quadrigemina MidCerebral
brain
aqueduct
Arbor vitae (of
cerebellum)
Fourth ventricle
Choroid plexus
Cerebellum
Spinal cord
Figure 12.12
Thalamus
• 80% of diencephalon
• Superolateral walls of the third ventricle
• Connected by the interthalamic adhesion
(intermediate mass)
• Contains several nuclei, named for their
location
• Nuclei project and receive fibers from the
cerebral cortex
Dorsal nuclei
Medial Lateral Lateral
dorsal posterior
Pulvinar
Anterior
nuclear
group
Reticular
nucleus
Ventral
Ventral Ventral posteroanterior lateral lateral
Medial
geniculate
body
Lateral
geniculate
body
Ventral nuclei
(a) The main thalamic nuclei. (The reticular nuclei that “cap” the
thalamus laterally are depicted as curving translucent structures.)
Figure 12.13a
Thalamic Function
• Gateway to the cerebral cortex
• Sorts, edits, and relays information
• Afferent impulses from all senses and all parts of the
body
• Impulses from the hypothalamus for regulation of
emotion and visceral function
• Impulses from the cerebellum and basal nuclei to help
direct the motor cortices
• Mediates sensation, motor activities, cortical arousal,
learning, and memory
Hypothalamus
• Forms the inferolateral walls of the third
ventricle
• Contains many nuclei
• Example: mammillary bodies
• Paired anterior nuclei
• Olfactory relay stations
• Infundibulum—stalk that connects to the
pituitary gland
Paraventricular
nucleus
Anterior
commissure
Preoptic
nucleus
Anterior
hypothalamic
nucleus
Supraoptic
nucleus
Suprachiasmatic
nucleus
Fornix
Arcuate
nucleus
Pituitary
gland
Optic
chiasma
Infundibulum
(stalk of the
pituitary gland)
(b) The main hypothalamic nuclei.
Dorsomedial
nucleus
Posterior
hypothalamic
nucleus
Lateral
hypothalamic
area
Ventromedial
nucleus
Mammillary
body
Figure 12.13b
Hypothalamic Function
• Autonomic control center for many visceral
functions (e.g., blood pressure, rate and force
of heartbeat, digestive tract motility)
• Center for emotional response: Involved in
perception of pleasure, fear, and rage and in
biological rhythms and drives
Hypothalamic Function
• Regulates body temperature, food intake,
water balance, and thirst
• Regulates sleep and the sleep cycle
• Controls release of hormones by the anterior
pituitary
• Produces posterior pituitary hormones
Epithalamus
• Most dorsal portion of the diencephalon;
forms roof of the third ventricle
• Pineal gland—extends from the posterior
border and secretes melatonin
• Melatonin—helps regulate sleep-wake cycles
Cerebral hemisphere
Septum pellucidum
Interthalamic
adhesion
(intermediate
mass of
thalamus)
Interventricular
foramen
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Corpus callosum
Fornix
Choroid plexus
Thalamus
(encloses third
ventricle)
Posterior commissure
Pineal gland
(part of epithalamus)
Corpora
quadrigemina MidCerebral
brain
aqueduct
Arbor vitae (of
cerebellum)
Fourth ventricle
Choroid plexus
Cerebellum
Spinal cord
Figure 12.12
Brain Stem
• Three regions
• Midbrain
• Pons
• Medulla oblongata
Brain Stem
• Similar structure to spinal cord but contains
embedded nuclei
• Controls automatic behaviors necessary for
survival
• Contains fiber tracts connecting higher and
lower neural centers
• Associated with 10 of the 12 pairs of cranial
nerves
Frontal lobe
Olfactory bulb
(synapse point of
cranial nerve I)
Optic chiasma
Optic nerve (II)
Optic tract
Mammillary body
Midbrain
Pons
Temporal lobe
Medulla
oblongata
Cerebellum
Spinal cord
Figure 12.14
View (a)
Optic chiasma
Optic nerve (II)
Crus cerebri of
cerebral peduncles
(midbrain)
Diencephalon
• Thalamus
• Hypothalamus
Mammillary body
Thalamus
Hypothalamus
Diencephalon
Midbrain
Oculomotor nerve (III)
Trochlear nerve (IV)
Pons
Brainstem
Medulla
oblongata
Trigeminal nerve (V)
Pons
Facial nerve (VII)
Middle cerebellar
peduncle
Abducens nerve (VI)
Vestibulocochlear
nerve (VIII)
Pyramid
Glossopharyngeal nerve (IX)
Hypoglossal nerve (XII)
Vagus nerve (X)
Ventral root of first
cervical nerve
Decussation of pyramids
Accessory nerve (XI)
Spinal cord
(a) Ventral view
Figure 12.15a
Crus cerebri of
cerebral peduncles
(midbrain)
Thalamus
View (b)
Infundibulum
Pituitary gland
Superior colliculus
Inferior colliculus
Trochlear nerve (IV)
Trigeminal nerve (V)
Pons
Superior cerebellar peduncle
Middle cerebellar peduncle
Facial nerve (VII)
Abducens nerve (VI)
Glossopharyngeal nerve (IX)
Hypoglossal nerve (XII)
Inferior cerebellar peduncle
Vestibulocochlear nerve (VIII)
Olive
Thalamus
Vagus nerve (X)
Hypothalamus
Diencephalon
Midbrain
Accessory nerve (XI)
Pons
Brainstem
Medulla
oblongata
(b) Left lateral view
Figure 12.15b
Thalamus
View (c)
Diencephalon
Pineal gland
Anterior wall of
fourth ventricle
Choroid plexus
(fourth ventricle)
Dorsal median sulcus
Dorsal root of
first cervical nerve
Midbrain
• Superior
Corpora
colliculus quadrigemina
• Inferior
of tectum
colliculus
• Trochlear nerve (IV)
• Superior cerebellar peduncle
Pons
• Middle cerebellar peduncle
Medulla oblongata
• Inferior cerebellar peduncle
• Facial nerve (VII)
• Vestibulocochlear nerve (VIII)
• Glossopharyngeal nerve (IX)
• Vagus nerve (X)
• Accessory nerve (XI)
Thalamus
Hypothalamus
Midbrain
Pons
(c) Dorsal view
Diencephalon
Brainstem
Medulla
oblongata
Figure 12.15c
Midbrain
• Located between the diencephalon and the
pons
• Cerebral peduncles
• Contain pyramidal motor tracts
• Cerebral aqueduct
• Channel between third and fourth ventricles
Midbrain Nuclei
• Nuclei that control cranial nerves III (oculomotor) and
IV (trochlear)
• Corpora quadrigemina—domelike dorsal protrusions
• Superior colliculi—visual reflex centers
• Inferior colliculi—auditory relay centers
• Substantia nigra—functionally linked to basal nuclei
• Red nucleus—relay nuclei for some descending
motor pathways and part of reticular formation
Tectum
Periaqueductal gray
matter
Oculomotor
nucleus (III)
Medial
lemniscus
Red
nucleus
Substantia
nigra
Fibers of
pyramidal tract
(a) Midbrain
Dorsal
Superior
colliculus
Cerebral aqueduct
Reticular formation
Ventral
Crus cerebri of
cerebral peduncle
Figure 12.16a
Pons
• Forms part of the anterior wall of the fourth ventricle
• Fibers of the pons
• Connect higher brain centers and the spinal cord
• Relay impulses between the motor cortex and the
cerebellum
• Origin of cranial nerves V (trigeminal), VI (abducens),
and VII (facial)
• Some nuclei of the reticular formation
• Nuclei that help maintain normal rhythm of breathing
Fourth
ventricle
Superior cerebellar
peduncle
Trigeminal main
sensory nucleus
Trigeminal
motor nucleus
Middle
cerebellar
peduncle
Trigeminal
nerve (V)
Medial lemniscus
(b) Pons
Reticular
formation
Pontine
nuclei
Fibers of
pyramidal
tract
Figure 12.16b
Medulla Oblongata
• Joins spinal cord at foramen magnum
• Forms part of the ventral wall of the fourth
ventricle
• Contains a choroid plexus of the fourth
ventricle
• Pyramids—two ventral longitudinal ridges
formed by pyramidal tracts
• Decussation of the pyramids—crossover of
the corticospinal tracts
Medulla Oblongata
• Inferior olivary nuclei—relay sensory
information from muscles and joints to
cerebellum
• Cranial nerves VIII, X, and XII are associated
with the medulla
• Vestibular nuclear complex—mediates
responses that maintain equilibrium
• Several nuclei (e.g., nucleus cuneatus and
nucleus gracilis) relay sensory information
Medulla Oblongata
• Autonomic reflex centers
• Cardiovascular center
• Cardiac center adjusts force and rate of heart
contraction
• Vasomotor center adjusts blood vessel
diameter for blood pressure regulation
Medulla Oblongata
• Respiratory centers
• Generate respiratory rhythm
• Control rate and depth of breathing, with
pontine centers
Medulla Oblongata
• Additional centers regulate
• Vomiting
• Hiccuping
• Swallowing
• Coughing
• Sneezing
Reticular formation
Fourth ventricle
Choroid
Hypoglossal nucleus (XII)
plexus
Dorsal motor nucleus
of vagus (X)
Inferior cerebellar
peduncle
Lateral
nuclear
group
Medial
nuclear
group
Raphe
nucleus
Medial lemniscus
(c) Medulla oblongata
Solitary
nucleus
Vestibular nuclear
complex (VIII)
Cochlear
nuclei (VIII)
Nucleus
ambiguus
Inferior olivary
nucleus
Pyramid
Figure 12.16c
The Cerebellum
• 11% of brain mass
• Dorsal to the pons and medulla
• Subconsciously provides precise timing and
appropriate patterns of skeletal muscle
contraction
Anatomy of the Cerebellum
• Two hemispheres connected by vermis
• Each hemisphere has three lobes
• Anterior, posterior, and flocculonodular
• Folia—transversely oriented gyri
• Arbor vitae—distinctive treelike pattern of the
cerebellar white matter
Anterior lobe
Cerebellar cortex
Arbor
vitae
Cerebellar
peduncles
• Superior
• Middle
• Inferior
Medulla
oblongata
(b)
Flocculonodular
lobe
Posterior
lobe
Choroid
plexus of
fourth
ventricle
Figure 12.17b
Anterior
lobe
Posterior
lobe
(d)
Vermis
Figure 12.17d
Cerebellar Peduncles
• All fibers in the cerebellum are ipsilateral
• Three paired fiber tracts connect the
cerebellum to the brain stem
• Superior peduncles connect the cerebellum to
the midbrain
• Middle peduncles connect the pons to the
cerebellum
• Inferior peduncles connect the medulla to the
cerebellum
Cerebellar Processing for Motor Activity
• Cerebellum receives impulses from the cerebral
cortex of the intent to initiate voluntary muscle
contraction
• Signals from proprioceptors and visual and
equilibrium pathways continuously “inform” the
cerebellum of the body’s position and momentum
• Cerebellar cortex calculates the best way to smoothly
coordinate a muscle contraction
• A “blueprint” of coordinated movement is sent to the
cerebral motor cortex and to brain stem nuclei
Cognitive Function of the Cerebellum
• Recognizes and predicts sequences of events
during complex movements
• Plays a role in nonmotor functions such as
word association and puzzle solving
Functional Brain Systems
• Networks of neurons that work together and
span wide areas of the brain
• Limbic system
• Reticular formation
Limbic System
• Structures on the medial aspects of cerebral
hemispheres and diencephalon
• Includes parts of the diencephalon and some
cerebral structures that encircle the brain
stem
Septum pellucidum
Diencephalic structures
of the limbic system
•Anterior thalamic
nuclei (flanking
3rd ventricle)
•Hypothalamus
•Mammillary
body
Olfactory bulb
Corpus callosum
Fiber tracts
connecting limbic
system structures
•Fornix
•Anterior commissure
Cerebral structures of the
limbic system
•Cingulate gyrus
•Septal nuclei
•Amygdala
•Hippocampus
•Dentate gyrus
•Parahippocampal
gyrus
Figure 12.18
Limbic System
• Emotional or affective brain
• Amygdala—recognizes angry or fearful facial
expressions, assesses danger, and elicits the
fear response
• Cingulate gyrus—plays a role in expressing
emotions via gestures, and resolves mental
conflict
• Puts emotional responses to odors
• Example: skunks smell bad
Limbic System: Emotion and Cognition
• The limbic system interacts with the prefrontal
lobes, therefore:
• We can react emotionally to things we
consciously understand to be happening
• We are consciously aware of emotional
richness in our lives
• Hippocampus and amygdala—play a role in
memory
Reticular Formation
• Three broad columns along the length of the
brain stem
• Raphe nuclei
• Medial (large cell) group of nuclei
• Lateral (small cell) group of nuclei
• Has far-flung axonal connections with
hypothalamus, thalamus, cerebral cortex,
cerebellum, and spinal cord
Reticular Formation: RAS and Motor Function
• RAS (reticular activating system)
• Sends impulses to the cerebral cortex to keep
it conscious and alert
• Filters out repetitive and weak stimuli (~99% of
all stimuli!)
• Severe injury results in permanent
unconsciousness (coma)
Reticular Formation: RAS and Motor Function
• Motor function
• Helps control coarse limb movements
• Reticular autonomic centers regulate visceral
motor functions
• Vasomotor
• Cardiac
• Respiratory centers
Radiations
to cerebral
cortex
Visual
impulses
Auditory
impulses
Reticular formation
Ascending general
sensory tracts
(touch, pain, temperature)
Descending
motor projections
to spinal cord
Figure 12.19
Electroencephalogram (EEG)
• Records electrical activity that accompanies
brain function
• Measures electrical potential differences
between various cortical areas
(a) Scalp electrodes are used to record brain wave
activity (EEG).
Figure 12.20a
Brain Waves
• Patterns of neuronal electrical activity
• Generated by synaptic activity in the cortex
• Each person’s brain waves are unique
• Can be grouped into four classes based on
frequency measured as Hertz (Hz)
Types of Brain Waves
• Alpha waves (8–13 Hz)—regular and rhythmic, lowamplitude, synchronous waves indicating an “idling”
brain
• Beta waves (14–30 Hz)—rhythmic, less regular
waves occurring when mentally alert
• Theta waves (4–7 Hz)—more irregular; common in
children and uncommon in adults
• Delta waves (4 Hz or less)—high-amplitude waves
seen in deep sleep and when reticular activating
system is damped, or during anesthesia; may
indicate brain damage
1-second interval
Alpha waves—awake but relaxed
Beta waves—awake, alert
Theta waves—common in children
Delta waves—deep sleep
(b) Brain waves shown in EEGs fall into
four general classes.
Figure 12.20b
Brain Waves: State of the Brain
• Change with age, sensory stimuli, brain
disease, and the chemical state of the body
• EEGs used to diagnose and localize brain
lesions, tumors, infarcts, infections,
abscesses, and epileptic lesions
• A flat EEG (no electrical activity) is clinical
evidence of death
Epilepsy
• A victim of epilepsy may lose consciousness,
fall stiffly, and have uncontrollable jerking
• Epilepsy is not associated with intellectual
impairments
• Epilepsy occurs in 1% of the population
Epileptic Seizures
• Absence seizures, or petit mal
• Mild seizures seen in young children where the
expression goes blank
• Tonic-clonic (grand mal) seizures
• Victim loses consciousness, bones are often
broken due to intense contractions, may
experience loss of bowel and bladder control,
and severe biting of the tongue
Control of Epilepsy
• Anticonvulsive drugs
• Vagus nerve stimulators implanted under the
skin of the chest can keep electrical activity of
the brain from becoming chaotic
Consciousness
• Conscious perception of sensation
• Voluntary initiation and control of movement
• Capabilities associated with higher mental
processing (memory, logic, judgment, etc.)
• Loss of consciousness (e.g., fainting or
syncopy) is a signal that brain function is
impaired
Consciousness
• Clinically defined on a continuum that grades
behavior in response to stimuli
• Alertness
• Drowsiness (lethargy)
• Stupor
• Coma
Sleep
• State of partial unconsciousness from which a
person can be aroused by stimulation
• Two major types of sleep (defined by EEG
patterns)
• Nonrapid eye movement (NREM)
• Rapid eye movement (REM)
Sleep
• First two stages of NREM occur during the
first 30–45 minutes of sleep
• Fourth stage is achieved in about 90 minutes,
and then REM sleep begins abruptly
Awake
REM: Skeletal
muscles (except
ocular muscles
and diaphragm)
are actively
inhibited; most
dreaming occurs.
NREM stage 1:
Relaxation begins;
EEG shows alpha
waves, arousal is easy.
NREM stage 2: Irregular
EEG with sleep spindles
(short high- amplitude
bursts); arousal is more
difficult.
NREM stage 3: Sleep
deepens; theta and
delta waves appear;
vital signs decline.
(a) Typical EEG patterns
NREM stage 4: EEG is
dominated by delta
waves; arousal is difficult;
bed-wetting, night terrors,
and sleepwalking may
occur.
Figure 12.21a
Sleep Patterns
• Alternating cycles of sleep and wakefulness
reflect a natural circadian (24-hour) rhythm
• RAS activity is inhibited during, but RAS also
mediates, dreaming sleep
• The suprachiasmatic and preoptic nuclei of
the hypothalamus time the sleep cycle
• A typical sleep pattern alternates between
REM and NREM sleep
Awake
REM
Stage 1
Stage 2
Non
REM Stage 3
Stage 4
Time (hrs)
(b) Typical progression of an adult through one
night’s sleep stages
Figure 12.21b
Importance of Sleep
• Slow-wave sleep (NREM stages 3 and 4) is
presumed to be the restorative stage
• People deprived of REM sleep become moody and
depressed
• REM sleep may be a reverse learning process where
superfluous information is purged from the brain
• Daily sleep requirements decline with age
• Stage 4 sleep declines steadily and may disappear
after age 60
Sleep Disorders
• Narcolepsy
• Lapsing abruptly into sleep from the awake
state
• Insomnia
• Chronic inability to obtain the amount or quality
of sleep needed
• Sleep apnea
• Temporary cessation of breathing during sleep
Language
• Language implementation system
• Basal nuclei
• Broca’s area and Wernicke’s area (in the
association cortex on the left side)
• Analyzes incoming word sounds
• Produces outgoing word sounds and grammatical
structures
• Corresponding areas on the right side are
involved with nonverbal language components
Memory
• Storage and retrieval of information
• Two stages of storage
• Short-term memory (STM, or working
memory)—temporary holding of information;
limited to seven or eight pieces of information
• Long-term memory (LTM) has limitless
capacity
Outside stimuli
General and special sensory receptors
Afferent inputs
Temporary storage
(buffer) in
cerebral cortex
Automatic
memory
Data permanently
lost
Data selected
for transfer
Short-term
memory (STM)
Forget
Forget
Data transfer
influenced by:
Retrieval
Excitement
Rehearsal
Association of
old and new data
Long-term
memory
(LTM)
Data unretrievable
Figure 12.22
Transfer from STM to LTM
• Factors that affect transfer from STM to LTM
• Emotional state—best if alert, motivated,
surprised, and aroused
• Rehearsal—repetition and practice
• Association—tying new information with old
memories
• Automatic memory—subconscious information
stored in LTM
Categories of Memory
•
Declarative memory (factual knowledge)
•
Explicit information
•
Related to our conscious thoughts and our
language ability
•
Stored in LTM with context in which it was
learned
Categories of Memory
•
Nondeclarative memory
•
Less conscious or unconscious
•
Acquired through experience and repetition
•
Best remembered by doing; hard to unlearn
•
Includes procedural (skills) memory, motor
memory, and emotional memory
Brain Structures Involved in Declarative
Memory
• Hippocampus and surrounding temporal lobes
function in consolidation and access to
memory
• ACh from basal forebrain is necessary for
memory formation and retrieval
Thalamus
Basal forebrain
Touch
Prefrontal cortex
Hearing
Vision
Taste
Smell
Hippocampus
Sensory
input
(a) Declarative
memory circuits
Association
cortex
Thalamus
Medial temporal lobe
(hippocampus, etc.)
Prefrontal
cortex
ACh
ACh
Basal
forebrain
Figure 12.23a
Brain Structures Involved in Nondeclarative
Memory
• Procedural memory
• Basal nuclei relay sensory and motor inputs to
the thalamus and premotor cortex
• Dopamine from substantia nigra is necessary
• Motor memory—cerebellum
• Emotional memory—amygdala
Sensory and
motor inputs
Association
cortex
Basal
nuclei
Thalamus
Dopamine
Premotor
cortex
Premotor
cortex
Substantia
nigra
Thalamus
Basal nuclei
Substantia nigra
(b) Procedural (skills) memory circuits
Figure 12.23b
Molecular Basis of Memory
• During learning:
• Altered mRNA is synthesized and moved to axons and
dendrites
• Dendritic spines change shape
• Extracellular proteins are deposited at synapses
involved in LTM
• Number and size of presynaptic terminals may
increase
• More neurotransmitter is released by presynaptic
neurons
Molecular Basis of Memory
• Increase in synaptic strength (long-term
potentiation, or LTP) is crucial
• Neurotransmitter (glutamate) binds to NMDA
receptors, opening calcium channels in
postsynaptic terminal
Molecular Basis of Memory
• Calcium influx triggers enzymes that modify
proteins of the postsynaptic terminal and
presynaptic terminal (via release of retrograde
messengers)
• Enzymes trigger postsynaptic gene activation
for synthesis of synaptic proteins, in presence
of CREB (cAMP response-element binding
protein) and BDNF (brain-derived
neurotrophic factor)
Meninges
• Three layers
• Dura mater
• Arachnoid mater
• Pia mater
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
Skin of scalp
Periosteum
Bone of skull
Periosteal Dura
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Figure 12.24
Dura Mater
• Strongest meninx
• Two layers of fibrous connective tissue
(around the brain) separate to form dural
sinuses
Dura Mater
• Dural septa limit excessive movement of the
brain
• Falx cerebri—in the longitudinal fissure;
attached to crista galli
• Falx cerebelli—along the vermis of the
cerebellum
• Tentorium cerebelli—horizontal dural fold over
cerebellum and in the transverse fissure
Superior
sagittal sinus
Straight
sinus
Crista galli
of the
ethmoid
bone
Pituitary
gland
Falx cerebri
Tentorium
cerebelli
Falx
cerebelli
(a) Dural septa
Figure 12.25a
Arachnoid Mater
• Middle layer with weblike extensions
• Separated from the dura mater by the
subdural space
• Subarachnoid space contains CSF and blood
vessels
• Arachnoid villi protrude into the superior
sagittal sinus and permit CSF reabsorption
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
Skin of scalp
Periosteum
Bone of skull
Periosteal Dura
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Figure 12.24
Pia Mater
• Layer of delicate vascularized connective
tissue that clings tightly to the brain
Superior
sagittal sinus
4
Choroid
plexus
Arachnoid villus
Interventricular
foramen
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
1
Right lateral ventricle
(deep to cut)
Choroid plexus
of fourth ventricle
3
Third ventricle
1 CSF is produced by the
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
of spinal cord
(a) CSF circulation
2
choroid plexus of each
ventricle.
2 CSF flows through the
ventricles and into the
subarachnoid space via the
median and lateral apertures.
Some CSF flows through the
central canal of the spinal cord.
3 CSF flows through the
subarachnoid space.
4 CSF is absorbed into the dural venous
sinuses via the arachnoid villi.
Figure 12.26a
Choroid Plexuses
• Produce CSF at a constant rate
• Hang from the roof of each ventricle
• Clusters of capillaries enclosed by pia mater
and a layer of ependymal cells
• Ependymal cells use ion pumps to control the
composition of the CSF and help cleanse CSF
by removing wastes
Ependymal
cells
Capillary
Section
of choroid
plexus
Connective
tissue of
pia mater
Wastes and
unnecessary
solutes absorbed
CSF forms as a filtrate
containing glucose, oxygen,
vitamins, and ions
(Na+, Cl–, Mg2+, etc.)
(b) CSF formation by choroid plexuses
Cavity of
ventricle
Figure 12.26b
Blood-Brain Barrier
• Composition
• Continuous endothelium of capillary walls
• Basal lamina
• Feet of astrocytes
• Provide signal to endothelium for the
formation of tight junctions
Capillary
Neuron
Astrocyte
(a) Astrocytes are the most abundant
CNS neuroglia.
Figure 11.3a