Download CNS (Ch12)

The Central Nervous System
Chapter 12
Regions and Organization of the CNS
Adult brain regions
1.
2.
3.
4.
Cerebral hemispheres
Diencephalon
Brain stem (midbrain, pons, and medulla)
Cerebellum
Cerebral
hemisphere
Diencephalon
(d) Birth
Cerebellum
Brain stem
• Midbrain
• Pons
• Medulla
oblongata
Figure 12.3d
Ventricles of the Brain
• Connected to one another and to the central
canal of the spinal cord
• Lined by ependymal cells
• 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
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
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
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
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 and
sends output to multiple areas
• Allow us to give meaning to information
received, store it as memory, compare it to
previous experience, and decide on action to take
• 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
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
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
• Includes: cingulate gyrus, parahippocampal
gyrus, and hippocampus
• Provides emotional impact that helps
establish memories
Lateralization of Cortical Function
• Lateralization
– Division of labor between hemispheres
– Left hemisphere
• Controls language, math, and logic
– Right hemisphere
• Insight, visual-spatial skills, intuition, and artistic skills
• Cerebral dominance
– Designates the hemisphere dominant for language
(left hemisphere in 90% of people)
Cerebral White Matter
• Myelinated fibers and tracts
• Communication between cerebral areas, and
between cortex and lower CNS
– Association fibers— horizontal; connect different
parts of same hemisphere
– Commissural fibers— horizontal; connect gray
matter of two hemispheres
– Projection fibers— vertical; connect hemispheres
with lower brain or spinal cord
Basal Nuclei (Ganglia)
• Subcortical nuclei (caudate nucleus, putamen,
globus pallidus)
• Functionally associated with subthalamic
nuclei (diencephalon) and substantia nigra
(midbrain)
Figure 12.9b Basal nuclei.
Anterior
Cerebral cortex
Cerebral white matter
Corpus callosum
Anterior horn
of lateral ventricle
Head of caudate nucleus
Putamen
Globus
pallidus
Thalamus
Tail of caudate nucleus
Third ventricle
Inferior horn
of lateral ventricle
Posterior
© 2013 Pearson Education, Inc.
Functions of Basal Nuclei
• Functions thought to be:
– Influence muscle movements
– Role in cognition and emotion
– Regulate intensity of slow or stereotyped
movements
– Filter out incorrect/inappropriate responses
– Inhibit antagonistic/unnecessary movements
Diencephalon
• Three paired structures
– Thalamus
– Hypothalamus
– Epithalamus
• Encloses the third ventricle
Thalamus
(encloses third
ventricle)
Pineal gland
(part of epithalamus)
Hypothalamus
Figure 12.12
Thalamus
• 80% of diencephalon
• 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 to help direct the motor
cortical areas
• Mediates sensation, motor activities, cortical arousal,
learning, and memory
Hypothalamus
• Autonomic control center for many visceral
functions
• Center for emotional response
• 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
• Pineal gland—extends from the posterior
border and secretes melatonin
– Melatonin—helps regulate sleep-wake cycles
Brain Stem
• Controls automatic behaviors necessary for
survival
• Associated with 10 of the 12 pairs of cranial
nerves
• Three regions
– Midbrain
– Pons
– Medulla oblongata
Midbrain
Pons
Medulla
oblongata
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
Midbrain
• Located between the diencephalon and the
pons
• Cerebral aqueduct
– Channel between third and fourth ventricles
• Nuclei that control cranial nerves III
(oculomotor) and IV (trochlear)
• Releases dopamine from the substantia nigra
Pons
• 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)
• Nuclei that help maintain normal rhythm of
breathing
Medulla Oblongata
• Joins spinal cord at foramen magnum
• Crossover of the corticospinal tracts
(decussation of the pyramids)
• Cranial nerves VIII, X, and XII are associated
with the medulla
• 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
• Additional centers regulate
– Vomiting
– Hiccupping
– Swallowing
– Coughing
– Sneezing
Cerebellum
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
The Cerebellum
• 11% of brain mass
• Dorsal to the pons and medulla
• Subconsciously provides precise timing and
appropriate patterns of skeletal muscle
contraction
• Two hemispheres connected by vermis
• Folia—transversely oriented gyri
• Arbor vitae—distinctive treelike pattern of the
cerebellar white matter
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
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
• 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
• Motor function
– Helps control coarse limb movements
– Reticular autonomic centers regulate visceral
motor functions
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)
1-second interval
Alpha waves—awake but relaxed
Alpha: 8-13 Hz
Beta waves—awake, alert
Beta: 14-30 Hz
Theta waves—common in children
Theta: 4-7 Hz
Delta waves—deep sleep
Delta: ≤ 4 Hz
(b) Brain waves shown in EEGs fall into
four general classes.
Figure 12.20b
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) is a signal
that brain function is impaired
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 Patterns
• Alternating cycles of sleep and wakefulness
reflect a natural circadian (24-hour) rhythm
(via Hypothalamus)
• Typical = alternates b/w REM and NREM
Language
• Language implementation system
– 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
Categories of Memory
1. Declarative (fact) memory
–
–
–
Explicit information
Related to conscious thoughts and language ability
Stored in LTM with context in which learned
2. 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
Figure 12.21a Proposed memory circuits.
Sensory
input
Thalamus
Basal
forebrain
Touch
Prefrontal
cortex
Hearing
Vision
Hippocampus
Declarative memory circuits
Thalamus
Taste
Smell
Association
cortex
Medial temporal lobe
(hippocampus, etc.)
ACh released
by basal
forebrain
Prefrontal
cortex
Figure 12.21b Proposed memory circuits.
Premotor
cortex
Sensory and
motor inputs
Association
cortex
Basal
nuclei
Dopamine released
by substantia nigra
Basal
nuclei
Thalamus
Substantia
nigra
Procedural (skills) memory circuits
© 2013 Pearson Education, Inc.
Thalamus
Premotor
cortex
Protection of the Brain
•
•
•
•
Bone (skull)
Meninges
Cerebrospinal fluid
Also…..Blood-brain barrier
Major Protective
Structures
Meninges
• Cover and protect the CNS
• Protect blood vessels and enclose venous
sinuses
• Contain cerebrospinal fluid (CSF)
• Form partitions in the skull
• Three layers
– Dura mater
– Arachnoid mater
– Pia mater
Dura Mater
• Two layers of fibrous connective tissue
– Periosteal and meningeal layers
– Layers separate to form dural venous sinuses
• Dural septa limit excessive movement of the
brain
Skin of scalp
Periosteum
Bone of skull
Periosteal Dura
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Superior
sagittal sinus
Subdural
space
Falx cerebri
(in longitudinal
fissure only)
Subarachnoid
space
Dural septa!
Figure 12.24
Arachnoid Mater
• Middle layer with weblike extensions
• Subarachnoid space contains CSF and blood
vessels
• Arachnoid villi protrude into the superior
sagittal sinus and permit CSF reabsorption
Pia Mater
• Layer of delicate vascularized connective
tissue that clings tightly to the brain
Cerebrospinal Fluid (CSF)
• Composition
– Watery solution
– Less protein and different ion concentrations than
plasma
• Functions
– Gives buoyancy to the CNS organs
– Protects the CNS from blows and other trauma
– Nourishes the brain and carries chemical signals
Choroid Plexuses
• Produce CSF at a constant rate
• Hang from the roof of each ventricle
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
Blood-Brain Barrier
• Helps maintain a stable environment for the
brain
• Separates neurons from some bloodborne
substances
Blood-Brain Barrier
• Composition
– Continuous endothelium of
capillary walls
– Basal lamina
– “Feet of astrocytes”
Blood-Brain Barrier: Functions
• Selective barrier
– Allows nutrients to move by facilitated diffusion
– Allows any fat-soluble substances to pass,
including alcohol, nicotine, and anesthetics
• Absent in some areas, e.g., vomiting center
and the hypothalamus, where it is necessary
to monitor the chemical composition of the
blood
Spinal Cord
• Location
– Begins at the foramen magnum, ends (conus
medullaris) at L1
• Functions
• Two-way communication to/from the brain, spinal
reflex centers
• Protection
– Bone, meninges, and CSF
Cervical
enlargement
Dura and
arachnoid
mater
Lumbar
enlargement
Conus
medullaris
Cauda
equina
Filum
terminale
(a) The spinal cord and its nerve
roots, with the bony vertebral
arches removed. The dura mater
and arachnoid mater are cut
open and reflected laterally.
Cervical
spinal nerves
Thoracic
spinal nerves
Lumbar
spinal nerves
Sacral
spinal nerves
Figure 12.29a
Spinal Cord
• Spinal nerves
– 31 pairs
• Cervical and lumbar enlargements
– The nerves serving the upper and lower limbs
emerge here
• Cauda equina
– The collection of nerve roots at the inferior end of
the vertebral canal
Cross-Sectional Anatomy
• Two lengthwise grooves divide cord into right
and left halves
– Ventral (anterior) median fissure
– Dorsal (posterior) median sulcus
• Gray commissure—connects masses of gray
matter; encloses central canal
Dorsal median sulcus
Dorsal funiculus
White
Ventral funiculus
columns Lateral funiculus
Dorsal root
ganglion
Gray
commissure
Dorsal horn Gray
Ventral horn matter
Lateral horn
Spinal nerve
Dorsal root
(fans out into
dorsal rootlets)
Ventral root
(derived from several
ventral rootlets)
Central canal
Ventral median
fissure
Pia mater
Arachnoid mater
Spinal dura mater
(b) The spinal cord and its meningeal coverings
Figure 12.31b
Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
Somatic
sensory
neuron
Visceral
sensory
neuron
Visceral
motor
neuron
Somatic
motor neuron
Spinal nerve
Ventral root
(motor)
Ventral horn
(motor neurons)
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
Figure 12.32
Pathway Generalizations
• Pathways decussate (cross over)
• Most consist of two or three neurons (a relay)
• Most exhibit somatotopy (precise spatial
relationships)
• Pathways are paired symmetrically (one on
each side of the spinal cord or brain)
See figures 12.30 and 12.31, Table 12.2
Spinal Cord Trauma
• Functional losses
– Parasthesias (abnormal sensation)
– Paralysis (loss of motor function)
• Transection
– Cross sectioning of the spinal cord at any level
– Results in total motor and sensory loss in regions
inferior to the cut
– Paraplegia—transection between T1 and L1
– Quadriplegia—transection in the cervical region