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prepared by
Janice Meeking,
Mount Royal College
CHAPTER
12
The Central
Nervous
System:
Part A
Copyright © 2010 Pearson Education, Inc.
Central Nervous System (CNS)
• CNS consists of the brain and spinal cord
• Cephalization
• Evolutionary development of the rostral
(anterior) portion of the CNS
• Increased number of neurons in the head
• Highest level is reached in the human brain
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Functions of the Nervous System
1. Sensory input
•
Information gathered by sensory receptors
about internal and external changes
2. Integration
•
Interpretation of sensory input
3. Motor output
•
Activation of effector organs (muscles and
glands) produces a response
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Sensory input
Integration
Motor output
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Figure 11.1
Divisions of the Nervous System
• Central nervous system (CNS)
• Brain and spinal cord
• Integration and command center
• Peripheral nervous system (PNS)
• Paired spinal and cranial nerves carry
messages to and from the CNS
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Dendrites
(receptive regions)
Cell body
(biosynthetic center
and receptive region)
Nucleolus
Axon
(impulse generating
and conducting region)
Nucleus
Nissl bodies
Axon hillock
(b)
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Impulse
direction
Node of Ranvier
Schwann cell
Neurilemma (one interTerminal
node)
branches
Axon
terminals
(secretory
region)
Figure 11.4b
Peripheral Nervous System (PNS)
•
Two functional divisions
1. Sensory (afferent) division
•
Somatic afferent fibers—convey impulses
from skin, skeletal muscles, and joints
•
Visceral afferent fibers—convey impulses
from visceral organs
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2. Motor (efferent) division
•
Transmits impulses from the CNS to
effector organs
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Motor Division of PNS
1. Somatic (voluntary) nervous system
•
Conscious control of skeletal muscles
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Peripheral nervous system (PNS)
Central nervous system (CNS)
Cranial nerves and spinal nerves
Communication lines between the
CNS and the rest of the body
Brain and spinal cord
Integrative and control centers
Sensory (afferent) division
Somatic and visceral sensory
nerve fibers
Conducts impulses from
receptors to the CNS
Somatic sensory
fiber
Motor (efferent) division
Motor nerve fibers
Conducts impulses from the CNS
to effectors (muscles and glands)
Somatic nervous
system
Somatic motor
(voluntary)
Conducts impulses
from the CNS to
skeletal muscles
Skin
Visceral sensory fiber
Stomach
Skeletal
muscle
Motor fiber of somatic nervous system
Sympathetic division
Mobilizes body
systems during activity
Sympathetic motor fiber of ANS
Structure
Function
Sensory (afferent)
division of PNS
Motor (efferent)
division of PNS
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Parasympathetic motor fiber of ANS
Autonomic nervous
system (ANS)
Visceral motor
(involuntary)
Conducts impulses
from the CNS to
cardiac muscles,
smooth muscles,
and glands
Parasympathetic
division
Conserves energy
Promotes housekeeping functions
during rest
Heart
Bladder
Figure 11.2
Embryonic Development Don’t copy
• Neural plate forms from ectoderm
• Neural plate invaginates to form a neural
groove and neural folds
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Surface
ectoderm
Head
Neural
plate
Tail
1 The neural plate forms from surface ectoderm.
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Figure 12.1, step 1
Neural folds
Neural
groove
2 The neural plate invaginates, forming the neural
groove, flanked by neural folds.
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Figure 12.1, step 2
Embryonic Development don’t copy
• Neural groove fuses dorsally to form the
neural tube
• Neural tube gives rise to the brain and spinal
cord
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Neural crest
3 Neural fold cells migrate to form the neural crest,
which will form much of the PNS and many other
structures.
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Figure 12.1, step 3
Head
Surface
ectoderm
Tail
Neural
tube
4 The neural groove becomes the neural tube, which
will form CNS structures.
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Figure 12.1, step 4
Anterior (rostral)
Metencephalon
Mesencephalon
Diencephalon
Telencephalon
Myelencephalon
(a) Week 5
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Posterior (caudal)
Midbrain
Cervical
Flexures
Spinal cord
Figure 12.3a
Cerebral hemisphere
Outline of diencephalon
Midbrain
Cerebellum
Pons
Medulla oblongata
(b) Week 13
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Spinal cord
Figure 12.3b
(c) Week 26
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Cerebral
hemisphere
Cerebellum
Pons
Medulla
oblongata
Spinal cord
Figure 12.3c
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*Regions and Organization of the CNS
•
Adult brain regions
1. Cerebral hemispheres
2. Diencephalon
3. Brain stem (midbrain, pons, and medulla)
4. Cerebellum
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Cerebral
hemisphere
Diencephalon
(d) Birth
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Cerebellum
Brain stem
• Midbrain
• Pons
• Medulla
oblongata
Figure 12.3d
Regions and Organization of the CNS
• Spinal cord
• Central cavity surrounded by a gray matter
core
• External white matter composed of myelinated
fiber tracts
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Regions and Organization of the CNS
• Brain
• Similar pattern with additional areas of gray
matter
• Nuclei in cerebellum and cerebrum
• Cortex of cerebellum and cerebrum
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Cortex of
gray matter
Inner gray
matter
Central cavity
Migratory
pattern of
neurons
Cerebrum
Cerebellum
Region of cerebellum
Outer white
matter
Gray matter
Central cavity
Inner gray matter
Outer white matter
Brain stem
Gray matter
Central cavity
Outer white matter
Spinal cord
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Inner gray matter
Figure 12.4
Ventricles of the Brain
• Connected to one another and to the central
canal of the spinal cord
• Lined by ependymal cells
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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
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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
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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
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*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
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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)
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Figure 12.6a
Frontal lobe
Central
sulcus
Gyri of insula
Temporal lobe
(pulled down)
(b)
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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)
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Posterior
Figure 12.6c
Left cerebral
hemisphere
Brain stem
Transverse
cerebral
fissure
Cerebellum
(d)
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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
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*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
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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
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Figure 12.12
*Motor Areas
• Primary (somatic) motor cortex
• Premotor cortex
• Broca’s area
• Frontal eye field
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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
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Figure 12.8a
*Primary Motor Cortex
• Allows conscious control of precise, skilled,
voluntary movements
• Motor homunculi: upside-down caricatures
representing the motor innervation of body
regions
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Posterior
Motor
Motor map in
precentral gyrus
Anterior
Toes
Jaw
Tongue
Swallowing
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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
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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
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Frontal Eye Field
• Anterior to the premotor cortex and superior to
Broca’s area
• Controls voluntary eye movements
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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
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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
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Posterior
Sensory
Anterior
Sensory map in
postcentral gyrus
Genitals
Primary somatosensory cortex
(postcentral gyrus)
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Intraabdominal
Figure 12.9
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
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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
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Figure 12.8b
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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
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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
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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
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Brain Stem
• Three regions
• Midbrain
• Pons
• Medulla oblongata
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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
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Medulla Oblongata
• Respiratory centers
• Generate respiratory rhythm
• Control rate and depth of breathing, with
pontine centers
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Medulla Oblongata
• Additional centers regulate
• Vomiting
• Hiccuping
• Swallowing
• Coughing
• Sneezing
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The Cerebellum
• 11% of brain mass
• Dorsal to the pons and medulla
• Subconsciously provides precise timing and
appropriate patterns of skeletal muscle
contraction
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Anterior lobe
Cerebellar cortex
Arbor
vitae
Cerebellar
peduncles
• Superior
• Middle
• Inferior
Medulla
oblongata
(b)
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Flocculonodular
lobe
Posterior
lobe
Choroid
plexus of
fourth
ventricle
Figure 12.17b
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
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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)
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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
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Categories of Memory
1. 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
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Categories of Memory
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
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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
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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
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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
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Figure 12.23b
Molecular Basis of Memory
• During learning:
• Altered mRNA is synthesized and moved to axons and
dendrites
• Extracellular proteins are deposited at synapses
involved in LTM
• More neurotransmitter is released by presynaptic
neurons
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Protection of the Brain
• Bone (skull)
• Membranes (meninges)
• Watery cushion (cerebrospinal fluid)
• Blood-brain barrier
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Meninges
• Three layers
• Dura mater
• Arachnoid mater
• Pia mater
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Superior
sagittal sinus
Subdural
space
Subarachnoid
space
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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
Cerebrospinal Fluid (CSF)
• Composition
• Watery solution
• Less protein and different ion concentrations
than plasma
• Constant volume
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Cerebrospinal Fluid (CSF)
• Functions
• Gives buoyancy to the CNS organs
• Protects the CNS from blows and other trauma
• Nourishes the brain and carries chemical
signals
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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
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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
• Antibodies are too large to cross the blood–
brain barrier, and only certain antibiotics are
able to pass
• Exceptions are the bacteria that causes
Lyme’s disease and syphilis
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Blood-Brain Barrier
• There are also some biochemical poisons that
are made up of large molecules that are too
big to pass through the blood–brain barrier.
• Composition
• Continuous endothelium of capillary walls
• Basal lamina
• formation of tight junctions
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Capillary
Neuron
Astrocyte
(a) Astrocytes are the most abundant
CNS neuroglia.
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Figure 11.3a
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
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Homeostatic Imbalances of the Brain
• Traumatic brain injuries
• Concussion—temporary alteration in function
• Contusion—permanent damage
• Subdural or subarachnoid hemorrhage—may
force brain stem through the foramen
magnum, resulting in death
• Cerebral edema—swelling of the brain
associated with traumatic head injury
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Homeostatic Imbalances of the Brain
• Cerebrovascular accidents (CVAs)(strokes)
• Blood circulation is blocked and brain tissue dies, e.g.,
blockage of a cerebral artery by a blood clot
• Typically leads to hemiplegia, or sensory and speed
deficits
• Transient ischemic attacks (TIAs)—temporary
episodes of reversible cerebral ischemia
• Tissue plasminogen activator (TPA) is the only
approved treatment for stroke
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Homeostatic Imbalances of the Brain
• Degenerative brain disorders
• Alzheimer’s disease (AD): a progressive degenerative
disease of the brain that results in dementia
• Parkinson’s disease: degeneration of the dopaminereleasing neurons of the substantia nigra
• Huntington’s disease: a fatal hereditary disorder
caused by accumulation of the protein huntingtin that
leads to degeneration of the basal nuclei and cerebral
cortex
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• The cranial nerves are:
• I - Olfactory nerve
• II - Optic nerve
• III - Oculomotor nerve
• IV - Trochlear nerve
• V - Trigeminal nerve/dentist nerve
• VI - Abducens nerve
• VII - Facial nerve
• VIII - Vestibulocochlear nerve/Auditory nerve
• IX - Glossopharyngeal nerve
• X - Vagus nerve
• XI - Accessory nerve/Spinal accessory nerve
• XII - Hypoglossal nerve
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• Odor Of Orangutan Terrified Tarzan After
Forty Voracious Gorillas Viciously Attacked
Him
• Old Opie Occasionally Tries Trigonometry
And Feels Very Gloomy, Vague And
Hypoactive
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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)
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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
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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
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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
• A typical sleep pattern alternates between
REM and NREM sleep
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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
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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
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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
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