Chapter
The central nervous system
• Identify and explain the function of different
types of neurons, and structures in the central
nervous system.
• Explain the functional organization of the
nervous system.
• These will be measured by lecture exams and
quizzes.
Outline
• Organization
• Protection
• Overview of components
–
–
–
–
–
–
–
–
Cortex
Basal nuclei
Thalamus
Hypothalamus
Limbic system
Cerebellum
Brain stem
Spinal cord
Central nervous system (CNS)
Brain and
spinal cord
Input
to CNS
from
periphery
Output
from
CNS to
periphery
Peripheral nervous
system (PNS)
Efferent
division
Afferent
division
Sensory
stimuli
•
•
KEY
Visceral
stimuli
Central nervous system (CNS)
–
Consists of brain and spinal cord
Peripheral nervous system (PNS)
–
Afferent division
•
Carries information to the
CNS
•
Two branches
– Sympathetic
– Parasympathetic
Central nervous system
Peripheral nervous system
Afferent division of PNS*
Efferent division of PNS
Somatic nervous system
Somatic
nervous system
Autonomic
nervous system
Stimuli in
digestive
tract
Motor
neurons
Sympathetic
Parasympathetic
nervous system nervous system
Enteric nervous
system
Skeletal
muscles
Smooth muscle
Cardiac muscle
Exocrine glands
Some endocrine
glands
Digestive
organs only
Autonomic nervous system
Enteric nervous system*
Effector organs
(made up of muscle and gland tissue)
Fig. 5-1, p. 136
Central
nervous system
(spinal cord)
Axon
terminals
Peripheral
nervous system
Cell
body
Functional Classes of Neurons
•
Afferent neuron
•
Central
axon
Peripheral axon
(afferent fiber)
Sensory
receptor
•
Interneuron
Afferent neurons
– Inform CNS about
conditions in both
the external and
internal
environment
Efferent neurons
– Carry instructions
from CNS to
effector organs –
muscles and
glands
Interneurons
– Found entirely
within CNS
– Responsible for
•
•
Efferent neuron*
Effector organ
(muscle or gland)
Integrating
afferent
information
and
formulating an
efferent
response
Higher mental
functions
associated
with the “mind”
Axon
(efferent fiber)
Axon
Cell
terminals
body
* Efferent autonomic nerve pathways consist of a two-neuron chain between
the CNS and the effector organ.
Fig. 5-2, p. 137
Neuroglia
• Also called glial cells
• Physically, metabolically, and functionally support
interneurons
• Four major types of cells
– Astrocytes
– Oligodendrocytes
– Microglia
– Ependymal cells
• 90% of CNS cells
Astrocytes
–
–
–
–
–
–
–
Main “glue” of CNS
– holds neurons
together
Guide neurons
during fetal brain
development
Aid in establishment
of blood-brain
barrier
Important in repair
of brain injuries and
in neural scar
formation
Play role in
neurotransmitter
activity
Take up excess K+
from brain ECF
Along with other
glial cells – enhance
synapse formation
and modify synaptic
transmission
•
Neuroglia
Oligodendrogytes
•
– Form myelin sheaths
around axons in CNS
Space containing
cerebrospinal fluid
Brain
interstitial
fluid
Neurons
Ependymal cells
•
Microglia
– Line internal, fluid-filled – Immune defense
cavities of the CNS
cells of the CNS
– In ventricles of brain, – In resting state
help form and circulate
release low levels
cerebrospinal fluid
of growth factors
that help neurons
and other glial
cells survive and
thrive. Can
move.
Ependymal
cell
Astrocyte
Oligodendrocyte
Capillary
Microglia
Fig. 5-3, p. 138
Protection of CNS
•
•
•
•
Enclosed by hard, bony structures
Wrapped by three protective and nourishing membranes – meninges
– Dura mater
– Arachnoid mater
– Pia mater
Floats in cushioning fluid – cerebrospinal fluid (CSF)
– Surrounds and cushions brain and spinal cord
– Shock absorbing
– Formed primarily by choroid plexuses
Blood-brain barrier limits access of blood-borne materials into brain tissue
Subarachnoid space of brain
Cerebrospinal fluid
Arachnoid villus
Lateral ventricle
Dural sinus
Venous blood
Cerebrum
Vein
5
Choroid plexus of lateral ventricle
Choroid plexus of third ventricle
Third ventricle
1
4
2
Pia mater
Arachnoid mater Cranial meninges
Dura mater
Cerebellum
Aperture of fourth ventricle
Choroid plexus of fourth ventricle
Spinal cord
Central canal
3
Pia mater
Arachnoid mater Spinal meninges
Dura mater
Brain stem
4
Fourth ventricle
Subarachnoid space of spinal cord
Fig. 5-6a, p. 141
Right lateral
ventricle
Front of
brain
Left lateral
ventricle
Third
ventricle
Back of
brain
Fourth ventricle
Central canal
of spinal cord
Fig. 5-5a, p. 139
Blood-Brain Barrier (BBB)
• Protects brain from chemical fluctuations in blood
• Minimizes possibility that harmful blood-borne
substances might reach central nervous tissue
• Prevents certain circulating hormones that could also act
as neurotransmitters from reaching brain
• Limits use of drugs for treatment of brain and spinal cord
disorders
– Many drugs cannot penetrate BBB
– Keeps K+ low and Na+ High
• Cells joined by tight junctions
•
an anatomic-physiologic feature
of the brain thought to consist of
walls of capillaries in the central
nervous system and surrounding
astrocytic glial membranes.
•
The barrier separates the
parenchyma of the central
nervous system from blood.
•
The blood-brain barrier prevents
or slows the passage of some
drugs and other chemical
compounds, radioactive ions,
and disease-causing organisms
such as viruses from the blood
into the central nervous system.
Central Nervous System
• Enables you to:
– Subconsciously regulate your internal
environment by neural means
– Experience emotions
– Voluntarily control your movements
– Be consciously aware of your own body and your
surroundings
– Engage in other higher cognitive processes such
as thought and memory
Cerebrum (the right
hemisphere, at the
longitudinal fissure
between it and the
left hemisphere)
Hypothalamus
Thalamus
Pineal gland
Corpus
callosum
Optic
chiasm
Top
Front
of
brain
Midbrain
Brain
stem Pons
Medulla
Cerebellum
(b) Brain, sagittal view
Fig. 5-7b, p. 146
Cerebrum (cortex)
• Highly developed
• Makes up about 80% of total brain weight
(largest portion of brain)
• Inner core houses basal nuclei
• Outer surface is highly convoluted cerebral
cortex
– Highest, most complex integrating area of the
brain
– Plays key role in most sophisticated neural
functions
– Organized into six well-defined layers
– Layers are organized into functional vertical
columns
Cerebral Hemispheres
Left cerebral
hemisphere
Right cerebral
hemisphere
– Excels in logical,
analytic,
sequential, and
verbal tasks
– Excels in
nonlanguage skills
• Spatial
perception and
artistic and
musical talents
• Math, language
forms,
philosophy
Longitudinal fissure
Central sulcus
Four major lobes
Frontal
lobe
Parietal
lobe
Responsible for
Voluntary motor activity
Speaking ability
Elaboration of thought
Somatosensory processing
Parietooccipital
notch
Occipital
lobe
Lateral
fissure
Carries out initial processing
Of visual input
Preoccipital
notch
Temporal
lobe
Initial reception of sound sensation
Brain stem
Cerebellum
Fig. 5-8, p. 143
Fig. 5-9b, p. 144
Fig. 5-9a, p. 144
Cerebral Cortex
• Primary areas of cortical specialization for
language
– Broca’s area
• Governs speaking ability
– Wernicke’s area
• Concerned with language comprehension
• Responsible for formulating coherent patterns of
speech
• Language disorders
– Aphasias
– Speech impediments
– Dyslexia
Cerebral Cortex
• Primary motor cortex
– Located in frontal lobe
– Confers voluntary control over movement
produced by skeletal muscles
– Primarily controls muscles on the opposite side of
the body
– Motor homunculus
• Depicts location and relative amount of motor cortex
devoted to output to muscles of each body part
Electroencephalogram (EEG)
• Record of postsynaptic activity in cortical
neurons
• “Brain waves”
• Three major uses
– Clinical tool in diagnosis of cerebral dysfunction
• epilepsy
– Used in legal determination of brain death
– Used to distinguish various stages of sleep
Electroencephalogram (EEG)
Cerebral Cortex
Schematic Linking
of Various Regions
of the Cortex
Flow of signals
Brain component
Cerebral cortex
Cerebral cortex
Basal nuclei
(lateral to thalamus)
*
Thalamus
(medial)
Basal nuclei
Thalamus
Hypothalamus
Hypothalamus
Cerebellum
Cerebellum
Midbrain
Brain stem
Brain stem
(midbrain, pons,
and medulla)
Pons
Medulla
Spinal cord
Table 5-2 (1), p. 140
Right cerebral
hemisphere
Left cerebral
hemisphere
Cerebral cortex
(gray matter)
White matter
Corpus callosum
Caudate
nucleus
Lateral ventricle
Basal
nuclei
Putamen
Globus pallidus gray
matter)
Claustrum
Thalamus
Third ventricle
Part of hypothalamus
Fig. 5-14a, p. 154
Basal Nuclei (ganglia)
• Act by modifying ongoing activity in motor pathways
• Signals from the cortex reach the basal ganglia, the
signals are processed and the output is sent back to the
motor cortex
• Primary functions
– Inhibiting muscle tone throughout the body
– Selecting and maintaining purposeful motor activity
while suppressing useless or unwanted patterns of
movement
– Helps monitor and coordinate slow, sustained
contractions, especially those related to posture and
support
– Links cortex and thalamus
Disorders of the basal ganglia
• Parkinson’s
– tremors of the hand
– dopamine deficiency
– Increased rigidity, resting tremors, slow initiation of motor
behavior
– http://www.youtube.com/watch?v=S5EE8EVv600
– http://www.youtube.com/watch?feature=fvwp&NR=1&v=xuVY7wS25rc
– http://www.youtube.com/watch?v=ECkPVTZlfP8
Huntington’s
– Uncontrollable movements
– http://www.youtube.com/watch?v=JzAPh2v-SCQ
Brain component
Cerebral cortex
Cerebral cortex
Basal nuclei
(lateral to thalamus)
Basal nuclei
Thalamus
(medial)
*
Thalamus
Hypothalamus
Hypothalamus
Cerebellum
Cerebellum
Midbrain
Brain stem
Brain stem
(midbrain, pons,
and medulla)
Pons
Medulla
Spinal cord
Table 5-2 (1), p. 140
Diencephalon
• Houses two brain components
– Thalamus
• Performs some primitive sensory processing
– Hypothalamus
• Controls many homeostatic functions important in
maintaining stability of internal environment
Thalamus
• Part of diencephalon
• Serves as “relay station” and synaptic integrating center
for processing sensory input on its way to cerebral cortex
• Screens out insignificant signals and routes important
ones to the somatosensory cortex (directs attention to
sensory stimuli of interest)
• Capable of crude awareness of various types of
sensation but cannot distinguish their location or
intensity
• Positive reinforcement of motor signals initiated by the
motor cortex
Disorders of the thalamus
• Thalamic pain syndrome
• Dejerine-Roussy syndrome
• http://www.youtube.com/watch?v=vEV6FompwZg
Brain component
Cerebral cortex
Cerebral cortex
Basal nuclei
(lateral to thalamus)
Basal nuclei
Thalamus
(medial)
*
Thalamus
Hypothalamus
Hypothalamus
Cerebellum
Cerebellum
Midbrain
Brain stem
Brain stem
(midbrain, pons,
and medulla)
Pons
Medulla
Spinal cord
Table 5-2 (1), p. 140
Hypothalamus
• Brain area most involved in directly regulating internal
environment
• Functions
–
–
–
–
–
–
–
–
–
Controls body temperature
Controls thirst and urine output
Controls food intake
Controls anterior pituitary hormone secretion
Produces posterior pituitary hormones
Controls uterine contractions and milk ejection
Serves as a major ANS coordinating center
Plays role in emotional and behavioral patterns
Participates in sleep-wake cycle
Limbic System
• Includes portions of the
hypothalamus and other
forebrain structures that
encircle brain stem
• Responsible for
– Emotion (preparing for
attack, crying,
laughing, joy
satisfaction, pleasure,
fear)
– Basic, inborn
behavioral patterns
related to survival and
perpetuation of the
species
– Plays important role in
motivation and learning
and memory
Memory
• Storage of acquired knowledge for later recall
• Memory trace
– Neural change responsible for retention or storage of
knowledge
• Short-term memory
– Lasts for seconds to hours
• Long-term memory
– Retained for days to years
• Consolidation
– Process of transferring and fixing short-term memory
traces into long-term memory stores
• Working memory
– Temporarily holds and interrelates various pieces of
information relevant to a current mental task
Comparison of Long-Term and Short-Term Memory
*
*
Habituation (in Aplysia)
Sensitization (in Aplysia)
Repetitious indifferent stimulus
Strong or noxious stimulus
Decreased response
to continued stimuli
Release of serotonin from
facilitating interneuron
Cyclic AMP in
presynaptic neuron
Blockage of K+ channels in
presynaptic neuron
Increased
response
to continued
stimuli
Prolongation of action potential
in presynaptic neuron
Closing of Ca2+ channels in
presynaptic neuron
Ca2+ channels in presynaptic
neuron kept open longer
Ca2+ influx
Ca2+ influx
Output of transmitter from
presynaptic neuron
Output of transmitter from
presynaptic neuron
Postsynaptic potential in
efferent neuron
Postsynaptic potential in
efferent neuron
Reduced behavioral response
to indifferent stimuli
Enhanced behavioral
response to mild stimuli
Fig. 5-18, p. 160
Long Term Potentiation
Prolonged increase in the strength of existing synaptic
Connections in activated pathways following brief
periods of repeated stimulation
Fig. 5-19, p. 162
Brain component
Cerebral cortex
Cerebral cortex
Basal nuclei
(lateral to thalamus)
Basal nuclei
Thalamus
(medial)
Thalamus
Hypothalamus
Hypothalamus
Cerebellum
RAS!
*
Midbrain
Brain stem
Cerebellum
Brain stem
(midbrain, pons,
and medulla)
Pons
Medulla
Spinal cord
Table 5-2 (1), p. 140
Cerebellum
Cerebellum disorders
• Ataxia (uncoordinated movement) and abnormal muscle tone
• Inherited, nutritional, developmental, vascular, TBI, demylenating
• Cerebellar lesions
– Incoordination of movements
– Delay initiation of movements
– Do not prevent their execution
– Not significant unless a great portion of the cerebellum is
lesioned.
– Speed effected
http://www.youtube.com/watch?v=DYP2hkkE9fQ
– http://www.youtube.com/watch?v=Dox3_ox8C2U&NR=1&feature
=endscreen
– http://www.youtube.com/watch?v=5eBwn22Bnio
Brain component
Cerebral cortex
Cerebral cortex
Basal nuclei
(lateral to thalamus)
Basal nuclei
Thalamus
(medial)
Thalamus
Hypothalamus
Hypothalamus
Cerebellum
Cerebellum
Midbrain
Brain stem
*
Pons
Medulla
Brain stem
(midbrain, pons,
and medulla)
Spinal cord
Table 5-2 (1), p. 140
Brain Stem
• Critical connecting link between rest of brain and
spinal cord
• Consists of
– Medulla
– Pons
– Midbrain
• Functions
Brain Stem
– Most of cranial nerves arise from brain stem
– Neuronal clusters within brain stem control heart
and blood vessel function, respiration, and many
digestive functions
– Plays role in regulating muscle reflexes involved
in equilibrium and posture
– Reticular formation within brain stem receives
and integrates all incoming sensory synaptic input
and forms the RAS which arouses the cortex.
– Centers that govern sleep are in brain stem
(evidence suggests center promoting slow-wave
sleep lies in hypothalamus)
= Sensory fibers
= Motor fibers
1. Olfactory nerve
Retina
Mucosa of
nasal cavity
Termination of fibers
of olfactory nerve
Olfactory
bulb
mnemonic
On
Old
Olympus
Towering
Top
A
Famous
Vocal
German
Viewed
Some
Hops
olfactory
optic
oculomotor
trochlear
trigeminal
abducens
facial
vestibulocochlear
glossopharyngeal
vagus
spinal accessory
hypoglossal
3. Oculomotor
nerve
2. Optic
nerve
6. Abducens
nerve
4. Trigeminal
nerve
Lateral
rectus
Motor—muscles
of face and
scalp; salivary
and tear glands
5. Trochlear nerve
Sensory—face
and head
Motor—
muscles of
mastication
Sensory—
taste buds on
anterior tongue
7. Facial nerve
Fig. 5-21, p. 165
Motor—muscles of
pharynx; parotid gland
= Sensory fibers
Sensory—taste buds on
posterior tongue; receptors in
pharynx and carotid sinus
= Motor fibers
8. Vestibulocochelar Vestibular
branch
nerve
Cochlear
branch
9. Glossopharyngeal
nerve
12. Hypoglossal
nerve
11. Accessory
nerve
Cochlea,
vestibule, and
semicircular
canals of
inner ear
10. Vagus nerve
Motor—muscles of pharynx and larynx;
thoracic and abdominal organs
Tongue muscles
Muscles of larynx, pharynx,
soft palate, shoulder,
and neck
Sensory—taste buds on
tongue and pharynx; thoracic
and abdominal organs
Fig. 5-21, p. 165
Brainstem disorders
• Locked in syndrome
– Quadraplegia, lack of speech, limited movement
of the eyes
– Conscious, aware, have cognitive function
– TBI, MS, stroke, Lou Gehrig’s disease
– http://www.youtube.com/watch?v=yidjnLXZ6Hg
– http://www.youtube.com/watch?v=xWHnkFaxMx
M
Spinal Cord
• Extends from brain stem through vertebral canal
• 31 pairs of spinal nerves emerge from spinal
cord through spaces formed between arches of
adjacent vertebrae
– Named for region of vertebral column from which
they emerge
•
•
•
•
•
8 pairs cervical (neck) nerves
12 pairs thoracic (chest) nerves
5 pairs lumbar (abdominal) nerves
5 pairs sacral (pelvic) nerves
1 pair coccygeal (tailbone) nerves
Spinal cord
Dorsal root
ganglion
Spinal
nerve
Meninges
(protective
coverings)
Vertebra
Intervertebral
disk
Sympathetic
ganglion
chain
Fig. 5-24, p. 168
Axon
Myelin
sheath
Connective tissue
around the axon
Connective tissue
around the nerve
Connective tissue
around a fascicle
Blood vessels
Nerve fascicle
(many axons
bundled in
connective
tissue)
Nerve
Fig. 5-30, p. 173
Ascending tracts
Descending tracts
Dorsal surface
Dorsal columns:
1. Fasciculus gracilis
2. Fasciculus cuneatus
Lateral corticospinal
Dorsal spinocerebellar
Gray
matter
Rubrospinal
Ventral spinocerebellar
Ventral corticospinal
Lateral spinothalamic
Ventral spinothalamic
Vestibulospinal
Ventral surface
Fig. 5-27, p. 170
Ascending tracts
Somatosensory
area
of cerebral
cortex
Descending tracts
Thalamus
Primary
motor
cortex
1
Cerebral
cortex
slice 1
2
3
4
Midbrain
5
slice 2
Cerebellum
slice 3
Ventral
corticospinal
tract
6
Lateral
corticospinal
tract
Pons
Ventral
spinocerebellar
tract
slice 3
Medulla
slice 4
Muscle
stretch
receptor
Fasciculus
cuneatus
Spinal cord
slice 5
Pressure
receptor in skin
Spinal cord
slice 5
Spinal cord
slice 6
Fig. 5-28, p. 172
Dorsal horn (cell bodies of interneurons
on which afferent neurons terminate)
Central
canal
Lateral horn (cell bodies of autonomic
efferent nerve fibers)
Ventral horn (cell bodies of somatic
efferent neurons)
Fig. 5-29, p. 173
Spinal Nerves
Spinal Cord
• Two vital functions
– Neuronal link between brain and PNS
– Integrating center for spinal reflexes
• Reflex
•
– Any response that occurs automatically without conscious effort
Two types of reflexes
– Simple, or basic, reflexes
• Built-in, unlearned responses
– Acquired, or conditioned, reflexes
• Result of practice and learning
• Reflex Arc
•
•
Neural pathway involved in accomplishing reflex activity
Five basic components
– Receptor
– Afferent pathway
– Integrating center
– Efferent pathway
– Effector
= excitatory interneuron
= inhibitory interneuron
= Synapse
= Inhibits
= Stimulates
Reflex arc example
withdrawal reflex
Thermal
pain receptor
in finger
Components of a
reflex arc
Receptor
Afferent pathway
Integrating center
Efferent pathway
Effector organs
Ascending pathway
to brain
Afferent
Pathway
Stimulus
Biceps
(flexor)
contracts
Hand
withdrawn
Efferent pathway
Triceps
(extensor)
relaxes
Integrating center
(spinal cord)
Effector
organs
Response
Fig. 5-31, p. 174
Crossed Extensor Reflex Coupled with the
Withdrawal Reflex
Strokes
Alzheimer’s disease
Sleep
• Function of sleep is unclear
• Sleep-wake cycle
– Normal cyclic variation in awareness of
surroundings
• Active process consisting of two types of sleep
characterized by different EEG patterns and
different behaviors
– Slow-wave sleep
– Paradoxical, or REM sleep
Comparison of Slow-Wave and Paradoxical Sleep
EEG
Patterns
During
Different
Types of
Sleep