Chapter 5
The Central Nervous System
V edit. Pg. 133-183
VI edit. Pg. 131-179
VII edit. Pg. 133-181
The endocrine system and the nervous
system are the main regulatory
systems of the body
Nervous System
(wired & specific)
Endocrine System
(wireless & diffuse)
Coordinate rapid,
precise responses
Control body activities
over long periods
Generate signals that
propagate rapidly
(action potentials)
Generate slowly acting
signals (hormones)
Target organs:
skeletal muscles,
heart, glands
Target organs: visceral
organs, heart, smooth
muscles, glands
Organization of the Nervous System
Nervous TissueNervous tissues are found in the brain, spinal cord,
and nerves
Main components:
Nerve cells (conduct nerve impulses)
Neuroglia (glial cells, support and nourish the
neurons)
Functional Classification of Neurons
Sensory neurons
(afferent)
Interneurons
Motor neurons
(efferent)
The spinal cord circuit as an example of
a neuronal networkCell body of
efferent neuron
Cell body of
afferent neuron
Efferent fiber
From receptors
To effectors
Spinal nerve
White matter Gray matter
Interneuron
Dorsal root
Dorsal root
ganglion
Ventral root
Classification of Glial Cells(Provide protection and nourishment to nerve cells)
Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
Function of Neuroglia (Glial Cells)Astrocytes: Star-like glial cells, found between neurons and blood
vessels.
Function: nourishment of neurons, support neurons and isolate group of
neurons into nuclei, buffer potassium ions and neurotransmitter from
the extracellular space, scaffold for brain development, synapse
formation and maintenance
Oligodendrocytes (Schwann cells in PNS): small glial cells with fewer
processes.
Function: insulation of axon with myelin sheath, guide the outgrowth of
axons
Function of Neuroglia (Glial Cells)
Microglia: Small glial cells, immune defense cells in CNS.
Function: removal of debris after injury
Ependymal cells: Ciliated cuboidal or elongated cells usually connected
through gap junctions. Found in the inner lining of the central canal of
the spinal cord, the lining of the brain ventricles and the choroid
plexus.
Function: form part of the blood-brain barrier (BBB), control transport of
substances into the cerebrospinal fluid, stem cells
Defense Mechanisms of Nerve Tissue
1) Skull and vertebral column
2) Meninges
3) Cerebrospinal fluid
4) Blood-brain barrier
The Meninges
Three layers of connective tissue that surround
and protect nerve tissue
Dura: toughest layer, consist of
connective tissue and
collagen fibers. Loosely
surrounds the brain and
spinal cord
Arachnoid: richly vascularized
layer
Subarachnoid space: contains
the cerebrospinal fluid (CSF)
Pia: closely adheres to brain and
spinal cord tissue, richly
vascularized
The cerebrospinal fluid (CSF)
surrounds and cushion the brain and
spinal cord
The cerebrospinal fluid is formed in the
choroid plexus and flow through the
ventricular system
The cerebrospinal fluid is reabsorbed in
the arachnoid villi
The CSF contains a higher
concentration of Na+ ions and less K+
than blood plasma
The Brain Ventricles
Aqueduct of
Sylvius
The Blood-Brain BarrierConsist of tightly packed endothelial cells that prevent
the unregulated flow of substances into the CSF and
the brain
Organization of the CNS
Cerebrum
Cerebellum
Diencephalon
Brain Stem
Spinal Cord
Structure and Function of Brain
Components
The Cerebral
Cortex
Central Sulcus
Convolutions
The Cerebral Cortex
Spinal Cord Cross Section
Grey matter White matter
The Cerebral Cortex
Layers of the Cerebral Cortex
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Functional Areas of the Cerebral
Cortex: Cortical Lobes
Functional Organization of the Cerebral
Cortex
Somatotopic MapsCortical areas that process information from specific areas of the
body
Left
hemisphere
Cross•-•sectional view
Temporal lobe
Sensory homunculus
Somatotopic Maps
Front
Left
hemisphere
Primary
motor
cortex
Top
view
Somato•-
sensory
cortex
Right
hemisphere
Frontal
lobe
Centralsulcus
Parietal
Occipital lobe
Back
Somatotopic MapsDifferent areas of the body are represented differently in the brain-
somatotopic maps
The area of representation is determined by the amount of
sensory/motor innervation on contralateral side of the body
Lefthemisphere
Cross•-•sectional view
Temporal lobe
Motor homunculus
Somatotopic Maps
Use-dependent competition
Plasticity (remodeling ability of the brain in response to changes in demand)
Lefthemisphere
Cross•-•sectional view
Temporal lobe
Motor homunculus
Control of Language
Control of Language
Association AreasBrain areas responsible for integration and processing of complex
information
Association AreasFunctional linking of various brain areas
Sensory input
Primary sensory areas
(somatosensory, visual,
auditory cortices)
Higher sensory areas
Association areas
Higher motor areas
Primary motor areas
Motor output
Basal Nuclei
Thalamus & Hypothalamus
Basal Nuclei(inhibit muscular tone, control of motor activity, control of slow
movements)
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Hypothalamus & Pituitary GlandCoordinate homeostatic functions in the body
© Brooks/Cole - Thomson Learning
Hypothalamus & Pituitary Gland
Function:
Body temperature
Urine output
Food intake
Uterine contractions
Milk production
Smooth and
cardiac muscles
CerebellumInvolved in balance maintenance, planning of voluntary
movements, motor skills learning
© Brooks/Cole - Thomson Learning
CerebellumInvolved in balance maintenance and planning of voluntary
movements
Unfolded
Regulation of
muscle tone,
coordination of
skilled voluntary
movement
Planning and
initiation of
voluntary activity
Maintenance of
balance, control
of eye movements
Vestibulocerebellum
Spinocerebellum
Cerebrocerebelum
Organization of the CNS: Brain Stem
Cerebrum
Cerebellum
Diencephalon
Brain Stem
Spinal Cord
Brain Stem
Brain Stem
Function:
1) Origin of 12 cranial nerves
innervating head, neck and
portions of the thoracic cavity http://www.wisc-online.com/objects/index.asp?objID=AP11504
2) Control of visceral functions
(vegetative): heart rate,
respiration, digestive activity
3) Control of arousal states via
the reticular formation
4) Basic reflexes: pupillary,
tympanic, oculocephalic
reflexes http://library.med.utah.edu/kw/animations/hyperbrain/oculo_reflex/oculocephalic2.html
Brain Stem and Neuronal Pathways
Somatosensory
area
of cerebral
cortex
Thalamus
Cerebral
cortex
Midbrain
Cerebellum
PonsVentral
spinocerebellar
tract
Primary
motor
cortex
Medulla
Fasciculus
cuneatus
Ventral
corticospinal
tract
Lateral
corticospinal
tract
Pressure receptor in skin
Muscle
stretch
receptor
Spinal cord
Spinal cord
Spinal cord
•1
•2•3
•4
•5
•6
Ascending tracts Descending tracts
Organization of the CNS: Spinal cord
Cerebrum
Cerebellum
Diencephalon
Brain Stem
Spinal Cord
The Spinal Cord
The Meninges
The Meninges
Functional Organization of the Spinal
Cord
Gray Matter Regions
Spinal Nerves: Mixed nerves
Function of the Spinal Cord
Conduct information to and from the brain
Control of motor functions
Spinal reflex
Spinal Cord Pathways
Somatosensory
area
of cerebral
cortex
Thalamus
Cerebral
cortex
Midbrain
Cerebellum
PonsVentral
spinocerebellar
tract
Primary
motor
cortex
Medulla
Fasciculus
cuneatus
Ventral
corticospinal
tract
Lateral
corticospinal
tract
Pressure receptor in skin
Muscle
stretch
receptor
Spinal cord
Spinal cord
Spinal cord
•1
•2•3
•4
•5
•6
Ascending tracts Descending tracts
Ascending Tracts
Fasciculus gracilis
and fasciculus
cuneatus
Spinothalamic
tract
Spinocerebellar
tract
Ascending axons leave
spinal cord at dorsal
funiculi
Ascending axons
leave spinal cord at
lateral and dorsal
funiculi
Ascending axons
leave spinal cord at
lateral funiculi
Axons cross to
contralateral site at the
medulla oblongata
Axons cross to
contralateral site at
the spinal cord
Dorsal tract: no
crossing of
ascending axons.
Ventral tract: cross at
the level of the
medulla
Conduct sensory
information about: touch
(vibration), pressure and
body movements
Conduct sensory
information about:
pain, temperature
and touch (crude)
Involve in motor
coordination
Descending Tracts
Corticospinal tract
(or Pyramidal tract)
Reticulospinal
tract
Rubrospinal tract
Axons cross to
contralateral site at the
medulla oblongata
Some axons cross
to contralateral site
but other remain
uncrossed
Axons cross to
contralateral site at
the cortex
Descending axons
enter spinal cord
segment at lateral and
ventral funiculi
Descending axons
enter spinal cord
segment at lateral
and ventral funiculi
Descending axons
enter spinal cord
segment at lateral
funiculi
Control of`
voluntary movements
Regulate muscle
tone and sweat
gland activity
Muscle coordination
and posture control
Neuronal Circuit and Spinal ReflexA reflex is an automatic response to an external stimuli that occurs
without any conscious effort
Central
nervous system
(spinal cord)
Peripheral
nervous system
Axon
terminals
Cell
bodyAfferent neuron
Central
axonPeripheral axon
(afferent fiber) Receptor
Interneuron
Efferent neuron*
Effector organ
(muscle or gland)Axon
(efferent fiber)
Axon
terminals
* Efferent autonomic nerve pathways consist of a two •-•neuron chain between
the CNS and the effector organ.
Cell
body
Muscle
spindles
Muscle SpindleSensory receptors inside skeletal muscles that sense changes in
length
Reflex Arc
Receptor
Afferent neuron
Interneuron
Efferent neuron
Effector muscle
Centralnervous system(spinal cord)
Peripheralnervous system
Axonterminals
Cellbody
Afferent neuron
Centralaxon
Peripheral axon(afferent fiber) Receptor
Interneuron
Efferent neuron*
Effector organ(muscle or gland)
Axon(efferent fiber)
Axonterminals
* Efferent autonomic nerve pathways consist of a two•-•neuron chain betweenthe CNS and the effector organ.
Cellbody
http://www.brainviews.com/abFiles/AniPatellar.htm
Patellar tendon
Extensor muscle of knee(quadriceps femoris)
Musclespindle
Alpha motorneuron
Monosynaptic Reflex:
The Knee-Jerk Reflex
Polysynaptic Reflex:
The Withdrawal Reflex
The Crossed Withdrawal Reflex