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Chapter 11Central and
Peripheral Nervous
Systems
Fascicles containing bundles of axons
Spinal Cord
• Major communication
link between brain &
PNS (spinal nerves)
• Participates in
– integration of incoming
information &
– produces responses
through reflex
mechanisms
Spinal Cord
• Gives rise to 31 pairs of
spinal nerves
– Cervical & lumbosacral
enlargements give rise to
spinal nerves of limbs
– Nerves from end of spinal
cord form cauda equina
• Shorter than vertebral
column
Meninges of the Spinal Cord
• 3 meningeal layers
• From superficial to deep:– Dura mater
– Arachnoid mater
– Pia mater
• epidural space– between periosteum of vertebral canal and dura
mater
– Adipose & Areolar connective tissue
• subarachnoid space– between arachnoid mater and pia mater
– CSF circulation
Fig. 11.2
Spinal Cord Cross Section
• peripheral white matter & central gray matter
• White matter– organized into columns (funiculi)
• subdivided into tracts (fasciculi or pathways)
– consist of ascending & descending axons
• Gray matter– divided into horns
• dorsal horns contain sensory axons that synapse with interneurons
• ventral horns contain neuron cell bodies of somatic motor neurons
• lateral horns contain neuron cell bodies of autonomic motor neurons
• gray and white commissures connect each half of spinal cord
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Spinal Cord Cross Section
• Spinal nerves arise from spinal cord in
numerous rootlets
• rootlets combine to form a ventral root
and a dorsal root
Fig. 11.3
Spinal Cord Cross Section
• dorsal root contains sensory axons
• ventral root has motor axons
• Spinal nerves have sensory and motor axons
Fig. 11.4
Reflexes• Stereotypic, unconscious, involuntary responses
to stimuli
• Maintain homeostasis
• 2 general types:– Somatic reflexes
• Mediated through somatic motor nervous system & includes responses that
– Remove body from painful stimuli
– Keep body from suddenly falling
– Cause movement because of external forces
– Autonomic reflexes• Mediated through ANS & are responsible for maintaining
variables within their normal ranges– Blood pressure
– Blood carbon dioxide levels
– Water intake
Reflexes
• “Reflex arc” = functional unit of nervous system
1. Sensory receptors respond to stimuli & produce action potentials in sensory neurons
2. Sensory neurons propagate action potentials to CNS
3. Interneurons in CNS synapse with sensory neurons and motor neurons
4. Motor neurons carry action potentials from CNS to effector organs
5. Effector organs, such as muscles or glands, respond to action potential
Reflex Arc
Fig. 11.5
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Spinal Reflex
• Higher brain centers can suppress or exaggerate reflexes
• Convergent & divergent pathways interact with reflexes
• Reflexes are integrated within brain and spinal cord
Fig. 11.6
The Stretch Reflex• Muscle spindles detect stretch of skeletal muscles & cause muscle to shorten
reflexively
• Ex: Postural muscles of back; reflex lets you not “tip over”
• knee-jerk reflex (tendons and quads stretched, muscles contract jerk)
Fig. 11.7
Golgi Tendon Reflex• Prevents excessive contraction from causing too much tension on tendons
• Golgi tendon organs (nerve endings w/collagen fibers in tendons) respond to increased tension within tendons and cause skeletal muscles to relax
• Athletes often don’t respond enough to increased muscle tension injuries
Fig. 11.8
Withdrawal Reflex
• Activation of pain receptors causes contraction of muscles and removal of some part of body from a painful stimulus
Fig. 11.9
Structure of Nerves
• Individual axons are surrounded by endoneurium
• Groups of axons(fascicles) are bound together by perineurium
• Fascicles form the nerve & are held together by the epineurium
Fig. 11.10
Spinal Nerves
• 31 pairs of spinal nerves– 8 cervical
– 12 thoracic
– 5 lumbar
– 5 sacral
– 1 coccygeal
• Spinal nerves have specific cutaneous distributions called dermatomes– Regions of skin w/that nerve’s
sensory input
– Useful in assessing numbness, injury, etc.
Fig. 11.11
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Fig.
11.12
Spinal Nerves and Plexuses
• Spinal nerves branch to form rami (ramus)
– dorsal rami supply muscles & skin near
middle of back
– ventral rami in thoracic region form intercostal
nerves, which supply thorax & upper
abdomen
– Cervical, lumbar, sacral & coccygeal ventral
rami join to form plexuses
– Communicating rami supply sympathetic
nerves
Fig.
11.13
Major Spinal Nerve Plexuses
• 5 major plexuses:
– Cervical (C1-C4)
• Phrenic nerve (diaphragm)
– Brachial (C5-T1)
• Axillary, radial, musculocutaneous, ulnar, and median nerves
– Lumbar (L1-L4)
– Sacral (L4-S4)
– Coccygeal (S5-coccygeal)
• lumbar & sacral plexuses often considered
together as lumbosacral plexus• Obturator, femoral, tibial, and common fibular nerves
Major Spinal Nerve Plexuses
• Axons from different levels of spinal cord intermingle within plexuses – give rise to nerves that
have axons from >1 level of spinal cord
• Brachial Plexus is demonstrated in Fig. 11.14
Fig.
11.14
Major Spinal Nerve Plexuses
• Nerves arising from
plexuses are
distributed to
skeletal muscles
throughout the body
• Table 11.1
Fig.
11.15
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Major Spinal Nerve Plexuses
• Nerves
arising from
plexuses
also supply
the skin
• Table 11.1
Fig.
11.16
Tab.
11.1
THE BRAIN!!!!
• Contained in cranial cavity
• Control center for many of body’s
functions
• Consists of
– Brainstem
– Cerebellum
– Diencephalon
– Cerebrum
Fig.
11.17
Brainstem
• Consists of
– Medulla oblongata
– Pons
– Midbrain
• Connects spinal cord & cerebellum to remainder of
brain
• 10 of 12 pairs of cranial nerves arise from it
• Damage to small areas of brainstem can cause
death, whereas damage to relatively large areas of
the cerebrum or cerebellum do not
Fig.
11.18
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Brainstem
• Medulla Oblongata
– Continuous with spinal cord
– contains ascending and descending tracts
– Medullary nuclei regulate heart, blood
vessels, breathing, swallowing, vomiting,
coughing, sneezing, hiccupping, balance and
coordination
– Pyramids are tracts controlling voluntary
muscle movement & Rt side of brain controls
L side of body, etc.
Brainstem
• Pons
– Superior to medulla
– Ascending & Descending tracts pass through
pons
– Connects (relay) cerebrum and cerebellum
– Pontine nuclei regulate breathing, swallowing,
balance, chewing, and salivation
Brainstem
• Midbrain
– Superior to pons
– Corpora quadrigemina consists of 4 colliculi
• 2 inferior colliculi are involved in hearing
• 2 superior colliculi in visual reflexes
– Substantia nigra and red nucleus help
regulate body movements
– Cerebral peduncles are major descending
motor pathway
Brainstem
• Reticular Formation
– Consists of nuclei scattered throughout
brainstem
– Regulates cyclic motor functions, such as
breathing, walking, and chewing
– Reticular activating system, part of reticular
formation, maintains consciousness and
regulates the sleep-wake cycle
Cerebellum
• Gray matter forms cortex & nuclei of cerebellum
• White matter– Arbor vitae
– Connects cerebellum to rest of CNS
– Connects cerebellar cortex & cerebellar nuclei
• The cerebellum has 3 parts:– Flocculonodular lobe controls balance & eye
movements
– Vermis & medial part of lateral hemispheres control posture, locomotion, & fine motor coordination
– lateral hemispheres are involved with planning, practice, & learning of complex movements
Fig.
11.19
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Diencephalon
• Located between brainstem & cerebrum
• Consists of
– Thalamus
– Subthalamus
– Epithalamus
– Hypothalamus
Fig.
11.20
Diencephalon
• Thalamus
– 2 lobes connected by interthalamic adhesion
– Functions as integration center
– All sensory input that reaches cerebrum, except for
sense of smell, synapses in thalamus
– Interacts with other parts of brain to control motor activity
– Involved in emotions & painperception
Fig.
11.20
Diencephalon
• Subthalamus
– Inferior to thalamus
– Involved in motor function
• Epithalamus
– Superior & posterior to thalamus
– Consists of• Habenular nuclei- influence emotions through the
sense of smell
• Pineal body- may play a role in onset of puberty and sleep-wake cycle
Diencephalon
• Hypothalamus: Main visceral control center of body & is vitally important to overall body homeostasis.– Autonomic control center (heart rate, blood pressure, etc.)
– Center for emotional response/behavior
– Circadian Rhythms
– Body temperature regulation
– Regulation of food intake (hunger)
– Regulation of water balance (thirst)
– Control of endocrine glands
– Mammillary bodies are reflex centers
for olfaction
Fig. 11.20
Fig.
11.20
Cerebrum
• Cortex of cerebrum folded into ridges called gyri
& grooves called sulci or fissures
• longitudinal fissure divides cerebrum into left &
right hemispheres
• Each hemisphere has 5 lobes
– Frontal lobes
– Parietal lobes
– Occipital lobes
– Temporal lobes
– Insula
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Fig.
11.21
Cerebrum
• Frontal lobes - involved in voluntary motor function, motivation, aggression, sense of smell, mood
• Parietal lobes contain major sensory areas receiving sensory input (touch, pain, temperature, balance, taste)
• Occipital lobes contain visual centers
• Temporal lobes evaluate smell & hearing input & involved in memory, abstract thought, & judgment
• Insula is located deep within lateral fissure; input from taste
Cerebrum
• Gray matter forms cortex and nuclei of cerebrum
• White matter forms cerebral medulla, which consists of 3 types of tracts
– Association fibers connect areas of cortex within same hemisphere
– Commissural fibers connect cerebral hemispheres
– Projection fibers connect cerebrum to other parts of brain and spinal cord
Fig.
11.22
Cerebrum
• Basal Nuclei
– Include corpus striatum (caudate and lentiform nuclei), subthalamic nuclei, and substantia nigra
– Important in controlling motor functions
Fig.
11.23
Cerebrum
• Limbic System– Includes parts of cerebral cortex, basal nuclei,
thalamus, hypothalamus, & olfactory cortex
– survival, memory, reproduction, and nutrition
– Involved in emotional interpretation of sensory input & emotions in general
Fig.
11.24
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Meninges
• brain & spinal cord covered by dura,
arachnoid & pia mater
• dura mater attaches to skull
– has 2 layers that can separate to form dural
folds and dural (venous) sinuses
• Beneath arachnoid mater, subarachnoid
space contains CSF
– helps cushion brain
• pia mater attaches directly to brainFig.
11.25
Ventricles
• lateral ventricles in cerebrum connected to 3rd ventricle in diencephalon by interventricular foramina
• 3rd ventricle connected to 4th ventricle in pons by cerebral aqueduct
• central canal of spinal cord connected to 4th ventricle
• 4th ventricle connected to subarachnoid space by median and lateral apertures
Fig.
11.26
Cerebrospinal Fluid (CSF)
• Produced from blood in choroid plexus of each
ventricle by ependymal cells
• Moves from lateral to 3rd & then to 4th ventricle
• From 4th ventricle, CSF enters subarachnoid
space through 3 apertures
• Leaves subarachnoid space through arachnoid
granulations & returns to blood in dural venous
sinuses
Blood Supply to the Brain
• brain requires tremendous amounts of blood to function normally
– High metabolic rate & brain cells cannot store high-energy molecules
– Only about 2% of body weight, but receives ~15%-20% of the blood pumped by the heart
• blood-brain barrier is formed by the endothelial cells of capillaries in brain.
– Limits what substances enter brain tissue
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Cranial Nerves
• 12 pairs of cranial nerves are designated by
Roman numerals (I - XII) or specific names
• In numeric order, can be identified with this
mnemonic
– On Occasion Our Trusty Truck Acts Funny; Very
Good Vehicle Any How…
• On: Olfactory (I)
• Occasion: Optic (II)
• Our: Oculomotor (III)
• TrustyL Trochlear (IV)
• Truck: Trigeminal (V)
• Acts: Abducent (VI)
• Funny: Facial (VII)
• Very: Vestibulocochlear (VIII)
• Good: Glossopharyngeal (IX)
• Vehicle: Vagus (X)
• Any: Accessory (XI)
• How: Hypoglossal (XII)
Cranial Nerves
• 2 types of general functions are sensory &
motor
– Sensory: special senses & general senses
– Motor: somatic motor & parasympathetic
• Table 11.2
Tab.
11.2
Tab.
11.2(Con
td.)
Tab.
11.2(Con
td.)
Tab.
11.2(Con
td.)