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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.)

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Tab.

11.2(Con

td.)

Tab.

11.2(Con

td.)

Brainstem Reflexes

• Many reflexes mediated through brainstem

• brainstem is considered nonfunctional

when

– Reflexes at all levels of brainstem are

nonfunctional

– There is no spontaneous breathing (mediated

through medulla oblongata)