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The PeripheralNervous System

PART 3

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Peripheral Nervous System

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The Peripheral Nervous System

•  Nervous structures outside the brain and spinalcord

•  Nerves allow the CNS to receive information andtake action

•  Functional components of the PNS • Sensory inputs and motor outputs categorized as

somatic or visceral

• Sensory inputs also classified as general  or special 

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Sensory Input and Motor Output

• Sensory (afferent) signals picked up by sensor receptors, carried by

nerve fibers of NS to the CNS• !otor (efferent) signals are carried away from the CNS, innervate

muscles and glands

• "ivided according to region they serve• Somatic body region

• #isceral body region• $esults in four main subdivisions

• Somatic sensory

• #isceral sensory

• Somatic motor 

• #isceral motor 

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PNS Afferent Division• %fferent (sensory) division & transmits impulses from

receptors to the CNS'• Somatic afferent fibers & carry impulses from skin, skeletalmuscles, and oints

• #isceral afferent fibers & transmit impulses from visceralorgans

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PNS Efferent Division• !otor (efferent) division & transmits impulses from the CNS to

effector organs' wo subdivisions*

• Somatic nervous system & provides conscious control of skeletalmuscles

• %utonomic nervous system & regulates smooth muscle, cardiacmuscle, and glands

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Types of Sensory and Motor Information

Figure 12.3

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Sensory

• +eneral somatic senses & include touch, pain, vibration, pressure, temperature

• roprioceptive senses & detect stretch intendons and muscle provide information on

 body position, orientation and movement of

 body in space

• Special Senses hearing, balance, vision,olfaction (smell), gustation (taste)

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Motor

• +eneral somatic motor 

• Signals contraction of skeletal muscles• -nder our voluntary control

• #isceral motor • !akes up autonomic nervous system (%NS)

• $egulates the contraction of smooth and cardiacmuscle, controls function of visceral organs

• %NS has two divisions• Parasympathetic

• Sympathetic

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Divisions of the ANS

• Sympathetic .fight or flight/• Catabolic (e0pend energy)• !ass activation prepares for intense

activity'

• 1eart rate (1$) increases'• 2ronchioles dilate'• 2lood 3glucose4 increases'

• arasympathetic .feed 5 breed/, .rest

5 digest/• !aintain homeostasis•  Normally not activated as a whole,

stimulation of separate parasympathetic nerves'

• $ela0ing effects*• "ecreases 1$'

• "ilates visceral blood vessels'• 6ncreases digestive activity'

• "ual innervation of many organs 7having a brake and an accelerator provides more control

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Sympathetic Division Organization

• reganglionic neurons in

segments 8 to 9:

• +anglia near the vertebralcolumn

• Sympathetic ganglia

• aired sympathetic chain

ganglia• -npaired collateral ganglia

• reganglionic fibers to adrenalmedullae

•  Epinephrine (adrenalin) into

 blood stream

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The Autonomic Nervous System 

• ;ffects of Sympathetic %ctivation• +eneralized response in crises

• 6ncreased alertness

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Parasympathetic Division Organization

• reganglionic neurons in

 brain stem and sacralspinal segment

• +anglionic neurons(peripheral ganglia) in ornear target organ

• Sacral fibers form pelvicnerves

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The Autonomic Nervous System

• ;ffects of arasympathetic %ctivation• $ela0ation

• =ood processing

• ;nergy absorption• 2rief effects at specific sites

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asic Structural !omponents of the PNS

• Sensory receptors & pick up stimuli from inside or outside the body

• Motor endings & a0on terminals of motor neurons innervate effectors(muscle fibers and glands)

•  Nerves and ganglia

• Nerves & bundles of peripheral a0ons

• "anglia & clusters of peripheral neuronal cell bodies

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Nerves

• Nerves & cablelike organs in the NS

• Consists of numerous a0ons wrappedin connective tissue• Endoneurium & layer of delicate connective

tissue surrounding the a0on

• Perineurium & connective tissue wrapping

surrounding a nerve fascicle• Nerve fascicles & groups of a0ons bound into

 bundles

• Epineurium & whole nerve is surrounded bytough fibrous sheath

• %0on is surrounded by Schwann cells

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!ranial Nerves

• %ttach to the brain and pass through foraminaof the skull

•  Numbered from 6&>66

• Cranial nerves 6 and 66 attach to the forebrain• %ll others attach to the brain stem

• rimarily serve head and neck structures• he vagus nerve (>) e0tends into the abdomen

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The #$ Pairs of !ranial Nerves

Figure 14.5

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Table 14.3 (1 of 12)

Olfactory Nerves %I&

• Sensory nerves of smell

olfactory nerve (I)

Olfactory bulb

Olfactory tract

Optic nerve (II)

Optic chiasa

Optic tract

Oculootor nerve (III)

Trochlear nerve (I!)

Trigeinal nerve (!)

"b#ucens nerve (!I)

$erebellu

%e#ulla

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Table 14.3 (2 of 12)

Optic Nerve %II&

• Sensory nerve of vision

Filaents of 

olfactory nerve (I)Olfactory bulb

Olfactory tract

Optic nerve (II)Optic chiasa

Optic tract

Oculootor nerve (III)

Trochlear nerve (I!)

Trigeinal nerve (!)

"b#ucens nerve (!I)

$erebellu

%e#ulla

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Oculomotor Nerve %III&

• 6nnervates four of the e0trinsic eye muscles

Table 14.3 (3 of 12)

Filaents of 

olfactory nerve (I)Olfactory bulb

Olfactory tract

Optic nerve (II)

Optic chiasa

Optic tract

Oculootor nerve (III)

Trochlear nerve (I!)

Trigeinal nerve (!)

"b#ucens nerve (!I)

$erebellu

%e#ulla

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Table 14.3 (4 of 12)

Trochlear Nerve %I'&

• 6nnervates the superior o(li)ue muscle (an

e0trinsic eye muscle)

Filaents of 

olfactory nerve (I)Olfactory bulb

Olfactory tract

Optic nerve (II)

Optic chiasa

Optic tract

Oculootor nerve (III)

Trochlear nerve (I!)

Trigeinal nerve (!)

"b#ucens nerve (!I)

$erebellu

%e#ulla

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Trigeminal Nerve %'&

• rovides sensory innervation to the face

• !otor innervation to chewing muscles

Filaents of 

olfactory nerve (I)Olfactory bulb

Olfactory tract

Optic nerve (II)

Optic chiasa

Optic tract

Oculootor nerve (III)

Trochlear nerve (I!)

Trigeinal nerve (!)

"b#ucens nerve (!I)

$erebellu

%e#ulla

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A(ducens Nerve %'I&

• %bducts the eyeball & innervates lateralrectus muscle

Table 14.3 (& of 12)

Filaents of 

olfactory nerve (I)Olfactory bulb

Olfactory tract

Optic nerve (II)

Optic chiasa

Optic tract

Oculootor nerve (III)

Trochlear nerve (I!)

Trigeinal nerve (!)

"b#ucens nerve (!I)

$erebellu

%e#ulla

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Table 14.3 (' of 12)

*acial Nerve %'II&• 6nnervates muscles of facial e0pression

Facial nerve (!II)

!estibulocochlear 

nerve (!III)

lossopharyngeal

nerve (I)

!agus nerve ()

"ccessory nerve (I)

*ypoglossal nerve (II)

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'esti(ulocochlear Nerve %'III&

• Sensory nerve of hearing and balance

Table 14.3 (+ of 12)

Facial nerve (!II)

!estibulocochlear 

nerve (!III)

lossopharyngeal

nerve (I)

!agus nerve ()

"ccessory nerve (I)

*ypoglossal nerve (II)

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"lossopharyngeal Nerve %I+&

• 6nnervates structures of the tongue and pharyn0

Table 14.3 (, of 12)

Facial nerve (!II)

!estibulocochlear 

nerve (!III)

lossopharyngeal

nerve (I)

!agus nerve ()

"ccessory nerve (I)

*ypoglossal nerve (II)

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'agus Nerve %+&• % mi0ed sensory and motor nerve .?anders/ into thora0 and abdomen

Table 14.3 (1- of 12)

Facial nerve (!II)

!estibulocochlear 

nerve (!III)

lossopharyngeal

nerve (I)

!agus nerve ()

"ccessory nerve (I)

*ypoglossal nerve (II)

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Table 14.3 (11 of 12)

Accessory Nerve %+I&

• %n accessory part of the vagus nerve innervates

trapezius muscle

Facial nerve (!II)

!estibulocochlear 

nerve (!III)

lossopharyngeal

nerve (I)

!agus nerve ()

"ccessory nerve (I)

*ypoglossal nerve (II)

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Table 14.3 (12 of 12)

,ypoglossal Nerve %+II&

• $uns inferior to the tongue innervates the tongue

muscles

Facial nerve (!II)

!estibulocochlear 

nerve (!III)

lossopharyngeal

nerve (I)

!agus nerve ()

"ccessory nerve (I)

*ypoglossal nerve (II)

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Spinal Nerves

• @8 pairs & contain thousands ofnerve fibers

• Connect to the spinal cord

•  Named for point of issue from thespinal cord

• A pairs of cervical nerves (C8 &CA)

• 8: pairs of thoracic nerves (8 &8:)• B pairs of lumbar nerves (98 &9B)

• B pairs of sacral nerves (S8 &SB)

• 8 pair of coccygeal nerves (Co8)

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Spinal Nerves

• Connect to the spinal cord

 by the dorsal root andventral root• Dorsal root & contains

sensory fibers

• "orsal root ganglion & ofafferent cell bodies

• 'entral root & containsmotor fibers arising fromanterior gray column

• 2ranch into dorsal ramus and ventral ramus (othcontain sensory and  motorfibers

• -ami communicantes connect to the base of theventral ramus and lead tothe sympathetic chainganglia 

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 Spinal Nerves

(a)

orsal root

ganglion

ray atter 

/hite atter !entral root

orsal rootorsal an# ventral

rootlets of spinal

nerveorsal raus

of spinal nerve

!entral raus

of spinal nerve

0ypathetic trun

(chain) ganglion

0pinal nerve

ai counicantes

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Innervation of the ac. 

• Dorsal rami 

• 6nnervate back muscles• =ollow a neat, segmented pattern

• 6nnervate a horizontal strip of muscle and skin

• 6n line with emergence point from the vertebral column

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Innervation of the Thoracic region

• 'entral rami arranged in simple, segmented pattern

• 6ntercostal nerves & supply intercostal muscles, skin, andabdominal wall• ;ach gives off lateral and anterior cutaneous (ranches

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Introduction to Nerve Ple/uses

• Nerve ple/us & a network of nerves

• 'entral rami (e0cept : & 8:)• 2ranch and oin with one

another

• =orm nerve ple0uses• Cervical

• 2rachial

• 9umbar 

• Sacral

• rimarily serve the limbs

• =ibers from ventral ramicrisscross

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The !ervical Ple/us• 2uried deep in the neck under the sternocleidomastoid muscle

• =ormed by ventral rami of first four cervical nerves (C 8 & )

• !ost are cutaneous nerves

• Some innervate muscles of the anterior neck 

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rachial Ple/us• 2rachial ple0us lies in the neck and a0illa

• =ormed by ventral rami of CB & CA give rise to cords• Cords give rise to main nerves of the upper limb

Figure 14.,#

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0um(ar Ple/us• %rises from 98 & 9C

• Smaller branches innervate the posterior abdominal wall and psoas

muscle• !ain branches innervate the anterior thigh

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The Sacral Ple/us• %rises from spinal nerves 9C &SC• Dften considered with the lumbar ple0us referred to as the lumbosacral ple0us• Sciatic nerve & the largest nerve of the sacral ple0us is actually two nerves in one sheath

• ibial nerve & innervates most of the posterior lower limb• Common fibular (peroneal) nerve & innervates muscles of the anterolateral leg