Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 14 Peripheral Nervous...

Mosby items and derived items © 2007, 2003 by Mosby, Inc.

Chapter 14Chapter 14Peripheral Nervous SystemPeripheral Nervous System


Spinal NervesSpinal Nerves OverviewOverview

Thirty-one pairs of spinal nerves are connected to the spinal cord Thirty-one pairs of spinal nerves are connected to the spinal cord (Figure 14-1)(Figure 14-1)

No special names; are numbered by level of vertebral column at No special names; are numbered by level of vertebral column at which they emerge from the spinal cavitywhich they emerge from the spinal cavity

• Eight cervical nerve pairs (C1 through C8)Eight cervical nerve pairs (C1 through C8)

• Twelve thoracic nerve pairs (T1 through T12)Twelve thoracic nerve pairs (T1 through T12)

• Five lumbar nerve pairs (L1 through L5)Five lumbar nerve pairs (L1 through L5)

• Five sacral nerve pairs (S1 through S5)Five sacral nerve pairs (S1 through S5)

• One coccygeal nerve pairOne coccygeal nerve pair

Lumbar, sacral, and coccygeal nerve roots descend from point of Lumbar, sacral, and coccygeal nerve roots descend from point of origin to lower end of spinal cord (level of first lumbar vertebra) origin to lower end of spinal cord (level of first lumbar vertebra) before reaching the intervertebral foramina of the respective before reaching the intervertebral foramina of the respective vertebrae, through which the nerves emergevertebrae, through which the nerves emerge

Cauda equina—describes the appearance of the lower end of the Cauda equina—describes the appearance of the lower end of the spinal cord and its spinal nerves as a horse’s tailspinal cord and its spinal nerves as a horse’s tail


Spinal NervesSpinal Nerves

Structure of spinal nervesStructure of spinal nerves

Each spinal nerve attaches to spinal cord by a Each spinal nerve attaches to spinal cord by a ventral (anterior) root and a dorsal (posterior) rootventral (anterior) root and a dorsal (posterior) root

Dorsal root ganglion—swelling in the dorsal root of Dorsal root ganglion—swelling in the dorsal root of each spinal nerveeach spinal nerve

All spinal nerves are mixed nervesAll spinal nerves are mixed nerves



Structure of spinal nerves (cont.)Structure of spinal nerves (cont.) RamusRamus

• One of several large branches formed after each spinal nerve One of several large branches formed after each spinal nerve emerges from the spinal cavity (Figure 14-2)emerges from the spinal cavity (Figure 14-2)

• Dorsal ramus—supplies somatic motor and sensory fibers to Dorsal ramus—supplies somatic motor and sensory fibers to smaller nerves that innervate the muscles and skin of the smaller nerves that innervate the muscles and skin of the posterior surface of the head, neck, and trunkposterior surface of the head, neck, and trunk

• Ventral ramusVentral ramus Structure is more complex than that of dorsal ramusStructure is more complex than that of dorsal ramus Autonomic motor fibers split from the ventral ramus and head Autonomic motor fibers split from the ventral ramus and head

toward a ganglion of the sympathetic chaintoward a ganglion of the sympathetic chain



Nerve plexusesNerve plexuses

Plexuses—complex networks formed by the ventral Plexuses—complex networks formed by the ventral rami of most spinal nerves (not T2 through T12) rami of most spinal nerves (not T2 through T12) subdividing and then joining together to form individual subdividing and then joining together to form individual nervesnerves

Each individual nerve that emerges contains all the Each individual nerve that emerges contains all the fibers that innervate a particular region of the bodyfibers that innervate a particular region of the body

In plexuses, spinal nerve fibers are rearranged In plexuses, spinal nerve fibers are rearranged according to their ultimate destination, reducing the according to their ultimate destination, reducing the number of nerves needed to supply each body partnumber of nerves needed to supply each body part



There are four major pairs of plexuses:There are four major pairs of plexuses:

• Cervical plexus (Figure 14-3)Cervical plexus (Figure 14-3) Located deep within the neckLocated deep within the neck

Made up of ventral rami of C1 through C4 and a branch of the Made up of ventral rami of C1 through C4 and a branch of the ventral ramus of C5ventral ramus of C5

Individual nerves emerging from cervical plexus innervate the Individual nerves emerging from cervical plexus innervate the muscles and skin of the neck, upper shoulders, and part of the headmuscles and skin of the neck, upper shoulders, and part of the head

Phrenic nerve exits the cervical plexus and innervates the Phrenic nerve exits the cervical plexus and innervates the diaphragmdiaphragm



• Brachial plexus (Figure 14-4)Brachial plexus (Figure 14-4) Located deep within the shoulderLocated deep within the shoulder

Made up of ventral rami of C5 through T1Made up of ventral rami of C5 through T1

Individual nerves emerging from brachial plexus innervate Individual nerves emerging from brachial plexus innervate the lower part of the shoulder and the entire armthe lower part of the shoulder and the entire arm



Four major pairs of plexuses (cont.):Four major pairs of plexuses (cont.):

• Lumbar plexus (Figure 14-5)Lumbar plexus (Figure 14-5)

Located in the lumbar region of the back in the psoas muscleLocated in the lumbar region of the back in the psoas muscle

Formed by intermingling fibers of L1 through L4Formed by intermingling fibers of L1 through L4

Femoral nerve exits the lumbar plexus, divides into many Femoral nerve exits the lumbar plexus, divides into many branches, and supplies the thigh and legbranches, and supplies the thigh and leg


• Sacral plexus and coccygeal plexus (Figure 14-5)Sacral plexus and coccygeal plexus (Figure 14-5)

Located in the pelvic cavity in the anterior surface of the Located in the pelvic cavity in the anterior surface of the piriformis musclepiriformis muscle

Formed by intermingling of fibers from L4 through S4Formed by intermingling of fibers from L4 through S4

Tibial, common peroneal, and sciatic nerves exit the sacral Tibial, common peroneal, and sciatic nerves exit the sacral plexus and supply nearly all the skin of leg, posterior thigh plexus and supply nearly all the skin of leg, posterior thigh muscles, and leg and foot musclesmuscles, and leg and foot muscles



Dermatomes and myotomes (Figure 14-6)Dermatomes and myotomes (Figure 14-6)

Dermatome—region of skin surface area supplied Dermatome—region of skin surface area supplied by afferent (sensory) fibers of a given spinal nerve by afferent (sensory) fibers of a given spinal nerve (Figure 14-7)(Figure 14-7)

Myotome—skeletal muscle(s) supplied by efferent Myotome—skeletal muscle(s) supplied by efferent (motor) fibers of a given spinal nerve (Figure 14-8)(motor) fibers of a given spinal nerve (Figure 14-8)


Cranial Nerves Cranial Nerves (Tables 14-2 and 14-3)(Tables 14-2 and 14-3)

OverviewOverview

Twelve pairs of cranial nerves connect to the brain, mostly Twelve pairs of cranial nerves connect to the brain, mostly the brainstem (Figure 14-9)the brainstem (Figure 14-9)

Identified by name (determined by either distribution or Identified by name (determined by either distribution or function) and/or number (order in which they emerge, function) and/or number (order in which they emerge, anterior to posterior)anterior to posterior)

Made up of bundles of axonsMade up of bundles of axons

• Mixed cranial nerve—axons of sensory and motor neuronsMixed cranial nerve—axons of sensory and motor neurons

• Sensory cranial nerve—axons of sensory neurons onlySensory cranial nerve—axons of sensory neurons only

• Motor cranial nerve—mainly axons of motor neurons and a Motor cranial nerve—mainly axons of motor neurons and a small number of sensory fibers (proprioceptors)small number of sensory fibers (proprioceptors)


Cranial NervesCranial Nerves

Olfactory nerve (I)Olfactory nerve (I)

Composed of axons of neurons whose dendrites and cell Composed of axons of neurons whose dendrites and cell bodies lie in nasal mucosa and terminate in olfactory bulbsbodies lie in nasal mucosa and terminate in olfactory bulbs

Carries information about sense of smellCarries information about sense of smell

Optic nerve (II)Optic nerve (II)

Composed of axons from the innermost layer of sensory Composed of axons from the innermost layer of sensory neurons of the retinaneurons of the retina

Carries visual information from the eyes to the brainCarries visual information from the eyes to the brain


Cranial Nerves Cranial Nerves

Oculomotor nerve (III)Oculomotor nerve (III) Fibers originate from cells in the oculomotor nucleus and Fibers originate from cells in the oculomotor nucleus and

extend to some of the external eye musclesextend to some of the external eye muscles Efferent autonomic fibers are also present, which extend to Efferent autonomic fibers are also present, which extend to

the intrinsic muscles of the eye to regulate amount of light the intrinsic muscles of the eye to regulate amount of light entering eye and aid in focusing on near objectsentering eye and aid in focusing on near objects

Sensory fibers from proprioceptors in the eye muscles are Sensory fibers from proprioceptors in the eye muscles are also presentalso present

Trochlear nerve (IV)Trochlear nerve (IV) Motor fibers originate in cells of the midbrain and extend to Motor fibers originate in cells of the midbrain and extend to

the superior oblique muscles of the eyethe superior oblique muscles of the eye Also contains afferent fibers from proprioceptors in the Also contains afferent fibers from proprioceptors in the

superior oblique muscles of the eyesuperior oblique muscles of the eye



Trigeminal nerve (V) (Figure 14-10)Trigeminal nerve (V) (Figure 14-10) Has three branches: ophthalmic nerve, maxillary Has three branches: ophthalmic nerve, maxillary

nerve, nerve, and mandibular nerveand mandibular nerve

Sensory neurons carry afferent impulses from skin Sensory neurons carry afferent impulses from skin and mucosa of head and teeth to cell bodies in the and mucosa of head and teeth to cell bodies in the trigeminal gangliontrigeminal ganglion

Motor fibers originate in trifacial motor nucleus and Motor fibers originate in trifacial motor nucleus and extend extend to the muscles of mastication through the to the muscles of mastication through the mandibular nervemandibular nerve



Abducens nerve (VI)Abducens nerve (VI) Motor nerve with fibers originating from a Motor nerve with fibers originating from a

nucleus in the pons on the floor of the fourth nucleus in the pons on the floor of the fourth ventricle and extending to the lateral rectus ventricle and extending to the lateral rectus muscles of the eyemuscles of the eye

Contains afferent fibers from proprioceptors in Contains afferent fibers from proprioceptors in the lateral rectus musclesthe lateral rectus muscles



Facial nerve (VII)Facial nerve (VII) Motor fibers originate from a nucleus in the lower part of Motor fibers originate from a nucleus in the lower part of

the pons and extend to superficial muscles of the face the pons and extend to superficial muscles of the face and scalp (Figure 14-11)and scalp (Figure 14-11)

Autonomic fibers extend to submaxillary and sublingual Autonomic fibers extend to submaxillary and sublingual salivary glandssalivary glands

Also contains sensory fibers from taste buds of anterior Also contains sensory fibers from taste buds of anterior two thirds two thirds of the tongueof the tongue



Vestibulocochlear nerve (VIII)Vestibulocochlear nerve (VIII) Two distinct divisions that are both sensory: Two distinct divisions that are both sensory:

vestibular nerve vestibular nerve and cochlear nerve: and cochlear nerve:

• Vestibular nerve fibers originate in the semicircular Vestibular nerve fibers originate in the semicircular canals in inner ear and transmit impulses that result in canals in inner ear and transmit impulses that result in sensations of equilibriumsensations of equilibrium

• Cochlear nerve fibers originate in the organ of Corti in Cochlear nerve fibers originate in the organ of Corti in the cochlea of the inner ear and transmit impulses that the cochlea of the inner ear and transmit impulses that result in sensations of hearingresult in sensations of hearing



Glossopharyngeal nerve (IX)Glossopharyngeal nerve (IX) Composed of sensory, motor, and autonomic Composed of sensory, motor, and autonomic

nerve fibersnerve fibers

Supplies fibers to tongue, pharynx, and carotid Supplies fibers to tongue, pharynx, and carotid sinus sinus (Figure 14-12)(Figure 14-12)



Vagus nerve (X)Vagus nerve (X)

Composed of sensory and motor fibers with many Composed of sensory and motor fibers with many widely distributed brancheswidely distributed branches

Sensory fibers supply pharynx, larynx, trachea, Sensory fibers supply pharynx, larynx, trachea, heart, carotid body, lungs, bronchi, esophagus, heart, carotid body, lungs, bronchi, esophagus, stomach, small intestine, and gallbladder (Figure stomach, small intestine, and gallbladder (Figure 14-13)14-13)

Somatic motor fibers innervate the pharynx and Somatic motor fibers innervate the pharynx and larynx and are mostly autonomic fiberslarynx and are mostly autonomic fibers



Accessory nerve (XI)Accessory nerve (XI)

Motor nerve that is an “accessory” to the vagus nerveMotor nerve that is an “accessory” to the vagus nerve

Innervates thoracic and abdominal viscera, pharynx, larynx, Innervates thoracic and abdominal viscera, pharynx, larynx, trapezius, and sternocleidomastoid (Figure 14-14)trapezius, and sternocleidomastoid (Figure 14-14)

Hypoglossal nerve (XII)Hypoglossal nerve (XII)

Composed of motor and sensory fibersComposed of motor and sensory fibers

Motor fibers innervate the muscles of the tongueMotor fibers innervate the muscles of the tongue

Contains sensory fibers from proprioceptors in muscles Contains sensory fibers from proprioceptors in muscles of the tongueof the tongue


Divisions of the Divisions of the Peripheral Nervous SystemPeripheral Nervous System

There are two functional divisions of the There are two functional divisions of the peripheral nervous system:peripheral nervous system:

Afferent (sensory) divisionAfferent (sensory) division

Efferent (motor) divisionEfferent (motor) division

Efferent division is divided further into the somatic Efferent division is divided further into the somatic motor nervous system and the efferent portions of motor nervous system and the efferent portions of the autonomic nervous systemthe autonomic nervous system


Somatic Motor Nervous SystemSomatic Motor Nervous System Basic principles of somatic motor pathwaysBasic principles of somatic motor pathways

Somatic nervous system—includes all voluntary motor Somatic nervous system—includes all voluntary motor pathways outside the central nervous systempathways outside the central nervous system

Somatic effectors—skeletal musclesSomatic effectors—skeletal muscles


Somatic Motor Nervous SystemSomatic Motor Nervous System

Somatic reflexesSomatic reflexes Nature of a reflexNature of a reflex

• Reflex—action that results from a nerve impulse passing Reflex—action that results from a nerve impulse passing over a reflex arc; predictable response to a stimulusover a reflex arc; predictable response to a stimulus

Cranial reflex—center of reflex arc is in the brainCranial reflex—center of reflex arc is in the brain Spinal reflex—center of reflex arc is in the spinal cordSpinal reflex—center of reflex arc is in the spinal cord

• Reflex consists of either muscle contraction or glandular Reflex consists of either muscle contraction or glandular secretionsecretion

Somatic reflex—contraction of skeletal musclesSomatic reflex—contraction of skeletal muscles Autonomic (visceral) reflex—either contraction of smooth Autonomic (visceral) reflex—either contraction of smooth

or cardiac muscle or secretion by glandsor cardiac muscle or secretion by glands


Somatic Motor Nervous SystemSomatic Motor Nervous System Somatic reflexes (cont.)Somatic reflexes (cont.)

Some somatic reflexes of clinical importance—reflexes deviate Some somatic reflexes of clinical importance—reflexes deviate from normal in certain diseases, and reflex testing is a valuable from normal in certain diseases, and reflex testing is a valuable diagnostic aiddiagnostic aid

• Knee jerk (also known as patellar reflex)—extension of the lower leg in Knee jerk (also known as patellar reflex)—extension of the lower leg in response to tapping the patellar tendon; tendon and muscles are stretched, response to tapping the patellar tendon; tendon and muscles are stretched, stimulating muscle spindles and initiating conduction over a two-neuron reflex stimulating muscle spindles and initiating conduction over a two-neuron reflex arc (Figure 14-15); may be classified in several different waysarc (Figure 14-15); may be classified in several different ways

• Ankle jerk (also known as Achilles reflex)—extension of the foot in response to Ankle jerk (also known as Achilles reflex)—extension of the foot in response to tapping the Achilles tendon; tendon reflex and deep reflex mediated by two-tapping the Achilles tendon; tendon reflex and deep reflex mediated by two-neuron spinal arcs; centers lie in first and second sacral segments of the cordneuron spinal arcs; centers lie in first and second sacral segments of the cord

• Babinski reflex—extension of great toe, with or without fanning of other toes, in Babinski reflex—extension of great toe, with or without fanning of other toes, in response to stimulation of outer margin of sole; present in normal infants until response to stimulation of outer margin of sole; present in normal infants until approximately 11⁄2 years of age and then becomes suppressed when approximately 11⁄2 years of age and then becomes suppressed when corticospinal fibers become fully myelinated; in humans over 11⁄2 years of age, corticospinal fibers become fully myelinated; in humans over 11⁄2 years of age, a positive Babinski reflex is one of the pyramidal signs indicating destruction of a positive Babinski reflex is one of the pyramidal signs indicating destruction of corticospinal (pyramidal tract) fiberscorticospinal (pyramidal tract) fibers


Somatic Motor Nervous SystemSomatic Motor Nervous System Somatic reflexes (cont.)Somatic reflexes (cont.)

• Plantar reflex—plantar flexion of all toes and a slight turning in and flexion Plantar reflex—plantar flexion of all toes and a slight turning in and flexion of anterior part of foot in response to stimulation of outer edge of soleof anterior part of foot in response to stimulation of outer edge of sole

• Corneal reflex—winking in response to touching the cornea; mediated by Corneal reflex—winking in response to touching the cornea; mediated by reflex arcs with sensory fibers in ophthalmic branch of fifth cranial nerve, reflex arcs with sensory fibers in ophthalmic branch of fifth cranial nerve, centers in pons, and motor fibers in seventh cranial nervecenters in pons, and motor fibers in seventh cranial nerve

• Abdominal reflex—drawing in of abdominal wall in response to stroking Abdominal reflex—drawing in of abdominal wall in response to stroking side of abdomen; superficial reflex; mediated by arcs with sensory and side of abdomen; superficial reflex; mediated by arcs with sensory and motor fibers in T9 through T12 and centers in these segments of the cord; motor fibers in T9 through T12 and centers in these segments of the cord; decreased or absent reflex may involve lesions of pyramidal tract upper decreased or absent reflex may involve lesions of pyramidal tract upper motor neuronsmotor neurons

Spinal cord reflex—center of reflex arc located in spinal cord gray matterSpinal cord reflex—center of reflex arc located in spinal cord gray matter Segmental reflex—mediating impulses enter and leave at same cord segmentSegmental reflex—mediating impulses enter and leave at same cord segment Ipsilateral reflex—mediating impulses come from and go to the same side of the bodyIpsilateral reflex—mediating impulses come from and go to the same side of the body Stretch or myotatic reflex—result of type of stimulation used to evoke reflexStretch or myotatic reflex—result of type of stimulation used to evoke reflex Extensor reflex—produced by extensors of the lower legExtensor reflex—produced by extensors of the lower leg Tendon reflex—tapping the tendon is stimulus that elicits reflexTendon reflex—tapping the tendon is stimulus that elicits reflex Deep reflex—result of deep location of receptors stimulated to produce reflexDeep reflex—result of deep location of receptors stimulated to produce reflex


The Autonomic Nervous SystemThe Autonomic Nervous System

OverviewOverview

Contains afferent (sensory) and efferent (motor) components Contains afferent (sensory) and efferent (motor) components (the efferent components are emphasized here)(the efferent components are emphasized here)

Carries fibers to and from the autonomic effectorsCarries fibers to and from the autonomic effectors

Major function—to regulate heartbeat, smooth muscle contraction, Major function—to regulate heartbeat, smooth muscle contraction, and glandular secretions to maintain homeostasisand glandular secretions to maintain homeostasis

Two efferent divisions—sympathetic division and parasympathetic Two efferent divisions—sympathetic division and parasympathetic divisiondivision

Sympathetic division consists of neural pathways that are separate Sympathetic division consists of neural pathways that are separate from parasympathetic pathwaysfrom parasympathetic pathways

Many autonomic effectors are dually innervated, which allows Many autonomic effectors are dually innervated, which allows remarkably precise control of effectorremarkably precise control of effector



Structure of the autonomic nervous systemStructure of the autonomic nervous system

Basic plan of efferent autonomic pathways (Figure 14-16)Basic plan of efferent autonomic pathways (Figure 14-16)

• Each pathway is made up of autonomic nerves, ganglia, and plexuses, Each pathway is made up of autonomic nerves, ganglia, and plexuses, which are made of efferent autonomic neuronswhich are made of efferent autonomic neurons

• All autonomic neurons function in reflex arcsAll autonomic neurons function in reflex arcs

• Efferent autonomic regulation ultimately depends on feedback from Efferent autonomic regulation ultimately depends on feedback from sensory receptorssensory receptors

• Relay of two efferent autonomic neurons conducts information from Relay of two efferent autonomic neurons conducts information from central nervous system to autonomic effectors:central nervous system to autonomic effectors:

Preganglionic neuron—conducts impulses from central nervous system to Preganglionic neuron—conducts impulses from central nervous system to an autonomic ganglionan autonomic ganglion

Postganglionic neuron—efferent neuron with which a preganglionic neuron Postganglionic neuron—efferent neuron with which a preganglionic neuron synapses within autonomic ganglionsynapses within autonomic ganglion


The Autonomic Nervous SystemThe Autonomic Nervous System Structure of the sympathetic pathwaysStructure of the sympathetic pathways

• Sympathetic chain gangliaSympathetic chain ganglia

Most ganglia of the sympathetic division lie along either side of the anterior Most ganglia of the sympathetic division lie along either side of the anterior surface of the vertebral column and are joined with the other ganglia surface of the vertebral column and are joined with the other ganglia located on the same sidelocated on the same side

Each chain runs from second cervical vertebra to level of coccyxEach chain runs from second cervical vertebra to level of coccyx

Usually there are 22 sympathetic chain ganglia on each side of vertebral Usually there are 22 sympathetic chain ganglia on each side of vertebral column: 3 cervical, 11 thoracic, 4 lumbar, and 4 sacralcolumn: 3 cervical, 11 thoracic, 4 lumbar, and 4 sacral

• Thoracolumbar divisionThoracolumbar division

Sympathetic preganglionic neurons with dendrite and cell bodies in lateral Sympathetic preganglionic neurons with dendrite and cell bodies in lateral gray horns of thoracic and lumbar segments of spinal cordgray horns of thoracic and lumbar segments of spinal cord

Axons leave the cord by way of ventral roots of thoracic and first four Axons leave the cord by way of ventral roots of thoracic and first four lumbar spinal nerves and split away from other spinal nerve fibers by the lumbar spinal nerves and split away from other spinal nerve fibers by the white ramus to a sympathetic chain ganglionwhite ramus to a sympathetic chain ganglion


The Autonomic Nervous SystemThe Autonomic Nervous System Structure of the sympathetic pathways (cont.)Structure of the sympathetic pathways (cont.)

• Preganglionic fiber may take one of three paths once inside the Preganglionic fiber may take one of three paths once inside the sympathetic chain ganglion:sympathetic chain ganglion:

Synapse with sympathetic postganglionic neuronSynapse with sympathetic postganglionic neuron Send ascending or descending branches through the sympathetic trunk to Send ascending or descending branches through the sympathetic trunk to

synapse with postganglionic neurons in other chain gangliasynapse with postganglionic neurons in other chain ganglia Pass through one or more chain ganglia without synapsingPass through one or more chain ganglia without synapsing

• Sympathetic postganglionic neuronsSympathetic postganglionic neurons Dendrites and cell bodies are mostly in sympathetic chain ganglia or Dendrites and cell bodies are mostly in sympathetic chain ganglia or

collateral gangliacollateral ganglia Gray ramus—short branch by which some postganglionic axons return to a Gray ramus—short branch by which some postganglionic axons return to a

spinal nervespinal nerve

• In the sympathetic division, preganglionic neurons are relatively short, In the sympathetic division, preganglionic neurons are relatively short, and postganglionic neurons are relatively longand postganglionic neurons are relatively long

• Axon of one sympathetic preganglionic neuron synapses with many Axon of one sympathetic preganglionic neuron synapses with many postganglionic neurons, terminating in widely spread organs postganglionic neurons, terminating in widely spread organs (Figure 14-17)(Figure 14-17)


The Autonomic Nervous SystemThe Autonomic Nervous System Structure of the parasympathetic pathwaysStructure of the parasympathetic pathways

• Parasympathetic preganglionic neurons—cell bodies are located in nuclei in the Parasympathetic preganglionic neurons—cell bodies are located in nuclei in the brainstem or lateral gray columns of the sacral cord; extend a considerable brainstem or lateral gray columns of the sacral cord; extend a considerable distance before synapsing with postganglionic neuronsdistance before synapsing with postganglionic neurons

• Parasympathetic postganglionic neurons—dendrites and cell bodies are located Parasympathetic postganglionic neurons—dendrites and cell bodies are located in parasympathetic ganglia, which are embedded in or near autonomic effectorsin parasympathetic ganglia, which are embedded in or near autonomic effectors

• Parasympathetic postganglionic neurons synapse with postganglionic neurons Parasympathetic postganglionic neurons synapse with postganglionic neurons that each lead to a single effector (Figure 14-17)that each lead to a single effector (Figure 14-17)

Autonomic neurotransmitters (Figures 14-18, 14-20)Autonomic neurotransmitters (Figures 14-18, 14-20)• Axon terminal of autonomic neurons release either of two neurotransmitters: Axon terminal of autonomic neurons release either of two neurotransmitters:

norepinephrine or acetylcholinenorepinephrine or acetylcholine

• Adrenergic fibers—release norepinephrine; axons of postganglionic sympathetic Adrenergic fibers—release norepinephrine; axons of postganglionic sympathetic neuronsneurons

• Cholinergic fibers—release acetylcholine; axons of preganglionic sympathetic Cholinergic fibers—release acetylcholine; axons of preganglionic sympathetic neurons and of preganglionic and postganglionic parasympathetic neuronsneurons and of preganglionic and postganglionic parasympathetic neurons



Autonomic neurotransmitters (cont.)Autonomic neurotransmitters (cont.)• Norepinephrine affects visceral effectors by first binding to one Norepinephrine affects visceral effectors by first binding to one

of two types of adrenergic receptors in plasma membranes: of two types of adrenergic receptors in plasma membranes: alpha receptors or beta receptorsalpha receptors or beta receptors

Binding of norepinephrine to alpha receptors in smooth muscle of Binding of norepinephrine to alpha receptors in smooth muscle of blood vessels is stimulating, causing the vessels to constrictblood vessels is stimulating, causing the vessels to constrict

Binding of norepinephrine to beta receptors in smooth muscle of Binding of norepinephrine to beta receptors in smooth muscle of blood vessels is inhibitory, causing blood vessels to dilate; in blood vessels is inhibitory, causing blood vessels to dilate; in cardiac muscle, has stimulating effectcardiac muscle, has stimulating effect

• Epinephrine also stimulates adrenergic receptors, enhancing Epinephrine also stimulates adrenergic receptors, enhancing and prolonging effects of sympathetic stimulationand prolonging effects of sympathetic stimulation

• Effect of a neurotransmitter on any postsynaptic cell is Effect of a neurotransmitter on any postsynaptic cell is determined by characteristics of the receptors, not by the determined by characteristics of the receptors, not by the neurotransmitterneurotransmitter


The Autonomic Nervous SystemThe Autonomic Nervous System Autonomic neurotransmitters (cont.)Autonomic neurotransmitters (cont.)

• Termination of actions of norepinephrine and epinephrineTermination of actions of norepinephrine and epinephrine

Monoamine oxidase (MAO)—enzyme that breaks up Monoamine oxidase (MAO)—enzyme that breaks up neurotransmitter molecules taken back up by the synaptic knobsneurotransmitter molecules taken back up by the synaptic knobs

Catechol-O-methyl transferase (COMT)—enzyme that breaks down Catechol-O-methyl transferase (COMT)—enzyme that breaks down the remaining neurotransmitterthe remaining neurotransmitter

• Acetylcholine binds to two types of cholinergic receptors: Acetylcholine binds to two types of cholinergic receptors: nicotinic receptors and muscarinic receptorsnicotinic receptors and muscarinic receptors

• Termination of action of acetylcholine is by the enzyme Termination of action of acetylcholine is by the enzyme acetylcholinesteraseacetylcholinesterase

• Autonomic neurotransmitters and receptors may influence Autonomic neurotransmitters and receptors may influence different types of presynaptic and postsynaptic receptors at different types of presynaptic and postsynaptic receptors at synapses with dually innervated effectors—this summation of synapses with dually innervated effectors—this summation of effects increases precision of controleffects increases precision of control



Functions of the autonomic nervous systemFunctions of the autonomic nervous system

Overview of autonomic functionOverview of autonomic function

• The autonomic nervous system functions to regulate The autonomic nervous system functions to regulate visceral effectors in ways that tend to maintain or quickly visceral effectors in ways that tend to maintain or quickly restore homeostasisrestore homeostasis

• Sympathetic and parasympathetic divisions are tonically Sympathetic and parasympathetic divisions are tonically active, often exerting antagonistic influences on visceral active, often exerting antagonistic influences on visceral effectorseffectors

• Doubly innervated effectors continually receive both Doubly innervated effectors continually receive both sympathetic and parasympathetic impulses, and the sympathetic and parasympathetic impulses, and the summation of the two determine the controlling effectsummation of the two determine the controlling effect



Functions of the autonomic nervous system Functions of the autonomic nervous system (cont.)(cont.) Functions of the sympathetic divisionFunctions of the sympathetic division

• Under resting conditions, the sympathetic division can act to maintain Under resting conditions, the sympathetic division can act to maintain the normal functioning of doubly innervated autonomic effectorsthe normal functioning of doubly innervated autonomic effectors

• Sympathetic impulses function to maintain normal tone of the smooth Sympathetic impulses function to maintain normal tone of the smooth muscle in blood vessel wallsmuscle in blood vessel walls

• Major function of sympathetic division is that it serves as an Major function of sympathetic division is that it serves as an “emergency” system—the “fight-or-flight” reaction (review Table 14-8)“emergency” system—the “fight-or-flight” reaction (review Table 14-8)

Functions of the parasympathetic division (review Table 14-7)Functions of the parasympathetic division (review Table 14-7)

• Dominant controller of most autonomic effectors most of the timeDominant controller of most autonomic effectors most of the time

• Acetylcholine—slows heartbeat and acts to promote digestion and Acetylcholine—slows heartbeat and acts to promote digestion and eliminationelimination


The Big Picture: The Peripheral Nervous The Big Picture: The Peripheral Nervous System and the Whole BodySystem and the Whole Body

The peripheral nervous system is made of all the afferent The peripheral nervous system is made of all the afferent nervous pathways coming into the central nervous system nervous pathways coming into the central nervous system and all the efferent pathways going out of the central and all the efferent pathways going out of the central nervous systemnervous system

Peripheral pathways are pathways that lead from the Peripheral pathways are pathways that lead from the integrator central nervous system to the effectorsintegrator central nervous system to the effectors

Peripheral motor pathways serve as an information- Peripheral motor pathways serve as an information- carrying network that allows the central nervous system to carrying network that allows the central nervous system to communicate regulatory information to all of the nervous communicate regulatory information to all of the nervous effectors in the bodyeffectors in the body

Every major organ is influenced, directly or indirectly, by Every major organ is influenced, directly or indirectly, by peripheral nervous system outputperipheral nervous system output

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