spinal nerves, cervical, lumbar and sacral plexus

Spinal nerves, cervical, lumbar and sacral plexus

The spinal cord• Gross anatomy

– 3 layers of meninges– Epidural space (fat & vessels)– CSF – subarachnoid space– Terminates at L1/2 vertebral level

(conus medullaris)• Dura extends to S2 vertebral

level– Connects via filum terminale &

denticulate ligaments (pia)– 31 pairs of spinal nerves (mixed)

• cauda equina– Cervical & lumbar enlargements

Lumbar Tap

Spinal Cord Anatomy

• Conus medullaris – terminal portion of the spinal cord• Filum terminale – fibrous extension of the pia mater; anchors

the spinal cord to the coccyx• Denticulate ligaments – delicate shelves of pia mater; attach

the spinal cord to the vertebrae• Spinal nerves – 31 pairs attach to the cord by paired roots

– Cervical nerves are named for inferior vertebra – All other nerves are named for superior vertebra

• Cervical and lumbar enlargements – sites where nerves serving the upper and lower limbs emerge

• Cauda equina – collection of nerve roots at the inferior end of the vertebral canal

Cross-Sectional Anatomy of the Spinal Cord• Anterior median fissure – separates anterior funiculi• Posterior median sulcus – divides posterior funiculi

The 3 Meningeal Layers

• Dura mater:– outer layer of spinal cord– subdural space:

• between arachnoid mater and dura mater

• Arachnoid mater:– middle meningeal layer– subarachnoid space:

• between arachnoid mater and pia mater

• filled with cerebrospinal fluid (CSF)

• Pia mater:– inner meningeal layer

Structures of the Spinal Cord

• Paired denticulate ligaments:– extend from pia mater to

dura mater– stabilize side-to-side

movement

• Blood vessels:– along surface of spinal pia

mater– within subarachnoid space

Cross-sectional anatomy

• Gray matter (cell bodies, neuroglia, & unmyelinated processes)– Posterior horns (sensory,

all interneurons)– Lateral horns

(autonomic, T1-L2)– Anterior horns (motor,

cell bodies of somatic motor neurons)

• Spinal roots– Ventral (somatic &

autonomic motor)– Dorsal (DRG)

Cross-sectional anatomy

• White matter– 3 funiculi (posterior, lateral,

anterior)• Ascending, descending,

transverse– Consist of “tracts” containing

similarly functional axons• All tracts are paired• Most cross over (decussate)

at some point• Most exhibit somatotopy

(superior part of the tracts are more lateral that inferior body regions)

• Most consist of a chain of 2 or 3 successive neurons

Gray Matter: Organization• Dorsal half – sensory roots and ganglia• Ventral half – motor roots• Dorsal and ventral roots fuse laterally to form spinal nerves • Four zones are evident within the gray matter – somatic sensory

(SS), visceral sensory (VS), visceral motor (VM), and somatic motor (SM)

White Matter in the Spinal Cord• Fibers run in three directions – ascending, descending,

and transversely• Divided into three funiculi (columns) – posterior,

lateral, and anterior• Each funiculus contains several fiber tracts

– Fiber tract names reveal their origin and destination– Fiber tracts are composed of axons with similar functions

• Pathways decussate (cross-over)• Most consist of two or three neurons• Most exhibit somatotopy (precise spatial relationships)• Pathways are paired (one on each side of the spinal

cord or brain)

White Matter: Pathway Generalizations

3 Connective Tissue Layers

• Epineurium:– outer layer– dense network of collagen

fibers• Perineurium:

– middle layer– divides nerve into fascicles

(axon bundles)• Endoneurium:

– inner layer– surrounds individual axons

Figure 13–7a

Peripheral Distribution of Spinal Nerves

• Each spinal nerve connects to the spinal cord via two medial roots

• Each root forms a series of rootlets that attach to the spinal cord

• Ventral roots arise from the anterior horn and contain motor (efferent) fibers

• Dorsal roots arise from sensory neurons in the dorsal root ganglion and contain sensory (afferent) fibers

Spinal Nerves: Rami

• The short spinal nerves branch into three or four mixed, distal rami– Small dorsal ramus – to back– Larger ventral ramus – to plexuses/intercostals– Tiny meningeal branch – to meninges– Rami communicantes at the base of the ventral

rami in the thoracic region – to/from ANS

Nerve Plexuses• All ventral rami except T2-T12 form interlacing nerve

networks called plexuses• Plexuses are found in the cervical, brachial, lumbar,

and sacral regions• Each resulting branch of a plexus contains fibers from

several spinal nerves• Fibers travel to the periphery via several different routes• Each muscle receives a nerve supply from more than

one spinal nerve• Damage to one spinal segment cannot completely

paralyze a muscle

Spinal Nerve Innervation: Back, Anterolateral Thorax, and Abdominal Wall

• The back is innervated by dorsal rami via several branches

• The thorax is innervated by ventral rami T1-T12 as intercostal nerves

• Intercostal nerves supply muscles of the ribs, anterolateral thorax, and abdominal wall

The 4 Major Plexuses of Ventral Rami

1. Cervical plexus2. Brachial plexus3. Lumbar plexus4. Sacral plexus

Cervical Plexus

• The cervical plexus is formed by ventral rami of C1-C4 (C5)

• Most branches are cutaneous nerves of the neck, ear, back of head, and shoulders

• The most important nerve of this plexus is the phrenic nerve

• The phrenic nerve is the major motor and sensory nerve of the diaphragm

Brachial Plexus

• Formed by C5-C8 and T1 (C4 and T2 may also contribute to this plexus)

• It gives rise to the nerves that innervate the upper limb

Trunks and Cords of Brachial Plexus• Nerves that form brachial plexus originate from:

– superior, middle, and inferior trunks – large bundles of axons from several spinal nerves– lateral, medial, and posterior cords – smaller branches that originate at trunks

Brachial Plexus: Nerves

• Axillary – innervates the deltoid and teres minor

• Musculocutaneous – sends fibers to the biceps brachii and brachialis

• Median – branches to most of the flexor muscles of forearm

• Ulnar – supplies the flexor carpi ulnaris and part of the flexor digitorum profundus

• Radial – innervates essentially all extensor muscles

Lumbar Plexus

• Arises from (T12) L1-L4 and innervates the thigh, abdominal wall, and psoas muscle

• The major nerves are the femoral and the obturator

Sacral Plexus• Arises from L4-S4 and

serves the buttock, lower limb, pelvic structures, and the perineum

• The major nerve is the sciatic, the longest and thickest nerve of the body

• The sciatic is actually composed of two nerves: the tibial and the common fibular (peroneal) nerves

Nerve plexuses - Summary

• Cervical – C1-C4– Phrenic nerve

• Brachial – C5 – T1 (roots/trunks/divisions/cords)– Axillary, MC, median, ulnar, radial

• Lumbar – L1-L4– Femoral, obturator

• Sacral – L4-S4– Sciatic (common peroneal/tibial), pudendal

Figure 13–8

Dermatomes

• Area of skin innervated by the cutaneous branches of a single spinal nerve.

• All segments except C1 have dermotomal distribution

• UE typically from C5-T1• LE typically from L1-S1

Figure 13–13a

5 Patterns of Neural Circuits in Neuronal Pools

1. Divergence:– spreads

stimulation to many neurons or neuronal pools in CNS

2. Convergence:– brings input

from many sources to single neuron

Figure 13–13c

3. Serial processing:– moves information

in single line

4. Parallel processing:– moves same

information along several paths simultaneously


Figure 13–13e

5. Reverberation:– positive feedback mechanism– functions until inhibited


Reflex activity• 5 components of

a reflex arc– Receptor– Sensory neuron– Integration center

(CNS)– Motor neuron– Effector

4 Classifications of Reflexes

1. By early development– Innate or Acquired

2. By type of motor response– Somatic or Visceral

3. By complexity of neural circuit– Monosynaptic or Polysynaptic

4. By site of information processing– Spinal or Cranial

Spinal Reflexes

• Range in increasing order of complexity:– monosynaptic reflexes– polysynaptic reflexes – intersegmental reflex arcs:

• many segments interact • produce highly variable motor response

Monosynaptic Reflexes

• Have least delay between sensory input and motor output:– e.g., stretch

reflex (such as patellar reflex)

• Completed in 20–40 msec

Muscle Spindles• The receptors in stretch

reflexes• Bundles of small,

specialized intrafusal muscle fibers:– innervated by sensory and

motor neurons• Surrounded by extrafusal

muscle fibers: – which maintain tone and

contract muscle

Postural Reflexes

• Postural reflexes:– stretch reflexes– maintain normal upright posture

• Stretched muscle responds by contracting:– automatically maintain balance

Polysynaptic Reflexes

• More complicated than monosynaptic reflexes• Interneurons control more than 1 muscle

group• Produce either EPSPs or IPSPs

The Tendon Reflex

• Prevents skeletal muscles from:– developing too much tension– tearing or breaking tendons

• Sensory receptors unlike muscle spindles or proprioceptors

Withdrawal Reflexes• Move body part away

from stimulus (pain or pressure):– e.g., flexor reflex:

• pulls hand away from hot stove

• Strength and extent of response:– depends on intensity

and location of stimulus

Reciprocal Inhibition

• For flexor reflex to work:– the stretch reflex of antagonistic (extensor)

muscle must be inhibited (reciprocal inhibition) by interneurons in spinal cord

Crossed Extensor Reflexes

• Occur simultaneously, coordinated with flexor reflex

• e.g., flexor reflex causes leg to pull up:– crossed extensor reflex

straightens other leg– to receive body weight– maintained by

reverberating circuits

Integration and Control of Spinal Reflexes

• Though reflex behaviors are automatic:– processing centers in brain can facilitate or inhibit

reflex motor patterns based in spinal cord• Higher centers of brain incorporate lower,

reflexive motor patterns • Automatic reflexes:

– can be activated by brain as needed – use few nerve impulses to control complex motor

functions– walking, running, jumping

Superficial reflexes• Stroking of the skin elicits muscle contraction

– Involves functional upper motor pathways as well as cord level reflex arcs

• Plantar reflex (L4-S2)…Babinski is normal in infants– Usually indicative of CNS damage in adults

• Abdominal reflex (T8-T12)– Absent with corticospinal lesion

Spinal Cord Trauma: Transection

• Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut

• Paraplegia – transection between T1 and L1

• Quadriplegia – transection in the cervical region

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Spinal Nerves• Spinal nerves attach to the

spinal cord via roots• Dorsal root

– Has only sensory neurons– Attached to cord via rootlets– Dorsal root ganglion

• Bulge formed by cell bodies of unipolar sensory neurons

• Ventral root– Has only motor neurons– No ganglion - all cell bodies of

motor neurons found in gray matter of spinal cord

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Spinal Nerves• 31 pair

– each contains thousands of nerve fibers– All are mixed nerves have both sensory and motor

neurons)• Connect to the spinal cord• Named for point of issue from the spinal cord

– 8 pairs of cervical nerves (C1-C8)– 12 pairs of thoracic nerves (T1-T12)– 5 pairs of lumbar nerves (L1-L5)– 5 pairs of sacral nerves (S1-S5)– 1 pair of coccygeal nerves (Co1)

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Formation of Rami• Rami are lateral branches of a

spinal nerve• Rami contain both sensory and

motor neurons• Two major groups

– Dorsal ramus• Neurons innervate the

dorsal regions of the body– Ventral ramus

• Larger• Neurons innervate the

ventral regions of the body• Braid together to form

plexuses (plexi)

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Dermatomal Map• Spinal nerves indicated by capital letter and number• Dermatomal map: skin area supplied with sensory

innervation by spinal nerves

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Introduction to Nerve Plexuses

• Nerve plexus– A network of ventral rami

• Ventral rami (except T2-T12)– Branch and join with one another – Form nerve plexuses

• In cervical, brachial, lumbar, and sacral regions• No plexus formed in thoracic region of s.c.

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The Cervical Plexus

• Buried deep in the neck– Under the sternocleidomastoid muscle

• Formed by ventral rami of first four cervical nerves• Most are cutaneous nerves• Some innervate muscles of the anterior neck• Phrenic nerve – the most important nerve of the

cervical plexus

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Branches of

Spinal Nerves

• Dorsal Ramus– Neurons within muscles of trunk and back

• Ventral Ramus (VR)– Braid together to form plexuses

• Cervical plexus - VR of C1-C4• Brachial plexus - VR of C5-T1• Lumbar plexus - VR of of L1-L4• Sacral plexus - VR of L4-S4• Coccygeal plexus -VR of S4 and S5

• Communicating Rami: communicate with sympathetic chain of ganglia– Covered in ANS unit

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Cervical Plexus• Buried deep in the neck

– Under the sternocleidomastoid muscle• Formed by ventral rami of first four cervical nerves

(C1-C4)• Most are cutaneous nerves• Some innervate muscles of the anterior neck, posterior

portion of head• Phrenic nerve – the most important nerve of the

cervical plexus• Phrenic nerve

– Innervate diaphragm

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Brachial Plexus• Formed by ventral rami of spinal

nerves C5-T1• Five ventral rami form

– three trunks that separate into – six divisions that then form – cords that give rise to nerves

• Major nerves– Axillary– Radial– Musculocutaneous– Ulnar– Median

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Brachial Plexus: Axillary Nerve• Motor neurons stimulate

– Deltoid, teres minor• Abducts arm- deltoid• Laterally rotate arm-teres

minor

• Sensory neurons– Skin: inferior lateral

shoulder

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Brachial Plexus: Radial Nerve• Motor components stimulate

– Posterior muscles of arm, forearm, and hand

• Triceps, supinator, brachioradialis, ECR, ECU, extensor digitorum

• Cause extension movements at elbow and wrist, thumb movements

• Sensory components– Skin on posterior surface of arm and

forearm, hand• Damage due to compression results in

crutch paralysis• Major symptom is ‘wrist drop’

– Failure of extensors of wrist and fingers to function

– Elbow, wrist, and fingers constantly flexed

12-55

Brachial Plexus:Musculocutaneous Nerve

• Motor components stimulate– Flexors in anterior upper arm:

(biceps brachii, brachialis)• Cause flexion movements at

shoulder and elbow

• Sensory: Skin along lateral surface of forearm

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Brachial Plexus: Ulnar Nerve• Motor components

stimulate– Flexor muscles in anterior

forearm (FCU, FDP, most intrinsic muscles of hand)

– Results in wrist and finger flexion

• Sensory: Skin on medial part of hand

• Most easily damaged– Hitting the “funny bone”

excites it

12-57

Brachial Plexus: Median Nerve• Motor components stimulate

– All but one of the flexors of the wrist and fingers, and thenar muscles at base of thumb (Palmaris longus, FCR, FDS, FPL, pronator)

– Causes flexion of the wrist and fingers and thumb

• Sensory components– Stimulate skin on lateral part of

hand

• Damaged in carpal tunnel and suicide attempts

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Lumbosacral Plexus• Lumbar plexus: formed by ventral

rami of L1-L4– Major nerves include

• Femoral nerve• Obturator nerve

• Sacral plexus: formed by ventral rami of L4-S4– Major nerve = Sciatic nerve (actually

2 nerves in one sheath)• Tibial nerve• Common fibular (peroneal) n.

• Usually considered together because of their close relationship

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Lumbar Plexus:Obturator Nerve• Motor components

– Innervate adductor group and gracilis in thigh

– Causes adduction of the thigh and knee (gracilis)

• Sensory: Skin of the superior middle side of thigh

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Femoral Nerve• Motor components

– Innervates flexors of hip• Iliopsoas (Iliacus and psoas),

rectus femoris• Cause flexion of the hip

– Innervates extensors of knee• Quadriceps group-Vastus and

rectus femoris• Cause extension of the knee

• Sensory: Skin- anterior and lateral thigh; medial leg and foot

12-61

Sciatic Nerve• Thickest and longest nerve of the

body• Composed of 2 nerves in one

sheath– Tibial nerve– Common fibular nerve– Leaves pelvis via greater sciatic notch– Courses deep to gluteus and enters

posterior thigh just medial to the hip joint

• The 2 divisions diverge just above the knee.

• Innervates posterior thigh and entire lower leg

12-62

Sciatic Branches:

Tibial Nerve

• Tibial nerve– Innervates

– Hamstring muscles –knee flexors, hip extensors

– Posterior leg muscles – gastrocnemius, soleus

– plantar flexors– FDL, FHL

–toe flexors– Branches in foot to form

–medial plantar nerve –lateral plantar nerve

–If injured, paralyzed calf muscles cannot plantar flex foot; shuffling gait develops

12-63

Common Fibular (Peroneal) Nerve

• Common fibular– Branches are deep and superficial

fibular (peroneal) nerves– Innervates

• anterior and lateral muscles of the leg and foot

– (extensors that dorsiflex the foot- Tibialis anterior, EDL, EHL)

– Skin distribution: lateral and anterior leg and dorsum of the foot

– susceptible to injury because of its superficial location at the head and neck of the fibula

- Foot drop (unable to hold foot horizontal)

- Toes drag while walking

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Other Nerves of the Lumbosacral Plexus

• Nerves that innervate the skin of the suprapubic area, external genitalia, superior medial thigh, posterior thigh– Iliohypogastric nerve

• Innervates muscles of abdominal wall and pubic region– Genitofemoral nerve

• Skin of scrotum (males) and labia (females); inferior abdominal muscles– Pudendal nerve

• Innervates muscles and skin of the perineum (see Fig 10.21, p. 346)– region encompasssing external genitalia and anus

• external anal sphincter• Stimulates muscle involved in developing an erection• Involved in voluntary control of urination• the “shameful” nerve

12-65

Coccygeal Plexus

• S4-S5; coccygeal nerve• Muscles of pelvic floor• Sensory information from skin over coccyx

The Autonomic Nervous System

The Autonomic Nervous System

Visceral sensory

Visceral motor&

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Autonomic nervous system

• The autonomic nervous system is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control

• Visceral motor innervates non-skeletal (non-somatic) muscles

• Visceral sensory will be covered later

69

• ANS is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control

• Visceral motor innervates non-skeletal (non-somatic) muscles

• Composed of a special group of neurons serving: – Cardiac muscle (the heart)– Smooth muscle (walls of viscera and blood vessels)– Internal organs– Skin

To repeat…

70

Basic anatomical difference between the motor pathways of the voluntary somatic nervous system (to skeletal muscles) and those of the autonomic nervous system

• Somatic division:– Cell bodies of motor neurons reside in CNS (brain or spinal

cord)– Their axons (sheathed in spinal nerves) extend all the way

to their skeletal muscles• Autonomic system: chains of two motor neurons

– 1st = preganglionic neuron (in brain or cord)– 2nd = gangionic neuron (cell body in ganglion outside CNS)– Slower because lightly or unmyelinated

(see next diagram)

71

• Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (ganglionic) neuron

• Axon of 2nd (ganglionic) neuron extends to the organ it serves

Diagram contrasts somatic (lower) and autonomic:

autonomic

somatic

Note: the autonomic ganglion is motor

this dorsal root ganglion is sensory

72

Divisions of the autonomic nervous system (visceral motor part of it)

• Parasympathetic division• Sympathetic division

73

Divisions of the autonomic nervous system

• Parasympathetic division• Sympathetic division

Serve most of the same organs but cause opposing or antagonistic effects

Parasysmpathetic: routine maintenance“rest &digest”

Sympathetic: mobilization & increased metabolism “fight, flight or fright” or “fight, flight or freeze”

74

Where they come from

Parasympathetic:craniosacral

Sympathetic:thoracolumbar

75

Parasympathetic nervous system“rest & digest”

• Also called the craniosacral system because all its preganglionic neurons are in the brain stem or sacral levels of the spinal cord– Cranial nerves III,VII, IX and X– In lateral horn of gray matter from S2-S4

• Only innervate internal organs (not skin)• Acetylcholine is neurotransmitter at end

organ as well as at preganglionic synapse: “cholinergic”

76

Parasympathetic continued

• Cranial outflow– III - pupils constrict– VII - tears, nasal mucus, saliva– IX – parotid salivary gland– X (Vagus n) – visceral organs of thorax & abdomen:

• Stimulates digestive glands• Increases motility of smooth muscle of digestive tract• Decreases heart rate• Causes bronchial constriction

• Sacral outflow (S2-4): form pelvic splanchnic nerves– Supply 2nd half of large intestine– Supply all the pelvic (genitourinary) organs

77

Parasympathetic

(only look at this if it helps you)

78

Sympathetic nervous system“fight, flight or fright”

• Also called thoracolumbar system: all its neurons are in lateral horn of gray matter from T1-L2

• Lead to every part of the body (unlike parasymp.) – Easy to remember that when nervous, you sweat; when

afraid, hair stands on end; when excited blood pressure rises (vasoconstriction): these sympathetic only

– Also causes: dry mouth, pupils to dilate, increased heart & respiratory rates to increase O2 to skeletal muscles, and liver to release glucose

• Norepinephrine (aka noradrenaline) is neurotransmitter released by most postganglionic fibers (acetylcholine in preganglionic): “adrenergic”

79

Sympathetic nervous system continued

• Regardless of target, all begin same

• Preganglionic axons exit spinal cord through ventral root and enter spinal nerve

• Exit spinal nerve via communicating ramus

• Enter sympathetic trunk/chain where postganglionic neurons are

• Has three options…

80

Options of preganglionic axons in sympathetic trunk

1. Synapse on postganglionic neuron in chain ganglion then return to spinal nerve and follow its branch to the skin

2. Ascend or descend within sympathetic trunk, synapse with a posganglionic neuron within a chain ganglion, and return to spinal nerve at that level and follow branches to skin

3. Enter sympathetic chain, pass through without synapsing, form a splanchnic nerve that passes toward thoracic or abdominal organs

– These synapse in prevertebral ganglion in front of aorta

– Postganglionic axons follow arteries to organs

(see next slides for drawing examples)

81

Synapse in chain ganglia at same level or different level

82

Pass through ganglia and synapse in prevertebral ganglion

83

Sympathetic

84

Adrenal gland is exception

On top of kidneys

Adrenal medulla (inside part) is a major organ of the sympathetic nervous system

85

Adrenal gland is exception

• Synapse in gland• Can cause body-wide

release of epinephrine aka adrenaline and norepinephrine in an extreme emergency(adrenaline “rush” or surge)

86

Summary

87

Visceral sensory system

Gives sensory input to autonomic nervous

system

88

Visceral sensory neurons• Monitor temperature, pain, irritation, chemical changes and

stretch in the visceral organs– Brain interprets as hunger, fullness, pain, nausea, well-being

• Receptors widely scattered – localization poor (e.g. which part is giving you the gas pain?)

• Visceral sensory fibers run within autonomic nerves, especially vagus and sympathetic nerves– Sympathetic nerves carry most pain fibers from visceral organs of

body trunk• Simplified pathway: sensory neurons to spinothalamic tract to

thalamus to cerebral cortex• Visceral pain is induced by stretching, infection and cramping

of internal organs but seldom by cutting (e.g. cutting off a colon polyp) or scraping them

89

Referred pain: important to know

Pain in visceral organs is often perceived to be somatic in origin: referred to somatic regions of body that receive innervation from the same spinal cord segments

Plus left shoulder,from spleen

Anterior skin areas to which pain is referred from certain visceral organs

90

Visceral sensory and autonomic neurons participate in visceral reflex arcs

• Many are spinal reflexes such as defecation and micturitionreflexes

• Some only involve peripheralneurons: spinal cord not involved(not shown)*

*e.g. “enteric” nervous system: 3 neuron reflex arcs entirely within the wall of the gut

91

Central control of the Autonomic NS

Amygdala: main limbic region for emotions

-Stimulates sympathetic activity, especially previously learned fear-related behavior-Can be voluntary when decide to recall frightful experience - cerebral cortex acts through amygdala-Some people can regulate some autonomic activities by gaining extraordinary control over their emotions

Hypothalamus: main integration center

Reticular formation: most direct influence over autonomic function

Human Anatomy 5th ed. 2005Benjamin Cummings

Autonomic Nervous System

• Makes all routine adjustments in physiological systems.

• The ANS pathway from the CNS to the effector always involves 2 neurons synapsing in an autonomic ganglion


ANS

– Preganglionic (neuron #1) – cell body is in the CNS, axon extends to the ganglion outside the CNS

– Postganglionic (neuron #2) – cell body is in the ganglion, axon extends to the visceral effector


Nerve Fibers of the ANS

• Preganglionic (neuron #1) – Always myelinated– Neurotransmitter is always ACh

• Postganglionic (neuron #2)– Always nonmyelinated– Neurotransmitter is Ach or norepinephrine


Subdivisions of the ANS

• Sympathetic Division – Fight-or-flight

• Parasympathetic Division– Rest-and-digest

• These divisions are anatomically distinct


Sympathetic

• Sympathetic division (thoracolumbar) – Cell bodies for all the neurons #1 reside in the

thoracic and lumbar portions of the spinal cord.• T1 – L2


Sympathetic

– Stimulates• heart beat • tissue metabolism, • increases alertness, • prepares the body to deal with emergencies • (“fight or flight” division)


T1-L2


Parasympathetic

•Parasympathetic division (craniosacral)–Cell bodies reside in the brain stem (cranial nerves) or in the sacral portion of the spinal cord.


Cranial & Sacral


Parasympathetic

– Slows the heart rate, – inhibits senses, – prepares the body for rest and relaxation; (“rest

and digest” division).


The Sympathetic Division


Sympathetic Chain Ganglia

– Synapses of neurons #1 and #2 are in a chain of ganglia that run alongside the spinal cord

– Extends on both sides of the vertebral column– Carries preganglionic fibers and cell bodies of

postganglionic neurons


Ganglia


Anatomy of the chain

• Rami communicantes from the spinal nerves connect to the chain


A closer look at spinal nerves


Routes of Preganglionic Axons

• Cell bodies of neurons #1 lie in the lateral gray horns of the spinal cord

• The axons of neurons #1 leave the spinal cord via the ventral root

• These axons pass to the spinal nerve• Axons leave the spinal nerve via the white

branches (rami communicantes)• Connect with the sympathetic chain ganglia



• There are 3 possible routes that sympathetic neurons may follow

• Possibility #1: synapses within the ganglion at that level and– Second neuron leaves at that level via the gray

ramus communicans, exits to the visceral effector



• Possibility #2: neuron #1 goes up or down the chain and synapses at some other level.– Second neuron: leaves at that other level via the

gray ramus communicantes, and exits to the visceral effector.



• Possibility #3: neuron #1 does not synapse in the chain (exception!!) but exits and synapses in a collateral ganglion near a major blood vessel.– Neuron #2 travels from that ganglion to the

visceral effector.


Where are the Collateral Ganglia ?

• Location –Near a major blood vessel– Celiac ganglion

• Innervates upper abdominal viscera – Superior mesenteric

• Innervates middle abdominal viscera– Inferior mesenteric

• Innervates lower abdominal & pelvic organs


The Adrenal Medulla

• Yet another type of innervation:– Going to the adrenal medulla– No synapse in ganglia– No synapse in collateral ganglia– YES synapse in the adrenal medulla


Adrenal Medulla

• Only preganglionic neurons are in this pathway

• Neuron #1 stimulates the medulla, • The medulla releases norepinephrine and

epinephrine (adrenaline) to blood


Adrenal Medulla


Effects of Sympathetic Stimulation

• Widespread– The sympathetic chain allows one preganglionic

fiber to synapse with many postganglionic neurons

• Enhanced & prolonged by the adrenal medulla


Convergence

• See heart


Neurotransmitters of Sympathetic Division

• Preganglionic fibers release acetylcholine (Ach) Therefore they are called:– Cholinergic

• Postganglionic fibers (most) release norepinephrine (NE) (=noradrenaline)– Adrenergic

• Adrenal medulla releases norepinephrine and epinephrine (adrenalin)


Functions of the Sympathetic Division

• Heart: increases rate• Lung bronchioles: dilates bronchioles• Salivary glands: produce viscous fluid• Stomach: decreases motility• Pupil: dilates• Sweat glands: produce secretions


Summary of Sympathetic Division

• Cell bodies are found in the thoracic and lumbar portions of the spinal cord

• Preganglionic fibers are short, connect to the sympathetic chain, and synapse with long postganglionic fibers

• Preganglionic fibers produce ACh, postganglionic fibers produce NE or Ach

• “Fight or flight” division


The Parasympathetic Division


Parasympathetic division

• Cell bodies are in the brain or in the gray matter of the spinal cord (sacral region)

• Neurons #1 exit the cranial region through cranial nerves 3, 7, 9, & 10 or

• Neurons #1 exit the spinal cord through the sacral spinal nerves


Parasympathetic


Parasympathetic

• Neurons #1 are long and synapse with neurons #2 (short) in ganglia

• Ganglia are found on, or –near the visceral effector


Parasympathetic


Parasympathetic ganglia


Neurotransmitter of Parasympathetic Division

• Preganglionic fibers: Acetylcholine

• Postganglionic fibers: Acetylcholine


General Functions of the Parasympathetic

• Prepares the individual for rest and repose• “Rest & digest” division


Effects on various organs:

Heart: decreases rate• Lung bronchioles: constricts bronchioles• Salivary glands: produces watery fluid

fluid• Stomach: increases motility• Pupil: constricts• Sweat glands: reduces secretions


Summary of the Parasympathetic Division

• Cell bodies are found in the brain and in the sacral region of the spinal cord

• Preganglionic fibers are long and synapse with short postganglionic fibers on or near the target viscera

• Both preganglionic and postganglionic fibers produce Ach

• “Rest & digest” division


Relationship Between the Sympathetic and Parasympathetic Divisions

• Most organs receive dual innervation• It is a tug of war between the two


ANS either increases excitation or inhibits the activity

– Ex. Sympathetic fibers increase heart rate, parasympathetic fibers decrease heart rate.

– Homeostasis comes from the balance of the two.


ANS either increases excitation or inhibits the activity

Ex.#2 Sympathetic fibers decreases stomach motility.Parasympathetic fibers increase stomach motitlity


Parasympathetic innervation

• The cranial nerve fibers involved are motor - control smooth muscle & glands in the upper body– Cranial nerve #3 – lens & pupil – Cranial nerve #7 – lacrimal glands, submandibular

& submaxillary glands (salivary)– Cranial nerve #9 – parotid gland (salivary)– Cranial nerve #10 - viscera of thorax & abdomen

• Sacral nerves innervate the kidneys, colon, & sex organs

spinal nerves, cervical, lumbar and sacral plexus

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