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Chapter 13Chapter 13The Spinal Cord & Spinal The Spinal Cord & Spinal

NervesNerves Together with brain forms the CNSTogether with brain forms the CNS FunctionsFunctions

spinal cord reflexesspinal cord reflexes integration (summation of inhibitory and integration (summation of inhibitory and

excitatory) nerve impulsesexcitatory) nerve impulses highway for upward and downward highway for upward and downward

travel of sensory and motor informationtravel of sensory and motor information

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Spinal Cord ProtectionSpinal Cord Protection

By the vertebral column, meninges, cerebrospinal fluid, and vertebral ligaments.

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Structures Covering the Spinal Structures Covering the Spinal CordCord

VertebraeVertebrae Epidural space filled with Epidural space filled with

fatfat Dura materDura mater

dense irregular CT tubedense irregular CT tube Subdural space filled Subdural space filled

with interstitial fluidwith interstitial fluid Arachnoid = spider web Arachnoid = spider web

of collagen fibersof collagen fibers Subarachnoid space = Subarachnoid space =

CSFCSF Pia materPia mater

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External Anatomy of Spinal External Anatomy of Spinal CordCord

Flattened cylinderFlattened cylinder 16-18 Inches long & 16-18 Inches long &

3/4 inch diameter3/4 inch diameter In adult ends at L2In adult ends at L2 In newborn ends at L4In newborn ends at L4 Growth of cord stops at Growth of cord stops at

age 5age 5 Cervical enlargementCervical enlargement

upper limbsupper limbs Lumbar enlargementLumbar enlargement

lower limbslower limbs

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Inferior End of Inferior End of Spinal CordSpinal Cord

Conus medullarisConus medullaris cone-shaped end of spinal cordcone-shaped end of spinal cord

Filum terminaleFilum terminale thread-like extension of pia thread-like extension of pia

matermater stabilizes spinal cord in canalstabilizes spinal cord in canal

Caudae equinae (horse’s tail)Caudae equinae (horse’s tail) dorsal & ventral roots of lowest dorsal & ventral roots of lowest

spinal nervesspinal nerves Spinal segmentSpinal segment

area of cord from which each area of cord from which each pair of spinal nerves arisespair of spinal nerves arises

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Spinal Cord & Spinal Spinal Cord & Spinal NervesNerves

Spinal nerves begin as rootsSpinal nerves begin as roots Dorsal or posterior root is incoming sensory fibersDorsal or posterior root is incoming sensory fibers

dorsal root ganglion (swelling) = cell bodies of sensory dorsal root ganglion (swelling) = cell bodies of sensory nervesnerves

Ventral or anterior root is outgoing motor fibersVentral or anterior root is outgoing motor fibers

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Spinal tap or Lumbar Spinal tap or Lumbar PuncturePuncture

TechniqueTechnique long needle into subarachnoid space long needle into subarachnoid space safe from L3 to L5safe from L3 to L5

PurposePurpose sampling CSF for diagnosissampling CSF for diagnosis injection of antibiotics, anesthetics or injection of antibiotics, anesthetics or

chemotherapychemotherapy measurement of CSF pressuremeasurement of CSF pressure

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Gray Matter of the Spinal CordGray Matter of the Spinal Cord

Gray matter is shaped like the letter H or a Gray matter is shaped like the letter H or a butterflybutterfly contains neuron cell bodies, unmyelinated axons contains neuron cell bodies, unmyelinated axons

& dendrites& dendrites paired dorsal and ventral gray horns paired dorsal and ventral gray horns lateral horns only present in thoracic spinal cordlateral horns only present in thoracic spinal cord

Note: colors in reverse due to staining of tissue

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White Matter of the Spinal CordWhite Matter of the Spinal Cord

White matter covers gray matterWhite matter covers gray matter

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Tracts of the Spinal CordTracts of the Spinal Cord Function of tractsFunction of tracts

highway for sensory & motor informationhighway for sensory & motor information sensory tracts ascendsensory tracts ascend motor tracts descend motor tracts descend

Naming of tractsNaming of tracts indicates position & direction of signalindicates position & direction of signal example = anterior spinothalamic tractexample = anterior spinothalamic tract

impulses travel from spinal cord towards brain impulses travel from spinal cord towards brain (thalamus)(thalamus)

found in anterior part of spinal cordfound in anterior part of spinal cord

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Location of Tracts inside Location of Tracts inside CordCord

Motor tractsMotor tracts Sensory tractsSensory tracts pyramidal tract (corticospinal)pyramidal tract (corticospinal) ---spinothalamic tract---spinothalamic tract extrapyramidal tractextrapyramidal tract ---posterior column---posterior column

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Spinal ReflexesSpinal Reflexes

Automatic response to change in environmentAutomatic response to change in environment Integration center for spinal reflexes is gray Integration center for spinal reflexes is gray

matter of spinal cordmatter of spinal cord ExamplesExamples

somatic reflexes result in skeletal muscle somatic reflexes result in skeletal muscle contractioncontraction

autonomic (visceral) reflexes involve smooth & autonomic (visceral) reflexes involve smooth & cardiac muscle and glands.cardiac muscle and glands.

heart rate, respiration, digestion, urination, etcheart rate, respiration, digestion, urination, etc

Note: cranial reflexes involve cranial nervesNote: cranial reflexes involve cranial nerves

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Reflex ArcReflex Arc Specific nerve impulse pathwaySpecific nerve impulse pathway 5 components of reflex arc5 components of reflex arc

receptor receptor sensory neuronsensory neuron integrating centerintegrating center motor neuronmotor neuron effectoreffector

4 important somatic spinal reflexes4 important somatic spinal reflexes stretch, tendon, flexor(withdrawal) & stretch, tendon, flexor(withdrawal) &

crossed extensor reflexescrossed extensor reflexes

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Stretch Reflex (patellar Stretch Reflex (patellar reflex)reflex)

Prevents injury from over stretching because Prevents injury from over stretching because muscle contracts when it is stretchedmuscle contracts when it is stretched

Events of stretch reflexEvents of stretch reflex muscle spindle signals stretch of musclemuscle spindle signals stretch of muscle motor neuron activated & muscle contractsmotor neuron activated & muscle contracts

Brain sets muscle spindle sensitivity as it Brain sets muscle spindle sensitivity as it sets muscle tone (degree of muscle sets muscle tone (degree of muscle contraction at rest)contraction at rest)

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Illustration of the Stretch Reflex Illustration of the Stretch Reflex

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Tendon ReflexTendon Reflex Controls muscle tension by causing Controls muscle tension by causing

muscle relaxation that prevents muscle relaxation that prevents tendon damagetendon damage

Both tendon & muscle are protectedBoth tendon & muscle are protected

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Illustration of Tendon Illustration of Tendon ReflexReflex

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Flexor (withdrawal) ReflexFlexor (withdrawal) Reflex

Step on tack (pain Step on tack (pain fibers send signal fibers send signal to spinal cordto spinal cord

More than one More than one muscle group muscle group activated to lift foot activated to lift foot off of tackoff of tack

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Crossed Extensor ReflexCrossed Extensor Reflex Lifting left foot Lifting left foot

requires extension requires extension of right leg to of right leg to maintain one’s maintain one’s balancebalance

Pain signals cross Pain signals cross to opposite spinal to opposite spinal cordcord

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Clinical ConsiderationsClinical Considerations

Checking a patient’s reflexes may help Checking a patient’s reflexes may help to detect disorders/injuryto detect disorders/injury

Plantar flexion reflex -- stroke the lateral Plantar flexion reflex -- stroke the lateral margin of the solemargin of the sole normal response is curling under the toesnormal response is curling under the toes abnormal response or response of children abnormal response or response of children

under 18 months is called Babinski sign under 18 months is called Babinski sign (upward fanning of toes due to incomplete (upward fanning of toes due to incomplete myelination in child)myelination in child)

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Spinal NervesSpinal Nerves 31 Pairs of spinal nerves31 Pairs of spinal nerves Named & numbered by the Named & numbered by the

cord level of their origincord level of their origin 8 pairs of cervical nerves8 pairs of cervical nerves

(C1 to C8) (C1 to C8) 12 pairs of thoracic nerves 12 pairs of thoracic nerves

(T1 to T12)(T1 to T12) 5 pairs of lumbar nerves5 pairs of lumbar nerves

(L1 to L5) (L1 to L5) 5 pairs of sacral nerves 5 pairs of sacral nerves

(S1 to S5) (S1 to S5) 1 pair of coccygeal nerves1 pair of coccygeal nerves

Mixed sensory & motor Mixed sensory & motor nervesnerves

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Branching of Spinal NerveBranching of Spinal Nerve

Spinal nerves formed from dorsal & Spinal nerves formed from dorsal & ventral rootsventral roots

Spinal nerves branch into dorsal & Spinal nerves branch into dorsal & ventral ramiventral rami

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A Nerve PlexusA Nerve Plexus

Joining of ventral rami Joining of ventral rami of spinal nerves to of spinal nerves to form nerve networks form nerve networks or plexusesor plexuses

Found in neck, arm, Found in neck, arm, low back & sacral low back & sacral regionsregions

No plexus in thoracic No plexus in thoracic regionregion

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Cervical PlexusCervical Plexus

Ventral rami of spinal Ventral rami of spinal nerves (C1 to C5)nerves (C1 to C5)

Supplies parts of head, Supplies parts of head, neck & shouldersneck & shoulders

Phrenic nerve (C3-C5) Phrenic nerve (C3-C5) keeps diaphragm alivekeeps diaphragm alive

Damage to cord above Damage to cord above C3 causes respiratory C3 causes respiratory arrestarrest

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Brachial Brachial PlexusPlexus

Ventral rami from C5 to Ventral rami from C5 to T1T1

Supplies shoulder & Supplies shoulder & upper limbupper limb

Passes superior to 1st rib Passes superior to 1st rib & under clavicle& under clavicle

Axillary n. = deltoid & Axillary n. = deltoid & teres m.teres m.

Musculocutaneous n. = Musculocutaneous n. = elbow flexorselbow flexors

Radial n. = shoulder & Radial n. = shoulder & elbow extensorselbow extensors

Median & ulnar nn. = Median & ulnar nn. = flexors of wrist & handflexors of wrist & hand

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Clinical CorrelationsClinical Correlations Erb-Duchene palsyErb-Duchene palsy

waiter’s tip positionwaiter’s tip position fall on shoulderfall on shoulder

Radial nerve injuryRadial nerve injury improper deltoid injectionimproper deltoid injection

or tight castor tight cast wrist dropwrist drop

Median nerve injuryMedian nerve injury numb palm & fingers; inability to pronate & flex numb palm & fingers; inability to pronate & flex

fingersfingers Ulnar nerve injury (clawhand)Ulnar nerve injury (clawhand)

inability to adduct/abduct fingers, inability to adduct/abduct fingers,

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Lumbar PlexusLumbar Plexus Ventral rami of L1 to Ventral rami of L1 to

L4 L4 Supplies abdominal Supplies abdominal

wall, external genitals wall, external genitals & anterior/medial thigh& anterior/medial thigh

Injury to femoral nerve Injury to femoral nerve causes inability to causes inability to extend leg & loss of extend leg & loss of sensation in thighsensation in thigh

Injury to obturator Injury to obturator nerve causes paralysis nerve causes paralysis of thigh adductorsof thigh adductors

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Sacral PlexusSacral Plexus Ventral rami of L4-L5 & S1-S4Ventral rami of L4-L5 & S1-S4 Anterior to the sacrumAnterior to the sacrum Supplies buttocks, perineum & Supplies buttocks, perineum &

part of lower limbpart of lower limb Sciatic nerve = L4 to S3 Sciatic nerve = L4 to S3

supplies post thigh & all below supplies post thigh & all below kneeknee Peroneal nerve injury produces Peroneal nerve injury produces

foot drop or numbnessfoot drop or numbness Tibial nerve injury produces Tibial nerve injury produces

calcaneovalgus (loss of function calcaneovalgus (loss of function on anterior leg & dorsum of foot)on anterior leg & dorsum of foot)

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Sciatic Nerve BranchesSciatic Nerve Branches

Notice: Common Notice: Common Peroneal nerve and Tibial Peroneal nerve and Tibial nerve behind the kneenerve behind the knee

Notice: Sciatica pain Notice: Sciatica pain extends from the buttock extends from the buttock down the leg to the footdown the leg to the foot

may be sign of herniated may be sign of herniated discdisc

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Dermatomes & MyotomesDermatomes & Myotomes Each spinal nerve contains both sensory Each spinal nerve contains both sensory

& motor nerve fibers& motor nerve fibers DermatomeDermatome

area of skin supplied by one spinal nervearea of skin supplied by one spinal nerve overlap prevents loss of sensation if one overlap prevents loss of sensation if one

damageddamaged sensory anesthesia requires 3 spinal nerves sensory anesthesia requires 3 spinal nerves

to be blockedto be blocked Skin on face supplied by Cranial Nerve Skin on face supplied by Cranial Nerve

VV

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DermatomesDermatomes Damaged regions of Damaged regions of

the spinal cord can be the spinal cord can be distinguished by distinguished by patterns of numbness patterns of numbness over a dermatome over a dermatome regionregion

Infusing local Infusing local anesthetics or cutting anesthetics or cutting roots must be done roots must be done over 3 adjacent spinal over 3 adjacent spinal nerves.nerves.

Spinal cord transectionSpinal cord transection injury that severs the injury that severs the

cord loss of sensation& cord loss of sensation& motor control below the motor control below the injuryinjury

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DisordersDisorders NeuritisNeuritis

inflammation of nervesinflammation of nerves caused by injury, vitamin deficiency or caused by injury, vitamin deficiency or

poisonpoison Shingles Shingles

infection of peripheral nerve by chicken infection of peripheral nerve by chicken pox viruspox virus

causes pain, skin discoloration, line of skin causes pain, skin discoloration, line of skin blistersblisters

PoliomyelitisPoliomyelitis viral infection causing motor neuron death viral infection causing motor neuron death

and possible death from cardiac failure or and possible death from cardiac failure or respiratory arrestrespiratory arrest