Spinal Cord and Peripheral Nerves 2011

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The Spinal Cordand Peripheral

NervesMina N. Astejada, MD, FPNAClinical Associate ProfessorDepartment of NeurosciencesUP-PGH

The Spinal Cord

• Extent: From Foramen Magnum tolower border of L1 vertebra or upperborder of L2 vertebra

• Length of human spinal cord – 45 cm (male) – 43 cm (female)

• Length of human vertebral column

– 70 cm

• Weight of human spinal cord – 35 g

DEVELOPMENT OF SPINAL CORD

4 cell columns of spinal cord• 2 dorsal (alar) plates form dorsalhorns

• 2 ventral (basal) plates formventral and lateral horns• dorsal & ventral plates areseparated by sulcus limitans

Compare the Development ofSpinal Cord & Vertebral Column

Vertebral body level:3rd fetal month - cord occupies entire canalBirth - L3 vertebral body

Adult - L1-L2 vertebral body

SPINAL CORD ANATOMY

• spinal cord is protected by:

– vertebral column

– meninges

– cerebrospinal fluid

The Spinal CordSegments and

Nerves

8 Cervical12 Thoracic

5 Lumbar5 Sacral1 Coccygeal

Gives rise to 31 pairs of spinal nerves

•Cervical level

- Wide flat cord, lots of white matter,ventral horn enlargements.

•Thoracic level- An extra cell column between the small

dorsal and ventral horns is called theintermediate horn . It is the source ofall of the sympathetics in the body &occurs only in the Thoracic sections T1 - L 2.

• Lumbar level- Round cord, ventral horn enlargements.

• Sacral level- Small round cord, lateral Horn.

Spinal Cord Segments

Gross Anatomy of the Spinal Cord

• It contains 2 enlargements

1.Cervical• Maximal Circumference is 38 mm•C5-T1 segments

•Give rise to nerve roots forming thebrachial plexus that innervates theupper extremities

2. Lumbar or lumbosacral• Maximal Circumference is 35 mm• Give rise to fibers forming lumbar

plexus (L1-L4) and sacral plexus(L4-S2)that innervates the lowerextremities

External Anatomy of Spinal Cord

Conusmedullaris

Conus medullaris:- conical termination of the spinal cord- S2-S4 cord segments- Located between L1 & L2 vertebrae

Cauda equina (“Horse’s tail”):- contain L2 to S5 nerve roots- distal to L2 vertebra

Filum terminale:- fibrous strand at inferior end

of conus medullaris- inserts at dorsum of coccyx

Denticulate ligament:- delicate shelves of pia mater

that attach the spinal cord to thevertebrae laterally

Spinal CordExternal Anatomy

Anatomy of the Spinal Cordsulcus & fissures

Posterior median sulcus

Anterior median fissure

Posterolateral sulcus

Antrolateral sulcus

Posterior intermediate sulcus

• Gray matter consists of soma, unmyelinated processes, & neuroglia• Pair of Posterior (dorsal) horns – interneurons• Pair of Anterior (ventral) horns – interneurons & somatic motorneurons• Pair of lateral horn – contain intermediolateral cell column which giverise to sympathetic preganglionic fibers•Connected by gray commissure punctured by a central canal continuousabove with 4th ventricle

Grey commissure

Central canal

Cross-Sectional Anatomy of the Spinal CordGray Matter

Lamina of Rexed

Lamina I Posteromarginal NucleusLamina II Substantia Gelatinosa of Rolando Lamina IIILamina IV, V, VI ----- Nucleus PropiusLamina VII

- Intermediate Gray- Intermediolateral cell column (ILM)- Clarke’s column (Nucleus dorsalis)- Intermediomedial cell column (IMM)

Lamina VIIILamina IX ---------- Anterior Horn (Motor) Cell Lamina X ----------- Gray Commissure

Cross-Sectional Anatomy of the Spinal CordWhite Matter

Posterior columns

Lateral columns

Antrolateral column

• Central area of gray matter shaped like a butterfly andsurrounded by white matter in 3 columns

Spinal Tracts

Somatotopical Arrangement of Spinal Tracts

Dorsal Column

spinothalamic

Corticospinal

Spinothalamic Pathway

1 st order Neuron:

Dorsal Root Ganglion

2nd order Neuron:

Dorsal Horn (Lamina I, II, V,)

3 rd order Neuron:

Thalamus (Ventral posterolateral)

Termination: Primary Somesthetic Area (S 1)

Modality : Pain & Temperature Sensation, Light Touch

1 st order Neuron:Dorsal Root Ganglion (Spinal Ganglion)

2nd order Neuron :Dorsal Column Nuclei in the medulla

(Nucleus Gracilis & Cuneatus)

3 rd order Neuron : Thalamus (VPLc)

Termination: Primary Somesthetic Area (S I)

Dorsal Column-Medial Lemniscal Pathway

Modality: Discriminative Touch Sensation (include Vibration) and Conscious Proprioception (Position Sensation, Kinesthesia)

Origin:

Cerebral CortexBrodmann Area 4 (Primary Motor Area)

Brodmann Area 6 (Premotor Area)

Brodmann Area 3,1,2 (Primary Somesthetic Area)

Brodmann Area 5 (Anterior Portion of Sup.Parietal Lobule)

Corona Radiata

lnternal Capsule, Posterior Limb

Crus Cerebri, Middle Portion Longitudinal Pontine Fiber

Pyramid decussation at the medulla

Corticospinal Tracts:

Termination: Spinal Gray (Rexed IV-IX)

The Corticospinal (Pyramidal) System

Spinal Cord Arterial Blood Supply

2.Radicular arteries• from segmental arteries (Vertebral, AscendingCervical, Intercostal, Lumbar & sacral artery)• Anterior radicular (2-17) & posterior radicular

(10-23)• vulnerable (“watershed”) areas of the spinal

cord ( T1-T4)

Artery of Adamkiewics:

- artery of the lumbar enlargement- anterior radicular artery- originates at T9-T12 in 75% of the cases- Left side in 2/3 of cases

Spinal Cord Venous Drainage

1.Three (3) anterior and three (3) posterior spinal sinuses/veins thatare drain by 6-11 anterior and 5-10 posterior radicular veins2. Internal vertebral plexus (epidural)

“Batson’s plexus”- valveless

- pathway for metastatic spreade.g. prostatic CA

3. All of them drain into vertebral veins in the neck, azygos veins in thethorax, lumbar veins in the lumbar region, lateral sacral veins in thesacral region through intervertebral foramina

Spinal nerves• 31 pairs arise from spinal cord

– each contains thousands of nerve fibers

– All are mixed nerves ( haveboth sensory and motorneurons)

• 5 groups correspond to regionsof origins from spinal cord

– Cervical 8 pr.

– Thoracic 12 pr.

– Lumbar 5 pr.

– Sacral 5 pr.

– Coccygeal 1 pr.

• Ventral roots arise from the ventral horn and contain

motor (efferent) fibers• Dorsal roots arise from sensory neurons in the

dorsal root ganglion and contain sensory (afferent)fibers

Spinal Nerves: Roots

Dermatomal Regions

– Topographical region of the body surfaceinnervated by one dorsal nerve root

• Collar region: C-3

• middle finger: C-7• Nipple line: T-4• Umbilicus: T-10• Big toe: L-5• Small toe: S-1

Formation of Rami• Rami are lateral branches of a

spinal nerve• It contain both sensory and

motor components• Two major groups

– Dorsal ramus: Innervate the

dorsal regions of the body – Ventral ramus

• Larger• Innervate the ventral

regions of the body• fused together to form

plexus es (plexi)• Rami communicantes to

sympathetic chain ganglion(ANS)

Spinal Nerve Plexuses

• Cervical plexus

• Brachial plexus

• Lumbar plexus• Sacral plexus

• network of ventralrami that branch and

join with one another

T2 – T12 do not form plexuses

Cervical plexus

• Buried deep in the neckunder thesternocleidomastoid muscle

• C1 – C4 (+ C 5)

– cutaneous nerves, mostlysensory from skin of neck& back of head

– Phrenic nerve (C3-5) to

diaphragm• Motor stimulation for

breathing!

Brachial Plexus

Posterior Cord: Axillary Nerve (C5-6)

• Motor component stimulate – Deltoid, teres minor

• Abducts arm- deltoid

• Laterally rotate arm-teres minor• Sensory component

– Skin: inferior lateral

shoulder

Posterior Cord: Radial Nerve (C5-8)• Motor components stimulate

- Posterior muscles of arm, forearm,and hand

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

• Cause extension movements atelbow and wrist, thumbmovements

• Sensory components: Skin on posteriorsurface of arm and forearm, hand

• Compression results in crutch paralysis• Major symptom is „wrist drop

– Failure of extensors of wrist andfingers to function

– Elbow, wrist, and fingers constantlyflexed

Lateral cord: Musculocutaneous Nerve (C5-7)

• Motor components stimulate – Flexors in anterior upper

arm: (biceps brachii,brachialis)• Cause flexion

movements at shoulder

and elbow• Sensory: Skin along lateralsurface of forearm

Medial Cord: Ulnar Nerve (C7-T1)

• Motor componentsstimulate – Flexor muscles in anterior

forearm (FCU, FDP, mostintrinsic muscles of hand)

– Results in wrist and fingerflexion

• Sensory: Skin on medialpart of hand

• Most easily damaged – Hitting the “funny bone”

excites it

Med & Lat Cord: Median Nerve (C5-T1)

• Motor components stimulate – All but one of the flexors of

the wrist and fingers, andthenar muscles at base ofthumb (Palmaris longus,FCR, FDS, FPL, pronator)

– Causes flexion of the wristand fingers and thumb

• Sensory components

– Stimulate skin on lateralpart of hand

• Damaged in carpal tunnel andsuicide attempts

Lumbar plexus• L1 – L4 (+ L5)

• Ilioinguinal nerve (L1) – mostly sensory from skin of

thigh & genitals – Abdominal & pubic muscles

• Genitofemoral nerve (L1-2)

– mostly sensory fromscrotum, labia majora, ant.Thigh

– Inferior abdominal muscles• Femoral Nerve (L2-4)

– to quadriceps, sartorius• Obturator (L2-4)

– Adductors of thigh andgracilis

Lumbar Plexus:Obturator Nerve (L2-4)

• Motor components – Innervate adductor group and

gracilis in thigh

– Causes adduction of the thighand knee (gracilis)

• Sensory: Skin of thesuperior middle side of

Femoral Nerve (L2-4)

• Motor components – Innervates flexors of hip

• Iliopsoas (Iliacus andpsoas), rectus femoris

• Cause flexion of the hip – Innervates extensors of knee

• Quadriceps group-Vastusand rectus femoris

• Cause extension of theknee

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

Sacral plexus

• L4 – S 4

• Superior & inferior glutealnerves (L4-S2) – To gluteus muscles

• Sciatic nerve (L4-S3) – To hamstrings & other

posterior thigh & legmuscles

• Pudendal nerve (S1-4) – Sensory from penis,clitoris, labia minora, anus(ext. anal sphincter)

– Voluntary micturation

S i i N (L4 S3)

Sciatic Nerve (L4-S3)• 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 justabove the knee.

• Innervates posterior thigh andentire lower leg

Common Fibular

Common Fibular(Peroneal) Nerve

• Common fibular (L4-S2) – Branches: deep & superficial

fibular (peroneal) nerves

– Innervates• anterior and lateral

muscles of the leg andfoot: (extensors thatdorsiflex the foot- Tibialisanterior, EDL, EHL)

– sensory: lateral and anteriorleg and dorsum of the foot

– susceptible to injury because

of its superficial location at thehead & neck of the fibula- Foot drop (unable to hold

foot horizontal)- Toes drag while walking

T h an k

Sensory territory of nerves

Brachial plexus serves to re-directspinal routes into named nervescovering certain territory

Cutaneous branches of

medial cord/ulnar nerve

Nerve anatomy of lower leg

Spinal Tap (Lumbar Puncture)

Withdrawing CSF from thesubarachnoid space

Spinal Cord and Peripheral Nerves 2011

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