Spinal Cord and Spinal Nerves Pre-Lab

Spinal Cord

• Spinal nerves– 31 pairs

• Cervical and lumbar enlargements• Cauda equina

Figure 12.29a

Cervicalenlargement

Dura andarachnoidmater

LumbarenlargementConusmedullarisCaudaequina

Filumterminale

Cervicalspinal nerves

Lumbarspinal nerves

Sacralspinal nerves

Thoracicspinal nerves

(a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally.

Spinal Cord

Cross-Sectional Anatomy

• Two lengthwise grooves divide cord into right and left halves

– Ventral (anterior) median fissure – Dorsal (posterior) median sulcus

• Gray commissure—connects masses of gray matter; encloses central canal

Figure 12.31a

(a) Cross section of spinal cord and vertebra

Epidural space(contains fat)

Pia mater

Spinalmeninges

Arachnoidmater Dura mater

Bone ofvertebra

Subdural space

Subarachnoidspace(contains CSF)

Dorsal rootganglion

Bodyof vertebra

Figure 12.31b

(b) The spinal cord and its meningeal coverings

Dorsal funiculus

Dorsal median sulcus

Central canal

Ventral medianfissure

Pia mater

Arachnoid mater

Spinal dura mater

Graycommissure Dorsal horn Gray

matterLateral hornVentral horn

Ventral funiculusLateral funiculus

Whitecolumns

Dorsal rootganglion

Dorsal root(fans out into dorsal rootlets)

Ventral root(derived from severalventral rootlets)

Spinal nerve

Gray Matter

• Dorsal horns• Ventral horns• Lateral horns (only in thoracic

and lumbar regions) • Dorsal root (spinal) ganglia

White Matter

• Consists mostly of ascending (sensory) and descending (motor) tracts

• Transverse tracts (commissural fibers) cross from one side to the other

• Tracts are located in three white columns

Figure 12.33

Ascending tracts Descending tracts

Fasciculus gracilisDorsalwhitecolumn

Fasciculus cuneatus

Dorsalspinocerebellar tract

Lateralspinothalamic tract

Ventral spinothalamictract

Ventral whitecommissure

Lateralcorticospinal tract

Lateralreticulospinal tract

Ventral corticospinaltract

Medialreticulospinal tract

Rubrospinaltract

Vestibulospinal tractTectospinal tract

Ventralspinocerebellartract

Spinal Nerves

• 31 pairs of mixed nerves– 8 cervical (C1–C8)

– 12 thoracic (T1–T12)

– 5 Lumbar (L1–L5)

– 5 Sacral (S1–S5)

– 1 Coccygeal (C0)

Figure 13.6

CervicalnervesC1 – C8

ThoracicnervesT1 – T12

LumbarnervesL1 – L5

Sacral nervesS1 – S5

Coccygeal nerve Co1

Cervical plexus

Intercostalnerves

Cervicalenlargement

Lumbarenlargement

Cauda equina

Brachial plexus

Lumbar plexus

Sacral plexus

Spinal Nerves: Roots

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

• Ventral roots– Contain motor (efferent) fibers

from the ventral horn motor neurons

– Fibers innervate skeletal muscles

Spinal Nerves: Roots

• Dorsal roots– Contain sensory (afferent) fibers

from sensory neurons in the dorsal root ganglia

– Conduct impulses from peripheral receptors

• Dorsal and ventral roots unite to form spinal nerves

Figure 13.7 (a)

Dorsal rootganglion

Gray matterWhite matterVentral rootDorsal root

Dorsal andventral rootlets of spinal nerve

Dorsal ramusof spinal nerveVentral ramusof spinal nerve

Sympathetic trunkganglion

Spinal nerve

Rami communicantes

Anterior view showing spinal cord, associated nerves, and vertebrae. The dorsal and ventral roots arise medially as rootlets and join laterally to form the spinal nerve.

Spinal Nerves: Rami

• Each spinal nerve branches into mixed rami– Dorsal ramus– Larger ventral ramus– Meningeal branch– Rami communicantes (autonomic

pathways) join to the ventral rami in the thoracic region

Figure 13.7 (b)

Dorsal ramus

Ventral ramus

Intercostal nerve

Spinal nerve

Rami communicantes

Dorsal rootganglion Dorsal rootVentral root

Sympathetic trunkganglion

Sternum

(b) Cross section of thorax showing the main roots and branches of a spinal nerve.

Branches of intercostalnerve

• Lateral cutaneous• Anterior cutaneous

Cervical Plexus

• Formed by ventral rami of C1–C4

• Innervates skin and muscles of the neck, ear, back of head, and shoulders

• Phrenic nerve– Major motor and sensory nerve of

the diaphragm (receives fibers from C3–C5)

Figure 13.8

Hypoglossalnerve (XII)

C1

C2

C3

C4

C5

Segmentalbranches

Lesser occipitalnerveGreater auricularnerve

Ansa cervicalis

Phrenic nerve

Supraclavicularnerves

Accessory nerve (XI)

Transversecervical nerve

Ventralrami:

Ventral rami

Brachial Plexus

• Formed by ventral rami of C5–C8 and T1 (and often C4 and T2)

• Major branches of this plexus: – Roots—five ventral rami (C5–T1)

– Trunks—upper, middle, and lower– Divisions—anterior and posterior – Cords—lateral, medial, and posterior

Figure 13.9 (a)

Upper

Middle Trunks

Lower

Roots (ventral rami):

Upper subscapular

Lower subscapular

Thoracodorsal

Medial cutaneousnerves of the armand forearm

Long thoracic

Medial pectoral

Lateral pectoral

Nerve tosubclaviusSuprascapular

Dorsal scapular

Posteriordivisions

Anteriordivisions

Lateral

PosteriorCords

Medial

Axillary

Musculo-cutaneousRadial

Median

Ulnar

Posteriordivisions

Trunks Roots

C4

C5

C6

C7

C8

T1

(a) Roots (rami C5 – T1), trunks, divisions, and cords

Brachial Plexus: Nerves

• Axillary • Musculocutaneous • Median• Ulnar• Radial

Figure 13.9 (c)

Median nerve

Musculocutaneous nerve

Radial nerveHumerus

Ulna

Ulnar nerveMedian nerve

Radius

Radial nerve (superficial branch)

Superficial branch of ulnar nerveDorsal branch of ulnar nerve

Digital branch of ulnar nerveMuscular branchDigital branch

(c) The major nerves of the upper limb

Axillarynerve

Anteriordivisions

Posteriordivisions

Trunks Roots

Lumbar Plexus

• Arises from L1–L4

• Innervates the thigh, abdominal wall, and psoas muscle

• Femoral nerve • Obturator nerve

Figure 13.10

(a) Ventral rami and major branches of the lumbar plexus

Iliohypogastric

L1

L2

L3

L4

L5

Ilioinguinal

Genitofemoral

Lateral femoralcutaneous

Obturator

Femoral

Lumbosacraltrunk

Lateral femoralcutaneous

Anterior femoralcutaneousSaphenous

Obturator

IliohypogastricIlioinguinalFemoral

Ventral rami Ventralrami:

(b) Distribution of the major nerves from the lumbar plexus to the lower limb

Sacral Plexus

• Arises from L4–S4

• Serves the buttock, lower limb, pelvic structures, and perineum

• Sciatic nerve

Figure 13.11 (a)

SuperiorglutealLumbosacraltrunkInferiorgluteal

CommonfibularTibialPosteriorfemoralcutaneousPudendal

Sciatic

Ventral rami and major branches of the sacral plexus

L4

L5

S1

S2

S3

S4

S5

Co1

Ventral rami Ventral rami:

Figure 13.11 (b)

Superior gluteal

Inferior gluteal

Common fibular

Deep fibular

Superficial fibular

Plantar branches

Tibial

Sural (cut)

Posterior femoralcutaneous

Pudendal

Sciatic

(b) Distribution of the major nerves from the sacral plexus to the lower limb