Spinal Nerves and Brachial Plexus.docx

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Western University
Anatomy and Cell Biology
Anatomy and Cell Biology 3319
Kem Rogers

Spinal Nerves and Brachial Plexus Spinal Nerves • Each contains thousands of nerve fibres, attach to spinal cord • Named according to their point of issue from column (31 pairs) o 8 pairs of cervical nerves (C1-C8) o 12 pairs of thoracic nerves (T1-T12 o 5 pairs of lumbar nerves (L 1L 5 o 5pairs of sacral nerves (S 1S 5 o 1 pair of coccygeal nerves (Co 1 • 8 pairs of cervical nerves but only 7 cervical vertebrae st st o 1 cervical nerve (C 1 lies superior to 1 vertebrae o Last cervical nerve (C 8 exits inferior to 7 cervical vertebrae o Below cervical region, every spinal nerve exits inferior to vertebra of same number • Each nerve has long branches that supply most of body inferior to head • Each nerve connects to spinal cord by dorsal root & ventral root • Each root forms from series of rootlets that attach along whole length of corresponding signal cord segment • Dorsal root contains axonal processes of sensory neurons arising from cell bodies in dorsal root ganglion • Ventral root contains axonal processes of motor neurons whose cell bodies are located in ventral gray column of spinal cord • Nerve lies at junction of the dorsal & ventral roots, just lateral to dorsal root ganglion • Nerves & dorsal root ganglia lie within intervertebral foramina, against body pedicles of vertebral arches • Directly lateral to its intervertebral foramen – each nerve branches into dorsal ramus & ventral ramus • Connecting to base of ventral ramus are rami communicantes leading to sympathetic trunk ganglia • Each of the branches of spinal nerve, like the spinal nerve itself, contains both motor & sensory fibres • Rami supply entire somatic region of body, outer tube (skeletal muscles & skin), from neck inferiorly • Dorsal rami supply the dorsum of the neck & back • Thicker ventral rami supply larger area: anterior & lateral regions of neck & trunk & all regions of limbs • Differences between roots & rami o Roots lie medial to spinal nerves & are either strictly sensory (dorsal root) or strictly motor (ventral root) o Rami are lateral branches of spinal nerves & each contains both sensory fibres & motor fibres Innervation of the Back • Posterior part of the trunk & neck by dorsal rami follows a neat, segmented pattern • Each dorsal ramus branches to innervate intrinsic muscles of the back & horizontal strip of skin in line with its emergence point from the vertebral column • Simpler than the innervation of rest of the body by ventral rami Innervation of Anterior Thoracic & Abdominal Wall • Only in the thorax are the ventral rami arranged in a simple, segmented pattern • Thoracic ventral rami run anteriorly, one deep to each rib, as the intercostal nerves • Nerves supply intercostal muscles, skin of anterior & lateral thorax, & most of abdominal wall inferior to rib cage • Each intercostal nerve gives off lateral & anterior cutaneous branches to the adjacent skin • Two nerves are unusual th o T12ies inferior to 12 rib & is called sub-costal (below ribs) nerve rather than intercostal nerve o 1 (most superior) intercostal nerve is small because most fibres of T e1ter brachial plexus Intervertebral Foramen • Created by 2 vertebrae stacked together • Inferior + superior vertebral notch = intervertebral foramen • Nerve splits into ventral rami & dorsal rami (both mixed) • Goes from rami to effector organ Dermatomes Shingles • Latent herpes zoster virus in DRG • Can become active when immune system is compromised • Infects the nerve – in the dorsal root ganglion it was dormant in • Neuropathic pain – burning/tingling along that nerve’s dermatome Nerve Plexuses • Nerve plexus is a network of nerves • Ventral rami of al spinal nerves except 2 -12branch & join one another lateral to vertebral column forming nerve plexuses • Interlacing network occur in cervical, brachial, lumbar & sacral regions & primarily serve the limbs • Plexuses are formed by ventral rami only • Within plexuses, fibers from different ventral rami converge & diverge & redistribute so that o Each end branch of plexus contains fibers from several different spinal nerves o Fibers from each ventral ramus travel to body periphery via several different routes or branches • Each muscle in a limb receives its nerve supply from more than one spinal nerve • As a result – destruction of a single spinal nerve cannot completely paralyze any limb muscle Brachial Plexus & Innervation of Upper Limbs • Brachial (arm) – plexus (braid) • Braid of networks supplying the upper limb (arms) • Lies partly in the neck and partly in the axilla (armpit) • Sometimes felt in posterior triangle of neck just superior to clavicle at lateral border of sternocleidomastoid muscle • Formed by intermixing of the ventral rami of cervical nerves C5-C8and most of ventral ramus of T1 o Combinations of spinal nerves o Mixing of terminal branches  Multiple spinal levels supplying muscles  Get paresis (weakness) instead of paralysis • May receive small contributions from C or T 4 2 • Arrangement - functional organization of structures innervated • Components from medial to lateral (The Castrated Dog Turns Rabid) are: o Ventral rami – ventral rami from spinal segments C5-T1 from the roots of brachial plexus o Trunks – ventral rami merge to form three trunks o Divisions – each trunk slits into two
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