November 5 - Spinal Nerves & Brachial Plexus.docx

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Western University
Anatomy and Cell Biology
Anatomy and Cell Biology 3319

November 5, 2013 Spinal Nerves & Brachial Plexus Pg. 439-449 Spinal Nerves - 31 pairs of spinal nerves each containing thousands of nerve fibers - 8 pairs of cervical nerves - Only 7 cervical vertebrae - C1 nerve lies superior to the first vertebrae, whereas C8 nerve lies inferior to the seventh vertebrae - 12 pairs of thoracic nerves - 5 pairs of lumbar nerves - 5 pairs of sacral nerves - 1 pair of coccygeal nerves - Below the cervical region, all nerves lie inferior to the vertebrae it correlates with - Each spinal nerve connects to the spinal cord by a dorsal root and a ventral root - Each root forms a series of rootlets that attach along the whole length of the corresponding spinal cord segment - Dorsal root contains axonal processes of sensory neurons from cell bodies in dorsal root ganglion - Ventral root contains axonal processes of motor neurons from cell bodies in ventral gray column of spinal cord - Each spinal nerve branches into a dorsal ramus and ventral ramus - Connecting to base of ventral ramus are rami communicantes leading to sympathetic trunk ganglia – visceral structures - Each branch of spinal nerve contains both motor and sensory fibers - Rami supply entire somatic region of body, the outer tube (skeletal musculature and skin), from the neck inferiorly - Dorsal rami supply dorsum of neck and back - Ventral rami (much thicker) supply a large area: anterior and lateral regions of neck and trunk, and all regions of limbs - Difference between roots and rami: - Roots lie medial to spinal nerves and are either strictly sensory (dorsal root) or strictly motor (ventral root) - Rami are lateral branches of spinal nerves, and each contains both sensory and motor fibers - Innervation of the back: - Posterior part of the trunk and neck - Innervation by dorsal rami follows a neat, segmented pattern - Each dorsal ramus branches to innervate a horizontal strip of muscle and skin in line with its emergence point from the vertebral column - Innervation of the anterior thoracic and abdominal wall - Only in the thorax are the ventral rami arranged in a simple and segmented pattern - Thoracic ventral rami run anteriorly, one deep to each rib, as the intercostal nerves - These nerves supply the intercostal muscles, the skin of the anterior and lateral thorax, and most of the abdominal wall inferior to the rib cage - Each intercostal nerve gives off lateral and anterior cutaneous branches Introduction to Nerve Plexuses - Nerve plexus: network of nerves - Ventral rami of all spinal nerves except T2-T12 branch and join one another lateral to the vertebral column, forming nerve plexuses - These interlacing networks occur in the cervical, brachial, lumbar and sacral regions and primarily
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