THE SPINAL CORD (ANOTOMY AND CLINICAL NEUROLOGY)

GENERAL FEATURES

        The spinal canal is housed in the vertebral canal.it is continous with the medulla below the pyramidal deccusation(chiasma: an intersection or crossing of two tracts in the form of the letter X)and terminates as the conus medullaris at the second lumbar vertebra of the adult. 

                          

1.       There are eight cervical pairs of spinal nerves (Cl through C8).

The cervical enlargement (C5through TI) gives rise to the rootlets that form the brachial plexus, which innervates the upper limbs.

2.       There are 12 thoracic pairs of spinal nerves (Tl through T12).

 Spinal nerves emanating from thoracic levels innervate most of the trunk.

3.  

terminates as the conus medullaris at the second lumbar vertebra of the adult.


The roots of 31 pairs of spinal nerves arise segmentally from the spinal cord.

     There are five lumbar pairs of spinal nerves (Ll through L5).

The  lumbar enlargement (Ll through 52) gives rise to rootlets that form the lumbar and sacral plexuses, which innervate the lower limbs.

4.       There are five sacral pairs of spinal nerves (51 through 55).

        Spinal nerves at the sacral level innervate part of the lower limbs and the pelvis.

5.       There is one coccygeal pair of spinal nerves.

The cauda equina consists of the dorsal and ventral roots of the lumbar, sacral, and coccygeal spinal nerves.

The cauda equina consists of the dorsal and ventral roots of the lumbar, sacral, and coccygeal spinal nerves.

·         Inside the spinal cord, gray matter is centrally located and shaped like a butterfly.

·         It contains neuronal cell bodies, their dendrites, and the proximal parts of axons.

       White matter surrounds the gray matter on all sides.

White matter contains bundles of functionally similar axons called tracts or fasciculi, which ascend or descend in the spinal cord.

cross section of spinalcord

NOTE:
dorsal root:ganglion found outside the CNS(spinal cord)
ventral root:ganglion found inside a specific part of grey matter(CNS)

white matter:tracts and faciculi 

grey matter:

dorsal horn(sensory)

ventral horn(motor)

intermediate zone(autonomic neurons T1-L2,S2-S4)

(CLARKE'S nucleus T1-L2)

dorsal ramus supplies:skin of back and dorsal neck,

deep intrinsic back musles(erector spinae)

ventral ramus supplies:skin of anteriolateral trunk and limbs,

skeletal museles of anterolateral trunk and limbs

• Every branch of every spinal nerve is mixed in that it contains both sensory and motor fibers.

• All spinal nerves branches in to a mixed ventral and dorsal ramus.

• All the branches of spinal nerves are mixed and every spinal nerve must have sensory(dorsal) root and motor(ventral) root. 

• All dorsal root Central process of axons enters in dorsolateral of spinal cord. Since all dorsal roots are derived from the neural crust cells their cell bodies are logically found in a ganglion which is out side the CNS in this case of dorsal root ganglion.

• The ventral root is derived from neural tube therefore their neuronal cell bodies are found inside a specific part of grey matter of the spinal cord and it is their axons that are coursing in a ventral root on the way to branching and forming a part of ventral or dorsal ramus.

     general spinal cord features

conus medullaris:caudal end of spinal cord(S3-S5).in adults,ends at the L2 vertebra

cauda equina:nerve roots of the lumbar,sacral and coccygeal spinal nerves

filum terminale: slender pial extension that tethers the spinal cord to the bottom of the vertebral column.

dorsal root ganglia:cell bodies of primary sensory neurons.

dorsal and ventral roots:each segment has a pair.

dorsal horns:sensory neurons.

ventral horns:motor neurons.

spinal horns:formed from ventral and dorsal roots(mixed nerves).

cervical enlargement:(C5-T1)----->branchial plexus-------->upperlimbs.

lumbar enlargement:(L2-S3------->lumbar and sacral plexuses-------->lower limbs.

before u go any further check the vedios below

TRACKS