nervous system

• spinal cord- nerve tissue continuous with that of the brain, extending inferiorly from the brain at the level of foramen magnum.
• spinal cord- covered by several layers of protective or nourishing tissue
• bony covering of the spinal cord is formed by the vertebral column
• spinal cord- lies within the spinal cavity formed by vertebral foramina of the stacked vertebrae
• dura mater- outermost membranous coverings or meninges of the spinal cord. Tough, skin-like and leathery
• arachnoid- deep to the dura mater is a much thinner and translucent meninx
• subarachnoid space- space deep to the arachnoid, filled with circulating cerebrospinal fluid in life
• pia mater- deepest meninx, thin vascular membrane adhering to the surface of the spinal cord
• anterior median fissure- deep groove on the anterior surface of the spinal cord
• posterior median sulcus- shallower groove along the dorsal surface of the spinal cord
• cervical enlargement- is seen in the cervical region of the spinal cord
• lumbar enlargement- found in the lower thoracic region and tapers to a cone-shaped end called medullary cone
• the spinal cord does not extend below vertebra L1. Instead, separate nerves trail inferiorly until each pair has excited the spinal cavity.
• cauda equina- group of nerves, resembling a horse's tail
• a cross-sectional view of the spinal cord shows a distinct H-shaped area of gray matter surrounded by areas of white matter.
• the two lateral sections of the gray matter are joined by a transverse gray commissure, in the center of which is the central canal which contains CSF in life
• each lateral mass of gray matter exhibits extensions called anterior and posterior gray horns
• the thoracic and lumbar regions have lateral extensions called lateral gray horns
• columns of white matter surround the central gray matter. These include the anterior white column, lateral white column, and posterior white column. Columns are called funiculi.
• afferent neurons- extending through the spinal cord enter as part of the spinal nerve.
• efferent neurons- exit in spinal nerves
• there are 31 pairs of spinal nerves communicating with the spinal cord by way of intervertebral foramina formed as the vertebrae stack on one another.
• spinal nerves consist of sensory (afferent) fibers that carry impulses from receptors to the CNS and motor (efferent) fibers that carry impulses away from the CNS to effectors.
• dorsal root ganglia contain cell bodies of afferent neurons
• ventral roots contain axons of efferent neurons
• the spinal nerves are named for the vertebral region with which they are associated
• lumbar nerves supply structures of the lower trunk, pelvis, buttocks, legs, feet, and perineum
• cervical nerves supply structures of the neck, shoulders, arms, hands, and thorax
• thoracic nerves supply structures of the chest wall, abdomen, back, diaphragm, and upper limbs
• coccygeal nerves supply muscles of the coccyx and skin over its upper part
• sacral nerves supply structures of the hips, thighs, buttocks, genitalia, and posterior surface of the leg
• each spinal nerve communicates with the cord by means of 2 separate spinal nerve root, each formed by 6 to 8 tiny rootlets
• ventral or anterior spinal nerve root- includes efferent fibers
• dorsal or posterior spinal nerve root- contains afferent fibers
• Nuclei of afferent neurons form an area of gray matter in the dorsal root called dorsal root ganglion
• The spinal nerve roots are found within the spinal cavity
• The spinal nerve passes through the intervertebral foramine
• outside the spinal cavity, each spinal nerve branches forming a ventral ramus and dorsal ramus
• ventral ramus- may branch into autonomic and somatic pathways
• The ventral rami's fibers may branch to form plexi