Nervous System Overview Nervous system central nervous system includes the brain spinal cord spinal cord ends at L3 at birth, and L1 at maturity peripheral nervous system contains the cranial nerves peripheral nerves autonomic nervous system sympathetic system a total of 22 ganglia (3 cervical, 11 thoracic, 4 lumbar, 4 sacral) cervical ganglia the three cervical include the stellate, middle, and superior the middle ganglion is most at risk at the level of C6 where it lies close to the medial border of the longus colli muscles injury to the middle ganglion/sympathetic chain will lead to Horner's syndrome parasympathetic nervous system hypogastric plexus formed by S2, S3, S4 parasympathetic fibers and lumbar sympathetic fibers (splanchnic nerves) Spinal Cord Overview Spinal cord extends from brainstem to inferior border of L1 conus medullaris is termination of spinal cord filum terminale is residual fragment of spinal cord that extends from conus medullaris to sacrum. thecal sac the dural surrounded sac that extends from the spinal cord and contains CSF, nerve roots and the cauda equina cauda equina nerve roots and filum terminale surrounded by dura that extend from the spinal cord Embryology of the spinal cord Neural Tube becomes spinal cord formed from the primitive Streak, which turns into the primitive (midsagittal) groove > which turns into the Neural Tube failure of the neural tube to close leads to anencephaly when it fails to close cranially spinal bifida occulta, meningocele, myelomeningocele when it fails to close distally Neural crest forms dorsal to neural tube becomes the peripheral nervous system pia mater spinal ganglia sympathetic trunk Notocord forms ventral to neural tube becomes vertebral bodies intervertebral discs nucleus pulposus from cells of notocord annulus from sclerotomal cells associated with resegmentation Layers of the spinal cord Layers of the spinal cord include the dura mater (outside) arachnoid pia mater (inside) Spinal Cord Functional Tracts Ascending Tracts (Sensory) dorsal columns (posterior funiculi) deep touch, proprioception, vibratory lateral spinothalamic tract pain and temperature site of chordotomy to alleviate intractable pain ventral spinothalamic tract light touch Descending Tracts (Motor) lateral corticospinal tract main voluntary motor upper extremity motor pathways are more medial(central) which explains why a central cord injury affects the upper extremities more than the lower extremities ventral corticospinal tract voluntary motor Blood Supply Spinal cord blood supply provided by anterior spinal artery primary blood supply of anterior 2/3 of spinal cord, including both the lateral corticospinal tract and ventral corticospinal tract posterior spinal artery (right and left) primary blood supply to the dorsal sensory columns Artery of Adamkiewicz the largest anterior segmental artery typically arises from left posterior intercostal artery, which branches from the aorta, and supplies the lower two thirds of the spinal cord via the anterior spinal artery significant variation exists in 75% it originates on the left side between the T8 and L1 vertebral segments Cerebral Spinal Fluid Function a colorless fluid that occupies the subarachnoid space surrounding the brain, spinal cord, and ventricular system the subarachnoid space is between the arachnoid mater and pia mater provides mechanical and immunological protection for the brain, spinal cord, and thecal sac Production location most human cerebrospinal fluid (CSF) is produced by the choroid plexus in the third, fourth, and lateral ventricles of the brain. CSF is an ultrafiltrate of blood plasma through the permeable capillaries of the choroid plexus volume total CSF volume between brain, spinal cord, and thecal sac is ~150 mL CSF formation occurs at rate of ~500mL per day thus the total amount of CSF is turned over 3-4 times per day Nerve Root Anatomy Cervical spine nerve roots exit above corresponding pedicle C5 nerve root exits above the C5 pedicle nerve root travel horizontally to exit there is an extra C8 nerve root that does not have a corresponding vertebral body Thoracic spine nerve root travel below corresponding pedicle T1 exits below T1 pedicle T12 exits below T12 pedicle Lumbar spine nerve roots descend vertically before exiting nerve root travel below corresponding pedicle L1 exits below L1 pedicle L5 exits below L5 pedicle intrathecal anatomy exiting (cranial) nerve roots are located more ventrally motor fibers are located more ventrally than sensory fibers