Nervous System Overview Nervous system central nervous system brain spinal cord login to view 1 more bullet peripheral nervous system cranial nerves peripheral nerves autonomic nervous system sympathetic system login to view 5 more bullets parasympathetic nervous system login to view 2 more bullets Spinal Cord Overview Spinal cord extends from the brainstem to the inferior border of L1 conus medullaris termination of the spinal cord filum terminale residual fragment of spinal cord that extends from the conus medullaris to the sacrum thecal sac dura-surrounded sac that extends from the spinal cord and contains cerebrospinal fluid, nerve roots, and the cauda equina cauda equina nerve roots and filum terminale that extend from the spinal cord and are surrounded by dura Embryology of the spinal cord Neural tube becomes the spinal cord formed from the primitive streak → turns into the primitive (midsagittal) groove → turns into the neural tube failure of neural tube closure leads to: anencephaly if it fails to close cranially spina bifida occulta, meningocele, or myelomeningocele if it fails to close distally Neural crest forms dorsal to the neural tube becomes: peripheral nervous system pia mater spinal ganglia sympathetic trunk Notochord forms ventral to the neural tube becomes: vertebral bodies intervertebral discs login to view 2 more bullets Layers of the spinal cord Layers of the spinal cord include: dura mater (outermost) arachnoid pia mater (innermost) Spinal Cord Functional Tracts Ascending tracts (sensory) dorsal columns (posterior funiculi) deep touch, proprioception, vibration 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 to the anterior 2/3 of spinal cord, including both the lateral corticospinal tract and ventral corticospinal tract posterior spinal arteries (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 login to view 1 more bullet Cerebrospinal Fluid (CSF) 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 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 ~500 mL per day login to view 1 more bullet Nerve Root Anatomy Cervical spine nerve roots exit above the corresponding pedicle C5 nerve root exits above the C5 pedicle nerve roots travel horizontally to exit there is an extra C8 nerve root does not have a corresponding vertebral body Thoracic spine nerve roots travel below the corresponding pedicle T1 exits below T1 pedicle T12 exits below T12 pedicle Lumbar spine nerve roots descend vertically before exiting nerve roots travel below the 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