Anatomy: Spinal Cord and nn
How many spinal nn are there
31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 fused coccygeal)
Epidural space
Area between bony and ligament outs walls of vertebral canal - where epidural anesthesia is administered during childbirth
What is the cauda equina?
'Horse's tail' - lumbar and sacral nn that have long dorsal and ventral roots and descend to reach their respective intervertebral foramina because the vertebral column grows more rapidly than the cord
GSA/somatosensory fibers
-Come from joints, skin, skeletal muscle into the CNS -cell bodies in the dorsal root ganglia -in cutaneous branches as postganglionic neurons of the sympathetic nn)
Dura mater
-Hard, tough outermost layer Closed sac from foramen magnum to S2 -surrounds nerve roots as they leave dural sac -becomes continuous with epineurum (outer CT sheath)
GVA/Viscerosensory fibers
-from viscera/vessels into the CNS -cell bodies in dorsal root ganglia -not in cutaneous nn
Epidural anesthesia
-larger space (epidural space) -catheter indwelling - additional injections -15-30min to kick in -can be given in cervical, thoracic, or lumbar level
GVE/Visceromotor fibers
-leave CNS and go to glands, smooth m, and cardiac m. (ANS) -2 neuron chain -preganglionic neuron cell body in lateral horn meets with postganglionic neuron -postganglioninc neuron in prevertebral or paravertebral ganglia goes to target organ
GSE/Somatomotor fibers
-leave CNS and innervate skeletal m. -cell bodies in the ventral horn -present in cutaneous n
General features of the spinal cord
-lies in vertebral canal -surrounded by coverings/meninges -length is from foramen magnum to L1 ish -continuous with brain -cervical and lumbar enlargements where more nn reside to supply the limbs
Spinal anesthesia
-smaller space (subarachnoid space) -usually 1 dose -5min onset -given below L2 to avoid spinal cord
Arachnoid mater
-spiders web -delicate membrane inside dura
Pia mater
-tender mother -thin, delicate membrane -intimately connected with surface of spinal cord and nerve roots -extends from conus medullaris to dural sac - 2 continuations: filum terminale and denticulate ligaments
Meninge definition
CT membrane that surrounds the spinal cord, nerve roots, and brain
What is the nervous system?
Central nervous system: brain and spinal cord Peripheral nervous system: 12 pairs of cranial nn, 31 pairs of spinal nn, and the autonomic ns
Denticulate ligaments
Continuation of pia mater that anchors spinal cord to dura mater so it is positioned laterally
Filum terminale
Continuation of pia mater that anchors the spinal cord. Spans from end of conus medullaris to coccyx
Ending of the spinal cord
Conus medullaris
3 meninges
Dura mater, arachnoid mater, and pia mater
Myotome
Group of mm supplied by single ventral root (motor) - more caudal supply distal mm and more rostral supply proximal mm
Gray matter of spinal cord
Nerve cell bodies in a butterfly shape containing a ventral horn, lateral horn (intermediate gray), and dorsal horn
Visceral fibers
Nerve fibers inner sting structures from smooth mm, cardiac m., and glands
Somatic fibers
Nerve fibers that Innervate skeletal mm, bones, joints, skin, and subcutaneous tissue
Peripheral nerve distribution
Nerves supplying the limbs are branches of plexuses and therefore contain nerve fibers from several spinal nn. Peripheral nerves are a bunch of nerves so damage depends on where the branches go to as well
Segmental nerve distribution
One nerve leaves the spinal cord and goes to a specific myotome, dermatome, or scleratome. It doesn't go to multiple places so any issues are more localized
Motor/efferent fiber direction
Out of the CNS
Dermatome
Patch of skin supplied by a single dorsal root and its ganglion (sensory) -trunk has identical dermatomes and peripheral n distributions -Limbs and have different
Nerve distribution in cervical, lumbar, and sacral region
Peripheral nerve distribution
Scleratome
Portion of bones and joints supplied by a single dorsal root and its ganglion (sensory)
Nerve distribution in the thoracic region
Segmental nerve distribution
Subarachnoid space
Space between arachnoid mater and pia mater where cerebrospinal fluid resides so spinal taps/lumbar punctures (detect hemorrhage or meningitis) and spinal anesthesia (L2-S2 - only filum terminale and cauda equina) occur here
Subdural space
Space between dura mater and arachnoid mater
How are the spinal nn organized with their associated vertebrae?
Spinal nerved C1-C7 are exit the vertebral column above their associated vertebrae. C8 exits below C7 and above T1 because there is no 8th cervical vertebrae. After this, each spinal n. Exits the vertebral column below their associated vertebrae.
Sensory/afferent fiber direction
To the CNS