Download ANPS 019 Beneyto-Santonja 10-29

ANPS 019 Beneyto-Santonja 10/29/12
Spinal Cord and Spinal Nerves
Spinal Cord Circuitry
1. Peripheral receptors bring in sensory information from body to spinal cord – somatic
from skin/muscle, visceral from organs
2. Sensory neuron enters dorsal part of spinal cord to synapse on gray matter neuron
3. Information integration by interneurons (not required for reflexes)
4. Motor neurons exit ventral part of spinal cord
5. Effector (muscle, gland) responds
Anatomy of the Spinal Cord
 Ventral root: motor/efferent axons
 Dorsal root: sensory/afferent axons
 Dorsal root ganglion: Cell body of afferent
 Spinal nerve = Sensory + Motor Axons (& autonomic in same)
 Spinal nerves leave the spinal cord in small spaces between the vertebrae
 Gray Matter: area containing neuron, cell bodies, dendrites, synapses
o Consists of columns of cells
 White matter: myelinated axon tracts: ascending sensory info; descending motor info
o Has ascending tracts carrying sensory info to the cortex and descending tracts
carrying motor info from the cortex.
 The spinal cord does not look exactly alike at all levels:
o More gray matter in cervical and lumbar enlargements because more motor
neurons to innervate arm & leg
o More white matter at the cervical level because of all motor axons descending
and all sensory axons ascending
Why Position Matters:
 Partial crushing of the vertebral column leads to compression of the spinal cord, but
symptoms will vary depending on which part of spinal cord is injured.
Composition of a Peripheral Nerve
 Nerves contain both sensory and motor axons and both somatic and autonomic fibers
Connective Tissue Components of a Peripheral Nerve
 Epineurium: Out layer
 Perineurium: middle layer; divides nerve into fascicles (axon bundles)
 Endoneurium: inner layer; surrounds individual axons
Spinal Cord Segments
 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
 Cervical Enlargment upper extremity
 Lumbar Enlargement  lower extremity
 Spinal segments do not coincide with vertebral level
o Spinal cord ends at L1 vertebra as the conus medullaris
o The spinal nerves below this level form the cauda equina “horse’s tail”
o The conus medullaris is anchored to dura via the filum terminale
Dermatome
 A topographic map of the body
 Region of skin innervated by the fibers of 1 spinal nerve
o Arm = cervical
o Leg = lumbar
Lumbar Puncture to Obtain CSF

The cauda equina is located in a sac (dura) filled with fluid (CSF). Since there is no
spinal cord, CSF can be drawn from here.
Some peripheral nerves (e.g., sciatic nerve) are formed from the union of branches of several
spinal nerves.
Nerve Plexuses
 Complex, interwoven networks of nerve fibers
 Formed from blended fibers of adjacent spinal neres
 Four major plexuses:
o Cervical; Brachial; Lumbar; Sacral
o Lumbar + Sacral are often combined as Lumbosacral
 Cervical Plexus  Innervates neck, thoracic cavity, diaphragm muscles
 Brachial Plexus  innervated pectoral girdle and upper limbs
 Lumbar and Sacral Plexuses  Innervate pelvic girdle and lower limbs
