Spinal Cord and PNS

What are the somatic and autonomic nervous system?

• part of the motor division of the PNS

• somatic = voluntary

• autonomic = automatic

What is gray matter in the PNS called?

ganglia

Why are there enlargements in the cervical and lumbar regions of the spinal cord?

arms and legs are very innervated, so more cell bodies are stored in the enlargements

Where does the spinal cord end?

near the L1 vertebrae

What is a lumbar puncture (spinal tap) and why is it performed?

• done below spinal cord to avoid hitting spinal cord

• done to get CSF from the subarachnoid space to look for bacteria

What are the parts of he spinal cord and what does each do?

• dorsal horn - gray matter, interneurons

• ventral horn - gray matter, motor neurons

• ventral root - carries motor neurons away from spinal cord

• dorsal root - carries sensory neurons towards spinal cord

• dorsal root ganglion - contains sensory cell bodies

• spinal nerve - carries both sensory and motor nerves

What are ascending and descending tracts?

• white matter (axons) in the spinal cord traveling to/from the brain

• ascending - info to the brain up spinal columns, decussation occurs in brainstem or spinal cord, 3 neuron circuits from receptor to primary somatosensory cortex (parietal lobe)

• descending - info to motor neurons from CNS, dessucation in brainstem/spinal cord, 2 or 3 neuron circuits from primary motor cortex to muscle

Why don’t spinal cords regenerate very well?

immune system puts fibroblasts, scar tissue, etc. in way of where axons need to grow

Describe the stem cell therapy treatment for spinal cord injuries and why they work

• occur between acute and subacute phase

• after inflammatory response but before scar forms, axons can regenerate before stuff gets in the way, especially if stem cells are injected

Describe electrical stimulators after spinal cord damage and why this can help

• even if axons are cute, many neurons below point of damage still function

• can stimulate nerves despite damage to other parts of the body

What are internal (visceral) and external (somatic) afferent inputs?

• visceral - signals from inside viscera, ex. blood vessel, heart

• somatic - signals associated with skin ex. touch, temperature, pain

What is white matter in the CNS?

nerve, root, ramus

What are rami? Describe the dorsal and ventral ramus

• branch like bundles of motor and sensory nerves after it exits the spinal cord

• dorsal - to back

• ventral - to front of body

Describe the structure of a nerve from deepest to most superficial

• axon surrounded by a myelin sheath (schwann cells)

• endoneurium surrounds individual axons and their myelin sheath

• perineurium surrounds fascicles (bundles of axons)

• epineurium surrounds a whole nerve (bundles of fasicles)

What is a fasicle?

group of axons bundled together

What do the endoneurium, perineurium, and epineurium surround? What kind of tissue are they?

• endonerium surronds an individual axon and its myelin sheath

• perineurium surrounds a fascicle (bundle of axons)

• epineurium surrounds a whole nerve

• connective tissue

Describe cranial nerves

• nerves coming off the brain

• can be only sensory, only motor, or both

• most connect to the brain stem

• most are involved with structures in the head and neck

Describe spinal nerves

• nerves coming off spinal cord

• mixed nerves, both sensory and motor fibers

What are nerve plexuses?

• branching and unbranching of axons (not necessarily synapses)

• branch to get specific nerves at a specific spot to innervate

• nerve roots generally map to parts of the body from superior to inferior