PNS / spinal nerves Flashcards
PNS
12 pairs cranial 31 pairs spinal - 8 C1-C8 - 12 T1-T12 - 5 L1-L5 - 5 S1-S5 - 1 coccygeal
Spinal nerves
- lumbar, sacral, and coccygeal nerve roots descend from their point of origin at the lower end of spinal cord (level of L1)
Cauda equina
Describes the appearance of the lower end of the spinal cord and its spinal nerves as ia horse’s tail
Structure of spinal nerves
- . Each spinal nerve attaches to the spinal cord by a ventral root and a dorsal root
- the dorsal root is easily recognizable by the dorsal root ganglion
- the dorsal root includes sensory fibers that carry information from receptors in peripheral nerves
- the ventral root includes motor neurons that carry information from the CNS and toward effectors (muscles and glands)
- all spinal nerves contain both motor and sensory fibers (mixed nerves)
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Ramus
One of several large branches formed after each spinal nerve emerges from the spinal cavity
- each spinal nerve splits into a distinct ventral ramus and dorsal ramus
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Dorsal ramus
Supplies somatic motor and sensory fibers to several smaller nerves
- these smaller nerves innervate the muscles and skin of the posterior surface f the head, neck, and trunk
- the structure for the ventral ramus is more complex than that of the dorsal ramus
Ventral ramus
Motor (autonomic and somatic) and sensory fibers innervate muscles and glands in the extremities and in the lateral and ventral portions of the neck and trunk
- autonomic motor fibers split from the ventral ramus and head toward a ganglion of the sympathetic chain
Nerve plexus facts
- plexuses are complex networks formed by the ventral rami of most spinal nerves (not T2-T12) subdividing and then joining together to form individual nerves
- each Indy nerve that emerges contains all the fibers that innervate a particular region of the body
- in plexuses, spinal nerve fibers are rearranged according to their ultimate destination, reducing the number of nerves needed to supply each body part
- correspond to spinal cord areas of enlargement
Cervical plexus
- deep within the neck
- ventral rami of C1-C4 (and a branch of C5 ventral ramus)
- innervates: muscles and skin of neck, upper shoulders, chest, and part of head
- phrenic nerve exits cervical plexus and innervates the diaphragm (ventral rami C3, C4, and C5)
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Brachial plexus
- deep in shoulder
- ventral rami of C5-T1
- nerves from the brachial plexus innervate lower part of the shoulder and entire arm
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Lumbar plexus
- deep to psoas muscle
- fibers of ventral rami L1-L4
- femoral nerve exits the lumbar plexus and divides into branches, supplying the thigh and leg
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Sacral and coccygeal plexus
- in peeve cavity, typically anterior to piriformis mm
- intermingling fibers from L4-S4
- tibial and common peroneal/fibular nerves
- sciatic nerve exits the sacral plexus and supplies nearly all the skin of the leg, posterior thigh muscles, leg and foot mm
- often combined with the lumbar plexus and referred to as the lumbosacral plexus