Chapter 13 - The Peripheral Nervous System and Reflex Activity - Review Questions - Page 522: 20a

Plexus. A nerve plexus is a network of interconnecting branches of rami of spinal nerves. There are four major nerve plexuses: the cervical plexus, the brachial plexus, the lumbar plexus and the lumbar plexus. 1. Cervical plexus; Composition: ventral rami of C1-C4)5 2. Brachial plexus Composition : ventral rami of C5-T1) + upper half T2 3. Lumbar Plexus:; Composition : ventral rami of L1-L4 4. Sacral plexus Composition;: ventral roots of L4-S4 Cervical plexus. Spinal nerves involved: C1-C4(C5) Composition : ventral rami of C1-C5 Location: deep in the neck under the sternocleidomastoid muscle Areas served: Sensory branches to skin of neck, ear area back of head and shoulder motor nerves to muscles of anterior neck; the phrenic nerve (C3-C4) provides sensory and motor supply to the daipragm which is the chief muscle of respiration. Brachial Plexus: Spinal nerves involved: C5-T1( +lower half of T2) Composition: Ventral rami of C5-T1 and lower half of T2 Location : under armpit Service area: chest, shoulder, arms and hands Lumbar Plexus Spinal nerves involved: L1-L5( and parts of T12) Composition: ventral rami of L1-L5 Location: within psoas major muscle Service area: abdominal wall muscles, psoas muscle,muscles of anterior and medial thigh, skin of thigh and medial surface of leg from thigh to foot Sacral Plexus Spinal nerves involved: L4-S4 Composition: ventral rami of L4-S4 Location: posterior wall of pelvic cavity Area served: pelvis, buttocks, genitals, thighs, calves , feet.

A spinal nerve plexus is a network of nerve fibers that derive from the ventral rami of spinal nerves. The ventral rami include both sensory and motor fibers, so both afferent and efferent nerve supplies derive from spinal nerve plexuses Cervical plexus. Spinal nerves involved: C1-C4(C5) Composition : Ventral rami of C1-C5 ( +some contributions from C5) Location: Deep in the neck under the sternocleidomastoid muscle Areas served: Sensory branches to skin of neck, ear area, back of head and shoulder; motor nerves to muscles of anterior neck; The phrenic nerve (C3-C4) provides sensory and motor supply to the diaphragm which is the chief muscle of respiration (ventilation). Brachial Plexus: Spinal nerves involved: C5-T1( +lower half of T2) Composition: Ventral rami of C5-T1 and lower half of T2 Location : Under armpit Area served: Chest, shoulder, arms and hands Lumbar Plexus Spinal nerves involved: L1-L5( and parts of T12) Composition: Ventral rami of L1-L5 Location: Within psoas major muscle Area served: Abdominal wall muscles, psoas muscle,muscles of anterior and medial thigh, skin of thigh and medial surface of leg from thigh to foot Sacral Plexus Spinal nerves involved: L4-S4 Composition: Ventral rami of L4-S4 Location: Posterior wall of pelvic cavity Area served: Pelvis, buttocks, genitals, thighs, calves , feet. Note: Each spinal nerve has a dorsal and a ventral root. A ventral ramus is a branch of a ventral root. Each ventral ramus carries both sensory and motor fibers.