Question

Define plexus, and locate the major plexuses of the spinal nerves (pp. 427-428).

A) A plexus is a single spinal nerve, and major plexuses are found throughout the body.
B) A plexus is a network of nerves that serves a specific region of the body, and major plexuses include the cervical, brachial, lumbar, and sacral plexuses.
C) A plexus is a part of the spinal cord, and major plexuses are localized only in the lower back.
D) A plexus is a bundle of sensory nerves, and major plexuses are limited to the head and neck region.

Answer 1

A plexus is a network of nerve fibers, and the major spinal nerve plexuses include the cervical, brachial, lumbar, and sacral plexuses, which innervate various body regions.

Step-by-step explanation:

In the context of spinal nerves, a plexus refers to a complex network of intersecting nerve fibers without associated cell bodies, and these plexuses play a crucial role in distributing nerves to specific regions of the body. The human body has several major plexuses, each serving distinct anatomical areas and functionalities.

The cervical plexus, derived from spinal nerves C1 through C5, forms a network supplying the posterior head, neck, and diaphragm. It plays a vital role in controlling muscles in the neck and diaphragm, contributing to movements involved in breathing and head positioning.

The brachial plexus, originating from spinal nerves C4 through T1, is responsible for innervating the nerves of the arms. This complex network gives rise to nerves that control the muscles and sensation of the shoulder, arm, and hand. It is integral for motor control and sensory feedback in the upper extremities.

The lumbar plexus arises from the lumbar spinal nerves and extends into the pelvic region and anterior leg. It provides innervation to muscles in the pelvic region and anterior thigh, contributing to movements and sensations in this area.

The sacral plexus, formed by the lower lumbar and sacral nerves (S1 to S4), supplies nerves to the posterior leg. It plays a crucial role in controlling muscles in the posterior thigh, leg, and foot, contributing to various motor functions and sensory feedback in the lower extremities.

These plexuses exemplify the efficiency of nerve distribution in the body, allowing for organized control and sensation across diverse anatomical regions. The intricate networks formed by the intersecting nerve fibers in these plexuses ensure the coordination of motor and sensory functions, highlighting their significance in maintaining proper physiological responses and movements throughout the human body.