Lumbosacral Plexuses

The lumbosacral (lum"bo-sa'kral) plexuses are formed by the last thoracic nerve and the lumbar, sacral, and coc-cygeal nerves. These networks of nerve fibers extend from the lumbar region of the back into the pelvic cavity, giving rise to a number of motor and sensory fibers associated with the lower abdominal wall, external genitalia, buttocks, thighs, legs, and feet. The major branches of these plexuses include the following (fig. 11.35):

1. The obturator nerves supply the adductor muscles of the thighs.

2. The femoral nerves divide into many branches, supplying motor impulses to muscles of the thighs and legs and receiving sensory impulses from the skin of the thighs and legs.

3. The sciatic nerves are the largest and longest nerves in the body. They pass downward into the buttocks and descend into the thighs, where they divide into tibial and common peroneal nerves. The many branches of these nerves supply muscles and skin in the thighs, legs, and feet.

Other nerves associated with the lumbosacral plexus that innervate various skeletal muscles include the following:

1. The pudendal nerve supplies the muscles of the perineum.

2. The inferior and superior gluteal nerves supply the gluteal muscles and the tensor fasciae latae muscle.

The anterior branches of the thoracic spinal nerves do not enter a plexus. Instead, they travel into spaces between the ribs and become intercostal (in"ter-kos'tal) nerves. These nerves supply motor impulses to the intercostal muscles and the upper abdominal wall muscles. They also receive sensory impulses from the skin of the thorax and abdomen. Clinical Application 11.7 discusses injuries to the spinal nerves.

99 How are spinal nerves grouped?

^9 Describe how a spinal nerve joins the spinal cord.

^9 Name and locate the major nerve plexuses.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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