ch14saladinIM - Chapter14: ChapterOverview The nervous...

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Chapter 14: The Spinal Cord and Spinal Nerves Chapter Overview The nervous system integrates functions of the body through its ability to receive, process, and send information. Chapter 13 focused on how this is accomplished at the cellular level by neurons. Chapter 14 focuses on a different structural level, organs, with emphasis on the spinal cord and spinal nerves. The spinal cord, part of the central nervous system, is the information highway between the brain and trunk and limbs. Spinal nerves are part of the peripheral nervous system. Spinal cord injuries result from a variety of accidents and can have a dramatic impact on quality of life. Thus, spinal cord structure and function is a focus of lively research. The Spinal Cord The spinal cord has three main functions. 1. Conduction Bundles of nerve fibers conduct information up and down, connecting different levels of the cord with each other and with the brain. 2. Locomotion Walking requires coordinated contractions of several muscle groups in the limbs. Groups of neurons in the cord serve as central pattern generators. They produce a sequence of outputs to the lower limb muscles, resulting in the alternating movement of limbs that does not require input from the brain. 3. Reflexes The cord is responsible for certain involuntary, stereotyped responses to stimuli. Surface Anatomy The spinal cord begins at the foramen magnum and passes through the vertebral canal to the inferior margin of L1. It gives rise to 31 pairs of spinal nerves. A deep groove, the ventral median fissure, runs anteriorly along the length of the cord, whereas the dorsal median sulcus runs posteriorly. The spinal cord is divided into cervical, thoracic, lumbar and sacral regions, named for the level of the vertebral column from which the spinal nerves emerge. It widens at two points: 1) the cervical enlargement where the nerves for the upper limb arise, and 2) the lumbar enlargement which gives rise to nerves that supply the pelvic region and lower limbs. At its inferior end, the cord tapers to a point called the medullary cone. From here, a bundle of nerve roots called the cauda equina (horse’s tail) occupies the vertebral column from L2 to L5. Meninges of the Spinal Cord The brain and spinal cord are enclosed in connective tissue membranes called meninges. The dura mater (literally, “tough mother”) is the most superficial. Its durable texture provides a protective sheath around the vulnerable nervous tissue. The space between the dura mater and the bone is the epidural space, occupied by blood vessels, adipose tissue, and loose connective tissue. It is the site for epidural anesthesia. 92
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The arachnoid mater is a spider web-like structure that adheres to the dural sheath. It consists of an arachnoid membrane composed of simple squamous epithelial tissue and
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This note was uploaded on 02/09/2012 for the course BIO 102 taught by Professor William during the Spring '11 term at Harvard.

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ch14saladinIM - Chapter14: ChapterOverview The nervous...

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