Central Nervous System

Central Nervous - Central Nervous System The Spinal Cord Now that we have looked at how nerve impulses are transmitted at the cellular level lets

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Central Nervous System
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The Spinal Cord Now that we have looked at how nerve impulses are transmitted at the cellular level, lets step back & look at the NS in a larger dimension. Let’s start by looking at the spinal cord, which serves two key functions. 1) It can act as a communication center on its own, receiving input from sensory neurons and directing motor neurons in response, with no input from the brain. 2) Most sensory impulses that go to the brain don’t go directly to the brain; they first go through the spinal cord.
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The Spinal Cord The spinal cord and brain are enclosed in three fibrous connective tissue membranes called meninges . From superficial to deep, they are the dura mater, arachnoid mater, and pia mater. The dura mater forms a loose-fitting sleeve called the dural sheath around the spinal cord. The space between the sheath and vertebral bones, called the epidural space , is occupied by blood vessels, adipose tissue, and loose connective tissue. Anesthetics are sometimes introduced to this space to block pain signals during childbirth or surgery. The arachnoid mater adheres to the dural sheath and apans the gap between the arachnoid membrane and the pia mater. This gap, called the subarachnoid space, is filled with CSF. The pia mater is a delecate, translucent membrane that closely follows the contours of the spinal cord.
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The Spinal Cord The spinal cord, like the brain, consists of two kinds of nervous tissue called gray and white matter. Gray matter has a relatively dull color because it does not contain myelin. It is the site of synaptic contact between neurons, thus it is the “integration center” of the CNS. White matter , by contrast, has a bright, pearly white appearance, which it gets from an abundance of myelin. It is composed of bundles of axons, called tracts , that carry signals from one part of the CNS to another. Grey matter looks somewhat like a butterfly or an H in cross section. The core consists mainly of two dorsal (posterior) horns, and two thicker ventral (anterior) horns. The white matter surrounds the gray matter and consists of bundles of axons which course up and down the cord and provide avenues of communication between different levels of the CNS. These bundles are arranged in three pairs called columns , or funiculi on each side. Each column consists of subdivisions called tracts , or fasciculi.
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Somatic Sensory and Somatic Motor Pathways also know as Ascending and Descending Tracts The nerve tracts of the spinal cord together with the spinal nerves provide a two-way communication system between the brain and body parts outside the N.S. The tracks that conduct sensory impulses to the brain are called ascending tracts : those that conduct motor impulses from the brain to motor neurons reaching muscles and glands are called descending tracts . (These tracts occur on both sides of the cord)
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The axons w/in a given tract originate from neuron cells located in the same part of the N.S. and end
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This note was uploaded on 04/17/2008 for the course BIO 146 taught by Professor Fishback during the Spring '08 term at Ozarks Tech.

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Central Nervous - Central Nervous System The Spinal Cord Now that we have looked at how nerve impulses are transmitted at the cellular level lets

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