Anatomical Organization of the Nervous System Pt 1

Anatomical Organization of the Nervous System Pt 1 -...

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Anatomical Organization of the Nervous System The nervous system is divided into the central and peripheral nervous systems. The central nervous system consists of the brain and spinal cord. The peripheral nervous system consists of nerves that originate either from the brain or the spinal cord and mainly travel to muscles, skin, glands, and viscera. Nerves originating from the brain are called cranial nerves and those from the spinal cord are termed spinal nerves . Spinal Nerves Let’s start from the periphery and work our way toward the brain. Spinal nerves consist of nerve fibers (axons) that are either sensory (afferent) or are motor (efferent ). Sensory fibers transmit information about cold, heat, pain, pressure, vibration, stretch, ect from a variety of specialized sensory structures in the skin and muscle to the central nervous system. This is sensory information. Spinal nerves also contain nerve fibers that cause muscles to move and glands to secrete; these are called motor or efferent fibers (axons). Motor and sensory fibers are typically wrapped together into a common nerve. Pure sensory or pure motor nerves tend to be rare. As an example, even though a nerve is going to a muscle it also carries sensory information about that muscle back to the central nervous system (CNS). Spinal nerves originate from the spinal cord as dorsal and ventral nerve roots . Dorsal nerve roots predominately carry afferent (sensory) fibers to the spinal cord (CNS) while the ventral roots carry efferent (motor) fibers away from the spinal cord. They merge together near the intervertebral foramen, which is an opening between the bodies of adjacent vertebrae. Once the dorsal and ventral roots merge, they are termed a spinal nerve . The spinal nerve passes through the intervertebral foramen and then splits into dorsal and ventral branches. These branches then go to innervate specific muscles, areas of the skin, or glands.
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Anatomical Organization of Spinal Nerves and the Spinal Cord The spinal cord starts at the caudal portion of the brain, the medulla, and runs caudally through a series of protective bones termed vertebrae . The number of vertebrae varies widely with the specific species. Vertebrae are classified according to the specific region of the body with which they are associated. In mammals, cervical vertebrae are associated with the neck, thoracic vertebrae with the chest and ribs, lumbar vertebrae with the abdomen, sacral vertebrae with the pelvis, and caudal vertebrae with the tail. The nomenclature for birds and fish will be a little different. Humans have 7 cervical (C), 12 thoracic (T), 5 lumbar (L), 5 sacral (S), and 4 caudal (coccygeal) vertebrae (Ca) .
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The spinal cord is divided into spinal segments that correspond to the vertebrae. There are 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and a single coccygeal spinal cord segment in humans. Each spinal cord segment
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This note was uploaded on 04/05/2011 for the course APC 100 taught by Professor Kelliewhited during the Spring '07 term at UC Davis.

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Anatomical Organization of the Nervous System Pt 1 -...

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