Please break down and clarify. 1."The spinal cord is about 17 to 18 inches long. It lies inside the spinal column and extends from the occipital bone down to the bottom of the first lumbar vertebra. The H-shaped core of the spinal cord consists of gray matter and is composed mainly of dendrites and cell bodies of neurons. Columns of white matter form the outer portion of the cord and bundles of myelinated nerve fibers, called spinal tracts, make up the white columns. The spinal cord functions as the primary reflex center of the body." 2. "Thirty-one nerve pairs are generated from the spinal cord. Eight pairs are attached to the cervical section, twelve pairs are attached to the thoracic section, five pairs are attached to the lumbar section, five pairs are attached to the sacrospinal section, and one pair is attached to the coccygeal section. Spinal nerves have no special name, but rather a letter and number identify each; for example, C1 indicates the pair of nerves from the first segment of the cervical part of the cord. A plexus is a network of intersecting or braided branches from several spinal nerves." 3. The structure of the sympathetic nervous system begins with the sympathetic preganglionic neurons. They have dendrites and cell bodies in the gray matter of the thoracic and upper lumber segments of the spinal cord. The axon leaves the spinal cord in the anterior root of a spinal nerve. It enters the spinal nerve but soon leaves it to extend to and through a sympathetic ganglion and terminate in a collateral ganglion. It synapses with several postganglionic neurons whose axons extend to terminate in the visceral effectors. The preganglionic neurons use acetylcholine as their neurotransmitter and the postganglionic neurons use epinephrine. The function of the sympathetic nervous system is to prepare the body for emergency situations, the "fight-or-flight" response. It causes the heart to beat faster and blood vessels to constrict, increases blood pressure, dilates blood vessels to skeletal muscles, and increases secretion of sweat glands and adrenal glands.
Please break down and clarify.
1."The spinal cord is about 17 to 18 inches long. It lies inside the spinal column and extends from the occipital bone down to the bottom of the first lumbar vertebra. The H-shaped core of the spinal cord consists of gray matter and is composed mainly of dendrites and cell bodies of neurons. Columns of white matter form the outer portion of the cord and bundles of myelinated nerve fibers, called spinal tracts, make up the white columns. The spinal cord functions as the primary reflex center of the body."
2. "Thirty-one nerve pairs are generated from the spinal cord. Eight pairs are attached to the cervical section, twelve pairs are attached to the thoracic section, five pairs are attached to the lumbar section, five pairs are attached to the sacrospinal section, and one pair is attached to the coccygeal section. Spinal nerves have no special name, but rather a letter and number identify each; for example, C1 indicates the pair of nerves from the first segment of the cervical part of the cord. A plexus is a network of intersecting or braided branches from several spinal nerves."
The human nervous system has an ectodermal origin. Out of three germ layers of a developing embryo, the mesoderm provides an inductive signal to the ectoderm in order to develop the entire nervous system at around 3rd week of gestation period. The nervous system constitutes a central nervous system (made up of the brain and the spinal cord) and a peripheral nervous system (made up of all the nerve fibres that branch off from the spinal cord). The nervous system maintains constant communication between the brain and the rest of the body parts.
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