Chap13_2401 - 1 THE SPINAL CORD AND SPINAL NERVES Chapter...

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1 THE SPINAL CORD AND SPINAL NERVES Chapter 13 Anatomy and Physiology Lecture
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2 THE SPINAL CORD AND THE SPINAL NERVES Spinal Cord and Spinal Nerves form a neuronal circuits that mediate some of your quickest reactions to environment changes . (For example, if you pick up something hot, the grasping muscle may reflex and you may drop it even before the sensation of extreme heat or pain reaches your conscious perception.) -A Spinal Cord Reflex - a quick, automatic response to certain kinds of stimuli that needs only neuron (nerve cells) in the spinal nerves and spinal cord. Overall Functions of the Spinal Cord : (i) The site for integration (summing) of nerve impulses that arise locally or arrive from the periphery and brain; (ii) The highway traveled by sensory nerve impulses headed for the brain and motor nerve impulses destined for spinal nerves. (iii) It is the communication link between the brain and the PNS inferior to the head. (iv) It integrates incoming information and produces responses through reflex mechanism. *Spinal cord is continuous with the brain. (Spinal cord + Brain => Central Nervous System (CNS))
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3 GENERAL STRUCTURE External Anatomy of The Spinal Cord Roughly cylindrical , but flattened slightly in its anterior posterior dimension. (Looks like a cylinder, but slightly flat in its anterior-posterior dimension) *Extends from the Foramen magnum to the upper border of the second lumbar vertebra (adults). *Extends to the third or fourth lumbar vertebra (newborn infant). (Since the vertebral column continues to elongate, the spinal cord does not extend the entire length of the vertebrae column.) (Elongation of the spinal cord stops at age 4 or 5 ) *Adult spinal cord ranges from 42 to 45 cm (16 to 18 inches) Two Conspicuous Enlargements seen on Spinal Cord - viewed externally 1. Cervical Enlargement (superior enlargement) - Extends from the fourth cervical to the first thoracic vertebra. -Nerves from and to the upper extremities arise from here. 2. Lumbar Enlargement (Inferior) - Extends from the ninth to the twelfth thoracic vertebra. -Nerves to and from the lower extremities arise from there.
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4 Below the Lumbar Enlargement (a) Conus medullaris - the tapered portion of the spinal cord below the lumbar enlargement. -Ends at the level of the intervertebral disc between the first and second lumbar vertebrae in an adult. (b) Filum Terminale - arises from the conus medullaris; An extension of the pia mater that extends inferiorly and attaches the spinal cord to the coccyx. A nonnervous fibrous tissue of the spinal cord. (c) Cauda Equina (horse's tail) - a taillike collection of roots of spinal nerves at the inferior and of the spinal cord. Some nerves that arise from the lower part of the cord do not leave the vertebral column at the same level as they exit from the spinal cord. Although the spinal cord is not actually segmented, it appears that way due
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Chap13_2401 - 1 THE SPINAL CORD AND SPINAL NERVES Chapter...

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