Chapter 13

Chapter 13 - Chapter 13 Spinal control of Movement Somatic...

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Chapter 13 – Spinal control of Movement Somatic Motor System Smooth Muscle o Lines digestive tract, arteries and related structures and is innervated by nerve fibers from the autonomic nervous system o Plays role in peristalsis (movement of materials through intestines) and control of blood pressure and blood flow Striated muscle o Cardiac Heart muscle, contracts rhythmically even in the absence of any innervation Innervation from ANS functions to accelerate or slow down the heart rate o Skeletal Bulk of muscle mass of the body and functions to move bones around joints, to move the eyes within the head, to control respiration , to control facial expression and to produce speech Enclosed in a connective tissue sheath that, at the ends of the muscle, forms the tendons Each muscle contains hundreds of muscle fibers (skeletal muscle cells) and each fiber is innervated by a single axon branch from the CNS Derived embryologically from 33 paired somites, these muscles and part of the nervous system that control them are called the somatic motor system Under voluntary control and generates behavior Lower Motor Neuron Axons of the lower motor neuron bundle together to form ventral roots; each ventral root joins with a dorsal root to form a spinal nerve that exits the cord through the notches between the vertebrae Segmental organization of lower motor neurons o cervical (C) 1-8 cervical enlargement from C3-T1 due to large ventral horns to accommodate the large number of motor neurons that control the arm musculature o Thoracic (T) 1-12 o Lumbar (L) 1-5 L1-S3 swollen ventral horn because that is where motor neurons controlling the leg musculature reside o Sacral (s) 1-5 Alpha motor neurons o Directly trigger the generation of force by muscles o One alpha motor neuron and all the muscle fibers it innervates collectively make up the elementary component of motor control
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Motor unit o Collection of alpha motor neurons that innervates a single muscle called a motor neuron pool o Graded control of muscle contraction by alpha motor neurons First way CNS controls muscle contraction is by varying the firing rate of motor neurons Alpha motor neuron communicates with a muscle fiber by releasing the NT Ach at neuromuscular junction High reliability of neuromuscular transmission, the Ach relased in response to one presynaptic action potential causes an EPSP in the muscle fiber large enough to trigger one postsynaptic action potential o Postsynaptic AP causes a twitch- a rapid sequence of contraction and relaxation- in the muscle fiber Size principle Extra tension provided by the recruitment of an active motor unit depends on how many muscle fibers are in that unit Smaller muscles that control the movement of finger and the rotation of the eyes are characterized by small ratios such as three muscle fibers per alpha motor neuron In general, muscles with a large number of small motor
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This note was uploaded on 04/17/2008 for the course NEURO 101 taught by Professor Mosh. during the Fall '08 term at NYU.

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Chapter 13 - Chapter 13 Spinal control of Movement Somatic...

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