Muscular System Summary

Muscular System Summary - BMED 3100: Systems Physiology...

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BMED 3100: Systems Physiology Muscular System-Summary Major functions: 1) generate motion, force 2) control of organ & blood vessel size 3) stabilize body position 4) thermogenesis Muscles only act by contraction Three major muscle types (differ in anatomy, speed of contraction, electrical properties): 1) skeletal 2) cardiac 3) smooth Skeletal Muscle Cardiac Muscle Smooth Muscle Striated; actin and myosin arranged in sarcomeres Striated; actin and myosin arranged in sarcomeres Not striated; more actin than myosin; actin inserts into dense bodies and cell membrane Well-developed sarcoplasmic reticulum and transverse tubules Moderately developed sarcoplasmic reticulum and transverse reticulum Poorly developed sarcoplasmic reticulum and transverse tubules Contains troponin in thin filaments Contains troponin in thin filaments Contains calmodulin, a protein that, when bound to Ca ++ , activates the enzyme myosin light-chain kinase Ca ++ released into cytoplasm from sarcoplasmic reticulum Ca ++ enters sarcoplasm from sarcoplasmic reticulum and extracellular fluid Ca ++ enters sarcoplasm from extracellular fluid, sarcoplasmic reticulum, and perhaps mitochondria Cannot contract without nerve stimulation; denervation results in muscle atrophy Can contract without nerve stimulation; action potentials originate in pacemaker cells of heart Maintains tone in absence of nerve stimulation; visceral smooth muscle produces pacemaker potentials; denervation results in hypersensitivity to stimulation Muscle fibers stimulated independently; no gap junctions Gap junctions present as intercalated discs Gap junctions generally present
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BMED 3100: Systems Physiology Skeletal muscle 1. Skeletal muscle position skeleton 2. Attach to bone with collagenous tendon 3. Origin – muscle end attached closest to trunk or more stationary bone 4. Insertion – more distal or more mobile end Actions : 1. flexor – muscle that brings connected bones closer together upon contraction; decreases angle of joint 2. extensor – muscle that moves connected bones away from each other upon contraction; increases angle of a joint 3. abductor – moves limb away from the midline of the body 4. adductor – move limb toward the midline of the body 5. levator – moves insertion upward 6. depressor – moves insertion downward 7. rotator – rotates a bone along its axis 8. sphincter – constricts an opening 9. Antagonistic muscle groups – flexor/extensor pairs Somatic motor pathway consists of one neuron 1. Cell bodies in gray matter of brain, spinal cord; long single axon-skeletal target tissue a. myelinated axons, up to 1 m 2. Axons branch close to targets-branches divide further into boutons (axon terminals) a. boutons lie on surface of muscle cell b. single motor neuron controls many muscle fibers at once
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Muscular System Summary - BMED 3100: Systems Physiology...

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