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Chapter 49

Chapter 49. A Brief Overview of Sensory & Motor Mechanisms – Focus on Muscle Contraction. Sensory Reception. Sensory receptors are modified neurons or cells that detect stimuli & typically trigger action potentials in neurons.

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Chapter 49

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  1. Chapter 49 A Brief Overview of Sensory & Motor Mechanisms – Focus on Muscle Contraction

  2. Sensory Reception Sensory receptors are modified neurons or cells that detect stimuli & typically trigger action potentials in neurons. The action potentials are propagated until they reach an integration center – located in the CNS. Then, responses can be initiated.

  3. Sensory Reception So, if you put your hand on a hot oven, pain receptors in your skin trigger action potentials and your brain triggers a response – your muscles contract and you remove your hand. You have many types of receptors: those that respond to pressure, touch, sounds, pain, temperature, chemicals, light…

  4. Muscle Structure & Contraction 1.) Our skeletal muscle (the muscle we can control the movement of) is composed of a bundle of muscle cells called fibers. a.) Each fiber is a bundle of myofibrils consisting of myofilaments (protein strands): i.) Thin filaments consisting of the protein actin. ii.) Thick filaments consisting of the protein myosin.

  5. Muscle Structure & Contraction 2.) The regular arrangement of the filaments produces a pattern of bands and repeating units. a.) The repeating units are called sarcomeres – these are the functional contracting units of muscles.

  6. Muscle Structure & Contraction 3.) Structure of sarcomere: a.) The end of each sarcomere is called the Z line. b.) Thin filaments (actin) originate at Z lines and project toward the center. c.) Thick filaments (myosin) lie in the center forming what is called the A band.

  7. Muscle Structure & Contraction d.) There is an area of overlap of thick & thin filaments. The area where thin filaments don’t reach is called the H zone. e.) The area where only thin filaments are is the I band.

  8. Muscle Structure & Contraction 4.) Sliding-filament model of muscle contraction: a.) Thick & thin filaments don’t change in length – they just slide past each other to shorten the sarcomere causing the muscle to shorten = contract. b.) Myosin hydrolyzes ATP, changes shape & binds to actin filament. c.) Myosin then relaxes & pulls the actin filament toward the center of the sarcomere. d.) The cycle repeats for furthering shortening of the filaments.

  9. Muscle Structure & Contraction 5.) Calcium regulates contraction: a.) At rest, the myosin binding sites on actin are blocked by a protein (tropomyosin). b.) When an action potential in a neuron reaches the synapse b/w a neuron & a muscle cell (called the neuromuscular junction), the NT acetylcholine is released.

  10. Muscle Structure & Contraction c.) This causes Ca to be released from the sarcoplasmic reticulum (an organelle in the muscle cell). d.) Ca binds to tropomyosin, changes its shape & exposes the actin so that myosin can bind and shorten the sarcomere = contraction. Check out the following animations: http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter42/animations.html# http://www.wisc-online.com/objects/index_tj.asp?objID=AP2904

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