Study Guide Week 7

Study Guide Week 7 - TA: Victoria Ha Email: viha@ucsd.edu...

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TA: Victoria Ha Section: (B03) Monday 5:00-5:50 Email: viha@ucsd.edu Office Hours: Thursday Hi Thai 2-3 Disclaimer: These notes are intended for you to supplement your studies. They are by no means a substitute for going to lecture!! Pages 1108 – 1110, 898 – 909 in textbook 8 th Edition Study Guide 7 Muscle contracts with increase of Ca2+, but where does the Ca2+ come from? Action potential reaches the synaptic terminal and releases NTs at the neuromuscular junction onto the muscle of the motor end plate The motor end plate contains ACh receptors, which are nicotinic receptors. The NTs open the nicotinic ACh receptors and allows Na+ into the cell depolarization. There are enough receptors on the motor end plate to allow the graded potential to reach threshold, which causes depolarization The T-tubules contain Na+/K+ channels and goes towards the middle of the muscle fibers As an action potential travels down the T-tubules, there are Ca2+ channels on the sarcoplasmic reticulum that are activated The Ca2+ enter the cytosol of the muscle fiber, which binds to troponin, moves tropomyosin out of the way revealing the myosin binding site, and then the myosin is now allowed to bind to actin What allows relaxation? The increase in Ca2+ in the cytosol stimulates the Ca2+ pumps to remove the Ca2+ from the cytosol back into the sarcoplasmic reticulum. The Ca2+ pump also acts like the Na+/K+ pump, keeping the membrane potential by keeping the concentration of Ca2+ low in the cytosol and high in the SR Increase in ACh open nicotinic ACh recpetors Na+ enters action potential t-tubule Ca2+ released from SR muscle contraction Ca2+ pumping relaxation
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TA: Victoria Ha Section: (B03) Monday 5:00-5:50 Email: viha@ucsd.edu Office Hours: Thursday Hi Thai 2-3 Motor unit: the functional unit of a skeletal muscle (organ) composed of a voluntary motor neuron and the one or more skeletal muscle fibers which it innervates
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TA: Victoria Ha Section: (B03) Monday 5:00-5:50 Email: viha@ucsd.edu Office Hours: Thursday Hi Thai 2-3 Muscles with large ratio motor units (1 neuron : many muscle fibers) can provide powerful muscle contractions but not for delicate, fine, precise movements (legs/arms) Muscles with small ratio motor units (1 neuron: 1 muscle fiber) cannot give powerful contractions but proves delicate fine movements for precise movements (fingers) Muscle twitch: the response of a skeletal muscle to a single stimulation (or action potential) Why do some muscles don’t get fatigued? Such as when holding a pencil or standing up or keeping your head up? It is not used at the maximum potential and some motor units innervating the same muscles take turn in stimulating it (highly simplified)
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TA: Victoria Ha Section: (B03) Monday 5:00-5:50 Email: viha@ucsd.edu Office Hours: Thursday Hi Thai 2-3 Summation: the degree of contraction of a skeletal muscle is influenced by the number of motor units being stimulated (with a motor unit being a motor neuron plus all of the
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Study Guide Week 7 - TA: Victoria Ha Email: viha@ucsd.edu...

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