Muscle and Muscle Tissue Lecture Outline 2015

Binding of acetylcholine to receptors on the

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binds to receptor proteins in the sarcolemma. Binding of acetylcholine to receptors on the sarcolemma transmits the signal from the nerve to the muscle cells, and results in excitation of the muscle cell. Excitation-Contraction Coupling: Excitation of the skeletal muscle fiber by a motor neuron is coupled to the contraction of the myofilaments in the muscle fiber. Relaxation After the impulse is over, the sarcoplasmic reticulum actively pumps calcium back into its sacs. As calcium is removed from the tropinin, tropomyosin returns to its position, blocking actin’s active sites. Mysosin can’t bind with actin. Since the thin and thick filaments are no longer connected, the muscle fiber returns to its resting length. 2015 3
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Energy Sources for Muscle Contraction: ATP: before contraction occurs, each myosin cross bridge moves to a resting position where an ATP molecule binds to it. The energy transferred from ATP is used to do the work of pulling the thin filaments during contraction Glucose: important energy source, often stored in skeletal muscle as the polymer glycogen Oxygen: needed for catabolism of glucose. Myoglobin is a protein in muscle that binds oxygen. It gives muscle fibers a red color. Muscle fibers use aerobic respiration when oxygen is available, and anaerobic respiration when oxygen is low. Use of anaerobic respiration results in lactic acid build up. The lactic acid eventually diffuses out of the fibers, into blood and is sent to the liver where it is converted back to glucose. Heat Production: Some of the energy released during catabolism of glucose is lost as heat. We can use this heat production to our advantage when we are cold (shivering) All-or-None principle of muscle fiber contraction : When muscle fibers are sufficiently stimulated they contract with all possible force under existing conditions. Each muscle fiber contracts maximally when stimulated and then quickly returns to the relaxed state. The minimal stimulation required to cause a fiber to contract is called the threshold stimulation. Muscle Contractions Twitch single contraction event Skeletal Muscle Response to Change in Stimulus Frequency Wave Summation Tetanus Treppe: multiple contractions increasing in muscle tension with each contraction Fatigue: decrease in muscle tension after multiple contractions Muscle Tone: A tonic contraction is a continual, partial contraction in a muscle organ This is the low level of continuous contraction characteristic of the muscles of healthy individuals when they are awake
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  • Fall '15
  • Dr.Drouin
  • muscle tension

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