TopicRevMuscleW11 - NPB101 – W11 Topical Review for Muscle Physiology 1 Know the types of muscle and the functions of each.

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Unformatted text preview: NPB101 – W11 Topical Review for Muscle Physiology 1. Know the types of muscle and the functions of each. Know the structure of skeletal, cardiac and smooth muscle fibers and understand why skeletal and cardiac muscle have a striated appearance and smooth muscle does not. Know the organization of the contractile and regulatory proteins, sarcolemma and transverse tubule system, and the sarcoplasmic reticulum in skeletal muscle. What is a sarcomere and understand why it is the force generating unit within a skeletal and cardiac muscle fiber. 2. Understand the events in neuromuscular transmission. Focus on the neurotransmitter release from the motor neuron and how the neurotransmitter generates the graded, muscle end plate potential. Understand the relationship between a normal end plate potential and the generation of an action potential across the sarcolemma of the muscle cell. Understand the effect of current spread into the transverse tubule and the effect of this current on the dihydropyridine receptor (DHP Receptor) and the Ryanodine Receptor (RyR1) on the lateral sacs of the sarcoplasmic reticulum. Recognize that the initial activation of the RyR1 receptor opens calcium channels in the lateral sacs initiating release of calcium stores. Understand the concept of calcium induced calcium release (CICR) from Ryanodine channels in the lateral sacs after the initial calcium release by activation of the DHP – RyR1 channel. 3. Understand the sequence of steps in cross ­bridge formation and cross ­bridge cycling in skeletal muscle. Understand the role of calcium in unmasking the myosin binding sites of actin and the dual role of ATP in cross ­bridge cycling. 4. Understand the change in the physical relationship between actin and myosin within the sarcomere with cross ­bridge formation and cross ­bridge cycling. Understand how sarcomere shortening can generate tension and move a load (external shortening of the whole muscle fiber or tissue.). 5. Recognize that in skeletal muscle the quantity of calcium released with excitation contraction coupling is sufficient to initially activate all the actin myosin cross ­bridges in a skeletal muscle cell. Therefore, for a single skeletal muscle cell the force of contraction can be altered through changes in the duration of cross ­bridge cycling. The duration of cross ­bridge cycling is a function of the steady ­state sarcoplasmic calcium present during excitation ­ contraction coupling (See frequency or temporal summation and force generation in skeletal muscle.) 6. Terminaton of contraction is through reducing sarcoplasmic calcium to below 10 ­5 through reuptake of the sarcoplasmic calcium into the longitudinal segments of the sarcoplasmic reticulum (recognize that release is from the lateral sacs and reuptake is at a different site, the longitudinal segments of the sarcoplasmic reticulum.). NPB101 – W11 Topical Review for Muscle Physiology 7. Contractile energy is always dissipated in sarcomere shortening. Understand the how dissipation of the contractile energy in sarcomere shortening can generate tension and not shorten the muscle, and, with other conditions it can generate both tension and shorten the whole muscle. 8. What is an isotonic contraction and an isometric contraction. Understand the changes in the sarcomere and whole muscle during an isotonic and an isometric contraction. 9. Understand the mechanical model of the contractile element (actin and myosin) and the series elastic element (Z line proteins and heads of the myosin) in explaining sarcomere shortening and tension development, and sarcomere shortening and shortening the whole muscle and moving a load. You have equal available contractile energy for an isotonic and an isometric contraction. Which contraction will develop greater tension? Why? 10. Understand the graphs relating Magnitude of External Shortening for a whole muscle and Tension developed for an isotonic contraction. Be able to explain why there is, for a given contractile energy, an inverse relationships between isotonic tension developed by the muscle and the magnitude of external, whole muscle shortening. 11. Understand the Length ­Tension Relationship for skeletal muscle. Understand the relative contributions of stretch induced calcium release and the overlap of the actin ­myosin binding sites in explaining the length – tension relationship for skeletal muscle. Recognize that physiologically muscle length does not change significantly (Why?). 12. Understand the Force (Tension) – Velocity of Sarcomere and Whole Muscle Shortening Relationship for skeletal muscle. Be able to identify Vmax and Po. 13. Understand the concept of the Motor Unit. You activate a motor neuron. Can you alter the number of muscle fibers that this motor neuron will stimulate to contract? What is the relationship between the size of the motor unit and increment in tension or force development by the motor unit? Would a small or large motor unit give you more fine control? Consider the parameters that determine generating and action potential in a motor neuron at the spinal cord (amplitude of the EPSP in the cell body) and those for stimulating an axon with a direct electrical stimulus (stimulating electrode). What would you predict would be recruitment sequence for motor units in vivo (through the spinal cord) and with direct stimulating of the axons? 14. The force of contraction of skeletal muscle can be graded through frequency (temporal) summation and through spatial summation (recruitment or more motor neurons and more muscle fibers). NPB101 – W11 Topical Review for Muscle Physiology 15. In skeletal muscle, why does frequency summation generate greater tension than a single activation, a single twitch? With frequency summation, which has the greater influence on tension development; removing the slack in the muscle, recruiting more actin ­myosin cross ­bridges or increasing the duration of cross ­bridge cycling? 16. Consider the concept of Absolute Refractory Period for a cell (nerve or muscle). If the absolute refractory period of a motor neuron were longer than the total duration of contraction of a skeletal muscle fiber, would you be able to have temporal or frequency summation? 17. Understand the molecular organization of smooth muscle. Recognize that increases in sarcoplasmic calcium have a role in skeletal, smooth and cardiac muscle contraction. What is the role of calcium in excitation ­contraction coupling in smooth muscle compared to skeletal muscle? What is the role of Calmodulin, Caldesmon and Calponoin in regulation of actin – myosin interaction in smooth muscle. What are the types of smooth muscle? Is neural input required, like skeletal muscle, for activation of smooth muscle? How does innervation of smooth muscle differ from that of skeletal muscle? Does the concept of motor unit apply to smooth muscle? Why? 18. Excitation ­Contraction Coupling in Cardiac Muscle will be presented with the cardiac lectures. ...
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This note was uploaded on 08/21/2011 for the course NPB 101 taught by Professor Fuller,charles/goldberg,jack during the Winter '08 term at UC Davis.

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