Styles To help you put together the two parts of the muscle lecture, answer the

Question

Styles To help you put together the two parts of the muscle lecture, answer the questions, then re- order the list of steps into the correct order, starting with the AP in the motor neuron (the step with an asterisk at the start). Resting conditions The muscle cell is at the Vn which is approximately-90 mV. o (high or low). o Caaoic (the concentration of Ca* inside the cell) is very o Troponin and tropomyosin lie in the o Myosin heads are bound to , and and are NOT in contact with actin because Steps of excitation/contraction coupling (ACh - acetylcholine) ACh binds to receptor channels in the motor end plate, opening the nonspecific cation . channels ACh-containing vesicles fuse to the presynaptic membrane and release ACh into the . neuromuscular junction (synaptic cleft) .Action potential arrives at the axon terminal of the motor neuron. . Action potential in the T tubules triggers release of Ca? from the sarcoplasmic reticulum . Action potential moves across the surface membrane of the muscle cell and into the muscle fiber's interior through the T tubules . ADP released after the power stroke because of conformational change in myosin head . Ca2. binds to troponin .Ca enters the terminal button and binds to vesicles that contain ACh · Ca . falls off of troponin, troponin and tropomyosin return to asin groove [Ca Ionais falls as Ca+ is returned to sarcoplasmic reticulum (or moved out of the cell) . Formation of the end-plate potential leads to an action potential in the muscle fiber causing many voltage-gated Nat channels to open Myosin is energized by splitting ATP into ADP and Pi(following a contraction - do not list this at the beginning) Myosin (while linked to actin) binds ATP .Myosin-ADP-P binds to myosin-binding site on actin . Myosin-binding sites on actin are revealecd Na' enters the muscle cell through the open. ACh-gated channels in the motor end plate, causing an end-plate potential (graded depolarization) P, is released during the power stroke because of conformational change in myosin head Power stroke of cross bridge is triggered by myosin-actin contact . Presence of ATP (lots of negative chargesl) in myosin head forces conformational change, resulting in detachment from actin Troponin-Ca changes conformation and pulls tropomyosin out of the actin groove Voltage-gated Ca channels in the terminal button (presynaptic neuron) open

Explanation / Answer

Fill in the blanks:

1. resting membrane potential

2. low

3. actin groove

4. ADP and Pi, the myosin binding site in actin is covered by tropomyosin

Correct order of steps:

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