Styles To help you put together the two parts of the muscle lecture, answer the
ID: 132486 • Letter: S
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 o The muscle cell is at theVn which is approximately-90 mv oCa oa(the concentration of Ca? inside the cell) is very o Troponin and tropomyosin lie in the o Myosin heads are bound (high or low). toand and are NOT in contact with actin because Steps of excitation/contraction coupline (ACh -acetylcholine) .ACh binds to receptor channels in the motor end plate, opening the nonspecific cation channels g 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 . Ca 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 actin groove Ca aclis 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 Na" 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 revealed .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 charges!) 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) openExplanation / Answer
Answer-1: Resting state
Answer-2 : Low
Answer-3: Actin filament
Answer-4: ADP and Pi ; because at low calcium concentration, no conformational change in troponin occurs and as a result, tropomyosin does not exposes the myosin binding site on actin.