Neuromuscular Junction

Figure 9.10 Synaptic cleft vesicle 1 ACh SR tubules (cut) SR 2 6 3 ADP Pi Net entry of Na+ Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. Removal of Ca2+ by active transport into the SR after the action potential ends. SR Tropomyosin blockage restored, blocking myosin binding sites on actin; contraction ends and muscle fiber relaxes. Ca2+ 1 2 3 4 5 6 Figure 9.10

Figure 9.10 Synaptic cleft vesicle ACh Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Figure 9.10

Figure 9.10 Synaptic cleft vesicle 1 ACh Net entry of Na+ Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma Synaptic cleft vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. 1 Figure 9.10

Figure 9.10 Synaptic cleft vesicle 1 ACh SR tubules (cut) SR Ca2+ 2 Net entry of Na+ Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca2+ release from terminal cisternae of SR into cytosol. SR Ca2+ 1 2 Figure 9.10

Figure 9.10 Synaptic cleft vesicle 1 ACh SR tubules (cut) SR 2 3 Ca2+ Net entry of Na+ Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. SR Ca2+ 1 2 3 Figure 9.10

Figure 9.10 Synaptic cleft vesicle 1 ACh SR tubules (cut) SR 2 3 Ca2+ Net entry of Na+ Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. SR Ca2+ 1 2 3 4 Figure 9.10

Figure 9.10 Synaptic cleft vesicle 1 ACh SR tubules (cut) SR 2 3 Ca2+ Net entry of Na+ Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. Removal of Ca2+ by active transport into the SR after the action potential ends. SR Ca2+ 1 2 3 4 5 Figure 9.10

Figure 9.10 Synaptic cleft vesicle 1 ACh SR tubules (cut) SR 2 6 3 ADP Pi Net entry of Na+ Initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft vesicle Axon terminal ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh receptors on the sarcolemma. Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. Removal of Ca2+ by active transport into the SR after the action potential ends. SR Tropomyosin blockage restored, blocking myosin binding sites on actin; contraction ends and muscle fiber relaxes. Ca2+ 1 2 3 4 5 6 Figure 9.10