Neuron Function The Membrane Potential – Resting potential Excess negative charge inside the neuron Created and maintained by Na-K ion pump Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Neuron Function Changes in Membrane Potential – Result from changes in ion movement – Ions move in transmembrane channels – Membrane channels can open or close – If Na + channels open  positive charges enter cell  membrane potential moves positive (depolarization) – If K + channels open  positive charges leave cell  membrane potential moves negative (hyperpolarization) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Neuron Function Generation of Action Potential – Depolarization of membrane to threshold – Rapid opening of voltage-gated Na + channels – Na + entry causes rapid depolarization – Voltage-gated K + channels open – K + exit causes rapid repolarization – Refractory period ends as membrane recovers the resting state Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure of _ 70 _ Transmembrane potential (mV) Threshold Resting potential REFRACTORY PERIOD DEPOLARIZATIONREPOLARIZATION Local current Depolarization to threshold Sodium ions Activation of voltage- regulated sodium channels and rapid depolarization Potassium ions Inactivation of sodium channels and activation of voltage-regulated potassium channels The return to normal permeability and resting state Time (msec) 0123

Control of Muscle Contraction The Neuromuscular Junction – Synaptic terminal Acetylcholine release – Synaptic cleft – Motor end plate Acetylcholine receptors Acetylcholine binding Acetylcholinesterase – Acetylcholine removal Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure 7-4(b-c) 2 of 5 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Synaptic cleft Arrival of an action potential at the synaptic terminal Sarcolemma of motor end plate Arriving action potential Vesicles ACh AChE molecules ACh receptor site Action potential Synaptic terminal Axon Sarcolemma Muscle fiber

Figure 7-4(b-c) 3 of 5 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Synaptic cleft Vesicles in the synaptic terminal fuse with the neuronal membrane and dump their contents into the synaptic cleft. Release of acetylcholine Arrival of an action potential at the synaptic terminal Sarcolemma of motor end plate Arriving action potential Vesicles ACh AChE molecules ACh receptor site Action potential Synaptic terminal Axon Sarcolemma Muscle fiber

Figure 7-4(b-c) 4 of 5 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Synaptic cleft Vesicles in the synaptic terminal fuse with the neuronal membrane and dump their contents into the synaptic cleft. The binding of ACh to the receptors increases the membrane permeability to sodium ions. Sodium ions then rush into the cell. ACh binding at the motor and plate Release of acetylcholine Arrival of an action potential at the synaptic terminal Sarcolemma of motor end plate Arriving action potential Vesicles ACh AChE molecules ACh receptor site Action potential Synaptic terminal Axon Sarcolemma Muscle fiber Na +

Figure 7-4(b-c) 5 of 5 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Synaptic cleft Vesicles in the synaptic terminal fuse with the neuronal membrane and dump their contents into the synaptic cleft. The binding of ACh to the receptors increases the membrane permeability to sodium ions. Sodium ions then rush into the cell. An action potential spreads across the surface of the sarcolemma. While this occurs, AChE removes the ACh. Appearance of an action potential in the sarcolemma ACh binding at the motor and plate Release of acetylcholine Arrival of an action potential at the synaptic terminal Sarcolemma of motor end plate Arriving action potential Vesicles ACh AChE molecules ACh receptor site Action potential Synaptic terminal Axon Sarcolemma Muscle fiber Action potential Na +

Anatomy of Skeletal Muscles The Contraction Process – Actin active sites and myosin cross-bridges interact – Thin filaments slide past thick filaments Cross-bridges undergo a cycle of movement – Attach, pivot, detach, return – Troponin-tropomyosin control interaction Prevent interaction at rest Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure of 7 Resting sarcomere Myosin head Troponin Actin Tropomyosin ADP P + P +

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure of 7 Resting sarcomere Myosin head Active-site exposure Troponin Actin Tropomyosin ADP P + P + P + Active site Sarcoplasm Ca 2+ ADP P +

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure of 7 Resting sarcomere Myosin head Active-site exposure Cross-bridge formation Troponin Actin Tropomyosin ADP P + P + P + Active site Sarcoplasm Ca 2+ ADP P + + P Ca 2+ ADP + P Ca 2+

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure of 7 Resting sarcomere Myosin head Active-site exposure Cross-bridge formation Pivoting of myosin head Troponin Actin Tropomyosin ADP P + P + P + Active site Sarcoplasm Ca 2+ ADP P + + P Ca 2+ ADP + P Ca 2+ ADP + P Ca 2+ ADP + P

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure of 7 Resting sarcomere Myosin head Active-site exposure Cross bridge detachment Cross-bridge formation Pivoting of myosin head Troponin Actin Tropomyosin ADP P + P + P + Active site Sarcoplasm Ca 2+ ADP P + + P Ca 2+ ADP + P Ca 2+ ADP + P Ca 2+ ADP + P Ca 2+ ATP Ca 2+

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure of 7 Resting sarcomere Myosin head Myosin reactivation Active-site exposure Cross bridge detachment Cross-bridge formation Pivoting of myosin head Troponin Actin Tropomyosin ADP P + P + P + Active site Sarcoplasm Ca 2+ ADP P + + P Ca 2+ ADP + P Ca 2+ ADP + P Ca 2+ ADP + P Ca 2+ ATP Ca 2+ ADP P + + P

Control of Muscle Contraction Summary of Contraction Process Table 7-1