Chapter 13 (part d) provides knowledge of motor endings and motor activity. In this chapter, students will be able to compare and contrast the motor endings of somatic and autonomic nerve fibers, outline the three levels of the motor hierarchy, compare the roles of the cerebellum and basal nuclei in controlling motor activity. | 13 The Peripheral Nervous System and Reflex Activity: Part D Motor Endings PNS elements that activate effectors by releasing neurotransmitters Review of Innervation of Skeletal Muscle Takes place at a neuromusclular junction Acetylcholine (ACh) is the neurotransmitter ACh binds to receptors, resulting in: Movement of Na+ and K+ across the membrane Depolarization of the muscle cell An end plate potential, which triggers an action potential Figure Nucleus Action potential (AP) Myelinated axon of motor neuron Axon terminal of neuromuscular junction Sarcolemma of the muscle fiber Ca2+ Ca2+ Axon terminal of motor neuron Synaptic vesicle containing ACh Mitochondrion Synaptic cleft Junctional folds of sarcolemma Fusing synaptic vesicles ACh Sarcoplasm of muscle fiber Postsynaptic membrane ion channel opens; ions pass. Na+ K+ ACh Na+ K+ Degraded ACh Acetylcholinesterase Postsynaptic membrane ion channel closed; ions cannot pass. Action potential arrives at axon terminal of motor neuron. Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal. Ca2+ entry causes some synaptic vesicles to release their contents (acetylcholine) by exocytosis. Acetylcholine, a neurotransmitter, diffuses across the synaptic cleft and binds to receptors in the sarcolemma. ACh binding opens ion channels that allow simultaneous passage of Na+ into the muscle fiber and K+ out of the muscle fiber. ACh effects are terminated by its enzymatic breakdown in the synaptic cleft by acetylcholinesterase. 1 2 3 4 5 6 Review of Innervation of Visceral Muscle and Glands Autonomic motor endings and visceral effectors are simpler than somatic junctions Branches form synapses en passant via varicosities Acetylcholine and norepinephrine act indirectly via second messengers Visceral motor responses are slower than somatic responses Figure Smooth muscle cell Varicosities release their neurotransmitters into a wide synaptic cleft (a diffuse junction). Synaptic vesicles Mitochondrion Autonomic nerve | 13 The Peripheral Nervous System and Reflex Activity: Part D Motor Endings PNS elements that activate effectors by releasing neurotransmitters Review of Innervation of Skeletal Muscle Takes place at a neuromusclular junction Acetylcholine (ACh) is the neurotransmitter ACh binds to receptors, resulting in: Movement of Na+ and K+ across the membrane Depolarization of the muscle cell An end plate potential, which triggers an action potential Figure Nucleus Action potential (AP) Myelinated axon of motor neuron Axon terminal of neuromuscular junction Sarcolemma of the muscle fiber Ca2+ Ca2+ Axon terminal of motor neuron Synaptic vesicle containing ACh Mitochondrion Synaptic cleft Junctional folds of sarcolemma Fusing synaptic vesicles ACh Sarcoplasm of muscle fiber Postsynaptic membrane ion channel opens; ions pass. Na+ K+ ACh Na+ K+ Degraded ACh Acetylcholinesterase Postsynaptic membrane ion channel closed; ions cannot pass. Action potential arrives at axon terminal of motor neuron. .
