Clicker questions Clicker channel 70 Response Ware Session ID psio201 What is this A A myofibril B A myofilament C A sarcomere 79 D The sarcoplasmic reticulum SR 16 4 A B 1 C D Name this Ca2 sensitive protein A Actin B Myosin 87 C Tropomyosin D Troponin 10 1 A 2 B C D What is this area of the sarcomere called A A band B H zone 91 C M line D Zone of overlap 7 A 2 B 1 C D Lecture 19 Excitation Contraction Coupling and Muscle Relaxation Claudia Stanescu Ph D Office hours Tuesday and Thursday 1 2pm in Gittings 108 or by appointment Objectives pp 304 308 sec 10 3 1 Diagram and label the key components of the neuromuscular junction 2 List in order the events that occur at the neuromuscular junction leading to the electrical stimulation of a skeletal muscle fiber 3 Describe the role of acetylcholine esterase AChE in the cessation of the electrical stimulation of a muscle fiber 4 Discuss the role of calcium in the regulation of contraction and relaxation of skeletal muscle 5 List in order the events of muscle contraction from excitation to excitation contraction coupling to contraction and lastly relaxation How is cross bridge cycling controlled Sequence of Events 1 Electrical signal transmitted from a motor neuron to a skeletal muscle fiber Excitation 2 Triggers release of Ca2 from SR Excitation Contraction Coupling 3 Ca2 binds to troponin on the thin filament thereby permitting crossbridges to form crossbridge cycling results in tension development Contraction 4 Removal of Ca2 resequestration into SR results in Relaxation The Electrical Signal Excitation Neuromuscular Transmission 1 Activation of skeletal muscle is voluntary requires a signal from the central nervous system CNS this signal results in an electrical impulse along a motor neuron that arrives at the Neuromuscular Junction the junction between the motor neuron and a muscle fiber Structural Organization of Skeletal Muscle Neuromuscular Junction Neuromuscular Junction Excitation Steps 1 Action potential arrives at the synaptic end bulb of motor neuron and causes opening of voltage gated Ca2 channels 2 Synaptic vesicles containing the neurotransmitter Acetylcholine ACh undergo exocytosis 3 ACh is released into the synaptic cleft and binds to ACh receptors on the sarcolemma motor end plate 4 ACh receptors open and allow Na to enter the muscle fiber generating an action potential on the sarcolemma 5 ACh is quickly broken down to Acetate and Choline by Acetylcholine Esterase AChE Neuromuscular junction animation Neuromuscular Junction captioned http www youtube com watch v JcUwsFpxr bU Release of Ca2 from the SR Excitation Contraction Coupling 1 AP runs along sarcolemma continues into T tubules 2 Triggers release of Ca2 from SR 3 Ca2 diffuses into sarcoplasm and myofibrils 4 Ca2 binds to troponin on thin filament myosin binding site on actin gets exposed 5 Crossbridges form tension is generated starts contraction Excitation contraction coupling animation Excitation Contraction Coupling captioned http www youtube com watch v ant19jZvnI SR T tubule Relaxation Sequestration of Ca2 1 When Action Potentials stop arriving at the NMJ the trigger to release Ca2 from the SR stops 2 Active Ca2 transporters in the SR membrane pump Ca2 back into the SR 3 Cytoplasmic Ca2 decreases 4 As Ca2 cyto falls Ca2 comes off troponin the myosin binding sites on actin get covered by tropomyosin 5 Crossbridge cycling stops and tension drops 6 Titin brings the sarcomere back to resting position Summary of Steps Suggested Learning Activities Draw the neuromuscular junction including the following synaptic end bulb synaptic cleft motor end plate synaptic vesicles ACh receptors calcium channels Watch the two animations provided in this lecture with your notes in front of you Pause the videos and review each step described List the steps of excitation excitation contraction coupling contraction and relaxation in order