BIO 240 1st Edition Lecture 18 Outline of Last Lecture II Anatomy of Skeletal Muscle Fibers A Structures B Skeletal Muscle Fiber C Anatomy of a Myofibril Outline of Current Lecture III Muscle Physiology A Nervous System Muscle System Contraction B Active Channels C Steps of excitation contraction coupling Current Lecture III Muscle Physiology A Nervous System Muscle System Contraction i Excitation Contraction Coupling A sequence of events by which transmission of an action potential along the sarcolemma causes myofilaments to slide past each other ii Electrical and chemical events occur to achieve a mechanical action 1 Mechanical action contraction iii Motor unit A single motor neuron and all the muscle fibers it innervates iv Electrochemical Equilibrium Resting Potential 1 85 mV 2 Na K Ca Cl Pr lo hi lo lo hi concentrations inside the cell 3 When gates for Na open it flows into the cell 4 When gates for Ca open it flows into the cell 5 All cells of the body are Passive they have leaky channels 6 Muscle and nerve cells are Active they have active channels and are excitable B Active Channels 2 types i Chemically gated channels Take a chemical key that binds with a receptor lock to open the gate Can have Na chemically regulated gates or Ca chemically regulated gates each of these would cause that chemical to flow into the cell respectively These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 1 Neurotransmitters The chemical that unlocks the gate Most common is Acetylcholine AcH ii Voltage regulated gate They open or close when there is a change in the charge of the cell They are closed at resting potential 85 mV They open when the cell goes from negative to positive depolarization 1 Depolarization Changing the electrochemical equilibrium from negative to positive further away from resting potential iii Motor end plate Divet in the sarcolemma with channels for the neuron to plug in to iv Synaptic knob The foot of the neuron that plugs into the motor end plate v Neuromuscular junction Area where the synaptic knob plugs into the motor end plate vi Synaptic vesicles The bags of neurotransmitters in the synaptic knob vii T tubules The deep invaginations on the muscle fibers viii Terminal cisternae The bags on either side of the T tubules ix Triad One T tubule with its two terminal cisternae C Steps of excitation contraction coupling i Impulse an electrical signal comes down the neuron ii This opens the voltage regulated Ca channels iii Ca flows into the synaptic knob of the neuron rupturing synaptic vesicles iv The synaptic vesicles release AcH v AcH flows into the neuro muscular junction vi AcH binds with chemically regulated Na channels opening them vii Na flows into the muscle cell viii This depolarizes the muscle cell moves it from negative to a more positive charge ix Depolarization opens the voltage regulated Ca channels on the terminal cisternae x Ca flows from the terminal cisternae into the muscle fiber 1 All previous steps were to increase intracellular Ca 2 80 of Ca is extracellular 20 is in the terminal cisternae xi This raises the charge of the cell even more getting the cell closer to action potential
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