BIO 240 1st Edition Lecture 18Outline of Last Lecture II. Anatomy of Skeletal Muscle Fibers A. StructuresB. Skeletal Muscle FiberC. Anatomy of a MyofibrilOutline of Current LectureIII. Muscle PhysiologyA. Nervous System + Muscle System = ContractionB. Active Channels C. Steps of excitation contraction coupling. Current LectureIII. Muscle PhysiologyA. Nervous System + Muscle System = Contractioni. 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 = contractioniii. Motor unit A single motor neuron and all the muscle fibers it innervates. iv. Electrochemical Equilibrium = Resting Potential 1. -85 mV2. 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 orCa 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 neuronto 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 platevi. 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-tubulesix. 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 AcHv. AcH flows into the neuro-muscular junctionvi. AcH binds with chemically regulated Na channels, opening themvii. 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 cisternaex. Ca flows from the terminal cisternae into the muscle fiber.1. All previous steps were to increase intracellular Ca2. 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
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