#musclecontraction

Ace Physiology For PG 2021 With Vijay Kumar Gupta - Muscle Contraction

In this session, we will discuss the physiology, applied physiology, and pharmacology of the molecular basis of muscle contraction. There will be an MCQ quiz at the end of the session.

Today 17th October

Live at 6 PM

When we engage in aerobic or anaerobic exercises, we don’t realize what is actually going on physiologically when our bodies are in motion. Our auditory stimulation of vibrations and sounds at a rate of 125 bmp, collects data and is interpreted by our mechanoreceptors in the brain. The brain sends a signal via central nervous system informing the body that it needs to be in motion. An action potential is fired at the axon hillock. Depolarization occurs, where positively charged sodium (Na+) ions from the extracellular fluid (ECF) enter the intracellular fluid (ICF) through Na+ channels raising the charge of the cell making it more positive than negative. As positively charged sodium ions enter the cell, negatively charged potassium (K+) ions exit the cell. The sodium continues to depolarize the neuron, traveling down the axon terminal. Depolarization opens Calcium (Ca2+) channels. Ca2+ goes into the neurotransmitter and triggers exocytosis of vesicles. Acetylcholine (ACh) is released into the synaptic cleft. ACh attaches to nicotinic receptors in the motor end plate (where the neuron connects to the muscle). Na+ goes into the muscle cell and depolarizes the cell. Membrane potential reaches threshold and fires an action potential through the sarcolemma (cell membrane of the cell) and down T-tubules. The action potential changes the shape of the DHP voltage gated channel allowing the RYR channel to open. Ca2+ is released out into the sarcoplasmic reticulum into the cytoplasm. Ca2+ binds to troponin on the actin instructing tropomyosin to move out of the way. The myosin head now attaches to the actin binding site. *note muscle contraction still has not occurred* Myosin has two binding sites available one for ATP (adenosine triphosphate) and one for actin. ATP attaches to binding site on myosin and myosin head detaches from actin. ATP is hydrolyzed into ADP + phosphate. Myosin moves towards the Z-disk and attaches to actin. Phosphate detaches from myosin making the myosin head power stroke moving actin towards the M-line and thus causing muscle contraction.