Nerve MUSCLE PHYSIOLOGY Molecular Mechanism Of Muscle Contraction

Nerve MUSCLE PHYSIOLOGY

Molecular Mechanism Of Muscle Contraction • Sliding filament mechanism • Walk along theory • Ratchet theory

Walk Along Theory

Interaction B/W Actin & Myosin

Walk Along (Ratchet) Theory

Relaxed & Contracted

NEUROMUSCULAR JUNCTION

Motor Unit Single Motor Neuron & all Muscle Fibers it innervates constitute a single Motor Unit. α- motor N

Neuro. Muscular Junction

Release of Acetylcholine

Ligand Gated Channel (Acetylcholine) Closed Open

• Safety factor for transmission at the Neuromuscular junction. • Fatigue of Neuromuscular Junction

Myasthenia Gravis • 1 in every 20, 000 persons. • Antibodies against acetylcholine receptors. • Autoimmune disease. • Muscle paralysis ---- inability of neuromuscular • junction to transmit enough signals. Neostigmine ---- anticholinesterase drug.

Sarcoplasmic Reticulum T-Tubule & Longitudinal Tubule

T Sarcoplasmic Reticulum T-Tubule & Longitudinal Tubule T L

Sarcoplasmic Reticulum(T-tubule) DHP & Ryanidin Receptor (Hypothetical Model)

A. P entering the Sarcoplasmic Reticulum causing release of Ca++ ions

Excitation-Contraction coupling “The process by which the depolarization of the muscle fiber initiates contraction”

Sequence of Events in contraction of Muscle u Stimulation of Motor Neuron. u Release of neurotransmitter (Acetylcholine) at Motor End-plate. u Binding of Ach to Nicotinic Receptors. u Increased Na+ conductance through Ach Channels u Generation of end-plate potential u Generation of Action Potential in Muscle Fiber

Sequence of Events in Contraction u Inward spread of depolarization along T-Tubule. Sensing by DHP receptors & opening of Rayanidine receptors in terminal cisterns. u Release of Ca++ from terminal cistern of Sarcoplasmic Reticulum and diffusion to myofilaments u Binding of Ca++ to Troponin-C, uncovering Myosin binding on Actin filaments u Formation of Cross linkages between Actin & Myosin leading to sliding of thin on thick filaments, producing movement of Z-lines toward the centre

Steps involved in Relaxation of Muscle u ATP attaches to Myosin head Ca++ Pumped Back in Sarcoplasmic Reticulum. (Ca++ Mg++ ATPase Pump always On ) u Release of Ca++ from Troponin u u Cessation of Interaction between Actin & Myosin filaments