Muscle Physiology Lecture 1 PDF

Muscle Physiology Dr Kwame Yeboah Department of Physiology UGMS  Muscle Tissue Skeletal Muscle Cardiac Muscle Smooth Muscle  Cardiac Muscle Branching cells One/two nuclei per cell Striated Involuntary Mediu...

Muscle Physiology Dr Kwame Yeboah Department of Physiology UGMS  Muscle Tissue Skeletal Muscle Cardiac Muscle Smooth Muscle  Cardiac Muscle Branching cells One/two nuclei per cell Striated Involuntary Medium speed contractions  Smooth Muscle Fusiform cells One nucleus per cell Nonstriated Involuntary Slow, wave-like contractions  Skeletal Muscle Long cylindrical cells Many nuclei per cell Striated Voluntary Rapid contractions  Skeletal Muscle Produce movement Maintain posture & body position Support Soft Tissues Guard entrance / exits Maintain body temperature Store nutrient reserves Skeletal Muscle Structure Skeletal Muscle Fiber Sarco-tubular system  PROTEINS OF MUSCLE: Composed of – Thin filament – Thick filament – Cytoskeletal proteins ACTIN & THIN FILAMENTS G-actin ↓ F-actin (6-7 nm long polymerized G- actin, double stranded in structure) ↓ Thin filaments Regulatory Proteins of the Muscles TROPOMYOSIN TROPONIN Rod-like protein Globular protein complex Forms part of thin filaments Under resting conditions, it covers the site for myosin attachment on F-actin Binds to Ca2+ molecule. Inhibitory in function Forms part of Thin filaments Attached to Tropomyosin  MYOSIN & THICK FILAMENTS: Thick filaments consist of 2 symmetrical halves that are mirror images of each other. Chief constituent is MYOSIN, It has 6 peptide chains: - 2 identical heavy chains - 4 light chains Protease digestion of myosin  Binding sites on Myosin molecule: The myosin molecule has 2 binding sites: 1. Binding site for ACTIN 2. ATPase site Sarcomere Z line Z line Sarcomere Relaxed Sarcomere Partially Contracted Sarcomere Completely Contracted  Anchoring proteins α-actinin: cross-link the actin filaments in the area of Z line Nebulin: is an inextensible filament which is connected at one end to the α-actinin in the area of Z line and at another end to the tropomyosin–troponin complex of thin filaments at regular intervals. Titin: is the largest known protein in the body. It connects the Z-line to the M-line in the sarcomere & It forms the series elastic components (SEC) of the muscle. Dystrophin:The dystrophin–glycoprotein complex forms the best known anchor protein complex which provides structural support and strength to myofibril.  THE CROSS-BRIDGE CYCLE Relaxed state Crossbridge Crossbridge energised attachment A + M l ADP l Pi Ca2+ present A – M l ATP AlMlADPlPi Crossbridge Tension detachment develops ADP + Pi ATP Al M A, Actin; M, Myosin Cross Bridge Cycle 38 Neuromuscular Junction T-Tubule & the Sarcoplasmic Reticulum The t-tubules have the Dihydropyridine Receptors (DHP) receptors in their membranes. When this receptor is activated because of an AP, it causes the opening of the voltage gated foot proteins/ Ryanodine channel/ Ca release channel. These channels are present in the cisterns of the Sarcoplasmic Reticulum. The opening of these channels leads to the release of Ca into the Sarcoplasm.  Degradation of Ach: The Ach present in the synaptic cleft is broken down by the enzyme Acetylcholinesterase, into Acetyl coA & choline. Both the products are reuptaken by the presynaptic terminal. The Ach is again synthesized by the nerve cell body and then send by anterograde flow to the presynaptic terminal for packaging into secretory vesicles.  EXCITATION-CONTRACTION COUPLING Steps in relaxation: ◼ Ca2+ pumped back into Sarcoplasmic Reticulum (SR) by the ATP-dependant Ca2+ pump in SR membrane. ◼ Release of Ca2+ from troponin C. ◼ A new ATP binds to the myosin head ↓ interaction between actin and myosin STOPS and RELAXATION of the muscle fiber takes place.