Acetylcholine Receptors of muscles The released acetylcholine diffuses across the synaptic cleft, reaches the postsynaptic membrane (sarcolemma), and binds with acetylcholine-specific receptors. This causes opening of ligand-gated ion channels in the sarcolemma. And diffusion of sodium ions into the muscle cell generating local potential change called end plate potential. Depolarization in the end plate potential opens voltage-gated Na+ channels […]

Neuromuscular junction The motor neuron branches at its end and each branch comes into a close opposition with the skeletal muscle at a specialized area called the neuromuscular junction or motor end plate. This synapse has a presynaptic membrane, a narrow space between the nerve and muscle, called synaptic cleft and a post synaptic membrane sarcolemma. The presynaptic knob is the terminal portion

Motor end plate The axon terminals of the motor neurons innervate each muscle cell. The innervation ratio is the number of muscle fibers or cells innervated by a single motor neuron (motor unit). In muscles where delicate control is required the innervation ratio is small (3 to 6) as in extrinsic eye muscles. In the

Types of whole muscle contraction Muscle contraction is principally of two types Isometric contraction and Isotonic contraction. Isometric contraction Muscle contraction without shortening in length that occurs during the manifestation of the process of muscle contraction. In isometric contraction, the muscle contracts between two fixed points. Hence during the process of contraction it does not

Series elastic component of a muscle The components such as sarcolemma sheath at the end of the muscle fibers, the tendon and the hinged arms of the cross bridges of the myosin filaments are known as series elastic components of the muscle. stretch slightly as tension increases. Consequently, the contractile unit must shorten an extra 3-5% to

Membrane potential of muscles The interstitial fluid and the intracellular fluid contain 147 mEq/litre of positive ions (cations) outside the cell, and about 155 mEq /L, of negative ions (anions) inside the cell. Higher concentration of Na+ ions (142 mEq/L) and lower concentration of K+ ions (5 mEq/L) characterise the interstitial fluid. The intracellular fluid has more

Excitability of muscles Excitability of muscles is the ability of any living cell or tissue to exhibit an electrochemical change (action potential) to a stimulus. However, nerve and muscle cells are highly excitable cells than other cells. Events of action potential of muscle fiber The action potential is caused by a sequence of changes or

Excitation Contraction Coupling The arrival of an Action Potential at Sarcoplasmic Reticulum causes release of Ca2+ down the concentration gradient to sarcoplasmic reticulum. Released Ca2+ causes conformational changes to effect contraction. As action potential passes, Ca2+ are pumped again to sarcoplasmic reticulum and relaxation happens. This cycle is known as Excitation Contraction Coupling.

Myosin and Actin filament Myosin Filament It is composed of multiple myosin molecules, each molecule having a molecular weight of 480,000. It has two polymerized portions, Heavy meromyosin and Light meromyosin . Heavy meromyosin is formed by HMM – S1 and HMM – S2 molecules. The myosin molecule is made up of six polypeptide chains: 2 heavy chains and 4 light chains. The two heavy chains

Sarcoplasm and Myofibrils Sarcoplasm Sarcoplasm is the fluid present inside each fiber in which the organelles like sarcosomes(mitochondria), sarcoplasmic reticulum and myofibrilare suspended. Large number of sarcosomes is placed in between the myofibrils, indicates the large quantity of energy (ATP) requirement for the contraction of fibrils. Cytoplasm of the muscle cell is called sarcoplasm which contains myoglobin.