Summation of muscle contraction Summation is the added effect of individual muscle twitches to get strong and powerful muscle contraction. Summation occurs in two different ways By increasing the number of motor units to contract simultaneously. By increasing the rapidity of contraction of individual motor unit of a contracting muscle. Multi-motor unit summation (Spatial summation) The strength […]

Properties of muscle contractions When a muscle fiber is stimulated by minimal or maximal effective stimuli, the whole fiber contracts to the maximum or it will not contract at all. This law is applicable to single motor unit (motor nerve and all the muscle fibers it supplies). Whole cardiac muscle obeys this law because of

Stimulus for muscle and types Stimulus is an external agent, when applied to an excitable tissue provoke a visible response. Types of Stimuli(Based on strength) Sub threshold : sub minimal/ low intensity, unable to produce a response Threshold : minimum intensity, strong enough to initiate an action potential Sub maximal : higher strength than threshold Maximal : highest threshold strength

Sliding mechanism of contraction “Walk- along theory” of contraction (Sliding mechanism of contraction) In the relaxed state, actin filaments lie adjacent and parallel to the myosin filaments. In contracted state, the actin filaments extending from the z-discs are also pulled inward by head portion of the free ends of myosin filaments. Thus, muscle contraction occurs

Muscle contraction Muscle contraction is accomplished by a sliding together or telescoping of the interdigitating thick and thin filaments and as a result narrowing and eventual disappearance of the H zone and shortening of I band happen. Summary of events Before contraction ie in the absence of Ca2+ in the sarcoplasm, troponin T strongly binds with

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