Muscle Physiology PDF

Muscle Physiology Dr. Asmaa Seddek Lecturer of Physiology FOM-SCU Objectives Types of muscles Skeletal muscles Cardiac muscles Smooth muscles  DEPENDING UPON STRIATIONS Depending upon the presence or absence of cross striations, the muscles are divided into two groups: 1. Stria...

Muscle Physiology Dr. Asmaa Seddek Lecturer of Physiology FOM-SCU Objectives Types of muscles Skeletal muscles Cardiac muscles Smooth muscles  DEPENDING UPON STRIATIONS Depending upon the presence or absence of cross striations, the muscles are divided into two groups: 1. Striated Muscle Striated muscle is the muscle which has a large number of cross-striations (transverse lines). Skeletal muscle and cardiac muscle belong to this category. 2. Non-striated Muscle Muscle which does not have cross-striations is called non-striated muscle. It is also called plain muscle or smooth muscle. It is found in the wall of the visceral organs. DEPENDING UPON CONTROL: classified into two types 1. Voluntary Muscle Voluntary muscle is the muscle that is controlled by the will. Skeletal muscles are the voluntary muscles. These muscles are innervated by somatic nerves. 2. Involuntary Muscle Muscle that cannot be controlled by the will is called involuntary muscle. Cardiac muscle and smooth muscle are involuntary muscles. These muscles are innervated by autonomic nerves DEPENDING UPON SITUATION Depending upon situation, the muscles are classified into three types: 1. Skeletal Muscle Skeletal muscle is situated in association with bones forming the skeletal system. The skeletal muscles form 40% to 50% of body mass and are voluntary and striated. These muscles are supplied by somatic nerves. Fibers of the skeletal muscles are arranged in parallel. In most of the skeletal muscles, muscle fibers are attached to tendons on either end. Skeletal muscles are anchored to the bones by the tendons. 2. Cardiac Muscle Cardiac muscle forms the musculature of the heart. These muscles are striated and involuntary. Cardiac muscles are supplied by autonomic nerve fibers. 3. Smooth Muscle Smooth muscle is situated in association with viscera. It is also called visceral muscle. It is different from skeletal and cardiac muscles because of the absence of cross striations, hence the name smooth muscle. supplied by autonomic nerve fibers. Smooth muscles form the main contractile units of wall of the various visceral organs. Skeletal Muscle Each muscle fiber is a single cell that is multinucleated, long, cylindrical, and surrounded by a cell membrane, called the sarcolemma. The muscle fibers are made up of myofibrils, which are subdivided into individual filaments. The filaments are made up of the contractile proteins. Sarcomere (Contractile Unit Of The Muscle) Skeletal muscle Transverse tubules (T tubules) narrow membranous “tunnels formed from and continuous with the sarcolemma Function: conduct action potential that stimulates the opening of voltage-gated Ca² channels. Sarcoplasmic reticulum modified endoplasmic reticulum consisting of interconnected sacs and tubes that surround each myofibril within the muscle cell Function : stores Ca ions Innervation Of Skeletal Muscle  Properties of Skeletal Muscle Excitability Excitability is defined as the reaction or response of a tissue to irritation or stimulation. It is a physicochemical Change CONTRACTILITY Contractility is the response of the muscle to a stimulus. Contraction is defined as the internal events of muscle with change in either length or tension of the muscle fibers. MUSCLE TONE Muscle tone is defined as continuous and partial contraction of the muscles with certain degree of vigor and tension. Excitation - Contraction Coupling (1) Acetylcholine (Ach) released by somatic motor neurons binds to ACh receptors in the sarcolemma, causing a depolarization that stimulates voltage-gated channels, producing action potential. (2) The conduction of action potential along the transverse tubules stimulates the opening of voltage-gated Ca channels. (3) Ca ² then diffuses into the cytoplasm, so that it stimulate muscle contraction  Role Of Calcium In Muscle Contraction calcium causes a shift in the position of the troponin complex on actin filaments, which exposes myosin- binding sites ) Myosin can then form cross-bridges with actin, and the release of ADP and Pi produces the power stroke that drives contraction. Cardiac Muscle (Myocardium)  Cardiac muscle forms the musculature of the heart.  These muscles are striated and involuntary. Its contraction propels blood through the circulatory system.  Cardiac muscle is able to produce action potentials automatically by a specialized group of cells called the pacemaker. However, the rate of this spontaneous depolarization, and thus the rate of the heartbeat, are regulated by autonomic innervation, hormones and chemical agents.  Cardiac Muscle Myocardial cells are short, branched, and interconnected Gap Junctions whereas skeletal muscle cells, are structurally and functionally separated from each other. The gap junctions are concentrated at the ends of each myocardial cell, which permits electrical impulses to be conducted from cell to another. Properties of Cardiac Muscle EXCITABILITY It is the ability of a living tissue to give response to a stimulus. In all the tissues, initial response to a stimulus is electrical activity in the form of action potential. It is followed by mechanical activity in the form of contraction. RHYTHMICITY Rhythmicity is the ability of a tissue to produce its own impulses regularly. It is also called autorhythmicity or self-excitation. Property of rhythmicity is present in all the tissues of heart. However, heart has a specialized excitatory structure, from which the discharge of impulses is rapid. This specialized structure is called pacemaker. From here, the impulses spread to of the parts through the specialized conductive system CONDUCTIVITY Human heart has a specialized conductive system through which impulses from SA node are transmitted to all other parts of the heart. CONTRACTILITY Contractility is ability of the tissue to shorten in length (contraction) after receiving a stimulus. Smooth muscle Sites of presence: Sheets of smooth muscle surround various hollow organs and tubes, including the stomach, intestines, urinary bladder, uterus, blood vessels, and airways in the lungs. General function of smooth muscles: 1- Contraction of the smooth muscle surrounding hollow organs may propel the luminal contents through the organ, 2- It may regulate internal flow by changing the tube diameter. (Blood vessels)  Smooth Muscle Sarcomere are absent in smooth muscles. So the alternate dark and light bands are absent. Absence of dark and light bands gives the non-striated appearance to the smooth muscle.  Control Of Contraction Of Smooth-muscle *It is controlled by the autonomic nervous system, hormones, and other chemical signals. *Compared to skeletal muscles, in smooth muscles, the contraction and relaxation processes are slow. Thanks for your attention