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Course: Locomotion and Movement -2 Lesson 3:Muscles and their types DR. P. K. AGRAWAL M.Sc, PH.D., CSIR NET (JRF), SRF, GATE, FIAZ 20 Years of Pre-medical teaching experience Ex Faculty, Allen Career Institute, Kota Watch my Live Classes on Unacademy Plus
Human Muscles and Their Types Muscular system is formed by muscles, which are the mesodermal tissues. Muscles form about 40% of the total body weight. . The cells of muscle tissues are called myocytes or myofibres. Muscles are characterized with special properties - .excitability, contractility extensibility and elasticity remaining 5 muscles are unpaired. . There are 639 muscles in human body. Out of these 634 muscles are found in 317 pairs while
Basic types of muscles Depending upon their nature, structure and functions, the muscles are of three basic types .(a) Striated, stripped, voluntary or skeletal muscles, .(b) Unstriated, unstripped, involuntary or smooth muscles. . (c) Cardiac muscles and
(a) Striated, stripped, voluntary or skeletal muscles These muscles are called voluntary muscles because these are under the control of conscious mind and can be moved at will. .These are attached to the bones by tendons and help in the movement of the parts of skeleton. Under the light microscope, these skeletal muscles exhibit transverse stripes, and hence, these are designated as striated or stripped muscles. The fibres of these muscles are unbranched and cells are multinucleated. Skeletal muscles exhibit a very high degree of contractility and extensibility .These muscles soon undergo fatigue. .These are responsible for the movements of various organs to facilitate locomotion.
A skeletal muscle Enlarged muscle fibre (Myofibre) Nuclei Sarcolemma Bands (strips) Skeletal or Stripped Muscle
(b) Unstriated, unstripped, involuntary or smooth muscles .Smooth muscles are made up of single nucleated, spindle- shaped cells. The cells are unbranched. . These get their name because no striations are visible in them. Nonetheless, each smooth muscle cell contains thick (myosin) and thin (actin) filaments that slide against each other to produce contraction of the cell. Myofibrils . The thick and thin filaments are anchored near the plasma Nucleus membrane (with the help of intermediate filaments). Smooth muscle (like cardiac muscle) does not depend orn motor neurons to be stimulated. However, motor neurons (of the autonomic system) reach smooth muscle and can stimulate it or relax it, depending on the neurotransmitter they release.
Smooth muscle can also be made to contract by other substances released in the vicinity (paracrine stimulation), e.g., release of histamine causes contraction of the smooth muscle lining our air passages (triggering an attack of asthma) .Similarly, oxytocin hormone stimulates the uterine smooth muscles and cause their contraction to facilitate childbirth. -Smooth muscles have low degree of contractility.
(C) Cardiac muscles . Cardiac or heart muscle resembles skeletal muscle in many ways as it is striated and each cell contains sarcomeres with sliding filaments of actin and myosin. However, cardiac muscle has . Cardiac muscle are made up of myocardial cells - each with a single nucleus. The cells are . The branches of different cells are intercommunicated. At the junction of two adjacent cells, .Presence of intercalated disc is the characteristic feature of cardiac muscles. a number of unique features that reflect its function of continuous blood pumping highly branched. the sarcolemma (plasma membrane) forms 'intercalated discs' Nucleus Branch Intercalated discs
. The discs are strong junctions, which enable the heart to contract forcefully without ripping the fibres apart. All the fibres of cardiac muscles contract in a synchronous wave. . Anything that interferes with this synchronous wave (such as damage to part of the heart muscle from a heart attack) may cause the fibres of the heart to beat at random-called fibrillation, which may lead to the death. . The refractory period in heart muscle is longer than the period it takes for the muscle to contract (systole) and relax (diastole). Thus, tetanus is normally not possible. Cardiac muscles have a much richer supply of mitochondria than skeletal muscle. This shows their greater dependence on cellular respiration for ATP. Cardiac muscles have little glycogen and get little benefit from glycolysis when the supply of oxygen is limited. There is almost no anaerobic pathway in these muscles. So, there is no chance of accumulation of lactic acid and therefore, these muscles do not undergo fatigue.
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