Muscle physiology

Muscle types and their physiology

1. MUSCLE PHYSIOLOGY By Gladys Stephen

2. Functions of Muscle Tissue sustained contraction or alternating contraction and relaxation, muscular tissue has four key functions: Produces body movements. Stabilizes body positions. Stores and moves substances within the body. Generates heat. By Gladys Stephen

3. Properties of Muscle Tissue Muscular tissue has four special properties that enable it to function and contribute to homeostasis: Electrical excitability Contractility Extensibility Elasticity By Gladys Stephen

4. Electrical excitability : a property of both muscle and nerve cells to respond to certain stimuli by producing electrical signals called action potentials Contractility ability of muscular tissue to contract forcefully when stimulated by an action potential. When a muscle contracts, it generates tension (force of contraction) while pulling on its attachment points. By Gladys Stephen

5. Extensibility ability of muscular tissue to stretch without being damaged. Extensibility allows a muscle to contract forcefully even if it is already stretched. Elasticity ability of muscular tissue to return to its original length and shape after contraction or extension By Gladys Stephen

6. Classification of Muscles Muscles are classified by three different methods, based on different factors: I. Depending upon the presence or absence of striations II . Depending upon the control III . Depending upon the situation. By Gladys Stephen

7. DEPENDING UPON STRIATIONS Depending upon the presence or absence of cross striations , the muscles are divided into two groups: 1. Striated muscle 2. Non-striated muscle. By Gladys Stephen

8. Striated Muscle Striated muscle is the muscle which has a large number of cross-striations (transverse lines). Examples are skeletal muscle and cardiac muscles. By Gladys Stephen

9. 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 . By Gladys Stephen

10. II. DEPENDING UPON CONTROL Depending upon control, the muscles are classified into two types : 1. Voluntary muscle 2. Involuntary muscle. By Gladys Stephen

11. 1. Voluntary Muscle Voluntary muscle is the muscle that is controlled by our own 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 By Gladys Stephen

12. DEPENDING UPON SITUATION Depending upon situation, the muscles are classified into three types: 1. Skeletal muscle 2. Cardiac muscle 3. Smooth muscle . By Gladys Stephen

13. 1. Skeletal Muscle Skeletal muscle is situated in association with bones forming the skeletal system. form 40 % to 50% of body mass and are voluntary and striated. Supplied by somatic nerves. Fibers of the skeletal muscles are arranged in parallel . Muscle fibers are attached to tendons on either end. Skeletal muscles are anchored to the bones by the tendons. By Gladys Stephen

14. Skeletal Muscle Description: Long, cylindrical, striated fibers with many peripherally located nuclei; voluntary control. Location: Usually attached to bones by tendons. Function: Motion, posture, heat production, and protection. By Gladys Stephen

15. Structure of Skeletal Muscle By Gladys Stephen

16. Skeletal muscle Longitudinal section of skeletal muscle tissue Skeletal muscle fiber nucleus striations Skeletal muscle fiber By Gladys Stephen

17. By Gladys Stephen

18. MUSCLE MASS OR TISSUE Muscle mass or muscle tissue is made up of a large number of individual muscle cells or myocytes . The muscle cells are commonly called muscle fibers because these cells are long and slender in appearance. Skeletal muscle fibers are multinucleated and are arranged parallel to one another with some connective tissue in between. By Gladys Stephen

19. Muscle mass is separated from the neighboring tissues by a thick fibrous tissue layer known as fascia. Beneath the fascia, muscle is covered by a connective tissue sheath called epimysium . In the muscle , the muscle fibers are arranged in various groups called bundles or fasciculi . Connective tissue sheath that covers each fasciculus is called perimysium . Each muscle fiber is covered by a connective tissue layer called the endomysium By Gladys Stephen

20. A. Skeletal muscle mass; B. Cross-section of muscle; C. One muscle fasciculus . By Gladys Stephen

21. MUSCLE FIBER Each muscle cell or muscle fiber is cylindrical in shape. Average length of the fiber is 3 cm (1-4 cm, depending upon the length of the muscle). The diameter of the muscle fiber varies from 10 μ to 100 μ and it varies in a single muscle . Muscle fibers are attached to a tough cord of connective tissue called tendon. Tendon is in turn attached to the bone. Tendon of some muscles is thin , flat and stretched but tough. Such type of tendon is called aponeurosis . Each muscle fiber is enclosed by a cell membrane called plasma membrane, that lies beneath the endomysium . It is also called sarcolemma . Cytoplasm of the muscle is known as sarcoplasm . By Gladys Stephen

22. Structures embedded within the sarcoplasm are: 1 . Nuclei 2 . Myofibril 3 . Golgi apparatus 4 . Mitochondria 5 . Sarcoplasmic reticulum 6 . Ribosomes 7 . Glycogen droplets 8 . Occasional lipid droplets . By Gladys Stephen

23. Sarcolemma It is the cell membrane of the muscle fiber . The sarcolemma consists of a true cell membrane, called the plasma membrane, and an outer coat made up of a thin layer of polysaccharide material that contains numerous thin collagen fibrils. At each end of the muscle fiber, this surface layer of the sarcolemma fuses with a tendon fiber. Tendon fibers in turn collect into bundles to form the muscle tendons that then insert into the bones. By Gladys Stephen

24. MYOFIBRIL Each muscle fiber contains several hundred to several thousand myofibrils. Myofibrils or myofibrillae are the fine parallel filaments present in sarcoplasm of the muscle cell. some of the myofibrils are arranged in groups called Cohnheim’s areas or fields. Each myofibril is composed of about 1500 adjacent myosin filaments and 3000 actin filaments , which are large polymerized protein molecules responsible for the actual muscle contraction. By Gladys Stephen

25. MYOFIBRIL The myofibrils contain 2 kinds of protein filaments . Thick filaments – composed of myosin . Thin filaments – composed of Actin , troponin and tropomyosin . c. striations are produced by alternating light and dark filaments . By Gladys Stephen

26. 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 . By Gladys Stephen

27. CARDIAC MUSCLE Heart Longitudinal section of cardiac muscle tissue Cardiac muscle fibers Nucleus Cardiac muscle fiber (cell) Striations By Gladys Stephen

28. CARDIAC MUSCLE Description: Branched striated fibers with one or two centrally located nuclei; contains intercalated discs; involuntary control. Location: Heart wall. Function: Pumps blood to all parts of the body. By Gladys Stephen

29. SMOOTH MUSCLE Description: Spindle-shaped (thickest in middle and tapering at both ends), nonstriated fibers with one centrally located nucleus; involuntary control. Location: Iris of the eyes, walls of hollow internal structures such as blood vessels, airways to the lungs, stomach, intestines, gallbladder, urinary bladder, and uterus. Function: Motion (constriction of blood vessels and airways, propulsion of foods through gastrointestinal tract, contraction of urinary bladder and gallbladder). By Gladys Stephen

30. 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. Smooth muscle is supplied by autonomic nerve fibers. Smooth muscles form the main contractile units of wall of the various visceral organs E.g. stomach. By Gladys Stephen

31. Artery Smooth muscle Longitudinal section of smooth muscle tissue Nucleus of smooth muscle fiber Smooth muscle fiber (cell) SMOOTH MUSCLE By Gladys Stephen