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Muscular System Functions  Body movement (Locomotion)  Maintenance of posture  Respiration * Diaphragm and intercostals contractions  Communication.

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Presentation on theme: "Muscular System Functions  Body movement (Locomotion)  Maintenance of posture  Respiration * Diaphragm and intercostals contractions  Communication."— Presentation transcript:


2 Muscular System Functions  Body movement (Locomotion)  Maintenance of posture  Respiration * Diaphragm and intercostals contractions  Communication (Verbal and Facial)  Constriction of organs and vessels  Heart beat  Production of body heat (Thermogenesis)

3 Typical cellsMuscle cell=fiber Plasma membraneSarcolemma CytoplasmSarcoplasm Endoplasmic reticulum Sarcoplasmic reticulum (SR) Many mitochondria Multiple nuclei

4 Muscle cell structures not found in other cells  Myofibrils: bundles of very fine fibers  Thick and thin myofilaments: very fine fibers that make up myofibrils  Sarcomere: segment of myofibril between two Z lines; contractile unit  T tubules: transmit electrical impulses through cell


6 Myofilaments  4 protein molecules that make up myofilaments: Myosin, actin, tropomyosin, troponin  Thin filaments: actin, tropomyosin, troponin  Thick filaments: mostly myosin

7 Properties of Muscle Excitability: Capacity of muscle to respond to a stimulus Contractility: Ability of a muscle to shorten and generate pulling force Extensibility: Ability stretches when pulled Elasticity: Ability to return to original shape and length after contraction or extension

8 Muscle structure Connective Tissue Sheaths Connective Tissue (CT) of a Muscle Epimysium: Dense regular CT surrounding entire muscle * Separates muscle from surrounding tissues and organs Perimysium: Collagen and elastic fibers surrounding a group of muscle fibers called a fascicle * Contains blood vessels and nerves Endomysium: Loose CT that surrounds individual muscle fibers * Also contains blood vessels and nerves * Collagen fibers of all 3 layers come together at each end of muscle to form a tendon or aponeurosis.


10 Motor neurons * Stimulate muscle fibers to contract * Neuron axons branch so that each muscle fiber (muscle cell) is innervated * Form a neuromuscular junction Capillary beds surround muscle fibers * Muscles require large amount of energy * Extensive vascular network delivers necessary oxygen and nutrients and carries away metabolic waste produced by muscle fibers

11 Energy for Muscle Contractions * ATP: adenosine triphosphate * CP: creatine phosphate Glucose & Oxygen * Glucose stored in form of glycogen in muscle * Excess oxygen molecules in sarcoplasm bound to myoglobin

12 Anaerobic respiration  Allows body to avoid use of oxygen in short term  Produces lactic acid  Accumulation of lactic acid in muscles causes burning sensation

13 Types of Muscle Skeletal * Attached to bones * Makes up 40% of body weight (Women’s skeletal muscle makes up 36% of their body mass, Men’s skeletal muscle makes up 42% of their body mass) * Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement * Voluntary in action; controlled by somatic motor neurons Smooth * In the walls of hollow organs, blood vessels, eye, glands, uterus, skin * Functions: propel urine, mix food in digestive tract, regulating blood flow * Controlled involuntarily by endocrine and autonomic nervous systems Cardiac * Heart: major source of movement of blood

14 Basic Features of a Skeletal Muscle Muscle attachments * Most skeletal muscles run from one bone to another * One bone will move – other bone remains fixed * Origin – less movable attachment * Insertion – more movable attachment * Muscles attach to origins and insertions by connective tissue Fleshy attachments – connective tissue fibers are short Indirect attachments – connective tissue forms a tendon

15 Skeletal Muscle Structure * Composed of muscle cells (fibers), connective tissue, blood vessels, nerves * Fibers are long, cylindrical, and multinucleated * Tend to be smaller diameter in small muscles and larger in large muscles. 1 mm - 4 cm in length * Striated appearance * Nuclei are peripherally located

16 Muscle Fiber Anatomy Sarcolemma - cell membrane * Surrounds the Sarcoplasm (cytoplasm of fiber) * Punctuated by openings called the transverse tubules (T-tubules) Myofibrils -cylindrical structures within muscle fiber * Are bundles of protein filaments (=myofilaments) * Two types of myofilaments 1. Actin filaments (thin filaments) 2. Myosin filaments (thick filaments) – When myofibril shortens, muscle shortens (contracts)

17 Sarcoplasmic Reticulum (SR)  SR is an elaborate, smooth endoplasmic reticulum  Runs longitudinally and surrounds each myofibril  SR stores Ca ++ when muscle not contracting  When stimulated, calcium released into sarcoplasm  SR membrane has Ca ++ pumps that function to pump Ca ++ out of the sarcoplasm back into the SR after contraction

18 Smooth Muscle * Cells are not striated * Fibers smaller than those in skeletal muscle * Spindle-shaped; single, central nucleus * More actin than myosin * No sarcomeres * Not arranged as symmetrically as in skeletal muscle, thus no striations.

19 Smooth Muscle Grouped into sheets in walls of hollow organs Longitudinal layer: muscle fibers run parallel to organ’s long axis Circular layer: muscle fibers run around circumference of the organ Both layers participate in peristalsis

20 Cardiac Muscle  Found only in heart where it forms a thick layer called the myocardium  Striated fibers that branch  Each cell usually has one centrally-located nucleus  Fibers joined by intercalated disks

21 Disorders of Muscle Tissue * Muscle Fatigue * Lack of oxygen causes ATP deficit * Lactic acid builds up from anaerobic respiration * Muscle Atrophy * a decrease in the mass of the muscle * Weakening and shrinking of a muscle * May be caused * Immobilization * Loss of neural stimulation

22 Disorders of Muscle Tissue * Muscle Hypertrophy * Enlargement of a muscle * More capillaries * More mitochondria * Caused by * Strenuous exercise * Steroid hormones * Muscle Tonus * Tightness of a muscle * Some fibers always contracted

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