Muscle Tissue Anatomy & Physiology PDF

Muscle Tissue Function of Muscle Tissue  Movement (Locomotion)  Skeletal muscle - attached to skeleton  Moves body by moving the bones  Smooth muscle – squeezes fluids and other substances through hollow organs  Maintenance of posture – enables th...

Muscle Tissue Function of Muscle Tissue  Movement (Locomotion)  Skeletal muscle - attached to skeleton  Moves body by moving the bones  Smooth muscle – squeezes fluids and other substances through hollow organs  Maintenance of posture – enables the body to remain sitting or standing  Respiration :Diaphragm and intercostals contractions  Communication (Verbal and Facial)  Joint stabilization  Heat generation  Muscle contractions produce heat (shivering)  Helps maintain normal body temperature (Thermogenesis) Special functional characteristics of muscle  Contractility  ability of a muscle to be shorten and generate pulling force  Excitability (irritability)  capacity of muscle to respond to a stimulus  nerve fibers cause electrical impulse to travel  Extensibility  muscle can be stretched back to its original length  Elasticity  ability of muscle to recoil to original resting length after stretched  Types of Muscle Tissue  Skeletal muscle (40% of body weight, attaches to bone, skin or fascia, cells are long, cylindrical with obvious striations, striated with light & dark bands visible with scope, fibers= multinucleate cells (embryonic cells fuse), voluntary control of contraction & relaxation)  Cardiac muscle (only in the wall of the heart, its function is to pump blood (involuntary control), cells are short, branched and striated in appearance, cells attached to other cardiac muscle cells at intercalated disks, one nucleus per cell)  Smooth muscle (attached to hair follicles in skin, in walls of hollow organs -- blood vessels & GI, cells are short, spindle- shaped and nonstriated in appearance, one nucleus per cell, involuntary)  Anatomy of skeletal muscles Epimysium Bone Epimysium Perimysium Tendon Endomysium Muscle fiber in middle of a fascicle (b) Blood vessel Fascicle (wrapped by perimysium) Endomysium (between individual muscle fibers) Perimysium Fascicle Muscle fiber (a)  Connective tissue sheaths of skeletal muscle:  Epimysium: dense regular connective tissue surrounding entire muscle  Perimysium: fibrous connective tissue surrounding fascicles (groups of muscle fibers)  Endomysium: fine areolar connective tissue surrounding each muscle fiber  Microscopic and Functional Anatomy of Skeletal Muscle  The skeletal muscle fiber  Fibers are long and cylindrical  Each cell formed by fusion of embryonic cells  Cells are multinucleate  Nuclei are peripherally located  Striations result from internal structure of myofibrils  Myofibrils  Long rods within cytoplasm  Make up 80% of the cytoplasm  Are a specialized contractile organelle found in muscle tissue  A long row of repeating segments called sarcomeres (functional unit of Skeletal MT) Muscle Fiber Sarcoplasmic Reticulum and T Tubules  Sarcoplasmic reticulum  A specialized smooth ER  Interconnecting tubules surround each myofibril  Some tubules form cross-channels called terminal cisternae  Cisternae occur in pairs on either side of a t-tubule  Contains calcium ions – released when muscle is stimulated to contract  Calcium ions diffuse through cytoplasm  Trigger the sliding filament mechanism  T (transverse) tubules are invaginations of the sarcolemma into the center of the cell  filled with extracellular fluid  carry muscle action potentials down into cell  Sarcolemma = muscle cell membrane  Sarcoplasm filled with myofibrils & myoglobin (red-colored, oxygen-binding protein)  Mitochondria lie in rows throughout the cell  near the muscle proteins that use ATP during contraction Sarcoplasmic Reticulum and T Tubules Sarcomere  Basic unit of contraction of skeletal muscle  Z disc (Z line) – boundaries of each sarcomere  Thin (actin) filaments – extend from Z disc toward the center of the sarcomere  Thick (myosin) filaments – located in the center of the sarcomere  Overlap inner ends of the thin filaments  Contain ATPase enzymes  A bands – full length of the thick filament  Includes inner end of thin filaments  H zone – center part of A band where no thin filaments occur.  M line – in center of H zone  Contains tiny rods that hold thick filaments together  I band – region with only thin filaments  Lies within two adjacent sarcomeres Sarcomere The Proteins of Muscle  Myofibrils are built of 3 kinds of protein  contractile proteins  myosin and actin  regulatory proteins which turn contraction on & off  troponin and tropomyosin  structural proteins which provide proper alignment, elasticity and extensibility  titin, myomesin, nebulin and dystrophin Actin and Myosin Filaments actin myosin Myosin (Thick) Filament Actin (Thin) Filament  1. Innervation of Skeletal Muscle (Excitation)  Each skeletal muscle is supplied by a nerve, artery and two veins.  Each motor neuron supplies multiple muscle cells (neuromuscular junction NMJ)  Neuromuscular junction is the point where nerve ending and muscle fiber meet  Each muscle cell is supplied by one motor neuron terminal branch and is in contact with one or two capillaries.  nerve fibers & capillaries are found in the endomysium between individual cells Biology 100 motor neurons Human Biology spinal cord neuromuscular junctions Motor Unit muscle fibers muscle bundle  2. Events Occurring After a Nerve Signal (ECC)  Arrival of nerve impulse at nerve terminal causes release of ACh from synaptic vesicles  ACh binds to receptors on muscle motor end plate opening the gated ion channels so that Na+ can rush into the muscle cell  Inside of muscle cell becomes more positive, triggering a muscle action potential that travels over sarcolemma and down the transverse tubules (T-tubules)  The release of Ca+2 from the SR into the sarcoplasm is triggered and the muscle cell will shorten & generate force  Ca+2 binds to troponin & causes troponin-tropomyosin complex to move & reveal myosin binding sites on actin--the contraction cycle begins  Acetylcholinesterase breaks down the ACh attached to the receptors on the motor end plate so the muscle action potential will cease and the muscle cell will relax. Stimulation of Skeletal Muscle EM of Myofibrils  3. Contraction Cycle  Repeating sequence of events that cause the thick & thin filaments to move past each other.  4 steps to contraction cycle  ATP hydrolysis. (ATP released P & ADP & energy) and myosin heads are activated by ATP  Attachment of activated heads of myosin to actin to form cross bridges & pull.  Thin filaments slide past the thick filaments (power stroke)  ATP binds to myosin head and detachment of myosin from actin  Cycle keeps repeating as long as there is ATP available & high Ca+2 level near thin filament 22  Contraction Cycle Steps  Notice how the myosin head attaches and pulls on the thin filament with the energy released from ATP Contraction proceeds as follows:  The arrival of a nerve impulse to the neuromuscular junction ------- depolarization of the sarcolemma of muscle fiber.  Depolarization is transmitted ------- the T- tubules ------- into the depth of the muscle fiber.  It stimulates the sER------ release the Ca++ into the sarcoplasm.  Ca++ facilitates ------ the sliding of the actin filaments over the myosin.  4. Relaxation  Acetylcholinesterase (AChE) breaks down ACh within the synaptic cleft  Muscle action potential ceases  Ca+2 release channels close  Active transport pumps Ca+2 back into storage in the sarcoplasmic reticulum  Calcium-binding protein (calsequestrin) helps hold Ca+2 in SR (Ca+2 concentration 10,000 times higher than in cytosol)  Tropomyosin-troponin complex recovers binding site on the actin Tendon ligament Regular dense fibrous Irregular dense C.T fibrous C.T Connect muscle to Connect bone to bone bone Transmit muscle Hold structures strength to bone together (stable) (movement) Tear or stretch in it Tear or stretch in it called (Strain) called (Sprain)