The Muscular System Produce movement or tension via shortening (contraction) Generate heat - body temp 3 types: Skeletal - moves bone, voluntary Smooth Cardiac Essential function is to shorten, so they are responsible for all types of body movement. Muscles move bones together. AND produce tension: keep things static. Ex. Posture, blood vessel diameter constant despite changes in pressure. Tension - forces equal and opposite. Muscle makes up almost half of our body mass. Movement - gross motor, fine motor, internal organs of urinary and digestive, circulatory systems. Posture - constantly maintaining balance agst gravity. Including when seated. Wheelchairs have belts and braces to help patients w/out muscle control. Stabilize joints - esp important in areas where bones do not fit together well or are not anchored together well. Ex. Shoulder. Generate heat to maintain body temp. Mostly done by skeletal muscle, as that is the majority of muscle within the body.. 3/4 of heat is from muscle. Muscle cells are elongated (muscle cell = muscle fiber) Elongated fibers true for skeletal and smooth muscle, not cardiac. Contraction of muscles is due to the movement of microfilaments, In all 3 types of muscle, contraction based on sliding microfilaments terminology Prefixes mys, myo refers to muscle Prefix sarco refers to flesh Ex. Sarcoplasm refers to cytoplasm of a muscle cell.

Skeletal Muscle Characteristics Voluntary Most are attached by tendons to bones Synergistic: groups work together Antagonistic: groups oppose each other Origin, insertion points on opposite sides of joints Cells are multinucleate, striated Skeletal muscle makes up at least 40% of body mass. Tendons are tough connective tissue (collagen fibers). Withstand stress applied by muscle fibers; can rub agst rough bone without tearing; smaller than muscle, so more tendons can connect around joint. Muscles move bones, usly attached at origin to stable bone (not much movement) and at insertion (bone that moves closer). Muscles go across joints. When a muscle contracts its insertion is pulled towards its origin. Multinucleate (fusion), some nearly 1 foot long. Striated - due to arrangement of filaments within cells, overlapping of fibers = band. Voluntary - respond to conscious control, but also contract “automatically” in reflexes. Structure - responsible for power of muscles, prevents tearing of fairly delicate cells.

Muscle Structure Whole muscle Fascicles: bundles of cells, CT covering on each one Muscle cells = fibers Whole muscle - various lengths: 1mm to 30 cm (quadricep). Every Ind’l cell extends entire length. Surrounded by tough connective tissue (CT) Epimysium - tougher membrane, more collagen fibers, blends into a connective tissue attachment. I.e., tendon. Sites of muscle attachment Bones Cartilages Connective tissue coverings skin (smiling) fascicles; more fibrous membrane, tougher. = Perimysium. From dozens to 1000’s of cells per fascicle. cell = muscle fiber. W/ Endomysium - fairly delicate covering Tendon – cord-like structure Aponeuroses – sheet-like structure Figure 6.3

Microscopic Anatomy of Skeletal Muscle Muscle cells multinucleate, striated –visible banding Myofibril - bundles of filaments 4. Myofibril - clump/cylinder of actin and myosin filaments. Sarcolemma - with channels that penetrate into cell, between myofibrils. Important in communication Sarcoplasmic reticulum - (smooth ER) wrapped around each myofibril, ; filled w/ Ca++ ions, used in contraction of myofibrils. Figure 6.3a

Skeletal Muscle Contractile Unit Sarcomere Actin and myosin Z Lines: attachment points for sarcomeres 5. Sarcomere - basic unit of contraction. Extends from one Z to next Z line. All sarcomeres of a cell shorten together. Up to 100K. Each works the same way. Sum is muscle shortening. Actin - thinner filaments attached to Z line Myosin - thicker filaments interspersed btw actin. Cross section shows distribution pattern: each myosin surrounded by actins, and vice versa. At rest, there is a bare zone that lacks actin filaments Sarcoplasmic reticulum (SR) – for storage of calcium. Extends throughout filaments, network of pipes that releases and takes up Ca++ as needed. Part of contraction mechanism. Figure 6.5

Nerve Stimulus to Muscles Skeletal muscles must be stimulated by a nerve to contract Motor unit One neuron Muscle cells stimulated by that neuron If muscle cells not stimulated, they will atrophy, or waste away. Eventually replaced by connective tissue, which is irreversible once complete. Use it or lose it. Problem for sedentary patients, couch potatoes, immobilized body parts. Figure 6.4a

Nerve Stimulus to Muscles Neuromuscular junctions – association site of nerve and muscle Muscle fiber and neuron do not touch .. Synaptic cleft - gap Neurotransmitter for skeletal muscle is acetylcholine Neurotransmitter attaches to receptors on the sarcolemma Sarcolemma becomes permeable to sodium (Na+) Sodium rushing into the cell generates an action potential Once started, muscle contraction cannot be stopped Figure 6.5b

Nerve Activation of Muscle Cells Acetylcholine released from motor neuron Electrical impulse transmitted along T tubules Calcium released from sarcoplasmic reticulum Figure 6.6

Troponin, tropomyosin are bound to actin filament in relaxed muscle fiber, covering binding sites for myosin. When Ca++ is released from sarcoplasmic reticulum, Ca++ binds to troponin, thus altering its shape and making it shift position such that binding sites on actin are revealed to myosin heads. So myosin heads bind, bend, and release.

Calcium Initiates the Sliding Filament Mechanism Thick filaments: myosin Thin filaments: strands of actin molecules Contraction = formation of cross bridges between thin and thick filaments Calcium released from sarcoplasmic reticulum Calcium binds to troponin Troponin-tropomysin complex shifts position Myosin binding site exposed Myosin heads form cross-bridges with actin Actin filaments pulled toward center of sarcomere Figure 6.7

Mechanism of Muscle Contraction (cont.) Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament Myosin heads then bind to the next site of the thin filament This continued action causes a sliding of the myosin along the actin The result is that the muscle is shortened (contracted) Figure 6.8

Troponin, tropomyosin are bound to actin filament in relaxed muscle fiber, covering binding sites for myosin. When Ca++ is released from sarcoplasmic reticulum, Ca++ binds to troponin, thus altering its shape and making it shift position such that binding sites on actin are revealed to myosin heads. So myosin heads bind, bend, and release.

Muscle Relaxation Nerve activation ends, contraction ends Calcium pumped back into sarcoplasmic reticulum Calcium removed from troponin Myosin-binding site covered No calcium = no cross-bridges Note that cycle ends when ATP binds to myosin and myosin attachment to actin is released. Rigor mortis = stiffness of muscles in a dead person, usly sets in about 4 hours after death.Why? Ca++ leaks out of sarcoplasmic reticulum (membrane falls apart without constant effort to maintain it. Ca++ interacts with troponin-tropomyosin complex and reveals binding sites on actin filaments. Myosin, already charged with ATP, binds to actin and will contract. But no more ATP available for binding to myosin again and allowing relaxation. So, muscles stay contracted and rigid.

Energy Required for Muscle Activity Principle source of energy: ATP ATP replenished by: Creatine phosphate Stored glycogen Aerobic metabolism of glucose, fatty acids, and other high-energy molecules Anaerobic use of glucose Bonds of ATP are broken to release energy Only 10 seconds worth of ATP is stored by muscles CP supplies are exhausted in about 30 seconds No oxygen needed for CP to work. Direct phosphorylation Muscle cells contain creatine phosphate (CP) CP is a high-energy molecule CP regenerates ATP Aerobic respiration - Slower reaction than direct phosphorylation. Generates more ATP per glucose. Can use many dift molcs in this pathway, including fatty acids, amino acids from proteins, sugars. So, muscles must switch to this after ATP runs out, 20-30 sec. Anaerobic resp. - Anaerobic glycolysis Glucose is broken down to pyruvic acid to produce some ATP Pyruvic acid is converted to lactic acid Oxygen not needed. Not very efficient. Little of the energy of glucose is captured as ATP, usable by the cells. This reaction is fast. Runs out of glu in about 30-60 sec. Huge amounts of glucose are needed Lactic acid produces muscle fatigue. Stretch after exercise to help metabolize lactic acid. Usly gone w/in minutes.

Aerobic metabolism 3 stages to convert energy of glucose to ATP High-energy electrons carried by NADH High-energy electrons carried by NADH GLYCOLYSIS ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS GLYCOLYSIS KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Glucose Pyruvic acid KREBS CYCLE Glucose Pyruvic acid See Ch 3 Fig 24. Note step of O2 use in ET Chain. CO2 production Cytoplasmic fluid Cytoplasmic fluid Mitochondrion Mitochondrion

Muscle Fatigue and Oxygen Debt A fatigued muscle is unable to contract anaerobic metabolism produces lactic acid Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less Oxygen is required to get rid of lactic acid GLYCOLYSIS Ability to deliver O2 then affects athletic performance. So, some will have their own blood withdrawn several weeks before competition, then dope up with their own RBCs to increase oxygen capacity. Lance Armstrong - heart is able to pump about 5-7 times more blood per minute than typical person. Gets more O2 to muscles, allows him to push in endurance contests. 2 Pyruvic acid 2 Lactic acid Glucose

Contraction of a Skeletal Muscle Muscle fiber contraction is “all or none” Within a skeletal muscle, not all fibers may be stimulated during the same interval Graded responses due to: - number of muscle cells in each motor unit - number of muscle cells stimulated - frequency of muscle stimulation Muscle force depends upon the number of fibers stimulated. Motor unit = nueron + many muscle firbers, 10 to 1000s. Fine moter control vs. gross movements with strength. Degree of nerve activation influences force Muscles can continue to contract unless they run out of energy The more fibers contracting, the more tension created. Ie stronger.

Muscle Contraction: Myogram Latent period Contraction Relaxation Summation vs. tetanus Diagram represents what happens during contraction of sgl fiber. Motor unit. Latent period while Ca++ floods out of sarcoplasmic reticulum. Contraction as sarcomeres shorten, relaxation. Filiaments slide back to original position. Summation - if stimulated again before full relaxation, get more force from muscle cell. Tetantic - if repeatedly stimulated, no relaxation at all. Muscle will likely fatigue. Figure 6.10

Types of Muscle Contractions Isotonic contractions Myofilaments slide past each other muscle shortens Isometric contractions Tension in muscles muscle is unable to shorten Some fibers are contracted even in a relaxed muscle Different fibers contract at different times to provide muscle tone The process of stimulating various fibers is under involuntary control Type of exercise causes different results in muscle tissue:endurance training vs bodybuilding Origin vs insertion cn be dept on which movement is being done. Ex. Raise hand vs doing chinups on a bar. Results of increased muscle use Increase in muscle size Increase in muscle strength Increase in muscle efficiency Muscle becomes more fatigue resistant

Muscle Activity Slow twitch vs. fast twitch fibers Slow twitch: endurance, long duration contraction, contain myoglobin Jogging, swimming, biking Fast twitch: strength, white muscle, short duration contraction Sprinting, weight lifting, tennis Every muscle is a combination of both types. Athletes good at certain types of activity can have predominantly one form or another. Slow twitch - dark meat of the turkey. Legs. These cells rely on aerobic metabolism, have lots of mitochondria and use Oxygen readily. So, plenty of blood vessels, myoglobin = dark, reddish color. Fast twitch - able to break down ATP more quickly, hence, fast twitch. short duration contractions, but very forceful. Not so aerobic, able to get by for brief periods without O2. Little myoglobin, fewer blood vessels. = white meat muscle.

Exercise Training Strength training Resistance training Short, intense Builds more fast-twitch myofibrils Aerobic training Builds endurance Increases blood supply to muscle cells Target heart rate at least 20 minutes, three times a week Strength training - challenge muscles with short, intense workload. Builds more fast tw. Myofibrils, but NOT more muscle cells. Muscles can bulk up (but not necessarily) as myofibrils increase in number. Aerobic training - endurance. So number of mito increases, number of blood vessels increases, amount of myoglobin (which stores O2 in cells) increases, but not much increase in muscle mass.

Features of Cardiac and Smooth Muscles Activation of cardiac and smooth muscles Involuntary Specialized adaptations Speed and sustainability of contractions Arrangement of myosin and actin filaments Involuntary: no conscious control. Both types will contract without nervous stimulus. Intrinsic rhythm of contraction. They DO respond to autonomic nervous system. Capacity to do this is due to gap junctions, which allow passage of electrical stimulation directly from cell to cell. Cardiac cells w’ some faster ones = pacemakers. Rest of cells follow. Intercalated discs at ends of short cells, w/ many gap junctions. So cells can stimulate each other, w/out neuron. Skeletal muscles require neuron. So, spinal cord injury will incapacitate skeletal muscle, but not smooth muscle. 2. Speed and sustainability - fastest - skeletal; med - cardiac; slowest - smooth. Each suited to its purpose. Smooth always partially contracted, as it moves slowly, doesn’t run out of ATP. Allows blood vessel diameter to be maintained at all times. Cardiac has periods of recovery which allow sustainability. 3. Filament arrangement - next pages

Smooth Muscle Characteristics Has no striations Spindle-shaped cells Single nucleus Involuntary – no conscious control Found mainly in the walls of hollow organs No striations, b/c filaments are not parallel, but crisscross cytoplasm, attach to cell membrane at dift angles. Produces a lumpy slug when contracted. Cells contract more slowly than skeletal muscle cells. Can produce ATP at rate to support its contractions. Arranged in sheets in 2 directions around organs, w/ axis parallel and circumnavigating the organ. Diag. Allows pushing of substances along length of organ. Ex. Food thru digestive tract, and bowel movements to empty colon. Blood vessels, urinary system Figure 6.2a

Cardiac Muscle Characteristics Has striations Branched cell with a single nucleus Joined to another muscle cell at an intercalated disc Involuntary Muscle bundles wrapped around heart Striations reflect filament arrangement within cells. Intercalated disc enables close coordination, fast communication btw cells. Direct stimulation of adjacent cells, such that heart muscle will continue rhythmnic contractions without outside stimulus. Pacemaker cells at one position - contraction initiates here. Involuntary, keeps beating without thought. Can also respond to CNS and beat faster. Bundles wrapped around heart in a way that allows power of contraction to push blood thru chambers in a coordinated way. Figure 6.2b

Diseases and Disorders of the Muscular System Muscular dystrophy Tetanus Muscle cramps Pulled muscles Fasciitis Muscular dystrophy - lack of a protein, dystrophin, which limits leakage of Ca++ into muscle cells. Eventually damages, kills cells. So, loss of muscle fibers, including cardiac, death in 30s. No cure Tetanus - bacterial infection that produced toxin which constantly stimulates muscle. Max contraction = tetanus. Often associated w jaw muscles,” lockjaw”. Respiratory failure, fatigue. Muscle cramps - imbalance of ions, probably K+, when muscle is used. Reflex-mediated muscle contractions. Fix by massage, helping to move fluids around muscle. Rehydrate. Pulled muscles. Stretch a muscle too far, tear some of the fibersl. Bleeding, swelling, pain. Fasciitis - inflammation of connective tissue around muscle. Often in sole of foot, around heel. Slow to heal, as w/ ligamnets, tendons.

Superficial Muscles: Anterior Figure 6.21

Superficial Muscles: Posterior Figure 6.22

Body Movements Flexion Extension Rotation Flexion - decreases the angle of the joint. 2 bones closer together Extension - inc angle btw bones. More than 180 is hyperextension Rotation - movement around a bone’s axis. Page 113 in text Johnson 3rd ed. Figure 6.13a–c

Body Movements Abduction Adduction Circumduction Abduction - moving a part away from the midline. Includes spreading apart of fingers, toes. Adduction - moving TOWARD the midlinel. Circumduction - combo of several such that circle is described. Figure 6.13d