Skeletal Muscle

Longest, striated, voluntary, responsible for overall body motility, contract readily & tires easily

Cardiac Muscle

Bulk of heart walls, striated, involuntary, contracts fairly steady rate

Smooth muscle

No striations, involuntary, slow sustained contractions, stomach and bladder

Muscle functions

Producing movement, maintaining posture and body position, stabilizing joints, generating heat, protection

Skeletal Muscle Gross Anatomy

Supplied with nerve ending, rich blood supply, need continuous delivery of oxygen, gives large amounts of waste

Endomysium 

Surrounds each muscle fiber

Surrounds a fascicle of muscle fibers

Surrounds the whole muscle

Long cylindreal cell, Multiple nuclei beneath the sarcolemma, sarcoplasm (contains glycosomes and myoglobin)

Each muscle fiber contains thousands, densely packed, contain sarcomeres, striations repeating series of dark a bands and light I bands

Lighter stripe in midsection of A band

Dark line, dissects each H Zone vertically

Darker area, Midline interruption of I band

Smallest contractile unit, functional unit of muscle fiber, region of myofibril between two successive z discs

Extend entire length of A Band, connected in middle of sarcomere, composed primarily of protein/myosin, tail and two heads, heads link thick and thin filaments together forming cross bridges

Extend across I band and partway into A Band, 2 discs anchor them, composed chiefly of protein, actin 

Help stiffen and stabilize actin, arranged end to end along actin, block myosin binding sites in relaxed fiber

Three polypeptide complex: inhibitory subunit binds to actin, binds tropomyosin and helps position it on actin, binds calcium

Composed of protein/titin, extends from z disc to thick filaments, runs within thick filament to M line, holds thick filaments in place, maintain organization of A band, helps muscle spring back into shape after stretched

Interconnecting tubules surrounding each myofibril, large number of mitochondria and glycogen granules, terminal cisterns, regulate intracellular levels of calcium

Form large channels, at junction of A-I bands, always appear in pairs

At each A-I band junction, continuations of the sarcolemma, protrudes deeply into muscle cell, greatly increase surface area, runs between paired terminal cisterns forming triads

Sliding Filament Model of Contraction

Relaxed muscle fiber

Thick and thin filaments overlap only at the ends of A band

Sliding Filament Model of Contraction

Muscle fibers stimulated

Myosin heads latch onto actin binding sites to begin sliding, cross bridge attachments formed and broken several times

Sliding Filament Model of Contraction

Occurs simultaneously in sarcomeres throughout cell

Muscle cells shorten, I band shortens, distance between successive z disc reduces, H zone disappears

Stimulated by nerve ending, generate an electrical current (AP), AP transmitted along sarcolemma, intracellular calcium levels rise briefly

Stimulates skeletal muscle cells, in brain or spinal cord

Region where motor neuron comes into close contact with skeletal muscle cell

Contain neurotransmitter, Ach

Part of the sarcolemma, helps for neurotransmitter junction, highly folded giving large surface area for ach receptors

Nerve impules reach end of axon, Ach released into synaptic cleft, Ach diffused across cleft, attaches Ach receptors to sarcolemma, ach binding triggers events causing an AP

Enzymes in synaptic cleft, breaks down Ach, prevents continued muscle contraction

Inside is negative relative to outer face, predominant extracellular: Sodium, predominant intracellular: potassium

Generation of AP across the sarcolemma

AP result of

Generation of end plate potential, depolarization, repolarization

Generation and propagation of AP, AP initiated, AP unstoppable, AP travels rapidly over entire sarcolemma

Sodium channels close, potassium channels open, potassium efflux rapidly restores resting polarity

Nerve impulses reaches axon terminal, voltage-gated calcium channels open, ach released into synaptic cleft, ap generated and sent, ap triggers release of calcium from SR, calcium binds to tropin changing its shape, contraction

Blocks myosin binding on actin, contraction ends, muscle fiber relaxes

Muscle cell is relaxed, active sites on actin blocked by tropomyosin, blockade removed when sufficient calcium is present

Rely on aerobic pathways

Rely on anaerobic pathways