Organization of Skeletal Muscles

Skeletal Muscle Fibers Sarcolemma (cell membrane) Sarcoplasm (muscle cell cytoplasm) Sarcoplasmic reticulum (modified ER) Stores calcium Myofibrils (made up of myofilaments) Actin or thin filament Myosin or tick filament

Skeletal muscle fibers Transverse tubule – it is the invagination of the sarcolemma. Terminal cisternae- it is the expanded terminal area of the sarcoplasmic reticulum Triad- formed by one T tubule plus one terminal cisternae on each side of it.

The Structure of a Skeletal Muscle Fiber

Skeletal muscle fibers Sarcomeres – it is the contractile unit of the muscle. From Z disc to Z disc. I band – formed by thin filaments only Z disc – in the middle of the I band. It anchors the thin filament and connects each myofibril to the next.

Skeletal muscle fibers A band- formed by thin and thick filaments that overlap. H band- light zone in the middle of the A band. M line – protein in the middle of the H band and holds the myosin filaments together.

Sarcomere Structure

Organization of the cell into muscles Aponeuroses are sheetlike dense connective tissue that connects muscle to each other or to bones Origin is usually immovable Insertion is usually movable

Neuromuscular junction Axon terminal Synaptic cleft Motor end plate

The synapse The axon terminal contain vesicles filled with neurotransmitter acetylcholine steps for the impulse conduction Impulse reaches the terminal Vesicles release ACh in the synapse ACh binds to the receptors on the sarcolemma Na and K channels open More Na comes in than K goes out Depolarization occurs

Organization of the cell into muscles Epimysium dense connective tissue that wraps the fascicle and the entire muscle Perimysium wraps several muscle fibers forming a bundle called fascicle Endomysium covers individual muscle fibers Tendons are cordlike dense connective tissue that connects muscles to each other or to bones

Smooth Muscle Cell No striations Dense bodies Intermediate filaments Actin and myosin Nerve Varicosities

Cardiac Muscle Cell T tubule orifice T tubule Sarcoplasmic reticulum Intercalated disc Z line (disc) M line I band A band