Sacromere: segment of myofibril between 2 z lines. Contains ½ of 2 I bands and a central A band. ZIAHAIZ: microstructure of muscle. I Band: only thin bands of actin (contains no myosin) Z Line: perpendicular to myofibril holds the actin together. A Band: thick myosin (appear dark under the microscope) H Zone: within the A band this part ‘shrinks’ during contraction and ultimately disappears

Sliding filament

Nerve and Blood Supply Normal activity of skeletal muscle is totally dependent on its nerve and blood supply Each skeletal muscle fiber is controlled by a nerve ending Contracting muscle fibers use huge amounts of energy which requires a continuous supply of oxygen and nutrients In general, each muscle is served by an artery and one or more veins

Neuromuscular Junction: area of contraction between the terminal end of a motor neuron and the sarcolemma of a skeletal muscle.

Resting Membrane Potential (RMP) – difference in charge across the membrane

Action Potential- when nerve cell is stimulated, its RMP is changed. stimulus

Fiber at rest: Ca 2+ ions, stored in sarcoplasmic reticulum Stimulus- causes action potential, which increases the sarcoplasmic reticulum permeability to Ca 2+ ions

Skeletal Muscle Actions origin – immovable end insertion – movable end prime mover (agonist) – primarily responsible for movement synergists – assist prime mover antagonist – resist prime mover’s action and cause movement in the opposite direction

Microscopic structure of muscle Muscle Fiber – single cell of skeletal muscle tissue (can be very long.5m in thigh. Sarcolemma – plasma membrane of the fiber. Sarcoplasm – cytoplasm of the fiber Sarcoplasmic reticulum – functions in the storage of calcium. Needed for muscle contraction.

Structure continued Transverse Tubule – connects with the sarcolemma to help in the calcium transport mechanism of muscle contraction. Myofibrils – small units of a single muscle fiber. Thick filaments: composed of myosin Thin filaments: actin, troponin, topomysin

The Motor Unit Each muscle is served by at least one motor nerve which contains hundreds of motor neuron axons As a nerve enters a muscle it branches into a number of axonal terminals, each of which forms a neuromuscular junction with a single nerve fiber A motor neuron and all the muscle fibers it supplies is called a motor unit

The Motor Unit When a motor neuron transmits an electrical impulse, all the muscle fibers that it innervates respond by contracting The average number of muscle fibers per unit is 150, but it ranges from 4 to several hundred

The Motor Unit Muscles that exert very fine control have small motor units (eyes, fingers) Large muscles of locomotion and weight bearing have large motor units and as a consequence have less precise control

The Motor Unit The muscle fibers in a unit are not clustered together but rather are spread throughout the entire muscle Stimulation of a single unit causes a weak contraction of the entire muscle This allows control of the intensity of the contraction

Smooth Muscles Smooth muscle lacks the courser connective tissue seen in skeletal muscle Small amounts of endomysium is found between smooth muscle fibers