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: Ca2+ ions, stored in sarcoplasmic reticulum

Stimulus- causes action potential, which increases the sarcoplasmic reticulum permeability to Ca2+ 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 muscleMuscle Fiber – single cell of skeletal muscle

tissue (can be very long .5m in thigh.Sarcolemma – plasma membrane of the fiber.Sarcoplasm – cytoplasm of the fiberSarcoplasmic 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