1. Organization of Skeletal Muscles

2. 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

3. 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.

4. The Structure of a Skeletal Muscle Fiber

5. 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.

6. 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.

7. Sarcomere Structure

8. 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

9. Neuromuscular junction
Axon terminal
Synaptic cleft
Motor end plate

10. 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

11. 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

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

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