1. Banding pattern Banding pattern seen in the electron microscope Banding pattern seen in the polarizing microscope

2. Light bands: I bands (I-LIGHT).Thin filaments only Dark bands: A bands (A-DARK).overlapping thick and thin filaments. Z line(Z disc) : dark line in the middle of an I- band.

3. H-zone : a lighter, central region in the middle of a dark A- band. Only thick filaments. Sarcomere : runs from Z-line to Z-line (functional contractile unit)

4. Sliding filament hypothesis of contraction Nerve impulses carried from brain/spinal cord to muscle by the axon of a motor neuron Axon meets muscle fiber at the neuromuscular junction(myoneural junction) Axon releases a chemical neurotransmitter called acetrylcholine, which binds to sarcolemma. A nerve impulse is generated in sarcolemma and it passes down the t-tubules. As a result the sarcoplasmic reticulum releases Ca++ ions

5. MUSCLE CELL OR FIBER

6. Sliding filament hypothesis of contraction Ca++ ions bind to thin filament This helps thick filament attach to the thin filament As a result thin filament is drawn further into A band. Myofilaments slides over one another; sarcomere shortens; muscle contracts. When nerve impulse stops,Ca++ returns to the sarcoplasmic reticulum and the myofilaments slide back to their resting state.