1. Muscle Contraction

2. Microscopic Anatomy Sarcolemma= plasma membrane of the muscle cell
Filled with myofibrils (look like tubes)
Sarcoplasmic Reticulum= organelle that holds Calcium ions

3. Myofibrils
Are made up of units called sarcomeres. (from Z to Z)

4. Myofibrils Composed of myofilaments: actin (thin) and myosin (thick).
I band= area with actin..thin bands protein
A band= area that contains actin and myosin bands alternating which is why they appear darker

5. I bands and A bands
Appear as light and dark striations…makes skeletal muscles look striated
H-zone= area where only myosin is located in relaxed muscle

6. Relaxed muscle shows H zone (bare zone)

7. Contraction
When nerve impulse reaches a muscle it triggers the sarcoplasmic reticulum to release large amounts of Ca 2+
Calcium binds to actin on regulatory proteins and causes those proteins to change shape and move revealing myosin binding sites.

8. Contraction continued
Myosin then binds to those sites on the actin.
The myosin pulls on the actin and pulls actin in toward the H-zone.
This happens multiple times until the muscle is fully contracted

9. Myosin Heads Move..attach to actin and move again….

12. 2- Muscle contraction: Cell events
Figure 11.13

13. Synaptic events The AP reaches the axonal bulb
Voltage-gated calcium channels open
The influx of Ca in the bulb activates enzymes the vesicles containing the neurotransmitter molecule dock and release the neurotransmitter in the synapse

14. The neurotransmitter for skeletal muscles is always acetylcholine
The receptors on the muscle fiber are cholinergic receptors

15. 2- The Mechanism of Force Generation in Muscle

16. Figure 12.7