muscle contraction. microscopic anatomy sarcolemma= plasma membrane of the muscle cell filled with...
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Muscle Contraction
Microscopic Anatomy• Sarcolemma= plasma membrane of the muscle cell• Filled with myofibrils (look like tubes)
• Sarcoplasmic Reticulum= organelle that holds Calcium ions
Myofibrils
• Are made up of units called sarcomeres. (from Z to Z)
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
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
Relaxed muscle shows H zone (bare zone)
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.
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
Myosin Heads Move..attach to actin and move again….
Figure 11.13
2- Muscle contraction: Cell events
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
• The neurotransmitter for skeletal muscles is always acetylcholine
• The receptors on the muscle fiber are cholinergic receptors
2- The Mechanism of Force Generation in Muscle
Figure 12.7