Filaments

Resting state

Electrical impulse (Action Potential) reaches axon terminal

Impulse opens Calcium Channels, rapid influx of Calcium into terminal

Vesicles with acetylcholine (Ach) bind to cell membrane & releases Ach into synaptic cleft

Vesicles with acetylcholine (Ach) bind to cell membrane & releases Ach into synaptic cleft

Ach

Ach binds to receptors on motor end plate

Ach receptors opens Na+ channels, causes an influx of sodium into muscle

Sodium influx triggers a muscle impulse (electrical signal) in all directions of muscle fiber.

Electrical impulse travels across Sarcolemma, down t-tubules, and across cisternae

Sarcolemma

Electrical impulse travels across Sarcolemma, down t-tubules, and across cisternae

Sarcoplasmic Reticulum releases Calcium into Sarcoplasm

Sarcoplasmic Reticulum

Ca2+ (Calcium) Triggers muscle contraction by binding to troponin

Tropomyosin moves and exposes actin filaments to cross bridges

Cross bridges bind to actin & pulls actin forward (ADP is released from cross bridge)

Cross bridges bind to actin & pulls actin forward (ADP is released from cross bridge)

Videos

• Breakdown of ATP

• Synapse Transmission

• Action Potential Across Sarcolemma

• Shortening Sarcomere

Relaxation• Calcium pumps return Calcium to Sarcoplasmic reticulum• Acetylcholinesterase clears ACh from synaptic cleft• ATP binds to cross bridge & myosin is released from actin *• ATPase converts ATP to ADP using energy to cock cross

bridge*• Tropomyosin cover actin filaments

• * Note: ATP is required for both muscle contraction & relaxation

Myofibrils

• Actin Filaments “thin”– Anchored to z-lines (filament proteins)– I bands (light color) = actin + z-lines

• Myosin Filaments “thick”– A-band (dark color) = Myosin filaments + overlapping Actin filaments– H-zone (slightly lighter) = Myosin filaments between overlapping actin

• Sarcomere

– Area between 2 z-lines– Functional unit of skeletal muscle– During contraction adjacent z-lines approach each other