Muscle Contraction

• Synapse – The site of connection between a neuron and a cell.

• Neurotransmitter – A chemical released at the neuron’s synapse that communicates with the cell

• Motor Neuron – Neuron that controls effectors (such as skeletal muscle movement)

• Neuromuscular Junction – Synapse where a motor neuron and a muscle fiber meet

• Synaptic Cleft – Space that separates the neuron and the muscle fiber

Neuromuscular Junction

• An action potential is conducted down a motor neuron

STEP 1

• The motor neuron terminal releases the neurotransmitter acetylcholine (ACh) into synaptic cleft

STEP 2

• ACh binds to ACh receptors on the sarcolemma.

STEP 3

• The sarcolemma is stimulated which sends an action potential throughout the sarcolemma and deep into the muscle fiber through T-Tubules

Step 4

• The action potential reaches the sarcoplasmic reticulum, which opens calcium channels

Step 5

• Calcium ions diffuse from the sarcoplasmic reticulum into the sarcoplasm where they bind with troponin molecules

Step 6

• Tropomyosin molecules move and expose specific binding sites for the myosin heads on actin

Step 7

• Actin and Myosin link, forming cross-bridges

Step 8

• POWER STROKE!!!• In other words the myosin heads use ATP to

pull the thin filaments towards the center of the sarcomere by cocking their heads

Step 9

• When sarcomeres shorten, the thick and thin filaments do not change length, rather the thin filament slides past the thick filament.

Sliding Filament Model

• If contraction is to continue, ADP and P are released from myosin heads

Step 10

• New ATP binds to myosin head which releases the linkage between myosin and actin

Step 11

• Actin and Myosin form cross bridge once again• Power Stroke• Thin filament slides past thick filament• ADP and P released

Step 12

• To relax, the neuron releases acetylcholinesterase, an enzyme that breaks down ACh

Step 13

• Action potential down the sarcolemma is eliminated

Step 14

• Calcium molecules are released from troponin and are transported back into the sarcoplasmic reticulum

Step 15

• Troponin and Tropomyosin molecules inhibit the myosin heads from attaching to actin

Step 16

• Muscle is relaxed, yet ready to be stimulated again

Step 17