Date post: | 21-Jan-2016 |
Category: |
Documents |
Upload: | raymond-lindsey |
View: | 223 times |
Download: | 0 times |
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