Muscle II Flashcards
Explain the sliding filament model.
it is the process by which muscles contract. The Z-lines are pulled closer together when the head groups of the thick filaments attach to the thin filaments and pull them over themselves.
Is the sliding filament model synchronous for all fibers in a muscle? Explain why or why not.
No; At a given time, the head groups are all at different stages of the cycling process when the muscle is contracting. If they all worked at the same time, it would be hard to anything.
When the sarcomere contracts, are thick and thin filaments changing length?
No- only their placement is changing to shorten the sarcomere and therefore the myofibril.
What energy source drives muscle contraction?
The hydrolysis of ATP.
The pulling of thin filaments over thick is called the […] cycle.
Cross-bridge.
Describe the 5 steps of the cross-bridge cycle.
- The myosin head group hydrolyzes ATP and are then associated with ADP + Pi, which gives it a high affinity for actin fibers.
- Myosin binds to actin, which causes a conformational change to the headgroup that causes the Pi to come off.
- The ADP is removed. This triggers another conformational change which allows for the power stroke that pulls the thin filament over the thick filament.
- The headgroup binds another ATP, causing the headgroup to detach from the actin filaments.
- The ATP is hydrolyzed, which allows the headgroup to reposition itself and for the cycle to restart.
How does voluntary muscle contraction get initiated?
Neurons from the brain activate motor neurons in the spinal cord, which are then the neurons whose axons that extend into the muscle fibers to communicate with them.
What is a motor unit?
A single motor neuron and all the motor fibers it innervates.
Each motor neuron can synapse with [one/many] muscle fibers.
Many
Each muscle fiber can be associated with [one/many] motor neurons.
One.
How does the number of fibers innervated by a single motor neurons vary?
In certain parts of the body, like the eyes, a single motor neuron can innervate around 10 fibers, while in other parts of the body, like the hand, it can innervate around 100.
What does the the number of fibers innervated by a single motor neuron say about the function of that part of the group?
Small number = small muscles with fine, precise movements. Large number = large muscles that need to generate large, imprecise force.
How do the synapses in muscle fibers compare to those in the brain?
They are much larger than those in the brain.
What is the muscle synapse called?
The neuromuscular junction.
What type of neurotransmitter is released at the neuromuscular junction?
Acetylcholine (ACh)
