Lab 6: Muscle Activation Flashcards
What are skeletal muscles controlled by?
Where are the cell bodies and were do axons project?
Skeletal muscles are controlled by somatic motor neurons. These neurons have their cell bodies in the ventral horn of the spinal cord, with a long single axon projecting in a peripheral nerve out to the skeletal muscle.
How many muscle fibers can a single motor neuron innervate?
Somatic motor neurons branch close to the muscle and innervate a number of muscle fibers to control them all at the same time.
How many motor neurons can each muscle fiber be innervated by?
Only one
Are somatic pathways excitatory or inhibitory?
Always excitatory
What is the neuromuscular junction?
The synapse of a somatic motor neuron onto a skeletal muscle fiber.
What are the 3 components of the neuromuscular junction?
What kind of receptors?
- Presynaptic axon terminal containing synaptic vesicles
- Synaptic cleft
- Postysynaptic membrane of the skeletal muscle fiber containing ionotropic, nicotinic AcH receptors
What is the acetylcholinesterase?
Where would you find it?
Present on the extracellular surface of the motor neuron to break down the AcH into acetyl and choline to limit the duration of its actions
How is an end plate potential generated?
Under normal conditions an end-plate potential reaches threshold and intiates a muscle action potential
When Ach binds to nAChR it triggers the influx of Na+ and K+ to depolarize the muscle fiber.
Describe excitation-contraction coupling.
- AP propogate along T-tubule system
- AP activates DHPR receptor which opens RyR in the sarcoplasmic reticulum
- Ca2+ is released into the cytoplasm
- Ca+ binds to toponin, allowing actin-myosin binding which leads to force production
- To end a contraction, Ca2+ must be removed by the Ca2+-ATPase pump
What determines the frequency and duration of an action potential?
The amplitude of the summed graded potentials determines the frequency and the duration of the summed activity determines the duration of time.
What is motor unit recruitment?
The number of activated motor units which influences the force of contraction
What is rate coding?
The rates at which activated motor units produce action potentials.
For stimulation intervals between 75-200 milliseconds why doesn’t the muscle fiber completely relax in between?
Ca2+ levels in the muscle do not have time to return to basline levels before the next action potential arrives.
When is peak force acheived?
When no more summation can occur because all crossbridge binding sites are occupied.
What is tetanic contraction?
What is unfused vs. fused tetanus?
Maximum tension is produced.
- unfused tetanus: when a tetanic contraction oscillates in force
- fused tetanus: maximum tension is maintained
