BME muscle stim and fatigue lab

What is an action potential

the rapid rise and fall of the membrane electrical potential.

What happens during an AP

1. stimulus reaches threshold voltage

2. rising phase: Na⁺ gated channels open = depolarization

3. Falling phase: K⁺ channels open = repolarization

What is the all or nothing principle

If a stimulus causes a depolarization that is above the membrane potential threshold, then a full action potential will occur. If the depolarization is sub-threshold, then no action potential occurs

Where does the all or nothing principle take place

muscles and neurons

What is the absolute refractory period

A brief period following the stimulation of a nerve cell or muscle fiber during which the nerve cell or muscle fiber remains completely unresponsive to a stimulus, no matter how strong the stimulus is.

What is the relative refractory period

A period of a few milliseconds following the absolute refractory period during which the excitation threshold is raised and a stronger-than-normal stimulus is required to initiate an action potential.

What happens when skeletal muscle is stimulated at less than 5 Hz

Intracellular [Ca2+] returns to normal levels between action potentials

What happens when skeletal muscle is stimulated at 5 - 15 Hz

[Ca2+] in the muscle only partially recovers before the next action potential occurs

What is tentanization

Stimulating a muscle cell before it has relaxed from previous stimulus.

What is fatigue

The stimulus is maintained but the tension of the muscle decreases

What is nervous fatigue

Nerve cannot maintain high frequency signals to muscle

What is metabolic fatigue

Shortage of substrates

• Accumulation of metabolites

• interferes with the release of calcium from the sarcoplasmic reticulum

• reduces sensitivity of actin and myosin to calcium