- action potential speed is increased by myelination
- action potential speed is modulated by fiber diameter

Michigan State University

Action potentials are changes in membrane potential that cause cells to become depolarized.  A single action potential only involves a small portion of the total cell membrane.  However, this signal can be propagated through the entire membrane as they do not diminish in strength over distance.  This makes action potentials reliable for long-distance signals.  

Action Potentials

Sherwood, L. (2010). Human Physiology: From Cells to Systems (7th ed.). Pacific Grove (Calif.): Brooks/Cole.

Human Physiology: From Cells to Systems (7th ed.)

- action potentials are conducted through nerve fibers
- action potentials are one-directional
- action potentials are all-or-nothing
- action potential signals are coded by frequency 

Properties of Action Potentials

- membrane potential rapidly reverses in action potentials
- changes in membrane permeability and ion movement lead to action potentials
- Na+-K+ pump restores the concentration gradient that was disrupted by action potentials
- the axon hillock propagates action potentials to axon terminals

Initiating an Action Potential

A specific neurotoxin is discovered that alters nerve cell function. When a signal is initiated at one end of a very long nerve cell, the signal's strength significantly decreases as it travels towards the other end. Based on this observation, what is the most likely functional consequence for the organism?

A nerve cell must transmit a signal from the spinal cord to a muscle in the foot, a significant distance. For the signal to arrive at the muscle with the same strength it had when it started, which of the following mechanisms is essential?

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