What is the primary feature of electrically excitable cells like muscle fibers and neurons?

Electrically excitable cells, such as muscle fibers and neurons, are characterized primarily by their ability to exhibit voltage changes in response to stimulation. This property is crucial for their function in both transmitting signals and generating contractions. When these cells are stimulated, ion channels in their plasma membranes open, allowing ions—especially sodium and potassium—to flow in and out, leading to depolarization and repolarization phases that constitute an action potential. This rapid change in membrane potential is fundamental for the function of neurons in transmitting electrical signals and for muscle fibers to initiate contraction.

The other aspects presented do not accurately reflect the nature of electrically excitable cells. For instance, having a high concentration of potassium outside the cell would conflict with the standard potassium gradient necessary for action potential generation. Also, while myelinated fibers increase signal transmission efficiency, unmyelinated fibers can also transmit signals; hence, signal transmission is not exclusively restricted to myelinated fibers. Lastly, neurotransmitters play a significant role in the communication between neurons, influencing their excitability and the generation of action potentials, making the claim that they are not influenced by neurotransmitters inaccurate. Thus, the primary feature of these excitable cells is indeed their ability to exhibit voltage changes in response to