Compare and contrast the voltage-gated sodium and potassium channels introduced in Chapter 8, with the acetylcholine receptor/channel. What may be confusing to the beginning physiology student trying to understand the ion specificity of the acetylcholine receptor? What type of change in the cell is produced by ion movement through each type of channel?

Question

What will be an ideal response?

Answer 1

The voltage-gated sodium channel opens in response to threshold voltage and allows sodium to enter the cell, thereby depolarizing the membrane potential. The potassium channel is also opened by threshold voltage and allows potassium to exit the cell, repolarizing or hyperpolarizing the membrane potential. The acetylcholine receptor is a neurotransmitter receptor as well as an ion channel. Because the channel is opened by binding of a chemical, it is a chemically gated channel. This channel is permeable to both sodium and potassium; when the channel opens, sodium diffuses into the cell and potassium diffuses out. The inward positive charge is sufficient to depolarize the skeletal muscle to threshold. Students are often confused by the fact that more than one type of ion moves through the acetylcholine receptor channel, and that the muscle cell is able to depolarize to threshold despite the exit of potassium.