Describe how an action potential occurs, including the role of ions and ion channels; why an action potential is considered an all-or-nothing event; why the negative after-potential occurs; and the importance of myelin during a saltatory conduction

Question

What will be an ideal response?

Answer 1

Answer will include that electrically charged molecules called ions are found inside and outside each neuron. When a neuron is inactive (in a resting potential), more of these "plus" charges exist outside the neuron and more "minus" charges exist inside the neuron. If the electrical charge rises to about -50 millivolts, the neuron will reach its threshold, or trigger point for firing. When a neuron reaches threshold, an action potential, or nerve impulse, sweeps down the axon at up to 200 miles per hour. The axon membrane is pierced by tiny tunnels or "holes," called ion channels, which pop open during the action potential. This allows sodium ions to rush into the axon first near the soma. then the "gates" of the ion channels open sequentially down the length of the axon. Each action potential is an all-or-nothing event, meaning a nerve impulse occurs completely or not at all. After each nerve impulse, the cell briefly dips below its resting level, and becomes less willing or ready to fire. This negative after-potential occurs because potassium ions flow out of the neuron while the membrane gates are open. The axons of some neurons are coated with a fatty layer called myelin. Small gaps in the myelin help nerve impulses move faster. Instead of passing down the entire length of the axon, the action potential leaps from gap to gap, a process called saltatory conduction. Without the added speed of saltatory action potentials, it would probably be impossible to brake in time to avoid many automobile accidents or hit a tennis serve.