The action potential changes the membrane potential from -70 mV (resting) to +30 mV and back again to the resting membrane potential. b. This results from a change in membrane permeability first to Na then to K due to the opening of what type of ion channels? Voltage gated channels 2. a. Where is the density of voltage-gated Na+ channels the greatest? Axon hillock b. What areas of the neuron generate signals that open these voltage-gated channels? Dendrites and the cell body c. Opening of these channels causes the membrane to epolarize. (voltage change). 3. a. If the membrane reaches the trigger point, known as Threshold, what electrical potential will be generated? Action potential. b. During the depolarization phase, voltage-gated Na channels open and Na enters the cell. 4. What are the two processes that stop the potential from rising above +30 mV? a. Inactivation of voltage gated Na channels b. Opening of voltage gated K channels 5. a. The opening of voltage-gated K+ channels cause the membrane to repolarize. b.
Does K+ move into or out of the cell? Out of c. If the membrane potential becomes more negative than –70 mV, this is called hyperpolarization. d. This potential is caused by what characteristic of K+ permeability? Slow decline 6. a. After an action potential, the neuron cannot generate another action potential because Na channels are inactived. This period is called the absolute refractory period. b. During the relative refractory period, the cell can generate another action potential but only if the membrane more depolarized. . a. Conduction velocity along the axon is increased by what two characteristics? 1. increased diameter 2. presence of myelin b. Conduction along a myelinated axon is called saltatory conduction. 8. a. Name the disease whose symptoms include loss of vision and increasing muscle weakness: Multiple sclerosis (from the quiz section) b. What does this disease destroy? Myelin sheaths of CNS axons c. How does this stop an action potential? Too few voltage gated Na channels between the nodes of Ranvier