21. During the generation of an action potential in a nerve cell axon, the depolarization of the membrane is caused by:T + a) opening of potassium channels in the axonal membraneT + b) opening of...

please answer 21,22

Extracted text: 21. During the generation of an action potential in a nerve cell axon, the depolarization of the membrane is caused by:T + a) opening of potassium channels in the axonal membraneT + b) opening of sodium channels in the axonal membraneT + c) closing of potassium channels in the axonal membraneT + d) closing of sodium channels in the axonal membrane. T 22. Myelinated axons: + 'a) have gaps in the myelin sheath, in which the membrane is exposed, called Nodes of - Ranvier. T + b) propagate impulses more rapidly that unmyelinated axons due to saltatory conduction. T + c) occur in white matter of the CNST + d) can be destroyed by diseases such as multiple sclerosis (MS) and amvlotrophic lateral sclerosis (Lou Gehrig's disease) T + e) All of the above (a, b, c and d) are correct. T