Relaxation of muscles near arteries entering the penis increases the arterial diameter, letting more blood volume enter the penis. Exit of blood from the penis is blocked in part by a narrowing of veins. The relaxation of smooth muscle cells, leading to increased arterial blood flow, is stimulated by nerve cells of the parasympathetic nervous system. Two sets of specific binding reactions are required for the sperm nucleus to gain access to the egg cell cytoplasm. Describe three types of ion channels found in a neuron and how they function during neuronal signaling.
Potassium channels maintain the resting potential.
Neurotransmitter channels depolarize or hyperpolarize the membrane, activating or inhibiting, respectively, the formation of action potentials. Voltage-gated sodium channels open in response to membrane depolarization, let sodium ions in, leading to more depolarization, etc., etc. Voltage-gated potassium channels open in response to membrane depolarization, letting potassium ions out, leading to hyperpolarization of the membrane back toward the resting potential the falling phase of the action potential. Myelin is made by Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system. The layers of membrane that make up myelin wrap axons and aid in spreading membrane depolarization during propagation of an action potential down the axons.