exocytosis is the type of ion channel that is necessary for the function of the axon and the axon terminal.
exocytosis is the type of ion channel that is necessary for the function of the axon and the axon terminal.
what type of ion channels is necessary for the function of the axon and the axon terminal?
exocytosis
calcium ion signaling to the axon terminal is the usual signal for presynaptic release of neurotransmitters. calcium ion diffusion into the presynaptic membrane signals the axon terminal to release quanta to generate either an ipsp or epsp in the postsynaptic membrane. release of different neurotransmitters will lead to different postsynaptic potentials. action potentials that transmit down to the axon terminal will depolarize the terminal's membrane and cause a conformational change in the membrane's calcium ion channels. these calcium channels will adopt an "open" configuration that will allow only calcium ions to enter the axon terminal. the influx of calcium ions will further depolarize the interior of the axon terminal and will signal the quanta in the axon terminal to bind to the presynaptic membrane. once bound, the vesicles will fuse into the membrane and the neurotransmitters will be released into the membrane by exocytosis.
quantal neurotransmitter release
neurons are electrically excitable cells composed, in general, of one or more dendrites, a single soma, a single axon and one or more axon terminals. dendrites are cellular projections whose primary function is to receive synaptic signals. their protrusions, known as dendritic spines, are designed to capture the neurotransmitters released by the presynaptic neuron. they have a high concentration of ligand-gated ion channels. these spines have a thin neck connecting a bulbous protrusion to the dendrite. this ensures that changes occurring inside the spine are less likely to affect the neighboring spines. the dendritic spine can, with rare exception (see ltp), act as an independent unit. the dendrites extend from the soma, which houses the nucleus, and many of the "normal" eukaryotic organelles. unlike the spines, the surface of the soma is populated by voltage activated ion channels. these channels help transmit the signals generated by the dendrites. emerging out from the soma is the axon hillock. this region is characterized by having a very high concentration of voltage-activated sodium channels. in general, it is considered to be the spike initiation zone for action potentials, i.e. the trigger zone. multiple signals generated at the spines, and transmitted by the soma all converge here. immediately after the axon hillock is the axon. this is a thin tubular protrusion traveling away from the soma. the axon is insulated by a myelin sheath. myelin is composed of either schwann cells (in the peripheral nervous system) or oligodendrocytes (in the central nervous system), both of which are types of glial cells. although glial cells are not involved with the transmission of electrical signals, they communicate and provide important biochemical support to neurons. to be specific, myelin wraps multiple times around the axonal segment, forming a thick fatty layer that prevents ions from entering or escaping the axon. this insulation prevents significant signal decay as well as ensuring faster signal speed. this insulation, however, has the restriction that no channels can be present on the surface of the axon. there are, therefore, regularly spaced patches of membrane, which have no insulation. these nodes of ranvier can be considered to be "mini axon hillocks", as their purpose is to boost the signal in order to prevent significant signal decay. at the furthest end, the axon loses its insulation and begins to branch into several axon terminals. these presynaptic terminals, or synaptic boutons, are a specialized area within the axon of the presynaptic cell that contains neurotransmitters enclosed in small membrane-bound spheres called synaptic vesicles.
action potential