What are initial segments?
The concept of an initial segment is often (and usually more clearly) referred to by its mundane description: the set of strictly preceding elements. Some sources refer to this concept as a segment. Some sources refer to this concept as a section.
What is another term for the initial segment of an axon?
At the base of axons sits a unique compartment called the axon initial segment (AIS). The AIS generates and shapes the action potential before it is propagated along the axon.
What is the function of the initial segment of the axon?
The axon initial segment (AIS) is a specialized structure in neurons that resides in between axonal and somatodendritic domains. The localization of the AIS in neurons is ideal for its two major functions: it serves as the site of action potential firing and helps to maintain neuron polarity.
Is axon hillock the initial segment?
The axon arises from the cell body at a small elevation called the axon hillock. The proximal part of the axon, adjacent to the axon hillock, is the initial segment.
What kind of channels are found in the initial segment of the axon?
The axon initial segment (AIS) is the cellular membrane domain near the proximal end of the axon that contains a concentrated cluster of sodium and potassium channels that are estimated to be much higher than in other membrane domains, based on intensity of immunostaining.
Where is initial axon segment?
The axon initial segment (AIS) is located at the proximal axon and is the site of action potential initiation. This reflects the high density of ion channels found at the AIS.
What is the importance of nodes of Ranvier?
The nodes of Ranvier allow for ions to diffuse in and out of the neuron, propagating the electrical signal down the axon. Since the nodes are spaced out, they allow for saltatory conduction, where the signal rapidly jumps from node to node.
What is absent in the axon?
The axonal region or compartment, includes the axon hillock, the initial segment, the rest of the axon, and the axon telodendria, and axon terminals. It also includes the myelin sheath. The Nissl bodies that produce the neuronal proteins are absent in the axonal region.
What is axon hillock?
Axon hillock (definition, medicine): an axon nerve fiber that is a long projection of a neuron that carries the outbound neuronal cell signals as opposed to dendrites, which are the short protrusions from the neuronal cell body that brings in the inbound signals to the neuron.
What is the function of the initial segment of an axon?
Initial segment. The axonal initial segment (AIS) is a structurally and functionally separate microdomain of the axon. One function of the initial segment is to separate the main part of an axon from the rest of the neuron; another function is to help initiate action potentials.
Where does the action potential start in the axon?
It is now thought that the earliest site of action potential initiation is at the initial segment: just between the peak of the axon hillock and the initial (unmyelinated) segment of the axon. However, the positive point, at which the action potential starts, varies between cells.
Which is part of the axon contains neuronal proteins?
The axonal region or compartment, includes the axon hillock, the initial segment, the rest of the axon, and the axon telodendria, and axon terminals. It also includes the myelin sheath. The Nissl bodies that produce the neuronal proteins are absent in the axonal region.
How is the axon hillock identified in a neuron?
Red labeled is pointing directly at the axon hillock. The axon hillock is a specialized part of the cell body (or soma) of a neuron that connects to the axon. It can be identified using light microscopy from its appearance and location in a neuron and from its sparse distribution of Nissl substance.