Axon hillock

The primary role of the sodium channels is to generate action potentials in excitable cells. In case of neurons, the sodium channel density is high at axon hillocks or axon initial segment where action potentials start to propagate. The sodium channels are also present in dendrites. The sodium channels contribute to amplifying synaptic inputs (particularly those distally located) and are actively involved in back propagation of action potentials into dendrites. Subtle differences in properties of sodium channels influence the dendritic processes of synaptic integration in and complex ways. 

Dendrites Synapse Perikaryon NksJ bodies Axon hillock Myelin... 

The transient change in the transmembrane potential upon excitation. An action potential cycle consists of a transient depolarization of the cell membrane of an excitable cell (such as a neuron) as a result of increased permeability of ions across the membrane, followed by repolarization, hyperpolarization, and finally a return to the resting potential. This cycle typically lasts 1-2 milliseconds and travels along the axon from the cell body (or, axon hillock) to the axonal terminus at a rate of 1-100 meters per second. See Membrane Potential... 

The membrane potential at an axon hillock below which an action potential will be generated. 

At the junction of the cell body and axcn is a region termed the axon hillock. At the axon hillock, chemical signals received by the dendrites may reach a threshold level to cause a wave of electrical depolarization and hyperpolarization of the axon cell membrane. The net movements of icns across the cell membrane are re cn-sible for these changes that move down the axcn to the axcn terminus as an action poterrtial. 

The axon ari.ses from a thickened area of the cell body called the axon hillock. Its membrane is mainly composed of lipids and proteins and is known as the axitlentnttt. Many of the axons of the CNS and PNS ate partly covered from near the axon hillock to the. synaptic knob by a sheath of myelin (myelinated axons), but some axons do not have this type of covering (unmyelinated axons). The myelin sheath of PNS myelinated axons is not continuous but is broken at about I-mm intervals to expose the axulenima to the extracellular fluid. These exposed areas, which are about I /[Pg.679]

De Zeeuw Cl, Ruigrok TJH, Holstege JC, Schalekamp MPA, Voogd J (1990c) Intracellular labeling of neurons in the medial accessory olive of the cat III. Ultrastructure of axon hillock and initial segment and their GABAergic innervation. J. Comp. Neurol., 300, 495-510. 

An action potential originates at the axon hillock, the junction of the axon and cell body, and is actively conducted down the axon to the axon terminals, small branches of the axon that form the synapses, or connections, with other cells. 

Action potentials are sudden membrane depolarizations followed by a rapid repolarlzatlon. They originate at the axon hillock and move down the axon toward the axon terminals, where the electric Impulse Is transmitted to other cells via a synapse (see Figures 7-29 and 7-31). 

A postsynaptic neuron generates an action potential only when the plasma membrane at the axon hillock is depolarized to the threshold potential by the summation of small depolarizations and hyperpolarlzatlons caused by activation of multiple neuronal receptors (see Figure 7-48). 

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