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Neurons may lack dendrites or have no axons. The term neurite is used to describe either a dendrite or an axon, particularly when the cell is undifferentiated. Most neurons receive signals via the dendrites and soma and send out signals down the axon. At the majority of synapses, signals cross from the axon of one neuron to the dendrite of another.
As a result, some parts of the membrane of a neuron may be excitable (capable of generating action potentials), whereas others are not. Recent studies have shown that the most excitable part of a neuron is the part after the axon hillock (the point where the axon leaves the cell body), which is called the axonal initial segment , but the axon ...
The soma of a neuron (i.e., the main part of the neuron in which the dendrites branch off of) contains many organelles, including granules called Nissl granules, which are composed largely of rough endoplasmic reticulum and free polyribosomes. [5] The cell nucleus is a key feature of the soma.
Trace of modeled oxytocin-sensitive neuron showing bursts [dubious – discuss]. Bursting, or burst firing, is an extremely diverse [1] general phenomenon of the activation patterns of neurons in the central nervous system [2] [3] and spinal cord [4] where periods of rapid action potential spiking are followed by quiescent periods much longer than typical inter-spike intervals.
Sometimes the axon of a neuron may synapse onto dendrites of the same neuron, when it is known as an autapse. Some synaptic junctions appear along the length of an axon as it extends; these are called en passant boutons ("in passing boutons") and can be in the hundreds or even the thousands along one axon.
A multipolar neuron is a type of neuron that possesses a single axon and many dendrites (and dendritic branches), allowing for the integration of a great deal of information from other neurons. These processes are projections from the neuron cell body. Multipolar neurons constitute the majority of neurons in the central nervous system.
A single motor neuron may innervate many muscle fibres and a muscle fibre can undergo many action potentials in the time taken for a single muscle twitch. As a result, if an action potential arrives before a twitch has completed, the twitches can superimpose on one another, either through summation or a tetanic contraction.
Depending on the sum total of many individual inputs, summation may or may not reach the threshold voltage to trigger an action potential. [1] Neurotransmitters released from the terminals of a presynaptic neuron fall under one of two categories, depending on the ion channels gated or modulated by the neurotransmitter receptor.