NEURON STRUCTURE and CLASSIFICATION

Neurons have actually four specialized structures that allow for the sending and receiving that information: the cell body (soma), dendrites, axon and also axon terminals (see shortest figure).

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Cell body or soma: The cell human body is the section of the cell the surrounds the nucleus and plays a major role in synthesizing proteins.

Dendrites: Dendrites space short, branched procedures that expand from the cabinet body. Dendrites role to get information, and also do for this reason through countless receptors located in their membranes that tie to chemicals, referred to as neurotransmitters.

Axon: an axon is a large process that extends from the cell human body at a suggest of origin-called the axon hillock-and functions to send information. In contrast to the much shorter dendrites, the axon can expand for more than a meter. As such length, the axon consists of microtubules and also is surrounding by myelin. Microtubules space arranged inside the axon together parallel arrays of long strands that act as highways because that the movement of materials to and also from the soma. Devoted motor protein "walk" along the microtubules, carrying product away native the soma (anterograde transport) or earlier to the soma (retrograde transport). This system can move products down the axon at prices of 400mm/day (see shortest figure). Myelin consists of completely separate cells that coil and wrap their membranes about the external of the axon. This are vital for electrical insulation and also to rate up activity potential propagation.

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Image produced by BYU-Idaho college student Jared Cardinet 2013

Image mirrors Anterograde and also Retrograde deliver in one axon.

Axon terminals: once an axon will a target, it terminates right into multiple endings, referred to as axon terminals. The axon terminal is draft to convert the electrical signal into a chemical signal in a procedure called synaptic transmission (further explained in the section "Physiology that the Neuron").

Most neurons are amitotic or shed their capability to divide. Exception to this rule are found in olfactory neurons (those associated with smell) and also hippocampal areas of the brain. Fortunately, lifespans of amitotic neurons is near 100 years. Still, if a neuron is damaged or lost, the is not conveniently replaced. Because that this reason, there is usually minimal recovery from serious brain or spinal cord injuries. Possibly the sluggish recovery rate or lack of rebirth is come ensure that learned behavior and also memories are kept throughout life. Neurons also have exceptionally high metabolic rates and subsequently need high levels of glucose and also oxygen. The body will go to good lengths come ensure that neurons space adequately fed; in fact, if because that some reason the mind detects the it is no receiving adequate amounts of nutrition, the body will shut down automatically (i.e., faint).

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Illustration of vital neuronal structures

Classification of Neurons

Structural group of neurons is based top top the number of processes that extend out native the cell body. Three major groups arise from this classification: multipolar, bipolar, and also unipolar neurons.

Multipolar neurons are characterized as having three or an ext processes that extend out native the cabinet body. They make up of much more than 99% the the neurons in humans, and also are the significant neuron form found in the CNS and also the efferent department of the PNS.

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Structural group of neurons. 1) Bipolar; 2) Multipolar and 3) Unipolar.

Bipolar neurons have only two procedures that prolong in opposite directions from the cell body. One process is referred to as a dendrite, and also another procedure is referred to as the axon. Return rare, this are found in the retina the the eye and also the olfactory system.

Unipolar neurons have actually a single, short procedure that extends native the cabinet body and also then branches right into two an ext processes that extend in the contrary directions. The process that expand peripherally is recognized as the peripheral procedure and is linked with sensory reception. The process that extends towards the CNS is the main process. Unipolar neurons are found primarily in the afferent division of the PNS.

Functional group of Neurons

Neurons are classified functionally according to the direction in i m sorry the signal travels, in relation to the CNS. This classification also results in 3 different species of neurons: sensory neurons, motor neurons, and also interneurons.

Sensory neurons, or afferent neurons transmit information from sensory receptors in the skin, or the interior organs towards the CNS because that processing. Practically all sensory neurons room unipolar.

Motor, or efferent neurons transmit info away indigenous the CNS toward some type of effector. Engine neurons are frequently multipolar.

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Interneurons space located between motor and sensory pathways and also are highly affiliated in signal integration. The vast majority of interneurons room confined in ~ the CNS.

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