Level 3 Unit 1 Part 02: Overview of neuron structure

Neurons in adults have a soma and processes called neurites, which are divided into dendrites or axons.

Dendrites are usually short, branched, and covered in small spines that increase the surface area.

An axon leaves the soma at a structure called the axon hillock, and the first part is called the axon initial segment. It then usually projects without branching for a wide range of distances, which may be one meter or more, and then ends in one or more structures called axon terminals. Axons are dependent on systems that transport substances from the soma to the axon terminals and vice versa. Thick axons are usually wrapped in a sheath of a material called myelin, which is regularly interrupted by short gaps called nodes of Ranvier.

Neurons contact their target cells at structures called synapses. These target cells may be another neuron, a muscle cell, or a gland cell.

A few neurons have axons that terminate on capillaries to secrete substances called hormones directly into the bloodstream.

There are multiple structural types of neurons.

Unipolar neurons have only one process, which an axon; these are present in humans mainly during development of the nervous system. Bipolar neurons have one dendrite and one axon. Multipolar neurons have multiple dendrites and one axon; this is the most common structural type of neuron in adult humans. Pseudounipolar neurons are quite different because they have a single short process attached to the soma that splits into two long axons. The axon bringing information in from the periphery is called the peripheral axon, and the axon transmitting information centrally is called the central axon. The end of the peripheral axon functions like the dendrites on the other types of neurons, and the axon initial segment is near the end of the peripheral axon instead of by the soma. The axon terminals are at the end of the central axon.


Level 3 Unit 1 Part 3: Overview of neuron function

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