What Is the Structure of a Neuron?

Nerve cells are the most basic structural and functional unit of the nervous system. It is divided into two parts: cell body and protrusion. The cell body consists of the nucleus, the cell membrane, and the cytoplasm. It has the function of contacting and integrating input information and transmitting information. There are two types of processes: dendrites and axons. The dendrites are short and multi-branched. They directly expand and protrude from the cell body to form a dendrite. Its role is to receive impulses from other neuron axons and pass them to the cell body. The axons are long and have few branches. They are slender protrusions of uniform thickness. They often occur in the axillary mounds, and their role is to receive external stimuli, which are then transmitted by the cell body. In addition to the lateral branches, the axons form dendritic nerve endings. The terminals are distributed in certain tissues and organs, forming various nerve terminal devices. Sensory nerve endings form various receptors; motor nerve endings are distributed in skeletal muscles, forming the ultimate motor.

Nerve cells are the most basic structural and functional unit of the nervous system. It is divided into two parts: cell body and protrusion. The cell body consists of the nucleus, the cell membrane, and the cytoplasm. It has the function of contacting and integrating input information and transmitting information. There are two types of processes: dendrites and axons. The dendrites are short and multi-branched. They directly expand and protrude from the cell body to form a dendrite. Its role is to receive impulses from other neuron axons and pass them to the cell body. The axons are long and have few branches. They are slender protrusions of uniform thickness. They often occur in the axillary mounds, and their role is to receive external stimuli, which are then transmitted by the cell body. In addition to the lateral branches, the axons form dendritic nerve endings. The terminals are distributed in certain tissues and organs, forming various nerve terminal devices. Sensory nerve endings form various receptors; motor nerve endings are distributed in skeletal muscles, forming the ultimate motor.

Chinese name

Nerve cells or neurons

Foreign name

neuron, neurone, neure

Constitute

Cell body and processes

Features

Receive stimulation, generate excitement and conduct excitement

Classification of protrusions

Dendrites and axons

Research History

Early 19th century

Neuron I. Classification:

(1) According to the number of protrusions issued by the cell body, neurons can be divided into three types from the morphology:

1. Pseudounipolar neurons:

The cell body is approximately circular, emitting a protrusion that divides into two branches not far from the cell body. One dendrite is distributed to the skin, muscle, or internal organs, and the other axon enters the spinal cord or brain.

2. Bipolar neurons:

The cell body is approximately spindle-shaped, with a dendrite and an axon, which are distributed in the retina and vestibular ganglia.

3. Multipolar neurons:

The cell body is polygonal, with an axon and many dendrites, which are most widely distributed. Neurons in the brain and spinal cord are generally of this type.

(2) Classification according to the function of neurons:

1. sensory (afferent) neurons:

It receives stimuli from inside and outside, and transmits nerve impulses to the central nervous system. The neuron's tip is free, and some differentiate into cells or tissues that specifically receive specific stimuli. Distributed throughout the body. In the reflex arc, it is generally connected to intermediate neurons. In the simplest reflex arc, such as the muscle stretch reflex that maintains skeletal muscle tension, it can also synapse with the outgoing neuron directly in the center. Generally speaking, the nerve fibers of afferent neurons, after entering the central nervous system, synaptic connection with other neurons is mainly radial divergence, that is, the establishment of synaptic connections with many neurons through the branches of axonal terminals can cause many Neurons excite or suppress at the same time to expand the range of influence.

2. Motor (outgoing) neurons:

Nerve impulses are transmitted from the cell body to the end through the axon, causing the muscles to contract or the glands to secrete. The efferent nerve fibers are distributed to the skeletal muscle to form the motor end plate; when they are distributed to the visceral smooth muscle and glandular epithelium, they surround the muscle fibers or pass between glandular cells. In the reflex arc, the general connection with intermediate neurons is aggregated, that is, many afferent neurons and the same neuron form synapses, so that impulses from many different sources act on the same neuron at the same time or in succession. It is the integration of the center, making the response more precise and coordinated.

3. Contact (middle) neurons:

It accepts nerve impulses from other neurons, and then transmits the impulses to another neuron. Interneurons are distributed in central nerves such as the brain and spinal cord. It is the largest of the three types of neurons. The arrangement is very complicated, including divergent, aggregate, chain-like, ring-shaped and so on. The contact point for information transmission between neurons is synapse. Complex reflex activity is a neuron chain formed by afferent neurons, intermediate neurons, and efferent neurons connected by synapses. The more intermediate neurons involved in reflexes, the more complicated the reflex activity that is caused. The thinking activity of the human cerebral cortex is an extremely complex reflex activity through a large number of intermediate neurons. The complex connections of intermediate neurons are the structural basis of the highly complex nervous system.

(3) According to the length of the neuron axon:

It can be divided into Gol-gi type I cells and Golgi type II cells.