(Reference of atlas "Structure of neurons": [1] ）
Types of neurons [1] The cell body is nearly round and emits a process, which is divided into two branches not far from the cell body. One dendrite is distributed to the skin, muscle or viscera, and the other axon enters the spinal cord or brain.
The cell body is spindle shaped, with a dendrite and an axon, which are distributed in the retina and vestibular ganglion.
The cell body is polygonal, with one axon and many dendrites, which are the most widely distributed. The neurons in the gray matter of the brain and spinal cord are generally of this type.
（2） According to the functional classification of neurons:
1. Sensory (afferent) neurons:
Receive stimuli from inside and outside the body, and transmit nerve impulses to the central nervous system. Some of the nerve endings are free, and some differentiate into cells or tissues that receive specific stimuli. It is distributed throughout the body. In the reflex arc, it is generally connected with interneurons. In the simplest reflex arc, such as muscle stretch reflex, which maintains skeletal muscle tension, it can also directly synapse with efferent neurons in the center. Generally speaking, after entering the central nervous system, the nerve fibers of afferent neurons have synaptic connections with other neurons, which are mainly divergent. That is, they establish synaptic connections with many neurons through branches of axon terminals, which can cause many neurons to excite or inhibit at the same time, so as to expand the scope of influence.
2. Motor (efferent) neurons:
Nerve impulses are transmitted from the cell body through the axon to the end, causing muscle contraction or gland secretion. The efferent nerve fibers distributed to the skeletal muscle to form the motor endplate; When it is distributed to visceral smooth muscle and glandular epithelium, it wraps around muscle fibers or passes between glandular cells. In the reflex arc, the mode of contact with the interneurons is generally convergent, that is, many afferent neurons form synapses with the same neuron, so that many impulses from different sources act on the same neuron at the same time or successively. It is the integration function of the center to make the response more accurate and coordinated.
3. Connecting (intermediate) neurons:
Accept the nerve impulse from other neurons, and then transmit the impulse to another neuron. The interneurons are distributed in the brain, spinal cord and other central nerves. It has the largest number of neurons in the three categories. Its arrangement is very complicated, including divergent, polymerized, chain like, ring like, etc. The contact point of information transmission between neurons is synapse. The complex reflex activity is a neuron chain composed of afferent neurons, intermediate neurons and efferent neurons connected by synapses. The more intermediate neurons involved in the reflex, the more complex the reflex activity caused. The thinking activity of human cerebral cortex is an extremely complex reflex activity through a large number of interneurons. The complex connection of interneurons is the structural basis of highly complicated nervous system.
（3） According to the length of neuron axon:
It can be divided into two types: Golgi type I cells and Golgi type II cells.
