What Is Synkinesis?

Synaptic facilitation is a phenomenon that makes certain physiological processes prone to occur through synaptic transmission.

Synaptic facilitation

Synaptic facilitation is a phenomenon that makes certain physiological processes prone to occur through synaptic transmission.

Chinese name

Synaptic facilitation

Foreign name

Synaptic facilitation

Features

Inhibition and facilitation of synapses

Solid

Basic neural activity

Synaptic inhibition and facilitation inhibition are another basic neural activity of the central nervous system. It is manifested in weakening or stopping some reflex activities in the body, and in the center itself, it shows reduced excitability, temporarily losing the ability to transmit excitement, and electrical activity is hyperpolarized. Therefore, the inhibition process is not simply rest or rest, but an active neural activity as opposed to the excitation process. Central inhibition has many basic characteristics similar to central excitation. For example, the occurrence of inhibition also needs to be caused by stimulation, and the inhibition also includes diffusion and concentration, sum, post-release and so on. According to the different mechanisms of inhibition in the central nervous system, it is currently believed that inhibition can be divided into two categories.

It has been mentioned in synaptic transmission that if the post-synaptic membrane is hyperpolarized, an inhibitory post-synaptic potential will be generated, which will reduce the excitability of the post-synaptic neurons and make it difficult to depolarize and show inhibition. This inhibition is called postsynaptic inhibition. In mammals, all post-synaptic suppression is caused by the release of inhibitory transmitters called inhibitory intermediate neurons. According to this, an excitatory neuron can cause other neurons to excite through synaptic connections, but cannot directly cause other neurons to produce post-synaptic inhibition. It must first excite an inhibitory intermediate neuron and then inhibit other neurons. Neurons. Post-synaptic inhibition can be divided into afferent collateral inhibition and recurrent inhibition according to the way neurons are connected.

Collateral inhibition Afferent collateral inhibition refers to the stimulus of a sensory afferent fiber that enters the spinal cord, on the one hand, directly excites a central neuron, and on the other, excites through its collaterals. An inhibitory intermediate neuron then in turn suppresses another central neuron by inhibiting the activity of the intermediate neuron. For example, when an animal is exercising, the impulse of the axillary fibers of the extensor muscles enters the center, which directly excites the ? Motor neurons of the extensor muscles, and simultaneously emits collaterals to excite an inhibitory intermediate neuron, which in turn inhibits ipsilateral flexor muscles. The -motor neurons cause the extensor to contract and the flexor to relax. This form of inhibition is not only found in the spinal cord, but also in the brain. Its role is to coordinate activities between different hubs. This inhibition was once called reciprocal inhibition.

Recurrent inhibition means that when a central neuron excites, its outgoing impulse is transmitted along the axon while it excites another inhibitory intermediate neuron through its axon collateral. The latter excites back along its axons to act on neurons that originally issued impulses. The structural basis of recurrent inhibition is the ring-shaped connection between neurons, which is typically represented by the feedback inhibition of motor neurons by the tassel cells in the spinal cord. When spinal ventral horn motor neurons emit axons to innervate skeletal muscle, their Before the axon has left the gray matter of the ventral horn of the spinal cord, the axon sends out a small inner cell, which is a small nerve cell in the gray matter of the ventral horn. Shao cell is an inhibitory intermediate neuron, and when it excites, it suppresses the original motor neurons that emit impulses. The neurotransmitter released from the axonal tip of the Shaoxing cell may be glycine, which can be destroyed by Shi Ning and tetanus toxin. If the function of the Shao cells is disrupted, intense muscle spasms will occur. Recurrent inhibition exists widely in the center, it makes the excitation of neurons can be terminated in time, and it plays a role of regulating negative feedback.

When the post-synaptic membrane is affected by the presynaptic axonal tip, the excitatory post-synaptic potential on the posterior membrane is reduced, causing the post-synaptic neurons to be difficult or unable to excite and appear to be inhibited. This is called pre-synaptic inhibition. This inhibition does not occur at the post-synaptic membrane but at the axonal tip before the synapse, because the post-synaptic membrane does not produce an inhibitory post-synaptic potential at this time. Presynaptic inhibition occurs through axonal-synaptic activity. When axon and motor neurons form axon-body synapses; axon and axon form axon-axon synapses, and axon does not directly contact motor neurons. When axon is excited alone, the motor neuron does not respond, but it can partially depolarize axon and reduce the resting potential. When axon I is excited alone, it can cause motor neurons to generate excitatory postsynaptic potential (about 10mV). If axon is excited first, then axon is excited, then the excitatory post-synaptic potential of the motor neuron will decrease (5mV). It can be seen that axon activity can inhibit the axon excitatory effect on motor neurons. .

Regarding the cause of presynaptic inhibition, it has been mentioned in excitatory synaptic transmission that action potential is a factor that triggers transmitter release. Larger action potential releases more transmitters, while smaller action potential releases less transmitters. The magnitude of the action potential depends on the magnitude of the membrane potential at rest. The greater the membrane potential, the greater the action potential, and vice versa. When axon is excited, it will cause a small degree of depolarization of axon , which will reduce the membrane potential of axon , so the action potential generated when axon is excited will become smaller, and the excitability will be released. Transmitters are also reduced, and the excitatory post-synaptic potential caused by it is also reduced, which can not reach the threshold potential level. Therefore, the post-synaptic neurons cannot enter the excited state and appear to be inhibited. Therefore, the greater the degree of depolarization of the presynaptic membrane, the smaller the excitatory postsynaptic potential on the postsynaptic membrane and the stronger the degree of inhibition. Presynaptic suppression is caused by depolarization of the presynaptic membrane, so it is also called depolarization suppression.

It has been shown that presynaptic inhibition is more common in the sensory afferent pathway of the spinal dorsal horn, which depolarizes primary afferent nerve endings. Its transmitter is gamma aminobutyric acid, which can increase the permeability of primary afferent nerve endings to certain ions. The effects of presynaptic inhibition are as follows: When the body is subjected to different stimuli at the same time, it can suppress the activities of those secondary neurons to highlight the activities of the neurons that are most meaningful to the body. Backward fibers from the cerebral cortex, brainstem, cerebellum, etc. can pass through the brainstem and spinal cord, and can also branch out collaterals to presynaptic inhibition of sensory afferent impulses, which may be the advanced central control of the transmission of sensory information, resulting in One of the principles of clear feeling and "attention" concentration.

Post-synaptic facilitation = EPSP. Pre-synaptic facilitation = Based on the same structure as pre-synaptic inhibition, due to prolonged AP time to reach axis I, Ca2 + channel opening time increases, and EPSP changes in motor neuron soma Big.