Isolation of neurotransmitters
Calcium ions act on vesicles (small, membrane-surrounded vesicles containing chemical transmitters - neurotransmitters) of the nerve end which approach the presynaptic membrane and merge with it, releasing the gap. The molecules of the neurotransmitter diffuse (penetrate). After interaction of the neurotransmitter with a specific receptor on the postsynaptic membrane, it is quickly released and its further fate is twofold. On the one hand, it is possible to completely destroy it under the action of enzymes located in the synaptic cleft, on the other hand - reverse capture into presynaptic endings with the formation of new vesicles. This mechanism ensures the short-term action of the neurotransmitter on the receptor molecule. Some prohibited drugs, such as cocaine, as well as some of the substances used in medicine, prevent the neurotransmitter from being re-captured (in the case of dopamine cocaine). At the same time, the period of action of the latter on the postsynaptic membrane receptors is prolonged, which causes a much more powerful stimulating effect.
Muscular activity
The regulation of muscle activity is carried out by nerve fibers, which move away from the spinal cord and end with a neuromuscular junction. When a nerve impulse arrives, acetylcholine is released from the nerve endings of the neurotransmitter. It penetrates the synaptic cleft and binds to the receptors of the muscle tissue. This triggers a cascade of reactions leading to a reduction in muscle fibers. Thus, the central nervous system controls the contraction of certain muscles at any time. This mechanism underlies the regulation of such complex movements as, for example, walking. The brain is an extremely complex structure; each of its neurons interacts with thousands of others scattered throughout the nervous system. Since the nerve impulses do not differ in strength, the information in the brain is coded on the basis of their frequency, that is, the number of action potentials generated per second is significant. In some ways, this code resembles Morse code. One of the most difficult tasks that today faces neurological scientists around the world is an attempt to understand how this relatively simple coding system actually works; for example how to explain a person's emotions at the death of a relative or friend or the ability to throw a ball with such precision that he hits the target from a distance of 20 meters. At present, it becomes apparent that information is not transferred linearly from one nerve cell to another. On the contrary, one neuron can simultaneously perceive nerve signals from many others (this process is called convergence) and is also capable of affecting a huge number of nerve cells, a divergence.
Synapses
There are two main types of synapses: in some, activation of the postsynaptic neuron occurs, in others - its inhibition (largely depends on the type of the transmitter emitted). The neuron emits a nerve impulse when the number of stimulating stimuli exceeds the number of inhibitory stimuli.
Strength of synapses
Each neuron receives a huge amount of both exciting and inhibitory stimuli. At the same time, each synapse has a greater or lesser effect on the probability of occurrence of an action potential. The synapses possessing the greatest influence are usually located near the zone of the nerve impulse in the body of the nerve cell.