The nervous system is the product of a long evolution, the most complex and wonderful part of the animal body, and the most important basis for animal classification. According to the presence or absence of a central nervous system, animals are divided into two major categories: invertebrates and vertebrates. Fish are the earliest animals with brains, from amphibians, reptiles to birds, mammals, brain divisions are becoming more and more obvious, and the proportion of brains is also increasing. The human brain accounts for 2-3% of body weight and 20% of total energy consumption, becoming the supreme "command", managing all major systems and organs in the body.
We can see how the nervous system works from primitive multicellular hydras. When hydra is stimulated by the outside world, such as contact with prey, sensory cells transmit signals to nerve cells, nerve cells transmit signals, signals reach the tentacles' dermal muscle cells to contract them, and tentacles can send prey to the mouth. This ternary reflex combination consisting of receptors, regulators, and effectors is the prototype of various reflex activities. Human reflexes are completed through five parts: receptors, afferent nerves, centers, efferent nerves, and effectors. Reflexes are the basic way of neural activity in humans.
Reflection seems simple, but figuring out how it works is still difficult. The British physiologist Sherrington contributed in this regard. He first studied the laws of simple reflexes at the spinal cord level, and very accurately referred to the anterior horn motor neurons of the spinal cord as the "last highway" of somatic movement. The fibers emitted by motor neurons in the anterior horn of the spinal cord reach the skeletal muscle cells of the trunk and limbs, causing the excitation and contraction of muscle cells through the release of chemical transmitters. For example, when we tap the patellar ligament below the knee joint, the muscles feel the stretch stimulus and transmit signals to the anterior horn motor neurons of the spinal cord that innervate the calf, and the calf kicks forward, which is the simplest spinal reflex.
The complex reflexes of the human body require the involvement of the brain. Basketball players will first rotate their head during the air turn, then the receptors of the head and neck are stimulated to cause the rotation of the upper body, and then the lower limbs are moved due to the stimulation of the receptors of the trunk and limbs, and finally land smoothly. This is done by a series of postural reflections, including state reflections, orthostatic reflections, linear and rotational acceleration motion reflections. Completing these reflexes requires not only the spinal cord, but also the higher centers, including the brain, cerebellum, and brainstem to integrate.
Not only does body movement require nervous system command, but internal organ activity is also inseparable from nervous system regulation. The nerves that regulate visceral activity are sympathetic and parasympathetic nerves, which are not innervated by consciousness and can "make their own claims", also known as the autonomic nervous system. In the case of the heart, we can't use our consciousness to give instructions to make the heart beat faster or slower, but when we are strenuous and emotional, the heart beats faster. This is because strenuous exercise and emotional agitation excite the sympathetic nerves, and the transmitter norepinephrine released by the sympathetic nerves binds to receptors on the membranes of cardiomyocytes, resulting in increased heart rate and increased contractility. Various visceral activities are usually innervated by the sympathetic and parasympathetic nerves, and can be strong or weak with environmental changes.
The command and regulation of the nervous system can make the body make various responses, but if it is only like this, the human body is just a delicate machine, without agility. The difference between humans and lower animals is that they can respond without relying on external stimuli and sensations, relying on the brain's thinking, such as reaching a crossroads, whether to turn left, right, or continue to move forward, which is the brain's thinking decision, rather than simply responding to external environmental stimuli. The most wonderful, complex, and incomprehensible thing about brain science lies in the process of cognition and thinking. It seems to have no rules, it is a collective carnival of countless neurons, and it is difficult to predict who is right or wrong.
In fact, countless brain scientists have repeatedly pondered the proposition: can human beings use biological and physiological research methods to completely solve the mystery of advanced brain functions such as reasoning, association, complex learning, and language communication? Within the framework of existing knowledge, the answer is almost impossible. At this stage, if we want to deeply understand the brain's way of thinking and upgrade our cognitive level, it is better to use psychology and the teachings of the sages of the past.
The nerve is the head of the body, the brain is the condensation of wisdom, we are eager to achieve what we want and live up to this life, we must continue to discover the inner treasure and make ourselves smarter.