The 31 pairs of spinal nerves separated from the spinal cord control sensations and activity throughout the body. Each spinal nerve consists of two parts, the dorsal sensory nerve branch and the anterior motor nerve branch.
Sensory nerve cells form a ganglion next to the spinal cord, which is connected to the spinal cord on the one hand, and on the other hand, it throws out a series of wires to connect the skin, muscles, ligaments, joint capsules, etc., and collects the collected information and transmits it back to the brain through the spinal cord. There is a large map of the whole body in the sensory center of the brain, and the situation is analyzed according to the reported information to adjust in time. It's a bit like a war movie, where the front-line commander (the sensor) reports the situation on the battlefield to the next command (sensory ganglia) over the phone, and the higher command calls the general staff (the sensory center of the brain), and the general and a large group of staff officers look at the sand table and the hanging map to analyze the current situation.
Not counting the muscles and joints, there are more than 5 million sensory nerve endings on the skin of the whole body alone. The denser the nerve endings, the sharper the sensation, like the tip of our finger has 300 per square centimeter, 120 finger roots, and 50 palms, each tip of the finger can distinguish a texture that is 10,000 times thinner than a human hair. It is said that the best Swiss watch craftsmen can know whether a gear in microns is qualified by just touching it by hand.
Chinese medicine has ten Xuan acupuncture points, just at the tip of ten fingers, acupuncture is similar to torture, and it is generally only used in emergencies. We have fewer sensory nerves in our backs, and you often feel like one finger when you press two fingers apart. Therefore, in the past, the punishment of prisoners was to be whipped on the back.
Nerve fibers, also known as "axons", are mainly used to conduct information, like optical cables wrapped in an insulating skin called a myelin sheath, so that they can be conducted quickly. Nerve conduction velocities in muscles can reach 450 kilometers per hour, almost 120 meters per second. Nerve fibers are only a few microns short, more than 1 meter long, like sciatic nerves, as thick as pencils.
A large nerve contains many tiny nerve fibers, and blood vessels play a role in nourishment. If the nerves are compressed, the blood supply is blocked, the nerves do not get nutrients, and the information cannot be transmitted back, numbness and weakness will occur in the corresponding parts.
Let's say you sit on the toilet and play a game. Played too much and forgot the time. As soon as he stood up, his legs did not listen to the call, and he could not move a step. In fact, this is the toilet side compression of the sciatic nerve for too long, the blood supply at the distal end of the nerve is blocked, the sensory nerve and motor nerve are paralyzed, the sensory nerve ischemia is insensitive, and the motor nerve ischemia is unable to move. You can only stand where you are and wait, and the nerves will slowly activate after they get the blood supply. The numbing and tingling sensation after the sensory nerve is activated is really a bit uncomfortable. If you don't have a long memory, you will do it next time.
Sometimes we sleep in a poor position or the pillow is not suitable, when we wake up, one arm is unconscious and cannot move, and after a while it is restored, also because of the compression of the brachial plexus nerve, commonly known as "pressure numbness!" "But if the compression time is too long, the nerve recovery is not for a while, and the severity may take several months."
There are many different neuroreceptors buried under our skin, like the gentle breeze, the gentle touch, the hard handshake, the tight hug, all of which give us infinite emotion. I once watched a European movie where the heroine expressed her thoughts to her lover and said, "Every inch of my skin longs for you!" "What a thrill to say! If only two crabs hadn't felt that way.
The most sensitive are the sensations of heat and cold and pain, these nerve endings are on the very surface of the skin, mainly afraid that you will be hurt. Generally we can feel the difference between hot and cold at 5-45 ° C, and above or below this range is not a feeling of cold and heat, it is pain.
Motor nerves emanate from the anterior horn of the spinal cord and connect with the corresponding muscles, controlling the contraction of the muscles to produce movement.
The spinal nerve merges the dorsal sensory nerve with the motor nerve on the anterior side before penetrating the intervertebral foramen between the vertebrae, also known as the nerve root, so the spinal nerve is a mixed nerve, that is, a sensory nerve that transmits information back and a motor nerve that transmits instructions.
The cervical spine has 8 pairs of spinal nerves, plus the spinal nerves of thoracic 1 together control the movement and sensation of the head, neck and shoulders and the entire upper limbs.
The upper 4 pairs of nerve roots of the cervical spine constitute the sensation of the cervical plexus innervate the muscles of the neck and the head and neck. Nerves like the occipital nerve and the small occipital nerve are penetrated from the muscles of the neck and distributed in the posterior occipital region (the back of the head) and the back of the ear. If the neck is used excessively, the head is bowed for too long, the muscles of the neck are spasmed due to fatigue, and the tense muscles may squeeze the nerves of the occipital part and cause pain in the posterior head, mainly near the wind pool acupoint, which is also called muscle tension headache.
The 4 pairs of nerve roots under the cervical spine and the 1 nerve root of the thoracic spine form a neural network, that is, the five nerve roots are woven into a network structure (plexus) between each other, and finally several terminal nerves innervate the sensation and movement of the entire upper limb. This neural network is called the "brachial plexus" and enters the upper limbs in our armpits.
This kind of network management is a bit like the leaders of the five departments are not only in charge of themselves but each department has a hand, perhaps afraid of a leader's problem, other leaders can take care of each other.
The nerves that penetrate from the cervical spine all the way to the fingertips, so a problem anywhere along this pathway can lead to nerve conduction disorders. For example, finger numbness may be compressed by nerve roots in the cervical spine (cervical disc herniation, foraminal hyperplasia), or there may be a jam in the upper arm, elbow or wrist, resulting in obstruction of nerve return. Therefore, a simple hand anesthesia still needs to be carefully examined by a doctor to find out the cause, and it cannot be said that there is a problem with the cervical spine.