Medically Reviewed by Dr. Elisabeth Vincent Hamelin
The body’s nervous system consists of the brain, spinal cord and nerves. The task of the nervous system is to receive and to transmit signals from and to the various parts of the body. This allows the different parts of the body to work together. The nervous system also controls our senses and allows us to remember things.
- 1 This is how the nerve cell is made up
- 2 Nerve cells conduct signals
- 3 The nervous system maintains contact between the parts of the body
- 4 The central nervous system consists of the brain and spinal cord
- 5 The peripheral nervous system consists of nerve fibers located outside the brain and spinal cord
- 6 Cranial nerves
This is how the nerve cell is made up
Nerve cells are constructed in a similar way to other cells in the body. They contain a cell nucleus and other parts of the cell that have different tasks.
Nerve cells have nerve fibers that carry signals
Something that distinguishes nerve cells from other cells is that they have thread-like protrusions. Each nerve cell has a long nerve cord called the axon. The axons transmit signals from the nerve cell. The nerve cell also has several shorter nerve fibers called dendrites. The dendrites carry signals into the cell. With the help of the nerve fibers, the cells have contact with other nerve cells, muscles or glands. The longest nerve fibers are over one meter long and are found in the sciatic nerve of the leg. Both the long and short nerve fibers are divided into several nerve ends so that they can have contact with many other cells.
Myelin protects some nerve fibers
Some nerve fibers are surrounded by a protection called myelin sheath. The myelin consists of fat and acts as insulation and protection for the nerve thread. The myelin does not cover the entire nerve, but there are small spaces called nodes.
Nerves with myelin sheath produce signals faster than nerves without myelin sheath. This is because the signal jumps between the nodes.
Nerve tissue heals poorly
Nerve tissue that is damaged does not heal very well. This is because fully developed nerve cells cannot divide and form new cells. Only the nerve cells that have not fully developed can divide. The immature nerve cells are called stem cells.
In contrast, a nerve thread, ie an axon, that has been damaged can grow out again.
Nerve cells conduct signals
Nerve cells can receive and send signals. The signal is disseminated in the nerve cell and further out to the nerve fibers. Then the signal continues to spread to other cells. A nerve cell can have contact with more than a thousand other nerve cells. A nerve cell can also be contacted by a thousand other cells. In this way, a network of cells is formed.
At the synapse, the nerve signal is passed from one cell to another cell
A synapse is the place where a nerve cell contacts another cell. Synapses may exist between two nerve cells, between a nerve cell and a muscle cell, or between a nerve cell and a gland cell.
Sometimes the nerve signal is not passed on
Sometimes the signal stops without any new signal being formed in the next cell. This is an important feature as this means that we do not get too many signals. An example of this is that the brain slows down signals that might otherwise develop into an epileptic seizure.
The nervous system maintains contact between the parts of the body
The nervous system has several important tasks in the body. Among other things, the nervous system allows the different parts of the body to quickly contact each other and work together. The nervous system also receives and records information from different parts of the body. It makes you aware of what you see, hear and feel. The experiences are then stored in memory. The nervous system also controls various tissues and organs, such as muscles and glands. For example, when you chew on something. Then it is the nerves from the brain that stimulate the salivary glands to form saliva.
The nervous system can be divided into two parts:
- Central nervous system consisting of the brain and spinal cord.
- The peripheral nervous system that consists of the nerves.
The central nervous system consists of the brain and spinal cord
The nerve signals are sent through the body between different body parts and the brain. For example, there may be signals from the skin that we feel heat, cold or touch. It can also be signals to and from different muscles that allow us to move. From the bladder and intestine, signals are sent that make us feel that we need to go to the toilet.
The nerve signals pass through the spinal cord
The task of the spinal cord is to receive and transmit nerve signals between the brain and the rest of the body. Damage to the spinal cord can prevent the nerve signals from being passed on. Then you can become paralyzed and lose the feeling in different parts of the body.
The brain interprets the signals
The signals that reach the brain are processed and interpreted. The brain thus makes us aware of what we are experiencing. The brain also sends out signals about how the body should respond to the experience.
The spinal cord takes care of the body’s reflexes
Sometimes it is enough that an impulse reaches the spinal cord for the body to react. Thus, the impulse does not need to reach the brain first. Such reactions are called reflexes. Some reflexes help protect the body from injury. For example, if you happen to put your hand on something hot and burn you, pull away before you become aware of the heat and pain. The reflex occurs faster than if the nerve impulse has to reach the brain before it causes the hand to be removed.
The brain and spinal cord consist of nerves
The spinal cord and brain are made up of nerve cells and nerve fibers called gray and white matter. In the gray matter are the cell bodies of the nerve cells. The white substance contains nerve fibers surrounded by support cells, called glial cells. The nerve fibers transmit further nerve signals. In the brain lies the gray and white substance protected within the skull. The spinal cord is protected in the vertebrae of the spine.
Fluid and membranes surround the brain and spinal cord
The brain and spinal cord are surrounded and protected by three membranes. The membranes that surround the brain are called brain membranes. Between the two innermost membranes is brain-spinal fluid.
The membranes that surround the spinal cord are called spinal cord membranes. The central spinal cord forms a sac in the lower part of the spine. There is also brain-spinal fluid. In case of suspected nervous disease, a so-called spinal fluid test can sometimes be taken from there.
The peripheral nervous system consists of nerve fibers located outside the brain and spinal cord
The peripheral nervous system consists of nerve fibers. The nerve fibers are called the axon. The nerve strands have their cell bodies in the brain or spinal cord, but the nerve strands extend to the different parts of the body, for example to the arms, legs and fingers.
The nerve fibers in the peripheral nervous system are bundled. The nerves pass on information between the central nervous system and the rest of the body.
There are three groups of nerves in the peripheral nervous system:
- cranial nerves
- spinal nerves
- nerves that cannot be controlled with the will.
The brain nerves are twelve pairs of nerves. They belong to the peripheral nervous system. The brain nerves control the movements of the body and receive signals from the different parts of the body. They all have their cell bodies in the brain or brain stem.
The tasks of the brain nerves
The brain nerves have the following tasks:
- The olfactory nerve allows us to feel the odor by passing information from the mucous membrane of the nose to the olfactory center in the brain.
- The optic nerve allows you to see by leading visual impressions from the retina to the visual center of the brain.
- Three pairs of brain nerves go to the muscles of the eyes. The nerves give impetus to the small muscles on the outside of the eyeball and allow us to look up, down and to the sides. The nerves also contract the pupil and allow the lens that sits in the eye to break the light.
- The oblique nerve is the largest brain nerve. It receives signals of emotion from the face. It also signals the muscles you use when you chew.
- The facial nerve leads to impulses to the muscles of the face, the tear glands and two of the salivary glands. In addition, the nerve conveys taste that is recorded on the front of the tongue.
- The nerve for hearing and balance conveys information from the inner ear to the brain.
- The nerves of the tongue and throat lead information to the muscles that cause you to swallow. It also receives information about taste from the back of the tongue and the sensation in the throat.
- The nerve for the lung and stomach control, for example, the larynx, heart, lungs, stomach and intestines.
- The so-called auxiliary nerve conveys impulses to the cuticle muscle and oblique neck muscle. The cutting muscle is the muscle that lifts on the shoulders, among other things. The oblique neck muscle is the muscle that rotates the head to the sides and bends the head forward.
- The tongue’s nerve controls the movements of the tongue.
From the spinal cord, spinal cord nerves go to the various muscles of the body
The spinal cord is 1 – 1.5 cm thick. It is made up of 31 parts called segments. From each part there are two spinal cord nerves to the different muscles of the body and to the skin.
Here are some of the most important spinal cord nerves:
- The sciatic nerve is the body’s largest and longest nerve. It extends from the lower part of the spinal cord all the way out into the big toe.
- The median nerve extends from the spinal cord to parts of the hand. This nerve can sometimes get trapped at the wrist and cause so-called carpal tunnel syndrome.
- Ulnar nerve conducts impulses to the small muscles of the hand. It goes around the elbow and can get trapped when the elbow is pushed. It is usually called that you get a widowhood.
Nerves that cannot be controlled with will
The nerves that control internal organs cannot be affected by the will. This includes, for example, nerves that control the heart’s work, breathing, blood pressure, bowel movements, ability to urinate and genital functions. These nerves belong to the autonomic nervous system. It is also called the autonomic nervous system.
The autonomic nervous system is divided into two parts:
- sympathetic nervous system
- Parasympathetic nervous system.
The sympathetic nervous system prepares the body for flight or fight
The sympathetic nervous system is triggered when the body needs to use much of its powers. For example, it can be when you are stressed or scared. The body is then affected to prepare to escape or fight.
The sympathetic nervous system affects the body as follows:
- The levels of stress hormones adrenaline and norepinephrine increase.
- The pulse increases.
- The heart pumps more powerfully.
- Blood flow to the muscles increases, while it decreases to the skin and intestines.
- Blood pressure increases.
- The trachea expands to make breathing easier.
- Blood sugar levels increase to give you extra energy.
- The pupils expand.
- You sweat more.
- Intestinal movements decrease.
- The digestion slows down.
The parasympathetic nervous system is most active at rest
The parasympathetic nervous system is most active at rest and in calm situations when the body’s reserves build up.
The parasympathetic nervous system affects the body as follows:
- The pulse decreases.
- Heart pumps with less force.
- Blood pressure drops.
- The trachea is contracted.
- The pupils are contracted.
- The amount of saliva in the mouth increases.
- Intestinal movements are increasing.
- The digestion increases.
- You can pee and poop.