Your nervous system is your body’s main communication network. Together with your endocrine system, it controls and maintains your body’s various functions. Additionally, it helps you to interact with your surroundings.
Your nervous system is composed of a network of nerves and nerve cells that carry messages to and from the brain and spinal cord and the rest of the body.
A nerve is a bundle of fibers that receives and sends messages between the body and the brain. The messages are sent by chemical and electrical changes in the cells, technically called neurons, that make up the nerves.
So, how many of these nerves are in your body? While no one knows exactly, it’s safe to say humans have hundreds of nerves — and billions of neurons! — from the top of our head to the tips of our toes.
Read on to learn more about the numbered and named cranial and spinal nerves, as well as what neurons are composed of, and some fun facts about your nervous system.
Organization of the nervous system
Your nervous system has two divisions:
- Central nervous system (CNS): The CNS is the body’s command center and is made up of your brain and spinal cord. The brain is protected within your skull while your vertebrae protect your spinal cord.
- Peripheral nervous system (PNS): The PNS is made up of nerves that branch off from your CNS. Nerves are bundles of axons that work together to transmit signals.
The PNS can be further broken up into sensory and motor divisions:
- The sensory division transmits information from both inside and outside of your body to your CNS. This can include things like feelings of pain, smells, and sights.
- The motor division receives signals from the CNS that cause an action to occur. These actions can be voluntary, such as moving your arm, or involuntary like the muscle contractions that help move food through your digestive tract.
Cranial nerves are a part of your PNS. You have 12 pairs of cranial nerves.
The cranial nerves can have sensory functions, motor functions, or both. For example:
- The olfactory nerve has sensory function. It transmits information on smell to the brain.
- The oculomotor nerve has motor function. It controls the movements of your eyes.
- The facial nerve has both sensory and motor function. It transmits taste sensations from your tongue and also controls movement of some of the muscles in your face.
The cranial nerves originate in the brain and travel outward to your head, face, and neck. The exception to this is the vagus nerve, which is the
Spinal nerves are also part of your PNS. They branch off of your spinal cord. You have 31 pairs of spinal nerves. They’re grouped by the area of the spine that they’re associated with.
Spinal nerves have both sensory and motor function. That means that they can both send sensory information to the CNS as well as transmit commands from the CNS to your body’s periphery.
Spinal nerves are also associated with dermatomes. A dermatome is a specific area of skin that’s served by a single spinal nerve. All but one of your spinal nerves transmits sensory information from this area back to the CNS.
So how many nerves all together?
There are several hundred peripheral nerves throughout your body. The many sensory nerves that bring sensation from the skin and internal organs merge together to form the sensory branches of the cranial and spinal nerves.
The motor portions of the cranial nerves and spinal nerves divide into smaller nerves that divide into even smaller nerves. So one spinal or cranial nerve may divide into anywhere from 2 to 30 peripheral nerves.
What makes up a nerve cell?
Your neurons work to conduct nerve impulses. They have three parts:
- Cell body: Similar to the other cells in your body, this area contains various cellular components like the nucleus.
- Dendrites: Dendrites are extensions from the cell body. They receive signals from other neurons. The number of dendrites on a neuron can vary.
- Axon: The axon also projects from the cell body. It’s typically longer than the dendrites and carries signals away from the cell body where they can be received by other nerve cells. Axons are often covered by a substance called myelin, which helps to protect and insulate the axon.
So how exactly do neurons work? Let’s explore one type of neuron signaling below:
- When neurons signal another neuron, an electrical impulse is sent down the length of the axon.
- At the end of the axon, the electrical signal is converted into a chemical signal. This leads to the release of molecules called neurotransmitters.
- The neurotransmitters bridge the gap, called a synapse, between the axon and the dendrites of the next neuron.
- When the neurotransmitters bind to the dendrites of the next neuron, the chemical signal is again converted into an electrical signal and travels the length of the neuron.
Nerves are made up of bundles of axons that work together to facilitate communication between the CNS and PNS. It’s important to note that “peripheral nerve” actually refers to the PNS. Axon bundles are called “tracts” in the CNS.
When nerves are damaged or aren’t signaling properly, a neurological disorder can result. There are a wide variety of neurological disorders and they have many different causes. Some you may be familiar with include:
The length of a neuron’s axon can vary. Some may be quite small while others may be up to
Similarly, nerves can vary in size as well. As your PNS branches out, your nerves tend to get smaller.
You may have heard of a condition called sciatica in which painful sensations radiate from your lower back and down your leg. This happens when the sciatic nerve is compressed or irritated.
Continue reading below for some more fast fun facts about your nervous system.
1. The electrical impulses of nerves can be measured
In fact, during a nerve impulse a net change of
2. Nerve impulses are fast
They can travel at a speed of up to
3. Neurons don’t undergo cell division
That means that if they’re destroyed they can’t be replaced. That’s one of the reasons why injuries to the nervous system can be so serious.
4. You don’t actually use just 10 percent of your brain
Your brain is divided up into different parts, each with different functions. Integration of these functions helps us to perceive and react to internal and external stimuli.
5. Your brain uses a lot of energy
Your brain weighs about three pounds. This is small in comparison to your overall body weight, but according to the Smithsonian Institute, your brain gets 20 percent of your oxygen supply and blood flow.
6. Your skull isn’t the only thing that protects your brain
A special barrier called the blood-brain barrier prevents harmful substances in the blood from entering your brain.
7. You have a multitude of neurotransmitters
Since the first neurotransmitter was discovered in 1926, more than 100 substances have been implicated in signal transmission between nerves. A couple that you may be familiar with are dopamine and serotonin.
8. The possible methods to repair nervous system damage are diverse
Researchers are hard at work to develop ways to repair damage to the nervous system. Some methods can include but aren’t limited to supplementation of growth-promoting cells, specific growth factors, or even stem cells to promote regeneration or repair of nerve tissue.
9. Stimulating the vagus nerve can help with epilepsy and depression
This is accomplished using a device that sends electrical signals to your vagus nerve. This, in turn, sends signals to specific parts of the brain.
Vagus nerve stimulation can help to lower the number of seizures in people with some types of epilepsy. It may also improve depression symptoms over time in people whose depression hasn’t responded to other treatments. Its effectiveness is being assessed for conditions like headaches and rheumatoid arthritis as well.
10. There’s a set of nerves connected to fat tissue
A 2015 study in mice used imaging to visualize nerve cells surrounding fat tissue. Researchers found that stimulating these nerves also stimulated the breakdown of fat tissue. Additional research is needed, but this could have implications for conditions like obesity.
11. Scientists have created an artificial sensory nerve
The system is able to collect information on applied pressure and convert it into electric impulses that can be integrated on a transistor.
This transistor then releases electrical impulses in patterns consistent with those produced by neurons. The researchers were even able to use this system to move the muscles in a cockroach’s leg.
You have hundreds of nerves and billions of neurons in your body.
The nervous system is divided into two components — the CNS and the PNS. The CNS includes your brain and spinal cord while the PNS is composed of nerves that branch off from the CNS and into your body’s periphery.
This vast system of nerves works together as a communication network. Sensory nerves deliver information from your body and your environment to the CNS. Meanwhile, the CNS integrates and processes this information in order to send messages on how to respond via motor nerves.