You’ve probably used the phrase, “you’re getting on my nerves,” but have you ever stopped to think about nerves? What are they? How many nerves are in the human body? How do they help us interact with the world?
This post has all the basic information you need to know about nerves in the human body. Look through and find answers to some of the most frequently asked questions on this fascinating part of our anatomy.
How Many Nerves Are In the Human Body?
Some 86 billion neurons make up a few billion nerve fibers. The exact number is impossible to count in each human! Instead, biologists, neurologists, and other experts focus on specific “pairs” or bundles of nerves that work together to perform certain functions.
For example, the vagus nerve is the “10th cranial nerve.” But that one “nerve” contains hundreds of thousands of fibers that carry out the vagus nerve’s functions. The exact number of nerves is not as important as the function of these nerves and how they communicate information throughout the body.
What Are Nerves?
Nerves are bundles of cells that send electrical and chemical signals between the brain and other parts of the body. These signals contain “messages” about the world around us: the hot stove, the cool breeze, the sight of danger, etc.
Nerves vs. Neurons
Neurons are the individual cells that make up nerves. (Neurons are also known as “nerve cells.”) Nerves look like cords, and are often referred to as “nerve fibers.” Certain structures of nerves make up the nervous system in the body. We can thank the nervous system for our ability to walk, our ability to smell, and more. We can also “thank” the nervous system for feelings of physical pain.
What Are the Two Nervous Systems in the Body?
The network of nerves in the human body forms two nervous systems: the central nervous system (CNS) and the peripheral nervous system (PNS.) Our CNS consists of nerves in the brain and spinal cord, while the PNS consists of nerves that extend to the rest of the body.
Throughout the CNS and PNS exist three types of nerves: autonomic, sensory, and motor nerves. All peripheral nerves send messages throughout the body.
Types of Nerves
Autonomic Nerves
Autonomic nerves control all the functions that keep us alive: digestion, swallowing, breathing, etc. We do some of these things without consciously thinking about them. (When was the last time you thought about blinking? How many times have you blinked since?) We can thank our autonomic nerves for keeping our body fueled with oxygen, expelling waste from the food we eat, and generally keeping us alive even as we’re sleeping or distracted!
Sensory Nerves
Sensory nerves send messages to the nervous system about the world around us. Our eyes, ears, nose, mouth, and skin collect sensory information sent to the brain with sensory nerves. Without sensory nerves, we would not be able to feel the coolness of our pillow or hear the sound of our cat meowing.
(Curious about how our eyes send information about what we see or our ears send information about what we hear? Keep clicking - you’ll find information on all these topics!)
Motor Nerves
Motor nerves work in the opposite direction of sensory nerves. These nerves send messages from the nervous system to the muscles of the body. Muscles pull on our joints and allow us to move our bodies. We couldn’t walk, talk, jump, or stretch if we didn’t have messages moving from our minds to our muscles.
Sympathetic vs Parasympathetic Nerves
If you’ve ever taken a yoga class, you might have heard about the “parasympathetic nervous system.” Teachers may instruct students to take deep breaths in order to kick that nervous system into gear. But what does that mean?
The sympathetic nervous system communicates messages throughout the body when it’s in “fight or flight mode.” If you see a bear, bungee jump, or hear “pop quiz!” you might go into this mode. The brain tells the body, through the sympathetic nervous system, to pump up your heart rate, start sweating, and get focused. In addition to these (and other) responses, the sympathetic nervous system shuts down certain systems, too. No time to use the restroom when you’re running from a bear!
Once the brain realizes that it’s not in danger, the parasympathetic nervous system kicks in. Instead of “fight or flight,” the body goes into “rest and digest” mode. The systems of the body that shut down during fight or flight kick back up again. Breathing slows, heart rate slows, and the mind feels calmer.
Locations of Nerves and Their Functions
Cranial Nerves (The 12 Nerves)
Twelve pairs of cranial nerves in the brain perform a variety of very important functions. Altogether, these nerves are known as the cranial nerves. Here’s what they do.
- Olfactory nerve: sends information from the nose to the brain
- Optic nerve: sends information from the eye to the brain
- Oculomotor nerve: transports information regarding eye movement and pupil constriction
- Trochlear nerve: transports information regarding eye movement
- Trigeminal nerve: transports somatosensory information throughout the face and head, and information to the muscles for chewing
- Abducens nerve: transports information regarding eye movement
- Facial nerve: sends information to muscles that carry out facial expressions, sends somatosensory and taste information to the brain
- Vestibulocochlear nerve: sends information to the brain regarding hearing and balance
- Glossopharyngeal nerve: sends taste and somatosensory information from the tongue and to the muscles in the mouth for swallowing
- Vagus nerve: communicates information throughout the parasympathetic nervous system, including signals regarding glands, digestion, and heart rate
- (Spinal) Accessory nerve: sends information to muscles that move the head
- Hypoglossal nerve: sends messages to muscles that move the tongue
How to Remember the 12 Nerves
These 12 nerves are some of the most important nerves to know, whether you are studying biology or neurology! If you need help remembering them all, use these mnemonic devices:
- On Old Olympus Towering Top A Famous Vocal German Viewed Some Hops.
- Ooh, Ooh, Ooh To Touch And Feel Very Good Velvet.
- Only Oranges On Tilting Towers Are Fun And Give Very Awkward Holes
- On Occasion Our Trusty Truck Acts Funny, Very Good Vehicle Any How
- Once One Openly Told Tourists About Fighting Vampires Gobling Various Antelope Herds
Choose the sentence that you remember the most, or create your own!
Spinal Nerves (31 Nerves)
Did you think there were a lot of cranial nerves? There are 31 pairs of spinal nerves! Don’t worry. You’re probably not going to have to name all 36 pairs on a basic test, but you might have to know how many pairs of nerves work with the different parts of the spinal cord. Out of the 31 pairs of nerves, there are:
- Eight cervical spinal nerves: (C1 - C8)
- Twelve thoracic spinal nerves (T1 - T12)
- Five lumbar spinal nerves (L1 through L5)
- Five sacral spinal nerves (S1 through S5)
- One coccygeal nerve (Co1)
Learn More About Nerves in the Body
Interested in learning more? The following resources offer more insights into the structure, number, and purpose of nerves in the body.
