The Human Nervous System: Parts & Functions

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  • 0:19 Nervous System
  • 1:05 CNS and PNS
  • 2:00 Subdivisions of PNS
  • 3:18 Somatic & Autonomic NS
  • 3:51 Divisions of the Autonomic NS
  • 4:50 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Your nervous system allows you to experience the world around you and react to it. It's a complex system that's split into two main parts, the central nervous system and the peripheral nervous system. Read on to learn the parts and functions of the system.

Nervous System

A ball comes toward you and you swing your bat. A big dog jumps out in front of you and you begin to sweat. You walk past a bakery and the wonderful aroma makes your mouth water. All of these functions are possible because you have a working nervous system. Your nervous system is a complex collection of nerves and cells that carry messages and control actions.

It has three main functions. First, it detects change going on inside and outside your body. This is possible thanks to sensory receptors found throughout your body and concentrated in your sensory organs, such as your eyes, ears, tongue, nose and skin. Your nervous system also interprets the information from the sensory receptors, and then effects a response by sending out an order to your muscles or glands. For example, when the pitcher winds up and throws the baseball toward you, your eyes see the ball, your brain says swing, and your arms move.


This is a nice, tidy way to look at the nervous system, but in reality it's a very involved system made up of billions of cells that carry out countless functions every minute of the day. To best understand how the entire system works, we will consider the two major divisions: the central nervous system and the peripheral nervous system. The central nervous system, or CNS, consists of the brain and spinal cord. It's the part that interprets the incoming sensory information and then issues the orders, so I like to think of it as the boss.

The peripheral nervous system, or PNS, is made up of nerves that travel to and from the central nervous system. It reports any sensory changes to the brain and spinal cord, and then carries out orders. So, you could say the PNS is like the workers.

Subdivisions of PNS

The peripheral nervous system is divided again, giving us two main subdivisions. This is easy to understand if you remember that some of the nerves of the PNS travel toward the brain, while others travel away from it. The nerves traveling toward the brain make up the sensory division or afferent division. Nerves in this division take information from sensory receptors and carry it to the CNS, like the frightening sound of a dog barking or the wonderful smell of freshly baked bread. In other words, the sensory division allows you to sense the word around you.

The nerves traveling away from the CNS make up the motor division, or efferent division, of the peripheral nervous system. The nerves in this division send messages to your muscles and glands to carry out the orders issued by the brain. If you think about it, some of these orders are things you consciously decide to do, like swinging a bat to try to hit a home run. But other things, like your mouth watering or sweating, are done without your conscious input. Because there are some body reactions that are voluntary and some that are not, we can further divide the motor division of the PNS into two additional subdivisions.

Somatic & Autonomic NS

The somatic nervous system is a subdivision of the motor division that allows us to consciously control our skeletal muscles. This includes any voluntary movement, like brushing your teeth or swatting a fly off your arm.

The autonomic nervous system is a subdivision of the motor division that allows the body to perform tasks that are not under conscious control. In other words, it's the system that regulates involuntary activities, like digestion, sweating and your heart beating even when you're sound asleep.

Divisions of the Autonomic NS

Do you remember when that dog jumped out in front of us at the beginning of this lesson? Well, not only would that make you sweat, it would also make your heart race. That's an example of an automatic function of the autonomic nervous system. You didn't tell your heart to beat faster, it just did. Once the dog runs off and the coast is clear, your heart rate returns to normal.

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