Functions of the Nervous System

Functions of the Nervous System

Animals interact with their environment. So, it's only logical that in order to take advantage of any benefits and avoid possible dangers, they need a way to be able to monitor their environment and then respond in an appropriate manner. In a nutshell, this is the job of the nervous system and it can be broken down into three main functions.

First, the nervous system collects sensory input from the body and external environment. Second, the nervous system then processes and interprets the sensory input. And finally, the third main function of the nervous system is to respond appropriately to the sensory input.

Let's take our friend Timmy as an example. Timmy likes to play in his backyard, and one of his favorite things to do in the backyard is to catch butterflies. Timmy's eyes scan the backyard. Actually, what his eyes are really doing is taking light input and converting it into electrical signals that are sent to the brain.

Timmy's eyes are sensory organs or organs which are devoted to gathering sensory input, and sending it to the brain. The brain then interprets these signals and converts them into a visual image which is how Timmy sees the butterfly land on a nearby flower. Not only does Timmy's brain give him a visual image, but it also categorizes what Timmy sees, so he immediately thinks, 'There's a butterfly landing on a flower.'

Neurons

The workhorses of the nervous system that do all of these things that allow Timmy to see the butterfly and recognize it are called neurons. Neurons are specialized cells of the nervous system that transmit signals throughout the body.

So, now that Timmy's neurons have gathered information from the environment, relayed this information to his brain, processed the information into a visual and categorized what he sees, Timmy now has a decision to make. What does he do with this information? Does he ignore it and continue scanning the backyard, or does he make use of this information and act on it?

Motor Neurons

Not surprisingly, Timmy decides he wants to catch the butterfly, so his brain sends signals to the muscles to slowly move towards the butterfly. The neurons that transmit this signal to the muscles are called motor neurons. Motor neurons are not just limited to sending signals to muscles, they can also send signals to glands within our body and stimulate or inhibit secretion of various substances that then carry out or regulate many body functions.

Reflex Reaction

But back to Timmy, who was just about to snatch the butterfly when the neighbor's dog barked and startled Timmy. Poor Timmy couldn't help it. The unexpected loud noise triggered a reflex reaction, an automatic, involuntary reaction to an unexpected stimulus, and Timmy jumped backwards before he knew what was happening. Timmy was scared. His brain remembered that the dog next door was big and mean, so it categorized the dog as a threat and told Timmy's legs to run away as fast as they could. So he ran, until he tripped, fell down, and scraped his knee when he fell.

Sensory Neurons

Specialized pain receptor neurons signal Timmy's brain that his knee is hurt and Timmy feels pain. Fortunately, Timmy's mother is just inside and hears him crying. She brings him inside and cleans his scraped knee. She puts Timmy's favorite lizard band-aid on his knee and puts an ice pack on it.

Now, another type of neuron is being stimulated in Timmy's knee: thermoreceptors which are neurons that sense temperature. These thermoreceptors are now signaling to Timmy's brain that his knee is suddenly very cold, but Timmy isn't worried about this; he knows that the ice pack will make his knee feel better.

You may have noticed that Timmy has lots of neurons that send sensory information to his brain like the neurons in his eyes that send visual information, the pain receptors in his knee that respond to injury, and the thermoreceptors that sense temperature. All of these are different types of sensory neurons, or neurons that collect sensory input and send it to the brain.

In addition to the sensory neurons already mentioned here, Timmy also has sensory neurons in his ears that allow him to sense sound, sensory neurons in his tongue that allow him to taste, sensory neurons in his nasal cavity that allow him to smell, and many more types of sensory neurons that are always sensing what is happening inside his body as well. Let's check back in with Timmy and take a look at an example of sensory neurons that monitor internal body conditions.

Autonomic vs. Somatic Nervous System

After Timmy was all patched up, his mother made him a grilled cheese sandwich, which was his favorite. Within five minutes, the whole sandwich was in Timmy's stomach. Sensory neurons in the stomach wall are stimulated by the presence of food and send a signal to the brain. The brain then relays a signal back to motor neurons in the stomach that stimulate the secretion of gastric juice, and contractions of stomach muscles to mix the food and gastric juice.

This nervous pathway is one example of a function controlled by the autonomic nervous system, which is the part of the nervous system that involuntarily regulates internal body functions. Other body functions that are also under autonomic control are breathing, heart rate, salivation, pupil dilation, sweating, and blood vessel constriction and dilation, to name a few.

In contrast, the somatic nervous system is the part of the nervous system that voluntarily responds to external stimuli. All of the different senses that Timmy experienced earlier in the lesson, like sight, hearing, pain and cold, and his conscious mental and physical responses to them, are all parts of the somatic nervous system. In many cases, both of these systems work in together in a coordinated fashion. When Timmy heard the neighbor dog bark and got scared, his heart rate and breathing rate were immediately increased by his autonomic nervous system so that he could run away, an action controlled by the somatic nervous system.

Lesson Summary

So let's review. The nervous system has three main functions:

1. To collect sensory input from the body and external environment
2. To process and interpret the sensory input
3. To respond appropriately to the sensory input

The workhorses of the nervous system are cells called neurons, which are specialized cells of the nervous system that transmit signals throughout the body. When Timmy's eyes scan the backyard, sensory neurons, or neurons that collect sensory input and send it to the brain, sense light input and convert it into electrical signals that are sent to the brain. Neurons in the brain then process this information and convert it into a visual image which is how Timmy sees the butterfly land on a nearby flower.

Not only does Timmy's brain give him a visual image, but it also categorizes what Timmy sees, so he immediately thinks, 'There's a butterfly landing on a flower.' Timmy decides he wants to catch the butterfly, so his brain sends signals to his muscles to move toward it. The neurons that transmit this signal to the muscles are called motor neurons, which are neurons that transmit signals to responsive tissues.

Timmy's muscles respond to the stimuli and he moves towards the butterfly. The functions that I just described are all controlled by the somatic nervous system, which is the part of the nervous system that voluntarily responds to external stimuli. All of the different senses that Timmy experienced earlier in this lesson, like sight, hearing, pain and cold, and his conscious mental and physical responses to them, are all parts of the somatic nervous system.

In contrast, the autonomic nervous system is the part of the nervous system that involuntarily regulates internal body functions. Some of the body functions that are under autonomic control are digestion, breathing, heart rate, salivation, pupil dilation and sweating.