Section 4: The Nervous System

Human brains are like a complex communication network.  The brain is a system of nerves that sends and receives electrical signals all throughout the body.   The nervous system’s two main organs, the brain and the spinal cord, both play a vital role in the body’s ability to collect information, process that information, and respond to it.

The nervous system is made up of two divisions that work together: the central nervous system and the peripheral nervous system.  The central nervous system is the control center of the body, which is made up of the brain and spinal cord.  It processes information and then creates a response, which is then delivered to the correct part of the body via the peripheral nervous system.

The control center of the nervous system is the brain.  The brain, located in the skull, is comprised of three main regions.  The cerebrum is the largest part of the brain, and it sits on top of the brain stem.  It controls movement, the senses, speech, and abstract thought.  This section of brain is divided into two hemispheres.  Each hemisphere controls different skills or ways of thinking.  The right hemisphere of the brain is referred to as the analog brain.  It controls three-dimensional sense, creativity, and artistic senses, processing information from the “big picture” first and then looking at the details. The left brain is sometimes referred to as the digital brain since it controls logical thinking, reading, and writing and processing information in an analytical and sequential way.  The outer layer of the cerebrum is called the cerebral cortex, which controls body movements and processes information from the sense organs.

The cerebellum is the second largest region of the brain and is found under the cerebrum and next to the brain stem.  It coordinates the action of muscles and helps maintain balance.  Hand-eye coordination develops here, giving the cerebellum an important role in decision making.  The brain stem is the smallest of the three parts and is found underneath the cerebrum.  It connects the brain and the spinal cord.  It filters data to and from other parts of the brain and controls involuntary actions like breathing and heart rate.

The other nerves that are not found inside the central nervous system are found in the peripheral nervous system.  The peripheral nervous system consists of a network of nerves that branch out from the central nervous system and connect it to the rest of the body.  There are two divisions within the peripheral nervous system: the motor division and the sensory division.  The motor division transmits impulses from the central nervous system to muscles and glands, allowing us to move.  The sensory division transmits impulses from sense organs to the central nervous system, sending messages to the brain about what something might smell, taste, feel, look or sound like.  A reflex is an automatic response that occurs very rapidly and without conscious control.  It helps protect the body.

The sensory receptors in our bodies allow us to detect or sense the physical aspects of our environment.  Our senses include stimuli both inside and outside of the body.  Vision, or sight, is our ability to see light.  Light enters our eyes and stimulates the rods and cones, which are cells found in the retina.  They send impulses to the optic nerve, and the brain then interprets the image we see.  Hearing is our ability to sense sound.  Ears pick up sound waves caused by vibrations that the brain interprets.  Taste and smell work closely together as both have sensory neurons that sense chemicals.  The chemicals trigger responses in receptors in the nose and mouth.  Taste is controlled by nerve cells on the tongue, whereas sensory neurons found in the nose detect numerous smells.  Touch is the body’s ability to sense pain, pressure, or temperature.   Sensory receptors pick up changes in these and send impulses to the brain or spinal cord.


  1. What is the function of the central nervous system?
  2. Describe characteristics of the cerebellum.
  3. Can you identify the five senses?

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