Nervous System

The nervous system provides electrical circuit pathways that can connect neurons throughout the body. When the body’s electrical stimulus connects neurons, this neural connection allows us the capacity to sense changes within and outside of the body, to interpret and understand those changes, to make very complex decisions and judgments, and to control our body functions and reactions.

The main component of the nervous system is the nerve cell, or neuron. Neurons are special cells with attributes that support the functions of the nervous system. The central nervous system’s organs, the brain and the spinal cord, are complex, organized collections of neurons. These organs connect to all parts of the body through neurons of the peripheral nervous system.

Neurons have a large cell body that includes two key parts. Dendrites are little extensions at the end of the neuron which receive electrical impulses. The impulse travels to the axon in the neuron, which then conducts the impulse toward a target.

Within the human body, there are three different types of neurons. Sensory neurons carry impulses toward the brain and spinal cord. Motor neurons carry impulses away from the brain and spinal cord, and interneurons carry impulses within the brain and spinal cord.

The electrical impulses that neurons receive and send travel extremely fast, in milliseconds. Impulses travel down the insulated axon. At the end of the axon, a chemical called a neurotransmitter is released into a space called the synapse. These neurotransmitters cause a change at the target site, such as a muscle contraction.

The central nervous system is composed of the brain and spinal cord. The spinal cord serves as a neuron highway of neurological information. It enables communication of information up to the brain and from the brain down to body organ systems.

The brain is the center of higher function in the human body. The large cerebrum is the part of the brain that connects to the spinal cord via the brain stem. The neuron activity of the cerebrum determines our personality, decision-making, behavior, and emotions. It also controls how we initiate body movement and speech as well as how we interpret everything in the world around us that we see, hear, taste, smell and feel. The cerebellum, a mini-brain attached to our brainstem, controls body movement and coordination.

The brain and spinal cord communicate with all other parts of the body through the nerves that make up the peripheral nervous system. A reflex is a motor response to a sensory stimulus and is either involuntary (automatic) or a learned response that serves as a controlled reaction to a challenging situation or stimulus. Reflex systems are found connected with muscles, tendons, ligaments and skin (somatic) and are also found within internal organs, such as in the control of urination and blood pressure.

Humans possess specialized neuron receptors in various regions of the head which respond to different stimuli and provide valuable, diverse information about the surrounding environment. These specialized neurons allow complex interpretations of data from sounds, sights, tastes, smells and the overall position of the body. The eyes, for example, interpret visual information, and the ears include neurons that capture sounds.

The neurons in our retinas translate light signals into impulses the body can comprehend. Light travels to the back of the eye to the retina where light stimuli are converted to neuron impulses. The neurons transmit these impulses to the back of the brain where the brain enables us to interpret what we see. Think how quickly this all happens!

Sound waves enter the ear and cause movements of the eardrum and the smallest bones in the body, the ossicles, within the middle ear compartment. Those movements ultimately cause nerve impulses to be generated that travel up to the brain so we can make sense of what we hear.

There are specialized neurons in our nose and tongue that respond to molecules in the air we breathe and the food and fluids we eat and drink. Impulses travel from these regions back to our brain so we can understand differences in taste and smell.

Neurons communicate with each other through the release of chemical neurotransmitters. Drugs and alcohol can alter the release and uptake of neurotransmitters, thus changing our reactions and perceptions. For example, alcohol inhibits neuron function of the brain and poisons other organ systems, such as the liver. Cocaine changes the release of “feel-good” neurotransmitters. This results in dependency and elevated feelings of pleasure that can lead to addiction.