Interneurons: Definition & Function

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  • 0:00 Definition and Role of…
  • 1:32 Example #1: Knee-Jerk Reflex
  • 2:19 Example #2: External…
  • 2:52 Example #3: Cognition…
  • 3:23 Lesson Summary
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Lesson Transcript
Instructor: John Williams
The central nervous system is designed to connect sensory and motor pathways for reflexes. Interneurons are the cells that serve as that connection. This article addresses interneurons and their function in the nervous system.

Types of Neurons

A reflex is either a subconscious or involuntary response to an external stimulus. Whether it is blinking when an object comes close to the eyes or snatching your hand back when touching something hot - reflexes are designed to adjust to these stimuli to protect the body from harm. While sensory neurons are responsible for detecting a stimulus and motor neurons are responsible for stimulating a muscular or glandular response, interneurons serve as the connection point between these two pathways.

Definition and Role of Interneurons

Interneurons (also known as association neurons) are neurons that are found exclusively in the central nervous system. That means that they are found in the brain and spinal cord and not in the peripheral segments of the nervous system. There are more than 100 billion interneurons in the human body, which makes them the most abundant of the three major neuron types (along with sensory and motor neurons). This abundance of interneurons is due to the complexity of integrating the sensory and motor segments of the nervous system and the diversity of functions that exist in the brain and spinal cord.

Reflex Arc with Interneuron
Reflex arc

As with all neurons, interneurons are able to stimulate tissues through the use of neurotransmitters, or chemical messengers; however, for the purpose of integration, interneurons utilize different neurotransmitters than the peripheral nervous system uses. Typically, interneurons will release glutamate, an excitatory neurotransmitter, to activate tissues in a reflex response. Similarly, they may utilize gamma-aminobutyric acid (GABA) when inhibition of a tissue is necessary.

Examples of Reflexes Integrated by Interneurons

There are many examples of the interneurons at work. Here are a few:

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