5.3.2 Types of Neuron

All neurons vary somewhat in size, shape, and characteristics depending on the function and role of the neuron. Based upon the function, there are three types of neurons: sensory neurons, motor neurons, and interneurons.

Definition

Types of Neuron: Based upon the function, there are three types of neurons: sensory neurons, motor neurons, and interneurons. Each type has a specific structure and function in the nervous system.

Main Idea

• All neurons vary somewhat in size, shape, and characteristics depending on the function and role of the neuron.
• Based upon the function, there are three types of neurons:

Core Concept

• Sensory neurons = pseudo-unipolar; carry sensory information to CNS
• Motor neurons = multipolar; transmit information from CNS to effectors
• Interneurons = multipolar; relay signals between neurons
• Effectors = muscles and glands
• Function determines type

Detailed Explanation

Sensory Neurons

• The sensory neurons convert signals received from the environment into corresponding stimuli.
• The sensory inputs activate the sensory neurons and carry sensory information to the brain and spinal cord.
• They are pseudo-unipolar in structure.

Motor Neurons

• These are multipolar and are located in the central nervous system extending their axons outside the central nervous system.
• This is the most common type of neuron and transmits information from the brain to the effector (muscles or gland) of the body.

Interneurons

• They are multipolar in structure.
• Their axons connect only to the nearby sensory and motor neurons.
• They help in passing signals between two neurons.

Do You Know? Interneurons are also called relay neurons, association neurons, connector neurons, intermediate neurons or local circuit neurons.

Effectors

• The two examples of effectors are muscles and glands.
• The nervous system responds by sending signals to muscles and glands.
• The signals cause muscles to contract.
• The signals cause glands to produce secretions.
• Muscles and glands are called effectors because they cause an effect in response to directions from the nervous system.

Summary Table of Neuron Types

Intermediate Level

Types of Neurons

Detailed Description of Each Type

Effectors

Other Names for Interneurons

• Relay neurons
• Association neurons
• Connector neurons
• Intermediate neurons
• Local circuit neurons

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Based upon function, there are three types of neurons.
• 2. Sensory neurons convert signals from environment into stimuli.
• 3. Sensory neurons carry sensory information to brain and spinal cord.
• 4. Sensory neurons are pseudo-unipolar.
• 5. Motor neurons are multipolar.
• 6. Motor neurons are located in the CNS.
• 7. Motor neurons extend axons outside the CNS.
• 8. Motor neurons transmit information from brain to effector.
• 9. Motor neurons are the most common type.
• 10. Interneurons are multipolar.
• 11. Interneurons connect to nearby sensory and motor neurons.
• 12. Interneurons help pass signals between two neurons.
• 13. Interneurons are also called relay neurons.
• 14. Effectors are muscles and glands.
• 15. Muscles contract; glands secrete.

Remember

• - Three types of neurons = sensory, motor, interneurons
• - Sensory neurons = pseudo-unipolar; carry sensory information to CNS
• - Motor neurons = multipolar; transmit information from CNS to effectors
• - Interneurons = multipolar; relay signals between neurons
• - Effectors = muscles and glands
• - **Muscles** = contract
• - **Glands** = secrete
• - Interneurons = relay neurons, association neurons, connector neurons, intermediate neurons, local circuit neurons
• - Motor neurons = most common type
• - Sensory neurons = convert signals into stimuli

Common Mistakes

• 1. Confusing sensory and motor neurons — Sensory = to CNS; motor = from CNS.
• 2. Mixing up the structure — Sensory = pseudo-unipolar; motor and interneurons = multipolar.
• 3. Forgetting the location — Sensory = dorsal root ganglion; motor and interneurons = CNS.
• 4. Confusing interneurons with motor neurons — Interneurons relay signals; motor neurons transmit to effectors.
• 5. Thinking effectors are receptors — Effectors = muscles and glands; receptors = sensory cells.
• 6. Mixing up the functions — Sensory input; motor output; interneurons relay.
• 7. Forgetting the role of interneurons — They pass signals between neurons.
• 8. Thinking motor neurons are sensory — Motor neurons transmit from CNS to effectors.
• 9. Believing sensory neurons are multipolar — Sensory neurons are pseudo-unipolar.
• 10. Mixing up the names of interneurons — Relay, association, connector, intermediate, local circuit neurons.

Quick Revision

All neurons vary somewhat in size, shape, and characteristics depending on the function and role of the neuron. Based upon the function, there are three types of neurons. Sensory neurons convert signals received from the environment into corresponding stimuli. The sensory inputs activate the sensory neurons and carry sensory information to the brain and spinal cord. They are pseudo-unipolar in structure. Motor neurons are multipolar and are located in the central nervous system extending their axons outside the central nervous system. This is the most common type of neuron and transmits information from the brain to the effector (muscles or gland) of the body. Interneurons are multipolar in structure. Their axons connect only to the nearby sensory and motor neurons. They help in passing signals between two neurons. Interneurons are also called relay neurons, association neurons, connector neurons, intermediate neurons or local circuit neurons. The two examples of effectors are muscles and glands. The nervous system responds by sending signals to muscles and glands. The signals cause muscles to contract. The signals cause glands to produce secretions.

60-Second Revision

• Three types of neurons = sensory, motor, interneurons
• Sensory neurons = pseudo-unipolar; carry sensory information to CNS
• Motor neurons = multipolar; transmit information from CNS to effectors
• Interneurons = multipolar; relay signals between neurons
• Effectors = muscles and glands
• Muscles = contract
• Glands = secrete
• Motor neurons = most common type
• Warning: Sensory neurons carry information to CNS; motor neurons carry information from CNS

NEXT TOPIC

• Chapter:
• 5. Nervous System of Man

• Topic:
• 5.3.3 EFFECTORS

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