The key difference between sensory and motor neurons is that the sensory neurons are the neurons that carry information from sense organs to the central nervous system while motor neurons are the neurons that carry information from the central nervous system to the muscle cells.
Neurons are the functional and structural units of the vertebrate nervous system. They make the communication network of the nervous system and transfer electrical impulses between sensory organs, and central and peripheral nervous systems. There are about 200 billion neurons in the nerve network of an average person. Further, a neuron consists of a cell body containing a nucleus and other cell organelles. Other than the body, there are special branching from the cell body that makes dendrites and axons. Usually, the axon is a long fibre that carries messages away from the neuron, and dendrites are small branching that is responsible for receiving messages from the outer environment. Also, there are three types of neurons based on their function namely sensory neurons, motor neurons, and interneurons. Therefore, the difference between sensory and motor neurons mainly relies on the function they perform.
CONTENTS
1. Overview and Key Difference
2. What are Sensory Neurons
3. What are Motor Neurons
4. Similarities Between Sensory and Motor Neurons
5. Side by Side Comparison – Sensory vs Motor Neurons in Tabular Form
6. Summary
What are Sensory Neurons?
Sensory neurons convey sensory impulses from sensory organs toward the central nervous system, which includes the spinal cord and brain. They follow ascending, or afferent pathways known as ‘afferent neurons’. Furthermore, the cell body of the sensory neurons locates in the peripheral sensory ganglia, in the peripheral nervous system. Also, sensory neurons are unipolar neurons with afferent fibres, which extend between sensory receptors and central nervous system.
Figure 01: Sensory Neurons
Moreover, the sensory neurons gather information from external and internal environments through sensory receptors. Accordingly, sensory neurons can be divided into two types; (1) Somatic sensory neurons; which monitor outside environment and our position, (2) Visceral sensory neurons; which monitor internal body conditions and the status of organ systems. There are about 10 million sensory neurons in an adult human.
What are Motor Neurons?
Motor neurons are responsible for carrying information from the central nervous system to peripheral effectors in a peripheral tissue or organ. The human body has about half a million of motor neurons. Furthermore, the motor neuron consists of a cell body, several dendrites and a single axon. The efferent fibre of the motor neuron is the axon that carries the impulse away from the central nervous system.
Figure 02: Motor Neuron
The actions such as speaking, walking, breathing, chewing, etc. are done by muscle cells. These actions occur when the muscle cells receive signals from the central nervous system via motor neurons. Also, there are two main types of motor neurons; upper motor neurons and lower motor neurons. The upper motor neurons initiate from the brain while the lower motor neurons start from the spinal cord. But both these neurons work together. Considering their functions, the movements such as walking, chewing, etc. occur by the lower motor neurons upon the direction of upper motor neurons. The movements of the arms, legs, face, throat, tongue etc. occur mainly due to the control of lower motor neurons.
What are the Similarities Between Sensory and Motor Neurons?
- Sensory and motor neurons are two types of neurons.
- They carry nerve impulses to and from the central nervous system.
- Sensory and motor neurons consist of a cell body, dendrites and axon.
- The action potential travels across these neurons.
What is the Difference Between Sensory and Motor Neurons?
Sensory neurons carry information from sense organs to the brain. Hence, they are afferent neurons. On the other hand, motor neurons carry information from the brain to the muscle cells. Hence they are efferent neurons. This is the main difference between sensory and motor neurons. Moreover, sensory neurons are situated at the dorsal root ganglion of the spinal nerve whereas the motor neurons are situated at the ventral root ganglion of the spinal cord.
The below infographic tabulates the difference between sensory and motor neurons in more detail.
Summary – Sensory vs Motor Neurons
Sensory and motor neurons are two types of main neurons found in the nervous system. Sensory neurons carry information from the sense organs to the central nervous system. They convert external stimuli into internal electrical impulses and send to the central nervous system. Motor neurons activate muscle cells. They receive nerve impulses from the central nervous system and bring to the effectors muscles or glands to control muscle cell actions such as speaking, breathing, chewing, etc. Sensory neurons are afferent neurons while motor neurons are efferent neurons. This is the difference between sensory and motor neurons.
Reference:
1.“Sensory Neuron.” Wikipedia, Wikimedia Foundation, 14 May 2018. Available here
Image Courtesy:
1.”Structure of sensory system (4 models) E”By Shigeru23 (CC BY-SA 3.0) via Commons Wikimedia
2.”Anatomy and physiology of animals Motor neuron”By Sunshineconnelly (CC BY 3.0) via Commons Wikimedia