Difference Between Afferent and Efferent

The key difference between afferent and efferent neuron is that the afferent neurons carry nerve impulses from the sensory organs to the central nervous system while the efferent neurons carry nerve impulses from the central nervous system to the muscles.

The nervous system is the director of all body activities. Its major functions include communication among the body parts and controlling of the body. Also, the nervous system comprises two major cells namely neuron and neuroglia. The neuron is the structural and functional unit of the nervous system. They are specialized cells which respond to chemical and physical stimuli and to conduct messages throughout the body. Generally, the human brain can regulate more than 10 billion neurons at all times. Each neuron has three parts; namely, a cell body, an axon, and numerous dendrites. Axon and dendrites are the processes of a neuron. Furthermore, depending on the shapes and functions of the neurons, there are three types of neurons; namely, afferent neurons, interneurons, and efferent neurons. These three types have different characteristic features and functions. Here, the afferent neurons are sensory neurons while the efferent neurons are motor neurons.

CONTENTS

1. Overview and Key Difference
2. What is Afferent
3. What is Efferent
4. Similarities Between Afferent and Efferent
5. Side by Side Comparison – Afferent vs Efferent in Tabular Form
6. Summary

What is Afferent?

Afferent neurons are the neurons that carry sensory information such as nerve impulse from sensory organs towards the central nervous system. Sensory organs receive stimuli from the environment and send those signals to the central nervous system via sensory neurons. These neurons are specialized cells, and from different parts of the body, they carry signals to the brain and the spinal cord. To describe further, the physical modalities such as light, sound, temperature, etc. activate the afferent neurons. The sensory receptors located on the cell membrane are capable of converting this stimuli into electrical nerve impulses.

Besides, afferent neurons are pseudounipolar neurons that have a single long dendrite and a short axon. Their cell bodies are smooth, round shaped and are located in the peripheral nervous system. Also, their axons travel from ganglion to ganglion and lead back to the spinal cord. Single long myelinated dendrite is similar to an axon and is responsible for transmitting sensory information or nerve impulse from sensory receptors to its cell body.

What is Efferent?

Efferent neurons (also known as motor neurons) can be found inside the central nervous system (in the grey matter of spinal cord and medulla oblongata), and they are responsible for receiving information from the central nervous system and transmitting nerve impulse to the periphery of the body such as muscles, glands etc.

The cell body of the motor neuron has a satellite shape. Also, it has a long axon and several shorter dendrites. Moreover, the axon forms a neuromuscular junction with the effectors. Hence, the impulse enters through dendrites and leaves it through the single axon to the other end.

What are the Similarities Between Afferent and Efferent?

• Afferent and Efferent are nerve cells of the nervous system
• They consist of a cell body, dendrites and an axon.
• Also, both connect with the central nervous system.
• They transmit nerve impulses.

What is the Difference Between Afferent and Efferent?

Afferent neurons carry nerve impulses towards the central nervous system from sensory organs. In contrast, efferent neurons carry nerve impulses from the central nervous system to the muscles. Therefore, this is the key difference between afferent and efferent neurons. Furthermore, afferent neurons are sensory neurons with a short axon while efferent neurons are motor neurons with a long axon. Hence, one other difference between afferent and efferent neurons is the length of the axon. That is, the afferent neurons have short axons compared to the efferent neurons, which have long axons.

The below infographic tabulates the difference between afferent and efferent neurons with more details.

Summary – Afferent vs Efferent

Afferent and efferent neurons are two major types of neurons present in the nervous system. Afferent neurons bring nerve impulses generated by the sensory organs to the central nervous system. Receptors of the sensory organs receive external stimuli and generate into nerve impulses and send to the brain and spinal cord by the afferent neurons, which are sensory neurons. Therefore, they send signals in one direction. On the other hand, efferent neurons start from the central nervous system and carry nerve impulses from the central nervous system to the muscles and glands. They are motor neurons. This is the difference between afferent and efferent neuron.

Reference:

1.“Overview of Neuron Structure and Function.” Khan Academy, Khan Academy. Available here 

Image Courtesy:

1.”Unipolar Sensory Neuron”By Artwork by Holly Fischer, (CC BY 3.0) via Commons Wikimedia  
2.”Anatomy and physiology of animals motor neuron”By Sunshineconnelly and Adrignola (CC BY 2.5) via Commons Wikimedia