The Difference between efferent and afferent nerves

In this post we will explain what the afferent and efferent nerves are, what their functions are and what is the difference between them.

Difference between efferent and afferent nerves

The difference between efferent and afferent nerves is that afferent is responsible for the transport of nerve impulses from the receptor organs to the central nervous system (CNS); while efferent neurons carry nerve impulses out of the CNS.

It is natural to associate the concepts “neuron” and “brain”. After all, neurons are the type of cell to which we normally attribute the ability to think, reason, and generally perform tasks related to the intellect.

However, neurons are also an essential part of the nerves that run throughout our body (along with glial cells). It is not strange if we consider what the function of these nerve fibres is: to make certain types of information travel through our organs and cell tissues.

Now, although these entire data transmission routes do basically the same thing, there are certain nuances and differences between them that make it possible for us to classify them according to their function. That is why we talk about the difference between the afferent pathway and the efferent pathway.

Neurons: The Messengers

The billions of neurons or nerve cells, which underlie all activity in the nervous system, form a communication network that coordinates all of the body’s systems and enables them to function. Neurons usually receive messages from other neurons through short fibres, called dendrites, which pick up the messages and carry them to the cell body of the neuron.

The neurons that carry messages from the sensory organs to the brain or spinal cord are called sensory (afferent) neurons. The neurons that carry messages from the brain or spinal cord to the muscles and glands are called motor (efferent) neurons.

And the neurons that carry messages from one neuron to another are known as interneurons (or associative neurons). The axon carries messages that leave the cell.

What kind of information do efferent pathways transmit?

Unlike the afferent pathway that receives sensory stimuli from receptors located in different areas of the body; The efferent pathway, when leaving the medulla, is responsible for sending the nerve impulses that activate the muscles and the function of the viscera.

Where do the efferent pathways come from?

The nuclei of the descending tracts come from both the cerebral cortex and the brainstem. According to the anatomy of the nervous system, these tracts exit from the primary motor cortex, midbrain, vestibular nuclei, reticular substance, and the medulla oblongata.

What is the role of efferent pathways?

Although all tracts have functions with respect to movements, they all fulfil a different role. Here is a brief description of the function of each downstream path:

• Pyramidal pathway. It is the main one in charge of the movement since it controls both the axial movements, as well as the trunk and the extremities.
• Rubroespinal. Control muscle tone.
• Tectospinal. Participate in the reflexes of the eyes, head and neck.
• Vestibulospinal. Maintains gravity.
• Reticulospinal. Participate in posture and locomotion.
• Rafespinal. It works by controlling communication between sensory neurons.

What diseases cause the alteration of the efferent pathways?

When talking about diseases of the efferent pathway, we must bear in mind that these are generated when there are blockages and interruptions in the path of motor functions. 

In these cases, we find both sensory and motor impairments, since the signal that indicates the sensations cannot be adequately responded to.

It is for this reason that the neurons of the central nervous system are affected, causing spinal injuries that include paralysis, abolished reflexes, low muscle tone, loss of sensation, and bladder disorders.

What function do the afferent pathways serve?

As the central nervous system is a specialized center, it is divided into different structures, each with specific functions. That is why there are ascending or afferent pathways that are the only ones in charge of carrying the sensory stimuli.

What information do the afferent pathways transmit?

The information transmitted by the ascending pathways varies depending on the track that receives the sensory stimuli, these tracts are the following:

• Spinothalamic tract: it rises through the medial lemniscus, reaches the thalamus and transmits painful sensitivity, changes in pressure, temperature and non-discriminatory touch.
• Spinoreticular tract is responsible for transmitting the sensation of pain.
• Spinocerebellar tract: there are 4 tracts that have the function of bringing unconscious sensitivity.
• Spinotectal tract: receives sensory impulses from sight.
• Thorn-olive tract: besides being sensitive, it is involved in movement and learning.

Where do the afferent pathways come from?

All the tracts mentioned above have their nuclei in the different parts of the central nervous system since they all have fibers that receive stimuli from the sensory receptors in order to send them to the different regions of the brain, brainstem, cerebellum, and brainstem. , reticular and gelatinous substance.

“While the afferent pathway receives the stimulus from different parts of the body, the efferent pathway sends the motor response, both pass through the spinal cord”

What diseases do afferent pathways cause?

Regarding diseases, there are many alterations that can occur in an afferent pathway and all its fibers, since they are areas located in different parts of the body, because they receive fibers from both internal and external structures.

Then, when the afferent pathways are injured, diseases can occur in which tactile, painful, proprioceptive, unconscious sensitivity, temperature and pressure are altered, depending on the injured tract.

Afference and efference: one letter changes everything

In order to understand the concepts of afferent and efferent, it is very useful to imagine the functioning of the nervous system as cognitive psychologists do, who use the metaphor of the computer as a descriptive model of neural networks.

According to this metaphor, both the brain and the entire nervous system work in a similar way to how a computer does; It has a part of its structure dedicated to being in contact with the environment that surrounds it and another that is dedicated to working with data that it has stored and processed to obtain new information.

Thus, the neurons of the brain and spinal cord would be this “internal” part of the computer, while the nerves that sprout from the spinal column and reach the most recondite corners of the body are the part in contact with the outside.

This last part of the nervous system, called the peripheral nervous system, is where the afferent and efferent pathways meet, which are the entry and exit channels of the central nervous system, respectively.

The pathways through which sensory information travels

Thus, all the information that enters through the sensory neurons travels through the afferent pathways, that is, those that transform the information collected by the senses and transform them into nerve impulses. Instead, efferent pathways are responsible for propagating electrical impulses that are intended to activate (or deactivate) certain glands and muscle groups.

Thus, if we wanted to stick to a simple explanatory scheme about what an afference and an efference are, we would say that the former informs the central nervous system about what happens in the rest of the body and in the data about the environment that it receives, while the efferent neurons are in charge of “transmitting the orders” and initiating the action.

In the same way, the word afference is used to designate the information that travels through these pathways of the peripheral nervous system, while the term efference is used to refer to the output of data that goes from the central nervous system to fibers and glands responsible for releasing all kinds of substances and hormones.

Help to remember better

The distinction between afferent and efferent is very useful for understanding how we perceive and act on the environment, but it can also be quite problematic because it is easy to confuse both terms and use them to designate the opposite of what is meant.

Fortunately, using simple mnemonic tricks it is very easy to remember what each thing is, and the fact that these words are only differentiated by one letter makes remembering one also remember the other. For example, the “a” for “afferent” may be related to the ‘’a’’ for ‘’arrival’’, and the “e” for “efferent”.

Pawn neurons?

The afferent and efferent pathways suggest a hierarchical functioning of the nervous system: while some neuronal groups report on what is happening in the rest of the body and transmit orders to implement plans, strategies and action protocols, others carry out decision-making. decisions and give orders that others will carry out.

However, the functioning of our nervous system is not as simple as it can be intuited in this very schematic vision of the travels that nervous information makes throughout our body, for two basic reasons.

The first is that the afferent and efferent neurons don’t just passively transmit information: they also cause it to transform.

What reaches the spinal cord and the glands and muscles is a burst of data whose shape depends in large part on how it has found each and every neuron through which it has travelled.

The second reason is that, although it is true that decision-making depends more on the brain than on the neural networks of the peripheral nervous system, it is not clear who commands whom, because they all occupy a place in a data cycle.

Ultimately, the afferent neurons send information to the brain without which action plans cannot be initiated, and the way in which the efferent pathways transmit the information will have an impact on the body and the environment that will then affect the processes and therefore to the brain.

Consider, for example, the fact of storing a box of cookies so as not to fall into the temptation to snack between meals: a modification of the environment makes us think and feel differently later than we would with the box of cookies in sight.

In short, afferent and efferent neurons may have a simpler and easier task to study than nerve cells in the brain, but they still play a vital role in our daily lives.

FAQS: Difference between efferent and afferent nerves

What is the difference between afferent nerves and efferent nerves?

Afferent neurons are sensory neurons that transport nerve impulses to the central nervous system and brain from external experiences, whereas efferent neurons are motor neurons that carry neural impulses that induce movement away from the central nervous system and towards muscles.

What are afferent neurons?

They are the neurons that transmit sensations from the periphery to the central nervous system.

What is another name for afferent nerves?

They are also known as sensory or receptor neurons

What is the difference between afferent and efferent neurons quizlet?

Efferent neurons transfer CNS-to-PNS information: cell bodies are normally located in the spinal cord or brain (CNS). Afferent neurons: Relay information to the CNS from the PNS.

What is the function of efferent nerves?

They carry nerve impulses out of the central nervous system to effectors such as muscles or glands.

In this post we explained what the afferent and efferent nerves are, what their functions are and what is the difference between them.

If you have any questions or comments please let us know!

References

Mai, J. K., & Paxinos, G. (Eds.). (2011). The human nervous system. Academic press.

Hergenhahn, B. R., & Henley, T. (2013). An introduction to the history of psychology. Cengage Learning.