Receptors

Receptors Definition

Let's start by looking at the definition of receptors.

These stimuli may be an external change, such as a decrease in the temperature outside, or an internal change such as a lack of food.

• The identification of these changes by receptors is called sensory reception.

• The brain then receives this information and makes sense of it. This is called sensory perception.

Function of Receptors

An important thing to note about receptors is that they are specific. This means that each receptor is specialised to respond to only certain types of stimuli.

Another key area to understand is that receptors act as transducers by converting the stimulus into a different form of energy, usually nerve impulses, that the body can understand. The word transducer may sound scary, but remember it just refers to something that converts energy from one form to another.

Receptors in the Body

Receptors convert energy from both external and internal environments into electrical impulses. Sense organs, such as the eye or ear, are formed by a mass of receptors. However, sometimes they can be scattered, like those in the skin and viscera.

The central nervous system receives signals from receptors through afferent nerve fibres. A neuron's receptive field refers to the area in the periphery from which it receives input.

Types of Receptors

We have many different types of receptors in our body which detect different types of stimuli. This table shows a couple of examples, though the list is not exhaustive.

Table 1. Examples of receptors.

What does the brain do with the information from receptors?

As mentioned above, some receptors send information to the brain. The brain is an example of a ‘coordinator’. Another coordinator in the human body is the spinal cord.

Both the brain and spinal cord are called coordinators because they cause other parts of the body (typically glands and muscles) to produce a response. Muscles will contract or relax while glands will secrete hormones.

The function of touch receptors

Touch receptors are key in helping humans distinguish between different sensations via the sense of touch. For example, we can feel different pressures of objects touching our skin due to Pacinian corpuscles, as they respond differently depending on the level of pressure. This is why we can tell the difference between a gentle touch and a sharp jab. Similarly, the thermoreceptors in the skin help us to distinguish between temperatures, which is why we can tell the difference between warmer and cooler air.

For example, this image shows a group of people touching a piece of paper. They can feel this paper due to the Pacinian corpuscles in their fingertips, which allow the mechanical pressure of their fingertips pressing against the paper to be transmitted into nervous impulses.

Examples of Receptors

Examples of receptors include receptors found on the sense organs. Each of them respond to specific stimuli (change in the environment) and stimulate electrical impulses in response.

Table 2. Sense organs and stimuli

A key example of a type of receptor that appears in the ‘Homeostasis’ topic is the thermoreceptor. Thermoreceptors can be found on the skin, or in the body core and monitor external and internal temperature. This information is sent out via nervous impulses from the thermoreceptors to the thermoregulatory centre in the brain.