Receptors are very important in the body as they facilitate communication between the brain and different parts of the body, helping us adjust to external and internal environmental conditions.
An example of a key receptor is the Pacinian Corpuscle. This receptor responds to mechanical pressure, which is pressure caused by a physical force (a heel pressing against the sole of your shoe while walking, or touching a piece of paper with your fingers).
Receptors Definition
Let's start by looking at the definition of receptors.
A receptor is a cell or a group of cells that receives information from stimuli.
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.
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.
The thermoreceptors of the skin will only respond to temperature changes and nothing else.
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.
Pacinian corpuscles transduce the mechanical energy of the stimulus (such as a touch to the skin) into a generator potential, which is a type of nervous impulse.
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.
Type of Receptor | Stimulus | Example Receptor |
Mechanoreceptor | Pressure and movement | Pacinian Corpuscle found in the skin. |
Chemoreceptor | Chemicals | Olfactory receptor found in the nose. |
Photoreceptor | Light | Rhodopsin found in the rod cell of the retina (eye). |
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.
Let’s continue with the example of the thermoreceptors in the skin.
If it is winter, for example, and we are too cold. The information that there is a decrease in body temperature will be sent via nervous impulses to the thermoregulatory centre of the brain. The thermoregulatory centre then will coordinate a response in the skeletal muscle. The skeletal muscle will contract, making us shiver. Shivering requires energy from respiration, and some of this is released as heat, causing us to warm up.
If it is a warm summer’s day, for example, and we are too hot, the information that there is an increase in body temperature will again be sent via nervous impulses to the thermoregulatory centre of the brain. This time, the thermoregulatory centre will coordinate a response with the sweat glands. The sweat glands will secrete sweat. This cools the skin by evaporation. Heat energy from the body will be lost as the liquid water in sweat evaporates into water vapour, so our body temperature cools down.
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.
How do we block pain receptors?
Pain receptors are called nociceptors. We find them in almost all organs except the brain.
Before surgeries, patients are administered an anaesthetic. This drug induces anaesthesia, which is a temporary loss of sensation or awareness. There are several different types of anaesthesic, but two of the main ones are general anaesthetic and local anaesthetic.
Local anaesthetic results in a reversible loss of sensation in only a limited area of the body and doesn’t necessarily affect consciousness. It is used in small surgeries such as stitching a deep cut.
General anaesthetic, on the other hand, results in a reversible loss of consciousness and may be used in more serious operations such as a hip replacement. General anaesthetic is thought to work by interrupting nerve signals in your brain and body, so the brain can’t process pain.
Certain medications numb pain receptors so we do not feel pain. For example, opioids such as morphine attach to opioid receptors on nerve cells in the brain, gut, spinal cord, and other areas of the body. This stops pain by blocking messages from the receptors being sent from the body to the spinal cord to the brain.
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
Sense Organ | Stimuli |
| Skin | Touch, temperature, pain |
| Tongue | Chemicals in food or drinks |
| Nose | Chemicals in the air |
| Eye | Light |
| Ear | Sound and position of head |
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.
Another example of a key receptor is the acetylcholine receptor (also known as the ACh receptor for short). Acetylcholine (ACh) is what binds to this receptor. Acetylcholine is a key neurotransmitter used throughout the nervous system for communication across cholinergic synapses.
- A neurotransmitter is just what the body uses as a chemical messenger to transmit messages across neurones, or from neurones to muscles. A cholinergic synapse is just a synapse that uses ACh as its neurotransmitter.
You can find more on this topic in the StudySmarter explanation about Transmission across a Synapse.
Receptors - Key takeaways
- A receptor is a cell or group of cells that receive information from stimuli such as a change in temperature. The proteins that detect stimuli at the molecular level are also called receptors.
- Receptors are specific and work as transducers.
- A key example of a receptor is the Pacinian corpuscle, which is a mechanoreceptor. Other examples include thermoreceptors, chemoreceptors and photoreceptors.
- The brain is an example of a ‘coordinator’ because it causes other parts of the body (typically glands and muscles) to produce a response.
- All organs have pain receptors except the brain. These receptors are called nociceptors.
- Touch receptors are key in helping humans distinguish between different sensations via the sense of touch.
- The thermoreceptors in the skin help us to distinguish between temperatures.
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