Receptors
This lesson covers:
- What a receptor cell is
- Different types of receptors and the stimuli they detect
- Mechanism of chemoreception
What is a receptor cell?
A receptor cell can recognise and respond to a particular stimulus in the environment.
These specialised cells act as sensors and transducers. This means that they can convert various forms of external stimuli into electrical signals. This transduction process is what enables the nervous system to detect changes in the environment.
Types of receptors
The human body uses a variety of receptor types, each specialised to detect different stimuli.
| Receptor type | Stimulus detected | Location |
|---|---|---|
| Photoreceptors | Light | Retinas in the eyes |
| Chemoreceptors | Chemicals | Nose, tongue, blood vessels |
| Mechanoreceptors | Pressure, touch | Skin, muscles, inner ear |
| Thermoreceptors | Temperature | Skin |
| Proprioceptors | Body movement and position | Muscles, joints |
Mechanism of chemoreception
Chemoreception is a complex process involving chemoreceptors that respond to chemical substances. These receptors are primarily located in the taste buds and olfactory regions.
For instance, the detection of salt involves several steps:
- Sodium ions from the ingested food diffuse through channel proteins into chemoreceptor cells on the tongue.
- These ions depolarise the chemoreceptor cell-surface membrane, creating a receptor potential.
- When this potential exceeds a certain threshold, it opens voltage-gated calcium ion channels.
- The influx of calcium ions triggers the fusion of neurotransmitter-containing vesicles with the cell-surface membrane.
- The neurotransmitters are released by exocytosis, and then bind to receptor proteins on the adjacent sensory neurone.
- This initiates an action potential that travels along the sensory neurone to the taste centre in the cerebral cortex of the brain, resulting in the perception of taste.