Receptors
Biology: Cambridge International A Level, topic 15.1.2
Receptors
Receptors have two important features:
Specificity
- Receptors only respond to specific stimuli. Examples of these stimuli include:
- Light.
- Temperature.
- Pressure.
- This means that a receptor that responds to light will not respond to temperature or pressure.
Generator potentials
- Receptors connect with sensory neurones. When stimulated, the receptor creates a generator potential in the sensory neurone.
- An example where stimulation of the receptor creates a generator potential is in the Pacinian corpuscle.
The Pacinian Corpuscle
The Pacinian corpuscle is a mechanoreceptor found in the skin. Mechanoreceptors respond to changes in pressure to establish a generator potential. The receptor reacts in the following way:
Resting potential
- The Pacinian corpuscle consists of concentric rings of connective tissue that surround a sensory neurone.
- When the corpuscle is not being stimulated it is at resting state.
- At resting state, the charge inside the neurone is more negative than outside (-70mV). This is because there are more Na+ ions outside the neurone than inside.
- A difference in charge across the cell membrane is called the potential difference.
Stimulation of the receptor
- When pressure is applied to the Pacinian corpuscle, the rings of connective tissue apply pressure on the sensory neurone.
- The sensory neurone has stretch mediated Na+ channels, these channels normally restrict the movement of Na+ ions.
- Applied pressure causes the stretch-mediated Na+ channels to open.
Generator potential
- Na+ ions flood into the sensory neurone through the open Na+ channels.
- There are now more Na+ ions inside the neurone than outside.
- The charge inside the neurone becomes more positive than outside, so the potential difference has changed.
- The generator potential has been established.
Action potential
- If the generator potential reaches the threshold level (about -50mV) then an action potential is produced in the sensory neurone.
Test yourself on Receptors
Which of the following statements about receptors are true?
What type of receptor is the Pacinian corpuscle?
Which of the following statements about the Pacinian corpuscle are true?