15.1.2

Receptors

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Receptors

Receptors have two important features:

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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.
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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:

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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.
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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.
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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.
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Action potential

  • If the generator potential reaches the threshold level (about -50mV) then an action potential is produced in the sensory neurone.

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