Receptors

• What is a pacinian corpuscle?

  Respond to changes in pressure

  They produce a generator potential by acting as a transducer
• What is a transducer?


  Converts one type of energy to another
• How does the Pacinian corpuscle transduce energy from the stimulus into a generator potential?

  • In a resting state, the stretch-mediated sodium ion channels do not allow sodium ions to pass through them
  • When pressure is applied it is deformed and the sodium ion channels become stretched, allowing sodium ions to enter
  • The influx of sodium ions depolarises the membrane, producing a generator potential
  • The generator potential then creates an action potential
• Rod cells:

  • Images seen in black and white
  • A number of rod cells are connected to a single bipolar cell so give low visual acuity
  • This also means the threshold value is more likely to be exceeded
  • The pigment rhodopsin must be broken down to make a generator potential, low light intensity is enough to do this
• Cone cells:

  • Allow us to see in colour
  • Each bipolar cell is connected to a single cone cell, so give high visual acuity
  • The pigment iodomust be broken down to produce a generator potential. A high light intensity is required to do this
  • Found only at the fovea
• The fovea:

  Where light is focused