6.1.2 Receptors

• The basic structure of a Pacinian corpuscle

  • found in deep skin
  • responds to pressure
  • contains sensory nerve endings wrapped in lamellae( layers of tissue) separated by gel
  • in plasma membrane there is stretch mediated sodium ion channels

  
• Deformation of stretch-mediated sodium ion channels in a Pacinian corpuscle leads to the establishment of a generator potential

  1. Mechanical stimulus eg. pressure deforms lamellae and stretch-mediated sodium ion (Na+) channels

  2. Na+ channels in membrane open and Na+ diffuse into sensory neurone

  3. Greater pressure causes more Na+ channels to open and more Na+ to enter

  4. This causes depolarisation, leading to a generator potential

  ● If generator potential reaches threshold it triggers an action potential

  
• What does the Pacinian corpuscle illustrate?

  ● Receptors respond only to specific stimuli – only responds to mechanical pressure

  ● Stimulation of a receptor leads to the establishment of a generator potential

  ○ When threshold is reached, action potential sent (all-or-nothing principle)
• Light

  Rods are more sensitive to light

  ● Several rods connected to a single neurone

  ● Spatial summation to reach / overcome

  threshold (as enough neurotransmitter released) to generate an action potentia

  vs Cones are less sensitive to light

  ● Each cone connected to a single neurone

  ● No spatial summation( multiple neurone working togethe)

  
• Visual acuity

  Rods give lower visual acuity

  ● Several rods connected to a single neurone

  ● So several rods send a single set of impulses to

  brain (so can’t distinguish between separate sources of light)

  vs Cones give higher visual acuity

  ● Each cone connected to a single neurone

  ● Cones send separate (sets of) impulses to

  brain (so can distinguish between 2 separate sources of light)

  
• Colour

  Rods allow monochromatic vision

  ● 1 type of rod / (containing one) pigment

  Vs Cones allow colour vision

  ● 3 types of cones

  ○ Red-, green- and blue-sensitive

  ● With different optical pigments → absorb different wavelengths

  ● Stimulation of different combinations / proportions of cones gives a range of colour perception