Receptors

• Describe the basic structure of a Pacinian Corpuscle:

  • Lamellae (layers of connective tissue)
  • Stretch mediated sodium ion channels (closed)
  • Sensory neuron ending
  • Sensory neuron axon
  • Myelin Sheath (Schwann Cells)
  • Gel
• Describe how a generator potential is established in a Pacinian Corpuscle:

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

  2)So Na+ channels in membrane open and Na+ diffuse into sensory neuron

  • Greater pressure causes more Na+ channels to open and more Na+ to enter

  3)This causes depolarisation, leading to a generator potential

  • If generator potential reaches threshold value it triggers an action potential
• Explain what the Pacinian Corpuscle illustrates:

  1)Receptors respond only to specific stimuli

  • Pacinian Corpuscle only responds to mechanical pressure

  2)Stimulation of a receptor leads to the establishment of a generator potential

  • When threshold value is reached, action potential sent (all or nothing principle)
• What are the two types of receptors in the eye?

  • Rods
  • Cones
• Describe the sensitivity to light in Rods:

  Rods are more sensitive to light:

  • Several rods connected to a single neuron
  • Spatial summation to reach threshold value to generate an action potential
• Describe the sensitivity to light in Cones:

  Cones are less sensitive to light:

  • Each cone is connected to a single neuron
  • No spatial summation
• Describe the visual acuity in Rods:

  Rods give a lower visual acuity:

  • Several rods connected to a single neuron
  • So several rods send a single set of action potentials to brain (so can't distinguish between separate sources of light)
• Describe the visual acuity of Cones:

  Cones give a higher visual acuity:

  • Each cone connected to a single neuron
  • Cones send a separate (set of) action potentials to brain (so can distinguish between two separate sources of light)
• Explain the sensitivity to colour in Rods:

  Rods allow monochromatic vision:

  • There is one type of rod / 1 pigment
• Describe the sensitivity to colour in Cones:

  • 3 types of cones - Red, Green, and Blue sensitive (allows Trichromatic vision)
  • With different optical pigments -> absorb different wavelengths
  • Stimulating different combinations of cones giving a range of colour perception
• Describe photobleaching in Rods:

  • When exposed to light, Rhodopsin is photobleached into Opsin and Retinal
  • When there is an absence of light Rhodopsin is resynthesized (requires ATP)
  • Takes time
• Describe photobleaching in Cones:

  • When exposed to light (colour), Iodopsin is photobleached into Iodo and Opsin
  • When there is an absence of light Iodopsin is resynthesized (requires ATP)