6.1.2 receptors

• describe the basic structure of a pacinian corpuscle

  lamellae (layers of connective tissue)

  stretch mediated sodium ion channel (closed)

  sensory ending neurone

  gel

  sensory neurone axon

  myelin sheath (schwann cells)
• describe how a generator potential is established in a pacinian corpuscle

  mechanical stimulus e.g pressure deforms lamellae and stretch mediated sodium ion channels

  so NA ion channels in membrane open and NA ions diffuse into sensory neurone

  greater pressure causes more NA ion channels to open and more NA ions to enter

  this causes depolarisation, leading to a generator potential

  if generator potential reachers threshold it triggers an action potential
• explain what the pacinian corpuscle illustrates

  receptors respond only to specific stimuli, pacinian corpuscle 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)
• explain the differences in sensitivity to light for rods and cones in the retina

  rods are more sensitive to light whereas cones are less sensitive to light

  several rods are connected to a single neurone whereas each cone is connected to a single neurone

  rods need spatial summation to reach/overcome threshold (as enough neurotransmitter released) to generate an action potential whereas cones have no spatial summation
• explain the differences in visual acuity for roads and cones in the retina

  rods give lower visual acuity whereas cones give higher visual acuity

  several rods connected to a single neurone whereas each cone is connected to a single neurone

  so several rods send a single set of impulses to the brain so can't distinguish between separate sources of light whereas cones send separate sets of impulses to the brain so can distinguish between 2 separate sources of light
• explain the differences in sensitivity to colour for rods and cones in the retina

  rods allow monochromatic vision whereas cones allow colour vision

  1 type of rod/1 pigment whereas 3 types of cone: red, green and blue sensitive, with different optical pigments so absorb different wavelengths, stimulating different combinations of cones gives range of colour perception