Sensory transduction & Plenary

• • neurones dont always generate action potentials at the cell body or the axon hillock
  • e.g. sensory receptors generate their action potentials from the periphery (near the terminal branches) and pass it towards the cell body
• Pseudo-unipolar cell:

  • e.g. sensory neurone
  • axon splits into 2 axons
  • so theres 2 axons and a cell body in a T junction shape
  • one axon ascends to the central nervous system, one axon descends to the peripheral nervous system - sensory neurones detect information in the PNS and transmit it up to the CNS
  • action potentials for these cells are generated at the terminal buttons

  A) Pseudo-unipolar

  
• • Diagram showing pseudo-unipolar neurone located in the dorsal root ganglion next to the spinal cord
  • this is where all sensory neurones are located
  • can see T junction shape with one axon going to the peripheral, one axon to the CNS and a cell body is present
  • at the end of the axon going to the periphery we have our sensory receptors (e.g. mechanoreceptor)

  
• Sensory Transduction:

  • the frequency of action potentials that are carried up from the mechanoreceptors, up the axon, depend on the amount of mechanical stimulus on the receptor
  • so the frequency of action potentials is proportionate to the level of mechanical deformation/stimulus
  • more mechanical deformation = more membrane permeability = more sodium influx = more depolarisation = higher frequency of action potentials
• Sensory Transduction:

  • mechanoreceptors membranes are covered in voltage gated channels for sodium and potassium
  • when mechanoreceptors receive mechanical deformation (pressure), there'll be deformation of nerve membrane, causing increase in membrane permeability
  • this allows sodium influx into the membrane via diffusion & electrostatic pressure, causing depolarisation
  • if depolarisation reaches more than -55 mv, voltage gated channels open, causing sodium influx, generating action potential that propagates up the axon, through; dorsal root, dorsal root ganglion, into spinal cord, to the brain