Roles of sensory receptors

• Change in light intensity

  • rods and cones in retina detect change
  • light to electrical
• change in temperature


  • temperature receptors in skin and hypothalamus
  • heat to electrical
• change in pressure on the skin


  • Pacinian corpuscles in the skin
  • movement to electrical
• change in sound

  • vibration receptors in cochlea of ear
  • movement to electrical
• movement


  • hair cells in inner ear
  • movement to electrical
• change in muscle length


  • muscles spindles in skeletal muscles
  • movement to electrical
• chemicals in the air

  • olfactory cells in epithelium lining the nose
  • receptors detect presence of a chemical and create an electrical nerve impulse
• chemicals in food 


  • chemical receptors in taste buds on tongue
  • receptors detect presence of a chemical and create an electrical nerve impulse
• Pacinian Corpuscles 


  • pressure sensor that detects changes in pressure on the skin
  • Corpuscle is an oval shaped structure that consists of a series of concentric rings of connective tissue wrapped around the end of a nerve cell
  • when pressure on skin changes this deforms the rings of connective tissue , which pushes against the nerve ending
  • corpuscle is sensitive only to changes in pressure that deform rings of connective tissue. Therefore, when pressure is constant they stop responding
• changing membrane permeability 1


  • if channels permanently open then ions diffuse across membrane and will do so until their concentrations on either side of membrane are in equilibrium.
  • if channels can be closed then action of active pumps can create concentration gradient across membrane
• changing membrane permeability 2


  • cells associated with the nervous system have specialised channel proteins. some of these, called sodium channels, are specific to sodium ions (Na+).
  • others called potassium channels are specific to potassium ions (K+). These channels also possess a gate that can open or close the channel.
• changing membrane permeability 3


  • sodium channels are sensitive to small movements of membrane, so when membrane is deformed by changing pressure the sodium channels open
  • this allows sodium ions to diffuse into cell producing a generator potential (receptor potential)
• changing membrane permeability 4

  • membranes also contain Na+/K+ pumps that actively pump Na+ ions out of the cell and K+ ions into the cell. three Na+ ions pumped out every two K+ ions pumped into cell.
  • when channel proteins are all closed, Na+/K+ ions pumps work to create a concentration gradient. concentration of Na+ ions outside cell increases, while concentration of K+ ions inside cell increases
  • membrane is more permeable to K+ ions so some of these leak out of cell. membrane is less permeable to sodium ions so few of these are able to leak into the cell.
• changing membrane permeability 5


  • result of ionic movements is a potential gradient across the cell membrane
  • cell is negatively charged inside compared with outside
  • negative potential is enhanced by the presence of negatively charged anions inside the cell.
• creating a nerve impulse 1


  • when cell is inactive the cell membrane is said to be polarised, that is negatively charged inside compared to the outside.
• creating a nerve impulse 2

  • nerve impulse is created by altering permeability of the nerve cell membrane to sodium ions. This is achieved by opening sodium ion channels
  • as sodium ion channels open, membrane permeability is increased and sodium ions can move across the membrane down their concentration gradient into the cell.
• creating a nerve impulse 3 


  • movement of ions across the membrane creates a change in potential difference (charge) across the membrane
  • inside of the cell becomes less negative (compared with outside) than usual. This is called depolarisation. The change in potential across a receptor membrane is often called a generator potential.
• creating a nerve impulse 4


  • if small stimulus detected, only few sodium channels will open.
  • the larger the stimulus, the more gated channels will open.
  • If enough gates opened and enough sodium ions enter the cell, the potential difference across cell membrane changes significantly and will initiate an impulse or action potential.