Mammalian Sensory Receptors

• Receptor cell


  A cell that responds to a stimulus
• Transducer


  Converts energy from one form (such as light, heat or sound) into energy in an electrical impulse within a sensory neurone
• Each receptor will only respond to a specific stimulus
• Receptors in the body

  • Rods and cones in the retina (detect light intensity)
  • Receptors in the skin (detect pressure, temperature, pain, touch)
  • Receptors in the hypothalamus (detect chemicals and body temperature in the blood)
  • Receptors in the ear (detect sound, movement and orientation)
  • Receptors in the muscles (detect how much muscles are stretched)
  • Receptors in the blood vessels (detect muscle stretch)
• Receptors of the body

  • Act as transducers
• Sensory receptors and their stimuli

  • Photoreceptors (light)
  • Chemoreceptors (chemicals)
  • Mechanoreceptors (mechanical strain or stretching)
  • Baroreceptors (blood pressure)
  • Osmoreceptors (body fluids)
• In any area of the skin, there are a range of different receptors present
• The different receptors have different structures and positions within the skin
• Pacinian corpuscle


  A type of mechanoreceptor found deep in the skin, present in the skin of fingers, soles of the feet as well as in joints, tendons and ligaments, responds to changes in pressure
• Process of converting mechanical pressure into a nervous impulse in a Pacinian corpuscle

  1. No pressure: Stretch mediated sodium ion channels are too narrow, sodium remains outside the membrane, resting potential is maintained

  2. Pressure is applied: The layers are distorted causing the stretch-mediated sodium channels to open, sodium ions enter the axon of the sensory neurone

  3. Generator potential is established: Influx of sodium ions changes the potential of the axon which causes depolarisation of the membrane, if enough generator potentials are produced, an action potential will be established and a nerve impulse moves along the axon
• Pacinian corpuscles are found at the ends of sensory neurone axons
• Pacinian corpuscles are not a separate cell, but instead are made of many layers of membrane around the end of the neurone separated by a gel
• The gel between the layers of the Pacinian corpuscle contains positively charged sodium ions (Na)
• The section of axon surrounded by layers of membrane contains stretch-mediated sodium ion channels which open when sufficient pressure is applied
• This allows (Na) to flow into the neurone, so that an electrical potential difference across the axon membrane is established-the generator potential
• Receptors can be cells, specifically adapted parts of a cell (e.g. the Pacinian corpuscle) or proteins on the cell surface membrane
• Many sensory receptors are found in sensory organs such as the eye or ear