Receptors

• What are photoreceptors?


  Type of receptor that detects light and other kinds of electromagnetic radiation
• What are mechanoreceptors?


  Type of receptors that detect movement, pressures, tension, gravity and sound waves
• What are chemoreceptors?


  Type of receptor that detects specific chemicals such as glucose, H+ or pheromones
• What are thermoreceptors?


  Type of receptor that detect hot and cold temperatures
• How are receptors are transducers?

  As they change one type of energy into electrical energy in a nerve impulse
• Where are receptors cells located?

  In some receptors, the receptor cell is the sensory neurone itself.

  In others, it is a separate receptor cell that synapses with a sensory neurone.

  Often part of a sense organ (e.g. ear, eye, skin)
• What receptors are found in the skin?

  Pacinian corpuscles (a type of mechanoreceptor)
• What are pacinian corpuscles?


  Receptors that's detect strong pressure and vibrations.

  -look like microscopic onion bulbs about 1mm long

  -they are situated deep in the skin

  
• What do Pacinian corpuscles consist of?

  A sensory neurone surrounded by a capsule of 20-60 layers of flattened Schwann cells and fluid called lamella

  
• How do pacinian corpuscles work?

  -Pressure distorts the neurone cell membrane and opens stretch-mediated sodium channels.

  -This allows sodium ions to diffuse in, causing a local depolarisation called the generator potential

  -The stronger the pressure, the greater the generator potentials until it reaches a threshold, when an action potential is triggered along the neurone
• What detects light in the eye?

  Photoreceptors cells in the retina called rods and cones
• Structure of the eye

  
• What is the fovea?


  the fovea is the region of the retina that only contains cones
• What is the blind spot of the eye?

  The optic disk where no receptor cells are present
• What do rods do?


  detect light intensity
• What do cones do?

  Detect wavelength of light = colour
• What are bipolar neurones?

  Special interneurones.

  Rods and cones form synapses with special interneurones called bipolar neurones which in turn synapse with sensory neurones

  The axons of these sensory neurones cover the inner surface

  
• How is visual acuity created in cones compared to rods?


  Each cone cell is connected to one bipolar neurone.

  Rod cells are connected to groups of up to 100 to a single bipolar neurone.
• What is retinal convergence?

  When more than one rod cells are connected to a single bipolar cell. This gives less visual acuity
• How do rods cells detect light?

  -membrane discs in the outer segments contain thousands of molecules of rhodopsin, the photoreceptor protein

  -when illuminated, rhodposin molecules break down which open opens the sodium channels allowing sodium ions to diffuse in. This allows a local depolarisation

  -when enough sodium channels are open the depolarisation reaches a threshold and an action potential is triggered in the rod cell

  -the action potential is passed to the bipolar neurone and then to the ganglion cells (sensory neurone) in the retina
• How do cone cells detect light?

  -cone cells contain a receptor protein called iodopsin which when illuminated, breaks down to create the generator potential

  -there are 3 types of cone cell in the eye, each with their own type of iodopsin that is stimulated by different wavelengths of light (red, blue, green)

  -stimulation of the different cone is interpreted by the brain as different colours
• What do cone/rod cells use to detect light?

  Membrane discs in the outer segments detect light
• What is the difference between rod and cone cells?

  -There is one type of rod cell and 3 type of cone cells

  -Rod cells are sensitive to low intensity light, cone cells are not sensitive to low intensity light

  -Rod cells give poor visual acuity, cone cells give good visual acuity

  -There are greater numbers of rod cells than cone cells

  -Rod cells are not found at the fovea, cone cells are concentrated at the fovea