Receptors (BIOL5)

Question 1

Features of receptors

Answer 1

• Receptors specific - only detect one particular stimulus
• When nervous system receptor in resting state, there’s a diff in charge b/w inside/outside of cell - generated by ion pumps/channels
  
  • Voltage across membrane - potential difference
  • Resting potential - potenial difference at rest
• When stimulus detected, cell membrane excited, becomes more permeable, allowing more ions to move in/out of cell, altering potential diff
  
  • Generator potential - change in potential diff
• Bigger stimulus excites membrane more, causing bigger movement of ions and change in potential diff - bigger generator potential made
• If gen pot reaches threshold, will trigger action potential (electrical impulse along neurone)
• AP all one size - strength of stimulus measured by freq. of AP
• If stimulus too weak, gen pot won’t reach threshold, so there’s no AP.

Question 2

Features of pacinian corpuscles

Answer 2

• Contain end of sensory neurone - sensory nerve ending
• Wrapped in lamellae
• When stimulated, lamellae deformed, press on sensory nerve ending
• Cause deformation of stretch-mediated Na channels in sensory neurone’s membrane
• Na channels open, Na+ diffuse w/ cell, creating gen pot
• If gen pot reaches threshold, triggers an act pot

Question 3

Features of photoreceptors

Answer 3

• Light detected by photoreceptors
• Fova contains lots of receptors
• Nerve impulses from photoreceptor cells carried from retina to brain by optic nerve
• Where optic nerve leaves eyes - blind spot
  
  • No photoreceptors!

Question 4

How do photoreceptors convert light into impulses?

Answer 4

• Light enter eye
• Hits photoreceptors, absorbed by light-sensitive pigments
• Light bleaches pigments, causing chemical change
• Nerve impulse sent along bipolar neurone
  
  • Bipolar neurone connect photoreceptors to optic nerve, send impulses to brain

Question 5

Features of rods

Answer 5

• Give info in black/white
• V. sensitive to light - fire AP in dim light as many join one neurone!
  
  • Many weak gen pot combine to reach threshold and trigger AP
• Low visual acuity - many rods join same neurone
  
  • 2 objects close can’t be told apart!

Question 6

Features of cones

Answer 6

• Give info in colour
• Less sensitive - one cone joins neurone
  
  • More light needed to reach AP
• High visual acuity - cones close together
  
  • One cone per neurone
  • When light from 2 points hits 2 cones, 2 AP go to brain
    
    • Can distinguish 2 points close together as 2 separate points!