E2 Perception of Stimuli

Question 1

List the four kinds of human sensory receptors and their functions

Answer 1

Mechanoreceptors - changes in pressure and texture
Chemoreceptors - changes in taste and smell
Photoreceptors - changes in light
Thermoreceptors - changes in temperature

Question 2

State two similarities between cone and rod cells

Answer 2

• Both types of cell are photoreceptors

* Both types of cell are found in the retina

Question 3

Distinguish between cone and rod cells with respect to their optimal light conditions

Answer 3

Rod cells are better in dim light, while cone cells are better in bright light

Question 4

Distinguish between cone and rod cells with respect to the type of vision they provide

Answer 4

Rod cells provide black and white, while cone cells provide colour

Question 5

Distinguish between cone and rod cells with respect to their relative abundance

Answer 5

There are much more rod cells than cone cells

Question 6

Distinguish between cone and rod cells with respect to their location

Answer 6

Rod cells are found throughout the retina, while cone cells are concentrated around the fovea

Question 7

Explain the processing of visual stimuli

Answer 7

• Lens focuses light onto rod and cone cells in the retina
  
  • Visual stimuli are processed by the retina and visual cortex in the brain
  • Bipolar cells in the retina combine impulses from groups of rod or cone cells and pass them on to ganglion cells
  • Receptive field is region of retina which communicates with one ganglion
  • Low ratio of cone/ganglion cells in the fovea gives high acuity (small visual fields)
  • There are two types of ganglion cells
  • One type of ganglia are stimulated by light hitting the centre of the receptive field and inhibited by light hitting the edge (and vice-versa)
  • Edge enhancement occurs when light/dark edges fall in the receptive field
  • Both the left and right visual cortex process images from both eyes
  • The optic nerves carries impulses from the retina to the visual cortex
  • Stimulus from the right visual field of both eyes is processed in the right visual cortex (and vice-versa)
  • This crossing over of nerves is called contralateral processing, and is facilitated by the optic chiasm

Question 8

Explain how sound is perceived by the ear

Answer 8

• Sound waves are collected by the pinna
  
  • Ear drum vibrated by air pressure changes (due to sound waves)
  • Middle ear bones stimulated by ear drum, enhancing sound by 20x
  • Oval window transmits vibrations from middle ear bones to cochlea
  • Tiny hairs in cochlea act as receptors for individual wavelengths of sound
  • Action potential generated in the cochlea
  • Auditory nerve transmits action potential to brain
  • Round windows of cochlea dissipate sound