Overview of the Main Sensory Organs

Question 1

Definition of sensory transduction

Answer 1

Conversion of stimulus energy to electrical energy

Question 2

Definition of receptor potential

Answer 2

Electrical impulse generated by receptors when stimulated

Question 3

What are the sense organs

Answer 3

Eyes
Ears
Tongue
Nose

Contain sensory receptors
Sensory transduction of stimuli energy => electrical energy

Question 4

What are the 5 types of sensory receptor

What do they do

Answer 4

Thermoreceptor
-somatosensory, temperature

Nociceptor
-somatosensory

Mechanoreceptor
-skin and hearing

Chemoreceptor
-taste and smell

Electromagnetic
-vision

Receptors are specialised to detect stimuli
Generate receptor potential

Question 5

Describe the pathway for taste transduction with sugar molecules

Answer 5

Taste bud consist of many taste receptor cells

Sugar molecule binds to sugar receptor => signal transduction pathway
K channels close
Influx of Na => depolarization
Fusion of NT vesicles in exocytosis
Receptor potential generated

Question 6

Describe the pathway for smell transduction

Answer 6

Odorants bind to receptors
Olfactory receptor cells activated, send receptor potentials
Signal relayed via converged axons
Transmitted to higher regions

Question 7

Describe the 2 types of electromagnetic receptors found here

Answer 7

Electromagnetic receptors => photoreceptors found on retina

Rods

• v sensitive to photons
• used in low light
• rhodopsin (retinol + opsin)

Cones

• colour vision
• needs lots of light
• photopsin

Question 8

Describe the sensory pathway of the rods in the dark

Answer 8

Inactive rhodopsin
Na channels open
Rod depolarised
Glutamate released
Bipolar cell depolarised/hyperpolarised depending on the receptor

Question 9

Describe the sensory pathway of the rods in the light

Answer 9

Active rhodopsin
Na channels closed
Rod hyperpolarised
No glutamate released
Bipolar cell depolarised/hyperpolarised depending on the receptor

Question 10

What happens when photoreceptors die

Answer 10

Blindless

Retinitis pigmentosa

Question 11

Describe the auditory pathway

Answer 11

Uses mechanoreceptors (hair cells)
Organ of Corti found in cochlea

Vibrations of air in ear => stereocilia bend
Influx of K into hair cell => depolarisation
Opens VGCC => fusion of NT vesicles
Exocytosis of NT onto spinal ganglion
Generation of receptor potential

Question 12

Describe how the intensity of the stimulus is coded

Answer 12

Intensity of stimulus reflected in amplitude of receptor potential

Stronger stimulus
Increased receptor potential
Increased frequency of AP firing

Question 13

Describe how different taste stimuli is coded in sensory transduction

Answer 13

Sugar stimulates sugar receptor cell
Salt stimulates salt receptor cell

Sugar neurone fire onto sugar interneuron => increased rate of AP firing
Salt neurone fires into salt interneuron => increased rate of AP firing

Question 14

How are different smell stimuli coded

Answer 14

100-200 different odorant receptor
Different combinations discriminate between many smells
Work in the same way as different taste receptors via interneurons

Question 15

How are different colour stimuli coded

Answer 15

3 types of cone
-blue photopsin
-green photopsin
-red photopsin
Combination of 3 cones => different colours

Question 16

Describe the pathway for sensory transduction of different positions in the visual field

Answer 16

Each point in space will activate the corresponding photopsin in the retina => map of visual space based on relative positions of the cells in the retina

Nasal hemifield => temporal retina
Lateral hemifield => nasal retina
Impulse sent down optic nerve to occipital lobe

Question 17

Describe the sensory transduction of pitch

Answer 17

Frequency of sound wave => pitch
Coded by position on cochlear

Highest pitches at the base of the cochlea
Lowest pitches at the apex of the cochlea