receptors

Question 1

what features are common to all sensory receptors

Answer 1

acts as energy transducers which establish a generator potential

respond to specific stimuli

Question 2

describe the basic structure of a pacinian corpuscle

Answer 2

• single nerve fibre surrounded by layers of connective tissue (lamella) which are separated by viscous gel and contained by a capsule
• stretched-mediated Na+ channels on plasma membrane
• capillary runs along base layer of tissue

Question 3

what stimulus does a pacinian corpuscle respond to

Answer 3

• pressure deforms membrane - lamellae
• stretch-mediated (pressure gated) Na+ ion channels open
• Na+ diffuses in, causing depolarisation
• influx of Na+ raises membrane to threshold potential
• generator potential is produced
• the more pressure - the more Na+ channels open, the larger the GP
• the large the GP, the more likely that a threshold level is reached - triggers action potential
• intensity of stimulus, determines the size of GP - determines frequency of action potentials

Question 4

why have lamellae

Answer 4

• reduced sensitivity of nerve ending - useful to prevent detection of stimuli below threshold
• lamellae and gel result in corpuscle only signalling changes in pressure

Question 5

2 types of photoreceptor cell

Answer 5

cone cells

rod cells

Question 6

where are rod and cone cells located in the retina

Answer 6

rod - evenly distributed around periphery but not in central fovea

cone - mainly central fovea - no photoreceptors at blind spot

Question 7

compare rods and cones

Answer 7

Pigment
Acuity (visual acuity)
Colour sensitivity
Light sensitivity

rods
P - rhodopsin
A - low acuity - many rod cells synapse with 1 bipolar neuron
C - monochromatic - all wavelengths of light detected
L - very sensitive - spatial summation of subthreshold impulses

cone
P - 3 types of iodopsin
A - high acuity - 1 cone cell synapse with 1 bipolar neuron - no retinal convergence
C - tricolour - red, blue, green wavelengths absorbed by different types of iodopsin
L - less sensitive

Question 8

outline the pathway of light from a photoreceptor to the brain

Answer 8

photoreceptor -> bipolar neuron -> ganglion cell of optic nerve -> brain

Question 9

rods

Answer 9

light causes rhodopsin to break down - sheets of membrane with photosynthetic pigment
causing production of generator potential
release of neurotransmitter to bipolar neuron
if enough neutransmitter Na+ release for action potential

connected in groups - spatial summation - low light but low acuity

Question 10

photoreceptors

Answer 10

specialised cells in eye to detect light and convert to neural signal