Sensory Receptors 2

Question 1

what are the implications of size range in receptive fields?

Answer 1

+ the smaller the receptive field is, the better the linear discrimination between stimuli is

+ this is not the same as high sensitivity

Question 2

why do all areas of the body not have high linear discrimination?

Answer 2

+ high linear discrimination needs more sensory fibres/neurons to cover area with small receptive fields

+ no requirement for torso to have that level of discrimination and extra neurons would present space problem in spinal cord

Question 3

what is signal convergence?

Answer 3

+ receptive fields of multiple primary neurons overlap to from one large receptive field

+ these primary sensory neurons converge onto one secondary neuron, from which the info goes to brain as one input from a single receptive field

Question 4

what is the role of lateral inhibition?

Answer 4

enhances contrast and makes a stimulus easier to perceive

Question 5

how is contrast enhancement achieved?

Answer 5

+ primary neurons (ABC) respond proportionally to stimulus
+ secondary neuron B (directly stimulated neuron) inhibits its neighbours
+ thus increasing contrast between A/B and B/C

Question 6

what are the limitations of sensory receptors?

Answer 6

+ poor at determining absolute levels of stimulus intensity

+ better at detecting changes in space/with time and often work using comparisons

Question 7

where do first order neurons terminate?

Answer 7

spinal cord or brain stem

Question 8

where do second order neurons project to?

Answer 8

thalamus

Question 9

where do third order neurons project to?

Answer 9

brain

Question 10

where in the brain does the sensory information go?

Answer 10

• passes through the thalamus and on to the primary sensory cortex, located in a strip posterior to the post central sulcus of brain
• sensory information is projected in a topographical manner to this area, with the areas of higher discrimination having a larger proportion of the space

Question 11

what is the precision of localisation of a particular stimulus determined by?

Answer 11

• the size of the individual nerve fibre receptive field
• the density of sensory units
• the amount of overlap in nearby receptive fields

Question 12

receptor field overlap

Answer 12

aids stimulus localisation (even though it could be thought to “muddy” the image)

Question 13

variations in the results of 2 point discrimination test

Answer 13

• seen across different regions of the body
• a result of the receptive field size and receptor density in the area
• does NOT represent sensitivity to stimulus

Question 14

lateral inhibition

Answer 14

• aids in enabling localisation of stimulus
• information from afferent neurones whose receptors are at edge of a stimulus are strongly inhibited compared to information from the stimulus’ centre

Question 15

implications of the size range in receptive fields

Answer 15

• the smaller the receptive field is, the better the linear discrimination between stimuli is
• this is not the same as high sensitivity

Question 16

why are not all areas of the body given high linear discrimination?

Answer 16

• high linear discrimination needs more sensory fibres/neurones to cover the area with small receptive fields
• there is no requirement fo the torso to be able to have that level of discrimination, and the extra neurones would present a space problem in the spinal cord

Question 17

what can loss of sensation in specific, discrete areas indicate?

Answer 17

where neuronal lesions may lie