Introduction to Sensory Physiology and Perception

Question 1

what do receptors do?

Answer 1

detect the stimulus

Question 2

types of receptors

Answer 2

photoreceptors, chemoreceptors, thermoreceptors, mechanoreceptors

Question 3

examples of mechanoreceptors

Answer 3

pressure on skin, pressure in musculoskeletal system (proprioception), head movement (equilibirum), sound

Question 4

samtosenroy system

Answer 4

inflammatory chemicals, temperature, pressure on skin, pressure in musculoskeletal system

Question 5

what is the main somatosensory pathway?

Answer 5

primary afferent -> medulla –> thalamus –> cortex

Question 6

what are somatosensory receptors also known as?

Answer 6

primary afferents

Question 7

what are all-in-one receptors resilient to?

Answer 7

injury

Question 8

whats different about other systems compared to somatosensory/olfactory?

Answer 8

receptors are separate cells. e.g. visual system, auditory and vestibular systems.

Question 9

what is special about separate receptors?

Answer 9

they are delicate and irreplaceable e.g. photoreceptors

Question 10

what are photoreceptors susceptible to?

Answer 10

light damage, genetic mutations, metabolic diseases, malnourishment

Question 11

what are auditory hair cells susceptible to?

Answer 11

noise trauma, genetic mutations, ototoxicity, (chemotherapy agents, amino-glycoside antibiotics)

Question 12

how can sensation be resorted?

Answer 12

if afferent survives, electronic system can stimulate sensation back. any acitivity in afferents will be interpreted as sensation so if rest of system is intact, function is restored

Question 13

what is cochlear implant?

Answer 13

25 electrodes in ear that can stimulate afferents

Question 14

how can gene therapy be used for photoreceptor restoration?

Answer 14

produce retinal cells to be photosensitive

Question 15

what does transduction do?

Answer 15

produce electronic potentials

Question 16

what does pressing on sensitive endings do?

Answer 16

produces receptor potentials that may give rise to action potentials

Question 17

action potential threshold

Answer 17

Membrane potential at which action potentials are triggered.

This is a function of the vgNa+ channel and can be treated as a constant

Question 18

‘activation’ threshold

Answer 18

Minimum stimulus strength that will depolarise a receptor enough to generate action potentials.
Sensory systems use receptors with a range of
different activation thresholds.

Question 19

“Perceptual” threshold

Answer 19

Minimum stimulus strength that will generate enough action potentials to be detected.
Perceptual threshold is the bit we can most easily test in a
clinical environment.

Question 20

is afferent signal a faithful copy of stimulus?

Answer 20

NO

Question 21

spatial resolution is limited

Answer 21

due to receptive field

Question 22

why cant you read braille with skin of arm?

Answer 22

receptive field sizes vary across the body

Question 23

why can you read braille with skin of fingertips?

Answer 23

1mm receptive fields. smaller receptive fields means higher innervation density

Question 24

spatial resolution is variable

Answer 24

the higher the innervation density, the more cortex needed to deal with the input

Question 25

characteristic of temporal resolution

Answer 25

it is limited and varies with receptor type

Question 26

what happens if you press down on skin with finger?

Answer 26

rigorous action potentials, but then the sensory systems will adapt to constant stimuli and go back to original state

Question 27

what is the implication of adapting to unchanging stimuli?

Answer 27

• By damping down responses to unchanging stimuli, adaptation highlights moments when stimulus strength changes
• and allows vigorous responses to small changes
  without saturation
• Different receptors types adapt at different rates

Question 28

why does sensory system adapt?

Answer 28

So that it can respond to changes in the stimulus pressure, instead of action potentials getting worse. It means it can notice the change better

Question 29

what is lateral inhibition?

Answer 29

same as adaptation but in spatial rather than temporal. highlights locations where stimulus strength changes. Increases spatial resolution

Question 30

what are inhibitory interneurones?

Answer 30

causes secondary afferents to dampen down responses to homogeneous stimuli. increase spatial resolution

Question 31

What are the dynamic ranges?

Answer 31

Adaptation and lateral inhibition damp down responses to homogeneous temporal and spatial stimulation

Question 32

what do afferents do?

Answer 32

encode changes/differences rather than absolute levels so that they can therefore respond strongly to small changes over large stimulus range

Question 33

what does increasing dynamic range mean?

Answer 33

reduces issue of saturation

Question 34

perceptual threshold

Answer 34

what youre measuring if you do clinical sensory testing

Question 35

receptive fields

Answer 35

determine the dimensions of test stimuli

Question 36

adaptation

Answer 36

determines the temporal characteristics of test stimuli

Question 37

lateral inhibition

Answer 37

feature of sensory processing

Question 38

Implication of Damage and Disease

Answer 38

Can differentially affect different types of receptor (you need to choose the right test)
Can increase perceptual threshold where receptors are lost (look for loss of sensation)
BUT neural damage can disrupt inhibitory systems and lead to hypersensitivity

Question 39

why are there different receptors in the skin?

Answer 39

they each detect different qualities of touch

Question 40

how are quaities represented in primary cortical areas?

Answer 40

by columns

Question 41

what do you actual experience?

Answer 41

a reconstruction based on the pattern of AP firing in the cerebral cortex

Question 42

examples of the brain/somatosensory system getting the reconstruction wrong?

Answer 42

• epileptic activity e.g. somatosensory system, can generate phantom sensations running across the body surface.
• phantom limbs
• synaesthsia e.g. auditory input activates visual colour processing area, so a person “sees” sounds as coloured.
• pain

Question 43

what is synaesthesia?

Answer 43

auditory input activates visual colour processing area, so a person “sees” sounds as coloured.