Senses and perception 1

Question 1

What is tactile input?

Answer 1

stimulation of skin receptors from touch, pressure, pain and temperature.

Question 2

What features of the tactile input does the body process?

Answer 2

quality (type of touch), intensity/magnitude, duration, location

Question 3

What structure converts a stimulus into an action potential (electrical signal)?

Answer 3

modality-specific sensory receptors

Question 4

How is the information from the stimulus transmitted to the brain?

Answer 4

via modality-specific sensory pathways (differs for each quality e.g. pain, touch…)

Question 5

What type of morphology does a sensory neuron have?

Answer 5

pseudounipolar morphology

Question 6

Why is a sensory neuron described as pseudounipolar?

Answer 6

it has an axon that projects from the cell body for a short distance before splitting into a central and peripheral branch

Question 7

Function of a sensory neuron (skin receptor)

Answer 7

relays information from the periphery to the CNS

Question 8

What part of the sensory neuron is activated by the stimulus?

Answer 8

receptor ending

Question 9

What determines the type of receptor ending of a neuron?

Answer 9

the modality of the sensory neuron

Question 10

What type of receptor detects mechanical stimuli?

Answer 10

Mechanoreceptor

Question 11

What type of receptor detects thermal stimuli?

Answer 11

thermoreceptor

Question 12

What type of receptor detects noxious stimuli?

Answer 12

nociceptor

Question 13

What type of sensation does a mechanical stimuli produce?

Answer 13

touch

Question 14

What type of sensation does a thermal stimuli produce?

Answer 14

temperature

Question 15

What type of sensation does a noxious stimuli produce?

Answer 15

pain

Question 16

What are the special senses?

Answer 16

taste, smell, vision, pain

Question 17

What type of stimuli is responsible for taste and smell?

Answer 17

chemical

Question 18

What type of receptor detects chemical stimuli?

Answer 18

chemoreceptor

Question 19

What type of stimulus is responsible for vision?

Answer 19

light

Question 20

What type of receptor detects light stimuli?

Answer 20

photoreceptor

Question 21

What modality of receptors are free nerve endings?

Answer 21

nociceptors (perceive pain)

Question 22

Examples of different types of mechanoreceptors

Answer 22

Meissner’s corpuscle, Merkel disk, hair follicle receptor, Pacinian corpuscle, Ruffini ending

Question 23

Why are there multiple, histologically distinct mechanoreceptors?

Answer 23

each mechanoreceptor is associated with a particular quality of mechanical tactile stimulation e.g. hair deflection (hair follicle receptor), vibration, slippage

Question 24

What term defines the distribution of a sensory neuron’s receptor endings?

Answer 24

receptive field

Question 25

Where are receptor endings (aka sensory receptors) located?

Answer 25

at the end of terminal/peripheral branches of sensory neurones

Question 26

Why do receptive fields of different sensory neurons overlap?

Answer 26

to ensure complete coverage and to allow responses to a range of stimuli

Question 27

What is the general trend in size variation of receptive fields in different body regions?

Answer 27

receptive fields are small in the periphery and increase in size towards the trunk (proximally)

Question 28

What technique is used to estimate receptive field size (spatial resolution)?

Answer 28

two point discrimination

Question 29

What does two point discrimination test?

Answer 29

ability to discern two separate mechanical stimuli

Question 30

When will 2 distinct stimuli be perceived as one point?

Answer 30

if the stimuli are applied close enough together to be within the same receptive field

Question 31

Why can 2 stimuli be felt as one point if they are applied closely together?

Answer 31

the 2 stimuli are applied within a single receptive field so only one sensory neurone is activated

Question 32

How are receptive field sizes measured?

Answer 32

the maximum distance between two points that are perceived as one stimulus

Question 33

What is meant by the transduction of a stimulus?

Answer 33

the conversion of a stimulus into an electrical signal (AP)

Question 34

What is the outline of the sequence of stimulus transduction?

Answer 34

stimulus causes a change in receptor membrane permeability allowing an influx of cations. This leads to depolarisation/receptor potential which results in an action potential if the threshold is reached.

Question 35

What is depolarisation also known as?

Answer 35

receptor potential

Question 36

What is the resting membrane potential is mV approximately?

Answer 36

-70mV

Question 37

What is the membrane potential in mV approximately at the peak of the action potential?

Answer 37

+35mV

Question 38

What are the 2 subtypes of receptors (/receptor endings)?

Answer 38

ionotropic and G-protein coupled receptors

Question 39

Describe the kinetics of ionotropic receptors

Answer 39

fast kinetics

Question 40

Describe the kinetics of G-protein coupled receptors?

Answer 40

slow kinetics

Question 41

What receptor modalities are ionotropic receptors?

Answer 41

mechanoreceptors and chemoreceptors

Question 42

What receptor modalities are G-protein coupled receptors?

Answer 42

chemoreceptors

Question 43

Describe an ionotropic mechanoreceptor in its inactive state

Answer 43

the ion channel is closed and tethered to the cell membrane by fibrils on the intracellular/cytoplasmic side of the phospholipid bilayer. Ions cannot enter the receptor ending

Question 44

How does stimulus transduction via an ionotropic mechanoreceptor occur?

Answer 44

a force deforms the membrane which pulls on the underlying fibrils causing the ion channel to open. Na+ can enter causing depolarisation

Question 45

Describe ionotropic chemoreceptors in their inactive state

Answer 45

the ligand binding sites on the extracellular surface of the ion channel are empty so the ion channel is closed. Ion passage cannot occur

Question 46

How does stimulus transduction via an ionotropic chemoreceptor take place?

Answer 46

A specific ligand binds to the binding site causing a conformation change in the ion channel structure. The ion channel opens which allows Na+ influx and depolarisation.

Question 47

Describe the structure of a G-protein coupled receptor

Answer 47

An extracellular ligand binding site is linked to an ion channel via a series of proteins

Question 48

Which type of receptors have a slower rate of action?

Answer 48

G-protein coupled receptors are slower (chain of events required for activation) than ionotropic receptors

Question 49

How are chemoreceptors activated?

Answer 49

by a ligand

Question 50

Describe the stimulus transduction via G-protein coupled chemoreceptors

Answer 50

The ligand binding site becomes occupied when a specific ligand binds. This triggers a chain of events relayed along a series of proteins which results in the opening of the ion channel.

Question 51

How is the quality (e.g. pain, temperature, touch) of the stimulus coded for?

Answer 51

via the type of receptor

Question 52

What are the 2 ways the intensity of a stimulus can be coded for?

Answer 52

via the AP frequency or the number of neurones activated

Question 53

Why does the number of activated neurones correspond to stimulus intensity?

Answer 53

different receptors have different thresholds therefore the greater the intensity, the more thresholds will be met and the more neurones depolarised

Question 54

What happens to the frequency of AP discharge as the stimulus intensity increases?

Answer 54

AP frequency increases

Question 55

Why is there a limit to the maximum AP frequency?

Answer 55

due to the refractory period (time taken for Na+ to become responsive and the resting membrane potential to be re-established)

Question 56

How is stimulus duration coded for?

Answer 56

by the duration of AP firing

Question 57

What is meant by adaptation of sensory receptors?

Answer 57

the decline in receptor potentials when sensory receptors are constantly exposed to a stimulus

Question 58

What is the pattern of AP firing in slowly adapting receptors?

Answer 58

there is a high frequency of AP firing at the onset which decreases towards the end of the stimulus. But a level of discharge is maintained as long as the stimulus persists.

Question 59

What is the pattern of AP firing in rapidly adapting neurones?

Answer 59

very high AP frequency at onset and then quickly adapts to become silent for remainder of stimulus

Question 60

How is the location of the stimulus coded for?

Answer 60

by the receptive field which is activated

Question 61

What is the name of the map depicting the cortical representation of sensory inputs from different body parts?

Answer 61

sensory homunculus

Question 62

What is the name of a fold of the cerebral cortex?

Answer 62

gyrus

Question 63

Where does the sensory homunculus run along?

Answer 63

the length of the gyrus of the primary sensory cortex

Question 64

Why is the body map distorted in the sensory homunculus?

Answer 64

Receptive field size and density varies. Regions with smaller receptive fields and so higher RF density have greater cortical representation, whereas areas with larger receptive fields have a lower RF density resulting in limited cortical representation.

Question 65

Example of an area of the body with small receptive fields and therefore a high density?

Answer 65

face, fingers

Question 66

Example of area of the body with large receptive fields and therefore a low density?

Answer 66

trunk, proximal areas of limbs