Sensing the world

Question 1

Define a threshold potential.

Answer 1

The minimum level of stimulus required to create an AP. If the stimulus is below this level no AP will be generated.

Question 2

How is the intensity of a stimulus conveyed?

Answer 2

By the frequency of APs.

Question 3

APs can be different sizes. True or false?

Answer 3

False - every AP is always the same size.

Question 4

Define a receptive field.

Answer 4

An area over which a neuron can pick up stimuli.

Question 5

Sensitivity of a neuron is equal across its receptive field. True or false?

Answer 5

False - sensitivity varies, e.g. is lower at the periphery etc.

Question 6

Do the receptive fields on adjacent neurons overlap?

Answer 6

Yes.

Question 7

What affects the size of a neuron’s receptive field?

Answer 7

Its location on the body.

Question 8

A smaller field has higher acuity than a larger one. What does this mean?

Answer 8

It is ‘sharper’ as it is able to distinguish independent stimuli much better.

Question 9

What 2 things affect conduction velocity of a neuron?

Answer 9

1. Axon diameter (bigger is better)

2. Myelination

Question 10

Fibres can either be a) slow-adapting or b) fast-adapting. What kind of receptors do the 2 have?

Answer 10

a) tonic receptors

b) phasic receptors

Question 11

What do slow-adapting fibres convey?

Answer 11

Information about stimulus size.

Question 12

Is the stimulation from slow-adapting fibres ongoing or phasic?

Answer 12

Ongoing.

Question 13

What do fast-adapting fibres convey?

Answer 13

Information about changes to the stimulus.

Question 14

The stimulation of fast-adapting fibres is phasic. What does this mean?

Answer 14

Firing rate rapidly decreases and stops. These neurons are active in bursts.

Question 15

What are the 4 main sensory receptors involved in touch?

Answer 15

1. Pacinian corpuscle
2. Meissner’s corpuscle
3. Merkel’s disc
4. Ruffini’s ending

Question 16

Which 2 touch receptors are slow-adapting?

Answer 16

Merkel’s disc and Ruffini’s ending.

Question 17

Which 2 touch receptors are fast-adapting?

Answer 17

Pacinian and Meissner’s corpuscle.

Question 18

Which 2 touch receptors have small receptive fields?

Answer 18

Meissner’s corpuscle and Merkel’s disc.

Question 19

Which 2 touch receptors have large receptive fields?

Answer 19

Pacinian corpuscle and Ruffini’s ending.

Question 20

What does the somatosensory cortex do?

Answer 20

Represent touch in the brain.

Question 21

How is the somatosensory cortex organised?

Answer 21

Adjacent regions of the body are closely associated in the cortex.

Question 22

What is cortical magnification?

Answer 22

Each sensory receptor is represented by an equal amount of area in the SS cortex, thus regions of the body with more receptors occupy more space in the brain.

‘Size devoted to an area of the body is relative to the number of neurons it has’.

Question 23

What is another name for cortical magnification?

Answer 23

The homunculus model.

Question 24

Where does the visual pathway lie?

Answer 24

Through the thalamus to the visual cortex.

Question 25

The optic nerve is composed of ganglion cells. What are midget cells?

Answer 25

A type of retinol ganglion cell that receives inputs from the rod and cone cells and then excites the optic tract.

Question 26

What do the parvocellular neurons do?

Answer 26

Receive input from the midget cells. P-cells are located in the LGN (lateral geniculate nucleus) of the thalamus.

Question 27

Why are they called parvocellular neurons?

Answer 27

Parvo means small.

Question 28

What are magnocellular neurons?

Answer 28

They are the neuroendocrine cells of the hypothalamus that synthesis the hormones AVP and OT (arginine vasopressin and oxytocin).

Question 29

Why are they called magnocellular neurons?

Answer 29

They are among the largest cells in the brain.

Question 30

What kind of perception are parvocellular neurons involved in?

Answer 30

Chromatic perception

Question 31

In monkeys, lesions to the magnocellular pathways had no effect on spatial perception, but caused an effect in...?

Answer 31

Flicker/motion information. The monkeys found it difficult to perceive moving objects.

Question 32

What is the fovea?

Answer 32

A spot in the centre of the retina with the highest visual acuity, where the cone cells are concentrated.

Question 33

The fovea is overrepresented in the SS cortex. Why?

Answer 33

It has a v. large number of receptors relative to its area on the body.

Question 34

Cortical magnification can be distorted. How? Give 2 examples.

Answer 34

1. The brain is highly plastic. When behaviours are repeated the associated area of SS cortex can increase. 2. If body parts are lost and no longer used, their area of the SS cortex is reclaimed by another body part, e.g. if a digit is lost then it will be used by adjacent fingers

Question 35

Why can people still feel sensations in phantom limbs?

Answer 35

The part of their cortex that was responsible for that limb has been reclaimed by another body part. Thus when this body part is touched it can also give the patient a sensation in a phantom limb.

Question 36

Why do people have phantom limb pain?

Answer 36

The severed nerves where the limb was lost continue to fire and stimulate the cortex, even though the limb is no longer there.

Question 37

What does phantom limb pain tell us about body image?

Answer 37

'The body is a construct of the mind' Not really relevant to rev just thought it was deep.