Sensing the world Flashcards
Define a threshold potential.
The minimum level of stimulus required to create an AP. If the stimulus is below this level no AP will be generated.
How is the intensity of a stimulus conveyed?
By the frequency of APs.
APs can be different sizes. True or false?
False - every AP is always the same size.
Define a receptive field.
An area over which a neuron can pick up stimuli.
Sensitivity of a neuron is equal across its receptive field. True or false?
False - sensitivity varies, e.g. is lower at the periphery etc.
Do the receptive fields on adjacent neurons overlap?
Yes.
What affects the size of a neuron’s receptive field?
Its location on the body.
A smaller field has higher acuity than a larger one. What does this mean?
It is ‘sharper’ as it is able to distinguish independent stimuli much better.
What 2 things affect conduction velocity of a neuron?
- Axon diameter (bigger is better)
2. Myelination
Fibres can either be a) slow-adapting or b) fast-adapting. What kind of receptors do the 2 have?
a) tonic receptors
b) phasic receptors
What do slow-adapting fibres convey?
Information about stimulus size.
Is the stimulation from slow-adapting fibres ongoing or phasic?
Ongoing.
What do fast-adapting fibres convey?
Information about changes to the stimulus.
The stimulation of fast-adapting fibres is phasic. What does this mean?
Firing rate rapidly decreases and stops. These neurons are active in bursts.
What are the 4 main sensory receptors involved in touch?
- Pacinian corpuscle
- Meissner’s corpuscle
- Merkel’s disc
- Ruffini’s ending
Which 2 touch receptors are slow-adapting?
Merkel’s disc and Ruffini’s ending.
Which 2 touch receptors are fast-adapting?
Pacinian and Meissner’s corpuscle.
Which 2 touch receptors have small receptive fields?
Meissner’s corpuscle and Merkel’s disc.
Which 2 touch receptors have large receptive fields?
Pacinian corpuscle and Ruffini’s ending.
What does the somatosensory cortex do?
Represent touch in the brain.
How is the somatosensory cortex organised?
Adjacent regions of the body are closely associated in the cortex.
What is cortical magnification?
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’.
What is another name for cortical magnification?
The homunculus model.
Where does the visual pathway lie?
Through the thalamus to the visual cortex.
The optic nerve is composed of ganglion cells. What are midget cells?
A type of retinol ganglion cell that receives inputs from the rod and cone cells and then excites the optic tract.
What do the parvocellular neurons do?
Receive input from the midget cells. P-cells are located in the LGN (lateral geniculate nucleus) of the thalamus.
Why are they called parvocellular neurons?
Parvo means small.
What are magnocellular neurons?
They are the neuroendocrine cells of the hypothalamus that synthesis the hormones AVP and OT (arginine vasopressin and oxytocin).
Why are they called magnocellular neurons?
They are among the largest cells in the brain.
What kind of perception are parvocellular neurons involved in?
Chromatic perception
In monkeys, lesions to the magnocellular pathways had no effect on spatial perception, but caused an effect in…?
Flicker/motion information. The monkeys found it difficult to perceive moving objects.
What is the fovea?
A spot in the centre of the retina with the highest visual acuity, where the cone cells are concentrated.
The fovea is overrepresented in the SS cortex. Why?
It has a v. large number of receptors relative to its area on the body.
Cortical magnification can be distorted. How? Give 2 examples.
- The brain is highly plastic. When behaviours are repeated the associated area of SS cortex can increase.
- 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
Why can people still feel sensations in phantom limbs?
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.
Why do people have phantom limb pain?
The severed nerves where the limb was lost continue to fire and stimulate the cortex, even though the limb is no longer there.
What does phantom limb pain tell us about body image?
‘The body is a construct of the mind’
Not really relevant to rev just thought it was deep.
