Lecture 21 - vision continued and hearing

Question 1

Retina is responsible for

Answer 1

The retina is responsible for converting light energy into patterned changes of membrane potential

Question 2

Information from what is combined for the retina …

Answer 2

nfo from photoreceptors and interneurons is combined, so that the output from ganglion cells depend critically on the spatial and temporal pattern of light stimulation on the retina.

Question 3

Receptive fields

Answer 3

Receptive fields – in the fovea very small, in the periphery of the retina much bigger (therefore the fovea has the best vision

Question 4

Refractions is done by

Answer 4

Lens and cornea

Question 5

Complete the pathway … Photoreceptors receive light

Answer 5

Photoreceptors receive light - goes through complex network of interneurons - then get an action potential firing from the retinal ganglion cells - axons of the retinal ganglion cells project to optic disk ( blind spot, called this because there are no photoreceptors here)

Question 6

Visual pathway

Answer 6

Information is sent from eye to visual centres in brain in such a way as to preserve spatial relationships between visual stimuli.
So, visual info from objects in left visual space is processed in right brain, and vice versa. For this to happen, some info must cross to opposite side of brain, some must remain on same side.

Question 7

Nasal retina

Answer 7

Nasal retina – contralateral (cross)

Question 8

Temporal retina

Answer 8

Temporal retina – Ipsilateral (don’t cross)
Information from our nasal retina crosses over to the other side of our brain contralaterally, information from our temporal retina stays on the same side of the brain (projects ipsilaterally)
The optic chasm is where the nasal retina retinal ganglion cells cross
Axons of the retinal ganglion cells project down the optic tract
There is one lateral geniculate nucleus on each side, here the info synapses and is sent to the visual cortex in the occipital lobe

Question 9

Retinal ganglion cells send

Answer 9

Retinal ganglion cells send axons to visual centres in the brain

Question 10

How many retinal ganglion cells per retina

Answer 10

There are approximately 1 million ganglion cells per retina (1 million nerve cells per optic nerve)

Question 11

Axons leave retina at

Answer 11

Axons leave retina at the optic disc

No photoreceptors at this point (blind spot)

Question 12

Axons from ganglion cells in nasal retina

Answer 12

Axons from ganglion cells in nasal retina cross at the optic chiasm to project contralaterally

Question 13

Axons from ganglion cells in temporal retina

Answer 13

Axons from ganglion cells in temporal retina do not cross, they project ipsilaterally

Question 14

Information from the two retinae is …

Answer 14

By this means, information concerning images from visual space falling on equivalent parts of the two retinae is brought together for central processing

Question 15

Ganglion cell axons project to 4 main subcortical visual areas

Answer 15

1) Superior colliculus
Concerned with eye movements and orientation to visual stimuli
2) Lateral Geniculate Nucleus
Concerned with the sensation of vision
these cells send axons and information to the visual cortex
3) Pretectum
Control of pupils
Near response = accommodation, convergence, constriction - constriction is controlled by the pretectum
4) Suprachiasmatic nucleus
Control of diurnal rhythms
Responsible for adapting our eyes to day and night vision

Question 16

Superior colliculus

Answer 16

Concerned with eye movements and orientation to visual stimuli

Question 17

Lateral Geniculate Nucleus

Answer 17

Concerned with the sensation of vision

these cells send axons and information to the visual cortex

Question 18

Pretectum

Answer 18

Control of pupils

Near response = accommodation, convergence, constriction - constriction is controlled by the pretectum

Question 19

Suprachiasmatic nucleus

Answer 19

Control of diurnal rhythms

Responsible for adapting our eyes to day and night vision

Question 20

After processing by visual cortex, information can be sent to…

Answer 20

Temporal lobe- for identification of objects in visual space (the “what”) ( what they are in our visual space)
Parietal lobe- for processing of information regarding the location of objects in space (the “where”) (whereabouts the object is)
(Once we sensed vision, you can see object but might require an action such as moving out of the way) information passes to frontal cortex (from the temporal and parietal lobe), where it is used to help direct actions

Question 21

Function in the visual cortex

Answer 21

The place where objects in and out of their visual context are analysed in detail.
For analysis of form, there are cells responding to edges and corners
For analysis of movement, there are cells responding to direction of movement and direction of movement in relation to background
For analysis of colour, there are cells responding to wavelengths coming from an object in relation to wavelengths coming from objects nearby, and an average of wavelengths from objects in other parts of the field of view.
All of this comes together to form our image/visual perception of the world

This information is used to discriminate between objects and backgrounds, to tell us what objects are, where they are, and where they are moving.

Question 22

Retinal is a

Answer 22

Retinal is a chromophore that sits within the membrane spanning protein called opsin

Question 23

In the dark =

Answer 23

Dark = intracellular concentration of cGMP level to be high

Question 24

Action potentials and neurotransmitter release in retina processing

Answer 24

All the photoreceptors and interneurons release neurotransmitter and excite each other locally and once it gets to the retinal ganglion cell, if they have been excited enough then they will fire action potentials to other parts of the brain

Question 25

Astigmatism

Answer 25

Astigmatism caused by aspherical curvature of the cornea and lens

Question 26

Hypermetropia

Answer 26

Hypermetropia = light is focused beyond the plane of the retina

Question 27

Majority of refractive power comes from

Answer 27

the cornea

Question 28

What would annular illumination activate?

Answer 28

Annular illumination would activate an ‘off-centre’ retinal ganglion cell.

Question 29

What would diffuse illumination activate?

Answer 29

Neither type are activated by diffuse illumination

Question 30

What is sound?

Answer 30

pressure waves in the atmosphere

Question 31

Zones of compression

Answer 31

Zones of compression = regions of high pressure due to particles being close together

Question 32

Zones of rarefactions

Answer 32

Zones of rarefactions = regions of low pressure due to particles being spread further apart

Question 33

Frequncy =

Answer 33

Frequency = pitch
Measured in hertz
Higher the frequency of the sound, the more waves there are per frequency
The lower the frequency, the less waves there are per second

Question 34

Amplitude =

Answer 34

Amplitude = loudness 
Also called intensity 
Quiet = small amplitude 
Loud = large amplitude 
Measured in decibels (dB)

Question 35

Peaks and troughs in graph represents

Answer 35

Peaks in graph are high pressure and troughs are low pressure

Question 36

Threshold of hearing

Answer 36

Humans can detect down to about 20 Hz
As you get older, your range of hearing reduces
Human voices range between 700 to 1200 Hz

U shaped graph

Question 37

Damage to hearing apparatus

Answer 37

Doesnt recover when you damage it so you have permanent hearing damage