Sensory: vision

Question 1

How many different opsins can the cones express, and how do they differ?

Answer 1

Three: OPN1SW (short waves=blue), OPN1MW (midlength waves=green), OPN1LW (long waves=red)

Question 2

What is the function of rods and cones?

Answer 2

Rods: spatial resolution, more light sensitive
Cones: colour vision

Question 3

What does the retinal molecules bind to?

Answer 3

Opsin

Question 4

Describe the signaling pathway in cilliary photoreceptors

Answer 4

Photon stimulates the conversion of 11-cis-retinal bound to the opsin to all-trans-retinal –> release of retinal, and activation of the opsin receptor. Opsin is coupled to a Gt protein, and by activation the G_alpha is released from G-beta-gamma. G-alpha activates PDE –> reduction of cGMP –> inhibition of CNG Na+ channel –> inhibition of Ca^2+ influx (and AP) –> inhibition of glutamine release

Question 5

How is the signal inhibited in cilliary cells, and when does this happen?

Answer 5

GRK1 phosphorylates opsin –> inactivation of opsin –> increase of cGMP –> increase of Ca^2+ –> depolarization of Vm –> release of glutamate
During darkness

Question 6

What does the dynamic range of an eye refer to and how is it controlled in the human eye?

Answer 6

The number of photons the rods and cones can absorb depending on the brightness of a habitat.
It’s controlled by the number of active opsins in the retina (called adaptation), by controlling the process of conversion all-trans-retinal to 11-cis-retinal.

Question 7

What is the lens involved in?

Answer 7

Accomodation: making sure the resolution matches the distance by contracting or extending the lens. Near/long sigthness is caused by a flaw in this mechanism.

Question 8

What is the fovea?

Answer 8

Cones lined in the back of the eye directly in line with the lens (in the centre of the optical axis of the eye) not covered by any other cells –> no interference. It is packed densely with cone cells.

Question 9

How does the pupil dialate, and which neuronss innervate the muscles responsible for this?

Answer 9

The radially smooth muscles of the iris (the dialator pupillae) contract, dialating the pupil. The dialator pupillae are innervated by adrenergic, sympathetic neurons

Question 10

How does the pupil constrict, and which neuronss innervate the muscles responsible for this?

Answer 10

The circular smooth muscles of the iris (the sphincter pupillae) contract, constricting the pupil. The sphincter pupillae are innervated by cholinergic, parasympathetic neurons.

Question 11

How many layers is the retina consisting?

Answer 11

3 layer: rods and cones in the back, bipolar, horizontal and amacrine cells in the middel and retinal ganglion cells in the front (+ ipRGCs)

Question 12

Describe a rod cell.

Answer 12

Glutamatergic, rod-shaped neuron containing discs. Discs are organels lined with rhodopsin. The ros are depolarized in the darkness, and hyperpolarized in the light.

Question 13

What is rhodopsin?

Answer 13

GPCR of the rods (opsin), with a bound retinal molecule (11´cis-retinal). They are light activated. When light hits the retinal, it converts from 11´cis- to all-trans-retinal, pushing the TM regions of the opsin. This configuration change activates the GPCR. Rhodopsin is tranducin coupled.

Question 14

What are ipRGCs involved in?

Answer 14

The circadian rhytm and pupillary light reflexes.

Question 15

Which regions of the brain does ipRGCs and rod cells project to, respectively.

Answer 15

ipGRCs project to the non-image forming center, the pineal gland (RHT -> suprachiasmatic nucleus -> paraventricular nucleus -> spinal cord -> SCG -> pineal gland).
Rod cells project to the image-forming center, the primary visual cortex (through the nucleus geniculatus).

Question 16

How is the retina formed?

Answer 16

As an outpocekting of the diencephalon

Question 17

What is accomodation?

Answer 17

When the eye is adjusted for sharp vision at short distances

Question 18

How are the response to light?

Answer 18

Graded: mirroring the light intensity

Question 19

What is the function of the pigment epithelium?

Answer 19

To move worn out photoreceptor discs

Question 20

What is the center-surround organization?

Answer 20

Can either be center on/off

Question 21

What type of NT does the horizotal cells use?

Answer 21

GABA

Question 22

What type of NT does the bipolar cells use?

Answer 22

Glutamate

Question 23

What type of NT does ganglion cells use?

Answer 23

Glutamate

Question 24

What types of ganglion cells are there, and how do they differ?

Answer 24

3:
P-type: parvocellular cells/midget cells
- small RF and dendrite tree
- slowly adapting, slow conduction of APs, low light sensitivity
- 90 % of ganglion cells
- specializes in visual acuity

M-type: magnocellular cells/parasol cells
- large RF, and dendritic tree
- fast adaption and conduction of APs, high light sensitivity
- 5 % of ganglion cells
- specializes in movement

K-type
- non-P, non-M type cells

Question 25

What is the term for having three types of cones?

Answer 25

Trichromat

Question 26

Describe the signal route from the retina to the brain.

Answer 26

--> optic nerve --> optic chiasm --> optic tract --> hypothalamus/pretectum/superior colliculus/lateral geniculate nucleus --> optic radiation --> primary visual cortex

Question 27

Which axons cross in the optic chiasm?

Answer 27

Axons from the nasal half of the retina

Question 28

Describe layer IV of the primary visual cortex.

Answer 28

- main input layer for thalamic projections - edge detectors - oriented in ocular dominance columns (right/left eye) and orientation columns - P- and M-type ganglion cells project to layer IV

Question 29

Describe the non-input layers of V1.

Answer 29

- binocularity - ON/OFF system convergence - partial M/P systems

Question 30

True/false: there are one visual area in the human brain.

Answer 30

False, there are multiple

Question 31

What are some of the other visual layers called, and what are their function?

Answer 31

V2 (corners, surfaces), V3, V4 (complex shapes) and inferior temporal cortex (faces etc)

Question 32

What are the dorsal and ventral stream perceiving, and where are they projecting to?

Answer 32

Dorsal: where? --> V1--> MT--> parietal lobe --> motor areas Ventral: what? --> V1 --> V4--> inferior temporal lobe --> limbic system

Question 33

What are cerebral akinetopsia, and what symptoms can it cause?

Answer 33

Bilateral damage to area MT from a stroke: - dorsal stream defect --> lack of ability to perceive movement - ventral stream defect --> lack of ability to perceive color

Question 34

What are prosopagnosia, and what can it be caused by?

Answer 34

Face blindness Can result from damage to the inferior temporal cortex (ventral stream)