the optic nerve and visual pathways

Question 1

what is in the outermost segment of rods and cones

Answer 1

discs containing light sensitive photo pigment

Question 2

what is the inner segment of rods and cones made of

Answer 2

cell body, axon and synaptic terminals

Question 3

what do the discs do

Answer 3

phototransduction - absorb light, send electrical signal

Question 4

what is the pigment in rods

Answer 4

rhodopsin

Question 5

what is the pigment in cones

Answer 5

opsin

Question 6

what are opsins

Answer 6

transmembrane proteins which contain the light sensitive molecule retinal
different opsin structures mean retinal absorbs different wavelengths of light

Question 7

effect of a photon on a rhodopsin molecule

Answer 7

triggers confirmation change to all trans form
this change triggers changes in the opsin structyre
this triggers a cascade within the cell

Question 8

what does it mean by graded response of photo receptors

Answer 8

greater light intensity results in greater reduction in neurotransmitter release

Question 9

signals in the retina

Answer 9

photoreceptor-> bipolar cell -> retinal ganglion cell

Question 10

where is information from the eyes transmitted to

Answer 10

the primary visual cortex of the occiptal lobe

Question 11

where do the eyes receive inputs from

Answer 11

from the temporal & nasal visual fields

Question 12

where is the primary visual cortex located

Answer 12

predominantly on the medial surface of
the hemisphere in the region above &
below the calcarine sulcus

Question 13

what is the visual association cortex

Answer 13

the rest of the occipital lobe that is not primary visual cortex

it is concerned with interpretation of visual images, recognition, depth perception & colour vision

Question 14

where is the optic nerve developed from

Answer 14

from the optic vesicle, an outpocketing of the forebrain

Question 15

what is the optic nerve surrounded by

Answer 15

cranial mengines

Question 16

what can the anatomical course of the optic nerve be divided into

Answer 16

1. extracranial (outside the cranial cavity)
2. intracranial components.

Question 17

describe extracranial optic nerve course

Answer 17

1. optic nerve is formed by the convergence of axons from the retinal ganglion cells.
2. These cells in turn receive impulses from the photoreceptors of the eye (the rods and cones).
3. optic nerve leaves the bony orbit via the optic canal, a passageway through the sphenoid bone.
4. it enters the cranial cavity, running along the surface of the middle cranial fossa (in close proximity to the pituitary gland).

Question 18

describe intracranial optic nerve course

Answer 18

1. within the middle cranial fossa, the optic nerves from each eye unite to form the optic chiasm.
2. At the chiasm, fibres from the nasal (medial) half of each retina cross over to the contralateral optic tract, while fibres from the temporal (lateral) halves remain ipsilateral
3. Left optic tract – contains fibres from the left temporal (lateral) retina, and the right nasal (medial) retina.
   Right optic tract – contains fibres from the right temporal retina, and the left nasal retina.
4. Each optic tract travels to its corresponding cerebral hemisphere to reach the lateral geniculate nucleus (LGN), a relay system located in the thalamus; the fibres synapse here.