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Y2 HNN > Visual Pathway Lab Briefing > Flashcards

Visual Pathway Lab Briefing Flashcards

1
Q

what is the role of the visual pathway

A

involved in the relay of light from the visual field of both eyes, to the primary visual cortex in the occipital lobe of the brain.

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2
Q

How do rays of light travel to the retina

A

Rays of light from the visual field are refracted by the cornea so that they pass through to the retina, which is located at the back of the eye.

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3
Q

Describe the structure of the retina and how it helps in the visual processing pathway

A

The retina is a multi-layered structure and the deepest layer consists of photoreceptor cells called rods and cones, which convert light energy into a neural impulse.

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4
Q

How is the neural signal produced by photoreceptor cells travel to the optic nerve

A

The neural signal is transmitted through intermediate layers of bipolar and horizontal cells, to the retinal ganglion cells (RGC) which reside within the innermost surface of the retina.
The cell bodies of retinal ganglion cells are close to the vitreous humour of the eye. Axons of the retinal ganglion cells (RGCs) exit the eye at the optic disc, where the axons then form the optic nerve.

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5
Q

Briefly name the components of the visual pathway

A 
*goes downwards*
Optic nerve
Optic chiasm 
Optic Tract
Lateral Geniculate Nucleus
Optic Radiation
Visual Cortex
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6
Q

Describe Optic nerve

A

2nd CN
Outgrowth of the brain
Paired nerve
Each optic nerve contains sensory afferent nerve fibres from the left or right eye
Axons of the retinal ganglion cells form the optic nerve

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7
Q

Describe optic chiasm

A

50-60% (partial) decussation of the nerve fibres contained within the optic nerve (50-60% of the nerve fibres from each eye cross over)

–> This allows the visual cortex of both the left and right cerebral hemispheres to receive visual information from BOTH eyes and permits binocular and stereoscopic vision- perception of depth and 3-dimensional structure is obtained.

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8
Q

Describe Optic Tract

A

Nerve fibres now travel as the optic tracts and are no longer part of the optic nerve.
This is because the optic nerves carry nerve fibres from one eye only, whereas the optic tract contains nerve fibres from both the left and right eyes.

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9
Q

Describe Lateral Geniculate Nucleus

A

Relay centre of thalamus
6 layers of alternating grey and white matter

Nerve fibres from optic tract project to LGN
Nerves of the optic tract terminate within the LGN and synapse with neurons located within the LGN.

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10
Q

Describe Optic Radiations

A

The neurons of the LGN then project to the visual cortex via the optic radiations, so called because the nerve fibres fan out to form a distinctive anatomical feature

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11
Q

what is the visual cortex also known as?

A

The primary visual cortex can also be called V1 (vision 1 – since it is the primary visual processing area) or the ‘striate cortex’, because of its striped appearance, which is due to a prominent band of myelinated nerves fibres

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12
Q

Not all nerve fibres within the visual pathway project to the lateral geniculate nucleus. some project somewhere else. what is this place and what are their functions

A

Midbrain area:

  • Superior colliculus: eye movements
  • pretectal area: pupillary light reflex
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13
Q

The left eye receives both right and left visual fields, but they are transmitted to different parts of the left eye. Name these

A

LEFT EYE:

  • LEFT visual field transmitted to NASAL retina of left eye
  • RIGHT visual field transmitted to TEMPORAL retina of left eye
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14
Q

What is the fate of the right visual field which transmits to the temporal retina of the left eye.

A
  • Axons from the retinal ganglion cells (RGC) of the TEMPORAL RETINA exit the left eye via the LEFT optic nerve and then STAY on the LEFT HAND SIDE of the pathway
  • Axons travel through optic tract and into the LEFT LGN
  • Neurons of the left LGN project to the LEFT visual cortex through optic radiations
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15
Q

Stimuli from the right visual field projects to the ______ visual cortex

A

left

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16
Q

What is the fate of the left visual field which transmits to the nasal retina of the left eye.

A
  • Axons from the Retinal ganglion cells (RGC) of the NASAL RETINA exit the left eye via the LEFT optic nerve and then CROSSES over to the RIGHT HAND SIDE of the pathway at the OPTIC CHIASM
  • Axons travel through RIGHT optic tract and into the RIGHT LGN
  • Neurons of the right LGN project to the RIGHT visual cortex through optic radiations
17
Q

stimuli from the left visual field projects to the _____ visual cortex

18
Q

what side do the nerve fibres stay on that arise from the temporal side of retina and nasal side of retina

A

temporal- stay on same side

nasal- crosses over to other side at optic chiasm

19
Q

Will lesion of optic nerve affect one or both eyes?

A

vision disturbance in one eye only

20
Q

Will lesion of optic chiasm and other downstream components of the pathway affect one or both eyes?

A

vision disturbance in both eyes

21
Q

partial and complete lesion of an optic nerve leads to what?

A
  • Partial lesion: Ipsilateral scotoma (blind spot in visual field)
  • Complete lesion: ipsilateral blindness
22
Q

what are the causes of lesions of optic nerve

A
  • Acute optic neuritis – demyelinating inflammation of the optic nerve occurs (can occur in MS patients)
  • Indirect traumatic optic neuropathy (blunt trauma to the optic nerve)
  • Optic atrophy
  • Fibres of the optic nerve can be lost as a result of ischaemia or tumours which may be compressing the nerve
23
Q

what does Central lesions of the optic chiasm result in

A
  • loss of nerve impulses from the NASAL RETINA of both eyes
  • (recall: nasal retina receives info from TEMPORAL VISUAL FIELD)
  • Therefore, central lesions would results in Loss of vision in temporal visual field of both eyes
  • -> called BITEMPORAL HEMIANOPIA
24
Q

What causes lesions of the optic chiasm

A

Tumours

  • pituitary adenoma (close proximity of pituitary stalk to optic chiasm)
  • meningioma (tumour of meninges)

Aneurysms
- Anterior communicating artery- can compress chiasm

25
Q

what does lesion of the optic tract result in

A

EXAMPLE:

  • A lesion of the right optic tract will lead to loss of vision from the left visual field of both eyes and vice versa
  • -> homonymous hemianopia
26
Q

what causes lesions of the optic tract

A

tumours, trauma, aneurysm of posterior cerebral artery

27
Q

what other lesions can also cause homonymous hemianopia

A

Lesions of the LGN, optic radiation & visual cortex can also lead to homonymous hemianopia

28
Q

what does the goldman perimetry test assess and how

A

Tests the extent of a patient’s visual field and therefore identify visual field defects

A test light is used as the stimulus (kinetic or static)
Visual field can be mapped according to detection of the light

Y2 HNN (34 decks)

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