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MODULE 8 - Neurology > FUNCTIONAL ANATOMY - Vision > Flashcards

FUNCTIONAL ANATOMY - Vision Flashcards

1
Q

What is the optical axis?

A

The axis that provides an optically clear image

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2
Q

What is the visual axis?

A

The axis that allows for colour perception

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3
Q

What is the focal point?

A

When light passes through the cornea and the lens, the light is refracted and will converge at a point behind the lens. This point is known as the focal point

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4
Q

How is the distance between the lens and the focal point influenced by the visual field?

A

If a visual stimulus is closer to the lens, the focal point will be further behind the lens whereas if the visual stimulus is further from the the lens, the focal point will be closer behind the lens.

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5
Q

What is the accommodation ability?

A

The ability of the eye to focus on visual stimuli at different distances through changing the shape and curvature of the lens through contraction of the ciliary muscles

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6
Q

Which species have a limited accommodation ability?

A

Horses

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7
Q

How do horses focus on visual stimuli at different distances?

A

The shape of the retina allows horses to focus on visual stimuli at different distances through moving their head up and down

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8
Q

What are the two main photoreceptors in the retina?

A

Rod cells
Cone cells

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9
Q

What is the function of rod cells?

A

Rod cells detect changes in light intensity

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10
Q

What is the function of cone cells?

A

Cone cells detect different wavelengths of visible light

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11
Q

Describe how photons of light are converted to neural impulses by photoreceptors (rod and cone cells)

A

Photons of light bind to retinal which is bound to the membrane protein opsin (collectively known as rhodopsin), activating the G-protein transducin which in turn activates the phosphodiesterase enzyme (PDE). PDE catalyses the hydrolysis of cGMP to GMP, triggering the closure of Na+ channels in the cells membrane of the photoreceptor, triggering hyperpolarisation of the photoreceptor

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12
Q

Why is the hyperpolarisation of photoreceptors (rod and cones cells) essential for the transmission of visual information?

A

In the absence of light, rod and cone cells continually inhibit the activation of bipolar cells. Hyperpolarisation of the rod and cone cells in response to light removes their inhibition of the bipolar cells allowing for these bipolar cells to activate ganglion cells

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13
Q

What is the function of ganglion cells?

A

Ganglion cells integrate information from the bipolar cells and transmit this information to the brain via the optic nerve

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14
Q

What is the receptive field of ganglion cells?

A

Ganglion cells are specifically sensitive to light in certain regions of the visual field (e.g. the centre or periphery), so, when light is detected by photoreceptors, this information will be conveyed to the appropriate ganglion cells to process that specific visual information

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15
Q

What is melanopsin?

A

Melanopsin is a photoreceptor expressed by the ganglion cells

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16
Q

What is the function of melanopsin?

A

Melanopsin is involved in regulating the circadian rhythm

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17
Q

Describe the central visual pathway

A

Neural impulses are transmitted from the retina along cranial nerve II (optic nerve) to the optic chiasm and via the optic tract to the lateral geniculate nucleus in the thalamus, followed by the optic radiation. Information is then transmitted to the visual cortex followed by either the dorsal or ventral streams

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18
Q

What is the function of the optic chiasm?

A

The optic chiasm is the point where the optic nerves (CNII) from the left and right eyes cross to allow for information from the left and right visual fields to be processed by both sides of the brain

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19
Q

What are the two cells types found within the lateral geniculate nucleus in the thalamus?

A

Parvocellular cells
Magnocellular cells

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20
Q

What is the function of parvocellular cells?

A

Parvocellular cells integrate information from cone cells and are essential for perceiving colour and form

21
Q

What is the function of magnocellular cells?

A

Magnocellular cells integrate information from rod cells and are essential for perceiving motion and depth

22
Q

How does the lateral geniculate nucleus exhibit a retinotopic topography?

A
23
Q

What is the function of the visual cortex in the visual pathway?

A

The visual cortex integrates information from the parvocellular and magnocellular cells to begin visual perception

24
Q

What are the three cells types found in the
visual cortex?

A

Simple cells
Complex cells
Hypercomplex cells

25
Q

What is the function of simple cells?

A

Simple cells process specific orientations of light (i.e. specific orientated edges)

26
Q

What is the function of complex cells?

A

Complex cells process specific orientations and movements of light

27
Q

What is the function of hypercomplex cells?

A

Hypercomplex cells process light with a well-defined end point or boundary

28
Q

What is the function of the dorsal stream?

A

The dorsal stream transmits information related to movement and spatial relationships in the visual field from the visual cortex to the parietal lobe

29
Q

What is the function of the ventral stream?

A

The ventral stream transmits information related to the object identification and recognition from the visual cortex to the temporal lobe

30
Q

What is the common clinical sign seen when there is damage to the dorsal stream?

A

Optic ataxia

31
Q

What is the common clinical sign seen when there is damage to the ventral stream?

A

Unable to recognise and identify objects

32
Q

Which region of the retina has the highest density of cone cells?

A

Fovea

33
Q

What are the three types of cone cells found in the retina?

A

Blue cone cells
Green cone cells
Red cone cells

34
Q

What is the trichromatic theory of colour vision?

A

The perception of colour is based on the three cone cells which are sensitive to different wavelengths of visual light

35
Q

What is the opponent-process theory of colour vision?

A

The perception of colour is based on the activity of opposing colour pairs

36
Q

What are ‘blobs’?

A

‘Blobs’ are regions of specialised neurones in the visual cortex which process colour information

37
Q

What are the six tests that can be done to asses vision in veterinary medicine?

A

Navigation of an unfamiliar environment
Cotton ball test
Visual placing
Pupillary light reflex (PLR)
Menace response
Dazzle reflex

38
Q

Describe the pupillary light reflex (PLR) pathway

A

Neural impulses are transmitted from the retina along cranial nerve II (optic nerve) to the optic chiasm and via the optic tract to the pretectal nucleus followed by the parasympathetic nucleus of cranial nerve III (oculomotor nerve) which initiates bilateral pupil constriction

39
Q

The function of which two cranial nerves is assessed by testing the pupillary light reflex?

A

Cranial nerve II (optic nerve)
Cranial nerve III (oculomotor nerve)

40
Q

Describe the menace response pathway

A

Neural impulses are transmitted from the retina along cranial nerve II (optic nerve) to the optic chiasm and via the optic tract to the lateral geniculate nucleus in the thalamus. Information is then transmitted to the visual cortex followed by the motor cortex, followed by the pontine nucleus and to the cerebellum. Information is then transmitted to parasympathetic nucleus of cranial nerve VII (facial nerve) which stimulates blinking

41
Q

The function of which two cranial nerves is assessed by testing the menace response?

A

Cranial nerve II (optic nerve)
Cranial nevre VII (facial nerve)

42
Q

What is the dazzle reflex?

A

The dazzle reflex is the involuntary blinking in response to a sudden bright light

43
Q

Describe the dazzle reflex pathway

A

Neural impulses are transmitted from the retina along cranial nerve II (optic nerve) to the optic chiasm and via the optic tract to the pretectal nucleus followed by the parasympathetic nucleus of cranial nerve VII (facial nerve) which initiates bilateral blinking

44
Q

What are the two classifications of blindness?

A

Cortical (central) blindness
Subcortical (peripheral) blindness

45
Q

Lesions in which two structures can cause cortical (central) blindness?

A

Lateral geniculate nucleus
Visual cortex

46
Q

What are the three clinical signs of cortical (central) blindness?

A

Normal pupillary light reflex (PLR)
Absent menace response
Blindness

47
Q

Lesions in which four structures can cause subcortical (peripheral) blindness?

A

Eye
Cranial nerve II (optic nerve)
Optic chiasm
Optic tract

48
Q

What are the three clinical signs of subcortical (peripheral) blindness?

A

Absent pupillary light reflex (PLR)
Absent menace respire
Blindness

MODULE 8 - Neurology (27 decks)

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