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Neuro > Neuro13: Neurology of the visual system > Flashcards

Neuro13: Neurology of the visual system Flashcards

1
Q

Outline the visual pathway anatomy

A

Eye,
optic nerve (ganglion nerve fibres),
Optic Chiasm – Half of the nerve fibres cross here

Optic Tract – Ganglion nerve fibres exit as optic tract

Lateral Geniculate Nucleus – Ganglion nerve fibres synapse at Lateral Geniculate Nucleus

Optic Radiation – 4th order neuron

Primary Visual Cortex or Striate Cortes – within the Occipital Lobe

Extrastriate Cortex

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2
Q

Outline pathway of 1st, 2nd, 3rd and 4th order neurones in the visual pathway

A

1st order are the rods and cones photoreceptors

2nd order are the retinal bipolar cells

3rd order are the retinal ganglion cells, the axons of which travel in the optic nerve and eventually synapse in the LGN of the thalamus

4th order neurons begin at the LGN adnd go to optic radiation

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3
Q

What percentage of 3rd order neurons decussate at the optic chiasm

A

53% of ganglion fibres cross the midline

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4
Q

T/F retinal ganglion fibres are myelinated

A

T, but only after entering the optic nerve

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5
Q

What us the receptive field of a photoreceptor

A

Retinal space within which incoming light can alter the firing pattern of a neuron- – a small circular space surrounding the photoreceptor

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6
Q

What is meant by convergence of receptive field

A

Number of lower order neurons field synapsing on the same higher order neuron….

retinal ganglion cells can bipolar cells from different photoreceptros synapsing onto them…

the more photoreceptors feeding into 1 retinal ganglion cell, the higher the convergence

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7
Q

Which photoreceptors have the highest convergence

Differentiate convergence of rods near macula vs in the periphery

A

Rods have higher convergence than cones so more rods synapse onto a retinal ganglion cell, than cones onto retinal ganglion cells

Nearer to the macula, there is lower convergence for rods than in the periphery (i.e. in the centre less rods synapse onto each retinal ganglia)

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8
Q

Differentiate the size of receptor fields for the ganglion cells in the cone system and rod system (and also rods near the macula vs in the peripher)

A

Ganglion cells in cone system have smaller receptive field than rod system,

Ganglion cells in rod system near macula have smaller receptive field than those near the peripohery

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9
Q

What does a small and large retinal ganglion receptive field give rise to

A

Small receptive field- fine visual acuity

large receptive field- higher light sensitivity

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10
Q

Differentiate on-centre and off centre ganglion cells

A

On-centre Ganglion:
stimulated by light at the centre of the receptive field
Inhibited by light on the edge of the receptive field

Off-centre Ganglion:
Inhibited by light at the centre of the receptive field
Stimulated by light on the edge of the receptive field

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11
Q

What is on-centre and off-centre ganglion cells important for

A

Contrast Sensitivity

Enhanced Edge Detection

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12
Q

Differentiatie the effect of a lesion anterior and posterior to optic chiasma

A

Lesions anterior to Optic Chiasma affect visual field in one eye only
Lesions posterior to Optic Chiasma affect visual field in both eyes

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13
Q

Which parts of the retina do i. crossed fibres (i.e. those than decussate at optic chiasma) and ii. uncrossed fibre come from

A

crossed fibres: originate from NASAL side of the retina, resposible for temporal visual field

uncrossed fibre: Uncrossed Fibres – originating from temporal retina, responsible for nasal visual field

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14
Q

What gives edge detection and sharpness

A

The positive stimulus of one part of the retina and the negative simulus to the neighbouring part

(i.e. on an off centre retinal ganglion cells, see above)

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15
Q

Effect of following lesions:

  1. Optic chiasma
  2. Lesion posterior to optic chiasma (on the right hand side in this case)
A
  1. You get damage to crossed fibres from nasal retina so loss of temporal vision in both eyes= BILATERAL HEMIANOPIA
  2. Right side- damage to uncrossed fibres temporal retina of right eye, and to crossed fibres from the nasal part of the left eye. So you lose temporal vision in left eye and nasal vision in your right eye…. so LEFT HOMONYMOUS HEMIANOPIA (and opposite for the right)

visual pathway lesion posterior to the chiasma produces contralateral Homonymous Hemianopia in both eyes.

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16
Q

Explain which lesions would lead to the following visual field disorders:

  1. Monocular blindness
  2. Right nasal hemianopia
  3. Bitemporal hemianopia
  4. Homonymous hemianopia
  5. Quadrant anopia
  6. Macular sparing
A
  1. Optic nerve on one side
  2. Half of optic chiasm affected (on the right side at front, as this will have nasal crossed fibres from right eye just before they cross)
  3. Middle of optic chiasm
  4. Optic tract (post. to optic chiasm)
  5. Damage far back in the visual pathway
  6. Damage further back (because back in the cortex, you have a really high representation of the macula here, so you need large damage in this area to lose the macula)

The further back you go, the smaller the damage to the receptive field

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17
Q

Cause of bitemporal hemianopia

A

Typically caused by enlargement of Pituitary Gland Tumour

Pituitary Gland sits under Optic Chiasma

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18
Q

Cause of homonymous hemianopia

A

Stroke (Cerebrovascular Accident)

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19
Q

Where is primary visual cortex located

A

Situated along Calcarine Sulcus within Occipital Lobe

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20
Q

PVC also known as

A

Striate Cortex

21
Q

Outline representation on the PVC

A

Disproportionately large area representing the macula

Superior Visual Field projects to below the Calcarine Fissure

Inferior Visual Field projects to above the Calcarine Fissure

Right Hemifield from both eyes projects to Left Primary Visual Cortex

Left Hemifield from both eyes projects to Right Primary Visual Cortex

22
Q

Function of PVC

A

Cortex specializes in processing visual information of static and moving objects.

23
Q

Organisation of the primary visual cortex

A

In columns which have a unique sensitivity to visual stimulus of a particular orientation

….. right eye and left eye doninant columns interspersed.

24
Q

Outline macular sparing homonymous hemianopia

A

DUE TO STROKE….

- leads to contralateral homonymous hemianopia but is macular sparing

25
Q

Why is the area of the PVC representing the macula usually spared in Macular Sparing Homonymous Hemianopia

A

Because this area of PVC receives dual blood supply from posterior cerebral arteries from both sides

26
Q

What is the extrastriate cortex

A

Area around Primary Visual Cortex within the Occipital Lobe

Converts basic visual information, orientation and position into complex information

27
Q

Outline the 2 pathways in the extrastriate cortex

A

DORSAL:
Primary Visual Cortex -> Posterior Parietal Cortex
for MOTION detection (think about motion in the back p)
Visually guided action
WHERE

VENTRAL:
Primary Visual Cortex -> Inferiotemporal Cortex

Object Representation, Face Recognition
Detailed fine central vision and colour vision
WHAT

28
Q

What might damage in dorsal pathway or ventral pathway of the extrastriate cortex result in?

A

Dorsal: Motion Blindness

Ventral:Cerebral Achromatopsia

29
Q

Outline what happens in pupillary constriction in light

A

decreases spherical aberrations and glare
—– spherical aberration is when light from the outside of the lens bent more than the light coming through the centre of the lens as the outside is more bent. Closing the pupil aperture prevents light from passing through the bent part of the lens, and ensures it only travels through the centre…. allowing less glare due to the reduced spherical anberation

increases depth of field – see Near Response Triad from Previous Lecture
reduces bleaching of photo-pigments

Pupillary constriction mediated by parasymapthetic nerve (within CN III)

iris circular muscle contracts,
and constricts the pupillary aperture.

30
Q

What happens in darkness with pupllary dilation

A

increases light sensitivity in the dark by allowing more light into the eye
pupillary dilatation mediated by sympathetic nerve activating the iris radial muscle

(but greater spherical aberration so some glare)

31
Q

Outline the afferent pathway in pupillary reflex (was year 1 neuro!)

A

AFFERENT
Rod and Cone Photoreceptors synapsing on Bipolar Cells synapsing on Retinal Ganglion Cells

Pupil-specific ganglion cells exits at posterior third of optic tract before entering the Lateral Geniculate Nucleus

Synpases at Brain Stem (Pretectal Nucleus)

Afferent (incoming) pathway from each eye synapses on Edinger-Westphal Nuclei on both sides in the brainstem

32
Q

Outline efferent pathway in pupillary reflex

A

Edinger-Westphal Nucleus -> Oculomotor Nerve Efferent ->

Synapses at Ciliary ganglion ->

Short Posterior Ciliary Nerve -> Pupillary Sphincter

33
Q

Differentiate a direct and consensal reflex

A

Direct Light Reflex –Constriction of Pupil of the light-stimulated eye
Consensual Light Reflex – Constriction of Pupil of the fellow (other) eye

34
Q

Explain why you get consensual reflex

A

Afferent pathway on either side alone will stimulate efferent (outgoing) pathway on both sides

35
Q

Explain the damage to the reflex in the following conditions:

  1. Right afferent defect
  2. Right efferent defect
  3. Unilateral afferent defect
  4. Unilateral efferent defect
A
  1. No constriction in either eye when light shines in right. When light shines in left, both eyes constrict
  2. Right eye doesn’t constrict, whether right or left stimulated w light….
    left eye constricts fine with either eye stimulated
  3. Difference response pending on which eye stimulated
  4. Same unequal response between left and right eye irrespective of the eye stimulated
36
Q

What is the RAPD

A

Relative afferent pupillary defect…..

there is still a small reflex response if there is damage afferent

If right is damaged, when left eye stimulated, both constrict normally,

when you then swing the torch to shine in the right eye,

there will be a dilation (from the constrction state as a result of relatively reduced dive for pupillary constriction IN BOTH EYES

37
Q 
Define following terms: 
Duction
Version
Vergence
Convergence
A

Duction – Eye Movement in One Eye

Version – Simultaneous movement of both eyes in the same direction (dextroversion to right and levoversion to left)

Vergence – Simultaneous movement of both eyes in the opposite direction

Convergence – Simultaneous adduction (inward) movement in both eyes when viewing a near object

38
Q

What is a sacade

A

short fast burst, up to 900deg/sec

Reflexive saccade to external stimuli

Scanning saccade

Predictive saccade to track objects

Memory-guided saccade

39
Q

What is a smooth pursuit and differentiate it to saccade

A

sustain slow movement
Slow movement – up to 60°/s

Driven by motion of a moving target across the retina.

Involuntary

A saccade is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction.[1] In contrast, in smooth pursuit movements, the eyes move smoothly instead of in jumps. The phenomenon can be associated with a shift in frequency of an emitted signal[clarification needed] or a movement of a body part or device.[2] Controlled cortically by the frontal eye fields (FEF), or subcortically by the superior colliculus, saccades serve as a mechanism for fixation, rapid eye movement, and the fast phase of optokinetic nystagmus

40
Q

Function of extraocular muscles

A

Attach eyeball to orbit

Straight and rotary movement

41
Q

Name the 4 straight muscles

A

Superior rectus
Inferior rectus
Lateral rectus
Medial rectus

42
Q

Name the 2 diagonanal muscles

A

Superior oblique

Inferior oblique

43
Q

Function of the Superior rectus

A

Attached at 12 o;clock… pulls the eye up

44
Q

Function of inferior rectus

A

Attached at 6 oclock pulls eye down

45
Q

Function of lateral rectus

A

Attaches on the temporal side of the eye

Moves the eye toward the outside of the head (toward the temple)

46
Q

Function of medial retus

A

Attached on the nasal side of the eye

Moves the eye toward the middle of the head (toward the nose)

47
Q

Superior oblique function and attachment

A

Attached high on the temporal side of the eye.
Passes under the Superior Rectus.
Moves the eye in a diagonal pattern – down and in.
Travels through the trochlea

BE CAREFUL OF THIS…. it’s kind of different to the anatomy…. I think the one from steve gentleman with my notes it generally better.

48
Q

Function of the inferior oblique and attahment

A

Attached low on the nasal side of the eye.
Passes over the Inferior Rectus.
Moves the eye in a diagonal pattern – up and out.

49
Q

State the innervation of the extraocular muscle

A

3rd–> superior branch: superior rectus (elevates eye) and lid levator. Inferior branch: medial rectus, inferior rectus, inferior oblique (elevates eye) and parasympathetic nerve to contstrict pupil
4th–> superior oblique
6th–> lateral rectus (abducts eye)

there’s some more to do with cranial nerve testing. and nerve palsy

Neuro (16 decks)

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