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Neuro > Neurology of the visual pathway > Flashcards

Neurology of the visual pathway Flashcards

1
Q

Visual pathway Landmarks

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

Neurones in the visual pathway

A

First Order Neurones – Rod and Cone Retinal Photoreceptors

Second Order Neurones – Retinal Bipolar Cells

Third Order Neurones – Retinal Ganglion Cells

Fourth Order Neurones- Optic Nerve

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3
Q

Optic Chiasm

A

53% of ganglion fibres cross over

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4
Q

Receptive Field

A

Retinal space within which incoming light can alter the firing pattern of a neurone

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5
Q

Receptive field of photoreceptors vs ganglion cells

A

The Receptive Field of Ganglion Cells covers a much larger area than that of a single photoreceptor.

It includes the Receptive Fields of all the photoreceptors, that synapse upon the Ganglion Cells indirectly via Bipolar Cells.

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6
Q

Convergence of Receptive fields

A

Convergence – Number of lower order neurons field synapsing on the same higher order neuron

Cone System Convergence > Rod System Convergence Central Retina Convergence > Peripheral Retina Convergence

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7
Q

Low convergence results in

A
  • Small Receptive Field
  • Fine Visual Acuity
  • Low Light Sensitivity
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8
Q

High convergence results in

A
  • Large Receptive Field
  • Coarse Visual Acuity
  • High Light Sensitivity
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9
Q

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.

Important for: Contrast Sensitivity and Enhanced Edge Detection

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10
Q

Lesions anterior and posterior to Optic Chiasma

A

Lesions anterior to Optic Chiasm affect visual field in one eye only

Lesions posterior to Optic Chiasm affect visual field in both eyes

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11
Q

What visual defect are caused by each lesion

A

Lesion in one optic nerve anterior to the Optic Chiasma- causes unilateral field loss

Lesion at Optic Chiasma- Bitemporal hemianopia

Lesion posterior to Optic Chiasma- Homonymous hemianopia (right lesion causes left homonymous hemianopia and visa versa)

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12
Q

Cause of bitemporal hemianopia

A

Typically caused by enlargement of Pituitary Gland Tumour

Pituitary Gland sits under Optic Chiasma

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13
Q

Cause of Homonymous hemianopia

A

Stroke

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14
Q

Primary Visual Cortex location

A

Situated along Calcarine Sulcus within Occipital Lobe

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15
Q

Representation of primary visual cortex(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

The right Hemifield from both eyes projects onto Left PVC

The left Hemifield from both eyes projects onto Right PVC

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16
Q

Organisation of primary visual cortex

A

Organized as columns with unique sensitivity to visual stimulus of a particular orientation

Right eye and left dominant columns intersperse each other

17
Q

Extrastriate Cortex

A

Area around PVC within the Occipital Lobe

Converts basic visual information, orientation and position into complex information

18
Q

Pathways from PVC- their function and what results if damaged

A

Dorsal Pathway

  • PVC to Posterior Parietal Cortex
  • Motion Detection
  • Visually-Guided Action
  • Damage results in Motion Blindnes

Ventral Pathway

  • Primary Visual Cortex to Inferiotemporal Cortex
  • Object Representation, Face Recognition
  • Detailed fine central vision and colour vision
  • Damage may result in Cerebral Achromatopsia
19
Q

Pupil constriction- what muscle causes it and whats the purpose

A

Iris muscle contracts to constrict the pupillary aperture

  • Decreases spherical aberrations and glare
  • Increases depth of field and reduces amount of light entering the eye
  • Reduces bleaching of photo-pigments
  • Pupillary constriction mediated by parasymapthetic nerve (within CN III)
20
Q

Pupil dilation- what muscle causes it and whats the purpose

A

Increases light sensitivity in the dark (allows more light into the eye) – radial muscle contracts

Pupillary dilatation mediated by sympathetic nerve

21
Q

Afferent pathway of Pupillary reflex

A

Pupil-specific ganglion cells exits at posterior third of optic tract before entering the LGN (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

22
Q

Efferent pathway of Pupillary reflex

A

Edinger-Westphal Nucleus -> Oculomotor Nerve Efferent

Synapses at Ciliary ganglion

Short Posterior Ciliary Nerve -> Pupillary Sphincter

23
Q

Direct vs consensual pupil reflex

A

Direct Light Reflex – Constriction of Pupil of the light-stimulated eye

Consensual Light Reflex – Constriction of Pupil of the fellow (other) eye

24
Q

Neurological basis of both pupils constructing even if only one is stimulated

A

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

25
Q

Afferent vs Efferent defects in the pupillary reflex

A

Efferent defect produces the same unequal responses between left and right eye, no matter whether left or right eye is stimulated.

Afferent defects cause no constriction in both eyes if the eye to the same side that the lesion is stimulated. But constriction in both if other eye is stimulated

26
Q

Terminology of eye movement

A

Duction- eye movement in only 1 eye

Version- Movement of both eyes in same direction

Vergence- both eyes move in opposite directions simultaneously

Convergence- simultaneous adduction

27
Q

Speed of eye movement

A

Saccade- short fast burst

Smooth pursuit- sustain slow movement

28
Q

CN III branches and functions

A

Superior Branch

o Superior Rectus – elevates eye
o Lid Levator – raises eyelid

Inferior Branch

o Inferior Rectus – depresses eye
o Medial Rectus – adducts eye
o Inferior Oblique – elevates eye
o Parasympathetic Nerve – constricts pupil

29
Q

Supraversion

A

The elevation of both eyes

30
Q

Infraversion

A

Depression of both eyes

31
Q

Dextroversion

A

Simultaneous right eye abduction, and left eye adduction.

32
Q

Levoversion

A

Simultaneous left eye abduction, and right eye adduction.

33
Q

Third nerve palsy

A

Lateral rectus muscle and superior oblique muscle only muscles working

Affected eye looks down and out

Droopy eyelid (ptosis)

34
Q

Sixth nerve palsy

A

Lateral rectus not working
Therefore causing abduction in the affected eye
Causes double vision

35
Q

Optokinetic Nystagmus

A

The eye movement elicited by the tracking of a moving field.

Uses Smooth Pursuit + Fast Phase Reset Saccade

Neuro (9 decks)

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