Neurology of the Visual System Flashcards
7 landmarks of the visual pathway?
- Eye
- Optic nerve- Ganglion nerve fibres
- Optic chiasm- Half of the nerve fibres cross here
- Optic tract- Ganglion nerve fibres exit as the optic tract
- Lateral Geniculate Nucleus- Ganglion nerve fibres synapse here
- Optic Radiation- 4th order neuron
- Primary Visual Cortex or Striate Cortex- within the occipital lobe
1st order neurons of the retina?
rod and cone photoreceptors
2nd order neurons of the retina?
retinal bipolar cells
3rd order neurons of the retina?
retinal ganglion cells
afferent innervation of the retina is via the …
optic nerve
Partial decussation of the optic nerve occurs in the …
optic chasm
Destination of the optic nerve/
Lateral geniculate nucleus
What is the receptive field of a neuron
a retinal space within which incoming light can alter the firing pattern of a neuron
In a retinal ganglion cell there is a convergence of XX from YY
receptive fields
neighbouring photoreceptors
Cone system divergence is [more/less] than rod system convergence
Less
- Central retina convergence is [more/less] than peripheral retina convergence
Less
Low convergence:
receptive field size?
Visual acuity level?
Light sensitivity?
Small receptive field, fine visual acuity, low light sensitivity
High convergence:
receptive field size?
Visual acuity level?
Light sensitivity?
Large receptive field, coarse visual acuity, high light sensitivity
What cell is between the rod/cone photoreceptor and the retinal ganglion cell
retinal Bipolar cells
ON-centre ganglions are stimulated by and inhibited by light where?
- Stimulated by light at the centre of the receptive field
- Inhibited by light on the edge of the receptive field
OFF-centre ganglions are stimulated by and inhibited by light where?
- Inhibited by light at the centre of the receptive field
- Stimulated by light on the edge of the receptive field
What are on and off centre ganglion cells important for
contrast sensitivity and enhanced edge detection
Fibres that cross in the optic chiasm originate in the X retina and correspond to the Y visual field
nasal
temporal
LESION AT OPTIC CHIASMA causes…
BITEMPORAL HEMIANOPIA
LESION posterior to the OPTIC CHIASMA causes…
- Right sided lesion- left homonymous hemianopia in both eyes
- Left sided lesion- right homonymous hemianopia in both eyes
7 types of visual field defects
monocular blindness bitemporal hemianopia right/left nasal hemianopia right/left homonymous hemianopia TR/TL/BR/BL quadrant-anoxia Macular sparing homonymous hemianopia
Cause of bitemporal hemianopia
pituitary gland tumour
Cause of bitemporal hemianopia
stroke
Primary visual cortex is located along the …
calcarine sulcus within occipital lobe
Primary visual cortex is characterised by….
a distinct stripe derived from the myelinated fibre of optic radiation projecting onto the visual cortex
Where are the superior/inferior/right/left visual fields found
- Superior visual field projects to below Calcarine fissure
- Inferior visual field projects to above Calcarine fissure
- Right hemifield from both eyes projects to left primary visual cortex
- Left hemifield from both eyes projects to right primary visual cortex
How is the primary visual cortex organised and what are they sensitive to
- Organised as columns with unique sensitivity to visual stimulus of a particular orientation
- Right and left eye dominant columns alternate
what causes MACULAR SPARING HOMONYMOUS HEMIANOPIA
Damage to primary visual cortex:
- Often due to stroke
MACULAR SPARING HOMONYMOUS HEMIANOPIA leads to…
contralateral homonymous hemianopia with macula sparing
Why is the macula spared in MACULAR SPARING HOMONYMOUS HEMIANOPIA
- Area representing macula in the primary visual cortex receives dual blood supply from posterior cerebral arteries from both sides so it is spared
Where is the EXTRASTRIATE CORTEX
around primary visual cortex within occipital lobe
What does the EXTRASTRIATE CORTEX do
Converts basic info, orientation and position into complex information
2 pathways of the extra striate cortex?
DORSAL pathway
VENTRAL pathway
What is the dorsal pathway of the extra striate cortex
- Primary visual cortex -> Posterior parietal visual cortex
What is the ventral pathway of the extra striate cortex
- Primary visual cortex -> Inferiotemporal visual cortex
What is the ventral pathway of the extra striate cortex responsible for (2)
- Motion detection
- Visually-guided action
Visual cortex is also known as the…
striate cortex
What is the ventral pathway of the extra striate cortex responsible for (4)
- Object representation
face recognition - Detailed fine central vision
colour vision
Damage to the dorsal visual pathway results in…
motion blindness
Damage to the ventral visual pathway results in…
Cerebral achromatopsia
What nerve mediates pupil constriction
Optic
Pupil constriction - [increases/decreases] depth of field
Increases
Afferent pathway of the pupillary reflex? (4)
- Rod and cone receptors synapsing on bipolar cells which synapse on retinal ganglion cells
- Pupil-specific ganglion cell exits at posterior third of optic tract before entering LGN
- Synapses at brainstem (pretectal nucleus)
- Afferent pathway from each eye synapses on EDINGER-WESTPHAL nuclei on both sides of the brainstem
Efferent pathway of the pupillary reflex? (4)
- Edinger-westphal nucleus Oculomotor nerve efferent
- Synapses at ciliary ganglion
- Short posterior ciliary nerve Pupillary sphincter
DIRECT light reflex is…
Constriction of pupil of the light-stimulated eye
CONSENSUAL light reflex is…
Constriction of pupil of the fellow (other) eye
Neurological basis of consensual light reflex?
afferent pathway on either side alone will stimulate efferent pathway on both sides
What is the result of a torch test on an eye with:
RIGHT AFFERENT defect
e.g. damage to optic nerve)- no pupil constriction on both eyes when right eye is stimulated with light but normal pupil constriction of both pupils when left eye is stimulated with light
What is the result of a torch test on an eye with:
RIGHT EFFERENT defect
(e.g. damage to right 3rd nerve)- no right pupil constriction whether right or left eye stimulated with light but left pupil constricts whether right or left eye stimulated with light
What is the result of a torch test on an eye with:
UNILATERAL AFFERENT defect
Difference in response depending on which eye is stimulated
What is the result of a torch test on an eye with:
UNILATERAL EFFERENT defect
Same unequal response between left and right eye irrespective of which eye is stimulated
How many extraocular muscles
6
DUCTION means?
Movement in one eye
VERSION means?
Simultaneous movement of both eyes in same direction
VERGENCE means?
Simultaneous movement of both eyes in the opposite direction
CONVERGENCE means?
Simultaneous adduction (inwards) movement in both eyes when viewing a near object
What is SACCADE movement
Short fast burst (up to 900/sec)
What is smooth pursuit movement
Sustained slow movement (up to 60/s)
- Driven by motion of a moving target across the retina
6 muscles of the eye names?
SUPERIOR RECTUS INFERIOR RECTUS LATERAL RECTUS MEDIAL RECTUS SUPERIOR OBLIQUE INFERIOR OBLIQUE
Attachment and movement of the eye of the superior rectus?
Attached to the eye at 12 o’clock- moves the eye up
Attachment and movement of the eye of the inferior rectus?
Attached to the eye at 6 o’clock- moves the eye down
Attachment and movement of the eye of the lateral rectus?
Also called the external rectus, it attaches to the temporal side of the eye and moves the eye outward of the head (toward the temple)
Attachment and movement of the eye of the medial rectus?
Also called the internal rectus, it attaches to the nasal side of the eye and moves the eye towards the middle of the head (toward the nose
Attachment and movement of the eye of the inferior oblique?
Attaches high on the temporal side of the eye, passes under the superior rectus and travels through the trochlea- it moves the eye in a diagonal pattern down and in
Attachment and movement of the eye of the superior oblique?
Attaches low on the nasal side, passes under the inferior rectus and move the eye in a diagonal pattern up and out
Innervation of the superior rectus?
superior branch of the oculomotor
Innervation of the inferior rectus?
Inferior branch of the oculomotor
Innervation of the medial rectus?
Inferior branch of the oculomotor
Innervation of the lateral rectus?
Abducens
Innervation of the superior oblique?
Trochlear
Innervation of the inferior oblique?
Inferior branch of the oculomotor
Innervation of the lid elevator?
superior branch of the oculomotor
Innervation of pupil constriction?
Inferior parasympathetic branch of the oculomotor nerve
What does the oculomotor nerve innervate? (6)
- superior branch Superior rectus Lid elevator - inferior branch Inferior rectus Medial rectus Inferior oblique Parasympathetic nerve- constricts pupil
What does the superior branch of the oculomotor nerve innervate? (2)
Superior rectus
Lid elevator
What does the inferior branch of the oculomotor nerve innervate? (4)
Inferior rectus
Medial rectus
Inferior oblique
Parasympathetic nerve- constricts pupil
What does the trochlear nerve innervate? (6)
Superior oblique
What does the abducens nerve innervate? (6)
Lateral rectus
What muscle abducts
Lateral rectus
Difference between -duction and -version
- duction is one eye
- version is two eyes
What muscle adducts
MEDIAL RECTUS
What is 3rd nerve palsy characterised by and what muscles cause the direction. Is there double vision
- Affected eye down and out
- Droopy eyelid
- Unopposed superior oblique innervated by 4th nerve (down)
- Unopposed lateral rectus action innervated by 6th nerve (out)
- No double vision
What is 6th nerve palsy characterised by and what muscles cause the direction. Is there double vision
- Affected eye unable to abduct and deviates inwards
- Double vision worsens when gazing to the side of the affected eye
- Optokinetic nystagmus is…
smooth pursuit and fast phase reset saccade
- Presence of ON in response to moving grating signifies that the subject has XXXXXXXX
sufficient visual acuity to perceive the grating pattern
