Visual Pathway Flashcards
Which part of the eye contains no photoreceptors?
The optic disc.
-blind spot on retina
Where is the optic disc located?
On the retina, medial to the fovea.
What is the retina?
The nerve layer that lines the back of the eye, senses light, and creates impulses that travel through the optic nerve.
What are the 2 layers of the retina?
- Non-neuronal layer
- Neuronal layer
What does the non-neuronal layer of the retina consist of?
Pigmented epithelium.
-sits against the choroid of the eyeball and absorbs photons
What are photons?
Particles of light energy.
What is the function of the pigmented epithelium?
Surrounds photoreceptors via melanin-filled microvilli.
-maintains their metabolic activity
What does the neuronal layer of the retina contain? (4)
- Photoreceptors
- Bipolar neurons
- Ganglionic cells
- Interneurons
What do photoreceptors do?
Receive photons and convert them into signals.
What are the 2 types of photoreceptors?
- Cone cells
- Rod cells
Why does light have to pass through other fibres to get to photoreceptors?
Decreases the intensity of light reaching the retina.
What do bipolar neurons do?
Connect photoreceptors to ganglionic cells.
What do ganglionic cells combine to form as they leave the retina?
The optic (II) nerve.
What is the function of interneurons?
Interconnect photoreceptors/bipolar neurons/ganglionic cells.
-modulate transmission and sharpen information to the cortex
What are the 2 types of interneuron?
- Horizontal
- Amacrine
Where are horizontal interneurons located?
At the level of photoreceptors and bipolar neurons.
Where are amacrine interneurons located?
At the level of bipolar neurons and ganglionic cells.
What process occurs in the neuronal layer of the retina?
Photochemical reactions tranduce photons (light energy) to electrical energy.
How many neurons are there from the retina to the cortex?
Three.
What is the pathway of light energy from the retina to the cortex?
Photoreceptors >> 1* BIPOLAR CELLS >> 2* GANGLIONIC CELLS >>Optic nerve >> Lateral geniculate nucleus (thalamus) >> 3* OPTIC RADIATION >> 1* visual cortex (cerebral cortex) >> Association centre
What is the optic nerve an outgrowth of?
The diencephlon.
-part of the CNS
What membranes surround the eyeballs?
Meninges.
What effect can increased CSF/ICP have on vision?
Can cause the optic nerve to swell and compress the retinal central vein»_space; PAPILLOEDEMA.
-lifts retina away from the pigmented epithelium
What is papilloedema?
Optic disc swelling due to increased ICP.
|»_space; headache, drowsiness, blurred vision
Which part of the thalamus does the visual pathway go to?
Lateral geniculate nucleus.
NB. Which part of the thalamus does the auditory pathway go to?
Medial geniculate nucleus.
Where does vision from the same area of the visual field travel?
Enters different eyes, but travels down the same optic tracts.
Where does the medial (nasal) retina send information to?
The contralateral thalamus.
Where does the lateral (temporal) retina send information to?
The ipsilateral thalamus.
Where does information from the medial retina cross over?
At the optic chiasma»_space; contralateral lateral geniculate nuclei.
On the medial surface of the brain, what lies either side of the calcarine sulcus?
Striate cortex (somatosensory).
What lies adjacent to the striate cortex?
The visual association cortex.
What is the function of the visual association cortex?
Receives information from the 1* visual cortex and processes it with memories»_space; understanding.
Where does information from the left half of the visual field travel to?
Right hemisphere.
Where does information from the right half of the visual field travel to?
Left hemisphere.
Where does information from the upper visual field travel to?
The lower bank of the calcarine sulcus.
Where does information from the lower visual field travel to?
The upper bank of the calcarine sulcus.
Where does information from the centre of the visual axis (macula) travel to?
Occipital pole.
-posterior occipital lobe
What is scotoma?
Localised patch of blindness.
What is anopia?
Loss of 1+ quadrants of the visual field.
What is hemianopia?
Loss of half of the visual field.
What does homonymous mean?
Visual losses are similar on both sides.
What does heminymous mean?
Visual losses are different on both sides
Damage to which part of the visual pathway leads to monocular damage?
Optic nerve.
Damage to which part of the visual pathway leads to heteronymous hemianopia?
Optic chiasma.
Damage to which part of the visual pathway leads to homonymous hemianopia?
Optic tract.
Damage to which part of the visual pathway leads to homonymous hemianopia with macular sparing?
Optic radiation.
How is scotoma often caused?
Banging the back of the head.
-1* visual cortex damage
Do all optic tract fibres go to the lateral geniculate nuclei?
No.
Where do 10% of optic tract fibres go?
Pre-tectal area (midbrain).
What does the pupillary light reflex test?
The ability of the pupill to respond to light.
What 2 cranial nerves are involved in the pupillary light reflex?
- Optic (II) nerve - sensory
- Occulomotor (III) nerve - motor
Which muscle is tested by the pupillary light reflex?
Iris sphincter muscle.
What is the iris sphincter muscle controlled by?
Parasympathetic innervation from the occulomotor (III) nerve, via the Edinger-Westphal nucleus.
What are the 2 components of the pupillary light reflex?
- Direct
- Consensual
What is the direct component of the pupillary light reflex?
Light in one eye causes the same pupil to constrict.
What is the consensual component of the pupillary light reflex?
Light in one eye causes the other pupil to constrict.
What does the Edinger-Westphal nucleus contain?
Preganglionic PS motor neurons from both sides of the visual field that leave the brain with the occulomotor nerve.
What happens in the pupillary light reflex if the patient has optic nerve damage (sensory)?
Other pupil would still react if light is shone into 1 eye.
What happens in the pupillary light reflex if the patient has occulomotor nerve damage (motor)?
No way to constrict the muscle.
-pupil slightly dilated
What is the accommodation reflex?
Changes that occur in the eye when gaze is transferred from a distant object to a near object.
What are the 3 changes that occur in the accomodation reflex?
- Accommodation
- Pupil constricts
- Ocular convergence
What is accommodation?
Ciliary muscles contract»_space; lens becomes more rounded.
-image focused on retina
What causes the pupil to constrict in the accommodation reflex?
Sphincter pupillae muscle.
What causes ocular convergence?
Medial rectus muscle.
-image focused on the fovea
Where do afferent fibres from the eye travel?
In the optic nerve
» cortex
» occulomotor nerve
Where do efferent fibres to the eye travel?
Within the occulomotor nerve.
