Visual Pathways Lab Flashcards
what is the fovea centralis?
it is the deepest part of the retina, and is the area with highest visual acuity
what is the macula lutea/fovea?
oval shaped, pigmented area near centre of retina
why does the optic disc correspond to a blind spot in the eye?
Because there are no rods or cones (photoreceptors) overlying theoptic disc
what does the optic nerve consist of?
contains nerve fibres from retinal ganglion cells (RGC)
what is papilloedema a clinical sign of?
Papilloedema is a clinical sign of increased intracranial pressure
how do moderate and severe papilloedema look different under an ophthalmoscope?
moderate: crescent of oedema around optic disc
severe: halo of oedema surrounds the optic disc
what can cause papilloedema?
Papilloedema can result from tumours, malignant hypertension, head injury, haemorrhage
what do the 3 layers of meninges form in relation to the optic nerve?
Outer sheath, the Intermediate sheath and the Inner sheath
What is “visible distortion of the optic disc”?
The “visible distortion of the optic disc” is
called papilloedema or optic neuritis.
what cranial nerve supplies the superior oblique muscle?
trochlear nerve (Cn4)
what cranial nerve supplies the lateral rectus muscle?
abducens nerve (CN6)
what cranial nerve supplies the superior rectus, medial rectus, inferior rectus and inferior oblique muscle?
oculomotor nerve (CN3)
the optic tract sweeps around the side of the midbrain to the _____?
lateral geniculate body
what happens at the lateral geniculate body ?
the retinal axons end by forming synapses with second order neurons whose axons carry information on to the visual cortex via the optic radiation
what happens to the fibres which do not travel to the visual cortex?
they project to either the superior colliculus for eye movement
or
the pretectal area for pupil light reflexes
What response may be elicited by shining a light into one eye?
Consensual constriction of the pupil in both eyes. This is called the light reflex.
Describe the light reflex (afferent and efferent pathways)
This nervous pathway involves collateral fibres from the optic tract forming synapses within the superior colliculus / pretectal nucleus and the accessory oculomotor (Edinger Westphal) nucleus in the tectum of the midbrain.
The efferent, consensual parasympathetic fibres of the reflex arc travel in the oculomotor nerve to synapse in the ciliary ganglion. Postganglionic fibres leave the ciliary ganglion and pass to the sphincter pupillae. Stimulation of these nerve fibres results in consensual constriction of the pupil in both eyes.
what is the light reflex used for clinically?
widely used as a screening test in brain injury and suggests injury to the upper brain-stem.
what results from damage to the pretectal nucleus?
damage to unilateral pretectal nucleus: pupil constriction to light in left and right eye because the other pretectal nucleus is unaffected (although one is damaged, the working pretectal nucleus sends fibres to BOTH E-W nuclei)
What would be the effect at the pupil of pressure on the right oculomotor nerve?
a fixed, dilated pupil in the right eye. (loss of light reflex)
What is the result of stimulation of neurons of superior colliculus?
Motor neurons within the superior colliculus
project either to part of the thalamus
- oculomotor nucleus to move the eyes
or to the tectospinal tract innervating
contralateral cervical cord motor neurons
to activate scalene muscles in the neck which
rotate the head.
What is the result of stimulation of neurons of superior colliculus?
Motor neurons within the superior colliculus
project either to part of the thalamus
- oculomotor nucleus to move the eyes or to the tectospinal tract innervating contralateral cervical cord motor neurons to activate scalene muscles in the neck which rotate the head.
what is the calcimine sulcus a landmark of?
The primary visual cortex within the superior and inferior calcarine gyri
what is the blood supply to the primary visual cortex? what would be the effect of an ischaemic lesion in this region?
Left posterior cerebral artery
Loss of vision in half of the visual field of both eyes
