7 - Opth - Pupillary reflexes - Constriction and Dilatation Flashcards
which fibres control constriction
parasympathetic fibres
Causes of constriction + their parts
light reflex - direct and consensual
near response - miosis, convergence, accomodation
What happens in the miosis part of near response
Afferent fibres in optic nerve:
-extraocular muscle spindles -> lateral genticulate body -> convergence centre in brain
Efferent fibres:
-convergence centre -> Edinger Westphal nucleus -> ciliary ganglion +pupils
-> constriction
How does accommodation occur
ciliary body contracts and lens relaxes
What is anisocoria ? - how prevalent physiologically is it? - how to confirm this?
inequality of pupil sizes
~20%
dim lights - both pupils react equal degree
Anisocoria occurs only in???
only in efferent pupillary defects
outline the afferent pathway
- Light generates AP from retinal ganglion cells
- axons (some decuss at chiasm) pass through each lateral genticulate body
- synapse in each pretectal nucleus at level of superior colliculus
outline the efferent pathway
- AP pass from pretectal nucleus > Edinger Westphal nucleus
- pass via CN III (nerve to inferior rectus), ciliary ganglion and short ciliary nerves
- then to sphincter pupillae muscle > constriction
Pupillary dilatation - name the 3 neurones in the pathway
1 - Sympathetic fibres from hypothalamas
2 - Preganglionic fibres from sympathetic trunk
3 - Postganglionic fibres form plexus around carotid bifurcation
outline the dilatation pathway
1 - hypothalamus > through midbrain > ciliospinal centre in SC (C8-T2)
2 - Sympathetic trunk > brachial plexus > over apex of lung > superior cervical ganglion (C2) in neck (at bifurcation of common carotid)
3 - internal carotid plexus fibres > opthalmic branch of trigeminal nerve > nasociliary and ciliary nerves > ciliary body and dilator pupillae
-> dilatation
