Pupillary control Flashcards
How do the preganglionic parasympathetic neurons control pupil size?
Innervate pupillary sphincter muscle → pupillary constriction
How do the preganglionic sympathetic neurons control pupil size?
innervate pupillary dilator muscle
PATHWAY that leads to constriction of ciliary muscle?
activation of the pretectal nucleus → activation of Edinger-Westphal nuclei → signal sent out to ciliary ganglion → contraction of sphincter muscle
PATHWAY that leads to dilation of pupils?
brain stem activation (reticular formation) → signal passed down lateral funiculus of spinal cord → signal passed to superior cervical ganglion → contraction of dilator muscle.
Describe the DIRECT pupillary light reflex:
- light strikes retina
- activates retinal gang. cells (temporal halves of retina) (1st synapse: Pretectal N)
- axons travel along the optic nerve but DO NOT cross the chiasm (ipsilateral) (2nd SYNAPSE: Edinger-Westphal N. )
- bypass the lateral geniculate nucleus
- ***3rd Synapse: CILIARY GANGION =activate the efferent limb (occulomotor n) of the light reflex on the ipsilateral side of the brain stem
- this causes reflex pupillary constriction in the ipsilateral iris
Describe the INDIRECT pupillary light reflex:
- light strikes retina
- activates retinal ganglion cells
- *SYNAPSE: Pre-tectal N
- travel through the posterior commissure to contralateral **SYNAPSE: Edinger-Westphal N.
- ***SYNAPSE: contralateral CILIARY GANGLION
- activate efferent limb of light reflex on contralateral side of brainstem
Name the components that make up the Accommodation reflex
- eyes undergo convergent movements (via the pre-tectal region of the mid-brain); MR both activated
- activation of PNS – EWNu. → lens to become more rounded/thicker and can focus on objects close to you
- activation of PNS – EWNu. and inhibition of the sympathetics. → iris to constrict (pupillary constriction)
