Pupillary reflexes lab briefing Flashcards
what two muscles does the iris have and what are their function
Sphincter pupillae- (parasympathetic innervation) constricts the pupil
Dilator pupillae- (sympathetic innervation)dilates the pupil
where are the dilator pupillae found in the iris
peripheral 2/3 of the iris
what is pupillary constriction a balance between
Balance between Parasympathetic and Sympathetic Nervous Systems
where does parasympathetic innervation begin and what happen
- Edinger-Westphal nucleus near the occulomotor nerve nucleus- The fibres from this nucleus enter the orbit with CN III and synpase at the ciliary ganglion
- Post-ganglionic fibres then supply sphincter pupillae.
where does sympathetic innervation occur and what happens
Sympathetic innervation has a three neurone chain:
- Begins in the hypothalamus and synpase to the cilliospinal centre in the spinal cord, between the levels of C8 and T2
- Post-synaptic neurones exit the spinal cord at T1 and travel through the cervical sympathetic chain to the superior cervical ganglion
- Third-order neurons travel through the carotid plexus and enter into the orbit through the first division of the trigeminal nerve, and then innervate the iris dilator muscles.
what is pupillary light reflex
Pupil constriction in response to Light (parasympathetic activity)
what is accomodation reflex
Pupil constriction and convergence of the eyes when looking from a distant object to a close one
what is the pupillary light reflex responsible for
responsible for regulating the amount of light falling on the retina in different light conditions
what are the afferent and efferent limb of the pupillary light reflex
AFFERENT pathway (sensory) – optic nerve (CN II)
EFFERENT pathway (motor) – oculomotor nerve (CN III) to the to the sphincter pupilae muscles (parasympathetic innervation).
light shone in one eye results in constriction of _____ pupils
both
Describe the afferent limb of the pupillary light reflex
- Light shone on eye
- Fibres for the pupillary light reflex leave the optic tract early and travel to the pretectal nuclei in the midbrain. So when light is shone in the right eye, the action potential reach both pre-tectal nuclei.
- Pretectal nuclei project fibres to the Edinger-Westphal nucleus on the same aside, and the Edinger-Westphal nucleus on the opposite side. (The Edinger-Westphal nuclei are also in the mid-brain).
- The fibres synapse in the Edinger-Westphal nuclei. This is where the afferent pathway ends
Describe the efferent limb of the pupillary light reflex
- The Edinger-Westphal nucleus projects pre-ganglionic parasympathetic fibres, which travel along the oculomotor nerve (CN III) and then synapse in the ciliary ganglion. Post-ganglionic parasympathetic fibres then innervate the sphincter muscle of the pupils resulting in pupillary constriction.
HOW IS pupillary light reflex clinically assessed and describe it
The pupil light reflex is clinically assessed by shining a pen torch light directly into the eye.
- The response in that same eye is the direct pupil response. The pupil should rapidly constrict.
- To test the indirect, or consensual, (opposite) pupil response, the light is moved away, allowing the pupil to dilate again.
repeated on opposite eye
what is a swinging flashlight test
Looks for Relative Afferent Pupillary Defect (RAPD). It is relative because it compares responses of two eyes, and it is afferent because it is comparing the sensory pathways. It compares the direct light reflex in one eye with the indirect reflex in the other eye.
Can identify asymmetry of afferent input in the pupillary light reflex
what does presence of a relative afferent pupillary defect show
disease of the optic nerve between retina and chiasm. E.g. optic neuritis (MS patients
