Pupillary reflexes lab briefing

Question 1

what two muscles does the iris have and what are their function

Answer 1

Sphincter pupillae- (parasympathetic innervation) constricts the pupil
Dilator pupillae- (sympathetic innervation)dilates the pupil

Question 2

where are the dilator pupillae found in the iris

Answer 2

peripheral 2/3 of the iris

Question 3

what is pupillary constriction a balance between

Answer 3

Balance between Parasympathetic and Sympathetic Nervous Systems

Question 4

where does parasympathetic innervation begin and what happen

Answer 4

• 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.

Question 5

where does sympathetic innervation occur and what happens

Answer 5

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.

Question 6

what is pupillary light reflex

Answer 6

Pupil constriction in response to Light (parasympathetic activity)

Question 7

what is accomodation reflex

Answer 7

Pupil constriction and convergence of the eyes when looking from a distant object to a close one

Question 8

what is the pupillary light reflex responsible for

Answer 8

responsible for regulating the amount of light falling on the retina in different light conditions

Question 9

what are the afferent and efferent limb of the pupillary light reflex

Answer 9

AFFERENT pathway (sensory) – optic nerve (CN II)

EFFERENT pathway (motor) – oculomotor nerve (CN III) to the to the sphincter pupilae muscles (parasympathetic innervation).

Question 10

light shone in one eye results in constriction of _____ pupils

Answer 10

both

Question 11

Describe the afferent limb of the pupillary light reflex

Answer 11

• 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

Question 12

Describe the efferent limb of the pupillary light reflex

Answer 12

• 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.

Question 13

HOW IS pupillary light reflex clinically assessed and describe it

Answer 13

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

Question 14

what is a swinging flashlight test

Answer 14

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

Question 15

what does presence of a relative afferent pupillary defect show

Answer 15

disease of the optic nerve between retina and chiasm. E.g. optic neuritis (MS patients

Question 16

describe swinging flashlight test

Answer 16

a light is shone into one eye, then moved quickly to the other eye, then back again, and so on for a few times. This is called the swinging light test. The pupil with the light being shine into it is always observed. A normal response will be slight constriction when the light first comes into the eye. Dilation of the pupil is abnormal and indicates an afferent pupillary defect in that eye.

Question 17

Describe Accommodation Convergence Reflex

Answer 17

Stimulus is an out-of-focus image

3 components:
- Pupil constriction (constrictor pupillae)
- Lens accommodation (Ciliary muscles)
- Convergence of the eyes (contraction both medial rectus muscles)
- Pathway is more complex as requires visual processing.
AFFERENT pathway – optic nerve
EFFERENT pathway – oculomotor nerve