BS - Pupil Anatomy & Innervation - Week 5

Question 1

Name the three major roles of the pupil.

Answer 1

• Controlling retinal illumination
• Minimising optical aberrations
• Increasing depth of focus for near vision

Question 2

Define miosis and mydriasis by the size of the pupil.

Answer 2

Miosis - <4mm

Mydriasis - >4mm

Question 3

How does the pupil change with age?

Answer 3

Gets smaller with age.

Question 4

Define anisocoria.

Answer 4

Difference in the size of the pupils.

Question 5

Define physiological anisocoria.

Answer 5

A <1mm difference in pupil sizes.

Question 6

Which is the stronger muscle, sphincter pupillae or dilator pupillae?

Answer 6

Sphincter pupillae is stronger

Question 7

What is the thickness of the sphincter pupillae vs the dilator pupillae?

Answer 7

Sphincter - 400-800um

Dilator - 20um

Question 8

How are the sphincter and dilator pupillae muscles arranged relative to each other?

Answer 8

They are orthogonal.

Question 9

What three inputs do pupils resond to?

Answer 9

Light reflex
Near reflex
Autonomic arousal

Question 10

Describe the pupillary afferent innervation pathway.

Answer 10

Retina > optic nerve > optic chaism > optic tract (bilaterally) > prerectal nuclei (bilaterally)

Question 11

In the afferent pupillary innervation pathway, does each eye project bilaterally or ipsilaterally onto the prerectal nuclei? Where do prerectal nuclei project onto, and is it bilaterla or ipsilateral?

Answer 11

Each eye projects bilaterally due to the optic chiasm.

Prerectal nuclei project bilaterally onto the edinger westphal nuclei.

Question 12

What is a consequence of how a signal is projected in the afferent pupillary innervation pathway?

Answer 12

As it is bilateral (post optic chiasm), it results in a consensual response by an unilluminated eye when only a single eye is illuminated.

Question 13

Describe the efferent pupillary innervation pathway.

Answer 13

Edinger-westphal nucleus > CNIII > ciliary ganglion > short ciliary nerves

Question 14

What are the distinguishing features of the two nerve pathway divisions (symp/parasymp)?
Name 2 for each.

Answer 14

Sympathetic
-Long post-ganglionic processes
-Noradrenaline used at effector site
Parasympathetic
-Short post-ganglionic processes
-Acetylcholine used at effector site

Question 15

What neural innervation is given to the dilator muscle, what neurotransmitter used, and what receptor?

Answer 15

Sympathetic
Noradrenaline
Adrenergic α1

Question 16

What neural innervation is given to the sphincter muscle, what neurotransmitter used, and what receptor?

Answer 16

Parasympathetic
Acetylcholine
Muscurinic

Question 17

Describe the pathway for innervation to the dilator pupillae.

Answer 17

Hypothalamus > ciliospinal centre > superior cervical ganglion > dilator pupillae

Question 18

Describe when dilation and constriction generally occurs. Are the sphincter and dilator muscle inputs and functions reciprocal?

Answer 18

Dilation occurs in the absence of light, the removal of drive to constrict the sphincter muscle.
Constriction occurs due to presence of light, increasing drive to constrict the sphincter.
They are not reciprocal.