IOA2 Exam 3 - Pupillary Pathway

What is required for autonomic control of the iris muscles during normal visual activities?

Balanced activation of the sympathetic and parasympathetic systems

Which muscle does the sympathetic system control in the iris?

Dilator pupillae muscle

What is the location of the dilator pupillae muscle fibers?

Radial muscle fibers distal to the pupillary entrance

Where is the origin of the sympathetic pathway of the iris?

T1-T3 levels of spinal cord

Which muscle does the parasympathetic system control in the iris?

Sphincter pupillae muscle

What is the location of the sphincter pupillae muscle fibers?

Circular muscle proximal to the pupillary entrance

Where is the origin of the parasympathetic pathway of the iris?

Midbrain/Pons

What are the sympathetic fibers of the iris controlled by?

Hypothalamus projections (descending pathway)

Where do the sympathetic fibers synapse in the spinal cord?

Laternal horn column of the cervical spinal cord (T1-T3)

How do the fibers from preganglionic neurons leave the spinal cord?

Thru the ventral root in one of the first 3 thoracic nerves

How do preganglionic fibers enter the sympathetic ganglion chain?

Thru the spinal nerve and white ramus communicante

Preganglionic fibers leave the 1)_________ in one of the first three thoracic nerves via the 2)___________, and enter the 3)___________ thru the 4)_________ and _________.

1) Spinal cord

2) Ventral root

3) Sympathetic ganglion chain

4) Spinal nerve & White ramus communicante

Where do preganglionic fibers synapse after ascending in the sympathetic chain?

Superior cervical ganglion

1)__________ ascend in the sympathetic chain to synapse in the 2)___________.

1) Preganglionic fibers

2) Superior cervical ganglion

Where is the superior cervical ganglion located?

At the level of the 2nd and 3rd cervical vertebrae (C2 and C3)

________ fibers leave the superior cervical ganglion.

Postganglionic

What do postganglionic fibers form after leaving the superior cervical ganglion?

The carotid plexus around the internal carotid artery

How do postganglionic fibers enter the skull?

Thru the carotid canal

Where do sympathetic fibers go after leaving the plexus in the cavernous sinus?

They take multiple pathways to target structures

Networks of sympathetic fibers leave the ____________ and take multiple pathways to the target structures.

plexus in the cavernous sinus

With which division of the trigeminal nerve do some sympathetic fibers travel?

Ophthalmic division

Once in the orbit, which nerve do sympathetic fibers follow?

Nasociliary nerve

Which nerves do sympathetic fibers travel with to innervate the dilator pupillae and ciliary muscle?

Long ciliary nerves

Sympathetic fibers travel with the 1)_________ to innervate the 2)___________ and 3)__________.

1) Long ciliary nerves

2) Dilator pupillae

3) Ciliary muscle

What is the effect of sympathetic stimulation on the iris dilator muscle?

Mydriasis (pupil dilation)

What is the effect of sympathetic stimulation on the ciliary muscle?

Relaxation (inhibitory effect- flattens the lens to see distance objects)

What does sympathetic stimulation do to the iris dilator muscles?

Activates them, causing pupillary dilation (mydriasis)

What is the effect of pupil dilation (mydriasis)?

Increases retinal illumination

What effect does sympathetic stimulation have on the ciliary muscle?

Inhibitory effect, causing relaxation

What role does the sympathetic pathway play in vision?

Imp for

-distant vision as part of the accommodation reflex

-dim light response

During distance vision, what happens to the ciliary muscles?

They relax, and the border of the choroid moves away from the lens

During distance vision, what happens to the suspensory ligaments?

They pull against the lens

What shape does the lens become during distance vision and why?

Lens becomes flatter to focus on distant objects

PLS SUMMARIZE THE SYMPATHETIC PATHWAY TO THE IRIS

1) Sympathetic fibers are controlled by the hypothalamus projections (descending pathway).

2) The fibers synapse in the laternal horn column of the cervical spinal cord (T1-T3).

3) Fibers from preganglionic neurons leave the spinal cord thru one of the first three thoracic nerves.

4) Fibers exit via the ventral root and enter the sympathetic ganglion chain thru the spinal nerve and white ramus communicante.

5) Preganglionic fibers ascend in the sympathetic chain to synapse in the superior cervical ganglion (C2 & C3).

6) Postganglionic fibers leave the superior cervical ganglion.

7) Postganglionic fibers form the carotid plexus around the internal carotid artery and enter the skull thru the carotid canal.

8) Postganglionic fibers may leave the plexus in the cavernous sinus, taking multiple pathways to the target structures.

9) Some sympathetic fibers travel with the ophthalmic division of the trigeminal nerve.

10) Once in the orbit, they follow the nasociliary nerve.

11) Finally, they travel with the long ciliary nerve to innervate the dilator pupillae and the ciliary muscle.

Effects:

-Sympathetic stimulation activates the dilator muscle, causing pupillary dilation (mydriasis), which increases retinal illumination.

-Sympathetic stimulation also has an inhibitory effect on the ciliary muscle, resulting in relaxation, and causing the lens to flatten to see distant objects.

Where does the sympathetic pathway to the iris originate?

T1-T3 levels of the spinal cord

Where do the preganglionic fibers exit?

Via the ventral root

Where do preganglionic fibers synapse?

Superior cervical ganglion

How do postganglionic fibers leave the superior cervical ganglion?

They travel through the internal carotid plexus, and some travel with ophthalmic division

Once in the orbit, what do the postganglionic fibers follow?

Nasociliary nerve

Finally, the postganglionic fibers travel with the 1)_________ to activate the 2)__________, causing 3)________.

1) Long ciliary nerve

2) Iris dilator

3) Mydriasis

What may the postganglionic fibers travel through instead of the long ciliary nerve, causing interruption?

Sympathetic root --> ciliary ganglion (no synapse) --> short ciliary nerves --> choroidal and conjunctival blood vessels --> vasoconstriction

Where are the preganglionic neuron fibers for the parasympathetic pathway to the iris located?

In the midbrain

Specifically where in the midbrain are the preganglionic fibers for the parasympathetic pathway to the iris located?

Edinger Westphal nucleus (In the parasympathetic accessory third-nerve nucleus)

The Edinger-Westphal nucleus is what type of component of the Oculomotor Nerve (CNIII)?

General visceral efferent (GVE)

With which nerve do preganglionic parasympathetic fibers leave the Edinger-Westphal nucleus?

Oculomotor nerve

After the preganglionic parasympathetic fibers leave the Edinger-Westphal nucleus, what do they follow to reach the orbit?

They follow the inferior division of the oculomotor nerve into the orbit

Preganglionic parasympathetic nerve fibers follow the 1)___________ into the 2)_________.

1) Inferior division of the oculomotor nerve

2) Orbit

Where do the parasympathetic fibers enter when they leave the inferior division?

Ciliary ganglion (where they synapse)

What is the size and shape of the ciliary ganglion?

-Small, flattened structure

-2x1mm

Where is the ciliary ganglion located?

Within the muscle cone, between the lateral rectus muscle and the optic nerve, approximately 1cm anterior to the optic canal (and slightly lateral)

How many roots does the ciliary ganglion have?

3

Name the 3 roots of the ciliary ganglion

1) Parasympathetic root

2) Sensory root

3) Sympathetic root

Where are the roots of the ciliary ganglion located?

At the posterior edge of the ciliary ganglion

Which root of the ciliary ganglion do parasympathetic fibers use to synapse?

Parasympathetic root

Where do the postganglionic parasympathetic fibers from the ciliary ganglion go? (ie. Where does the parasympathetic root carry information to?)

Sphincter pupillae muscle

Where does the sensory root carry information from?

-Cornea

-Iris

-CB

Do sympathetic fibers synapse in the ciliary ganglion?

NO, they pass thru the sympathetic root

Where does the sympathetic root carry information to?

Dilator pupillae muscle

What emerges from the anterior edge of the ciliary ganglion?

Short ciliary nerves

Which type of fibers are carried by the short ciliary nerves?

-Parasympathetic fibers

-Sensory fibers

-Sympathetic fibers

Which muscles do the parasympathetic fibers target?

Sphincter pupillae muscle

Which muscles do the sensory fibers target?

-Cornea

-Iris

-Ciliary muscle

Which muscles do the sympathetic fibers target?

Dilator pupillae muscle

Are postganglionic parasympathetic neurons myelinated?

Yes

Where are the soma (cell bodies) of postganglionic parasympathetic neurons located?

Ciliary ganglion

Where do postganglionic parasympathetic fibers project?

Towards the short ciliary nerves

Which part of the eye do the postganglionic parasympathetic fibers synapse?

Anterior segment

What structures in the anterior segment of the eye do postganglionic parasympathetic neurons innervate?

-Ciliary muscle

-Sphincter pupillary muscle

What is the effect of parasympathetic innervation on the ciliary muscle?

Contraction, leading to accommodation

What happens to the lens during parasympathetic stimulation of the ciliary muscle?

Lens thickens

What is the effect of parasympathetic innervation on the sphincter pupillary muscle?

Miosis (pupil constriction)

What are the effects of parasympathetic stimulation?

-Pupillary constriction

-Contraction of the ciliary muscle

What is the effect of parasympathetic stimulation on the pupil?

Pupillary constriction (miosis)

What is the effect of pupillary constriction due to parasympathetic stimulation?

Decreases intraretinal illumination

When does parasympathetic stimulation cause pupillary constriction?

During sleep and accommodation

What is the effect of parasympathetic stimulation on the ciliary muscle?

Contraction

What does contraction of the ciliary muscle enable the eye to do?

Enables the eye to focus on near objects in accommodation

During near vision, what happens to the ciliary muscles?

They contract, pulling the border of the choroid towards the lens

During near vision, what happens to the suspensory ligaments?

They relax

What shape does the lens become during near vision and why?

Lens becomes thicker and rounder, to focus on near objects

Where do preganglionic parasympathetic fibers originate?

Edinger-Westphal nucleus in the midbrain

Which cranial nerve do preganglionic parasympathetic fibers travel with?

Oculomotor nerve

Which division of the oculomotor nerve do the preganglionic parasympathetic fibers follow?

Inferior division of oculomotor nerve

Where do preganglionic parasympathetic fibers synapse?

Ciliary ganglion

The ciliary ganglion is located within the 1)_________, between the 2)_________ and ________.

1) Muscle cone

2) Lateral rectus muscle and optic nerve

How do postganglionic parasympathetic fibers leave the ciliary ganglion?

Via short ciliary nerves

What muscles do the postganglionic parasympathetic fibers innervate?

-Iris sphincter

-Ciliary muscle

What is the effect of parasympathetic innervation on the iris sphincter muscle?

Miosis (pupillary constriction)

What's the effect of parasympathetic innervation on the ciliary muscle?

Accommodation (to focus on near objects)

PLS SUMMARIZE THE PARASYMPATHETIC PATHWAY TO THE IRIS

1) Preganglionic neuron fibers originate in the Edinger-Westphal nucleus in the midbrain.

2) Preganglionic fibers leave the midbrain as part of the oculomotor nerve (CNIII).

3) These fibers travel within the inferior division of the oculomotor nerve.

4) Preganglionic fibers enter the ciliary ganglion.

5) Preganglionic fibers synapse within the ciliary ganglion.

6) Postganglionic fibers leave the ciliary ganglion via the short ciliary nerves.

Effects:

7) Postganglionic fibers innervate the iris sphincter muscle, causing pupillary constriction (miosis).

8) Postganglionic fibers innervate the ciliary muscle, causing contraction for accommodation (focusing on near objects)

T/F: In normal awake individuals, parasympathetic and sympathetic nerves are in balance.

True

To reflect the balance in parasympathetic and sympathetic nerves, the size of the pupil ________.

changes constantly and rhythmically

Physiologic pupillary unrest

Hippus

What happens to pupil size during sleep, and why?

Pupils are small during sleep.

-The sympathetic system shuts down so the parasympathetic system predominates

During sleep, the pupils are small because the 1)___________ system shuts down and the 2)_________ system predominates.

1) Sympathetic

2) Parasympathetic

What does disruption of the sympathetic pathway lead to?

Miosis

What happens to the dilator pupillae during disruption in the sympathetic pathway?

Loses tone

What is the result of the dilator pupillae muscle losing tone?

There is no counteracting pull against the sphincter muscle, leading to a smaller pupil

Which abnormality is characterisitic of sympathetic pathway disruption?

Anisocoria

What is anisocoria?

Difference in pupil size