Pupillary Pathway

Question 1

Hippus

Answer 1

balance between sympathetic and parasympathetic muscle tone

constant rhythmic contractions and dilations of the pupil

results from low tonic firing of autonomic nervous system

Question 2

Parasympathetic

Answer 2

Sphincter pupillae muscle contraction decreases pupil size

Question 3

Sympathetic:

Answer 3

dilator pupillae muscle contraction increases pupil size

Question 4

Iris

Answer 4

sphincter pupillae

dilator pupillae

Question 5

Sphincter

Answer 5

smooth muscle fibres that circulate the pupillary border of the iris

Iris sphincter innervated by the parasympathetic nervous system

Question 6

Dilator

Answer 6

smooth muscle fibres that run radially out from the sphincter throughout the iris

Iris dilator innervated by the sympathetic nervous system

Question 7

tonus

Answer 7

result of muscle tension from the nerve input

Pupil size dependent on tonus of both dilator and sphincter muscles

Resultant balance = pupil size

Question 8

Sympathetic Nervous System evokes Survival Responses

Answer 8

tonus increases pupil dilates. Dilator pupillae muscle contraction increases pupil size.

Release adrenaline, stop digestion, mucous secretion

Sympathetic tonus increases = pupil dilates

Question 9

Parasympathetic nervous system evokes rest, relax & digest responses.

Answer 9

Increase in GIT digestion/ motility, decrease in heart rate and respiration rate

Parasympathetic system tonus is higher than the sympathetic the pupil constricts

Sphincter pupillae muscle contraction decreases pupil size

Question 10

Parasympathetic defect

Answer 10

pupil gets larger

Question 11

sympathetic pathway

Answer 11

pupil gets smaller

Question 12

Sympathetic Efferent Pupil Pathway

Answer 12

1, 2, 3 order neurons

Question 13

1st order neuron

Answer 13

• Contained fully in the CNS
  
  • Descends down spinal column from hypothalamus to the ciliospinal centre of budge
  • Ciliospinal centre budge is where 1st order neurons synapse with 2nd order neurons
    Ciliospinal centre budge is located in the intermedial lateral columns of the spinal cord at C8 T2 level

Question 14

2nd order neuron

Answer 14

• Leave spinal cord known as preganglionic neurons
  
  • Targets are dendrites of the 3rd neuron pathway located in the superior cervical ganglion (in jaw)
  • Ciliopsinal centre of budge –> apex of lungs –> under subclavian
  • Course around apex of lung under subclavian to the superior cervical ganglion
    Pupil abnormalities serious marker of life threatening disease

Question 15

3rd order neuron

Answer 15

• Emerge from superior cervical ganglion neurons from plexus that surrounds external carotid artery
  
  • Fibres that innervate face follow external carotid artery, other sympathetic fibre, including those innervate the pupil dilator enter through the internal carotid canal
  • These fibres travel through the middle cranial fossa and into cavernous sinus where they join 6 th cranial nerve prior to joining ophthalmic division with the trigeminal nerve entering the orbit
  • Then branch off with the naos ciliary branch off CN6 and enter orbit through superior orbital fissure
    The pupillary fibres pass through the ciliary ganglion without synapses and terminate on the dilator muscle, mullers muscle and lacrimal glands

Question 16

Horners Syndrome

Answer 16

Inability to dilate pupil means there is a disruption of normal sympathetic innervations of eye. In dim light conditions, pupil affected will look smaller than other eye as it cannot dilate

Patient can still open eyelid as lavador is innervated by ocular motor nerve which is not included in sympathetic pathway

Question 17

Parasympathetic Pathway

Answer 17

1. Edinger - Westphal nucleus
2. Surface of oculomotor nerve (CNIII)
3. Cavernous sinus
4. Inferior division of oculomotor nerve
5. Ciliary ganglion
6. Post-ganglionic short ciliary nerves supply ciliary muscle & iris sphincter

Question 18

Detailed parasympathetic pathway

Answer 18

Efferent parasympathetic signal starts in Edinger Westphal nucleus in pretectal midbrain. From here preganglionic fibres of the ciliary muscle and pupil travel along surface of oculomotor nerve (CNIII) because they run along outside of nerve, they are more vulnerable to compressions/ damage.

Parasympathetic pupil fibres travel with CNIII through cavernous sinus and enter the orbit through the superior orbital fissure. At the anterior end of the cavernous sinus, CNIII divides into superior and inferior divisions and the pupillary motor fibres travel through the inferior division of CNIII. They then branch to the inferior oblique muscle and synapse at the ciliary ganglion

Ciliary ganglion is located between optic nerve and lateral rectus muscle. From here approx 6-10 postganglionic short ciliary nerves originate and penetrate the posterior sclera and supply the ciliary muscle and iris sphincter.

As the parasympathetic pathway innervates the sphincter muscle, its most pronounced action is the constriction of the pupil in light reflex process

Inability to constrict the pupil in response to light stimulus may mean interruption to the normal efferent parasympathetic innervation to the eye. Could also be due to afferent pathway

Question 19

Separating Afferent from parasympathetic efferent

Answer 19

Afferent fibres desiccate before synapsing with the Edinger Westphal nucleus. This means that an afferent signal from a light stimulus applied to only eye is communicated from the pretectal nucleus to the Edinger Westphal nucleus in both hemispheres

Question 20

Direct response

Answer 20

• When light is shone into one eye it constricts

Shows afferent and parasympathetic efferent pathway for that eye on the side are functional

Question 20

Direct response

Answer 20

• When light is shone into one eye it constricts

Shows afferent and parasympathetic efferent pathway for that eye on the side are functional

Question 21

Consensual response

Answer 21

• When light shone into one eye, the other eye constricts
  
  • This means fibres that dissecate from pretectal nucleus to the contralateral Edinger Westphal nucleus are in tact and functioning
    Follows other eye that has had light reflex shone in it

Question 22

Afferent Defect

Answer 22

If light is shone into right eye and it doesn’t react and left eye also then doesn’t react

Question 23

Parasympathetic Efferent defect

Answer 23

If light is shone into right eye and it doesn’t react but light into the left eye does

Question 24

Pupil constriction and near response

Answer 24

Pupil constricts when focusing on near objects despite light remaining the same

Near triad response:

- Convergence 
- Accommodation 
- Pupil constriction 

Thought to originate in the occipital association cortex

Pathway for near response located more ventrally in the midbrain than the afferent portion of the light reflex so innervation signal added to light signal resulting in greater pupil constriction

If someone has parasympathetic defect testing to see if the near response is preserved can help localise where the problem is occurring

Question 25

Argyll Robertson Pupil

Answer 25

Where both pupil don’t restrict to a light stimulus but both constrict to a near stimulus.

This results from tertiary syphilis caused by Treponema Pallidum

No focal lesions in autonomic pathways.

Damage to the efferent pupillary fibres on dorsal side of Edinger Westphal Nuclei occurs causing lack of light response. Ventral side escapes damage and as nerve fibres responsible for accommodation response travel through the ventral midbrain constriction to a near target is preserved.

Conditions that present similar to Neuro-syphilis:
- Sarcoidosis
- Encephalitis
Multiple sclerosis lesions