21B18: Exam Report

Outline the neural pathways for the pupillary light, corneal, oculomotor and gag reflexes. The anatomical course of nerves is NOT required.

43% of candidates passed this question.

This is a fact-based question with little integration of knowledge required.

Those candidates who synthesised their knowledge into a succinct and precise description of afferent and efferent pathways with a description of the various sensor and integrator components scored very high marks.

A good working knowledge of all the cranial nerve reflex pathways are crucial to the practise of intensive care medicine.

Marks were not awarded for any anatomical description related to these pathways.

K1i / 21B18: Outline the neural pathways for the pupillary light, corneal, oculomotor and gag reflexes. The anatomical course of nerves is NOT required.

Sensor

Afferent

Integrators

Efferent

Motor

Pupillary light reflex

Sensor

Photoreceptors in retina

Afferent

CN II

Integrators

Pretectal nucleus (midbrain)

Bilateral Edinger Westphal nuclei (midbrain)

Efferent

CN III

Changes in acute or chronic liver disease?

Iris sphincter muscles > bilateral pupillary constriction

Corneal reflex

Sensor

Free nerve endings or mechanoreceptors within epithelium of cornea

Afferent

CN V1 (ophthalmic branch)

Integrators

Spinal nucleus of trigeminal nerve

Motor nucleus of facial nerve

Efferent

CN VII

Motor

Orbicularis oculi > contraction leads to bilateral eye closure

Vestibular-occular reflex

Sensor

Semicircular canals and the otolith organs

Afferent

CN VIII

Integrators

  • Vestibular nuclear complex (medulla and pons)
  • Medial longitudinal fasciculus
  • Motor nucleus of III, IV, and VI
  • Inhibitory and excitatory pathways

Efferent

CN III, IV, VI

Motor

III > medial rectus

VI > lateral rectus

IV > superior oblique

 

VOR leads to opposite movement of eyes to head movement in order to stabilise eye gaze

 

e.g. L cervical rotation leads to contraction of R lateral rectus + L medial rectus (and inhibition of L lateral rectus and R medial rectus)

Gag reflex

Sensor

Mechanoreceptors in oral mucosa of

posterior pharyngeal wall, tonsillar pillars, base of the tongue

Afferent

CN IX

Integrators

Nucleus ambiguus

Efferent

CN X

Motor

Posterior pharyngeal muscles (bilateral contraction)

Author: Madeline Coxwell Matthewman