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