Cranial Nerves

Question 1

What are the 12 cranial nerves?

Answer 1

Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulo-cochlear, Glossopharyngeal, Vagus, Accessory, Hypoglossal.

Question 2

Fundus examination?

Answer 2

By causing the dilation of the pupil pharmacologically, the physician can examine the fundus through the ophthalmoscope.

The optic nerve head (optic disk) can be easily identified by the radially emerging blood vessels originating in the center of the optic nerve. It is the area in which all the fibers converge to create the optic nerve.
The fovea forms the center of the retina and is surrounded by the macula (fovea and macula can be identified by the relative absence of large diameter blood vessels).

Question 3

Types of visual abnormalities ?

Answer 3

Pupillary reflex physiology and abnormalities : The pupillary reflex involves direct and consensual pupil constriction (miosis) when light is directed toward the eye. It is controlled by two pathways —> Parasympathetic pathway (sphincter pupillae) and the sympathetic pathway (dilator pupillae). An abnormality is ANISOCORIA or unequal pupil size due to parasympathetic deficits (e.g., III nerve palsy or Adie’s pupil) in bright light or sympathetic deficits (e.g., Horner’s syndrome) in dim light.

Optic nerve lesions : lesions based on location such as
- prechiasmal lesions : monocular vision loss due to complete nerve lesion, concentric visual field constriction and central scotoma.
- chiasmal lesions : bitemporal heteronymous hemianopsia and junctional field defect.
- post chiasmal lesions : homonymous hemianopsia, superior and inferior quadrantanopia and altitudinal hemianopsia.
Specific disorders include optic neuritis, papilledema, central retinal artery occlusion, Horner syndrome and infectious disorders.

Disorders of eye movements : main causes are muscle diseases or neuromuscular junction issues, lesions at nerve or isolated causes like trauma and ischemic lesions.
- strabismus : horizontal can be exotropia (outward) or esotropia. Vertical can be hypertropia (higher eye) or hypertropia.
Isolated nerve palsies :
- CNIII ptosis, fixed dilated pupil caused by compression or ischemia.
- CN IV vertical diplopia and head tilt.
- CN VI horizontal diplopia and inward eye deviation.
Complex syndromes include internuclear opthalmoplegia, horizontal gaze palsy and one and a half syndrome.

Question 4

Trigeminal nerve anatomy?

Answer 4

It is the largest cranial nerve and contains both sensory and motor components (mixed nerve).
- sensory components innervate the face and the head region anterior to the vertex. Not only the skin but also internal components.
- motor components innervate the muscles involved in mastication.
The biggest sensory ganglion is called the trigeminal (gasserian) ganglion from which three main branches arise : Ophthalmic (V1), Maxillary (V2) and Mandibular (V3). These three different branches exit the skull from three different foramina : Superior Orbital Fissure (V1), Foramen Rotundum (V2) and Foramina Ovale (V3). The ganglion is found a at antero lateral portion of the pons.