Cranial Nerves Flashcards
How many cranial nerves are there?
12 pairs of nerves emerging from the cranium
Why are nerves prone to compression due to inflammation, tumours, fractures?
Nerves are soft and squashy
They have to pass through holes in hard bone
What motor fibres may cranial nerves contain?
Somatic motor fibres (supplying striated muscle)
Visceral motor fibres (cranial division of the parasympathetic supply innervates smooth muscle and glands)
What sensory fibres may cranial nerves contain?
Visceral sensory
-Afferent inputs from pharynx, larynx, heart, lung, gut etc
(not normally conscious)
General sensory
-Afferent inputs (e.g. touch, temperature, pain) from skin and mucous membranes
Special sensory
-Taste, smell, vision, hearing and balance
How are the cell bodies of cranial nerves placed?
Sensory (afferent) fibres
-Pseudounipolar
Somatic motor (efferent) fibres
- Cell body in CNS
- Axon runs to muscle
Autonomic motor (efferent) fibres -Synapse in PNS
What is the pathway of the Olfactory Nerve (I)?
Receptors in olfactory epithelium of nasal cavity
Olfactory nerve fibres pass through foraminifera in cribriform plate of ethmoid bone and enter olfactory bulb in the anterior cranial fossa
What are the nerve components of the Olfactory Nerve (I)?
Special sensory (smell)
What is the clinical significance of the Olfactory Nerve (I)?
Fractured cribriform plate may tear olfactory nerve fibres causing anosmia
What is anosmia?
loss of sense of smell
What is the pathway of the Optic nerve (II)?
Enters via optic canal
Nerves join to form the optic chiasm
Fibres from medial (nasal) half of each retina cross to form optic tract
What are the nerve components of the optic nerve (II)?
Special sensory (vision)
What is the clinical significance of the optic nerve?
Increase in CSF pressure can cause papilloedema
Section of right optic nerve causes blindness through right eye
Section of optic chiasm causes loss of peripheral vision (bitemporal hemianopsia)
Section of right optic tract causes blindness in left temporal and right nasal fields (left homonymous hemianopsia)
What is papilloedema?
Optic disc swelling due to increase in intracranial pressure
What is the pathway for the Oculomotor nerve (III)?
Emerges from midbrain and exits via superior orbital fissure
What are the nerve components of the Oculomotor nerve (III)?
Somatic motor
-Extraocular muscles (superior, medial and inferior rectus and inferior oblique)
Visceral motor
-Parasympathetic to pupil causes constriction and to ciliary muscle causing accommodation of the lens
What is the clinical significance of the oculomotor nerve?
Drooping of upper eyelid (ptosis)
Eyeball abducted and pointing down
No pupillary reflex
No accommodation of the lens
What is the pathway of the trochlear nerve (IV)?
Emerges from dorsal surface of the mid brain and exits via the superior orbital fissure
What are the nerve components of the trochlear nerve?
Somatic motor
-Superior oblique
What is the clinical significance of the trochlear nerve?
Diplopia when looking down
double vision as one eye can look down but other can’t
What is the pathway of the Abducent nerve (VI)?
Emerges between pons and medulla and exits via the superior orbital fissure