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
What are the nerve components of the abducent (VI) nerve?
Somatic Motor
- Extraocular muscle
- Lateral rectus
What is the clinical significance of the abducent nerve?
Medial deviation of the affected eye causing diplopia
What is the Pathway for the Ophthalmic division of the trigeminal nerve (V1)?
Emerges from the pons, travels through the trigeminal ganglion and exits via the superior orbital fissure
What are the nerve components of the ophthalmic division of the trigeminal nerve?
General sensory
-From cornea, forehead, scalp, eyelids, nose and mucosa of nasal cavity and sinuses
What is the pathway of the maxillary division of the trigeminal nerve?
Emerges from the pons, travels through the trigeminal ganglion and exits via the foramen rotundum
What is the nerve component of the maxillary division of the trigeminal nerve (V2)?
General sensory:
-Face over maxilla, maxillary teeth, TMJ, mucosa of nose, maxillary sinuses and palate
What is the pathway for the mandibular division of the trigeminal nerve?
Emerges from the pons, travels through the trigeminal ganglion and exits via the foramen ovale
What are the nerve components of the mandibular division of the trigeminal nerve (V3)?
General sensory:
-face over mandible, mandibular teeth, TMJ, mucosa of mouth and anterior 2/3rd of tongue
Somatic motor:
-Muscles of mastication, part of digastric, tensor veil palatini, tensor tympani
What is the clinical significance of the trigeminal nerve?
-Paralysis of muscles of mastication
-Loss of corneal or sneezing reflex
-Loss of sensation in the face
-Trigeminal neuralgia
(one of the most painful conditions known to man)
What is the pathway of the facial (VII) nerve?
Emerges between pons and medulla and exits via internal acoustic meatus, facial canal and stylomastoid foramen
What are the motor nerve components of the facial nerve (VII)
Somatic motor
- Muscles of facial expression and scalp
- Stapedius
- Part of digastric
Visceral motor
- Parasympathetic innervation of:
- –Submandibular and sublingual salivary gland
- –Lacrimal glands
- –Glands of nose and soft palate
What are the sensory nerve components of the facial nerve (VII)?
Special sensory
-Taste from anterior 2/3rd of tongue and soft palate
General sensory
-From external acoustic meatus
What is the clinical significance of the facial nerve?
Most frequently injured cranial nerve due to long pathway through bone
Bell’s palsy
-Cannot frown, close eyelid or bare teeth
What is the pathway for the vestibulocochlear nerve (VIII)?
Emerges from between pons and medulla and exits via internal acoustic meatus, dividing into vestibular and cochlear nerves
What are the nerve components of the vestibulocochlear nerve (VIII)?
Special sensory
- Vestibular sensation from semicircular ducts, utricle, saccule gives sense of position and movement
- Hearing from cochlea
What is the clinical significance of the vestibularcochlear nerve (VIII)?
Tinnitus (ringing in the ears)
Deafness (conductive vs sensorineural)
Vertigo (loss of balance)
Nystagmus (involuntary rapid eye movement)
What is the pathway for the glossopharyngeal nerve (IX)?
Emerges from medulla and exits via jugular foramen
What are the sensory nerve components of the glossopharyngeal nerve (IX)?
Special sensory
-Taste from posterior 3rd of tongue
General sensory
-Cutaneous sensations from middle ear and posterior oral cavity
Visceral sensory
-Sensation from carotid body and carotid sinus
What are the motor nerve components of the glossopharyngeal nerve (IX)?
Visceral motor
-Parasympathetic innervation of parotid gland
Somatic motor
-To stylopharyngeus, helps with swallowing
What is the clinical significance of the glossopharyngeal nerve?
- Loss of gag reflex and taste from back of tongue
- Associated with injuries to CNs X and XI (jugular foramen syndrome)
What is the pathway for the vagus nerve (X)?
Emerges from medulla and exits via jugular foramen, then everywhere
What are the sensory nerve components of the vagus nerve?
Special sensory
-Taste from epiglottis and palate
General sensory
-Sensation from auricle, external acoustic meatus
Visceral sensory:
-From pharynx, larynx, trachea, bronchi, heart, oesophagus, stomach, intestine
What are the motor nerve components of the vagus nerve?
Visceral motor
-Parasympathetic innervation muscle in bronchi, gut, heart
Somatic motor
-Pharynx, larynx, palate and oesophagus
What is the clinical significance of the vagus?
Damage to pharyngeal branches cause difficulty in swallowing
Damage to laryngeal branches causes difficulty in speaking
What is the pathway for the accessory nerve (XI)?
Small cranial (medulla) and large spinal roots exit via jugular foramen
What are the nerve components of the accessory nerve?
Somatic motor
- Striated muscle of soft palate, pharynx and larynx
- Sternocleidomastoid and trapezius
What is the clinical significance of the accessory nerve?
Weakness in turning head and shrugging shoulder
What is the pathway for the hypoglossal nerve (XII)?
Emerges from medulla and exits through the hypoglossal canal
What are the nerve components of the hypoglossal nerve?
Somatic motor
-Muscles of the tongue
What is the clinical significance of the hypoglossal nerve?
Vulnerable to damage during tonsillectomy
Causes paralysis and atrophy of ipsilateral half of tongue
Tip deviates towards affected side
