Cranial Nerves Flashcards
What are the cranial nerves?
12 pairs of nerves that emerge from the cranium
Why are the cranial nerves prone to compression?
- They are soft and squashy
- They have to pass through holes in hard bone
- They are prone to compression due to inflammation, tumours and fractures
- Symptoms relate to the function of the nerves
What may cranial nerves contain?
- Somatic motor fibres
- Visceral motor fibres
- Visceral sensory
- General sensory
- Special sensory
What do somatic motor fibre supply?
Striated muscle
What do visceral motor fibres supply?
Cranial division of the parasympathetic supply innervates smooth muscle and glands
What do visceral sensory fibres supply?
Afferent inputs from pharynx, larynx, heart, lung, gut (not normally concious)
What do general sensory fibres supply?
Afferent inputs (touch, temperature, pain) from skin and mucous membranes
What do special sensory fibres supply?
- Taste
- Smell
- Vision
- Hearing
- Balance
What do all nerve fibres need?
Cell bodies
What fibres have the cell bodies in the CNS?
- Somatic motor fibres
- Autonomic motor fibres
What fibres have cell bodies outwith the CNS?
- Sensory fibres
- Autonomic motor fibres
CNVI
Abducent
CNIV
Trochlear
CNX
Vagus
CNXII
Hypoglossal
CNII
Optic
CNV
Trigeminal
CNVIII
Vestibulocochlear
CNI
Olfactory
CNXI
Accessory
CNVII
Facial
CNIII
Oculomotor
CNIX
Glossopharyngeal
Olfactory pathway
- 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
Olfactory components
Special sensory smell
Olfactory clinical application
Fractured cribriform plate may tear olfactory nerve fibres causing anosmia
Optic pathway
- Enters via optic canal
- Nerves join to form optic chiasm
- Fibres from medial half of each retina cross to form optic tract
Optic components
Special sensory vision
Optic clinical applications
- Increase in CSF pressure can cause papilledema
- 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)
Oculomotor pathway
Emerges from midbrain and exits via superior orbital fissure
Oculomotor components
- Somatic motor: extraocular muscles (superior,medial,inferior rectus and inferior oblique) and eyelid
- Visceral motor: parasympathetic to pupil causing constriction and to ciliary muscle causing accommodation of the lens
Oculomotor clinical application
- Drooping of upper eyelid (ptosis)
- Eyeball abducted and pointing down
- No pupillary reflex
- No accommodation of the lens
Trochlear pathway
Emerges from dorsal surface of the midbrain and exits via the superior orbital fissure
Trochlear components
Somatic motor: extraocular muscle (superior oblique turns eye downwards)
Trochlear clinical application
Diplopia when looking down
Abducent pathway
Emerges between pons and medulla and exits via the superior orbital fissure
Abducent components
Somatic motor: extraocular muscle (lateral rectus abducts the eye)
Abducent clinical application
Medial deviation of the affected eye causing diplopia
Trigeminal V1
Ophthalmic
Trigeminal V3
Mandibular
Trigeminal V2
Maxillary
Trigeminal V1 pathway
Emerges from the pons, travels through the trigeminal ganglion and exits via the superior orbital fissure
Trigeminal V1 components
General sensory: from cornea, forehead, scalp, eyelids, nose and mucosa of nasal cavity and sinuses
Trigeminal V2 pathway
Emerges from the pons, travels through the trigeminal ganglion and exits via the foramen rotundum
Trigeminal V2 components
General sensory: from face over maxilla, maxillary teeth, TMJ, mucosa of nose, maxillary sinuses and palate
Trigeminal V3 pathway
Emerges from the pons, travels through the trigeminal ganglion and exits via the foramen ovale
Trigeminal V3 components
- General sensory: from face over mandible, mandibular teeth, TMJ, mucosa of mouth and anterior 2/3 of tongue
- Somatic motor: muscles of mastication, part of digastric, tensor veli palatinin and tenor tympani
Trigeminal V3 clinical application
- Paralysis of muscles of mastication
- Loss of corneal or sneezing reflex
- Loss of sensation in the face
- Trigeminal neuralgia
Facial pathway
Emerges between pons and medulla and exits via internal acoustic meatus, facial canal and stylomastoid foramen
Facial components
- Somatic motor: muscles of facial expression and scalp, stapedius of middle ear, part of digastric muscle
- Visceral motor: parasympathetic of submandibular and sublingual salivary glands, lacrimal glands, glands of nose and palate
- Special sensory: taste from anterior 2/3 of tongue and soft palate
- General sensory: from external acoustic meatus
Vestibulocochlear pathway
Emerges from between pons and medulla and exits via internal acoustic meatus, dividing into vestibular and cochlear nerves
Vestibulocochlear components
Special sensory: vestibular sensation from semi-circular ducts, utricle saccule gives sense of position and movement, hearing from spiral organ
Vestibulocochlear clinical application
- Tinnitus (ringing in the ears)
- Deafness (conductive vs sensorineural)
- Vertigo (loss of balance)
- Nystagmus (involuntary rapid eye movements)
Glossopharyngeal pathway
Emerges from medulla and exits via jugular foramen
Glossopharyngeal components
- 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
- Visceral motor: parasympathetic innervation of parotid gland
- Somatic motor: to stylopharyngeus, helps with swallowing
Glossopharyngeal clinical application
- Loss of gag reflex and taste from back of the tongue
- Associated with injuries to accessory and vagus nerves: jugular foramen syndrrome
Vagus pathway
Emerges from medulla and exits via jugular formane then goes everywhere
Vagus components
- 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
- Visceral motor: parasympathetic innervation muscle in bronchi, gut, heart
- Somatic motor: to pharynx, larynx, palate and oesophagus
Vagus clinical application
- Damage to pharyngeal branches cause difficulty swallowing
- Damage to laryngeal branches cause difficulty in speaking
Accessory pathway
Small cranial (medulla) and large spinal roots exit via jugular foramen
Accessory components
Somatic motor: striated muscle of soft palate, pharynx and larynx, sternocleidomastoid and trapezius
Accessory clinical application
Weakness in turning head and shrugging shoulders
Hypoglossal pathway
Emerges from medulla and exits through the hypoglossal canal
Hypoglossal components
Somatic motor: to muscles of tongue
Hypoglossal clinical application
- Vulnerable to damage during tonsillectomy
- Causes paralysis and atrophy of ipsilateral half of tongue. Deviates towards affected side
Smell
Olfactory
Sight
Optic
Taste
- Facial
- Glossopharyngeal
- Vagus
Hearing and balance
Vestibulocochlear
Movement of eyes
- Oculomotor
- Trochlear
- Abducent
Movement of face
Facial
Sensation from the face
Trigeminal
Chewing
Trigeminal V3
Swallowing
- Glossopharyngeal
- Accessory
Movement of the tongue
Hypoglossal
Movement of the vocal cords
Vagus
Visceral sensory input
- Vagus
- Glossopharnygeal
Movement of the neck
Accessory
Facial Clinical Application
- Most frequently injured due to long pathway though bone
- Bell’s palsy, cannot frown, close eyelid or bare teeth
