Cranial Nerves Flashcards
How many pairs of cranial nerves are there?
12
What is the pathway of the olfactory nerve?
Receptors = olfactory epithelium in nasal cavity
Fibres pass through foramen in cribiform plate of ethmoid bone and enter olfactory bulb in anterior cranial fossa
What are the components of the olfactory nerve?
Special sensory = smell
What is clinically important about the olfactory nerve?
Fractured cribiform plate may tear olfactory nerve causing anosmia
What is the pathway of the optic nerve?
Enters via optic canal
Nerves join to form optic chiasm
Fibres from medial half of each retina cross = optic tract
What are the components of the optic nerve?
Special sensory = vision
Why is the optic nerve clinically important?
Increase in CSF pressure = papilloedema
Section of right optic nerve = blindness in right eye
Section of optic chiasm causes loss of peripheral vision (bitemporal hemianopsia)
Section of right optic tract = blindness in left temporal and right nasal fields
What is the pathway of the oculomotor nerve?
Emerges from midbrain
Exits via superior orbital fissure
What are the components of the oculomotor nerve?
Somatic motor = extraocular muscles and eyelid
Autonomic motor = parasymp. to pupil = constriction and to ciliary muscle = accommodation of lens
What is the clinical application 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?
Emerges from dorsal surface of midbrain
Exits via superior orbital fissure
What are the components of the trochlear nerve?
Somatic motor = Extraocular muscles
What is the clinical application of the trochlear nerve?
Diplopia when looking down
What is the pathway of the abducent nerve?
Emerges between pons and medulla
Exits via superior orbital fissure
What are the components of the abducent nerve?
Somatic motor = extraocular muscle
What is the clinical application of the abducent nerve?
Medial deviation of the affected eye causing diplopia
What is the pathway of the opthalmic branch of the trigeminal nerve?
Emerges from pons
Travels through trigeminal ganglion
Exits via superior orbital fissure
What are the components of the opthalmic branch of the trigeminal nerve?
General sensory = from cornea, forehead, scalp, eyelids, nose, mucosa of nasal cavity and sinuses
What is the pathway of the maxillary branch of the trigeminal nerve?
Emerges from pons
Travels through trigeminal ganglion
Exits via foramen rotundum
What are the components of the maxillary branch of the trigeminal nerve?
General sensory = face over maxilla, maxillary teeth, TMJ, nose mucosa, maxillary sinuses and palate
What is the pathway of the mandibular branch of the trigeminal nerve?
Emerges from pons
Travels through trigeminal ganglion
Exits via foramen ovale
What are the components of the mandibular branch of the trigeminal nerve?
General sensory = face over mandible, mandibular teeth, TMJ, mouth mucosa, ant. 2/3rds of tongue
Somatic motor = mastication muscles, part of digastric, tensor veli palatini and tensor tympani
What is the clinical application of the mandibular branch of the trigeminal nerve?
Paralysis of muscles of mastication
Loss of corneal/sneezing reflex
Loss of sensation in face
Trigeminal neuralgia
What is the pathway of the facial nerve?
Emerges at pontomedullary junction
Exits via internal acoustic meatus, facial canal and stylomastoid foramen
What are the components of the facial nerve?
Somatic motor = muscles of facial expression and scalp, stapedius (middle ear), part of digastric
Autonomic motor = parasymp. innervation of submandibular and sublingual salivary glands, lacrimal glands, glands of nose and palate
Special sensory = taste from ant. 2/3rd of tongue and soft palate
General sensory = from external acoustic meatus
What is the clinical application of the facial nerve?
Most frequently injured - due to long pathway through bone
Bell’s palsy - can’t frown, close eyelid or bare teeth
What is the pathway of the vestibulocochlear nerve?
Emerges from pontomedullary junction
Exits via internal acoustic meatus
Divides into vestibular and cochlear nerves
What are the componenets of the vestibulocochlear nerve?
Special sensory = vestibular sensation from SC ducts, utricle, saccule - sense of position and movement
Hearing from spiral organ
What is the clinical application of the vestibulocochlear nerve?
Tinnitus
Deafness (sensorineural)
Vertigo
Nystagmus
What is the pathway of the glossopharyngeal nerve?
Emerges from medulla
Exits via jugular foramen
What are the components of the glossopharyngeal nerve?
Special sensory = taste from post. 3rd of tongue
General sensory = cutaneous sensations from middle ear and posterior oral cavity
Visceral sensory = sensation from carotid body and carotid sinus
Autonomic motor = parasymp. innervation of parotid gland
Somatic motor = to stylopharyngeus, helps with swallowing
What is the clinical application of the glossopharyngeal nerve?
Loss of gag reflex and taste from back of tongue
Associated with injuries to CN X and XI = jugular foramen syndrome
What is the pathway of the vagus nerve?
Emerges from medulla
Exits via jugular foramen
What are the 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
Autonomic motor = parasymp. innervation of muscle in bronchi, gut, heart
Somatic motor = pharynx, larynx, palate, oesophagus
What is the clinical application of the vagus nerve?
Damage to pharyngeal branches = difficulty swallowing
Damage to laryngeal branches = difficulty speaking
What is the pathway of the accessory nerve?
Small cranial + large spinal roots exit via jugular foramen
What are the components of the accessory nerve?
Somatic motor = striated muscle of soft palate, pharynx and larynx, and to sternocleidomastoid and trapezius
What is the clinical application of the accessory nerve?
Weakness in turning head and shrugging shoulders
What is the pathway of the hypoglossal nerve?
Emerges from medulla
Exits via hypoglossal canal
What are the components of the hypoglossal nerve?
Somatic motor = muscles of tongue
What is the clinical application of the hypoglossal nerve?
Vulnerable to damage during tonsillectomy
Causes paralysis and atrophy of ipsilateral half of tongue - tip deviates towards affected side
