Cranial nerves Flashcards
List all 12 cranial nerves in order?
- olefactory
- optic
- occulomotor
- trochlear
- trigeminal
- abucens
- facial
- vestibulocochlear
- glossopharyngeal
- vagus
- accessory
- hypoglossal
From where do each of the cranial nerves arise?
1 and 2 from the brain// 3 and 4 from midbrain// 5,6,7,8 from pons and 9,10,11,12 from medulla
What runs through the cavernous sinus?
occulomotor, trochlear, opthalmic division of trigeminal nerve, maxillary branch of trigeminal nerve, internal carotid artery and abudcens nerve
Describe the path of the olfactory nerve
form nose, up through cribiform foramina, to the olfactory bulb, which runs does olfactory tract to the forebrain
What is the function of the olfactory nerve? How can it be tested?
Smell
Tested by asking about any change in sense of smell or do smelling salts test
What may cause anosmia (loss of smell)? (3)
- blocked nose/ a cold
- head injuries damaging olfactory tract of cribiform foramina shearing force
- tumours at base of frontal lobe
Describe the path of the optic nerve
From eye, through optic canal, the nerves mix at the optic chiasm and then run through optic tracts to occipital lobes at back of brain
What are the functions of the optic nerve and how are they tested?
Vision and afferent limb of pupillary light reflex,
Tested by visual feilds tests, snellen charts and pupil light reflexes
What can be inferred about the location of the nerve legion if an eye doesn’t react to light directly of consensually?
It is a motor probelm- so occulumotor nerve lesion
What can be inferred if one eye fails to respond directly to light but when light is shone in the other eye it does constrict?
It is an optic nerve injury as sensory limb lost
How can the optic nerve be affected?
By papillodema- the optic nerve runs in an extension of the meninges so raised ICP will also impinge on the optic nerve.
Pituitary tumours may also impinge on it and cause tunnel vision
Describe the route of the occulomotor nerve
From midbrain, through cavernous sinus, exits at superior orbital fissure into orbit.
Which cranial nerves carry autonomics?
occulomotor, facial, glossopharyngeal, vagus (3,7,9,10)
What are the motor and autonomic functions of the occulomotor nerve?
Motor: medial, superior and inferior rectus and inferior oblique as well as levator palberae superioris which opens eyelid
Parasymapthetic to sphincter pupillae (constricts pupil) and cillary muscle (thickens lens)
How can the occulomotor nerve be affected by raised ICP? Why are the pupillary light reflexes and accomodation reflex affected first?
it runs along the tentorium cerbelli, so it can be compressed by the encus movement when the ICP raises. The parasympathetic fibres run along the outside of the nerve bundle, so are impinged first.
Other than raised ICP, what may cause occulomotor nerve dysnfunctions?
- cavernous sinus thrombus
- aneurysms
- diabetes and hypertension
Describe the route of the trochlear nerve
From the mid brain, through the cavernous sinus and out through the superior orbital fissure
What is the function of the trochlear nerve and how can it be tested?
Motor innervation to the superior oblique muscle.
Tested by testing whether eye can be moved into a down and in position
What may cause trochlear nerve injuries?
cavernous sinus thrombus or any of raised ICP eg head injury
Describe the route of the trigeminal nerves branches
All originate in the pons.
Opthalmic branch exits through superior orbital fissure.
Maxillary branch exits at the foramen rotundum.
Mandibular branch passes through the foramen ovale.
Describe the functions of the trigeminal nerve
Motor control to muscles of mastication
Sensory control to the face, eyes (sensory part of corneal reflex), mouth and anterior 2/3 of the tongue.
How can the trigeminal nerve functions be tested?
- test dermatomes of Va,b and c
- test muscles of mastication
- test corneal relfex (sensory part)
Which nerves are venerable in fractures of the mandible?
lingual nerve (to tongue) and inferior alveolar nerve (to lips and chin) are both branches of the mandibular nerve which run within the mandible so are venerable
What is trigeminal neuralgia?
Transient shooting pain in the face (usually cheeks) due to compression of the trigeminal nerve- usually due to blood vessel/ cyst/ tumours.
Describe the path of the abducens nerve
from pons, through cavernous sinus and out through superior orbital fissure
What is the function of the abducens nerve and how is it tested?
It supplies the lateral rectus muscle. Test this by testing ability to move eye laterally
Describe the course of the facial nerve?
Comes out of pons, enters the pytrous part of the temporal bone through the internal auditory meatus, in here there is the genticulate ganglion which creates the greater petrosal nerve branch, chordae tympani and nerve to the submandibular ganglion which goes to the salivary glands. The bulk of the nerve exits at the base of the skull and gives off 5 branches (T,Z,B,M,C)
What are the 4 functions of the facial nerve?
- Motor control to muscles of facial expression
- taste to anterior 2/3 tongue
- Autonomics to lacrimal, submandibular and sub lingual glands
- Dampen excessive vibration of stapedius
How can the facial nerve be tested?
- test muscles of facial expression (can they tightly shut eyelids against resistance)
- test corneal eye reflex (controls efferent limb/ closes eyelid)
- ask about changes to taste or sensitivity to noises
What is bells palsy?
Injury of facial nerve with no explanation (some think its due to a viral infection), causing one sided facial weakness
Describe the course of the vestibularcochlear nerve?
It comes from the pons, through the internal auditory meatus and to the inner ear to the vestible and cochlear
How is the vestibularcochlear nerve tested?
hearing tests, ask about balance, vertigo
What is presbyacusis?
A multifactoral hearingloss in old age
What is vertigo?
Balance loss and dizziness due to pathology to the semicircular canals, nerve or brain nucleus
What is an acoustic neuroma and what effects can it have?
A benign tumour of the vestibularcochlear nerve. It may also impinge on the trigeminal and facial nerves as theyre nearby causing numbness and trigeminal neuralgia
Describe the route of the glossopharyngeal nerve
Comes off the medulla, exits through the jugular foramen, gives off a branch to the parotid gland and then giving off branches to stylopharyngeus, the pharynx, the middle ear and the carotid body & sinus.
What are the functions of the 9th cranial nerve? (6)
- General sensory to middl ear
- Autonomic to the parotid gland
- Taste and general sensation to posterior 2/3 tongue
- General sensation to soft palate, tonsils and oropharynx (therefor afferent in the gag reflex)
- Motor to stylopharyngeus (elevates pharynx/ thryoid cartilage)
- Special sensory to carotid body and sinus
Describe the course of the vagus nerve
Exits medulla, goes through the jugular foramen, gives off superior laryngeal nerve (splits in to external and internal) and recurrent laryngeal nerve branches as it descends down carotid sheath. It then travels to abdomen to supply autonomics to the viscera there.
How is the glossopharyngeal nerve tested?
Test gag reflex (afferent)
Ask about taste
Test in conjunction w/ CN X
Why is pain from a sore throat commonly referred to the ear?
the glossopharyngeal nerve innervates both places, the brain is unable to distinguish between which area the pain originated from
What are the 3 functions of the vagus nerve in relation to the head and neck
- sensory to layngopharynx and larynx
- motor innervation to muscles of soft palate, pharynx (except stylopharyngeus), internal muscles of the larynx (facilitates speaking, swallowing)
- striated muscle to first part of oesphagus
How is vagus nerve function tested?
- note speech
- test swallow (fluids) and cough
- look for uvula deviation
- gag reflex (efferent limb)
Describe the course and actions of the spinal accessory nerve?
travels from medulla/ spinal cord and through the jugular foramen and then the posterior triangle to innervate the sternocleidomastoid and trapezius muscles.
When can the spinal accessory nerve be injured?
In trauma (eg stab wounds) to the posterior triangle as it runs through here
Describe the course of the hypoglossal nerve
it runs from the medulla through the hypoglossal canal (on the rim of the foramen magnum)
What is the function of the hypoglossal nerve and how is this tested?
It controls the intrinsic muscles of the tongue except palatoglossus. Test it by asking them to stick their tongue out, it may deviate towards to affected side or/ and show atrophy
Describe the consensual light reflex
Light -> optic nerve (afferent) -> brainstem (pre-tectal
nucleus)/midbrain -> Edinger Westphal nuclei on both sides -> parasympathetic fibres on oculomotor nerve (CN III) which is efferent limb (to both eyes) to constrictor muscle of iris (sphincter pupillae)-> causes pupillary constriction
