Cranial Nerves Flashcards
Difference between cranial nerves and spinal nerves?
Different location of cell bodies
Cranial nerves from the brain, spinal nerves from the spinal cord
What are the two atypical CNs and why?
I and II (olfactory and optic)
True brain tracts, not just nerves
Where are the structures that the cranial nerves supply derived from?
The same branchial arch from which each cranial nerve is derived from (usually)
From which surface do all but one exit the brain?
From the inferior surface of the brain
The number of the cranial nerve gives its rostro-caudal position, but there is an exception, which one?
CNXII (hypoglossal) is just infront of CNXI (accessory)
Name the cranial nerves
I = olfactory II = optic III = occulomotor IV = trochlear V = trigeminal VI = abducens VII = facial VIII = auditory vestibulocochlear IX = glossopharyngeal X = vagus XI = accesory XII = hypoglossal
What are the three primary segments/vesicles of the brain called? What can they be further divided into?
Prosencephalon
- telencephalon (cortex)
- diencephalon (hypothalamus)
Mesencephalon
Rhombencephalon
- metencephalon (pons)
- myelencephalon (medulla)
Problems with the foramina of the skull?
Make the base weak - fractures
Can compress nerves
Peripheral nerve diseases and metastases can pass to the brain via the foramina
Which CNs are sensory?
Some Say Marry Money But My Brother Says Big Brains
Matter More
Olfactory, Optic, Auditory vestibulocochlear,
Which CNs are motor?
Oculomotor, Trochlear, Abducens, Accessory, Hypoglossal
Which CNs are both?
Trigeminal
Facial
Glossopharyngeal
Vagus
What does the olfactory nerve do?
Sensory only
Supplied nasal cavity - sense of smell
What is the path of the olfactory nerve?
Leaves the nasal cavity to ascend intra-cranially via the cribriform plate of the ethmoid bone where they form the olfactory bulb
How is the first cranial nerve tested?
Get the patient to identify smells
What could also cause anosmia?
Infection of the upper respiratory tract
Functions of CNII?
Optic nerve - sensory only
Vision
How is CNII tested?
Acuity - Snellen chart Colour - Ishihara plate Visual fields - wiggle fingers Visual reflexes - shine a torch in one eye and check both pupils constrict Fundoscopy on both eyes
What can cause damage to the optic nerve?
Direct trauma to eye or orbit
Hypothalamic tumour
Aneurysm of internal carotid near hypothalamus
Increased intracranial pressure causing increased CSF pressure
Fracture of optic canal
General functions of the oculomotor nerve?
Somatic motor and autonomic
Somatic motor functions of the oculomotor nerve?
All extraocular muscles except for lateral rectus and superior oblique
Levator palpebrae superioris muscle
Autonomic function of the oculomotor nerve?
Constrictor pupillae of the eye (parasympathetic)
Ciliary muscles
What is seen in oculomotor nerve palsy and why?
Eye is down and out due to unopposed action of the lateral rectus and superior oblique
Dilated pupil
Ptosis
Pupillary reflex on the side of the region is lost
How to test the levator palpebrae superioris?
Look up to see if elevation of the eyelid accompanies effort
What is oculomotor nerve palsy associated with?
Aneurysm of posterior communicating artery
Cavernous sinus thrombosis
Where does the trochlear nerve emerge from?
Dorsal aspect of the midbrain
Function of the trochlear nerve?
Supplies the superior oblique muscle
Sign of trochlear nerve damage?
Diplopia when looking down and medially
Difficulty walking downstairs
Divisions of the trigeminal nerve?
Maxillary
Mandibular
Ophthalmic
Function of the ophthalmic division?
Sensation over forehead
Corneal reflex
What is the route for the corneal reflex?
Ophthalmic sensory division
Fibres synapse with facial neurones to orbicularis oris
Contracts - blink
How do you know if just the facial nerve is effected when testing the corneal reflex?
If touching the cornea of one eye produces a blink in the other eye only, ophthalmic division not affected
What does the mandibular division of the trigeminal nerve innervate?
Anterior two thirds of the tongue (general sensation) Skin, lower teeth and cheek Muscles of mastication including -temporalis -masseter -medial and lateral pterygoids -anterior belly of digastric
How is the trigeminal nerve tested?
Assess touch and pain in three regions of face on both sides
Corneal reflex
Clench teeth and feel bulk of masseter and temporalis muscles
Open mouth against resistance
Jaw jerk
Function of the maxillary branch?
Sensory innervation of skin and mucous membranes of nose, palate and upper dental arcade
Function of the abducens nerve?
Lateral rectus muscle
Sign of damage to the abducens nerve?
Patient unable to look outwards, squint if they do
Why is the abducens nerve liable to damage if there is increased intra-cranial pressure?
Long intra-cranial course
Sensory function of the facial nerve?
Taste of anterior two thirds of tongue
External acoustic meatus and auricle
Motor functions of the facial nerve?
Muscles of facial expression
Parasympathetic secretomotor to submandibular and sublingual salivary glands via chorda tympani
Parasymp to glands of nasal mucosa and paranasal sinuses, palate and lacrimal gland
What is seen in damage to the facial nerve in the parotid region
Paralysis of facial muscles
Eyes remain open
Angle of mouth droops
Forehead does not wrinkle
What is seen if there is a fracture of the temporal bone and damage to the facial nerve?
Bell’s Palsy
Involvement of cochlear nerve and chorda tympani; dry cornea; loss of taste in anterior 2/3rds tongue
What is seen because of damage from an intracranial haematoma
Forehead wrinkles because of bilateral innervation of frontalis muscle
Paralysis of contralateral facial muscles
How to test the facial nerve?
Crease forehead
Close eyes and keep them closed against resistance
Puff out cheeks and prod
Show teeth
Function of the auditory vestibulocochlear nerve?
Sensory
Vestibular branch - balance
Cochlear branch - hearing
What can cause auditory vestibulocochlear nerve lesions?
Skull fracture
Ear infection
Tumour of the nerve (acoustic neuroma)
How to test the auditory vestibulocochlear nerve?
Rinne test (mastoid and next to ear, latter should be louder normally) Weber's test (centre of forehead)
Sensory function of the glossopharyngeal nerve?
Posterior third of the tongue
Pharynx, oropharyngeak isthmus, dorsum of palate, auditory tube, mastoid antrum, mastoid air cells
Carotid body and sinus
Motor function of the glossopharyngeal nerve?
Stylopharyngeus
Parotid salivary gland (parasympathetic secretomotor fibres)
How to test function of the glossopharyngeal nerve?
Gag reflex
Motor functions of the vagus nerve?
All muscles of the pharynx except stylopharyngeus
Muscles of airways, larynx, heart and GI tract
All palate muscles except tensor veli palatine
Sensory function of the vagus nerve?
General sensory of lower pharynx and larynx
External auditory meatus
Taste to epiglottis
A lesion of which nerve can lead to hoarseness? What can cause it?
Recurrently laryngeal branch of the vagus
Paralysis of the vocal cord
Left recurrent laryngeal nerve is lower than the right. Bronchial/oesophageal carcinoma or enlarged mediastinal lymph nodes
How can mitral stenosis lead to hoarseness?
Causes an enlarged left atrium, pushed up left pulmonary artery, compresses left recurrent laryngeal against the aortic arch
Which nerve can be damaged in a thyroidectomy and how?
Superior laryngeal nerve, branch of the vagus
Lies close to the superior thyroid artery and can be damaged when lighting the blood vessel
How to test the function of the vagus nerve?
Observe the uvula while the patient says ‘aah’
Check that it does not deviate
Would deviate away from the affected side
Function of the accessory nerve?
Cranial component innervates the pharynx, larynx and soft palate
Spinal component innervates the trapezius and SCM (C2-4)
What happens if there is damage to the accessory nerve?
Paralysis of SCM and superior fibres of trapezius
Shoulder droop
How to test the accessory nerve?
Ask patient to shrug shoulders against resistance
Function of the hypoglossal nerve?
All extrinsic and intrinsic muscles of the tongue
-except palatoglossus
What can cause a lesion of the hypoglossal nerve?
Neck laceration
Basal skull fracture
Which way does a protruded tongue deviate if there is damage to the hypoglossal nerve?
Towards the affected side
