Cranial Nerves VII-XII Flashcards
What four cranial nerves rive from the pons?
Trigeminal
Abducens
Facial
Vestibulocochlear
What is the intercranial route of the facial nerve?
Lower pons (junction between pons and medulla)
Enters petrous part of the temporal bone via the internal acoustic meatus
3 branches then arise from this part
It then exits through the base of the skull via the stylomastoid foramen
After exiting, it gives off the 5 extra-cranial branches.
What are the three intercranial branches of the facial nerve?
Greater petrosal
Chordi tympani
Nerve to stapedius
What are the extracranial branches of the facial nerve?
Temporal Zygomatic Buccal Marginal Mandibular Cervical
What are some of the functions of thee facial nerve?
Special sensory - anterior 2/3 of tongue (taste)
Autonomic - lacrimal glands (tears), mucosal glands in nose and roof of mouth, salivary glands (all except parotid)
Motor - facial expression (extracranial), Stapedius muscle
General sensory - Small area of the external ear.
What are the two roots of the facial nerve?
Motor root - just motor axons
Nervous intermedius - sensory and parasympathetic axons
How do you clinically test facial nerve?
Mainly by testing muscles of facial expression and the corneal reflex.
How can different facial nerve lesions present?
They present differently depending on where they are.
Ask about other symptoms e.g: hyperacusis (noise sensitivity), dry eyes, altered taste.
Many other nerves have a close relationship with the facial nerve (e.g. vestibulocochlear) so can present with other nerve symptoms too.
What is Bell’s palsy?
A facial nerve palsy
What are the afferent and efferents of corneal reflex?
Ophthalmic branch of the Trigeminal = afferent limb of reflex (sensory)
Facial = efferent limb of reflex (motor)
Where does the vestibulococular nerve go?
Cochlea and semicircular canals from the vestibular system combine to make the vestibulochchlear nerve.
This travels through the internal acoustic meatus and to the lower pons (junction between the pons and the medulla)
What does the vestibulocochlear nerve do?
Special Sensory - Hearing and balance.
How do you test vestibulocochlear nerve?
Test hearing and enquire about balance.
What places can be damaged that cause hearing loss?
Cochlea, cochlea component of vestibulocochlear nerve or brain stem nucleus.
What is an acoustic neuroma?
Benign tumour of Schwann cells surrounding the vestibular component of the vestibulocochlear nerve.
Their physical presence causes compression of the whole nerve ad maybe the CNs in close proximity.
Symptoms and signs include:
- Unilateral hearing loss
- Tinnitus
- Vertigo
- Numbness, pain or weakness down one side of face (Facial nerve / Trigeminal nerve…)
What four cranial nerves come from the medulla?
Glossopharyngeal
Vagus
Accessory
Hypoglossal
They are all in the carotid sheath but they quickly exit (except vagus) to go to place high up in head and neck. Only the vagus runs the length of the carotid sheath.
What does the glossopharyngeal nerve do?
General sensation - Palatine tonsils and oropharynx
Middle ear and tympanic membrane
Sensory from carotid body and sinus
Special sensory - Taste and general sensation from posterior 1/3 of tongue
Autonomic - parasympathetic innervation to parotid gland
Motor - One muscle - stylopharyngeus - which helps with swallowing
How do you test the glossopharyngeal nerve?
Gag reflex (sensory limb) only tested if concerned around swallowing and integrity of nerves involved in this reflex because it is uncomfortable.
It is nor formally tested but when tested, it is tested in conjunction with the vagus nerve because this stimulates the contraction of the muscles in gag reflex.
Isolated lesions of CN IX are rare.
Where does the vagus nerve go?
Medulla
Jugular foramen
Carotid sheath
Through neck into thorax and abdomen.
What does CN X do?
General sensory - Sensory to lower pharynx and larynx
Motor - Muscles of soft palate, pharynx and larynx
Autonomic - Parasympathetic to thoracic (e.g. heart, tracheobronchial tree) and abdominal viscera.
Where does the recurrent laryngeal nerve go?
Carry motor fibres to larynx (so speak)
Left - under arch of the aorta
Right - under right subclavian
How do you test the vagus nerve?
Speech, cough and ability to swallow.
Note movements of uvula and soft palate when saying ‘Ahhh’ -uvula would be pulled off centre off centre is issue.
Gag reflex to test the efferent limb.
Injury to its branches e.g. recurrent laryngeal nerve following thyroid surgery can cause hoarseness and dysphonia.
What does the spinal accessory nerve do?
Motor - SCM and trapezius
Where does accessory nerve go?
Emerges through the jugular foramen and passes deep to SCM and provides its motor innervation.
It then runs posteriolaterally across posterior triangle.
It enters deep into trapezius and provides its motor innervation.
How do you test CN XI?
Shrug shoulders against resistance (trapezius)
Turn head against resistance (sternacleidomastoid)
In what area is CN XI susceptible to injury?
Posterior triangle because it is quite superficial.
What does CN XII do?
MMotor - muscles of tongue (all except one)
Where is it?
Runs medial to angle of mandible. Crosses internal and external carotid arteries in the neck.
Can’t see it unless move mandible
How do you test CN XII?
Inspect and movement the tongue
How would damage to the hypoglossal nerve present?
Weakness and atrophy of the tongue muscle on the ipsilateral side.
It is rare.
