Cranial Nerves 2 Flashcards
What is the path of CN via
Lower pons (junction between pons and medulla)
Enters petrous part of temporal bone via internal acoustic meats
Three branches within petrous bone
- greater petrosal nerve
- chords tympani nerve
- nerve to stopedius
Exits through base of skull (stylomastoid foramen)
Then gives extracranial branches which supplies the muscles of facial expression - temporal, zygomatic, buccaneers, marginal mandibular, cervical
Describe teh function of cn vii
Special sensory - Anterior 2/3 of tongue (taste) - special sensory
Autonomic - Lacrimal glands (tears), mucosal glands in nose and roof of mouth, salivary glands (all except parotid gland)
Motor: muscles of facial expression
General sensory - Small area of the external ear
What determines the fibres that will form a cranial nerve
See slide
What are the 2 roots of the facial nerve
Facial nerve described as having two roots at cerebellopontine angle
• Motor root (larger- just motor axons )
• Nervus intermedius (sensory & parasympathetic
axons)
Describe the paths of the branches of the facial nerve
See slide
What are clinical points about cn vii
• Clinical testing is mainly by testing muscles of facial expression and the corneal reflex
• Given its many functions, facial nerve lesions can present with a variety of signs and symptoms depending on where along the nerve route the pathology is
• Important therefore to ask about other symptoms e.g. hyperacusis (sensitivity to Loud noises - problem with nerve to stapedius), dry eyes, altered taste
• Middle ear pathology (in petrous bone) can sometimes involve the facial nerve
• Close relationship with vestibulocochlear nerve within posterior cranial fossa and both
enter internal acoustic meatus
• Extracranial branches of facial nerve have close relationship with parotid gland
Benign condisiotns of parotid gland such as mumps do not usually involve facial nerve. Malignancies eg parotid cancer
What are the afferent and efferent limbs of the corneal reflex
Va - afferent
Facial efferent
Descrbe the path of cn viii
Cochlea + Semicircular canals (vestibular system)
->
Vestibulocochlear nerve ->
Internal acoustic meatus ->
Lower pons (junction between pons and medulla)
What is the function of cn viii
Special Sensory
Hearing and balance
What are clinical pointsa bout cn viii
- Clinical testing will involve testing hearing and enquiring about balance
- Damage involving cochlea, cochlear component of vestibulocochlear nerve, or brainstem nucleus causes hearing loss (sensorineural)
- Presbyacusis: a type of old-age related hearing loss
- Pathology involving semicircular canals, vestibular component of vestibulocochlear nerve, or brain nucleus causes disturbance of balance (vertigo)
- Acoustic neuroma: benign tumour involving vestibulocochlear nerve
What are is an acoustic neuroma
Acoustic Neuromas are benign tumours of the Schwann cells surrounding (the vestibular component of) CN VIII. Their physical presence causes compression of the whole nerve +/- CNs in close proximity
Symptoms and Signs include • Unilateral hearing loss • Tinnitus • Vertigo • Numbness, pain or weakness down one half of face
Describe the path of cn IX X XI XII
IX X and XI All exit via jugular foramen with IJV
XII - exits via hypoclossal canal
All 4 cranial nerves arising from the medulla exit base of skull to enter into superior part of carotid sheath: most quickly exit to travel towards target tissues Only cranial nerve X runs length of carotid sheath
What are the functions of cn IX
General sensation (main function)
• (Palatine) tonsils and oropharynx
• Middle ear and tympanic membrane (inner surface)
• Sensory from carotid body and sinus
Special sensory
• Taste and general sensation pos. 1/3 tongue
Autonomic
• Carries parasympathetic innervation to parotid gland
Motor
• Supplies one muscle (stylopharyngeus) which assists in swallowing
What are clinical points about cn IX
• Gag reflex (sensory limb): only tested if concerns around swallowing and integrity of nerves
involved in this reflex
• Taste not formally tested
• Tested in conjunction with vagus nerve (CN X) - Baker the neck contracting in
• Isolated lesions of CN IX are rare
What os the path of cn x
Medulla Juglar foramen Carotid sheath Through neck, into thorax and abdomen Gives many branches on its route down the length f the neck - innervated many structures
What is the function of cn x
General Sensory
• Sensory to lower pharynx, and larynx
• (Sensory to posterior part of external ear and tympanic membrane)
Motor
• Muscles of soft palate, pharynx, larynx
Autonomic
• Parasympathetic to thoracic (e.g. heart, tracheobronchial tree) and
abdominal viscera
What are sime branches of cn x
Right vagus nerve runs in carotid sheath
Right recurrent laryngeal nerve turns under right subclavian
Left vagus nerve runs in carotid sheath
Left recurrent laryngeal nerve turns under arch of aorta
What are clinical points about cn x
• Note patient’s speech, cough and ability to swallow
• Note movement of uvula and soft palate when saying ‘Aaah’ - normal movement - both sides of soft palate move up
• Gag reflex (efferent limb)
• Isolated lesions of CN X are rare
• Injury to its branches e.g recurrent laryngeal nerve following thyroid surgery can cause hoarseness
and dysphonia
What is teh function of cn XI
Motor to sternocleidomastoid and trapezius
What is teh route of cn XI
Emerges through jugular foramen
Passes deep to SCM and provides its motor innervation
Runs posterolaterally across posterior triangle
Enters deep to trapezius and provides its motor innervation
What are clinical points about cn XI
Shrug shoulders against
resistance (trapezius)
• Turn head against resistance
(sternocleidomastoid
• Spinal accessory runs inferiorly through neck in posterior triangle (is quite superficial)
• Susceptible to injury in this area e.g. in lymph node biopsies, surgery, stab wound
What is the function of cn xii
Muscles of the tongue (all except one)
What is the route of cn xii
CN XII runs medial to angle of mandible; Crosses internal and external carotid arteries in neck
Wont see it uncles mandible removed
What are clinical points about cn xii
• Inspection and movement of
the tongue
• Rare • Damage to CN XII causes weakness and atrophy of
the tongue muscles on ipsilateral side
