Session 5 Flashcards
CN VII Facial Nerve
Lower pons (junction between pons and medulla) ->Enters petrous bone via . -> Three branches within petrous bone ->Exits through base of skull (stylomastoid foramen) Extracranial branches innervating muscles of facial expression. Extracranial branches also innervates posterior belly of digastric and stylohyoid muscle
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CN VIII Vestibulocochlear
Cochlea + Semicircular canals (vestibular system) ->Vestibulocochlear nerve -> Internal acoustic meatus -> Lower pons (junction between pons and medulla)
Special Sensory - Hearing and balance
Clinical Points • Crude hearing test (whispering 99 in each ear)* and enquiring about balance
• Damage involving cochlea, cochlear component of vestibulocochlear nerve, or brainstem nucleus causes hearing loss (sensorineural)
• Presbyacusis: 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
Acoustic neuromas
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
how do the cranial nerves from the medulla leave the base of the skull?
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
CN IX Glossopharyngeal Nerve
Main function is sensory supply of oropharynx, posterior ⅓ tongue and middle ear
General sensation - • (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
Clinical Points • Tested in conjunction with vagus nerve (CN X) (when asking patient to swallow)
• Gag reflex (sensory limb): only tested if concerns around swallowing and integrity of nerves involved in this reflex
• Taste not formally tested
• Isolated lesions of CN IX are rare
CN X Vagus
Mixed motor and sensory nerve and innervates structures neck, thorax and abdomen
Medulla -> Juglar foramen -> carotid sheath -> through neck into thorax and abdomen. Gives many branches along its route
General Sensory - • Sensory to lower pharynx, and the whole larynx • Sensory to small part of external ear and tympanic membrane
Motor - • Muscles of soft palate, pharynx, larynx
Automomic - • Parasympathetic to thoracic (e.g. heart, tracheobronchial tree) and abdominal viscera
Clinical Points • Note patient’s speech, cough and ability to swallow
• Note movement of uvula and soft palate when saying ‘Aaah’
• 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
Recurrent laryngeal nerve route
Left vagus nerve runs in carotid sheath - Left recurrent laryngeal nerve turns under arch of aorta
Right vagus nerve runs in carotid sheath - Right recurrent laryngeal nerve turns under right subclavian
CN XI Spinal Accessory Nerve
Motor - • Motor to sternocleidomastoid and trapezius
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
Testing • Shrug shoulders against resistance (trapezius)
• Turn head against resistance (sternocleidomastoid)
Clinical points
• 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
CN XII Hypoglossal
Motor - • Muscles of the tongue (all except one)
CN XII runs medial to angle of mandible; Crosses internal and external carotid arteries in neck
Testing: Inspection and movement of the tongue
clinical points
injury rare
damage to CN XII causes weakness and atrophy of the tongue muscles on the ipsilateral side
Describe the face, head and neck at week 4 of embryological development
- Early week 4
- FACE: no distinguishing external features
- BUT: head and neck represent ~½ length of embryo
What are the pharyngeal arches?
• Comprised of a system of mesenchymal proliferations in the neck region of the embryo • 5 in total, numbered 1 to 6 – (i.e. 5th does not form in humans) • Together with FNP constitute the building blocks for the head and neck region
Associations of the cranial nerves with the pharyngeal apparatus
- CN V, CN VII, CN IX & CN X
- Mixed sensory & motor functions
- Supply the derivatives of the pharyngeal arches
- CN XI (cranial accessory) and CN XII have relationship with pharyngeal arch system
Muscular derivatives of the pharyngeal arches
- Muscles of the face – Muscles of mastication are Ph Arch 1 derivatives – Muscles of facial expression are Ph Arch 2 derivatives
- 3rd arch – stylopharyngeus • 4th arch – Cricothyroid – Levator palatini – Constrictors of the pharynx • 6th arch – Intrinsic muscles of the larynx
Cartilages of the pharyngeal arches
• Each of the pharyngeal arches develops a neural crest - derived cartilage bar – Ph A 1 – Meckel’s: malleus & incus plus a template for formation of the mandible – Ph A 2 – Reichert’s : stapes plus upper part hyoid bone – Ph A 3 – remainder of hyoid bone – Ph A 4 & 6 • Cartilages of the larynx
Aortic arches formation
• Aortic sac lies in floor of the pharynx – 1st & 2nd arch arteries disappear – 3rd arch artery = internal carotid – 4th arch artery = arch of aorta (L) & brachiocephalic A (R) – 6th arch artery = “pulmonary arch”
