Cranial Nerves + The Eye PDF

CN VIII: Vestibulocochlear Nerve Function: Special sensory → Hearing and balance Course: Vestibular component + Cochlear component originate separately and combine in the pons, exiting the cranium via the internal acoustic meatus Intracranially, it splits back into the vestibular nerve...

CN VIII: Vestibulocochlear Nerve Function: Special sensory → Hearing and balance Course: Vestibular component + Cochlear component originate separately and combine in the pons, exiting the cranium via the internal acoustic meatus Intracranially, it splits back into the vestibular nerve and cochlear nerve Vestibular nerve → Vestibular system of inner ear → Vestibular ganglion → Balance Cochlear nerve → Cochlea of inner ear → Spiral ganglia → Hearing CN VIII: Vestibulocochlear Nerve Vestibular Neuritis: Inflammation of the vestibular branch Vertigo - sensation of yourself or the room spinning Nystagmus - repetitive involuntary oscillation of the eyes Loss of equilibrium - adjustment of pupil size Nausea and vomiting Vestibulocochlear Nerve Damage: Sensorineural hearing loss (vs. to conduction hearing loss) Damage can occur as the nerve passes through the internal acoustic meatus as a result of a basilar skull fracture They would also have bleeding from the ears and nose, and CSF leaking from the ears (CSF otorrhoea) and nose (CSF rhinorrhoea) CN IX: Glossopharyngeal Nerve Function: Bit of everything Sensory: Oropharynx, carotid body and sinus, posterior ⅓ tongue, middle ear, Eustachian tube Special sensory: Posterior ⅓ tongue taste Parasympathetic: Parotid Motor: Stylopharyngeus muscle Palsy: Loss of gag reflex (due to loss of afferent sensory signals) CN IX: Glossopharyngeal Nerve Course: Leaves the cranium via the jugular foramen Gives off the tympanic nerve → tympanic plexus → sensation to middle ear, tympanic membrane, Eustachian tube The rest of the nerve descends down the neck with the ICA to innervate stylopharyngeus and the carotid sinus and body via the carotid sinus nerve It then passess between the superior and middle pharyngeal constrictors to terminate in the pharynx with three branches ○ Lingual - mucosa of oropharynx ○ Tonsil - palatine tonsils ○ Pharyngeal - posterior ⅓ of tongue sensation and taste Parasympathetics travel with the tympanic nerve → lesser petrosal nerve → otic ganglion → auriculotemporal nerve → parotid gland (promote secretions) CN X: Vagus Nerve Function: All the things Within the thorax: ○ Right vagus → Posterior vagal trunk Course: Longest cranial nerve (by a mile) ○ Left vagus → Anterior vagal trunk Within the cranium: Originates from the medulla, gives ○ Branches from each contribute to the off the Auricular branch oesophageal and cardiac plexus Exits the cranium via the jugular foramen The vagal trunks enter the abdomen via the oesophageal Within the neck: Travels in the carotid sheath (with IJV hiatus of the diaphragm and common carotid), passing anterior to the subclavian Within the abdomen: Vagus supplies parasympathetic Several branches arise in the neck: innervation and sensation to the oesophagus, stomach, ○ Pharyngeal (pharynx and soft palate muscles) small and large bowel (up to the splenic flexure) ○ Superior laryngeal Internal (laryngopharynx sensation) External (cricothyroid muscle) Gives off the Recurrent laryngeal nerve (larynx muscles) ○ Right recurrent laryngeal loops under the subclavian ○ Left recurrent laryngeal loops under the aortic arch CN X: Vagus Nerve - Sensory Sensory Functions: Somatic sensory: Skin of posterior external auditory canal and external ear (auricular) Visceral sensory: ○ Laryngopharynx and larynx up to the vocal cords (internal laryngeal) ○ Heart (cardiac branches) ○ GIT up to the splenic flexure Special sensory: Taste at the root of the tongue and epiglottis CN X: Vagus Nerve - Motor Motor Functions: Muscles of the pharynx except stylopharyngeus (pharyngeal branches) ○ Pharyngeal constrictor muscles ○ Palatopharyngeus ○ Salpingopharyngeus Muscles of the larynx (recurrent laryngeal) ○ Thyroarytenoid ○ Posterior and lateral crico-arytenoid ○ Transverse and oblique arytenoids ○ Vocalis Cricothyroid (external laryngeal) Palatoglossus and soft palate muscles CN X: Vagus Nerve Parasympathetic Function: Heart (cardiac branches) ○ Supplies the SA and AV nodes ○ Constant vagal tone keeps the heart rate at a normal level ○ Damage to vagus = more rapid resting HR Gastrointestinal ○ Branches supply the oesophagus, stomach, small intestine and large intestine up to the splenic flexure ○ Stimulates smooth muscle contraction and glandular secretion CN X: Vagus Nerve Lesions Key Features: 1. Uvula deviation away from the side of the lesion 2. Loss of gag reflex - impaired because motor function is lost 3. Dysphagia - paralysis of pharyngeal muscles 4. Hoarse voice - if recurrent laryngeal nerve is involved Paralysis of the vocal cords Unilateral recurrent laryngeal nerve injury = hoarse voice ○ Paralysis of one vocal fold means it cannot adduct to meet the other vocal fold = hoarseness ○ Within weeks the other vocal fold will cross the midline to compensate Bilateral recurrent laryngeal nerve injury = stridor ○ Both vocal folds are unable to adduct for phonation nor abduct for respiration CN XI: Spinal Accessory Nerve Function: Somatic motor → Sternocleidomastoid and trapezius muscles Course: Cranial portion: Leaves the cranium via the jugular foramen, then becomes part of the vagus nerve Spinal portion: C1-C5/C6 nerve roots ○ These fibres join then run superiorly to enter the cranial cavity via the foramen magnum ○ They then traverse the posterior cranial fossa to exit via the jugular foramen, briefly meeting the cranial portion ○ It descends with ICA to innervate the sternocleidomastoid then crosses the posterior triangle superficially to innervate the trapezius Palsy: Paralysis of SCM and trapezius SCM: Weakness/inability to rotate the head Trapezius: Weakness/Inability to shrug the shoulders +/- Muscle wasting Commonly iatrogenic (damaged during cervical lymph node biopsy or cannulation of the IJV) CN XII: Hypoglossal Nerve Function: Somatic motor → Muscles of the tongue (except palatoglossus) Course: Exits the cranium via the hypoglossal canal before being joined by branches of the cervical plexus (C1/C2 fibres) It passes inferior to the angle of the mandible and across the carotids before moving anteriorly to the tongue CN XII Palsy: Paralysis of the tongue muscles: Extrinsic Intrinsic Genioglossus Superior longitudinal Hyoglossus Inferior longitudinal Styloglossus Transverse NOT palatoglossus (vagus innervation) Vertical Tongue deviates towards the side of the lesion +/- fasciculations or wasting Causes include malignancy, penetrating trauma or dissection of the ICA Ansa Cervicalis Function: Motor → Neck muscles Roots: C1/C2 (not cranial nerves) Course: 1. Some C1/C2 fibres travel with the hypoglossal nerve and give branches to a. Geniohyoid (elevates hyoid bone) b. Thyrohyoid (depresses hyoid bone) 2. A separate set of C1/C2 fibres descends and is joined by the above fibres to create the ansa cervicalis (a loop). This gives branches to a. Omohyoid b. Sternohyoid c. Sternothyroid All depress the hyoid bone Parasympathetics of the Head and Neck COPS 3977 Cranial Nerve Pre-ganglionic Ganglion Post ganglionic Target CN III Oculomotor Ciliary ganglion Short ciliary Pupillary sphincter CN IX Lesser petrosal Otic ganglion Hitchhike with Mucous membranes auriculotemporal Parotid gland CN VII Greater petrosal Pterygopalatine Hitchhike with Mucous membranes of nose ganglion maxillary nerve and pharynx Lacrimal gland CN VII Chorda tympani Submandibular - Submandibular and sublingual ganglion salivary glands