Cranial nerves

Question 1

What are the main branches of the trigeminal nerve?

Answer 1

Opthalmic
- sensory
Maxillary
- sensory
Mandibular nerve
- sensory and motor

Question 2

Where does the mandibular branch of the trigeminal nerve exit the brainstem and what are its 4 branches and what does these supply?

Answer 2

§ Buccal
□ Innervates skin of the cheek overlying buccinator and mucus membrane

§ Inferior alveolar nerve
□ Sensory to mandibular teeth
□ Gives off nerve to mylohyoid - which supplies mylohyoid muscle and anterior belly of digastric

§ Auriculotemporal nerve
□ Cutaneous supply to ear, external meatus and parotid gland
□ Carries secretomotor nerves from the otic ganglion (from the glossopharyngeal nerve) - which supply the parotid gland for salivary secretion.

§ Lingual nerve
□ Sensory supply to anterior 2/3 of tongue - touch pain and temperature (not taste). Floor of mouth
□ Taste fibers from the corda tympani (branch of the facial nerve) hitchhike along the lingual nerve

Question 3

What does the corda tympani connect?

Answer 3

Connects branches from the facial nerve to the lingual nerve which are involved in TASTE to the anterior 2/3 of the tongue.

Also gives secretomotor fibers to the submandibular ganglion

Question 4

Where does the facial nerve leave the skull base and what are its branches?

Answer 4

Stylomastoid foraemen
- gives posterior auricular nerve
- gives a branch to posterior belly of digastric and then stylohyoid muscle.

Just before entering the parotid gland it divides into a superior and inferior division.

5 muscular branches
- temporal
- zygomatic
- buccal
- marginal mandibular
- cervical

Question 5

What do the 5 branches of the facial nerve supply and what are its actions?

For each nerve - how do you test if it is damaged?

Answer 5

Temporal
- frontalis
- wrinkles forehead
- tell patient to wrinkle forehead

Zygomatic
- supplies orbicularis oclui.
- control blinking and allows tears to be spread
- tell patient to blink

Buccal
- supplies buccinator
- helps empty cheek pouch
- to test - push on buccinator - air should not escape

Marginal mandibular
- supplies depressors of lower limb
- ask patient to show teeth

Cervical
- supplies platysma
- get patient to tense neck

Question 6

What is the course of the glossopharyngeal nerve?

What are its branches?

Answer 6

Exits the brainstem via the jugular foramen

Descends between the internal carotid artery and internal jugular vein.

Enters the pharynx between the superior and middle constrictors.

Branches
- tympanic
- carotid - to carotid sinus
- Pharyngeal
- muscular - innervates stylopharyngeus
- tonsillar
- lingual - general sensory and tatse to posterior 1/3 of tongue

Question 7

What is the path of the Vagus nerve?

Answer 7

Emerges from the brain via the jugular foramen.
Lies vertical in the carotid sheath, in the gutter between the internal/common carotid artery + jugular vein

Branches in the neck
- provides motor and sensory fibers for the pharyngeal plexus on the middle constrictor.
- supplies muscles of the pharynx - except stylopharyngeus
- supplies muscles of the soft palate

Superior laryngeal nerve
- runs down deep to the carotids and divides into the external and internal laryngeal nerve
- internal laryngeal nerve - pierces the thyrohyoid membrane to supply to the mucosa in the pharynx and larynx above the vocal folds.
- external laryngeal nerve - supplies the cricothyroid muscles (only muscle in the larynx not supplied by the RLN)

Vagus nerves in the chest
- R side - gives of RLN at subclavian artery. Lies in contact with the trachea
- L side - gives of RLN at aortic arch - held away from trachea by great vessels from the aorta.
- Each vagus passes down BEHIND the root of the lung (as opposed to the phrenic nerve which passes in front)

Anterior vagus in the abdomen
- composed mainly of the left vagus.
- lies in contact with the oesophageal wall
- gives off the greater anterior gastric nerve - suppliese pylorus
- also gives 1-2 hepatic branches which run in the lesser omentum

Posterior vagus in the abdomen
- composed mainly of right vagal fibers
- lies in loose tissue behind and to the right, not in contact with the posterior surface of the oesophagus.
- gives coeliac branches the run backwards along left gastric to coeliac plexus

Question 8

What are the consequences of dividing the vagus nerves at the hiatus

Answer 8

Truncal vagotomy divides both vagal trunks 4cm proximal to GOJ
- results in reduced acid production from parietal cells.
- decreases emptying of solids - removes relaxation of pylorus.

Question 9

What is the path of the RLN?

Answer 9

Left RLN
○ Recurves around the arch of the aorta in superior mediastinum
○ Is lateral to the ligamentum arteriosum
○ Passes into the root of neck moving from left towards midline to enter tracheoesophageal groove.
○ More likely to have entered the groove and lie posterior to inferior thyroid artery.

Right RLN
○ Recurves around the subclavian artery at the root of the neck.
○ May be more lateral to the trachea.
○ Has a very variable relationship to the inferior thyroidal artery - can be anterior, posterior, or in-between its branches.
○ Has a more vertical course than the left.
- The nerve can either lie superficial, within, or deep to the suspensory ligament of Berry (a thickening of pre-tracheal fascia which attaches to the cricoid cartilage and upper tracheal rings).
- Nerve runs behind the cricothyroid joint
- Passes behind the tubercle of Zuckerkandl - this is also where the inferior thyroid artery is.
- Passes upwards behind the inferior constrictor (cricopharyngeus)
- 1/3 of the time - at the level of the isthmus - RLN will divide into two.
○ Anterior (larger branch) is motor to larynx
○ Posterior (smaller) is sensory
- Innervation
○ All muscles of the larynx (except cricothyroid - supplied by the external laryngeal nerve).
○ Supplies mucus membranes of the folds and larynx below the vocal colds
§ Above is supplied by the internal laryngeal nerve.

Question 10

What is the anatomy of the accessory nerve?

Answer 10

• Has cranial fibers and cervical fibers.
  
  • Nerve occupies the middle compartment of the jugular foramen.
  • All cranial fibers are given to the vagus - thus when it leaves jugular foramen only has spinal/cervical fibers.
  • Nerve runs downwards and backwards on internal jugular vein
  • Nerve lies infront of transverse process of the atlas
  • Passes deep to the posterior belly of digastric
    ○ Where it is crossed by the occipital artery
  • Reaches sternocleidomastoid with the upper branch of the occipital artery
  • Enters the substance of SCM between upper 2 quarters of the muscle - via its deep surface.
  • Emerges from SCM, about 1/3 of the way down its posterior border - Erbs point.
  • Passes downwards and backwards, with a characteristic wavy course adherent to the inner surface of the fascia of the root of the triangle.
  • Disappears between the anterior border of trapezius - about 2/3 of the way down, 3-5cm above the clavicle.

Question 11

What is the anatomy of the hypoglossal nerve?

Answer 11

• Exits the cranial cavity via the hypoglossal canal in the occipital bone.
  
  • Emerges between the internal carotid and internal jugular vein deep to the posterior belly of digastric
  • C1 fibres joint the nerve at this point - these will go onto be the superior root of the ansa cervacalis.
  • Hooks around the occipital artery
  • Curves forwards lateral to the internal and external carotids and the loop of the lingual artery.
  • Gives off superior root of the ansa cervacalis as it crosses the internal carotid
    ○ Joins with the inferior roots of the ansa cervacalis which come from C2 and C3 spinal nerves.
  • Gives off the nerve to thyrohyoid as it lies on the lingual artery
  • Gives off branches to Geniohyoid as it passes on the lateral surface of hyoglossus, deep to mylohyoid
  • Supplies all nerves of the tongue except for palatoglossus (supplied by vagus)