Trigeminal Nerve Revision

Question 1

The trigeminal nerve has ___ sensory nuclei and ___ motor nuclei?

Answer 1

3 sensory nuclei

1 motor nucleus

Question 2

What are the names of the 3 sensory nuclei of the trigeminal nerve?

Answer 2

mesencephalic, principal sensory, spinal nuclei of trigeminal nerve

Question 3

Where does the trigeminal nerve emerge from the brainstem?

Answer 3

Lateral pons

Question 4

What is a nucleus?

Answer 4

a collection of neurone cell bodies within the central nervous system

Question 5

Where do the sensory nuclei of the trigeminal nerve merge to form a sensory root?

Answer 5

At the level of the pons

The motor nucleus continues to form a motor root

(N.B. These roots are analogous to the dorsal and ventral roots of the spinal cord)

Question 6

What is the trigeminal ganglion?

Answer 6

A ganglion refers to a collection of the neurone cell bodies outside the central nervous system.

The trigeminal ganglion contains the cell bodies of the sensory root of the trigeminal nerve.

Question 7

Where is the trigeminal ganglion located?

Answer 7

• Middle cranial fossa

- Lateral to the cavernous sinus, in a depression of the temporal bone –> trigeminal cave.

Question 8

The peripheral aspect of the trigeminal ganglion gives rise to 3 divisions. What are these?

Answer 8

ophthalmic (V1), maxillary (V2) and mandibular (V3).

Question 9

The motor root passes inferiorly to the sensory root, along the floor of the trigeminal cave.

What is the only division of the trigeminal nerve that has motor fibres?

Answer 9

Mandibular branch - motor fibres of motor root are only distributed to this division

Question 10

Via which foramen does each division of the trigeminal nerve enter/exit the cranium?

Answer 10

V1 - superior orbital fissure
V2- foramen rotundum
V3 - foramen ovale

Question 11

What is the sensory function of all 3 divisions of the trigeminal nerve?

Answer 11

The three terminal branches of CN V innervate the skin, mucous membranes and sinuses of the face (see diagram)

Question 12

The opthalmic division of the trigeminal nerve also has a parasympathetic function.

What is this?
Fibres from which parasympathetic ganglion travel with V1 to carry out this function?

Answer 12

Parasympathetic innervation of the lacrimal gland

Post ganglionic fibres from the pterygopalatine ganglion (derived from the facial nerve), travel with the zygomatic branch of V2 and then join the lacrimal branch of V1.

Question 13

What is the corneal reflex?

Answer 13

The corneal reflex is the involuntary blinking of the eyelids – stimulated by tactile, thermal or painful stimulation of the cornea.

Question 14

In the corneal reflex, which nerve acts as;

a) the afferent limb
b) the efferent limb?

Answer 14

a) the ophthalmic nerve acts as the afferent limb – detecting the stimuli
b) the facial nerve is the efferent limb - causing contraction of the orbicularis oculi muscle.

Question 15

Which muscle contracts during the corneal reflex?

Answer 15

orbicularis oculi

Question 16

If the corneal reflex is absent, what is this a sign of?

Answer 16

it is a sign of damage to the trigeminal/ophthalmic nerve, or the facial nerve.

Question 17

Describe the pathway of the corneal reflex

Answer 17

1. Tactile, thermal or painful stimulation of cornea detected by opthalmic nerve
2. Trigeminal ganglion
3. Trigeminal nerve nucleus in brainstem
4. Right/left facial nerve via interneurons
5. Orbicularis oculi act to cause bilateral blinking

Question 18

The maxillary nerve also has 2 parasympathetic functions.

What are these?

Answer 18

1. Lacrimal gland

2. Nasal glands

Question 19

What is the parasympathetic effect on the lacrimal gland?

Answer 19

Stimulates fluid secretion from the lacrimal gland

Question 20

Describe the pathway of parasympathetic fibres to the lacrimal gland

Answer 20

1. Preganglionic fibres are carried in the greater petrosal nerve (branch of the facial nerve) and then the nerve of pterygoid canal, before synapsing at the pterygopalatine ganglion.
2. Postganglionic fibres travel with the maxillary nerve, and finally the zygomatic nerve.
3. Stimulates fluid secretion from the lacrimal gland

Question 21

Which branch of V2 do parasympathetic fibres (post ganglionic fibres from the pterygopalatine ganglion) travel with to the lacrimal gland?

Answer 21

Zygomatic

Question 22

Motor supply of the mandibular division of the trigeminal nerve?

Answer 22

• Muscles of mastication; medial pterygoid, lateral pterygoid, masseter, temporalis
• Anterior belly of the digastric muscle and the mylohyoid muscle (these are suprahyoid muscles)
• Tensor veli palatini
• Tensor tympani

Question 23

The mandibular division of the trigeminal nerve also has 2 parasympathetic functions. What are these?

Answer 23

1. Submandibular and Sublingual glands

2. Parotid gland

Question 24

How does mandibular division of the trigeminal nerve provide parasympathetic innervation to the submandibular and sublingual glands?

(Note; think which parasympathetic ganglion)

Answer 24

Post-ganglionic fibres from the submandibular ganglion (derived from the facial nerve), travel with the lingual nerve to innervate these glands.

Question 25

How does mandibular division of the trigeminal nerve provide parasympathetic innervation to the parotid gland?

(Note; think which parasympathetic ganglion)

Answer 25

Post-ganglionic fibres from the otic ganglion (derived from the glossopharyngeal nerve, CN IX), travel with the auriculotemporal branch of the V3 to innervate the parotid gland.

Question 26

During a clinical examination, how can you test the sensory component of the trigeminal nerve?

Answer 26

Ask the patient to close their eyes and introduce a cotton wisp to areas of the face supplied by the three divisions of the trigeminal nerve to detect tactile sensory competence.

Question 27

During a clinical examination, how can you test the motor component of the trigeminal nerve?

Answer 27

Ask the patient to clench their jaw as you palpate superior to the zygomatic arch to feel for contraction of the temporalis and then repeat palpating inferiorly for the masseter.

Ask the patient to open their mouth and deviate their mandible to the right and left to check for competence of the medial and lateral pterygoid muscles.