0414 - Cranial Nerves 2 - CS

Question 1

a. Describe the types of nerve fibres in CN V

Answer 1

1-Mainly sensory - tactile innervation to most superficial and deep facial structures

2-Some (important) motor

3-Something special - jaw proprioceptors

4-Autonomics: Sympathetics - picks up postganglionic axons of superior cervical ganglion, from the carotid nerve

Question 2

aa. What are the three branches of V and what type of nerve fibres do they contain?

Answer 2

V1: opthalmic

V2: maxillary

V3: mandibular

Question 3

b. Describe the type of fibres in CN VII

Answer 3

facial (V) nerve: mixture of 4 types

1-Some (important) sensory - skin on external ear

2-Mainly motor - muscles of facial expression

3-Something special - taste anterior ⅔ o tongue

4-Autonomic: Major parasympathetic component - provides (almost) all parasymp to face and deep face

Question 4

c. Describe the type of fibres in CN IX

Answer 4

1-Sensory - tactile from post ⅓ of tongue, visceral sensory from carotid artery

Sensory - from middle ear and auditory tube

2-Some motor - to striated muscles in pharynx

3-Special - taste from posterior ⅓ of tongue

4-Parasympathetic - innervate the parotid gland

Question 5

d. Describe the type of fibres in CN X

Answer 5

1-Sensory - some tactile fibres

2-Motor - contains fibres from XI that innervate striated muscle in the larynx and pharynx

2-Parasympathetic - innervate the heart, bronchi and GIT

Question 6

e. Describe the type of fibres in CN XI

Answer 6

1-Motor - Made up of fibres from two different sources - spinal and cranial that innervate striated muscle in the larynx and pharynx

Question 7

1a. Describe the attachment to the brainstem, intracranial course and cranial exit of CN V

Answer 7

Trigeminal nerve (V) emerges from the brainstem at the anteriolateral surface of the pons as a large sensory root and small motor root. It continues towards the middle cranial fossa where its sensory root expands into the trigeminal ganglion. It then branches into three:

V1: goes under the anterior clinoid process to enter the orbit via the superior orbital fissure (cranial exit) then branches into three (frontal, lacrimal and naso-ciliary)

V2: passes through the foramen rotundum (cranial exit) to reach the pterygopalatine fossa then gives off several branches (including the zygomatic branch which communicates with CN VII by receiving postganglionic parasympathetic fibres)

V3: passes through foramen ovale (cranial exit) to enter the infratemporal fossa then branches into four sensory branches (auriculotemporal, inferior alveolar, lingual, nervus spinosum) and communicates with CN VII (lingual branch is joined by chorda typani branch of CN VII) and some motor branches (to muscles of mastication)

Question 8

1b. Describe the type of fibres, attachment to the brainstem, intracranial course and cranial exit of CN VII

Answer 8

Facial nerve emerges from the lateral surface of the brainstem, between the pons and medulla oblongata as a large motor root and smaller sensory and parasympathetic root (nervus intermedius). These roots enter the skull through the internal acoustic meatus then reform within the facial canal, distal to the ganglion, then split into three branches:

1. ‘Motor’ nerve - exits skull through stylomastoid foramen and innervate the muscles of facial expression
2. Chorda tympani - crosses the ear drum and exits the skull near the foramen ovale and carries parasymp fibres and taste fibres and communicates w CN V (joins branch of V3)
3. Greater petrosal nerve - carries only pregang parasymp fibres and branches off at the geniculate ganglion. Has its own ganglion at the pterygopalatine ganglion (behind the orbit)

Question 9

How many ganglions does CN VII have?

Answer 9

1x sensory ganglion - geniculate

2x parasympathetic ganglia - pterygopalatine and submandibular

Question 10

What nerve is affected by Bell’s Palsy and why is this condition particularly dangerous?

Answer 10

Facial nerve (VII).

Affects muscles of facial expression

Dangerous because can’t blink, cornea dries out

Question 11

1c. What is the cranial exit for CNs IX, X and XI?

Answer 11

all through the jugular foramen

Question 12

1d. Describe the attachment to the brainstem, intracranial course and cranial exit of CN IX and X

Answer 12

Glossopharangeal (IX) nerve arises from the brainstem as several rootlets on the anterolateral surface of the upper medulla oblongata.

Vagus (X) nerve arises from the brainstem as a group of rootlets on the anteriolateral surface of the medulla oblongata (just inferior to IX)

Rootlets of IX and X both cross the cranial fossa

IX and X rootlets all enter the skull at the jugular foramen

Within the jugular foramen, the IX rootlets merge to form the IX nerve and the X rootlets merge to form X.

All exit the skull via the jugular foramen. Immediately outside the jugular foramen are the superior and inferior ganglia

Question 13

1d. Describe the attachment to the brainstem, intracranial course and cranial exit of CN XI

Answer 13

Accessory nerve (XI) roots arise from motor neurons in the upper five segments of the cervical spinal cord.

Rootlets of XI join together as they ascend.

XI enters the cranial cavity through the foramen magnum.

Passes through the cranial fossa and exits via the jugular foramen, along with IX and X

Question 14

2. Explain communications between V and VII, and its significance in innervation of the face and deep face

Answer 14

1 TEARS: Zygomatic branch of V2 (innervates skin lateral to orbit) receives postganglionic parasympathetic fibres (secretomotor fibres that make tears) from ? branch of VII and carries them to the lacrimal gland

There are 3 crucial areas in which there are exchanges of fibres between V and VII

Question 15

3. Explain the relationships between CNn IX, X and XI

Answer 15

All three exit the skull through the jugular foramen

CNs X and XI each have a superior and inferior ganglion (four ganglions in total)

The cranial component of XI joins X at X’s inferior ganglion (see diagram)

Fibres from X branch off at X’s superior ganglion and join IX at IX’s inferior ganglion

IX has many small parts (including sensory, motor, special sensory, parasymp)

Together they:

1. Provide parasympathetic innervation to the parotid gland (IX), the bronchial tree (X), the heart (X), and to the GIT (X) as far as the left colic flexure.
2. Sensory innervation from the soft palate (IX), larynx, pharynx (IX) and middle ear (IX).
3. Special sensory (taste) info from the posterior ⅓ of the tongue and soft palate (IX).
4. Info about blood pressure, blood chemistry from the division of the carotid (IX) and from the aortic synus (X)
5. Motor innervation of the pharyngeal (IX, XI), laryngeal (XI) muscles and to the large superficial neck/back muscles

Question 16

Draw a diagram showing the relationship between IX X and XI

Answer 16

Diagram to be added!

Question 17

4. Describe the relationships of preganglionic and postganglionic fibres to the named parasympathetic ganglia in the head, and the distribution and function of the postganglionic fibres.

Answer 17

Four CNs (III, VII, IX, X)

Five ganglia (VII broken into two ganglia, others have one each):

Branch of preganglionic oculomotor (III) fibres -> ciliary ganglion -> motor fibres to iris (makes pupil smaller) and ciliary body (relaxes lens)

Branch of preganglionic facial (VII) fibres -> pterygopalatine ganglion -> secretomotor fibres to produce nasal and pharyngeal mucous

Branch of preganglionic facial (VII) fibres -> submandibular ganglia -> ?salivary glands

Branch of preganglionic glossopharyngeal (IX) fibres -> otic ganglion -> parotid salivary glands

Branch of preganglionic vagus (X) fibres -> enteric ganglia (in walls of viscera) -> visceral organs of neck, thoracic and abdominal cavities