2 : Innervation ✍🏻

Question 1

How is the neonatal skull different from that of the adult?

Answer 1

　- Open sutures and fontanelles to allow moulding during birth 2 frontal bones normally fuse, but occasionally persist in the adult (metopic suture)

• Bony proportions different

– facial skeleton small at birth - Alveolar processes and paranasal sinuses rudimentary at birth

Question 2

What consequence during childbirth may result from the relative small size of the foetal mastoid process?

Answer 2

The mastoid air cells do not develop until the 2nd or 3rd year – the small mastoid process leaves the facial nerve exposed as it exits from the stylomastoid foramen. A superficially placed nerve is likely to be injured during forceps delivery.

Question 3

What is the “antrum” in the facial skeleton?

Answer 3

The word “antrum” is frequently used to describe the maxillary air sinus which is located in the body of the maxilla.

Question 4

What is Paget’s disease and what is its effect on the skull?

Answer 4

Paget’s disease, also known as ‘ostetis deformans’ affects people past middle age. The bones most frequently involved are the pelvis, femora, vertebrae and skull. There is a rapid, irregular and exaggerated resorption and replacement of bone, causing thickening, swelling and increased vascularity, often with severe pain.

When the skull is affected, it slowly enlarges, as do the jaws – the maxilla more frequently than the mandible that necessitates adjustments to dentures. The teeth may become displaced and become fused with bone, complicating extractions. Oral surgery may become complicated by severe haemorrhage.

Question 5

What is the ligamentum nuchae?

Answer 5

Ligamentum nuchae, also called the nuchal ligament, is found in the cervical region and is a continuation of the interspinous and supraspinous ligaments of the thoracic and lumbar vertebrae. It is a thickened fibroelastic tissue that attaches to the external occipital protuberance and the posterior border of the foramen magnum to the spinous processes of the cervical vertebrae. It preserves the normal curvature of the cervical spine.

Question 6

Why are cervical vertebrae prone to dislocation in whiplash injuries?

Answer 6

The cervical vertebrae are prone to dislocation due to the almost horizontal alignment of the articular facets between adjoining vertebrae.

Question 7

Why might posterior prolapse of intervertebral disc between C2 and C3 prove fatal?

Answer 7

The prolapse may cause pressure on the spinal cord above the phrenic nerve outflow of C3, C4 and C5. If this happens suddenly, respiration will cease.

Question 8

Which are the most important muscles of facial expression?

Answer 8

The sphincters of the face (i.e. orbicularis oris and two orbiculares oculi). Not only do they contribute to expression but they are also the anchors into which the majority of the other small muscles attach. Orbicularis oculi is the protector of the cornea and is therefore necessary for normal vision. Loss of orbicularis oris may lead to a mouth which drools uncontrollably, and is commonly seen in facial nerve palsy or Bell’s palsy).

Question 9

Which nerves provide sensory innervation for the face and the neck?

Answer 9

The sensory innervation of the face and the neck is via the cutaneous branches of the cervical nerves from the cervical plexus (for the neck and extending upwards onto the face – parotid region; area overlying the angle of the mandible) and the cutaneous branches of the three divisions (ophthalmic, maxillary and mandibular) of the trigeminal nerve. CN

Question 10

What is the Pterion?

Answer 10

It is an anatomical landmark in the osteology of the cranium whereby the temporal bone, sphenoid bone, parietal bone and frontal bone meet to form an H-shaped joint complex

Question 11

What is clinical the Importance of the pterion in high energy impacts to the temporal region?

Answer 11

•The pterion is not only a structurally weak joint in itself but the temporal bone in the region of the pterion is very thin and closely associated with the anterior branch of the middle meningeal artery which is susceptible to puncture in “depression” fractures of this region

Question 12

Explain what is meant by an “extradural haematoma”?

Answer 12

Separation of the periosteal layer of the dura mater from the cranium creates a

space into which blood from a torn meningeal vessel accumulates giving rise to an

extradural haematoma. In normal situation, no space exists between the two layers

(periosteal and meningeal) of the dura mater except in the region of the dural

venous sinuses where the two layers are separate.

Question 13

Which blood vessel would have been severed as a result of being struck in the temporal area of the head?

Answer 13

The middle meningeal artery (or precisely its anterior branch) is the most likely blood vessel to have been severed as a result of this injury.

The middle meningeal artery, which is a branch of the maxillary artery, enters the cranial cavity via the Foramen spinosum and lies just behind the pterion. The hit would fracture the thin bones forming the pterion, severing the anterior branch of the middle meningeal artery.

Question 14

Why should a fracture of the pterion constitute a medical emergency?

Answer 14

Fracture of the pterion would most likely lead to puncture of the middle meningeal artery, leading to an extradural hematoma, which if not evacuated would lead to sigificant brain injury if not death

Question 15

What type of a cranial fracture would a blow to the head cause?

Answer 15

Hard trauma to the head in the thin areas of the side of the cranium often result in depressed fractures – the bone fragment compresses or injures the underlying structures. In this case the branch of the artery

Question 16

Why might a fractured cribriform plate of the ethmoid bone lead to a loss of smell and a runny nose? State which clinical term is used to describe loss of smell and a runny nose (in this case)Why might a fractured cribriform plate of the ethmoid bone lead to a loss of smell and a runny nose? State which clinical term is used to describe loss of smell and a runny nose (in this case)

Answer 16

•Damage to olfactory nerves in the cribriform plate as they enter the floor of the anterior cranial fossa

•Anosmia

•Can mention CSF rhinorrhea here if need be

Question 17

A patient complains that he cannot turn his right eye to the right. What nerve lesion is the likely cause?

Answer 17

•This is the presenting sign of abducent nerve palsy.

•It results in paralysis of lateral rectus, hence failure to abduct the eye.

•This gives rise to diplopia in adults

•It can also gives rise to convergent strabismus

Question 18

Why might pressing a boil on the cheek lead to abducent nerve palsy?

Answer 18

　

•There would be an increased risk of introducing pathogens from the boil into the carvenous sinus through venous channels of the face that are devoid of valves.

•This could then lead to carvenous sinus thrombosis

•Cranial nerves III, IV, V and VI are close relations of the carvenous sinus and could thus be damaged if there is thrombosis in their vicinity of proximity to the carvenous sinus

Question 19

Why might a lesion of the ophthalmic division of the trigeminal nerve be dangerous to the eye?

Answer 19

Why might a lesion of the ophthalmic division of the trigeminal nerve be dangerous to the eye?　

•The ophthalmic division of the trigeminal nerve provides for sensation of the cornea

•If this nerve is lesioned, the cornea will be at increased risk of abrasion from foreign substances on the cornea

•Blinking will also be abolished, leading to drying and pathogenic settlement on the cornea.

Question 20

If the auriculotemporal nerve is cut some distance beyond its origin, what will happen to the parotid gland?

Answer 20

Proximal damage to the auricolotemporal nerve as it emerges from the brain can lead to parasympathectomy of the parotid gland as this gland receives its autonomic supply from the glossopharyngeal nerve via the auriculotemporal nerve

Question 21

Babies Delivered using the Forceps Method Are At Risk of Presenting With Temporary Facial Assymetry? By What Name is This Palsy Commonly Known As?

Answer 21

　

•Compression damage to the motor branch of the facial nerve as it exists the cranium via the exposed stylomastoid foramen

•The Mastoid Process is less developed in the newborn

•This is Facial Nerve Palsy

Question 22

Where does the dentist inject an anaesthetic if he wishes to numb your lower teeth?

Answer 22

The inner face of the infratemporal fossa at the level of the mandibular foramen, aiming at the inferior alveolar nerve as it enters the alveolar canal

Question 23

Why might a tumour of the middle ear cause abnormal sensations of taste?

Answer 23

　

Compression of the facial nerve by a tumour in the middle ear may lead to damage extending to the chorda tympani branch that supplies general sensation the anterior 2/3 of the tongue hence the alteration to taste.

Question 24

Following the removal of the submandibular gland from a cancerous growth, why might the patient have a ‘drooped’ lower lip?

Answer 24

•Excision of the submandibular gland may lead to paralysis of the facial nerve supplying the lower lip, which will then droop.

•It may also lead to numbness of the tongue due to bruising of the lingual nerve

Question 25

How might a patient present if she had a right hypoglossal nerve (RXII) palsy?

Answer 25

•When asked to protruding the tongue, this will be found to deviate towards the side of the lesion. In this case, the tongue will point to the right hand side.

•Chronically, the tongue will atrophy on the affected side

•The tongue will show furrows on the denervated side

Question 26

What is the relationship of the XII cranial nerve to the carotid artery?

Answer 26

The hypoglossal nerve is the twelfth cranial nerve (XII), On emerging from the hypoglossal canal, it gives off a small meningeal branch and picks up a branch from the anterior ramus of C1. It spirals behind the vagus nerve and passes between the internal carotid artery and internal jugular vein lying on the carotid sheath. After passing deep to the posterior belly of the digastric muscle, it passes to the submandibular region to enter the tongue.

It supplies motor fibres to all of the muscles of the tongue, except the palatoglossus muscle, which is innervated by the vagus nerve (cranial nerve X

Question 27

Discuss the effects on breathing and speech of an external laryngeal nerve palsy

Answer 27

　

•The external laryngeal nerve is the smaller, external branch (ramus externus) of the superior laryngeal nerve.

•It descends on the larynx, beneath the sternothyroid muscle, to supply the cricothyroid muscle.

•It tenses vocal cords by activating the cricothyroid muscle, thus increasing pitch.

•The cricothyroid muscle is one of a number of intrinsic muscles of the larynx that control expiration of air in phonation

•Paralysis of the criothyroid muscle can lead to problems with maintenance of patent airways during breathing and also swallowing.

Question 28

In a patient with a carcinoma of the parotid gland - Explain how could this tumour cause weakness of the face.

Answer 28

　

The facial nerve on exiting the skull via the sylomastoid foramen passes into the substance of the parotid gland where it divides into its extracranial branches (temporal, zygomatic, buccal, mandibular, cervical and posterior auricular nerves) that supply the superficial muscle of the neck and chin (platysma), muscles of facial expression, muscle of the cheek (buccinator), muscles of the ear and muscles of the scalp (occipitofrontalis muscle). Trauma (compression) or disease of the facial nerve would cause weakness of the muscles innervated by the respective branches of the nerve.

Question 29

What would a patient with a parotid gland tumour experience difficulty playing a trumpet?

Answer 29

The injury to the facial nerve branch supplying to the buccinator muscle has affected the patient’s ability to play his trumpet. The buccinator is used during blowing a wind instrument.