Session 5 Flashcards

1
Q

Describe the embryo at 4 weeks

A
  • No face yet discernible
  • Head and neck take up almost half of body
  • Structure of embryonic head is becoming increasingly complex, but follows a familiar segmental pattern
  • Each segment contains structures from various systems
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2
Q

Describe the ectoderm of the pharyngeal arches

A
  • Forms lining of GI and respiratory tracts
  • Forms glands
  • Covers superficial surface of arch
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3
Q

Describe the cartilage bar of the pharyngeal arches

A
  • Mesodermal
  • Supports the arch (similar to ribs)
  • Has associated muscles (like intercostal muscle)
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4
Q

Describe the cranial nerves of the pharyngeal arches

A
  • Come off from neural tube
  • Each arch has a different nerve
  • Motor to muscles associated with cartilage bars
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5
Q

Describe the arteries of the pharyngeal arches

A
  • Mesodermal
  • One of the aortic arches
  • Branches individually feed each pharyngeal arch with blood
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6
Q

Describe the endoderm of the pharyngeal arches

A
  • Contributes to pharynx
  • Forms GI and respiratory endothelium
  • Forms endocrine glands
  • Covers deep aspect of arch
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7
Q

Give the derivatives for the 1st pharyngeal arch

A
  • Trigeminal nerve (V)
  • Aortic arch 1
  • Gives muscles of mastication
  • Gives mandible, malleus and incus
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8
Q

Give the derivatives of the 2nd pharyngeal arch

A
  • Facial nerve (VII)
  • Aortic arch 2
  • Gives muscles of facial expression
  • Gives stapes and superior part of hyoid bone
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9
Q

Give the derivatives of the 3rd pharyngeal arch?

A
  • Glossopharyngeal nerve (IX)
  • Aortic arch 3
  • Stylopharyngeus muscle
  • Inferior part of hyoid bone
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10
Q

Give the derivatives of the 4th and 6th pharyngeal arches

A
  • Vagus nerve (X)
  • Aortic arches 4 and 6
  • Pharyngeal and laryngeal muscles
  • Laryngeal cartilages
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11
Q

What are the pharyngeal clefts and pouches?

A
  • Pharyngeal arch has adjacent swellings
  • Between adjacent swellings there are depressions of ectoderm and endoderm
  • Pouches = evaginations of endoderm
  • Clefts = invaginations of ectoderm
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12
Q

How many pharyngeal pouches are there?

A
  • 4
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13
Q

What structures are given by the first pharyngeal pouch?

A
  • Eustachian tube
  • First pharyngeal cleft becomes external acoustic meatus
  • Thin membrane between first pouch and first cleft forms tympanic membrane
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14
Q

How many pharyngeal clefts are there?

A
  • Just 1
  • Downwards growth of 2nd aortic arch obliterates the others
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15
Q

What structures are formed from the 2nd, 3rd and 4th pharyngeal pouches?

A
  • 2nd pouch forms palatine tonsil
  • 3rd and 4th pouches form thymus and parathyroid tissue
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16
Q

What is the difference between a branchial cyst, sinus and fistula?

A
  • Cyst is enclosed
  • Sinus communicates with skin
  • Fistula connects skin with pharynx
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17
Q

What causes branchial cysts, sinuses and fistulas?

A
  • Obliteration of clefts 2, 3 and 4 can be disordered and 2nd arch grows down
  • Obliteration is incomplete
  • Presents with lump in neck
  • Branchial cysts sit anterior to sternocleidomastoid
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18
Q

Outline the development of the nose

A
  • Frontonasal processes give rise to anterior parts of forehead and nose
  • Nasal placodes invaginate to form nasal pits
  • Nasal pits become nostrils
  • Medial nasal process and lateral nasal process move medially to form bridge of nose in the midline
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19
Q

Outline the development of the mandible and maxilla

A
  • Mandibular processes of first pharyngeal arch fuse in the midline to form mandible
  • Maxillary processes visible just above 1st pharyngeal arch move towards midline to form maxilla
  • Maxillary processes also fuse with medial nasal processes resulting in formation of nose and philtrum of upper lip
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20
Q

Outline the development of the mouth

A
  • Buccopharyngeal membrane disappears by apoptosis to form stomodeum which connects directly with embryonic pharynx
  • Stomodeum = primitive mouth
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21
Q

Outline how the ear develops

A
  • External ear ascends until it sits at the same level as the nose
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22
Q

How does the palate develop?

A
  • Palatal shelves grow medially and fuse in midline
  • Tongue must drop down to allow fusion to happen
  • Nasal septum grows down and fuses with palate
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23
Q

What palatal abnormalities can occur?

A
  • Small defect (hole) in palate due failure of palatal shelves to fuse in midline
  • Failure of fusion of frontal nasal process with maxillary process - leads to cleft lip
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24
Q

What are the auricular hillocks?

A
  • Surround 1st pharyngeal cleft
  • Should ascend and become external ear
  • This process involves neural crest cells
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25
How does alcohol affect foetal development?
- Ingestion of toxins during early stages of development causes cellular migration to become disordered - Leads to foetal alcohol syndrome
26
What is the appearance of someone with foetal alcohol syndrome?
- Low-set ears - Small head - Low nasal bridge - Underdeveloped jaw
27
Outline how the tongue develops
- Anterior 2/3 develops from first arch - Posterior 3rd develops from 2nd and 3rd arches - Muscles arise from somites at level of hypoglossal nerve
28
What is the innervation of the tongue?
- Anterior 2/3 gets general sensation from trigeminal nerve and taste from facial nerve - Posterior 1/3 gets general sensation and taste from glossopharyngeal nerve
29
How does the thyroid gland develop?
- Thyroid develops in foramen caecum of tongue -Thyroid diverticulum grows downwards and takes cells with it to the embryonic neck - Thyroglossal duct breaks down
30
What happens if the thyroglossal duct doesn't break down?
- Cysts and fistula are present at the foramen caecum - Ectopic thyroid tissue can sometimes be found anywhere along the path of descent
31
What fibres are found in the trigeminal nerve?
- General sensory - Motor
32
From where does the trigeminal nerve arise?
- Pons
33
What are the target tissues of the trigeminal nerve?
- Skin and tissues of face, portion of scalp, and deep facial structures - Anterior 2/3 of tongue (general sensation only, not taste) via branch of Vc - Muscles of mastication via branches of Vc
34
How do we clinically examine the trigeminal nerve?
- Light touch of Va, Vb and Vc dermatomes - Muscles of mastication action - Corneal reflex
35
What presentation would you see in a patient with a trigeminal nerve lesion?
- Sensory deficits within dermatomal regions on affected side - Weakness in muscles of mastication if Vc involved - Absent corneal reflex (Va is sensory part of reflex)
36
Which virus can cause a trigeminal nerve lesion?
- Herpes zoster virus - Causes ophthalmic shingles - Virus reactivated in trigeminal ganglion - Can affect cornea and conjunctiva
37
What are the causes of trigeminal nerve lesions?
- Trigeminal herpes zoster - Trigeminal neuralgia (compression from an aberrant blood vessel) - Orbital and mandibular fractures - Posterior cranial fossa tumours
38
Outline the route taken by the trigeminal nerve
- After it exits pons, trigeminal splits into 3 divisions - Va (ophthalmic) passes through cavernous sinus and into superior orbital fissue - Vb (maxillary) passes through cavernous sinus and foramen rotundum - Vc (mandibular) passes into foramen ovale to exit intracranial cavity - All branches then divide into other branches
39
What are the key sensory divisions of Va?
- Frontal nerve - gives rise to supraorbital and supratrochlear nerve of forehead - Nasociliary nerve - supplies sensory to eye and skin over nose
40
What are the key sensory divisions of Vb?
- Infra-orbital nerve - Superior alveolar nerves - supplies upper teeth and gums
41
What are the key sensory divisions of Vc?
- Auriculotemporal nerve - sensory to side of scalp, part of external ear and TMJ - Lingual nerve - general sensation from anterior 2/3 of tongue - Inferior alveolar nerve - supplies lower teeth and gums - Mental nerve
42
What is Hutchinson's sign?
- If vesicles are present over the tip of the nose in ophthalmic shingles, there is increased risk that eyes will be affected
43
What injury can involve the infraorbital nerve?
- Orbital fractures - Can also include superior alveolar nerve - Pt will present with deficit in sensory information in lower eyelid and part of cheek
44
What information does the mental nerve carry?
- Sensation from lower lip and chin and incisors on lower mandible
45
Where does nerve Vc branch to give the nerves supplying the muscles of mastication?
- Infratemporal fossa
46
Outline the route taken by the mental nerve
- Enters mandibular canal - Then becomes inferior alveolar nerve running within bone of mandible - Makes it vulnerable in mandibular fractures - Pt will present with sesnory loss over lower lip or chin
47
What fibres are found within the facial nerve?
- Motor - Special sensory (taste) - Parasympathetic
48
What are the target tissues of the facial nerve?
- Motor to muscles of facial expression and nerve to stapedius - Special sensory to anterior 2/3 of tongue - Parasympathetic to glands (lacrimal. nasal and salivary)
49
What do we examine when we suspect a facial nerve lesion?
- Muscles of facial expression - Will see unilateral facial droop including forehead - Pt may report symptoms due to absence of other facial nerve functions e.g. altered taste
50
What can cause facial nerve lesions once it has left the brainstem?
- Lesions in/ around internal acoustic meatus - Posterior cranial fossa tumours - Basal skull fracture involving petrous bone - Middle ear disease - Inflammation in facial canal causing facial nerve palsy e.g. Bell's Palsy, Ramsay Hunt syndrome - Parotid disease
51
Outline the route taken by the facial nerve
- Passes through internal acoustic meatus - Moves into petrous bone where it gives off 3 branches - Rest of nerve continues through facial canal - Close relationship with middle ear - Emerges via stylomastoid foramen through base of skull - Passes through parotid gland - Gives of several extracranial branches that supply muscles of facial expression
52
Which branches does the facial nerve give off at the petrous bone?
- Nerve to stapedius - innervates muscle that dampens vibration of stapes - Greater petrosal nerve - carries parasympathetic fibres to lacrimal and nasal mucosal glands - Chorda tympani - taste from anterior 2/3 of tongue, carries parasympathetic fibres to salivary glands (except parotid)
53
How do we tell the difference between facial droop involving the facial nerve and facial droop due to a stroke?
- Facial nerve lesion causes ipsilateral droop involving entire half of face - Stroke patients can still close eyelid and their forehead is spared
54
Why is the forehead spared in a stroke?
- If you have a stroke, it affects the connection between the brain and the facial nerve - It affects the facial nerve before it exits the brainstem - The primary motor cortex with dominant control is found in the side of the brain affected by stroke - The facial nerve has back-up from the primary motor cortex on the other side of the brain - This back-up only helps the upper half of the face
55
Why is the forehead affected in a facial nerve lesion?
- Injury involves facial nerve anywhere after it exits the brainstem and along its route to target tissue - No backup
56
What fibres are found in the vestibulocochlear nerve?
- Special sensory
57
From where does the vestibulocochlear nerve arise?
- Pons
58
What are the target tissues of the vestibulocochlear nerve?
- Cochlea - hearing - Semi-circular canals - balance
59
How do we examine the vestibulocochlear nerve?
- Gross bedside hearing tests - Tuning fork testing - Patients can present with hearing loss, vertigo and tinnitus
60
What can cause vestibulocochlear lesions?
- Vestibular schwannoma or other posterior cranial fossa tumours - Occlusion of labyrinthine artery (supplies the nerve) - Base skull fracture involving petrous bone - Brainstem lesion of pons (very very rare)
61
What is a vestibular schwannoma?
- Benign tumour involving Schwann cells associated with vestibulocochlear nerve - Slow growing - Usually unilateral
62
What are the symptoms and signs of a vestibular schwannoma?
- Unilateral hearing loss - Tinnitus - Vertigo - Numbness, pain or weakness down one half of the face
63
What are the similarities between the glossopharyngeal and vagus nerves?
- Arise from medulla - Run through posterior cranial fossa - Exit through jugular foramen - Both carry parasympathetic fibres - Enter into carotid sheath - Close relationship with ECA and ICA - Glossopharyngeal nerve leaves sheath superiorly
64
What are the targets of the glossopharyngeal nerve?
- Mainly sensory to oropharynx, tonsils, middle ear cavity - Sensory and special sensory to posterior 1/3 of tongue - 1 swallowing muscle - Parasympathetic to parotid gland - Afferents from carotid sinus and body
65
What are the targets of the vagus nerve?
- Motor and sensory - Muscles of larynx and pharynx including soft palate - Sensory to larynx and laryngopharynx - Parasympathetic to many tissues
66
How will patients present with a lesion of the glossopharyngeal nerve or vagus nerve?
- Difficulty with swallowing - Weak cough (vagus nerve only) - Difficulties with speech or changes in voice (vagus nerve only)
67
How do we examine patients with a suspected glossopharyngeal/vagus nerve lesion?
- Speech, swallow, cough - Soft palate movement and uvula position (vagus nerve) - Can also test gag reflex though not commonly done
68
What can cause lesions of the glossopharyngeal/vagus nerve?
- RLN branch of vagus nerve vulnerable in thyroid pathology or surgery and superior thorax/mediastinal pathology - Pathology or surgery involving carotid sheath structures - Posterior cranial fossa tumours - Base of skull fractures - Brainstem lesions e.g. infarct
69
What are the key branches of the vagus nerve in the neck?
- Right recurrent laryngeal nerve - Left recurrent laryngeal nerve
70
What are the similarities between the accessory and hypoglossal nerves?
- Arise from medulla - Run through posterior cranial fossa - Enter into carotid sheath and leave superiorly - Hypoglossal exits and travels towards tongue - Accessory exits and travels towards posterior triangle - Both nerves are motor
71
What is the target of the hypoglossal nerve?
- Muscles of tongue
72
How do we examine the hypoglossal nerve?
- Tongue movements and protrusion
73
What can cause lesions to the hypoglossal nerve?
- Surgery/pathology in proximity to or involving contents of upper carotid sheath and internal/external carotid arteries - Posterior cranial fossa tumours - Brainstem (medullary) lesions involving hypoglossal nucleus
74
What happens to the tongue when one of the hypoglossal nerves is injured?
- It deviates towards the wounded side
75
What are the targets of the spinal accessory nerve?
- Sternocleidomastoid - Trapezius
76
How do we examine the spinal accessory nerve?
- Turn head (tests actions of SCM) - Shrug shoulders (tests action of trapezius)
77
What can cause spinal accessory nerve injury?
- Injuries, surgery or pathology involving posterior triangle - Posterior cranial fossa tumours - Base of skull fractures - Brainstem (medullary lesions) e.g. infarct
78
Where does the spinal accessory nerve run?
- Emerges deep to posterior border of SCM to enter posterior triangle - Runs superficially in posterior triangle to reach trapezius