Session 5 Flashcards
Describe the embryo at 4 weeks
- 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
Describe the ectoderm of the pharyngeal arches
- Forms lining of GI and respiratory tracts
- Forms glands
- Covers superficial surface of arch
Describe the cartilage bar of the pharyngeal arches
- Mesodermal
- Supports the arch (similar to ribs)
- Has associated muscles (like intercostal muscle)
Describe the cranial nerves of the pharyngeal arches
- Come off from neural tube
- Each arch has a different nerve
- Motor to muscles associated with cartilage bars
Describe the arteries of the pharyngeal arches
- Mesodermal
- One of the aortic arches
- Branches individually feed each pharyngeal arch with blood
Describe the endoderm of the pharyngeal arches
- Contributes to pharynx
- Forms GI and respiratory endothelium
- Forms endocrine glands
- Covers deep aspect of arch
Give the derivatives for the 1st pharyngeal arch
- Trigeminal nerve (V)
- Aortic arch 1
- Gives muscles of mastication
- Gives mandible, malleus and incus
Give the derivatives of the 2nd pharyngeal arch
- Facial nerve (VII)
- Aortic arch 2
- Gives muscles of facial expression
- Gives stapes and superior part of hyoid bone
Give the derivatives of the 3rd pharyngeal arch?
- Glossopharyngeal nerve (IX)
- Aortic arch 3
- Stylopharyngeus muscle
- Inferior part of hyoid bone
Give the derivatives of the 4th and 6th pharyngeal arches
- Vagus nerve (X)
- Aortic arches 4 and 6
- Pharyngeal and laryngeal muscles
- Laryngeal cartilages
What are the pharyngeal clefts and pouches?
- Pharyngeal arch has adjacent swellings
- Between adjacent swellings there are depressions of ectoderm and endoderm
- Pouches = evaginations of endoderm
- Clefts = invaginations of ectoderm
How many pharyngeal pouches are there?
- 4
What structures are given by the first pharyngeal pouch?
- Eustachian tube
- First pharyngeal cleft becomes external acoustic meatus
- Thin membrane between first pouch and first cleft forms tympanic membrane
How many pharyngeal clefts are there?
- Just 1
- Downwards growth of 2nd aortic arch obliterates the others
What structures are formed from the 2nd, 3rd and 4th pharyngeal pouches?
- 2nd pouch forms palatine tonsil
- 3rd and 4th pouches form thymus and parathyroid tissue
What is the difference between a branchial cyst, sinus and fistula?
- Cyst is enclosed
- Sinus communicates with skin
- Fistula connects skin with pharynx
What causes branchial cysts, sinuses and fistulas?
- 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
Outline the development of the nose
- 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
Outline the development of the mandible and maxilla
- 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
Outline the development of the mouth
- Buccopharyngeal membrane disappears by apoptosis to form stomodeum which connects directly with embryonic pharynx
- Stomodeum = primitive mouth
Outline how the ear develops
- External ear ascends until it sits at the same level as the nose
How does the palate develop?
- 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
What palatal abnormalities can occur?
- 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
What are the auricular hillocks?
- Surround 1st pharyngeal cleft
- Should ascend and become external ear
- This process involves neural crest cells
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
What is the appearance of someone with foetal alcohol syndrome?
- Low-set ears
- Small head
- Low nasal bridge
- Underdeveloped jaw
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
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
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
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
What fibres are found in the trigeminal nerve?
- General sensory
- Motor
From where does the trigeminal nerve arise?
- Pons
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
How do we clinically examine the trigeminal nerve?
- Light touch of Va, Vb and Vc dermatomes
- Muscles of mastication action
- Corneal reflex
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)
Which virus can cause a trigeminal nerve lesion?
- Herpes zoster virus
- Causes ophthalmic shingles
- Virus reactivated in trigeminal ganglion
- Can affect cornea and conjunctiva
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
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
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
What are the key sensory divisions of Vb?
- Infra-orbital nerve
- Superior alveolar nerves - supplies upper teeth and gums
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
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
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
What information does the mental nerve carry?
- Sensation from lower lip and chin and incisors on lower mandible
Where does nerve Vc branch to give the nerves supplying the muscles of mastication?
- Infratemporal fossa
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
What fibres are found within the facial nerve?
- Motor
- Special sensory (taste)
- Parasympathetic
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)
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
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
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
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)
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
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
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
What fibres are found in the vestibulocochlear nerve?
- Special sensory
From where does the vestibulocochlear nerve arise?
- Pons
What are the target tissues of the vestibulocochlear nerve?
- Cochlea - hearing
- Semi-circular canals - balance
How do we examine the vestibulocochlear nerve?
- Gross bedside hearing tests
- Tuning fork testing
- Patients can present with hearing loss, vertigo and tinnitus
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)
What is a vestibular schwannoma?
- Benign tumour involving Schwann cells associated with vestibulocochlear nerve
- Slow growing
- Usually unilateral
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
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
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
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
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)
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
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
What are the key branches of the vagus nerve in the neck?
- Right recurrent laryngeal nerve
- Left recurrent laryngeal nerve
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
What is the target of the hypoglossal nerve?
- Muscles of tongue
How do we examine the hypoglossal nerve?
- Tongue movements and protrusion
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
What happens to the tongue when one of the hypoglossal nerves is injured?
- It deviates towards the wounded side
What are the targets of the spinal accessory nerve?
- Sternocleidomastoid
- Trapezius
How do we examine the spinal accessory nerve?
- Turn head (tests actions of SCM)
- Shrug shoulders (tests action of trapezius)
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
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
