Head And Neck Session 3 Flashcards
What does the facial skeleton arise from?
Neural crest cell infiltration of the mesenchyme core of PA1
Where do the muscles of mastication originate from?
Mesoderm of PA1
Where do the muscles of facial expression arise from?
Mesoderm of PA2
What are neural crest cells?
Specialised population of cells that originate in the neuroectoderm upon induction by the neural tube (4th germ lineage)
What happens to neural crest cells at the lateral border after being induced by the neural tube?
Displace and ente mesoderm instead of becoming CNS. Then migrate throughout body to give rise to many structures
What are the external features that derive from the FNP?
Forehead, bridge of nose, nose and philtrum
What is located at the base of the stomatodeum?
Buccopharyngeal membrane
What is the external feature that derives from the stomatodeum?
Oral fissure
Where do the cheeks, lateral upper jaw and lip derive from?
Maxillary prominence of PA1
What arises from the mandibular prominence of PA1?
Lower lip and jaw
Describe the process of formation of the nose.
Nose placodes appear on FNP and sink to form nasal pits –> medial and lateral prominences on either side of pit are pushed together by maxillary prominence moving medially –> maxillary fuse with medial nasal –> medial prominences fuse in the midline
What does fusion of the medial nasal prominences create?
Intermaxillary segment consisting of labial component, philtrum, upper jaw, 4 incisors and primary palate
What is the main part of the definitive palate?
Secondary palate
Where is the secondary palate derived from?
Palatial shelves of maxillary prominences
How is the secondary palate formed?
Palatal shelves grow vertically downwards into oral cavity either side of tongue –> mandible enlarges –> tongue drops –> palatal shelves fuse in the midline
What initially separates the nasal pit and oral cavity but quickly degenerates?
Oronasal membrane
How does the nasal septum form?
Mid-line down growth that fuses with palatal shelves
What is the cause of lateral cleft lip?
Failure of fusion of medial nasal prominence and maxillary prominence
What is the cause of lateral cleft lip involving the primary palate?
Failure of fusion of medial nasal prominence and maxillary prominence
What is the cause of cleft lip and cleft palate?
Failure of fusion of medial nasal prominence and maximally prominence combined with failure of palatal shelves to meet in the midline
What are the consequences of cleft lip and left palate?
Difficulty suckling and with speech
What is the fate of the FNP?
Forehead, bridge of nose and medial and lateral nasal prominences
What is the fate of the medial nasal prominence?
Philtrum, primary palate and mid upper jaw
What is the fate of the lateral nasal prominence?
Sides of the nose
What is the fate of the maxillary prominence?
Cheeks, lateral upper lip, secondary palate and lateral upper jaw
What is the fate of the mandibular prominence?
Lower jaw and lip
When does development of the eyes begin?
In the 4th week at the3-vesical brain stage
How do the eyes develop?
Forebrain pouches grow outwards –> met overlying ectoderm (optic placodes) –> optic placode invaginates and pinches off
What forms the lens of the eye in the developed foetus?
Optic placodes
Where does the retina derive from?
Diencephalon (forebrain) as part of the optic vesicle
What transforms to give the optic nerve?
Optic stalk
What causes humans to have binocular vision?
Growth of facial prominences pushing eye primordia from the side of the head to the front of the face
What do all common chromosomal abnormalities have associated anomalies with?
External ear
What arises in the neck to form the external ear?
External auditory meatus from 1st pharyngeal cleft and auricles from proliferation of PA1&2 surrounding meatus
What causes ascension of the ears from the neck to be in line with the eyes on the sides of the head?
Mandible growth
How is the inner ear formed?
Otic placodes invaginate to form auditory vesicles and membranous labyrinth forms cochlea and semi-lunar canal system
What is foetal alcohol syndrome?
Exposure of the developing foetus to alcohol causing disruption to neural crest cell migration and brain development causing characteristic facial features and severe restriction of cognitive development
What is alcohol-related neurodevelopment disorder (ARND)?
CNS, behavioural and learning dysfunction due to alcohol exposure in utero without characteristic facial features of FAS
What are the characteristic facial features seen in FAS?
Short palpebral fissure lengths Smooth philtrum Thin upper lip Short, upturned nose Microcephaly
What is the incidence of FAS and ARND?
1 in 100 births
What drives development of the face?
Expansion of the cranial neural tube, appearance of complex tissue systems, development of sense organs and need to separate resp from GI tracts
What is the function of the cervical spine?
Support skull, allow a large range of movement, provide passage for descending nerves
What type of curvature does the cervical spine have?
Secondary
What ligaments support the cervical spine?
Anterior and posterior longitudinal Ligamentum flavum Interslinous ligament Nuchal ligament Transverse ligament of atlas
Where are the anterior and posterior longitudinal ligaments positioned?
Along bodies and discs of the vertebral column
What does the ligamentum flavum connect?
Laminae of adjacent vertebrae along length of vertebral column
What does the inter spinous ligament connect?
Adjacent spinous processes along length of vertebral column
Describe the nuchal ligament.
Continuation of supraspinous ligament to C1-7 spinous tips giving attachment for rhomboids and trapezius
What does the transverse ligament of atlas connect?
Lateral masses of atlas to anchor dens in place
What are the characteristic features of C1?
No body, no spinous process
Where does the vertebral artery pass in relation to C1?
Through groove, not transverse foramen
What movement of the head does C1 facilitate?
Nodding
What movement of the head does C2 facilitate?
Shaking
What are the characteristics of C2?
Dens/odontoid peg and bifilar spinous process
Why do cervical vertebrae have characteristic large vertebral foramen?
For passage of the vertebral artery
What are the characteristic features of C7?
Prominent, easily palpable non-bifid spinous process and large transverse process
Where do the vertebral artery, vein and nerves run in relation to C7?
Vertebral artery around vertebra, vein and nerves pass through the foramen
Which ligaments are unique to the cervical spine?
Nuchal and transverse ligament of atlas
Which 3 lines of reference can be used to see if the cervical vertebrae are in alignment?
Anterior vertebral bodies
Posterior vertebral bodies
Spinolaminar
What forms the spinolaminar line?
Point at which the spinous process and lamina fuse
What is Jefferson’s fracture?
Vertical fall on extended neck –> compression of lateral masses between occipital condyles and axis causing fracture of anterior and poster arches
Why is spinal cord damage at C1 level unlikely in burst/Jefferson fracture?
Large vertebral foramen
What is hangman’s fracture?
Hyperextension of head and neck –> compression of spinal cord and lower brainstem
What is the definition of the skull?
Cranium and mandible formed by 22 discrete flat bones joined by fibrous joints (sutures) with the only moveable joint being the TMJ
What can the cranium be divided into?
Clavarium (roof) and cranial base
Which bones form the calvarium?
Frontal
Occipital
2 parietal bones
Which bones form the cranial base?
Frontal Sphenoid Ethmoid Occipital Parietal Temporal
What is the purpose of them many foramina present in the skull?
Allow entry of sensory nerves, arterial supply to the brain and meninges, sympathetic fibres and venous blood.
Allow exit of cranial motor nerves, PS outflow, veins and lymph
What is the cribiform plate?
Part of ethmoid bone at top of nasal sinuses with lots of foramina allowing passage of CNI
What is the optic foramen?
Located at the back of the eye socket allowing passage of CNII
What is the superior orbital fissure?
At the rear of the eye socket in the sphenoid bone allows passage of CNIII, IV and V
What is the foramen rotundum?
Opening in the middle of the skull allowing passage of CNV maxillary branch
What is the foramen ovale?
Opening in the base of the skull that allows passage of the mandibular branch of CNV
What is the stylomastoid foramen?
Opening at the base of the skull allowing passage of CNVIII
What is the hypoglossal canal?
Opening at the base of the skull in the occipital bone allowing passage of CNXII
What is the jugular foramen?
Opening at the base of the skull bounded by the temporal and occipital bones allowing passage of CNIX, X and XI
What is the contents of the foramen magnum?
Medulla oblongata, meninges, spinal roots of accessory nerve, vertebral arteries, anterior and posterior spinal arteries, tectorial membrane and alar ligaments
Why is the cranial floor likely to fracture in high energy impact to the head?
Foramina weaken it
What are the functions of the skull?
Enclose and protect brain and special sense organs, creates cranial cavity and provide site of attachment for muscles and meninges
What forms the meninges?
Periosteal layer of dura mater
Where is the cranium thick?
Occipital and frontal bones
What are the layers of the cranium?
Inner plate of cortical bone, middle layer of spongy bone (diploe), outer compact bone layer
What are the cavities of the skull?
Orbit, cranial cavity, nasal cavity, paranasal sinuses, oral cavity, auditory canal
Describe the structure of the mandible.
L&R mandibles joined by midline fibrous joint called the mental symphysis
What is found at the mental symphysis?
Many foramina
What does the condylar process of the mandible articulate with?
Skull
What are the three divisions of the cranial fossa/floor/base and what do they contain?
Anterior: CNI and part of CNII
Middle: CNII-VII
Posterior: CNVII-XII
What are the three lines that divide the calvaria?
Coronal suture line, sagittal suture line and lamboid suture line
What is bregma?
Point of intersection of the coronal and sagittal suture lines
What is lambda?
Point of intersection of sagittal and lamboid suture lines
What does the frontal bone form?
Anterior part of skull vault, upper border of orbital margins and orbit roof
Where is the ethmoid bone found?
Midline of anterior cranial fossa
What gives the ethmoid bone a serrated appearance?
Passage of olfactory nerve fibres
What can fracture of the ethmoid bone lead to?
Anosmia
What are the notable features of the ethmoid bone?
Cribiform plate, crista galli, ethmoid bulla, ethmoid air cells
Where are the olfactory bulbs located?
Either side of crista galli
What are the components of the sphenoid bone?
Central body, greater wing, lesser wing and pterygoid process
Where is the sphenoid bone located?
Upper nasal cavity associated with the pituitary and hypothalamus
What does the body of the sphenoid bone form?
All of the median middle cranial fossa
What are the notable features of the sphenoid body?
Optic groove, tuberallum sellae, sella turcica, dorsum sellae with posterior clinoid process, clivus
What does the parietal bone form?
Large part of side and roof of the cranial cavity
What does the internal surface of the parietal bone have?
Grooves of MMA, sagittal sulcus, granular pits from CSF valves and grooves for the sigmoid sinus
What are the 6 parts of the temporal bone?
Squamous, mastoid, tympanic, styloid process, zygomatic process and petrous part
What is the importance of the temporal bone?
Senses of hearing and balance and passage of the facial nerve
Which part of the temporal bone is involved in the inner auditory meatus?
Petrous part
What are the four parts of the occipital bone found around the foramen magnum?
Squamous, L&R condylar and basilar
What do each of the four parts of the occipital bone form?
Squamous: posterior vault
L&R condylar: edges of foramen magnum
Basilar: anterior foramen magnum
What holds together bones in the neonatal skull?
Thick CT matrix
Why are the bones of the skull not joined by sutures in the neonate?
To allow for movement of the cranial bones during the birthing process
Why does the neonatal skull not collapse during the child birth process?
Serrated bone edges temporarily interlock
What is the risk to the neonatal skull in pre-term birth?
Sutures too wide therefore no interlocking of bones causing high probability of brain damage during the normal birthing process
What are bregma and lambda known as in the neonatal skull?
Anterior and posterior fontanelles
Are the proportions between the cranium and facial skeleton the same in the neonate and adult?
No
How many bones articulate to form the facial skeleton?
14
