Head And Neck Week 2 Flashcards
1
Q
How many bones are there in the skull?
A
22
2
Q
How many bones in the neurocranium?
A
8
3
Q
Which part of the skull houses the brain?
A
Neurocranium
4
Q
What is the viscerocranium and how many bones are involved in its structure?
A
The bones forming the facial skeleton
14
Or 15 if include part of ethmoid
5
Q
How is the neurocranium divided anatomically?
A
The calvaria (roof) The cranial base
6
Q
Which bones make up the calvarium?
A
Frontal, occipital and two parietal
7
Q
Which bones make up the cranial base?
A
Frontal, sphenoid, ethmoid, occipital, parietal and temporal
8
Q
What do the bones of the cranial base articulate with?
A
Bones of the facial skeleton and mandible
1st cervical vertebra
9
Q
Name the bones of the viscerocranium
A
Zygomatic (2) Lacrimal (2) Nasal (2) Inferior nasal conchae/turbinates (2) Palatine (2) Maxilla (2) Vomer Mandible Part of ethmoid
10
Q
What type of joints are between the bones of the skull?
A
Sutures (fibrous joints)
11
Q
How do the bones of the calvaria form?
A
Intramembranous ossification
12
Q
At what age do the joints of the skull fuse and why?
A
Around age 20
To allow growth of the brain in adolescence
13
Q
Name the sutures of the skull and which bones they fuse together
A
Coronal suture - frontal bone with the two parietal bones
Sagittal suture - both parietal bones to each other
Lambdoid suture - the occipital bone to the two parietal bones
Squamous suture - the squamous part of the temporal bone to the inferior border of the parietal bone
14
Q
Why are sutures of clinical importance?
A
Can be points of potential weakness in both childhood and adulthood
15
Q
What is a fontanelle?
A
The membranous gap between the bones of the skull in neonates due to incompletely fused suture joints
16
Q
What are the two major fontanelles?
A
The frontal fontanelle (At the joint of the coronal and sagittal sutures)
The occipital fontanelle (At the joint of the sagittal and lambdoid sutures)
17
Q
What is the only mobile joint in the skull?
A
Temporomandibular joint (TMJ)
18
Q
At what age do fontanelles close?
A
In the first two years of life
19
Q
What is the function of fontanelles?
A
Makes skull more flexible for passage through birth canal
Allows for brain growth
20
Q
What kind of bones form the calvaria?
A
Flat bones
21
Q
What kind of bones form the cranial base?
A
Primarily irregular bones with substantial flat portions
22
Q
How are bones of the cranial base formed?
A
Endochondral ossification or by more than one type of ossification (e.g. Intramembranous and endochondral)
23
Q
Why is the name flat bone not quite correct to describe the bones of the neurocranium?
A
They are actually curved - convex external and concave internal surfaces
24
Q
What are sutures called before they fuse around the age of 20 and what are they made up of?
A
Synchondroses - hyaline cartilage
25
Through which structure is the spinal cord continuous with the brain and where is the structure located?
Foramen magnum
| Cranial base
26
From what do the bones of the viscerocranium develop?
Mesenchyme of the embryonic pharyngeal arches
27
What structures do bones of the viscerocranium form?
Orbits
Nasal cavity
Mouth
28
What kind of bones are the bones of the viscerocranium?
Irregular
29
Why do bones of the skull contain air spaces?
To decrease their weight
30
What is the name of bones with air spaces/large sinuses?
Pneumatised bones
31
What happens to the volume of air spaces in these bones with age?
Increase
32
What is the orbitomeatal plane?
The "anatomical" position
Cranium orientated so inferior margin of orbit and superior margin of external acoustic opening of external acoustic meatus of both sides lie in same horizontal plane
33
Draw and label the frontal bone
| Squamous part, glabella, nasion, supraorbital margin, supraorbital foramen or notch, supraciliary arch
Look at picture in workbook
34
Which bones does the squamous part of the frontal bone articulate with inferiorly ?
Nasal, maxillae and zygomatic bones
35
What is a metopic suture?
Persistent frontal suture or remnant that is visible in some people in midline of the glabella
36
What is the glabella?
The smooth, slightly depressed area between superciliary arches of the frontal bone
37
What is the intersection of the frontal and nasal bones called?
Nasion
38
What is the nasion also known as?
The bridge of the nose
39
What other bones does the frontal bone articulate with? (Through horizontal orbital portion)
Lacrimal, ethmoid, sphenoid
40
What does the orbital part of the frontal bone form?
Roof of the orbit and part of the floor of the anterior cranial cavity
41
What structures pass through the supraorbital foramen/notch?
Supraorbital nerve and vessels
42
How does the prominence of the supraciliary arch differ between the sexes?
More prominent in males
43
Draw and label the zygomatic bone (Zygomatic arch, Zygomaticofacial foramen)
Check workbook or textbook
44
What is the zygomatic arch made up of?
The temporal process of the zygomatic bone
| The zygomatic process of the temporal bone
45
What do the zygomatic bones form?
Prominence of the cheeks
The anterolateral rims, walls and floor of orbits
Lateral infraorbital margins
46
Which bones do the zygomatic bones articulate with?
Frontal, temporal, sphenoid and maxillae
47
What is the name of the anterior nasal opening in the cranium?
Piriform aperture
48
Draw and label the maxilla (Zygomatic process, Palatine process, Alveolar process, Frontal process, Infraorbital foramen)
Check workbook, textbook
49
What do the maxillae form?
The upper jaw
Surround most of the piriform aperture
Form the infraorbital margins medially
50
How are the two maxilla united?
Intermaxillary suture
51
What is the alveolar process of the maxilla and what does it do?
Includes tooth sockets (alveoli)
| Constitutes the supporting bone for maxillary teeth
52
What structures pass through the infraorbital foramen?
Infraorbital nerve and vessels
53
Draw and label the mandible (Body, Ramus, Angle, Coronoid process, Condyloid process (head + neck), Mental protuberance, Mental foramen, Mandibular foramen)
Check workbook , textbook
54
What structures are transmitted through the mental foramena?
The mental nerves and vessels
55
What passes through the mandibular foramen?
The inferior alveolar nerve and vessels - branch of mandibular division of trigeminal nerve (exit at mental foramen)
56
What are the boundaries of the temporal fossa?
Superior and posterior - Superior and inferior temporal lines
Anterior - frontal and zygomatic bones
Inferior - zygomatic arch
57
What does the superior border of the zygomatic arch correspond to?
The inferior limit of the cerebral hemisphere of the brain
58
What is the pterion?
Junction of greater wing of sphenoid, squamous temporal, frontal and parietal bones
Overlies the course of the anterior division of the middle meningeal artery
59
Where is the pterion found?
In the anterior part of the temporal fossa, 3-4cm superior to the midpoint of the zygomatic arch
60
Draw and label the temporal bone (squamous part, zygomatic process, petrous part, mastoid process, styloid process, articular fossa for mandible, external and internal auditory meatus, foramen lacerum, carotid canal, stylomastoid foramen, opening for Eustachian tube)
Look in textbook or workbook
61
Draw and label the occipital bone (internal and external occipital protuberance, superior nuchal line, inferior nuchal line, foramen magnum, articular condyles for atlas (C1), Clivus, hypoglossal canal, Jugular foramen)
Look in workbook or textbook
62
What is lambda?
The junction of the sagittal and lambdoid sutures
| Lies in the centre of the occiput
63
What are sutural bones?
Accessory bones that may be found at lambda or near the mastoid process
64
Draw and label the ethmoid bone (Crista gala, cribriform plate, perpendicular plate, superior concha, cribriform foramina)
Look in workbook or textbook
65
Draw and label the sphenoid bone (Great and small wings, body, pterygoid processes, anterior and posterior clinoid processes, sella turcica, dorsum sellae, hypophyseal fossa, superior orbital fissure, optic canal, foramen rotundum, foramen ovale, foramen spinous)
Look in workbook or textbook
66
What is Bregma?
The site where the sagittal and coronal sutures join
67
What is the vertex?
The most superior point of the calvaria
| Near the midpoint of the sagittal suture
68
What is the infratemporal fossa?
An irregular space inferior and deep to the zygomatic arch and the mandible and posterior to the maxilla
Communicates with inferior orbital fissure and pterygopalatine fossa
Medial and lateral pterygoid muscles here
69
What is the parietal foramen?
A small, inconsistent aperture located posteriorly in the parietal bone near the sagittal suture - paired foramen may be present
An emissary foramen
70
What are emissary foramina?
Transmit emissary veins - connecting scalp veins to venous sinuses of the dura mater
71
What does the free posterior border of the hard palate form?
Projects posteriorly in the median plane as the posterior nasal spine
72
What is the incisive fossa?
Depression in the midline of the bony palate into which the incisive canals open
73
What passes through the incisive canals?
The right and left nasopalatine nerves pass from the nose through a variable number of incisive canals and foramina
74
Where are the greater and lesser palatine foramina ?
They lie posterolaterally in the hard palate
75
What are the choanae?
Posterior nasal apertures
Superior to the posterior edge of the palate
Separated from each other by the vomer
76
What is the vomer?
A flat, unpaired bone of trapezoidal shape that forms a major part of the bony nasal septum
77
Where does the groove for the cartilaginous part of the pharyngotympanic tube lie?
Medial to the spine of the sphenoid
| Inferior to the junction of the greater wing of the sphenoid and the petrous part of the temporal bone
78
What structures accommodate the mandibular condyles when the mouth is closed?
The mandibular fossae
79
What structures pass through the foramen magnum?
Spinal cord, meninges, vertebral arteries, the anterior and posterior spinal arteries and the spinal accessory nerve (CNXI), dural veins, medulla
80
How does the cranium articulate with the vertebral column?
Through the occipital condyles (articulate with C1)
81
What passes through the jugular foramen?
Internal jugular vein
| CNIX-XI
82
What passes through the stylomastoid foramen?
CNVII (facial nerve) and stylomastoid artery
83
What are the names of the three large depressions on the internal surface cranial base, which form the floor of the cranial cavity?
Anterior, middle and posterior cranial fossae
84
Which parts of the brain lie in the anterior cranial fossa?
The inferior and anterior parts of the frontal lobes of the brain
85
Which bones form the anterior cranial fossa?
Anteriorly - frontal bone
Medially - ethmoid bone
Posteriorly - the body and lesser wings of the sphenoid bone
86
What makes up the greatest part of the anterior cranial fossa?
The orbital part of the frontal bone - shows sinuous impressions of the orbital gyri of the frontal lobes
87
What is the role of the foramen caecum of the frontal bone?
Gives passage to vessels during foetal life but insignificant postnatally
88
What is transmitted in the cribriform foramina?
CN I (olfactory nerves)
89
Describe the middle cranial fossa
Central part - sella turcica of sphenoid bone
Laterally - Greater wings of sphenoid and squamous part of the temporal bone laterally and posteriorly the petrous part of the temporal bone
90
How is the middle cranial fossa separated from the anterior cranial fossa?
It is posteroinferior to it
| Separated by the sphenoidal crests laterally and the sphenoid limbus centrally
91
What part of the brain is supported by the lateral part fo the middle cranial fossa?
The temporal lobes
92
What separates the middle cranial fossa from the posterior cranial fossa?
Laterally - superior border of petrous part of temporal bone
| Medially - dorsum sella of sphenoid
93
What lies in the hypophyseal fossa?
The pituitary gland
94
Where is the superior orbital fissure located and what does it transmit?
Between the greater and lesser wings of sphenoid, opens anteriorly into the orbit
Ophthalmic veins, ophthalmic nerve (CN V), CN III, IV, VI and sympathetic fibres
95
Where is the foramen rotundum and what does it transmit?
Posterior to the medial end of superior orbital fissure
Runs a horizontal course from anterior root of great wing of sphenoid to the pterygopalatine fossa
Maxillary nerve (CN V)
96
Where is the foramen ovale and what does it transmit?
Posterolateral to foramen rotundum
Opens inferiorly into infratemporal fossa
Maxillary nerve and accessory meningeal artery
97
Where is the foramen spinosum and what does it transmit?
Posterolateral to foramen ovale
Opens into infratemporal fossa in relationship to spine of sphenoid
Middle meningeal artery, vein, and meningeal branch of CN V
98
What is the foramen lacerum ?
An artefact of a dried skull
Lies posterolateral to hypophyseal fossa
In life it is closed by cartilaginous plate
Only some meningeal arterial branches and small veins are transmitted vertically through it
99
Where is the groove for the greater petrosal nerve located?
Extends posterolaterally from the foramen lacerum
| Also a small groove for the lesser petrosal nerve
100
Which parts of the brain are encased in the posterior cranial fossa?
Cerebellum, pons, medulla oblongata
101
Which bones form the posterior cranial fossa?
Occipital bone
Dorsum sellae marks anterior border centrally
Petrous and mastoid parts of temporal bone make up antero-lateral walls
102
What are the cerebellar fossae?
Bilateral concave impressions in the internal surface of the occipital bone formed by the internal occipital crest
103
What is transmitted in the jugular foramen?
CN IX,X,XI
Superior bulb of IJV
Inferior petrosal and sigmoid sinuses
Meningeal branches of ascending occipital and pharyngeal arteries
104
What passes through the carotid canal?
The internal carotid artery
105
What is transmitted in the hypoglossal canal?
Hypoglossal nerve (CNXII)
106
How do the walls of the cranial cavity differ between gender?
Thinner in females than males
107
How do the walls of the cranial cavity differ with age?
Thinner in the very young and the very old
108
Where are the cranial walls thinnest?
In areas covered by muscle e.g. Squamous part of temporal bone
Pterion
109
Describe the structure of bones of the calvaria
Consist of internal and external tables of compact bone
| Separated by diploe (spongy bone/cancellous)
110
Describe the diploe
Cancellous bone containing red marrow, through which run canals formed by diploic veins
111
How are the internal and external tables of bone different?
Internal is thinner than external
112
Do diploe exist in all areas of the calvaria?
In some areas there is only a thin plate of compact bone
| No diploe
113
What are the buttresses and what function do they perform?
Because strong muscles of mastication attach proximally to bones of the neurocranium and processes from them - causing traction around the nasal cavities and orbits...
Thickened portions of cranial bone that form strong pillars (buttresses) transmit forces to bypass more fragile areas of the skull
Frontonasal buttress - extends from region of canine teeth between the nasal and orbital cavities to the central front bone
Zygomatic arch-lateral orbital margins buttress - region of the molars to the lateral frontal and temporal bones
Occipital buttress - transmit forces received lateral to foramen magnum from the vertebral column
114
Draw and label the surface regions of the neurocranium and the viscerocranium
Textbook
115
Why is the pterion important clinically?
Fragile, thin area
Middle meningeal artery runs underneath
Common cause of brain bleed
116
What are the clinical features of basilar skull fractures?
CSF Rhinorrhoea or bleeding from nose - fractured ethmoid
Blood or CSF in external auditory canal, middle ear behind the tympanic membrane - Haemotympanum - fractured petrous part of temporal
Periorbital ecchymosis - fractured frontal bone
Battle sign (mastoid bruising) - fractured petrous part of temporal - blood can leak into soft tissues surrounding ear
117
How common are basilar skull fractures?
<5% skull fractures
| Uncommon
118
What are some complications of basilar skull fractures?
Meningeal tears:
Bleeding into soft tissues/ sinuses/ tympanic cavity
CSF leakage --> chance of meningitis
Cranial nerve palsy
119
Why is it important to do a CT scan in a suspected basilar skull fracture (or any skull fracture)?
Significant force is needed to fracture the basilar skull
Potential to have damaged the brain or cranial nerves (intracranial structures)
Also would perform a full neurological exam
Should also check cervical spine
120
Why is damage to the middle meningeal artery important?
Runs between dura and bone
If bleeds accumulates in the space between dura and bone
Causes extradural haemorrhage
If significant can increase intracranial pressure and compress intracranial structures
Brainstem can herniate through foramen magnum - very serious complications
121
What kind of X-ray should be ordered for a suspected mandibular fracture?
OPG
122
How many fractures should you look for in a suspected mandibular fracture
Frequently if there is one fracture there will be a second
123
What can also occur in a mandibular fracture?
Dislocation of the TMJ
124
How do mandibular fractures commonly occur?
Significant force to the jaw e.g. A punch
125
What do patients frequently complain of in mandibular fractures?
Malocclusion- Abnormalities of their bite because upper and lower jaw not lining up
126
What should always be done in suspected c spine injury?
Full in-line spinal immobilisation
Determine mechanism of injury
Symptoms
Clear spine clinically or send for CT in adults or X-ray/MRI paeds
If fracture or other injury identified then further management depends on type of damage found
127
Which part of the cervical spine tends to be involved in hyperflexion injuries?
Lower
128
What are potential complications of hyperflexion injuries?
Crush fractures of vertebral body (wedge fractures) - commonly related to osteoporosis
Rupture of supraspinous ligament
Rupture of lower IVDs --> compressions of nerve roots
129
Which part of the cervical spine is affected by hyperextension injuries?
Upper
130
What are the complications of hyperextension injuries?
Vertebral fracture, disc prolapse, cervical spinous process or odontoid fracture, tearing of anterior longitudinal ligament or kinking of posterior longitudinal ligament (degenerative spine)
131
How would you identify a vertebral wedge fracture on X-ray?
Loss of height of vertebral body
132
What condition is the most common risk factor for wedge fractures ?
Osteoporosis
133
What is cervical spondylosis?
Broad term describing degeneration of the spine e.g. Due to osteoarthritis of the spine
134
What are the features of cervical spondylosis?
```
Loss of joint space
Osteophytes
Subchondral sclerosis
Subchondral cysts
Facet joint hypertrophy
Disc herniation
Disc space narrowing
```
135
What is cervical spondylosis radiculopathy?
Narrowing of the intervertebral foramen (due to osteoarthritis changes or disc herniation) causing compression of the nerve root
Pain along distribution of the dermatome +/- muscle weakness in the associated myotome
136
What is cervical spondylotic myelopathy?
Compression of the spinal cord
Caused by the degenerative changes of the disc and facet joints
Loss of function
Loss of fine motor skills in upper limbs
137
What are the most common sites of facial fractures?
Nasal bone, zygomatic bone, mandible
138
What is the pterygopalatine/pterygomaxillary fossa?
Tiny space visible by looking on the interior of the skull
Lies between palatine bone of maxilla and pterygoid plate of sphenoid bone
Lies towards medial end of inferior orbital fissure
Bilateral, cone shaped depression
Extends from infratemporal fossa to the nasal cavity via the sphenopalatine foramen
139
Which foramen opens into the pterygopalatine fossa?
Foramen rotundum - conducts the maxillary nerve
140
What muscles origin is in the temporal fossa?
Temporalis muscle
141
Which bones contribute to the temporal fossa?
Temporal, sphenoid, parietal and frontal
142
Name two other fontanelles present at birth
Sphenoidal
| Mastoid
143
Highlight some features on a baby's skull that differentiate it from an adult skull
Fontanelles - anterior fuses 18 months, posterior fuses first couple of months
Small facial aspect compared to calvaria (1/8th cranium (1/3 of cranium in adult))
Halves of frontal bone separated by frontal suture - obliterated in 8th year- 8% of people - metopic suture remains - much less commonly entire suture remains
No mastoid and styloid processes
No diploe - smooth and unilaminar bones of calvaria
Frontal and parietal eminences prominent
Small maxillae, mandible and paranasal sinuses
Intermaxillary suture - doesnt fuse
Mandibular symphysis - fuses in 2nd year
Absence of teeth
144
Why are fontanelles important clinically?
Enable the clinician to determine:
- Progress of development of frontal and parietal bones
- Dehydration - sunken
- Raised intracranial pressure - bulging - meningitis etc.
- If enlarged - premature - could have suffered brain damage during birth due to high degree of flexibility of skull
145
Where is mesenchyme for the formation of the head region derived from?
Paraxial mesoderm
Lateral plate mesoderm
Neural crest
Ectodermal placodes (thickened regions of ectoderm)
146
What does the paraxial mesoderm develop into?
Forms large portion of membranous and cartilaginous neurocranium (skull)
All voluntary muscles of craniofacial region
Dermis and connective tissue in dorsal region of head
Meninges caudal to prosencephalon
147
What does the lateral plate mesoderm form?
```
Laryngeal cartilages (arytenoid and cricoid)
Connective tissue in this region
```
148
What do the neural crest cells form?
Migrate from forebrain, midbrain and hindbrain regions - ventrally into pharyngeal arches and rostrally around forebrain and optic cup into facial region
Form entire viscerocranium (Face)
Parts of membranous and cartilaginous neurocranium
Form all other tissues in this region (cartilage, bone, dentin, tendon, dermis, pia and arachnoid, sensory neurons and glandular connective tissue)
149
What do cells from the ectodermal placodes form?
Together with neural crest form neurons of the 5th, 7th, 9th and 10th cranial sensory ganglia
150
What is the other term for pharyngeal arches?
Branchial arches (old term)
151
In what week do the pharyngeal arches appear?
4th and 5th weeks
152
What do the pharyngeal arches consist of initially?
Mesenchymal tissue separated by deep clefts - pharyngeal clefts
153
What else appears simultaneously to pharyngeal arches and clefts?
Pharyngeal pouches
154
Where do pharyngeal pouches appear?
Lateral walls of the pharynx - cranial part of the foregut
| Penetrate the surrounding mesenchyme - do not establish open communication with the external clefts
155
Describe a pharyngeal arch
Core of mesenchymal tissue
Covered on outside by surface ectoderm
Covered on inside by epithelium of endodermal origin
Core receives substantial numbers of neural crest cells - contribute to skeletal components of the face
Mesoderm gives rise to musculature of face and neck
Therefore each arch characterised by own muscular components
Which each have their own cranial nerve
Where ever the muscle cells migrate - take their nerve component with them
Each arch has own arterial component
156
Describe the first pharyngeal arch and its derivatives
Consists of dorsal portion - maxillary process
Ventral portion - mandibular process - contains Meckel's cartilage
Meckel's cartilage disappears except two small portions at its dorsal end - persist and form the incus and malleus
Mesenchyme of 1st arch - premaxilla, maxilla and zygomatic bone, part of temporal bone, mandible (surrounds Meckel's cartilage) - membranous ossification
- also contributes to bones of middle ear
Musculature - muscle of mastication, anterior belly digastric, mylohyoid, tensor tympani and tensor palatini
Motor nerve supply - Mandibular branch of trigeminal nerve
Sensory nerve supply (Face) - Trigeminal nerve (all branches)
157
Describe the second pharyngeal arch and its derivatives
The cartilage (Reichert's cartilage) of the second arch (hyoid arch) gives rise to - stapes, styloid process of temporal bone, stylohyoid ligament, lesser horn and upper part of the body of hyoid bone
Muscles - stpedius, stylohyoid, posterior belly of digastric, auricular, muscles of facial expression
Nerve - facial nerve
158
Describe the derivatives of the third pharyngeal arch
Cartilage produces - lower part of the body and the greater horn of the hyoid bone
Muscles - stylopharyngeus muscles
Nerve - glossopharyngeal nerve
159
Describe the derivatives of the fourth and sixth pharyngeal arches
Cartilaginous components of each arch fuse to form - thyroid, cricoid, arytenoid, corniculate and cuneiform cartilages of the larynx
Muscles of the fourth arch - cricothyroid, levator palatini, constrictors of the pharynx
Nerve of the fourth arch - superior laryngeal branch of the vagus nerve
Muscles of the sixth arch - Intrinsic muscles of the larynx
Nerve of the sixth arch - recurrent laryngeal branch of the vagus nerve
160
How many pharyngeal pouches are there?
Four pairs (fifth is rudimentary)
161
What are the derivatives of the first pharyngeal pouch?
Forms stalk-like diverticulum - tubotympanic recess - comes in contact with epithelial lining of the first pharyngeal cleft (future external auditory meatus)
Distal portion widens - primitive tympanic or middle ear cavity - lining laters aids in tympanic membrane formation (eardrum)
Proximal portion remains narrow - auditory (eustachian) tube
162
Describe the derivatives of the second pharyngeal pouch
Epithelial lining proliferates and forms buds - penetrate into surrounding mesenchyme - buds are secondarily invaded by mesodermal tissue
Palatine tonsils
In 3rd and 5th months - tonsil is infiltrated by lymphatic tissue
Part of the pouch remains - found in adult - tonsillar fossa
163
Describe the third pharyngeal pouch and its derivatives
Characterised at distal extremity by dorsal and ventral wing
5th week - epithelium of dorsal region differentiates into inferior parathyroid gland, ventral region forms the thymus - both lose their connection with pharyngeal wall - thymus migrates in caudal and medial direction - pulls inferior parathyroid with it
Main portion of thymus moves rapidly to final position - anterior thorax - fuses with counterpart from opposite side
Tail portion sometimes persists embedded in thyroid gland or as isolated thymic nests
Growth and development of thymus continues until puberty
Occupies considerable space in young children
Difficult to recognise in adults - atrophied - replaced by fatty tissue
Parathyroid tissue - comes to rest on dorsal surface of thyroid gland - forms inferior parathyroid gland
164
Describe the fourth pharyngeal pouch and its derivatives
Distal extremity - dorsal and ventral wing (like 3rd)
Epithelium of dorsal region - superior parathyroid gland - loses contact with pharyngeal surface - attaches self to dorsal surface of caudally migrating thyroid
Ventral region - ultimobranchial body - later incorporated into the thyroid gland - give rise to C cells (parafollicular) of thyroid - secrete calcitonin
165
How many pharyngeal clefts are there?
Four (5th week)
166
How many pharyngeal clefts contribute to the definitive structure of the embryo?
One
167
Which pharyngeal cleft contributes to the definitive structure of the embryo ?
The first cleft
168
Describe the derivatives of the first pharyngeal cleft
Dorsal part penetrates underlying mesenchyme - gives rise to external auditory meatus
Epithelial lining at bottom of the meatus participates in formation of the eardrum
169
What happens to the other pharyngeal clefts (apart from the first)?
Active proliferation of mesenchymal tissue in second arch causes it to overlap third and fourth arches
Merges with epicardial ridge in lower part of neck
Second, third and fourth clefts lose contact with outside - form a cavity lined with ectodermal epithelium - cervical sinus - with further development this disappears
170
In early week 4, how much of the length of the embryo do the head and neck represent?
~1/2 length of embryo
171
Where is the 5th pharyngeal arch?
No recognisable derivatives of 5th pharyngeal arch in humans - does not form
172
Describe what happens to the neural tube (briefly)
```
Anterior end begins to form brain
3 vesicle stage
Prosencephalon - forebrain
Mesencephalon - midbrain
Rhombencephalon - hindbrain
Brain expands and develops rapidly
Spinal cord doesnt really change throughout embryonic life
```
173
Where are the cranial nerves derived from?
All except CN I and II are from mid or hind brain
174
Which cranial nerves have relationships with pharyngeal arches but arent technically nerves of a pharyngeal arch?
CN XI
| CN XII
175
What is the facial skeleton derived from?
Frontonasal prominence and 1st pharyngeal arch
176
Where are the ossicles derived from?
Malleus and incus - first pharyngeal arch
| Stapes - second pharyngeal arch
177
Where does the aortic sac lie?
Floor of pharynx
178
What are the derivatives of the aortic arches?
3rd arch - internal carotid
4th arch - arch of aorta (L) and brachiocephalic (R)
6th arch - "pulmonary arch"
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What are branchial fistulas?
Occur when second pharyngeal arch fails to grow caudally over third and fourth arches
Leaves remnants of second, third and fourth clefts in contact with the surface by a narrow canal
Found lateral aspect of neck anterior to SCM - provides drainage for a lateral cervical cyst
Lateral cervical cyst- remnants of cervical sinus - most often just below angle of jaw - can be found anywhere along anterior SCM - frequently not visible at birth - becomes evident as enlarges during childhood
Internal bronchial fistulas - rare - cervical sinus connected to lumen of pharynx by small canal - opens in tonsillar region - results from rupture of membrane between second pharyngeal cleft and pouch sometime during development
