Week 1.0 - Embryonic Overview Flashcards
What 3 tissue systems are notably involved during the development of the pharyngeal arches?
- Brain
- CVS
- Special Sensory organs
Describe the sections of the pharynx?
- Nasal -> base of skull to soft palate
- Oral -> Soft palate to larynx
- Laryngeal -> Posterior larynx to oesophagus
What tissue first composes the pharyngeal arches? How do they initially appear?
- Mesenchyme
- A series of mitotic divisions in the neck region of the embryo formed 5 external buldges
What 2 tissue structures contribute to the development of the head and neck?
- Frontonasal prominence
- Pharyngeal arches
How are the pharyngeal arches numbered and why?
-The 5 arches are numbered 1-6 because the 5th does not form in humans
What causes the development of the frontonasal prominence?
-Growth of the neural tube in the cephalic region
What 3 specific features are associated with each pharyngeal arch?
-Each has an associated artery, cranial nerve and cartilage bar
In general, what happens to the cartilage bars associated with the pharyngeal arches?
-They are remodelled into skeletal structures
Describe the structure of a basic pharyngeal arch
-Mesenchymal core with an ectodermal outer covering and an endodermal lining
In basic terms, describe the formation of the neural tube
- The notochord signals to the overlying ectoderm to differentiate into neuroectoderm (neural plate).
- Neuroectoderm proliferates and raises out of the plane of the trilaminar disc
- The edges of the disc curl towards each other, fuse and form the neural tube
Describe the anatomical structure of the early neural tube
- Anterior neural tube begins to form the brain by expanding into 3 vesicles which surround the lumen of the tube (forebrain, midbrain and hindbrain)
- The remainder of the neural tube contributes to the spinal cord
State the embryonic term for forebrain, midbrain and hindbrain
- Forebrain-> Prosencephalon
- Midbrain -> Mesencephalon
- Hindbrain -> Rhombencephalon
What are the pharyngeal arches?
-Complex tissue system which represent the embryonic head and neck
How does pharyngeal arch 1 differ from the rest?
-It has two prominents ;maxillary and mandibular
How do the arches get there associated nerves?
-Cranial nerves emerge from the neural tube and grow into their corresponding arch
What is a pharyngeal cleft?
-The groove between each arch
How many pairs of cranial nerves?
-12
Which cranial nerves are derived from the mid- or hindbrain?
-All but CN I and II
Which cranial nerves are the nerves of the pharyngeal arches?
-CN V, VII, IX and X (XI and XII have a relationship with the arches but do not directly supply its derivatives)
Are the nerves of the pharyngeal arches sensory, motor or mixed?
-Mixed
From where is the facial skeleton derived?
-FNP and 1st pharyngeal arch
From where are the muscles of mastication derived?
-Ph Arch 1
From where are the muscles of facial expression derived?
-Ph Arch 2
Which CN supplies muscle of mastication?
-Trigeminal (V)
Which CN supplies muscles of facial expression?
-Facial (CN VII)
What are the muscle derivatives of the 3rd Ph Arch?
-Stylophargyngeus
What are the muscle derivatives of the 4th Ph Arch?
- Cricothyroid
- Levator Palatini
- Constrictors of the pharynx
What are the muscle derivatives of the 6th Ph Arch?
-Intrinsic muscles of the larynx
Which nerve supplies the 1st pharyngeal arch?
-Trigeminal
Which CN supplies the 2nd Ph Arch?
-Facial
What is the sensory component of the facial nerve?
- Chorda Tympani -> supplies taste buds in anterior 2/3rd of tongue
- General sensory to the auricle
What are the branches of trigeminal nerve?
- Ophthalmic
- Maxillary
- Mandibular
What are the branches of facial nerve?
- Temporal
- Zygomastic
- Buccal
- Mandibular
- Cervical
What is the CN of the 3rd Ph Arch? What are its related functions?
- CN IX (Glossopharyngeal)
- Innervate stylopharyngeus
- General sensory and special sensory to posterior 1/3 tongue
What is the CN of the 4th and 6th Ph Arch? Which branches to which arch?
- Vagus nerve
- 4th by superior laryngeal nerve
- 6th by recurrent laryngeal nerve
From where are the cartilage bars derived from?
-Neural crest
What is the name of the cartilage bar of the 1st Ph arch?
-Meckel’s
What is the name of the cartilage bar of the 2nd Ph arch?
-Reichert’s
Which Cartilage bars contribute to the cartilage of the larynx?
-4 and 6
Within the 1st Ph Arch, where does meckel’s cartilage form?
-Within the mandibular prominence
What skeletal structure(s) does meckel’s cartilage form?
- Malleus and Incus
- Template for mandible (which forms by membranous ossification)
What skeletal structure(s) does reichert’s cartilage form?
- Stapes
- Styloid process
- Hyoid bone (lesser cornu and upper body)
What skeletal structure(s) does 3rd Ph cartilage form?
-Contributes to hyoid bone
What structure(s) do the 4th and 6th Ph cartilages form?
-Thyroid, arytenoid and cricoid cartilages
From where is the epiglottis dervided?
-Mesenchyme of 4th and 6th Ph Arch
Describe the fates of the aortic arches associated with each Ph Arch
- 1st and 2nd disappear
- 3rd -> internal carotid
- 4th -> arch of aorta (L) and brachiocephalic (R)
- 6th -> Pulmonary arch
Where does the left recurrent laryngeal nerve loop?
-Under aortic arch
Where does the right recurrent laryngeal nerve loop?
-Right subclavian
What is a pharyngeal pouch?
-The groove between the endodermal lining of each arch
What is the derivative of the 2nd Ph pouch? How does it form?
- Palatine tonsil
- Epithelial proliferation followed by colonisation of lymphoid precursors
Describe the fates of the 3rd and 4th Ph pouches
- Split into dorsal and ventral compartments
- 3 and 4D form the parathyroid gland
- 3V forms the thymus
From where are the tympanic cavity and eustachian tube derived?
-1st Ph pouch derivatives
Describe the fates of the Ph clefts
- 1st is all that remains
- Remainder are obliterated by the growth of the 2nd Ph arch
Why can branchial cysts and fistulae form?
-Remnant of the pharyngeal clefts which can form anywhere along the anterior border of sternocleidomastoid
