Week 3 - The Development of the Pharyngeal Arches Flashcards
What is the Pharyngeal Apparatus?
Segmental series of paired swellings surrounding the developing pharynx
Some textbooks may refer to them as the Branchial Apparatus
What are Pharyngeal Arches?
Paired swellings located between developing forebrain and heart, consisting of mesenchymal tissue covered by ectoderm and endoderm
How are Pharyngeal Arches numbered?
In a cranio-caudal sequence
What does a typical Pharyngeal Arch contain?
- Mesenchyme
- Cartilaginous bar
- Artery
- Cranial nerve
What is Meckel’s cartilage?
Cartilaginous component of the 1st pharyngeal arch
What does the dorsal end of Meckel’s cartilage form?
Malleus and incus of the middle ear
What is the role of mesenchyme surrounding Meckel’s cartilage?
Guides the formation of the mandible
What does the 2nd pharyngeal arch cartilage become?
Reichert’s cartilage
What does the dorsal end of Reichert’s cartilage form?
Stapes of the middle ear and styloid process of temporal bone
What muscles are derived from the 1st pharyngeal arch?
- Muscles of mastication
- Anterior belly of digastric
- Tensor tympani
- Tensor veli palatini
- Medial and lateral pterygoid
- Temporalis
- Masseter
- Mylohyoid
Which cranial nerve is associated with the 1st pharyngeal arch?
Trigeminal (V)
What are the derivatives of the 3rd pharyngeal arch?
- Greater horn of hyoid bone
- Lower ½ body of hyoid bone
- Stylopharyngeus muscle
What cranial nerve is associated with the 3rd pharyngeal arch?
Glossopharyngeal (IX)
What cartilages are derived from the 4th and 6th pharyngeal arches?
- Thyroid cartilage
- Cricoid cartilage
- Arytenoid
- Corniculate
- Cuneiform
What is Treacher Collins Syndrome?
Inherited condition characterized by underdevelopment of maxilla, mandible, and zygomatic bones
What genetic mutation causes Treacher Collins Syndrome?
Mutation in the TCOF1 gene
What is the first pouch derivative?
Tympanic cavity and auditory tube
What does the second pouch develop into?
Palatine tonsil
What do the dorsal and ventral wings of the 3rd pouch differentiate into?
- Dorsal wing: inferior parathyroid gland
- Ventral wing: thymus
What is the developmental origin of the tongue?
Two lateral lingual swellings and one medial swelling (tuberculum impar) from the first pharyngeal arch
What is the innervation of the anterior 2/3 of the tongue?
- General sensory: mandibular division of trigeminal nerve (CN V)
- Special sensory: chorda tympani (CN VII)
What is the innervation of the posterior 1/3 of the tongue?
- Glossopharyngeal nerve (CN IX)
- Vagus nerve (CN X)
Fill in the blank: The 2nd pharyngeal arch is also known as the ______.
Hyoid arch
True or False: The 5th pharyngeal arch is always visible on the external surface.
False
What is the general sensory innervation of the tongue?
Mandibular division of trigeminal nerve (CN V) - lingual branch
This innervation is primarily responsible for the sensation in the anterior two-thirds of the tongue.
What provides special sensory innervation (taste) to the anterior two-thirds of the tongue?
Chorda tympani (branch of facial nerve - CN VII)
The chorda tympani carries taste sensations from the anterior part of the tongue.
Which nerves provide sensory innervation to the posterior one-third of the tongue?
Glossopharyngeal nerve (CN IX) and Vagus nerve (CN X)
CN IX innervates the majority of the posterior tongue while CN X innervates the epiglottis.
What is the primary nerve for motor innervation of the tongue muscles?
Hypoglossal nerve (CN XII)
The hypoglossal nerve is responsible for the movement of the majority of the tongue muscles.
What structures contribute to facial development during Week 4?
Frontonasal prominence, Nasal placode, Maxillary prominence, Mandibular prominence
These structures are crucial in the initial formation of the face.
What occurs during facial development in Weeks 5-6?
Nasal placodes invaginate to form nasal pits, lateral and medial nasal prominences develop, maxillary prominences merge with medial nasal prominences to form upper lip, and mandibular prominences merge to form lower lip and jaw
This period is essential for the shaping of the facial structure.
During Weeks 6-7 of facial development, what is formed between the lateral nasal prominence and maxillary prominence?
Nasolacrimal groove
This groove eventually leads to the formation of the nasolacrimal duct.
What is the intermaxillary segment composed of?
Labial component, Upper jaw component, Palatal component
The intermaxillary segment is vital for the development of the upper lip and palate.
What are the two parts that compose the palate?
Primary palate and Secondary palate
The primary palate is part of the intermaxillary segment, while the secondary palate forms the definitive hard and soft palates.
What is the clinical significance of cleft lip and/or palate?
Affects 1/700 babies in the UK, causes defective speech, breathing, feeding, and dental problems
Clefts can be anterior or posterior and are often related to environmental factors during pregnancy.
What defines anterior cleft deformities?
Clefts anterior to the incisive foramen, involving cleft lip and/or primary palate
These deformities result from a lack of fusion of the maxillary prominence with the medial nasal prominence.
What defines posterior cleft deformities?
Clefts posterior to the incisive foramen, involving the secondary palate and cleft uvula
These deformities are due to failure of fusion of palatine shelves.
What is the surgical intervention timeline for cleft lip and cleft palate?
Cleft lip surgery: 3-6 months; Cleft palate surgery: 6-12 months
Timely surgical intervention is crucial for improving outcomes in affected individuals.
Fill in the blank: The primary palate is part of the _______.
intermaxillary segment
True or False: The nasolacrimal duct forms from a thickened cord that undergoes apoptosis.
True
This process is crucial for the proper formation of the nasolacrimal system.
