✅ EMBRIOLOGÍA de la CABEZA y el CUELLO (Parte 1°)👅🙇🏻♀️
Embryology of the Head and Neck: Part One
Introduction to Embryology
- The video introduces the topic of embryology focused on the head and neck, addressing previous feedback regarding audio clarity from an earlier video.
- The region encompassing the head and neck is termed "Cefálica," characterized by its complex mesenchyme structures.
Origin of Structures
- Key origins for these structures include:
- Neural crest (blue)
- Paraxial mesoderm (red), also known as somites or somitomeres
- Lateral mesoderm (yellow)
- Ectodermal placode cells alongside neural crest cells.
Pharyngeal Apparatus Development
- In a four-week-old human embryo, regions of the head and neck resemble those in fish embryos at similar developmental stages, leading to historical references to "Branchial Apparatus."
- Currently, this is referred to as "Pharyngeal Apparatus," which consists of arches, pouches, grooves or clefts, and pharyngeal membranes.
Pharyngeal Arches Formation
- Pharyngeal arches begin developing when neural crest cells migrate to future head and neck areas.
- By the end of week four, four pairs of visible pharyngeal arches exist; however, the fifth and sixth are rudimentary and not externally visible.
Structure of Each Arch
- Each pharyngeal arch comprises:
- A core of mesenchymal tissue,
- An outer layer covered by surface ectoderm,
- An inner layer lined with endoderm-derived epithelium.
Components of Pharyngeal Arches
Muscular Components & Innervation
- The first arch gives rise to muscles involved in mastication including:
- Digastric anterior belly,
- Mylohyoid,
- Tensor tympani,
- Stapedius muscle.
Second Arch Contributions
- The second arch contributes muscles such as:
- Stapedius,
- Stylohyoid,
- Posterior digastric belly,
- Auricular muscles,
- Facial expression muscles innervated by the facial nerve.
Third & Fourth Arch Muscles
- The third arch forms stylopharyngeus muscle innervated by glossopharyngeal nerve; while fourth arch includes:
- Cricothyroid muscle,
- External stapedial muscle,
- Pharynx constrictors innervated by superior laryngeal branch of vagus nerve.
Cartilage Development from Arches
First Arch Cartilage Formation
- The first arch consists of dorsal maxillary process and ventral mandibular process leading to formation of maxillae, zygomatic bone, temporal bone, and mandible.
Second Arch Cartilage Contributions
- Contains Reichert's cartilage giving rise to:
- Stapes (stirrup),
- Styloid process,
- Stylohyoid ligament ventrally;