Embryology: Development of Speech and Hearing Systems Flashcards
Embryology
Human Embryology is the study of human development during the first 8 weeks
Embryogenesis
The process of cell division and cellular differentiation of the human embryo that occurs during the early stages of development
How does human development begin and occur?
Occurs along a continuum
Begins with germ cells (ovum and spermatozoon) and progressing to growth to adulthood
After the first 8 weeks, the embryo is then referred to as a fetus
How many cells does a mature human body have?
10^14 cells
These cells will form and differentiate as the body grows
Some cells are replaced as they mature and die
What is the first step in cell division?
Duplication of genes and chromosomes
The process of development is characterized by?
The coordination of spatial and temporal changes in gene expression, cell growth or maturation, and cell differentiation
This process ultimately leads to the development of organs and systems
Prenatal Development Means
Development that occurs during the first 8 weeks of gestation
Prenatal Development - Week 2
The amniotic cavity develops, along with the primary germ or germinal layers of tissue:
Extoderm, mesoderm, and endoderm
These 3 layers of primary tissue ultimately give rise to all of the structures of the body
Ectoderm
Outer most layer and forms the epidermis of the skin, much of the teeth, the entire nervous system (both PNS and CNS), hair nails, and epithelial tissue
Mesoderm
The intermediate layer that ultimately gives rise to most of the connective tissue in the body.
In other words, it comprises the bones, muscles, blood vessels, and cartilages of the body
endoderm
Deepest of the three layers. It gives rise to the epithelial lining of the entire digestive tract and respiratory tract
except for the linings of the oral and pharyngeal cavities, which are formed by ectoderm
Endoderm is sometimes referred to as “inner skin”
Prenatal Development - 3rd week
The primitive streak appears, followed by rapid development of the CNS, heart, notochord, neural tube, limbs, digits, and facial features
Primitive Streak is comprised of
number of cells that proliferate caudally
Significance of the primitive streak is that it is capable of forming new germ tissue (ectoderm, mesoderm, and endoderm)
Notochord
Primitive axial (forming or relating to axis) skeleton of the embryo
Cephalically (of or related to the head), some tissues of the notochord will develop that will form the buccopharyngeal membrane
At 3 weeks, the facial area is
Very primitive (early stage)
Consists of smooth, relatively undifferentiated bulge known as the PROSENCEPHALON, which is the forebrain or anterior brain of the embryo
Caudal to the prosencephalon (forebrain) lies a?
Transverse furrow called the oral groove or stomodeum (primitive mouth)
STOMODEUM means
primitive mouth and is regarded as the center of the developing facial structures
At week 3, the ectoderm…
begins to thicken in an area immediately overlying the notochord
thickened layer of ectoderm is called the MEDULLARY or NEURAL PLATE - the lateral margins of which grow upward to form the NEURAL FOLDS
Eventually, the NEURAL FOLDS will meet at midline, fuse, and form the NEURAL TUBE
Importance of the neural tube
Ultimately gives rise to the entire CNS, which comprises the brain and spinal cord
3 subdivisions of neural tube
- prosencephalon
- mesencephalon
- rhombencephalon
Prosencephalon
Subdivision of neural tube
will further develop into the telencephalon (cerebrum) + diencephalon (optic vessels + hypothalamus)
Mesencephalon
Subdivision of neural tube
Will eventually develop into mid brain
Rhombencephalon
subdivision of neural tube
Will eventually develop into metencephalon (pons and cerebellum) and the myencephalon (medulla oblongata)
The 4th and final subdivision of the neural tube will form the ?
Spinal cord
Neural tube is open both cranially and caudally before finally closing during the 4th week of development
Openings in the neural tube called
Neuropores
Failure of the neuropores to properly close may result in
neural tube defects
Example is spina bifida
In the 4th week, what happens to the buccopharyngeal membrane
It ruptures, allowing the stomodeum (primitive mouth or oral cavity) to articulate with the pharynx
4th week - migrating neural crest cells
These form the frontonasal process located in the anterior portion of the forebrain
A number of neural crest cells will form the branchial or pharyngeal arches
Together, the frontonasal process and branchial arches contribute greatly to the development of the FACE and ORAL CAVITY
4-5 week of development Branchial and Pharyngeal arches are comprised of what
6 paired thickenings that form a LATERAL PLATE
Mandibular Arch
First of the branchial arches
Gives rise to the lower lip, the muscles of mastication, and mandible proper, the anterior portion of the tongue, malleus and incus, tensor tympani, tensor veli palatini, mylohyoid, and the anterior belly of digastric
Hyoid Arch
Second of the branchial arches
Gives rise to the upper body and lesser horns of the hyoid bone, the stapes, the muscles of facial expression, stapedius, stylohyoid, and the posterior belly of digastric
Branchial arch 3
Gives rise to the lower body of the hyoid bone, the posterior portion of the tongue, and the stylopharyngeus
Branchial Arch 4
Cartilages of the larynx, all muscles of the larynx and pharynx except stylopharyngeus, and all muscles of the soft palate (except tensor veli palatini)
Branchial Arch 5 (mystery arch)
Some research suggests that it gives rise to the cricoid + arytenoid cartilages and the cartilages of the trachea
HOWEVER, more recent research has suggested that the 5th arch disappears during embryonic development and does not give rise to any structures or muscles in human embryo development
Branchial Arch 6
Gives rise to the muscles sternocleidomastoid and trapezius
All Branchial arches are innervated (supplied with nerves) by the CN
First: Trigeminal (V)
Second: Facial (VII)
Third: Glossopharyngeal (IX)
Fourth: Vagus (X)
Sixth: Accessory (XI)
5th week: frontonasal process
Rapidly develops caudally
Gives rise to upper face, forehead, bridge o the nose, and nasal septum
5th week - maxillary process
Develop and give rise to the maxilla
5th week - mandibular process
Gives rise to the mandible
6th week - maxillary and mandibular process can be distinguished from one another
T/F?
True
Towards the end of the 6th week of development, the hard and soft palates begin to develop
7th week - soft palate + hard palate
soft palate forms through the fusion of the medial nasal processes
Hard palate forms through the fusion of the palatine processes of the maxillae + the horizontal lamina of the palatine bones
These fusions complete the formation of the ceiling of the oral cavity and the floor of the nasal cavity
7-8 weeks - tongue formation
Tongue begins to form at about the same time as the hard and soft palates
It extends from various protuberances along the pharyngeal floor
It is derived from all pharyngeal arches contributing different components
