Week 1 Topic 1 / 1 Flashcards
morphogenesis
The biological process through which an organism develops its shape.
(It’s taking place on a systems level, we are looking at changes in size and shape.)
differentiation
The process by which a more specialised cell is generated from a less specialised cell.
(Relative to the NS at the cellular level cells change from dividing progenitors into mature neurons with complex morphologies, interconnected in circuits)
cleavage
The rapid cell division that a zygote undergoes to generate a spherical ball of cells called a blastula.
blastocyst
A fertilised egg, which cleaves to give rise to a ball of cells is called a blastocyst.
The blastocyst is the human embryo 5-6 days after fertilization where cells have become organised into two types:
the outer layer or trophectoderm that will give rise to the placenta and a cluster of cells called the inner cell mass that will give rise to the embryo.
Embryonic Stem Cells
(ES cells)
Undifferentiated cells derived from the inner cell mass of blastocyst-stage embryos that have the capacity to generate all the different cell types in the body.
When does the implantation of the embryo occur?
Implantation of the embryo into the uterine wall occurs at the end of the first week.
What happens after the implantation of the embryo?
Further development generates a two-layered embryonic disc, consisting of a hypoblast and an epiblast.
What is the process of gastrulation and when does it happen throughout embryonic development?
Gastrulation happens at the end of the second week.
The process of gastrulation transforms the two-layered embryonic disc into a three-layered structure consisting of three so-called ‘germ’ layers (the ectoderm, mesoderm, and endoderm) which give rise to all the tissues of the body.
Gastrulation
The phase during embryonic development when the blastula is reorganized into a three-layered structure known as the gastrula.
These three germ layers are known as the ectoderm, mesoderm, and endoderm.
These layers fall and start to become different types of tissues in the third week.
Germ layers
Primary layers of cells that make up the gastrula.
They form during gastrulation and they contribute to the formation of all organs and tissues.
What is neurulation and when does it happen?
Neurulation is the process in which the neural tube forms.
It happens at week 3-4.
The formation of the neural plate and neural folds is followed by fusion of the neural folds to form the neural tube.
After the tissue becomes neural it undergoes morphogenetic changes in shape. This is called neurulation.
The neural tube will form the brain, the spinal cord, the meninges, as well as part of the bones that surround them.
What are the tailbud and the tailbud stage?
The tailbud is a dividing mass of cells that is found at the caudal (tail) end of an embryo.
In weeks 4-5 the embryo starts to be recognizable with a head, tail, and some of the embryonic structures that will be present in the adult, such as the limb buds, which grow into the limbs.
This is called the tailbud stage.
What is the embryonic period?
In humans, the second month of gestation is referred to as the embryonic period, during which the major organ systems start to form.
What is the foetal period?
Months three to nine is the foetal period, which is mainly concerned with growth.
Large amounts of cell proliferation take place, a process that is particularly important for the brain.
What is neural induction?
Further development of the nervous system involves the ectoderm, which develops under the influence of signals from the underlying mesoderm (from the notochord), a process called neural induction.
During this process, a portion of the ectodermal germ layer is induced to become neural tissue, which will form the nervous system.
As the tissue becomes neural, it also undergoes morphogenetic changes in shape, called neurulation.
What is a scanning electron microscope?
A scanning electron microscope is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons.
The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample.
What are the features of the embryo at the tailbud stage?
By the tailbud stage (4-5 weeks of gestation), cranial and caudal folding has occurred, arching the body to give it what has sometimes been referred to as a ‘comma’ shape.
Lateral folding has also occurred to enclose all forming internal organs in a covering of ectoderm, which will become the skin.
We can see that the embryo has acquired a more recognisable appearance, with a head and tail somite blocks, and structures called branchial, or pharyngeal, arches, which will form elements of the lower jaw and neck.
The diagram highlights the developing eye, and the otic vesicle, which will give rise to the inner ear
What are the subdivisions of the neural tube?
(day 28)
Whereas the region of the developing spinal cord remains with a small diameter, the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon) have started to expand.
The prosencephalon is divided into the telencephalon more cranially, and the diencephalon more caudally.
What are the flexures and the subdivisions of the neural tube?
Initially, the anterior end of the tube forms a crook, giving it the shape of a cane handle. The end of the cane nearest the sharper bend, or cephalic flexure, balloons out to form the forebrain, or prosencephalon.
The midbrain, or mesencephalon, forms as a bulge called the cephalic flexure.
The hindbrain, or rhombencephalon, forms in the long, relatively straight stretch between the cephalic flexure and the more caudal cervical flexure.
Caudal to the cervical flexure, the neural tube forms the precursor of the spinal cord.
This bending and folding constricts or enlarges the lumen enclosed by the developing neural tube. These lumenal spaces eventually become the ventricles of the mature brain.
