The Development of the Nervous System Flashcards
What is the first stage of embryonic development after fertilisation (Day 4)
Morulation
The zygote forms a solid ball of about 16 cells
What is the second stage of embryonic development after fertilisation (Day 5)
The cells in the morula are split into two groups
The inner cell mass becomes an embryo
The trophoblast is cells that create a protective layer and eventually become the placenta. They secrete fluid to create a fluid-filled cavity- blastocoel
How does the inner cell mass change after the blastocyst stage?
How do these relate to functioning of the final embryo?
At days these differentiate into cell groups. The inner cell mass differentiates into the epiblast or the hypoblast. The epiblast forms the embryo. The hypoblast becomes part of the embryo’s gut and also helps create structures that supply blood to the embryo. So the epiblast is essential to the developing embryo
What occurs in Gastrulation?
days 13-19- A groove forms in the surface of the blastocyst (the primitive streak). This then forms the midline of the developing embryo. This then develops to create 3 layers of cells- the ectoderm- develops into the nervous system, the mesoderm- forms things like bones and connective tissue and the endoderm- forms out of the hypoblast so is involved in the lining of the lungs, guts, liver, pancreas etc (top to bottom). These 3 layers are called the Gastrula.
How does the formation of the neural plate relate to the of the neural groove?
The “neuroectoderm” (containing the primitive streak) forms the neural plate- which drives the development of the nervous system as a whole. On either side of the primitive streak, cells divide rapidly, creating a groove- the neural groove, which will become the midline of the embryo.
How does the neural groove change SHAPE to form the shape of our primitive brain?
What stage of primitive neural development does this relate to (N_________n)
The rapid cell division on either side of the groove continues until the ridges meet to form a tube- the neural tube. The central canal carries fluid, which then becomes the ventricles of the brain and the central canal of the spinal cord. This is neurulation- as it creates a neurula.
What happens in day 24 of the development of the nervous system?
(relates to the subdivisions of the nervous system and the brain areas)
The 3 main divisions of the nervous system become apparent- the telencephalon and diencephalon combine to create the prosencephalon, the mesencephalon becomes apparent and we develop the rhombencephalon (a combination of the metencephalon and the myelincephalon)
How does the primitive, tubular CNS become a closed organ with distinct brain areas and regions?
The channel between the primitive “spinal chord” and primitive “brain” is closed off, causing a build up of pressure from cerebrospinal fluid.
Cells are proliferating rapidly. Therefore, specific regions begin to protrude and take shape- such as the retina, optic nerve and ventricles. The 5 brain areas now become distinct as well (T, D, MT, ML, MY)
How does the brain change from being tubular/cylindrical to have the arch shape we now associate with it?
At 3-4 weeks, the structure bends and brings the forebrain downwards. At 5 weeks there is a second bend at the head of the spinal chord (creating the arch). The telencephalon then moves backwards and folds back over itself, carrying a fluid filled sack with it and causing the cerebral cortex to form.
What important elements of the brain (like lesions, but not) begin to develop at 6 months?
The sulci and gyri in the cerebral cortex, as well as some of the major fissures (i.e. the lateral fissure)
What are neural precursor cells?
They are stem cells that are likely to divide to form into neurons. They are formed when cells in the ectotherm, near the midline (notochord) recieve specific chemical signals during gastrulation
What are the two different ways neural precursor cells divide before and after gastrulation?
Where does this occur?
Before neurulation, NPCs divide symmetrically (meaning they form two identical neural precursor cells when they divide). After neurulation, they divide asymmetrically, so either develop into a primitive glial cell (glioblast) or a primitive neuron (neuroblast)
Near the canal of the tubular primitive brain, in the ventricular zone
Where do glioblasts and neuroblasts travel to and from where in the primitive brain structure?
They form in the ventricular zone, which is like the core of the brain, so must migrate upwards to get to the area which will become the cerebral cortex/other areas.
How do glioblasts and neuroblasts travel up the primitve brain? What assists them?
They are assisted by radial glial cells, which create processes along the primitive brain that the glioblasts and neuroblasts follow along.
What happens when neuroblasts and glioblasts reach their target after traveling along the processes of radial glial cells up the primitive brain?
They differentiate into specific type of glial cell/neuron, based on the chemical environment and interactions with neighbouring cells that they end up with. These then interconnect to form neural circuits/the connectome.
