Development of the Nervous System Flashcards
When does the development of the central nervous system occur?
At the beginning of the third week
Describe the formation of the neural tube
The neural folds continue to elevate, approach each other in the midline, and finally fuse to form the neural tube
Where does fusion of the neural folds begin and how does it proceed onward?
Fusion begins in the cervical region and proceeds in cephalic and caudal directions
What are the open ends of the neural tube called?
Cranial and Caudal Neuropores
When do these neuropores close?
The cranial neuropore closes around the 25th day and the caudal neuropore closes approximately 3 days later
What is Neurulation?
Formation of the neural tube
What are the 3 dilations at the cephalic end of the neural tube?
The Primary Brain Vesicles
1) Prosenchphalon (forebrain)
2) Mesencephalon (midbrain)
3) Rhombencephalon (hindbrain)
Around the 28th day how many flexures are formed? What are they called and where are they located?
Two
1) the cervical flexure at the junction of the hindbrain and spinal cord
2) the cephalic flexure in the midbrain
When the embryo is 5 weeks old what are the two parts of the prosencephalon?
- Telencephalon
- Diencephalon
When the embryo is 5 weeks old what are the two parts of the rhombencephalon?
- Metencephalon
- Myelencephalon
What are neural crest cells?
When the neural folds fuse and elevate, they are the cells found at the lateral or crest of the neuroectoderm that begin to dissociate from their neighbors.
What 7 things do the neural crest cells give rise to?
1) spinal, cranial nerve (V, VII, IX, and X), and autonomic ganglia
2) ensheathing cells of the peripheral nervous system (Schwann cells)
3) pigment cells (melanocytes) of the skin and some muscles in the head and neck
4) some connective tissues
5) some bones of pharyngeal arch origin (pharyngeal arch cartilages)
6) suprarenal medulla
7) conduction tissue in the heart
How is a 3D embryo produced?
Folding in the Longitudinal and Horizontal Planes resulting from rapid growth of the embryo.
Growth along which plane occurs more rapidly?
The growth rate at the sides of the embryonic disc fails to keep pace with the rate of growth in the long axis
Describe folding at the cranial and caudal ends and sides of the embryo
It occurs simultaneously, resulting in a relative constriction at the junction of the embryo and umbilical vesicle (yolk sac)
Describe Head Folding
The developing forebrain grows cranially beyond the oropharyngeal membrane and overhangs the developing heart. At the same time, the septum transversum, primordial heart, pericardial coelom, and oropharyngeal membrane move onto the ventral surface of the embryo.
Describe what happens to the septum transversum after head folding
The septum transversum lies caudal to the heart where it subsequently develops into the central tendon of the diaphragm.
How is the foregut produced during head folding?
Part of the endoderm of the yolk sac is incorporated into the embryo and is called the foregut.
The foregut leads to the ______ membrane, which will breakdown to form what?
Oropharyngeal
the mouth
Describe the order of the diaphragm, heart, and mouth before and after head folding
Before the sequence is diaphragm, heart, and then mouth
After the sequence is mouth, heart, diaphragm
Folding at the caudal end of the embryo results primarily from what?
Growth of the distal part of the neural tube (the primordium of the spinal cord)
As the embryo grows caudally what does the tail region project over?
The colacal membrane, which is the future site of the anus.