Lesson 5: Neural Development Flashcards
Neurulation
The first organs to take shape in the chordate embryo are the neural tube and the
notochord.
The notochord develops from a condensation of dorsal mesoderm cells just above the hollow space in the gastrula (archenteron).
Neurulation is the process by which the neural tube is formed.
This occurs during the first month of gestation in humans. Once the neural tube has formed the developing embryo is known as a neurula.
Neurulation Process
The neural tube originates as a plate of the dorsal ectoderm just above the notochord.
The neural plate cells change
shape causing the neural plate to bend inwards forming the neural groove.The edges of the neural plate join together
separating the neural plate cells from the ectoderm.
The cells at the edges of the neural plate form the neural crest which ultimately forms the PNS.
The neural tube cells continue to proliferate by mitosis and differentiate to form the mature neurons of the CNS.
The neural tube lengthens as the animal grows. In humans the central canal in the spinal cord is the remainder of the embryonic neural tube.
Cell division stops before birth in most of the nervous system, the brain however has regions that continue to divide until early adulthood.
Spina bifida
Incomplete closure of the neural tube leads to a
condition known as spina bifida.
Sometimes the two parts of the neural arch do not fuse completely, leaving a gap.
This lack of closure exposes the developing neural tissue to the amniotic fluid. This condition produces a range of effects from very mild to debilitating.
Migration of Neurons
Neurons do not always develop in the location they will ultimately be used.
Neuronal migration occurs in three stages:
Leading edge extension
Nuclear translocation
Retraction of trailing process
The cytoplasm and organelles are moved along contractile actin filaments from trailing end to leading edge.
Axon Growth and Development
Immature neurons do not have an axon. One axon develops from each neuron and many dendrites often develop from the cell body.
Chemical signals determine the development of the axon and the direction of growth.
In some cases the cells in the neural tube form short axons to connect to other axons in the CNS while others can form axons more than one meter long in humans.
As long as the cell body remains undamaged, the axon may be able to regrow if damaged. However, recovery is dependent upon the cells ability to re-establish connections with the other cells it needs to communicate.
Synapses
Synapses develop between neurons and the cells they communicate with.
Synapse development requires the production of both the synaptic vesicles
and receptors as well as changes must be made to the synaptic cleft.
Most neurons form multiple synapses to allow for more complex communication
