Development Flashcards
How does a human embryo first begin it’s development?
The human embryo first develops into three layers:
- The endoderm (Bottom layer)
- Mesoderm (middle layer)
- The ectoderm (top layer) –> becomes the nervous system (and skin).
What happens to the ectoderm between conception to day 25 of development?
The cells of the ectoderm thicken to become the neural groove. between 20-22 days, the tips of the neural groove rise and come together to form the neural tube.
The neural tube develops into the forebrain, mid brain, and hindbrain. The interior of the neural tube becomes the cerebral ventricles and the central canal of the spinal cord.
Describe the characteristics of an 8 week old embryo
The embryo shows the rudimentary start of almost all organ systems. At this point it’s head is equal to about half of it’s total size.
What is the distinction between an embryo versus a fetus?
Embryo is a developing human before 10weeks. A fetus is a developing human after 10 weeks before birth.
What are the 6 stages of nervous system development?
- Neurogenesis: the mitotic division of non neuronal cells to produce neurons.
- Cell Migration: The massive movement of nerve cells (or their precursors to establish distinct nerve cell populations.) Cells on the inner layers of the brain are older than cells on the outer layer.
- Cell differentiation: the refining of cells into distinctive types of neurons and glial cells
- Synaptogenesis: the establishment of synaptic connections as axons and dendrites grow.
- Neuronal death: the selective death of many nerve cells.
- Synapse rearrangement: the loss of some synapses and the development of others to refine synaptic connections which extend throughout our lifespan.
What makes humans different from most other primates in terms of neural development?
Human Brains massively develop and grow after birth unlike most other primates.
Describe the process of neural development through the six stages (don’t list the stages here, say what is actually happening).
Neurogenesis: non-neuronal cells divide through mitosis and they form the ventricular zone inside the neural tube. During cell migration, they leave the ventricular layer. When they reach their destination, during cell differentiation, they begin to express particular genes to make the proteins they need. Once they have their specific appearance and function, they begin synaptogenesis and begin to send signals to each other. Cell-cell interactions affect the development of each cell they communicate with. Cell death, also called apoptosis is the result of complex interactions and competition for neurotrophic factors with other cells causing the cell to express its own death gene (which then affects other cells too). Cell death leads to the surviving neurons growing longer and more elaborate dendrites and forming more complex networks of synapses.
What is the purpose of cell-cell interactions?
Cell-cell interactions ensure that there are enough cells of each kind to develop, communication between the cells tells them what other cells are around them and what types of cells are needed. This way they can differentiate appropriately and become properly integrated.
What causes the postnatal increase in brain weight?
Not caused by an increase in neurons. Is caused by increase in neuron size, branching of dendrites, elaboration of synapses, increase of myelin, and addition of glial cells.
Is adult neurogenesis possible?
Yes, to a limited extent. It mostly occurs in the hippocampus and seems to enhance hippocampal dependent learning.
Why is cell death (apoptosis) important?
It ensures that the brain fits inside the skull and ensures that only strong, relevant synapses live.
What is the process through which cells compete for neurotrophic factors?
Neurotrophic factors are chemicals that “feed” neurons to keep them alive. Different Neurotrophic factors are produced by different target cell groups. Innervating neurons take up particular neurotrophic factors and transport them to their cell bodies. When they reach the cell body, the neurotrophic factors regulate the expression of various genes and influence the cell’s development. If the cell gets sufficient amounts of the appropriate neurotrophic factor than they survive. Because the amount of neurotrophic factor matches the number of target cells, this process results in a rough matching of the size of the target cell and the number of innervating neurons.
Does neurotrophic competition stop after the cell death stage of development?
No, later in development, axons also compete for neurotrophic factors. Active synapses compete more successfully than inactive synapses meaning that they are more likely to survive. Out experience affects synaptic activity therefore our experience helps determine which synapses live and which die.
What happens to spinal motor neurons during synaptic rearrangement?
Before synaptic rearrangement, many spinal motor neurons innervate each muscle fiber. During synaptic rearrangement, the spinal motor neurons retract their axons until only one neuron innervates one muscle fiber. (i.e. every muscle fiber has a single spinal motor neuron that innervates it.)
How long does synaptic rearrangement go on for?
It begins in earnest after the prenatal major cell death stage and ultimately continues until our 20s. During adolescence, the thinning of synapses is focused on the cerebral cortex.
