The Basic Processes of Neurodevelopment Flashcards
What are the 6 processes?
Cell birth Cell migration Cell differentiation and maturation Synpatogenesis Cell death and synaptic pruning Myelination
What does cell birth refer too?
The production of new neurons
How many neurons are found in one hemisphere?
10 billion cells
What is the peak of neural development?
250,000 neurons are born per minute
Where does cell birth take place?
The neural tube - in the cerebral spinal fluid
What are stem cells?
Immature cells
What do stem cells form?
They divide, some stay and continue to be a stem cell and some become Progenitor (precursor cells)
What can the progenitor cell be?
Either a neuroblast (will become a neuron) or a glioblast (will become glia)
What happens once the progenitor cells are formed?
They are formed in the centre of the neural tube but won’t stay there - start to migrate out of this location of birth (migration)
What does migration refer too?
The movement of newly formed neurons and glia to their final destinations
Why does migration occur?
Because they need to populate different parts of the brain
When do the neurons reach their destination?
Some don’t reach it till adulthood
How does migration occur?
Chemical signals - signals which attract them to migrate to a particular location
Physical support - from radial glia
What are radial glia?
Special cells which are temporarily there for physical support - cells climb along the radial glia with the help of extensions
Axons extend to the outer part of the tube - immaturing neurons use them to find a way and to migrate towards layers
What is the function of radial glia?
Scaffolding - help them migrate in a particular way
Where do the cells migrate too?
First neurons which migrate stay closer to the inner surface
the rest stand on their shoulders, climbing higher and higher, filling all the layers of the cortex
Why is it important migration takes place undisturbed?
Because the cortex has different layers of cells with different functions - need the neurons to migrate to the correct place
What happens when neurons meet their point of destination?
They start to differentiate
What does differentiation mean?
Expressing particular genes that will allow them to become a cell
Start to form an axon and dendrites that give them a distinctive shape
How do they differentiate?
Dendritic arborisation - branching
Growth of dendritic spines
Why are dendritic spines there?
To increase the surface area of the dendrites, the more spines we have, the more area we have on the dendrites
other neurons can make other contact - synapsing on other neurons - more available places for them to make contact
What is the difference in Brocas area in a newborn compared with older children?
More dendritic branches in the cells in brocas area in the older child - more differentiation
What causes the neuron to differentiate in a particular way?
The destination - final region
What do immature cells acquire when differentiating?
The characteristics of the cells in the region of implantation, If implanted early - if neurons reach maturity, we cannot do that, they will always have characteristics they came from
Why is the area of destination important?
They will acquire the characteristics of the area that brain has
What does morphology of neurons refer too?
Many different neurons found in different locations depending on where you look
Can have lots of different neurons in the brain
What does synaptogenesis refer too?
The formation of synapses / connections between neurons
When does synaptogenesis occur?
Begins after the neuron has differentiated
occurs throughout life as a response to our experiences, slows down later on
neurons are constantly forming new connections and disregarding old ones
What does synaptic pruning mean?
Neurons are constantly forming new connections and disregarding old ones - have more than we need
What is the growing end of an axon called?
A growth cone - searching for contact
How are contacts made between neurons?
Neurons have a growth cone, these develop extensions known as filopodia - make contact with another cell
What are growth cones attracted too?
Chemicals released from target cells:
cell adhesion molecules
tropic molecules - attract or repel growth cones
What are filopodia?
The extensions on the growth cone
What happens when axons reach their targets?
They form synapses with several cells - but have more connections than they will even need
What does neural darwinism mean?
Some connections will be strengthened and some will be eliminated - lots of competition in regards to synapses
Most successful connections will survive
What instructs neuron to survive?
Proteins secreted by target cells promote the survival and growth - survival signals
What factors aid survival of neurons?
Neurotophic factors
What happens if a neuron doesn’t receive a survival signal?
It will degenerate and die through apoptosis
What is apoptosis?
Programmed cell death, silent, good death, happens as we have more than we need
Function of apoptosis
Enables the exact matching of the number of incoming axons to the number of receiving cells
if things going well, apoptosis is inhibited
What is necrosis?
Loud, powerful, damaging death which occurs after injury
How can immature neurons avoid apoptosis?
Neurotrophin (growth factors) from its target cell
Active communication with other neurons which leads to strengthening of their synapses
What does synaptic pruning mean?
Dendritic branches are not fixed, they extend, retract or even disappear
spines can appear or disappear over a short period of time
these are related to learning or experience
What does myelination mean?
The process by which glia produce the fatty sheath which covers the axons of neurons
occurs in the spinal cord then in the hindbrain, midbrain and forebrain - front to back
Function of myelination
Speed up transition of neural impulses
Aids motor behaviour - correlation between myelination and ability to grasp
How long does myelination take?
It is a slow process - occurs gradually for decades - depending on the region - Cortex till 18 but prefrontal cortex takes longe
Difference between myelination in the PNS and the CNS
PNS - Schwann cells - dedicate themselves exclusively to the axon, 2 Schwann cell on one part of the axon
CNS - oligodendroglia (have a few branches) - not all of the branches are on one axon, each branch wraps around a different segment of a different axon. Lots of axon segments covered by one oligodendroglia
