Trophic factors and neuronal survival 1 Flashcards
What do axons do when they reach their appropriate targets?
Form synapses
What do trophic factors allow in the final stages of neurodevelopment?
Survival of a subset of neurons.
Formation and maintenance of appropriate connections.
What are neuromuscular junctions?
Junctions between nerve cells and muscle cells
What happens to neurons that do not connect with a target?
They undergo apoptosis
Why do a lot of the motor neurons that are formed die off?
Having a lot formed provides a check that they made the correct connections–> make a lot hoping some make the right connection, and the ones that dont are killed off
How are neuromuscular junctions made?
Many attempts at connections are made, and each one is eliminated until each muscle fibre is innervated by only one motor neuron
What do axons require from the target tissue to survive?
Survival (trophic) factors
What happens to inappropriate connections?
cells in the projecting neuronal group and the target begin apoptosis
What happens to good connections?
They are preserved (axon and thing axon has made contact with)
Programmed cell death in neuronal connections?
elimination of excess cells by selecting those that make the correct connection followed by pruning of redundant connections
Purpose of refinement in neuronal connections?
Have a limited number of neurons innervating the target, and the innervation from a single neuron is focused on a particular component of the target
Why are neurons not initially dependent on target cells?
In some places (e.g. targets in the foot) the target is very far away from the origin
Other than the final target, what are growth cones dependent on?
Intermediate targets that also provide a trophic input
Factors in the pathway–> glia etc
What is target switching?
During development of the brain some neurons must innervate multiple targets or they must innervate a secondary target first before reaching the primary target
What are the neurotrophins?
A family of neurotrophic factors for neuronal survival
What are neurotrophins secreted by?
target cells (neurons or innervated tissues)
What is a neurotrophic factor?
Something that promotes the survival of a neuron
How was NGF identified?
Via its roles in the PNS
Where is NGF most prominent?
Sensory ganglia
What are the sensory ganglia?
Sensory ganglia are neurons of the peripheral nervous system (PNS) derived from neural crest cells
What did Rita Levi-Montalcini discover about tumour sarcoma cells?
They secrete a factor that promotes the growth of neurites
What is a neurite?
A fine projection from a neuron
Which animal secretion did Rita Levi-Montalcini discover was rich in NGF?
Snake venom
What is NGF necessary for?
Neuronal survival
