Chapter 5: Development and Plasticity of the Brain Flashcards
processes of growth and differentiation of the brain
starts developing at 2 weeks
-processes: proliferation, migration, differentiation, myelination, and synaptogenesis *diagram pg 124-5
Proliferation
- production of new cells, cell division
* diagram pg 124-5
Migration
- neurons and glia move to where they are needed
- guided by immunoglobulins and chemokines
- diagram pg 124-5
Differentiation
- forms axons and dendrites
- initially looks like any other cell
- diagram pg 124-5
Myelination
- glia produces myelin
- forms 1st in spinal cord, then hindbrain, midbrain, forebrain
- continues gradually for decades
- diagram pg 124-5
synaptogenesis
- formation of synapses
- begins before birth and continues throughout life as neurons form new synapses and discard old ones
- diagram pg 124-5
why there is initial overproduction of neurons and how axons follow chemical paths to their destinations and make functional connections, thereby allowing them to survive.
competition between axons in forming functional synapses.
- growing axons follows path of cell- surface molecules attracted by some chemicals and repelled by others in a process that steers axon in the right direction
- follow specific chemical gradient
ex) axons with high concentration of ToPov connect to tectal cells with highest concentration of ToPov, lowest concentration connect to tectal cells with lowest concentration - process does not have to have perfect accuracy as axons form synapses onto many cells in the correct general location, over time some connections are strengthened and others eliminated
- neurtrophins steer new axonal branches in the right direction
Neural darwinism
- start with more neurons and synapses than we can keep because synapses form with approximate accuracy and a selection process keeps some and rejects others
- competing axons
Survival of the neuron
after neuron forms synapse onto a muscle, the muscle delivers nerve growth factor (protein) that promotes survival and growth of the axon
- if the axon does not receive NGF it dies
- if axon does not make contact with correct post synaptic cell by a certain age the neuron kills itself (apoptosis)
- overproduces because CNS is able to match # of incoming axons to receiving cells, it doesn’t know exactly how many it will need
reasons why the developing brain is vulnerable to chemical insults
- early stages of life are critical (gastrulation) because if something goes wrong here you have problems for the rest of your life
- fetal alcohol syndrome: alcohol suppresses release of excitatory glutamate and enhances GABA (inhibitory) meaning far less neurons receive excitation and neurotrophins than normal resulting in apoptosis
- also susceptible to cocaine, smoking, antidepressants, and stressful experiences
describe the effects of experience on the brain
- axons and dendrites continue to modify structure throughout life
- physical activity enhances cognitive processes and brain anatomy
- ex) blind- increases attention to touch or sound which the brain adapts to, does not change receptors in ears or skin, auditory and sensory stimuli in blind activate area usually meant for visual area of cortex
ex) - reading- learned to read in adulthood vs hot had more grey matter than non readers - musicians= parts of brain related to hearing and finger control are larger in professionals
describe the processes by which strokes damage the brain and several means of lessening the damage
- blood clot reduces blood flow to the brain (stroke
- ischemia more common
- ruptured artery (hemorrhage) less common
- neurons deprived of blood lose O2 and glucose (ischemia) or flooded with excess O2, Ca2+, and chemical can lead to edema
- both types impair K+/Na+ pump
- edema and increased concentration of Na+= excess glutamate released which over stimulates neurons, excess positive ions block metabolism in mitochondria and kills neurons
- as neurons die microglia proliferate and remove products of dead neurons and supply neurotrophins that promote survival of remaining neurons
Treatment of stroke ASAP
ASAP:
- drug tissue plasminogen activator within 3 hours breaks up clots, can make hemorrhage stroke worse therefore need an MRI to confirm which type
- block glutamate synapses, block Ca2+ entry, have not seen much benefit in humans yet
- cool people down to slow harmful processes (34-35C)
- exposure to cannabinoids (lab animal tested) by slowing glutamate release
mechanisms of recovery after brain damage and how various therapies promote recovery
- increase brain stimulation
- increase activity in opposite side of brian because connection has been compromised
- damaged axons grow back under certain circumstances
- In peripheral NS axon extends into 1 of the limbs and grows back 1mm/day if crushed, if cut may not have a path to follow
- scar tissue on a cut axon blocks regrowth later researchers working on ways such as:
- > building protein bridge
- > injecting neurotrophins
- > deleting gene responsible for inhibiting mTOR (enables regrowth of axons in adult spinal cord)
- relearning how to do things with parts of the brain that are left, may still have memory of how to do something but need to relearn the motor movements
Axon sprouting
-other axons form new branches to take up open space (diagram p.145)
