Flashcards in Neuroplasticity Deck (47):
What is neuroplasticity?
The ability of neurons to change their function, chemical profile, or structure
What are 2 essential characteristics of neuroplasticity?
- It is spatial in that it can occur at all levels
- It is temporal in that it can occur over a long period of time and is not periodic
What is neuroplasticity involved in?
Learning and creation of new memories and skills and is essential for recovery from damage to the CNS
Neuroplasticity encompasses what 3 mechanisms?
- Experience-dependent plasticity (learning and memory)
- Cellular recovery after injury
What does habituation refer to?
a decrease in response to a repeated, benign stimulus
What is habituation due to?
a decrease in synaptic activity between sensory neurons and interneurons
PT/OT are techniques and exercises that intended to do what in terms of habituation?
decrease the neural response to a stimulus by repeatedly putting a patient in positions of increased sensitivity in hopes to decrease these levels over time
Unlike habituation, learning and memory require what?
What is experience-dependent plasticity?
A complex process involving persistent, long-lasting changes in the strength of synapses between neurons and in neural networks
Describe brain activity during the initial phases of motor learning
large and diffuse regions of the brain are active
Describe brain activity when tasks are repeated
the number of active regions in the brain are reduced in comparison to the initial phases
Describe brain activity when a task is learned
only small, distinct regions of the brain show an increased activity when performing the task
What does experience-dependent plasticity require?
The synthesis of new proteins, the growth of new synapses, and the modification of existing synapses
The cellular mechanism for learning and memory results from what 5 things?
- activation of second-messenger systems
- alteration in the level of intracellular C2+ in the postsynaptic neuron
- alteration in activity of protein kinase
- mediate the early stage of synaptic plasticity
- long-lasting synaptic strength by alteration in the gene transcription
What are the 2 main types of plasticity?
- Long-term potentiation (LTP)
- Long-term depression (LTD)
LTP and LTD can occur presynaptically through what? And postsynaptically through what?
- presynaptically through changes in NT release
- postsynaptically through changes in receptor density and efficiency
Silent vs. Active Synapses
- Silent synapses are characterized by lack of functional glutamate AMPA receptors
- Active synapses occur when mobile AMPA receptors are inserted into the synaptic membrane
Describe the mechanism of LTP
the conversion of silent synapses to active synapses via the activation of NMDA which increases Ca2+ which results in the insertion of AMPA receptors into the cell membrane, which increases the likelihood that the postsynaptic neuron will be depolarized when glutamate is released
Describe the mechanism of LTD
the conversion of active synapses to silent synapses by the removal of AMPA receptors from the postsynaptic membrane, making the membrane less likely to be depolarized when glutamate is released from the presynaptic neuron
What does Transcranial Magnetic Stimulation (TMS) to the motor complex and other brain areas involved in motor learning do?
Enhances or inhibits motor learning and memory formation, depending on the frequency and experimental protocol used
Magnetic stimulation of the brain is thought to induce synaptic plasticity via what two things?
LTP- or LTD-type mechanisms
How do astrocytes contribute to experience-dependent plasticity?
Neurons release a NT that stimulates the release of gliotransmitters by the astrocyte which modulate neuronal activity and synaptic transmission
How do astrocytes influence synaptic plasticity?
Through modulating NT release and receptor expression at the postsynaptic membrane
Damage to axons results in what? Damage to the cell body results in what?
Injuries that damage or sever axons cause degeneration but may not result in cell death, whereas injury that destroys the cell body of a neuron leads to death of the cell
Describe the changes involved in Wallerian degeneration
1) the axon terminal degenerates
2) myelin breaks down and forms debris
3) the cell body undergoes metabolic changes
4) presynaptic terminals retract from the dying cell body
5) postsynaptic cells degenerate
Following an injury, nervous system goes through a process called what?
What are the 2 forms of sprouting?
Describe collateral sprouting
a denervated neuron attracts side sprouts from nearby undamaged axons
Describe regenerative sprouting
the injured axon issues side sprouts to form new synapses with undamaged neurons
Axon recovery typically progresses with a growth rate of __ per day
When should exercise begin following a lesion and why?
5 days after lesion to ensure axonal regeneration and muscle re-innervation
The functional regeneration of axon occurs due to what?
The production of nerve growth factor by Schwann cells
Describe the process following axonal injury in the CNS
The same processes (retraction, degeneration and chromatolysis) that follows a peripheral axonal injury also occur in the axonal injury in the CNS, however regeneration does not occur
Why does regeneration not occur in the CNS?
due to glial scars or an absence of nerve growth factor
The extent of deficits following damage to the CNS depends on what?
the degree of damage to white fiber tracts in the spinal cord and the vertebral level of the injury
What are the 4 synaptic mechanisms to overcome damage following CNS injury?
- Recovery of synaptic effectiveness
- Denervation hypersensitivity
- Synaptic hypereffectiveness
- Unmasking of silent synapses
How is synaptic effectiveness recovered?
When local edema that interferes with action potential conduction is reduced synaptic effectiveness is restored
When does denervation hypersensitivity occur?
When presynaptic axon terminals are destroyed and new receptor sites develop on the postsynaptic membrane in response to the reduction in the NT released, so when NT are released from nearby axons, there is a hypersensitive response.
When does synaptic hypereffectiveness occur?
When only some branches of presynaptic axon are destroyed this leads to an accumulation of NT in the undamaged axon terminals, resulting in excessive release of transmitter at the remaining terminals
How are silent synapses unmasked?
when (AMPA) receptors move into the postsynaptic membrane making the synapse active
Cortical representation areas, referred to as cortical maps or homunculus, can be modified by what 4 things?
- sensory input
- brain injury
Cortical areas routinely adjust to changes in _________ and develop new functions dependent on ___________.
required motor output
Repeated stimulation of somatosensory pathways can cause what? What does this lead to?
Increases in inhibitory neurotransmitters which decreases the sensory cortex response to overstimulation
Why do oxygen-deprived neurons die?
They release large quantities of glutamate which is toxic to neurons
What is Excitotoxicity?
cell death caused by overexcitation of neurons
What are the 3 pathways in which excitotoxicity can occur?
- increased glycolysis
- increased intracellular water
- activated protein enzymes