Chloe Zhang
Neuroplasticity, also known as neural plasticity or brain plasticity, is the ability of the brain to adapt and reorganise its neural connections in response to new experiences, learning, and environmental changes. It involves functional and structural changes in the brain, allowing it to modify its behaviour and thoughts. Synaptic plasticity, a key aspect of neuroplasticity, refers to the changes in synaptic strength and the effectiveness of neuronal communication. These changes are influenced by the quantity of neurotransmitters released into the synapse and the number of neurotransmitter receptors present. The release of neurotransmitters and the dynamics of plasticity are regulated by calcium accumulation and subsequent biochemical modifications. The understanding of neuroplasticity has evolved since the early 1900s, with pioneers like Santiago Ramón y Cajal and Donald Hebb contributing significantly to the field.
| Characteristics | Values |
|---|---|
| Definition | Neuroplasticity, also known as neural plasticity or brain plasticity, is the ability of the brain to change and adapt to new information. |
| Synapses | Synapses are the junctions between neurons that allow them to communicate. |
| Neurotransmitters | Neurotransmitters are chemicals that transmit signals between neurons. Changes in the quantity of neurotransmitters released into a synapse can lead to synaptic plasticity. |
| Calcium | Calcium plays a crucial role in synaptic plasticity by regulating the release of neurotransmitters and modifying biochemical processes. |
| Stimulation | Repetitive or tetanic stimulation of synapses can lead to longer-lasting forms of plasticity, such as augmentation and post-tetanic potentiation (PTP). |
| Depression | Some synapses exhibit depression or a decrease in synaptic strength, which can last for several seconds or minutes. |
| Regulatory Forms | Scaling and metaplasticity provide negative feedback to prevent positive feedback loops that could lead to unstable neural activity. |
| Homeostasis | Homeostatic plasticity helps maintain the stability of the synaptic network over time. |
| Neurogenesis | Adult neurogenesis refers to the brain's ability to generate new neurons, which has been observed in animals but not conclusively in humans. |
| Learning and Memory | Synaptic plasticity is important for learning and memory formation, with long-term potentiation (LTP) being a key mechanism. |
| Recovery | Neuroplasticity plays a role in recovering from brain injuries, such as strokes or traumatic brain injuries (TBIs). |
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What You'll Learn
Short-term plasticity
Neuroplasticity, also known as neural plasticity or brain plasticity, is a process that involves adaptive structural and functional changes to the brain. It is defined as the ability of the nervous system to change its activity in response to intrinsic or extrinsic stimuli by reorganizing its structure, functions, or connections.
Synaptic plasticity is the ability of synapses to strengthen or weaken over time in response to increases or decreases in their activity. It is one of the important neurochemical foundations of learning and memory. Synaptic plasticity can be further classified into short-term plasticity and long-term plasticity.
STP plays an important role in short-term adaptations to sensory inputs, transient changes in behavioral states, and short-lasting forms of memory. It is also involved in processes such as motor control, speech recognition, and working memory. Most forms of STP are triggered by short bursts of activity causing a transient accumulation of calcium in presynaptic nerve terminals, which then causes changes in the probability of neurotransmitter release.
Mathematical and computational models have been extensively used to study the mechanisms and roles of STP. These models provide insights into the biological basis and dynamics of STP, including the involvement of calcium channels and the activation of presynaptic autoreceptors.
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Long-term plasticity
Long-term synaptic plasticity was first reported in 1973 by Terje Lømo and Tim Bliss, who studied the rabbit hippocampus. They discovered that rapidly and repeatedly activating the synapses made them stronger, and this long-lasting increase in synaptic strength was termed long-term potentiation. The reverse phenomenon, in which synapses become weaker for extended periods, is called long-term depression. The direction in which synapses change depends on their activity patterns. Very active synapses are likely to become stronger (LTP), while less active synapses tend to become weaker (LTD).
Presynaptic LTP has been observed in various brain regions, and the number of pathways implicated in its induction and expression has greatly expanded. Scientists have debated whether the change in synaptic strength during long-term plasticity is primarily due to presynaptic alterations in neurotransmitter release or postsynaptic modifications in receptor numbers and/or biophysical properties.
Two regulatory forms of plasticity, scaling and metaplasticity, also exist to provide negative feedback. Synaptic scaling maintains the strengths of synapses relative to each other, gradually changing the numbers of NMDA receptors at the synapse over hours or days. Metaplasticity varies the threshold level at which plasticity occurs, allowing integrated responses to synaptic activity spaced over time and preventing saturated states of LTP and LTD.
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Neurotransmitter release
Neurotransmitters are chemical substances that are released from neurons in response to a given stimulus. Neurotransmitter release occurs at synapses, which are the sites of transmission of electrical nerve impulses between two neurons or between a neuron and a gland or muscle cell. Each synapse consists of a presynaptic cell, from which neurotransmitters are released; a postsynaptic cell, where neurotransmitters bind to receptors to exert their effects; and a synaptic cleft, the gap between the presynaptic cell and the postsynaptic cell that neurotransmitters move across once they are released.
Neurotransmitters are contained within synaptic vesicles, which are membrane-bound sacs. These vesicles are typically concentrated at high density in the ends of presynaptic neurons. The arrival of an action potential (a nerve impulse characterised by a rapid change in voltage across a membrane) at the presynaptic terminal stimulates the release of neurotransmitters into the synaptic gap. The binding of neurotransmitters to receptors on the postsynaptic membrane stimulates the regeneration of the action potential in the postsynaptic neuron.
There are many different neurotransmitters that may be released from neurons, including epinephrine, serotonin, dopamine, and glutamate. Each postsynaptic neuron may also form hundreds of competing synapses with many neurons. These variables account for the complex responses of the nervous system to any given stimulus.
The release of neurotransmitters is a crucial neurological mechanism for communication between neurons. Changes in the release of neurotransmitters can be indicative of a pharmacological response to a drug or toxin, pathology such as Parkinson's disease or addiction, or neuronal plasticity. Measuring neurotransmitter release is an important technique, and various methods are used to do so. For example, microdialysis is a minimally invasive method to measure neurotransmitter and other mediator releases in vivo. Fast-scanning cyclic voltammetry is another technique commonly used to measure dopamine and other monoamine releases from neurons.
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Calcium's role
Calcium is a key signalling ion involved in various intracellular and extracellular processes, including synaptic activity and cell-cell communication. Calcium is essential for the control of synaptic activity and memory formation, and it plays a crucial role in maintaining neuronal integrity and long-term cell survival.
In the context of neuroplasticity, calcium is particularly important for synaptic plasticity, which refers to the ability of synapses to strengthen or weaken over time in response to changes in their activity. Synaptic plasticity is one of the important neurochemical foundations of learning and memory. It often results from alterations in the quantity of neurotransmitters released into a synapse and changes in how effectively cells respond to those neurotransmitters.
Calcium is involved in synaptic plasticity through its role in regulating the release of neurotransmitters. Short-term synaptic plasticity, for example, is triggered by short bursts of activity that cause a transient accumulation of calcium in presynaptic nerve terminals. This increase in calcium leads to changes in the probability of neurotransmitter release by directly modifying the biochemical processes that underlie the release of neurotransmitters.
Additionally, calcium is involved in longer-lasting forms of synaptic plasticity, such as augmentation and post-tetanic potentiation (PTP). These forms of plasticity involve an increase in the probability of transmitter release due to the buildup of calcium concentration in the presynaptic terminal during stimulus trains. The residual calcium can combine with the calcium influx from subsequent stimuli, leading to an enhanced release of neurotransmitters or biochemical modifications in the presynaptic terminal.
Furthermore, calcium is essential for the activation of specific calcium-dependent signal transduction pathways and the expression of key protein effectors such as CaMKs, MAPK/ERKs, and CREB. Properly regulated calcium homeostasis supports normal brain physiology and neuronal health. Disruptions in calcium homeostasis, on the other hand, have been implicated in neurodegeneration and neurological disorders, highlighting the critical role of calcium in maintaining brain function and health.
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Synaptic strength
Synaptic plasticity can occur in both the short and long term. Short-term synaptic plasticity acts on a timescale of milliseconds to a few minutes, while long-term plasticity lasts from minutes to hours. Short-term changes in synaptic strength can be triggered by short bursts of activity, causing a transient accumulation of calcium in presynaptic nerve terminals. This increase in calcium leads to a higher probability of neurotransmitter release by modifying the biochemical processes involved in synaptic vesicle exocytosis.
Longer-lasting forms of synaptic plasticity can be observed following repetitive or tetanic stimulation of synapses with prolonged trains of high-frequency stimulation. Augmentation and post-tetanic potentiation (PTP) are two such forms of long-term synaptic plasticity, characterised by an enhancement of transmitter release lasting from seconds to several minutes. These processes are also mediated by an increase in calcium concentration in the presynaptic terminal, which enhances neurotransmitter release or leads to biochemical modifications of proteins in the terminal.
The balance between synaptic strengthening and weakening is crucial for effective information encoding. Regulatory forms of plasticity, such as scaling and metaplasticity, provide negative feedback to prevent positive feedback loops that could lead to cells firing too much or too little. Synaptic scaling, for instance, helps maintain the relative strengths of synapses by adjusting the amplitudes of excitatory postsynaptic potentials in response to continual excitation or inhibition.
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Frequently asked questions
Synaptic plasticity is the ability of synapses to strengthen or weaken over time, in response to increases or decreases in their activity.
Neurotransmitters play a crucial role in synaptic plasticity. Changes in the quantity of neurotransmitters released into a synapse and changes in how effectively cells respond to those neurotransmitters contribute to synaptic plasticity.
When a presynaptic neuron stimulates a postsynaptic neuron, the postsynaptic neuron responds by adding more neurotransmitter receptors, which lowers the threshold needed for stimulation by the presynaptic neuron. This enhances the synapse over time.
N-methyl D-aspartate receptors (NMDA receptors) and AMPA receptors are key players in synaptic plasticity. The number of these receptors on the membrane can be altered by synaptic activity, influencing the strength of the synaptic connection.
Synaptic plasticity is a specific form of neuroplasticity, which refers to the brain's ability to adapt and reorganize its neural connections. Neuroplasticity encompasses a broader range of functional and structural changes in the brain, including synaptic plasticity, neuronal regeneration, and functional reorganization.
