biology

Synaptic scaling

Synaptic scaling is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Synaptic scaling rather than just read about it. In short: In neuroscience, synaptic scaling (or homeostatic scaling) is a form of homeostatic plasticity, in which the brain responds to chronically elevated activity in a neural circuit with negative feedback, allowing individual neurons to reduce their overall action potential firing rate. Where Hebbian plasticity mechanisms modify neural synaptic connections selectively, synaptic scaling normalizes all neural synaptic conn…

Key takeaways

Synaptic scaling belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Synaptic scaling to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Synaptic scaling from memory before moving on to harder problems.

Reference excerpt

In neuroscience, synaptic scaling (or homeostatic scaling) is a form of homeostatic plasticity, in which the brain responds to chronically elevated activity in a neural circuit with negative feedback, allowing individual neurons to reduce their overall action potential firing rate. Where Hebbian plasticity mechanisms modify neural synaptic connections selectively, synaptic scaling normalizes all neural synaptic connections by decreasing the strength of each synapse by the same factor (multiplicative change), so that the relative synaptic weighting of each synapse is preserved.

Cellular components involved (Chemical) Synaptic connection: At chemical synapses, pre-synaptic neurons release vesicles containing neurotransmitters into the synaptic cleft. The extracellular neurotransmitters then interact with particular post-synaptic transmembrane protein receptors to allow a fraction of the neurotransmitters into the post-synaptic neuron. Pre-synaptic vesicles : Vesicles are the means of chemical-synaptic plasticity. Pre-synaptic neurons relay information (in the form of neurotransmitters) to post-synaptic neurons via vesicles. The neurotransmitters inside vesicles are transported to the synaptic cleft where they interact with neurotransmitter specific post-synaptic protein receptors. Glutamate: Glutamate is the primary excitatory neurotransmitter within vertebrates and plays a large role in synaptic plasticity. Stimulus to the pre-synaptic neurons triggers glutamate release into the synaptic cleft via pre-synaptic vesicle release. Once in the synaptic cleft, glutamate can bind and activate post-synaptic glutamatergic protein receptors such as NMDA and AMPA receptors. Post-synaptic AMPA receptor: AMPA Receptors are trans-membrane protein ionotropic receptors that open and close quickly and are responsible for fast excitatory synaptic communication in the central nervous system. AMPA receptors have four subunits that glutamate can bind to. Depending on the AMPA receptor subunit compositions, the receptor can be permeable to cations such as calcium, sodium, or potassium

Interactions Synaptic scaling is a post-synaptic homeostatic plasticity mechanism that takes place with changes in the quantity of AMPA receptors at a post-synaptic terminal (the tip of the dendrite belonging to the post-synaptic neuron that meets with the tip of an axon belonging to the pre-synaptic neuron) of a neuron. This closed-loop process gives a neuron the ability to have global negative feedback control of synaptic strength of all its synaptic connections by altering the probability of glutamate (the most common excitatory neurotransmitter) making contact with post-synaptic AMPA receptors. Therefore, a neuron's ability to modulate the quantity of post-synaptic AMPA receptors gives it the ability to achieve a set action potential firing rate. The probability of glutamate making contact with a post-synaptic AMPA receptor is proportional to the concentration of both trans-membrane glutamate and post-synaptic AMPA receptors. When glutamate and post-synaptic AMPA receptors interact, the post-synaptic cell experiences a temporary depolarizing current, known as an EPSP (excitatory postsynaptic potential). Spatial and temporal accumulation of EPSPs at the post-synaptic neuron increases the likelihood of the neuron firing an action potential. Therefore, the concentrations of extra-cellular glutamate (and other cations) and the quantity of post-synaptic AMPA receptors are directly correlated to a neurons' action potential firing rate. Some theories suggest each neuron uses calcium-dependent cellular sensors to detect their own action potential firing rate. These sensors also formulate input for cell-specific homeostatic plasticity regulation systems. In synaptic scaling, neurons use this information to determine a scale factor. Each neuron subsequently uses the scaling factor to globally scale (either up-regulate or down-regulate) the quantity of transmembrane AMPA receptors at all post-synaptic sites. Some research indicates there are two mechanistically distinct forms of homeostatic plasticity involving trafficking or translation of AMPA receptors at post-synapse of synaptic connections:

Local synthesis of AMPA receptors: Local area AMPA receptor synthesis takes place within a time scale of 4 hours. mRNA translation frequency inside the post-synaptic neuron alters the quantity of local AMPA receptors produced. This mechanism is used to alter the quantity of post synaptic AMPA receptors over short time periods. Global synaptic scaling: This form of homeostatic plasticity takes place over a time period of days (24–48 hours) and has a more pronounced effect on the overall firing rate of neurons than local AMPA receptor synthesis. Various intra-cellular transport mechanisms help AMPA receptors migrate to the post-synaptic cleft from the entire cell.

Mechanisms

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Synaptic scaling

Start with the simplest possible case. Write down what Synaptic scaling claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Synaptic scaling before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Synaptic scaling ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Synaptic scaling

In research: Synaptic scaling appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Synaptic scaling in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Synaptic scaling is common in secondary-school and first-year university syllabi. It links to neighbouring topics Neuroplasticity, so understanding it makes those chapters shorter.
In everyday life: Look for Synaptic scaling outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Synaptic scaling in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Synaptic scaling means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Synaptic scaling out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Synaptic scaling in simple terms?

Why does Synaptic scaling matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Synaptic scaling?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Synaptic scaling.