--- title: "Synaptic Plasticity and the Molecular Rules of Change" description: "Synaptic strength can change with activity. In a common timing rule, repeated input-before-target firing favours strengthening and reversed timing favours weakening. At many glutamate synapses, NMDA r" canonical: https://lightmysky.com/learn/science/synaptic-plasticity-and-the-molecular-rules-of-change-mt_HldevO4Lzw source: https://lightmysky.com/learn/science/synaptic-plasticity-and-the-molecular-rules-of-change-mt_HldevO4Lzw.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Synaptic Plasticity and the Molecular Rules of Change Synaptic strength can change with activity. In a common timing rule, repeated input-before-target firing favours strengthening and reversed timing favours weakening. At many glutamate synapses, NMDA receptors detect overlapping transmitter binding and depolarisation, allowing calcium entry that can initiate change. Subject: Science · Area: The Human Body · Ages 19 to 21 Page: https://lightmysky.com/learn/science/synaptic-plasticity-and-the-molecular-rules-of-change-mt_HldevO4Lzw ## Ready when they can - Explains how NMDA receptors detect overlapping glutamate binding and local depolarisation, with a suitable co-agonist bound. - Uses a stated spike-timing rule to predict strengthening or weakening without treating that rule as universal. - Links a lasting change in strength to a change in receptor number or transmitter release. ## Lesson: How synapses change strength At a synapse, a sending cell signals to a receiving cell. A spike is a brief electrical signal. Synaptic plasticity changes how strongly the connection transmits a signal. Long-term potentiation (LTP) is a lasting increase in strength; long-term depression (LTD) is a lasting decrease. In a common spike-timing rule, repeated close input-before-target spike pairs favour LTP. Reversing their order favours LTD. Other synapses can follow different rules. You have met receptors that open ion channels. At many glutamate synapses, NMDA receptor channels respond to overlapping binding and voltage conditions. Glutamate and a co-agonist, such as glycine, must bind. The receiving membrane must also depolarise enough to relieve a magnesium block. Depolarisation means becoming less negative. Calcium can then enter. Glutamate binding alone at resting voltage does not remove the block. *(drawing: Read from left to right. This shows the order of a repeated pairing protocol, not measured time intervals or a rule for every synapse.)* Calcium entry through NMDA receptors can start signalling that changes synaptic strength. It does not guarantee LTP. The calcium signal's size and time course, and the synapse's state, affect which pathways respond. Some pathways add AMPA receptors during LTP; others remove them during LTD. AMPA receptors are glutamate-gated channels that carry much of the fast excitatory current at these synapses. Calcium entry may also produce no lasting change. Strength changes can involve either side of a synapse. Adding working AMPA receptors can let the same glutamate release open more channels and produce a larger current under matched conditions. Removing receptors can reduce the response. Moving receptors into or out of the membrane is receptor trafficking. The sending terminal may instead change transmitter release per spike. A larger response alone does not identify which mechanism changed. NMDA channels can pass calcium when glutamate and a co-agonist are bound and local depolarisation relieves the magnesium block. Summed inputs can provide this depolarisation without a target spike. Input-before-target timing does not prove that one input caused the spike alone: other inputs may contribute. An active input need not strengthen, and an input outside a timing window need not weaken. **Recap.** Apply a timing rule only where it fits. NMDA receptors detect overlapping conditions; calcium signalling can lead to changes in receptor response or transmitter release. *Lesson, questions and flashcards written for this dataset. OpenStax Biology and Anatomy and Physiology were consulted for scientific background.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Transmitter Systems and Two Kinds of Receptor](https://lightmysky.com/learn/science/transmitter-systems-and-two-kinds-of-receptor-mt_yXaSbrBxua) ## Opens up - [Memory Systems: What Amnesia Separates](https://lightmysky.com/learn/science/memory-systems-what-amnesia-separates-mt_oNFXpEHl8b)