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• If axons are active at a very slow rate, their synapses may decrease in responsiveness—a process known as long term depression (LTD)
• Habituation of the gill-withdrawal reflex in Aplysia depends on a mechanism that decreases the release of transmitter from a particular presynaptic neuron
• At many synapses, LTP relates to increased release of transmitter from the presynaptic neuron, in addition to or instead of changes in the postsynaptic neuron
• Hebbian synapse


  One that is strengthened by being repeatedly active when the postsynaptic neuron produces action potentials
• When calcium enters through the NMDA-controlled channels


  1. It activates a protein that sets in motion a series of events that build more AMPA receptors and increase the growth of dendritic branches

  2. These changes increase the later responsiveness of the dendrite to incoming glutamate at AMPA receptors
• Long-term potentiation (LTP) is an enhancement of response at certain synapses because of a brief but intense series of stimuli delivered to a neuron, generally by two or more axons delivering simultaneous inputs
• LTP in hippocampal neurons


  1. Repeated glutamate excitation of AMPA receptors depolarizes the membrane

  2. The depolarization removes magnesium ions that had been blocking NMDA receptors

  3. Glutamate is then able to excite the NMDA receptors, opening a channel for calcium ions to enter the neuron
• Although researchers hope to develop drugs or procedures to improve memory, at this point no such procedure is safe and effective, with the exception of mild stimulants such as caffeine
• Sensitization of the gill-withdrawal reflex in Aplysia occurs when serotonin blocks potassium channels in a presynaptic neuron and thereby prolongs the release of transmitter from that neuron
• BDNF (Brain-Derived Neurotrophic Factor)


  • Protein crucial for growth, survival, and maintenance of neurons
  • Involved in synaptic plasticity, learning, and memory processes in the brain
• NMDA receptor


  • Type of ion channel receptor found in the brain involved in the transmission of signals between neurons
  • Plays a crucial role in synaptic plasticity and important for learning and memory processes
• Hebbian synapse


  • Concept stating "cells that fire together, wire together"
  • Synaptic connections are strengthened when presynaptic neuron repeatedly activates postsynaptic neuron
• Specificity


  • In the context of synaptic plasticity, ability of synapses to undergo changes in strength selectively in response to specific patterns of neuronal activity
  • Precisely encodes and stores information in the brain
• Habituation


  • Form of non-associative learning where an organism reduces or ignores its response to a repeated or irrelevant stimulus
  • Basic form of learning that filters out repetitive or unimportant stimuli from the environment
• Sensitization


  • Form of non-associative learning where organism's response to a stimulus becomes stronger after repeated exposure to a noxious or arousing stimulus
  • Associated with increased responsiveness or sensitivity to subsequent stimuli
• Associativity


  • Ability of two or more inputs to activate a neuron and strengthen the connections between them
  • Fundamental property of synaptic plasticity important for learning and memory formation
• Long-term potentiation (LTP)


  • Form of synaptic plasticity leading to a long-lasting increase in the strength of synaptic connections
  • Associated with an increase in the number or function of neurotransmitter receptors at the synapse
  • Considered a cellular mechanism underlying learning and memory
• AMPA receptor


  • Ion channels found in the brain involved in the transmission of signals between neurons
  • Important for fast excitatory synaptic transmission in the central nervous system
• Cooperativity


  • Phenomenon where multiple synapses acting together produce a stronger response than the sum of their individual responses
  • Important mechanism for strengthening synaptic connections and enhancing neuronal communication
• Long-term depression (LTD)


  • Form of synaptic plasticity leading to a long-lasting decrease in the strength of synaptic connections
  • Associated with a decrease in the number or function of neurotransmitter receptors at the synapse
• Retrograde transmitter


  • Chemical messenger released from postsynaptic neuron acting on presynaptic neuron
  • Modulates synaptic strength and plasticity