Lesson 10: Memory and Learning Flashcards
Neurotransmitters
There are two basic types of neurotransmitters:
Excitatory – excite the post synaptic neuron for a time , producing a depolarization that might trigger action potentials
Inhibitory – inhibit the formation of action potentials in the post synaptic neuron due to the membrane potential becoming more
negative when the neurotransmitter binds. This is called hyperpolarization.
Summation
Neurons often synapse with more than one other neuron. This is especially
true in the brain.
The release of excitatory neurotransmitter from one presynaptic neuron is
usually insufficient to trigger an action potential.
Some presynaptic neurons release an inhibitory neurotransmitter.
Summation is the combining of effects of all neurotransmitters from all
presynaptic neurons by a post synaptic neuron.
The formation of an action potential in a postsynaptic neuron depends upon
whether or not the threshold potential is reached.
The overall potential of a post synaptic neuron depends on the balance between excitatory and inhibitory effects of the neurotransmitters at every
synapse.
Speed of Neurotransmitter Action
Neurotransmitters can also be classified by the speed of their effects on a
postsynaptic neuron.
Slow-acting – also called neuromodulators. These neurotransmitters
take longer to affect the post synaptic neuron.
Fast –acting – affect the post synaptic neuron less than a millisecond
after release.
Fast – Acting
The fast – acting neurotransmitter receptors are gated ion –channels, which cause an immediate change in membrane potential.
Slow – Acting
Usually diffuse through surrounding fluid allowing them to affects several
neurons at once.
Do not affect ion movement across post synaptic membranes directly.
Use secondary messengers inside the neuron to affect the fast synaptic
transmission.
Dopamine, noradrenalin and serotonin are slow acting.
Memory and Learning
Memories can be held for a short time in short-term memory locations and
discarded if they become irrelevant or moved to long-term memory locations for
later retrieval.
The hippocampus is essential in forming new long-term memories but not in
maintaining them.
All memories are stored in the cerebral cortex.
Short-term memories are accessed via temporary links formed in the
hippocampus
Long-term memories involve permanent connections to the cerebral cortex
itself.
The delay in forming permanent connections to memories is believed to
allow for more meaningful associations through gradual integration with
existing knowledge and experience .
Motor skills are usually learned through repetition which allows the
performance of these skills without conscious recall of the steps
necessary to complete them. This relies on the creation of new
connections
Memorizing facts may rely on strengthening existing connections.
Slow-acting neurotransmitters have a role in memory and learning.
They cause the release of secondary messengers inside the post synaptic
neuron that can increase the number of receptors or increase the rate of ion
movements across the membrane.
These secondary messengers can affect the post synaptic neuron for days
causing what is known as long-term potentiation. (LTP)
Long-term
Potentiation
Long-term potentiation (LTP) is the lasting increase in
the strength of synaptic transmission and is thought to
be one of the fundamental processes by which
memories are stored and learning takes place.
Long-term potentiation in a post synaptic neuron
occurs when
A high frequency series of action potentials in a
presynaptic neuron releasing the excitatory
neurotransmitter glutamate arrive at the same
time as the post synaptic cell receives a
depolarizing stimulus at another synapse.
Glutamate activates AMPA & NMDA postsynaptic
receptors which begins a cascade of events
leading to a strengthening of synaptic
transmission in the post synaptic neuron.
Stem Cells in the Brain
Neurogenesis in hippocampus
appears to be crucial for learning &
memory
Hippocampus contains neural stem
cells that continually produce new
neurons (neurogenesis)
Stress or depression impede
learning & cause hippocampus to
shrink
Stress reduction and
anti-depressants return size to
normal
