3. Define memory and classify it into various types.
Describe the role of synaptic inhibition and
synaptic facilitation in memory.
Describe the mechanism of short term
,intermediate , and long term memory.
4. Definition:
Memory is defined as the ability to recall past
experience and retention of the learned material.
5. The processes of memory are:
Putting information into memory (encoding).
Maintaining the coded information (storage),
Getting the stored information back into
consciousness (retrieval).
6. Of concern also is forgetting (losing stored
information or having difficulty or failure in
retrieving it), which may occur because of
problems in any of the three memory processes.
7. We know that some memories last for only a few
seconds, whereas others last for hours, days,
months, or years.
9. Short-term memory:
Includes memories that last for seconds or at
most minutes unless they are converted into
longer-term memories.
Intermediate long-term:
Includes memories, which last for days to weeks
but then fade away.
10. Long-term memory: which, once stored, can be
recalled up to years or even a lifetime later.
Memories are frequently classified according to
the type of information that is stored. One of these
classifications divides memory into declarative
memory and skill memory.
11. It basically means memory of the various
details of an integrated thought, such as memory
of an important experience.
12. It includes memory of :
(1) The surroundings,
(2) Time relationships,
(3) Causes of the experience,
(4) The meaning of the experience,
(5) One’s deductions that were left in the
person′s mind.
13. It is frequently associated with motor activities of
the person’s body, such as all the skills
developed for hitting a tennis ball.
14. Including automatic memories to:
(1) sight of the ball,
(2)calculate the relationship and speed of the
ball to the racquet.
(3) deduce rapidly the motions of the body
the arms and the racquet required to hit
the ball as desired.
15. All of these activated instantly based on previous
learning of the game of tennis ,then moving on to
the next stroke of the game while forgetting the
details of the previous stroke.
16. Although we often think of memories as being
positive recollections of previous thoughts or
experiences, probably the greater share of our
memories are negative memories, not positive.
That is our brain is inundated with sensory
information , from all our senses.
17. Fortunately, the brain has the capability to learn to
ignore information that is of no consequence. This
results from inhibition of the pathways for this
type of information; the resulting effect is called
habituation.
This is a type of negative memory.
18. Conversely, for incoming information that causes
important consequences such as pain or pleasure,
the brain has a different automatic capability of
enhancing and storing the memory traces. This is
positive memory.
19. It results from facilitation of the synaptic
pathways, and the process is called memory
sensitization.
20. It is typified by one’s memory of 7 to 10 numerals
in a telephone number (or 7 to 10 other discrete
facts) for a few seconds to a few minutes at a time
but lasting only as long as the person continues to
think about the numbers or facts.
21. This short term memory is caused by continual
neural activity resulting from
nerve signals that travel around and around a
temporary memory trace in a circuit of
reverberating neurons.
22. • Another possible explanation of short term
memory is presynaptic facilitation or inhibition.
• This occurs at synapses that lie on terminal nerve
fibrils immediately before these fibrils synapse
with a subsequent neuron.
23. These may last for many minutes or even weeks.
They will eventually be lost unless the memory
traces are activated enough to become more
permanent; then they are classified as long-term
memories.
24. At the molecular level the habituation effect in
the sensory terminal results from progressive
closure of calcium channels through the terminal
membrane, so much smaller than normal amounts
of calcium ions can diffuse into the habituated
terminal, and much less sensory terminal
transmitter is released because calcium entry is
the principal stimulus for transmitter release.
25. Experiments in primitive animals have
demonstrated that memories of the intermediate
long-term type can result from temporary chemical
or physical changes, or both, in either the synapse
presynaptic terminals or the synapse postsynaptic
membrane, changes that can persist for a few
minutes up to several weeks.
26.
27. One terminal is from a sensory input neuron and
terminates directly on the surface of the neuron
that is to be stimulated; this is called the sensory
terminal.
28.
29. The other terminal is a presynaptic ending that lies
on the surface of the sensory terminal, and it is
called the facilitator terminal.
30. . When the sensory terminal is stimulated
repeatedly but without stimulation of the facilitator
terminal, signal transmission at first is great, but it
becomes less and less intense with repeated
stimulation until transmission almost ceases. This
phenomenon is habituation.
31.
32. Conversely, if a stimulus excites the facilitator
terminal at the same time that the sensory
terminal is stimulated, then instead of the
transmitted signal into the postsynaptic neuron
becoming progressively weaker, the ease of
transmission becomes stronger and stronger.
33. It will remain strong for minutes, hours, days, or,
with more intense training, upto about 3 weeks
even without further stimulation of the facilitator
terminal.
34. It is especially interesting that even after
habituation has occurred, this pathway can be
converted back to a facilitated pathway with only a
few noxious stimuli.
35.
36.
37. Long term memory results from structural changes
at the synapse that enhance or suppress signal
conduction.
38. These changes include increase in :
1. the number of synaptic vesicle release sites.
2. number of available synaptic vesicles.
3. number of synaptic terminals
And
4. Changes in shape or number of post synaptic
terminals.
39. With long-term potentiation (LTP), changes take
place as a result of increased use at a given
preexisting synapse that enhance the future ability
of the presynaptic neuron to excite the
postsynaptic neuron. That is, this connection gets
stronger the more often it
is used.
40. Such strengthening of synaptic activity results in
the formation of more EPSPs in the postsynaptic
neuron in response to chemical signals from this
particular excitatory presynaptic input. The
increased excitatory responsiveness is ultimately
translated into more action potentials being sent
along this postsynaptic cell to other neurons.
41.
42. Glutamate is released from activated presynaptic
neuron.
Glutamate binds with both AMPA and NMDA
receptors.
Binding opens AMPA receptor-channel.
Na+ entry through open AMPA channel depolarizes
postsynaptic neuron, producing EPSP.
Binding opens gate of NMDA receptor-channel but
Mg2+ still blocks channel. Sufficient depolarization
from this AMPA opening plus other EPSPs drives
Mg2+ out.
43. Ca2+ entry through open NMDA channel activates
Ca2+ second-messenger pathway.
Second-messenger pathway promotes insertion of
additional AMPA receptors in postsynaptic
membrane, increasing its sensitivity to glutamate.
Second-messenger pathway also triggers release of
retrograde paracrine (likely nitric oxide).
Nitric oxide stimulates long-lasting increase in
glutamate release by presynaptic neuron.
44.
45. Learning is the acquisition of knowledge or skills
as a consequence of experience instruction, or
both. It is widely believed that rewards and
punishments are integral parts of many types of
learning.
46. Learning is a change in behavior that occurs as a
result of experiences. It highly depends on the
organism’s interaction with its environment. The
only limits the effects that environmental
influences can have on learning are the biological
constraints imposed by species-specific and
individual genetic endowments.
47. Hall John E. ,Guyton C.Arthur.” Guyton and Hall
Textbook of Medical Physiology”.12th
Edition;Elseveir.
Sherwood Lauralee.”Principles of Human
Physiology”.6th
edition;Cengage .
