Psychology’s
biological roots:
neurons and
neural
communication
The neuron
A cell that specializes in communication
A neuron:
a) receives information from other
neurons, through its dendrites
b) integrates those signals, and
c) sends messages to other neurons
through its terminal buttons
Neural structure
Three main components
1) Cell Body – contains the nucleus
collects info from other cells
cite of genetic activity
2) Axon - long, narrow outgrowth of a neuron
transmits messages to other neurons
through its terminal buttons
3) Dendrites
short outgrowths from the neuron’s
cell body that receive signals from other
neuron’s terminal buttons
An axon’s terminal buttons communicate
with another cell’s dendrites across a tiny,
but empty space known as the synaptic
cleft
Noteworthy Neuron
News
We used to think that:
a) damaged neurons could never
recover, and
b) neuron production stopped after
infancy.
We were wrong
Rehabbing neurons
Even severed cns neurons can be
repaired if immersed with certain natural
neural substances
Rescue from spinal cord injuries?
Neurogenesis
Undeveloped mice brain cells bathed in a
special protein can produce new neurons.
Better yet, these new neurons will
continue to divide and multiply.
We now call these – stem cells.
Talk about challenging assumptions!
Implications
It appears that this neural fertility can go
on throughout adulthood.
Learning & memory cells even.
Exercise and mental engagement spurs
these changes further.
Stress kills this process.
Controversy but incredible promise
neuronal firing
Dendrites are constantly bombarded with
messages from other neurons
These can be excitatory, prompting the
neuron to fire off its own message, or
inhibitory, decreasing the probability that
the neuron will fire
The power to restrain is just as crucial as
important as the power to engage in action
Neuronal firing ii
After weighing the input it receives from
other neurons, a neuron can decide to
send a message to another neuron
It does so through an electro-chemical
process called action potential or
neuronal firing
Neuronal firing iii
An action potential is the transmission of
the signal down the axon through a
complex exchange of sodium and
potassium ions
The signal does not travel through
electrical conduction like an electrical
current
Neuronal firing iv
In this manner, the signal passes at a
steady rate, like a series of dominoes and
is not slowed by electrical resistance
This protects a giraffe’s toes just as much
as a mouse’s nose
The message is sped along even faster if
the axon is coated with myelin
It insulates like the plastic tubing of an
electric cord
Neural
communication
Neurons influence each other through the
release of neurotransmitters – chemical
substances that carry signals across the
synaptic cleft
When the action potential reaches the
end of the axon at its terminal button the
neurotransmitters are released to travel
across the synaptic cleft
Neural comm. ii
After passing through the empty synaptic
cleft the neurotransmitters attach or bind
to receptors on the postsynaptic neuron
These neurotransmitters can then make
the receiving neuron either more or less
likely to fire
It is in this infinitesimally small space that
irregularities can have profound effects
neurotransmitters
There are dozens (at least 60) types and
each activates many types of receptors
Once they contact the postsynaptic neuron
they can either:
a) go through reuptake (reabsorbtion)
b) be swept away through diffusion,
c) or leave and then reexcite the neuron
Major
neurotransmitters
Serotonin – while involved in many
behaviors, especially important for
emotional states, impulse control, and
dreaming
Low levels lead to sadness, anxiety,
aggression, and food cravings
LSD bears a close structural resemblance,
when it binds to serotonin receptors
involved in dreaming, hallucinations result
Ssri’s
Selective Serotonin Reuptake Inhibitors
Prevent serotonin from being quickly reabsorbed
Introduced in 1987- prozac
Now wildly popular – even
with dogs
Effective and relatively side
effect free
Should we all be “better than well”?
dopamine
Essential influence on motivation and
motor control
Many think it “tells” us what we find
pleasurable
Kicks in when we are hungry, thirsty, and
aroused to guide us to behaviors which
will satisfy our cravings
Do drugs enhance its effects (addiction) ?
epinephrine
Formerly called adrenaline
Activated by our sympathetic nervous
system when we need great bursts of
energy to flee or stand and fight
endorphins
Involved in the suppression of pain
Kicks in when pain becomes maladaptive,
helping animals feed and breed despite
discomfort
Administered through drugs like morphine
May account for the placebo effect – we
feel less pain because we convince
ourselves that we should, and release it,
confirming our hopes