Transcript Psychology`s biological roots: neurons and neural communication

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
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
When the action is over, the positive
sodium is pumped back out until next time
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
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
Neuronal Firing II
An Action Potential is the transmission of
the signal down the axon through a
complex exchange of sodium and
potassium ions
When the action is over, the positive
sodium, is pumped back out until next time
The nervous system
From the perspective of
contemporary psychology
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A survey of the
nervous system
Within the broad heading of the Nervous
System we find many component systems and
subdivisions
The first are:
a) The Central Nervous System –
the brain and the spinal cord, and
b) The Peripheral Nervous
System – bundles of axons connecting the
spinal cord and the rest of the body.
The spinal cord
A rope of neural tissue that runs inside the
hollows of the vertebrae from just above
the pelvis into the base of the skull
Connected to both sensory ( pain, touch,
and pleasure) and motor ( contract and
relax muscles) neurons
Facilitates reflexes - rapid, involuntary
responses to stimulus
Neuron types
Afferent – sensory
Efferent – motor
Interneurons - connective
Can neurons be repaired?
For decades, we thought not
Now, as we begin to understand
neuroplasticity, hope grows
The promise and
controversy of stem cells
the peripheral
nervous system
Divides into :
a) the Somatic Nervous
System – nerves which
communicate with the skin and
muscles and
b) the Autonomic Nervous
System – nerves which control
the involuntary muscles, internal
organs (heart, lungs, stomach,
etc.) and glands
The autonomic
nervous system
Two divisions:
1) Sympathetic – prepares your body for
action, fight or flight
blood flows to muscles
epinephrine increases heart rate
lungs pull in more oxygen
sweat forms for cooling
The autonomic
nervous system
2) Parasympathetic –
returns your body to its
resting state, conserves
energy
heart rate slows
epinephrine cut off
lungs relax
stomach resumes
digestion
The endocrine
system
A set of glands that produce and release
hormones
These hormones influence thoughts,
behaviors and actions
Transmitted through the blood
Have a global effect as compared to the
local effect of neurotransmitters
Include the hypothalamus and pituitary