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 a) receives information from other neurons, through its dendrites b) integrates those signals, and b) integrates those signals, and c) sends messages to other neurons through its terminal buttons 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 collects info from other cells cite of genetic activity cite of genetic activity 2) Axon - long, narrow outgrowth of a neuron 2) Axon - long, narrow outgrowth of a neuron transmits messages to other neurons transmits messages to other neurons through its terminal buttons through its terminal buttons

3) Dendrites 3) Dendrites short outgrowths from the neuron’s cell body that receive signals from other neuron’s terminal buttons 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 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 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 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) a) go through reuptake (reabsorbtion) b) be swept away through diffusion, b) be swept away through diffusion, c) or leave and then reexcite the neuron 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 prozac Now wildly popular – even with dogs with dogs Effective and relatively side effect free 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