PSYC 1010 Lecture Notes - Postsynaptic Potential, Twin, Central Nervous System

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10 Feb 2013
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Psychology Chapter 3 Notes:
Nervous Tissue: Basic Hardware
Neurons:
cells that receive, integrate and transmit information
Soma or cell body contains nucleus and organelles
Dendrites extend from the cell and allow it to communicate with other cells
Axons are long thin fibre that communicate with other cells
Axons are covered in myelin sheath that conducts signals
MS is due to depletion of myelin sheaths
Axon ends in cluster of terminal buttons
Small knobs that secrete neurotransmitters
Neurons meet at the synapse
Glia:
Cells that support and nourish the neurons
Much smaller than a neuron
Supportive, nutritive, insulate, protective (SNIP)
Account for over 50% of brains volume
Provide insulation around many axons
Myelin sheaths are derived from specialized glia cells
Orchestrate development of nervous system in the human embryo
May also send and receive signals
Play an important role in memory formation and experience of chronic pain
Impaired glial cells may contribute to schizophrenia and mood disorders
The Neural Impulse: Using Energy to Send Information
Work of Alan Hodgkin and Andrew Huxley (squid axons used)
The Neuron at Rest: a Tiny Battery
Resting potential of a neuron is its stable, negative charge when the cell is inactive
-70 millivolts
Action Potential
When neuron is stimulated, Na + ions rush into the cell
Creates a positive action potential
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Channels that allows sodium ion in the cell then close and remain closed for a refrac-
tory period
Makes sure the signal only travels one way
Relative refractory period occurs after this
Neuron can still be stimulated, just takes more intense stimulation to initiate an ac-
tion potential
The All or None Law
A neuron either fires or doesn’t
Signals travel at 100 m/s or 300 km/h
The Synapse
Sending Signals: Chemicals as Couriers
Neurons do not touch they are separated by synaptic cleft
Neurotransmitters are transferred through the cleft and to the post synaptic vesicle
Postsynaptic potential is a voltage change at the receptor site
Postsynaptic potentials are graded: they vary in size and increase or de-
crease probability of a neural impulse in receiving cell
2 types of messages can be sent from cell to cell:
Excitatory PSP
Positive voltage change that increases likelihood that postsynaptic neuron
will fire action potentials
Inhibitory PSP
Negative voltage change that decreases the likelihood that the postsynaptic
neuron will fire an action potential
Neurotransmitters are reabsorbed into the presynaptic neuron or are metabolized by
enzymes on the post synaptic neuron
Integrating Signals: Neural Networks
Thousands of signals are fired at a specific neuron at one time
If enough excitatory PSPs are fired, the threshold will be reached and an action poten-
tial will be fired
Conversely, if enough inhibitory PSPs are fired, they can cancel the effects of the exci-
tatory PSPs
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The nervous system is constantly forming more synapses and eliminating less active
synapses (synaptic pruning)
Donald Hebb:
Argued that understand the brain and its processes was key in understand-
ing behaviour
Neurons work together in cell assemblies
“Hebbian Learning Rule”
Specifying how linkages might come about
One neuron stimulating another neuron repeatedly produces a
change in synapse
Meaning: learning has taken place
Ideas are often referred to as “Hebb synapse”
Neurotransmitters and Behaviour
There are 9 well established neurotransmitters
40 additional neuropeptide chemicals that sometimes act as neurotransmitters
Neurotransmitters are specific to receptors
Acetylcholine
Only transmitter between motor neurons and voluntary muscles
Contributes to attention, arousal, and memory
Inadequate amounts are associated with memory loss and even Alzheimer’s
Drug treatments available to amplify levels of acetylcholine to treat Alzheimer's
Agonist: chemical that mimics the action of a neurotransmitter (ex. Nicotine)
Antagonist: chemical that blocks the receptor but does not stimulate a PSP
Monoamines
Parkinson’s disease:
Decline in synthesis of dopamine
Treated with “L-dopa” which is converted to dopamine in the brain (crosses
blood-brain barrier)
Monoamines include 3 neurotransmitters:
Dopamine, norepinephrine, and serotonin
Dopamine: used by neurons that control voluntary movements
Serotonin releasing neurons also play an important role in:
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