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