PSYC 1001 Chapter Notes - Chapter 3: Hebbian Theory, Myelin, Synaptic Pruning
16 Jun 2018
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Psychology Chapter 3 Notes
Einstein’s brain
- Studied by Sandra witelson
- notices that Eistei’s brain is highly similar overall to most brains; but there were some
exceptions
- wider parietal region
- distinct sylvian fissure
- primary motor and somatosensory areas where distinctive
- ratio of glial cells per neuron is higher than average in the left parietal lobe
Communication in the Nervous System
- two types of cells in the nervous system: glia and neurons
- information is received at the dendrites, passed through the soma and along the axon,
then is transmitted to the dendrites of other cells at the synapse
Term
Definition
Neurons
individual cells in the nervous system that
receive, integrate, and transmit information
Soma
(cell body) contains the cell nucleus and much of
the chemical machinery common to most cells
Nucleus, sustaining
Dendrites
the parts of a neuron that are specialized to
receive information
receive signals
Axon
a long, thin fiber that transmits signals away from
the soma to other neurons or to muscles or
glands
electrical transmission
Myelin Sheath
insulating material, derived from glial cells, that
encases some of the axons
myelin sheath speeds up the transmission of the
signals that move along axons
Terminal Buttons
small knobs that secrete chemicals called
neurotransmitters (axon ends here)
Synapse
a junction where information is transmitted from
one neuron to another
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2
Glia, glue
- cells found throughout the nervous system that provide various types of support for
neurons
- account for over 50% of the brains volume
- supply nourishment to neurons, help remove neuron waste product, provide insulation
around many axons
- also play a role in orchestrating the development of the nervous system in the human
embryo
- some types of glia can detect neural impulses and send signals to other glia cells
Neural Impulses
- Hodgkin and Huxley (1952) did research on squid axons to learn more about neural stimulation
- The resting potential of a neuron: a stable negative charge when the cell is inactive (approximately
270 volts)
- When a neuron is stimulated channels in its cell membrane open, allowing positive sodium ions
to come in and an action potential is created
- Resting potential: neuron at rest
- Action potential: very brief shift in a neurons electrical charge that travels along an axon
- Absolute refraction period: the minimum length of time after an action potential during which
another action potential cannot begin
- Relative refractory period: the neuron can fire, but its threshold for firing is larger so more intense
stimulation is required to initiate an action potential
- All or nothing principle: eithe the euo fies o it does’t
- Neurons can convey information about the strength of a stimulus by varying the rate at which
they fire action potentials
- Myelin sheath: fatty insulation that increases speed of travel along axon
- Various neurons transmit neural impulses at different speeds
- Sodium/potassium pump re-establishes balance after wave passes
The Synapse
- To euos do’t touh
- Synaptic cleft: a microscopic gap between the terminal button of one neuron and the cell
membrane of another neuron
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- Presynaptic neuron: the neuron that sends a signal across the gap
- Postsynaptic neuron: the neuron that receives the signal
- Neurotransmitters: chemicals that transmit information from one neuron to another
- Synaptic vesicles: neurotransmitters storage vesicle
- Neurotransmitters are released when the vesicle merges with the membrane of the
presynaptic cell and the neurotransmitters are released into the synaptic cleft
- Neurotransmitters diffuse across the membrane and bind to their designated receptor
sites
- When a neurotransmitter and a receptor molecule combine the reaction causes PSP
- Postsynaptic potential (PSP): a voltage change at a receptor site on a postsynaptic cell
membrane
- Postsynaptic potentials do not follow the all or nothing principle
- Post synaptic potential as graded (vary in size and increase or decrease the probability of
a neural impulse in the receiving cell in proportion to the amount of voltage change
- Two types of messages can be transmitted from cell to cell: excitatory and inhibitory
- Excitatory PSP: a positive voltage shift that increases the likelihood that the postsynaptic
neuron will fire action potentials
- Inhibitory PSP: a negative voltage shift that decreases the likelihood that the post synaptic
neuron will fire action potentials
- The nature of the PSP depends on which receptor site is activated in the post synaptic
neuron
- Reuptake: a process in which neurotransmitters are sponged up from the synaptic cleft
by the presynaptic membrane
Neural Networks
- The nervous system generally forms more synapses than needed and then gradually
eliminates the less active synapses
- Synaptic pruning: the elimination of old or less active synapses
- Donald Hebb: understanding the brain allows us to understand behavior
- Hebbian learning rule: specifies how cell assemblies come about and might operate
- Long term potentiation: a long-lasting increase in neural excitability in synapses along a
specific neural pathway
- Repeated synaptic activity leads to a strengthening of the synapse
Neurotransmitters and Behavior
- Nine well established neurotransmitters, and about 40 additional neuropeptide chemicals
that function part time as neurotransmitters
- Specific transmitters can deliver signals only at certain locations on a cell membrane
- Specialization of neurotransmitters reduces cross talk between densely packed neurons
- Agonist: A chemical that mimics the action of a neurotransmitter
- Antagonist: chemicals that block the action of the natural transmitter by occupying the
receptor site rendering them unusable
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Document Summary
Notices that ei(cid:374)stei(cid:374)"s brain is highly similar overall to most brains; but there were some exceptions. Primary motor and somatosensory areas where distinctive ratio of glial cells per neuron is higher than average in the left parietal lobe. Definition individual cells in the nervous system that receive, integrate, and transmit information (cell body) contains the cell nucleus and much of the chemical machinery common to most cells. Dendrites the parts of a neuron that are specialized to receive information receive signals. Axon a long, thin fiber that transmits signals away from the soma to other neurons or to muscles or glands electrical transmission. Myelin sheath insulating material, derived from glial cells, that. Terminal buttons encases some of the axons myelin sheath speeds up the transmission of the signals that move along axons small knobs that secrete chemicals called neurotransmitters (axon ends here) Synapse a junction where information is transmitted from one neuron to another.
