chapter 3 text.notes - only imp. things u need to know for test

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2 Dec 2010
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Psychology Notes: Chapter 3
GENETIC AND BIOLOGICAL FOUNDATIONS
- 23 pairs of chromosomes in all
ACTION POTENTIALS CAUSE NEURONAL COMMUNICATION
- Action potential: (i.e. neuronal firing) is the electrical signal that passes along the axon and
causes release of chemicals that transmit signals to other neurons
- Resting membrane potential: when not active the inside and outside of a neuron differ
electrically cuz of the balance of ions in the intracellular fluid Æ negatively charged
o Microelectrode: measure neuron[]vP}v]olÆuoÇ]vÇÀ]ZP]
electric currents
o Polarization: diff of charge inside and outside of neuron/creates electrical energy
necessary to power action potential
o Due to selective permeability, there is more potassium inside the neuron than sodium,
which contributes to polarization
CHARGES IN ELECTRICAL POTENTIAL LEAD TO ACTION
- Signals arrive at dendrites
o Excitatory t stimulates neuron to fire
o Inhibitory t reduce likelihood of neuron firing
o How they work: by affecting polarization Æ either it depolarizes or hyperpolarizes cell
membrane
- Depolarization and hyperpolarization
o Neurons fire when cell membrane is depolarized past certain threshold Æ causes
change in permeability of cell membrane= opens gates of sodium channels and allows
sodium to rush into neuron(inside = slightly more positively charged)
o Hyperpolarization: sodium channels become even more resistant to passage of sodium
- Action Potentials Spread along the Axon
o
o Once gating stops flow of sodium into neuron, potassium stops leaving Æ momentarily
creating state of hyperpolarization
Absolute refractory period: during this time it is impossible for the neuron to
fire, which keeps action potential from repeating up and down the axon in a
kind of ripple effect
Relative refractory period: when neuron can fire, but only in response to an
especially strong signal
Normally action potentials move along the axon in only one direction
o All or none principle: a neuron cannot partially fire, it fires with same potency each time,
but at diff intervals of diff frequency depending on the strength of stimulation
o Myelin sheath: makes it go faster
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