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Chapter 3

Psychology 1000 Chapter Notes - Chapter 3: Aphasia, Positron Emission Tomography, Ct Scan


Department
Psychology
Course Code
PSYCH 1000
Professor
Dr.Mike
Chapter
3

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Psychology
Chapter 3: Biological Foundations of Behaviour
THE NEURAL BASES OF BEHAVIOUR
Neurons: the basic building blocks of the nervous system. These nerve cells are linked
together in circuits. A neuron has 3 main parts:
1. The cell body or soma- contains the biochemical structures needed to keep the
neuron alive and a nucleus which carries the genetic information
2. Dendrites- specialized receiving units that collect messaged from neighbouring
neurons and send them to the cell body
3. Axon- conducts electrical impulses away from the cell body to other neurons,
muscles, or glands
4. Axon terminals
They also do 2 important things:
1. Generate electricity that creates nerve impulses
2. Release chemicals that allow hem to communicate with other neurons and with
muscles and glands
Glial cells
Surround neurons and hold them in place
Manufacture nutrient chemicals that neurons need
Form the myelin sheath around some axons
Absorb toxins and waste materials that might damage neurons
Protect the brain from toxins
Blood-brain barrier: prevents many substances, including a wide range of toxins, fro
entering the brain
Nerve activation involved three basic steps:
1. At rest, the neuron has an electrical resting potential due to the distribution of
positively and negatively charged chemicals (ions) inside and outside the neuron
2. When stimulated, a flow of ions in and out through the cell membrane reverses
the electrical charge of the resting potential, producing an action potential, or
nerve impulse
3. The original distribution of ions is restored, and the neuron is again at rest
Outside
the neuron:
Positively charged sodium ions and negatively charged chloride ions
Positive
Inside
the neuron:
Negatively charged protein molecules (anions) and positively charged potassium
ions
Negative

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Psychology
Resting potential: in the electrical activity of neurons, the internal difference of the
sodium ions outside the cell and the negatively charge protein ions inside the cell
Action potential: a sudden reversal in the neuron’s membrane voltage, during which the
membrane voltage momentarily moves from -70 millivolts (inside) to +40 millivolts
Depolarization: the shift from negative to positive voltage. The reversal of the resting
potential of a neuron’s cell membrane that produces the action potential
Generation of Action potential
In the resting state, sodium and potassium channels are closed and the
concentration of Na+ ions is 10x higher outside the neuron than in it
When the neuron is stimulated, Na+ channels open up
Attracted by the negative protein ions inside, positively charged Na+ flood into
the axon, creating a state of depolarization
The interior is now positive +40MV in relation to the outside, creating the action
potential
In a reflex action to restore the resting potential, sodium channels close and
potassium ions flow out through their channels
This restores the negative resting potential
Eventually, excess Na+ flow out of the neuron, and the escape K+ are recovered
Absolute refractory period: the recovery period as K+ ions flow out of the interior. The
membrane is not excitable and cannot generate another action potential
* In humans the limit is about 300 impulses
All-or-none law: action potentials occur at a uniform and maximum intensity, or they do
not occur at all
Action potential threshold: the intensity of stimulation (excitatory minus inhibitory)
needed to produce action potential
Graded potentials: a change in the electrical potential of a neuron that is proportional to
the intensity of the incoming stimulation, but not sufficient to produce action potential
Myelin sheath: a fatty, whitish insulation layer covering axons derived from glial cells
during development
Nodes of Ranvier: interrupt the myelin sheath at regular intervals
Unmyelinated
axons, the action potential travels own the axon length like a burning
fuse
Myelinated
axons, electrical conduction can skip from node to node
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Psychology
Synapse: the microscopic space between neurons over which the nerve impulse is
biochemically transmitted
Synaptic cleft: a tiny gap between the axon terminal of one neuron and the dendrite of
the next neuron
Neurotransmitters: chemical substances that carry messages across the synapse to
either excite or inhibit their firing
Process of Chemical Communication
1.
Synthesis
of neurotransmitter
2.
Storage
in synaptic vesicles
3.
Release
into synaptic space
4.
Binding
to receptor sites
5.
Deactivation
through reuptake or breakdown
Types of Neurotransmitters
Excitatory
Neurotransmitter Depolarizes neuron’s membrane Increases liklihood of
action potential
Inhibitory
Neurotransmitter hyperpolarizes neuron’s membrane decreases liklihood
of action potential
Reuptake: the transmitter molecules are reabsorbed into the presynaptic axon terminal
Acetylcholine (ACh): an excitatory neurotransmitter that operates at synapses with
muscles and is also the transmitter in some neural networks involving memory
Dopamine: an excitatory neurotransmitter whose overactivity may underlie some of the
disordered behaviours seen in schizophrenia
Seratonin: a neurotransmitter that seems to underlie positive mood states;
underactivity may be a factor in depression
Endorphins: natural opiate-like substances that are involved in pain reduction
Neuromodulators:neurotransmitter substances that are released by neurons and
circulate within thenervous system to affect the sensitivity of many neurons to their
natural transmitter substances
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