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Chapter 3 Notes Notes on chapter 3 in point form

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Eileen Wood

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Psychology- Chapter 3
Yen Hoang
Communication in the Nervous System:
Nervous tissue: the basic hardware
Cells in the nervous system fall into two major categories: glia and neurons
o Neurons: individual cells in the nervous system that receive, integrate and
transmit information
Basic links that permit communication within the nervous system
Vast majority of them communicate only with other neurons
A small minority receive signals from outside the nervous system (from
sensory organs) or carry messages from the nervous system to the muscles
that move the body
There is no one single drawing of a neuron, there’s many varieties of types
and shapes
Parts of the neuron:
Soma (cell body) contains the cell nucleus and much of the
chemical machinery common to most cells
o The rest of the neuron is devoted exclusively to handling
Dendrites are parts of a neuron that are specialized to receive
o They are branch like structures
o Most neurons receive information from many other cells
(sometimes thousands of others) therefore more extensive
dendritic trees
Axon is a long, thin fibre that transmits signals away from the
soma to other neurons or to muscles or glands
o They may be quite long and they may branch off to
communicate with a number of other cells
Myelin sheath is insulating material, derived from glial cells, that
encases some axons
o It speeds up the transmission of signals that move along
o If an axon’s myelin sheath deteriorates, its signals may not
be transmitted effectively
Terminal buttons are small knobs that secrete chemicals called
o They’re at the end of axons
o These chemicals serve as messengers that may activate
neighbouring neurons
Synapse is a junction where information is transmitted from one
neuron to another
o ie the parts at which neurons interconnect

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In summary, information is received at the dendrites, passed through the
soma and along the axon and is transmitted to the dendrites of other cells
at meeting points called synapses
Types of neurons: afferent (sensory) and efferent (motor)
Afferent (sensory): relay information from the senses of the brain
and spinal cord
Efferent (motor): sends information from the central nervous
system to the glands and muscles, enabling the body to move
o Glia are cells found throughout the nervous system that provide various types of
support for neurons
They tend to be much smaller than neurons but they outnumber neurons
by about 10 to 1
Therefore they appear to account for over 50% of the brain’s
They supply nourishment to neurons, help remove neurons’ waste
products and provide insulation around many axons
The myelin sheaths that encase many axons are derived from
special types of glial cells
They also play a complicated role in orchestrating the development of the
nervous system in the human embryo
Glia may also send and receive chemical signals
They may also play an important role in memory formation
Some types of glia cells can detect neural impulses and send signals to
other glial cells
The Neural Impulse: Using Energy to Send Information
o The Neuron at Rest: A Tiny Battery
o The resting potential of a neuron is its stable, negative charge when the cell is
The charge is about -70 millivolts
o The Action Potential:
o An action potential is a very brief shift in a neuron’s electrical charge that travels
along an axon
As long as the voltage of a neuron remains constant, the cell is quiet and
no messages are being sent
When the neuron is stimulated, channels in its cell membranes open where
it briefly allows positively charged sodium ions to enter
For an instant, the neuron’s charge is less negative or even
positive, creating an action potential
o Ie shift in electrical charge
o The absolute refractory period is the minimum length of time after an action
potential during which another action potential cannot begin
After the firing of an action potential, the channels in the cell membrane
that opened to let the sodium in close up

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Some time is needed before they are ready to open again and until
that time the neuron cannot fire
Usually lasts 1-2 milliseconds
It’s followed by a brief relative refractory period
During the relative refractory period, the neuron can dire but its
threshold for firing is elevated so more intense stimulation is
required to initiate an action potential
o The All or None Law:
o Either the neuron fires or it doesn’t and its action potentials are all the same size
Therefore weaker stimuli do not produce smaller action potentials
o Neurons can convey information about the strength of a stimulus
They do this by varying the rate at which they fire action potentials
In general, a stronger stimulus will cause a cell to fire a more rapid
volley of neural impulses than a weaker stimulus will
o Various neurons transmit neural impulses at different speeds
Thicker axons transmit neural impulses more rapidly than thinner ones do
The Synapse: Where Neurons Meet
o The neural impulse functions as a signal
o For that signal to have a meaning for the system as a whole, it must be transmitted from
the neuron to other cells
o This transmission takes place at special junctions called synapses, which depend
on chemical messengers
o Sending Signals: Chemicals as Couriers:
o The two neurons don’t actually touch in a synapse, they are separated by the
synaptic cleft
o A synaptic cleft is a microscopic gap between the terminal button of one neuron
and the cell membrane of another neuron
Signals have to cross this gap to permit neurons to communicate
The neuron that sends a signal across the gap is called the presynaptic
The neuron that receives the signal is called the postsynaptic neuron
o Neurotransmitters are chemicals that transmit information from one neuron to
The arrival of an action potential at an axon’s terminal buttons triggers the
release the of neurotransmitters
Within the buttons, most of the neurotransmitters are stored in small sacs
called synaptic vesicles
o Lock + key model except that only one neuron is needed for the interaction
Neurotransmitters and Behaviour:
o Acetylcholine is the only transmitter between motor neurons and voluntary muscles
o They’re throughout the nervous system
o Agonists excite therefore increase likelihood of firing
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