Study/lecture notes for first-year psychology on Components of a neuron and neuronal transmission
*Please note that the information in the document is not my own knowledge, it belongs to the Unversity of the Witwatersrand and is comprised of notes from lectures and textbooks.
Lecture notes Introduction in Psychology (PSYC101) Psychology
Lecture notes Introduction in Psychology (PSYC101) Psychology
Lecture notes Introduction in Psychology (PSYC101) Psychology
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University of the Witwatersrand (wits)
PSYC1009A
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Contents
VIDEO the components of a neuron ........................................................................................................................... 3
the cells of the nervous system ...................................................................................................................................... 8
Glial cells ..................................................................................................................................................................... 8
Neurons ...................................................................................................................................................................... 9
A typical motor neuron ........................................................................................................................................... 9
Neuronal transmission.................................................................................................................................................. 10
At cellular level ......................................................................................................................................................... 10
Neurons and neural transmission ............................................................................................................................. 10
structure of a neuron ................................................................................................................................................ 10
NEuron and its parts ............................................................................................................................................. 11
Dendtrites ..................................................................................................................................................... 11
Axon .............................................................................................................................................................. 11
Myelin sheath ............................................................................................................................................... 12
terminal buttons and synapses ..................................................................................................................... 12
electrical transmittion in the neuron ........................................................................................................................ 13
the action potential .................................................................................................................................................. 13
the resting neuron ................................................................................................................................................ 13
the action potential – depolarization .................................................................................................................... 13
THE ACTION POTENTIAL........................................................................................................................................ 14
.............................................................................................................................................................................. 14
when an action potential is realised, certain stages occur.................................................................................... 16
I ............................................................................................................................................................................. 16
in summary: the characteristics of action potentials ............................................................................................ 17
The synapse – the gap between neurons ............................................................................................................. 17
The synaptic gap and synaptic transmission:The chemical process .......................................................................... 18
.............................................................................................................................................................................. 18
Postsynaptic potentials ......................................................................................................................................... 19
The structure and action of a synapse .................................................................................................................. 20
Types of neurotransmitters ...................................................................................................................................... 21
Maintaining the balance ....................................................................................................................................... 22
Psychopharmacology ................................................................................................................................................ 22
Classes, uses and effects of drugs ......................................................................................................................... 22
Interesting facts about neurotransmitters ............................................................................................................ 23
Tools of the trade ......................................................................................................................................................... 24
The Active Brain: overview ................................................................................................................................... 24
How principles of Basic Neuroscience help us treat patients ............................................................................... 24
Mapping brain Function: figuring out what the parts do ...................................................................................... 25
Imaging – Radiology (CT), Magnetic (MRI). Metabolic (fMRI) ............................................................................... 25
1
,Radiologic Procedures .............................................................................................................................................. 26
X-Ray ..................................................................................................................................................................... 26
Angiography/Arteriography .................................................................................................................................. 26
Computed Transaxial Tomography (CT scan) ........................................................................................................ 26
Magnetic Procedures ................................................................................................................................................ 26
Magnetic Resonance Imaging (MRI) ..................................................................................................................... 26
Functional Magnetic Resonance Imaging (fMRI)................................................................................................... 26
Transcranial magnetic stimulation (TMS) ............................................................................................................. 26
Diffusion Tensor imaging (DTI).............................................................................................................................. 27
Imaging of Brain Metabolism .................................................................................................................................... 27
Photon Emission Tomography (PET) ..................................................................................................................... 27
Cerebral Blood Flow .............................................................................................................................................. 27
Single-Photon Emission Computed Tomography (SPECT) ..................................................................................... 27
Electrophysiologic Procedures .................................................................................................................................. 28
Electroencephalography ....................................................................................................................................... 28
Evoked potential (EP) ............................................................................................................................................ 28
Example of BAEP recording; auditory nerve and brainstem potentials ................................................................ 28
Neurohistology Techniques ...................................................................................................................................... 29
Golgi Stain ............................................................................................................................................................. 29
Nissl Stain.............................................................................................................................................................. 29
Myelin Stain .......................................................................................................................................................... 29
Other methods ......................................................................................................................................................... 29
Lumbar Puncture .................................................................................................................................................. 29
Neurologic examination ........................................................................................................................................ 29
Neuropsychological assessment ........................................................................................................................... 29
The neuropsychologist in south Africa ...................................................................................................................... 30
2
,VIDEO THE COMPONENTS OF A NEURON
Plenty of individual chemicals in and around the neuron, but we only care about 3 right now.
Sodium and potassium – positively charged ions
Chloride – negative
At rest
Before any action potential starts, there are more sodium ions outside the neuron than inside
Greater concentration of Potassium ions inside of the cell than outside
Potassium can easily pass
Some Sodium might pass but not nearly enough as potassium
So there is some of each ion on
both sides of the membrane but
at rest this is the general pattern
This is called a concentration
gradient. Having different
concentrations of a chemical on
each side of a membrane
This is where electricity and the graph below come in
3
,The Y axis is the membrane potential; it’s a voltage which means the difference in charge between 2
points.
At any given point on the graph we are looking at
how much more positive or negative each side of the
cell membrane is from the other
The outside of the membrane is very positive, and the
inside is very negative; that’s a big voltage.
Meanwhile the x-axis is Time, and while there some
variation depending on which source you use, we’re
talking units of milliseconds here
So if we apply this resting to the membrane potential,
the graph starts out super negative since there were
all those positive ions outside the cell, and very few
inside the cell
On the other hand, the inside of this cell would be
more positive
Let’s say a neurotransmitter comes out and it’s an
excitatory neurotransmitter and goes to the dendrite
and says “hey…WAKE UP” that allows loads of
positive ions into the neuron, so now the inside of our
cell is getting more positive and our graph ticks up.
And if it gets to -55mV, we cross the threshold of
excitation where the axon hillock throws its sodium
channels open.
This is because those particular channels are Voltage
Gated – an ion channel that opens at a certain voltage.
Now all of a sudden these positive sodium ions rush in
and more positive ions inside the cell means our graph
goes up as well.
4
,It usually tops out at around +30mV. This part of the action potential, that crossing of the threshold
and positive shoot up, or depolarization is all or nothing.
If the voltage wiggles between -70mV and – 56mV = no depolarisation
After that action potential kicks off, a bunch of voltage gated
channels open up all along the axon and in a period of less than a
millisecond an action potential went from Soma to terminals
The peak of that action potential, the sodium channels close and
the potassium channels open.
This is repolarisation.
On a graph this looks like a sharp drop in the membrane potential
since the bulk of positive ions is exiting the cell
The inside of our cell is going to become more negative again
During repolarisation those sodium channels will not open and if
you can’t get sodium into the cell, you won’t get concentration
gradient, so no action potential. This is called the Refractory Period
where you could not stoke another action potential no matter
how big of a stimulus you had.
While sodium is slipping out, a few more potassium ions are
slipping out as well. This creates something called hyperpolarization,
so the voltage ends up more negative than when we started
5
, Now all that’s to say that we took a message from the dendrites down the axon, now we got to
do something with it.
At the end of the axon are those axon terminals and they bud up against other types of cells in
something call synapse.
And there are two types of synapses; electrical synapses (Gap junctions) and chemical synapses
Electrical synapses are easy; they are really tiny gaps between
each synaptic membrane that let ions through to make for super
fast signalling
On the other hand chemical synapses are trickier
Chemical synapse
Within the synapses we have got the axon terminal
releasing those neurotransmitters to the dendrite, gland, or
muscle and in between them is the synaptic cleft, the dead
space there.
Because that receiver can be a few things, we
end up labelling those surfaces the presynaptic
membrane and postsynaptic membrane
So when the action potential gets to the end of the line it
triggers those little containers called synaptic vesicles; little
pockets wrapped in membrane that hold chemicals called
neurotransmitters; each of which can signal something
different
6
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