The differences between action
potential and synaptic transmission is thus
describe under the following headings;
1.
Location/place of action
2.
Means/method of transmission
3.
Rate of conduction
4.
Integration of information
5.
Principle of action.
LOCATION/PLACE OF
ACTION
Action potential, a brief change
in the electrical charge of a neuronal membrane; the physical basis of the
signal that travels the length of the neuron i.e the signal is sent from one
end of the neuron to the other. The signal sent from one end of the neuron to
the other is the neuron’s main response to input as well as the fundamental
information carrier of the nervous system. In other words, action potential is
the onset of communication among neurons in the nervous system.
Synaptic transmission otherwise
known as communication between neurons i.e involving more than one neurons,
occurs at the synapse; the small gap between two adjacent neurons, consisting
of the pre-synaptic and post-synaptic neurons’ membranes and space between them.
Synaptic transmission depends on neural succession and not just on a single
neuron.
MEANS/METHOD OF
TRANSMISSION
ACTION POTENTIAL
The core of action potential is electrical
changes, specifically the differential voltage between the inside of the cell
and the outside of the cell alter by the in/out flux of ions (K+, Na+ Cl-)
concentration due to the action of ion pumps locate in the cell membrane.
When a neuron is at a state of
rest (i.e, not stimulated), the inside of the cell contains both positive ions
and negative ones, and the same is true for the fluid outside the cell
membrane. But the concentration of ions inside and outside the cell membrane
are not the same, for the most part ion pumps work to move sodium (Na+) out of
the cell and potassium (K+) into the cell.
When a neuron is at rest, sodium
ion are being hindered from passing through the ion channels but potassium ion
freely pass through the ion channel. Hence potassium ion moves from the inside
of the cell to the outside of the cell
membrane (osmosis) thereby decreasing the positivity of charge inside
the cell until it is negatively charge and increasing the concentration of
positive charge outside the cell membrane. This action is the main source of
resting potential (the voltage difference between the inside and the outside of
a neuronal membrane when the neuron is not firing.)
When a neuron is stimulated
(mechanically, electrically or chemically) another ions channel that allow
sodium ion to pass freely sprung open enabling sodium ion to rush into the cell
thereby leading to excess of positively charge ions inside of the cell and
eliminating the negatively charge particles and causing the neuron to attain
excitation threshold; the voltage difference between a neuron’s interior and
exterior that, id exceeded, causes the neuron to fire.
SYNAPTIC TRANSMISSION
Beginning at the axon terminals of
the pre-synaptic neuron which contains the synaptic vesicles filed with
neurotransmitter (chemicals released by one neuron (usually the pre-synaptic
neuron) which triggers a response in another neuron(usually the post synaptic
neuron)
When the pre-synaptic neuron
fires, the action potential stimulate the pre-synaptic vesicles to discharge
their contents (neurotransmitters) in the gap (synapse) between the pre-synaptic
membrane and the post-synaptic membrane. The neurotransmitter molecules diffuse
across the synapse and latch onto receptor sites on the membrane of the
post-synaptic neuron. This sequence certain ion channels in the post-synaptic
membrane to open or close.
RATE OF CONDUCTION
ACTION POTENTIAL
The conduction rate in action
potential is faster compare to synaptic transmission due to propagation and
myelination.
Propagation: This is the spread
of the action potential down an axon caused by successive changes in electrical
charge along the length of the axon’s membrane. That is depolarization at one
point on the membrane causes the other nearby ion channels to open, and so
sodium rushes into the cell at that location.
Salutatory conduction
Because myelin sheath isn’t continuous,
but is segmented.(the axon is actually exposed at the nodes of Ranvier), the
action potential jumps from one nodes to another down the axon.(i.e myelinated
axons can propagate their action potential at speed up to 120meters per
second.) about 260 miles per hour.
SYNAPTIC TRANSMISSION
Conduction in synaptic
transmission is slow compare to conduction in the action potential due to the
fact that the terminal buttons are not myelinated and that synaptic
transmission involve chemical signaling (neurotransmitter) which have to be
released from their storage site before moving to the synapse and then binding
at the receptor site in order to trigger the depolarization of the cell
membrane of the post-synaptic neuron.
INTEGRATION OF
INFORMATION
Action potential integrate its
information in a single direction across the axon of the stimulated neuron i.e,
information moves from the dendrite downward across the neuron’s axon. But in
the case of synaptic transmission the integration of information is from many
sources.
PRINCIPLE OF ACTION
The principle guiding action potential is the ALL – or –
NONE LAW, which holds that all action potentials have the same strength and
speed regardless of the triggering stimulus.
On the other hand the principle is the lock and key
hypothesis and summation principle.
In summary the differences between action potential and
synaptic transmission is therefore summarize in the table below
S/N
|
ACTION POTENTIAL
|
SYNAPTIC TRANSMISSION
|
1
|
It takes place within the neuron (it involve a single neuron)
|
It takes place between neurons’ synapse (i.e it involve more than one
neuron)
|
2
|
Mode of transmission is electrical signaling
|
Mode of transmission is by chemical signaling
|
3
|
The rate of transmission/conduction is faster
|
The rate of transmission/conduction is slow
|
4
|
Information is integrated from a single direction (i.e across the
axon)
|
It allows the receiving neurons to integrate information from many
sources.
|
5
|
It is govern by All – or – None Law
|
It is govern by lock and key hypothesis and summation principle.
|
SIMILARITIES
1.
They both causes ion channel to open and close
2.
They both involve cell wall polarity
3.
They both transmit information at all the level
of sensory input.
REFERENCES
Henry Gleitman, James Gross, Daniel Reisberg (2011). Psychology
Eight Edition. The brain and the
nervous system,
3, 92 – 101. New York: W.W. Norton & Company
Richard Gross (2010). Psychology; the science of mind and
behavior, sixth edition. The nervous system,
4, 51 – 52. UK
hodder education.
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