The Difference Between Action potential and Synaptic Transmission

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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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