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Synapses has the effect of slowing down nerve impulse by about 0.5ms per synapse, it can thus be assumed that their advantages out weight their disadvantages, before we go further let us look at what it is.



 What is a synapse?
It’s a place where the surface of the membrane of two neurone separated by synaptic cleft are joined together to allow transmission of impulses from one neurone to the other in one direction.

       The afferent is the pre-synaptic neurone
       The efferent is the post-synaptic neurone

 The arrival of action potential in the pre-synaptic terminal releases transmitter substances, which require calcium ion. The transmitter diffuses across the synaptic cleft to depolarize the post-synaptic membrane, by increasing permeability of Na+(PNa) via ion-selection Na+ channels. As a result of this an Excitatory Post-synaptic Potential (EPSP) is produced which if greater than threshold cause action potential to be initiated the post-synaptic neurone.

 Inhibition occurs when Inhibitory Post Synaptic Potential (IPSP) is developed due to an inhibitory inter neurone. The chemical substance during IPSP causes hyperpolarization due to opening of K+ and Cl- channel.

Characteristic of synaptic transmission
-          Are unidirectional (one direction)
-          Can be inhibited
-          There is usually delay of about 0.5ms
-          Susceptible to chemicals and drug
-          Inhibited by hypoxia, acidosis, and Mg2+
-          Facilitated by ca2+
-         Interaction can occur leading to summation, facilitation or occlusion of responses.

Advantages of synapses
 The advantages of synapses are summarized as follows
 
- Amplification: Sufficient acetylcholine is released at  neurotransmitter junction  by each nerve impulse to excite the post-synaptic membrane to produce respond in the muscular fiber , but there is a steep concentration gradient between the inside  and the outside of the axon membrane and sodium ion rapidly diffuse down this gradients.

- The relatively high potential difference between the axon encourages the inward movement of sodium ion.


-  Unidirectional: The discharge of transmitter substances at the pre-synaptic membrane and the locations of receptor site on the pre-synaptic membrane allow impulse to travel only in one direction.

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