Synaptic Transmission:

Types of Synapses:

a)One to one synapse-such type of synapses are found in neuromuscular junction where an action potential in presynaptic element produces an action potential in postsynaptic element.

b)Many to one Synapse-such types of synapses are found on spinal motor neurons where many cell synapses on postsynaptic cell are required to depolarize.The synaptic input may be excitatory or inhibitory.

Excitatory postsynaptic potentials(EPSPs)

• EPSP is produced by depolarization of the postsynaptic cell membrane immediately under the presynaptic ending.
• it is excitatory because membrane potential moves towards  its threshold.
• produced as a result of increase in conductance to Na+ and Ka+.
• Na+ influx causes depolarization.
• The EPSPs at synapses between neurons are similar to the  EPSPs at neuromuscular junctions.
• Excitatory neurotransmitters include ACh,Norepinephrine, Epinephrine,Dopamine,Glutamate,and Serotonin.

Inhibitory postsynaptic potentials(IPSPs):

• It hyperpolarizes the postsynaptic cell,moving away from threshold.
• Hyperpolarization is caused by opening of Cl- channels.
• Inhibitory  neurotransmitters are glycine and GABA.

Summation at synapses:

• Spatial Summation occurs when two excitatory inputs arrive at postsynaptic neurons simultaneously and produce greater depolarization
• Temporal  Summation occurs when  two excitatory inputs arrive at postsynaptic neurons in a rapid succession.because resulting postsynaptic depolarization overlap in time,they add in stepwise fashion.