Synaptic fatigue is due to a- decreased synthesis of neurotransmittersb- inability to release neurotransmitters by exocytosis cc- failure of action potentials to open voltage-gated Ca ++ channels in presynaptic terminald- imbalance in between rates of synthesis and release of neurotransmit

Synaptic fatigue, also known as synaptic depression, is a temporary inability of neurons to communicate with each other due to previous over-activity. This can occur due to several reasons:

a) Decreased synthesis of neurotransmitters: Neurotransmitters are chemicals that transmit signals across a synapse from one neuron to another. If the synthesis of these neurotransmitters decreases, it can lead to synaptic fatigue as the neurons are unable to communicate effectively.

b) Inability to release neurotransmitters by exocytosis: Exocytosis is the process by which neurotransmitters are released from the neuron into the synapse. If this process is impaired, it can lead to synaptic fatigue as the neurotransmitters are not able to reach the other neuron.

c) Failure of action potentials to open voltage-gated Ca++ channels in presynaptic terminal: The opening of these channels is crucial for the release of neurotransmitters into the synapse. If the action potentials fail to open these channels, it can lead to synaptic fatigue as the neurotransmitters are not released.

d) Imbalance in between rates of synthesis and release of neurotransmitter: If the rate of synthesis of neurotransmitters is not in balance with their release, it can lead to a buildup of neurotransmitters in the neuron, leading to synaptic fatigue.

Therefore, all of the above options (a, b, c, and d) can contribute to synaptic fatigue.