Excitatory Effects: Some neurotransmitters (e.g., Adrenaline) increase the positive charge of the postsynaptic neuron. This makes the neuron more likely to reach the threshold required to fire an action potential.
Inhibitory Effects: Other neurotransmitters (e.g., Serotonin) increase the negative charge of the postsynaptic neuron. This hyperpolarization makes it significantly less likely that the neuron will fire.
Summation: The postsynaptic neuron 'adds up' the excitatory and inhibitory signals it receives; the net change in charge determines whether a new impulse is generated.
Enzymatic Degradation: Specific enzymes in the synaptic cleft break down neurotransmitters into inactive components, preventing continuous, uncontrolled stimulation of the postsynaptic neuron.
Reuptake: The presynaptic neuron may re-absorb the neurotransmitter molecules through specialized transporter proteins to be recycled and reused for future impulses.
Significance: Without these termination mechanisms, the postsynaptic neuron would remain permanently 'on' or 'off', leading to a loss of signal control and potential cellular fatigue.
| Feature | Excitatory Neurotransmitters | Inhibitory Neurotransmitters |
|---|---|---|
| Effect on Charge | Increases positive charge (Depolarization) | Increases negative charge (Hyperpolarization) |
| Likelihood of Firing | Increases | Decreases |
| Example | Adrenaline | Serotonin |
Sequence Accuracy: When describing the process, ensure you mention the arrival of the impulse before the release of neurotransmitters. Forgetting the initial action potential is a common point loss.
Terminology Precision: Use the term 'diffuse' when describing movement across the cleft. Do not say the neurotransmitters 'jump' or 'travel' without specifying the mechanism of diffusion.
Structure-Function Link: Be prepared to explain why transmission is unidirectional. The answer lies in the asymmetrical distribution of vesicles (presynaptic) and receptors (postsynaptic).
Check the Question: If asked for 'structures', focus on the knob, cleft, and receptors. If asked for 'process', focus on exocytosis, diffusion, and binding.
