Demyelination reduces the effectiveness of saltatory conduction, where action potentials normally jump between nodes of Ranvier along myelinated axons. Without proper myelin insulation, action potentials must propagate through slower continuous conduction along the entire axon membrane, significantly reducing transmission speed. This slower neural conduction directly translates to increased reaction times in behavioral responses. The action potential itself still follows the all-or-none principle, but travels much more slowly to reach axon terminals where neurotransmitter release occurs. The electrochemical nature of neural communication remains the same - electrical signals within neurons and chemical signals across synapses - but the reduced speed affects the timing of the entire neural circuit. The refractory period still occurs after each action potential, but the overall message delivery is delayed.

Since action potentials follow the all-or-none principle and maintain constant amplitude regardless of stimulus strength, stimulus intensity cannot be encoded by varying the size of individual action potentials. Instead, stronger stimuli are encoded through increased firing rate (frequency coding) and by recruiting more neurons to fire simultaneously (population coding). A weak stimulus might cause a neuron to fire slowly and activate fewer neurons, while a strong stimulus causes rapid firing and activates many neurons in the network. Each individual action potential travels down the axon with the same amplitude and triggers the same amount of neurotransmitter release at terminals. The electrochemical communication across synapses remains consistent, and each neuron experiences the same refractory period after firing. This frequency and population coding allows the nervous system to represent stimulus intensity despite the binary nature of action potentials.

When a toxin prevents vesicles from fusing with the presynaptic membrane, it blocks the crucial step of neurotransmitter release into the synaptic cleft. The action potential can still travel down the axon following the all-or-none principle and reach the terminals, but the electrical signal cannot be converted to chemical communication because neurotransmitter-containing vesicles cannot release their contents. This disrupts the normal electrochemical transmission process where electrical action potentials trigger chemical signaling across synapses. Without neurotransmitter release, the postsynaptic neuron cannot receive the chemical message, even though the presynaptic neuron fired normally and experienced its typical refractory period. This blockade effectively breaks the chain of neural communication at the critical electrical-to-chemical conversion step that occurs at axon terminals.

The myelin sheath acts as electrical insulation around axons, enabling saltatory conduction where action potentials jump rapidly between nodes of Ranvier rather than traveling continuously along the membrane. This jumping pattern dramatically increases the speed of neural transmission, which is crucial for quick reflex responses. The action potential maintains constant amplitude due to the all-or-none principle as it propagates to the axon terminals. Fast transmission ensures that the electrochemical signal - electrical within the neuron and chemical across synapses - reaches its target quickly. At the terminals, neurotransmitter release occurs when the action potential arrives, and during the subsequent refractory period, the neuron cannot immediately fire another action potential. This rapid, efficient transmission is essential for protective reflexes that require immediate responses.

Neural communication begins when an action potential travels down the axon as an electrical change in membrane voltage, maintaining constant amplitude due to the all-or-none principle. When this electrical signal reaches the axon terminals, it triggers vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft. These chemical messengers then diffuse across the gap and bind to specific receptor sites on the postsynaptic neuron, converting the signal back to electrical changes in the receiving neuron. If sufficient excitatory input reaches threshold, the postsynaptic neuron fires its own all-or-none action potential. The refractory period after each firing ensures that signals travel in one direction and maintains proper timing in neural networks.

When reuptake transporters are inhibited, neurotransmitters remain in the synaptic cleft for a longer duration because they cannot be efficiently removed by the presynaptic neuron. This prolonged presence increases the time that neurotransmitters can bind to postsynaptic receptors, potentially amplifying and extending their effects. The action potential that originally triggered neurotransmitter release followed the all-or-none principle, maintaining constant amplitude as it traveled down the axon. Normal neural communication involves electrochemical signaling - electrical action potentials within neurons and chemical neurotransmitter signaling across synapses. During the refractory period following the action potential, the presynaptic neuron cannot immediately fire again, but the extended presence of neurotransmitters in the cleft can continue to influence the postsynaptic neuron.

The all-or-none principle states that once a neuron reaches threshold, it fires a complete action potential of fixed amplitude, or if threshold is not reached, no action potential occurs at all. The size and speed of the action potential do not vary based on stimulus intensity - a barely threshold stimulus produces the same action potential as a much stronger stimulus. This electrical signal travels down the axon maintaining constant amplitude until it reaches the terminal buttons. There, the action potential triggers neurotransmitter release into the synaptic cleft, where chemical messengers cross to the postsynaptic neuron. Following each action potential, the refractory period temporarily prevents another firing, ensuring proper signal timing and preventing backward propagation of the electrical signal.

When an inhibitory neurotransmitter binds to postsynaptic receptors, it typically causes hyperpolarization by opening ion channels that allow negative ions to enter or positive ions to exit the cell. This makes the membrane potential more negative than resting level (more negative than -70 mV), moving it farther from threshold (-55 mV) and decreasing the likelihood that the neuron will fire an action potential. If the neuron does eventually reach threshold despite inhibitory input, it will still fire a full all-or-none action potential that travels down the axon with constant amplitude. The action potential triggers neurotransmitter release at synapses, and the refractory period following firing temporarily prevents another immediate action potential, maintaining proper neural timing.

During the refractory period, a neuron cannot fire another action potential immediately after the previous one, which serves several important functions in neural communication. This temporary inability to fire helps ensure that action potentials travel in one direction down the axon (from cell body to terminals) and limits the maximum firing rate of neurons. The refractory period occurs because sodium channels become temporarily inactivated and potassium channels remain open longer, making it difficult or impossible to reach threshold again. This mechanism is crucial for proper neural timing and prevents the chaotic firing that would occur if neurons could fire continuously. The action potential itself follows the all-or-none principle, maintaining constant amplitude as it travels to trigger neurotransmitter release at synapses.

Receptor sites are specialized protein molecules located on the postsynaptic neuron's membrane (typically on dendrites and cell body) that bind specific neurotransmitters in a lock-and-key fashion. When neurotransmitters released from presynaptic terminals cross the synaptic cleft and bind to these receptors, they cause ion channels to open or close, altering the postsynaptic neuron's membrane potential. This binding can either increase (excitatory) or decrease (inhibitory) the likelihood that the postsynaptic neuron will reach threshold and fire an all-or-none action potential. This represents the crucial chemical-to-electrical conversion in electrochemical neural communication. If threshold is reached, the action potential travels down the axon to trigger further neurotransmitter release. During the refractory period following any action potential, the postsynaptic neuron cannot immediately fire again, ensuring proper timing of neural signals.