COMO A SINAPSE e o potencial de ação ACONTECEM!

Summary

The video explains how neurons communicate through chemical synapses. It organizes the process into four stages: receiving signals, integrating them, conducting an action potential, and releasing neurotransmitters.

Neuron structure

• Dendrites receive signals from other neurons.
• Cell body (soma) performs cellular functions and integrates incoming signals.
• Axon conducts the action potential and transports materials, including neurotransmitter-filled vesicles, toward the neuron’s end.
• Axon terminal releases neurotransmitters into the synaptic cleft.

The four stages of synaptic communication

1. Signal reception in the dendrites

   • Neurotransmitters bind to ligand-gated receptors on the dendritic membrane, causing ion channels to open.
   • Excitatory signals generally allow positive ions, often sodium, to enter the neuron. This produces an excitatory postsynaptic potential and makes the membrane less negative.
   • Inhibitory signals can cause positive ions to leave or negative ions to enter, making the membrane more negative and less likely to fire.

2. Integration in the cell body

   • The neuron combines excitatory and inhibitory inputs arriving across its dendrites.
   • If the overall effect brings the membrane to threshold—described in the video as changing from about −70 mV at rest to about −55 mV—an action potential is initiated. If it does not reach threshold, the neuron does not fire.

3. Action-potential conduction along the axon

   • At the nodes of Ranvier, voltage-gated sodium channels open when the local membrane reaches threshold. Sodium enters, briefly making the inside of the neuron more positive.
   • This voltage change activates channels at the next node, allowing the signal to travel along the axon. In myelinated axons, the action potential is regenerated at the nodes of Ranvier.
   • Sodium channels then close and potassium channels open, allowing potassium to leave the cell and restoring the membrane toward its resting state. A brief hyperpolarization may occur before the membrane returns to rest.

4. Neurotransmitter release at the axon terminal

   • When the action potential reaches the terminal, voltage-gated calcium channels open and calcium enters.
   • Calcium helps vesicle and cell membranes connect and fuse, releasing neurotransmitters into the synaptic cleft.
   • The neurotransmitters bind to receptors on the next neuron, beginning the signaling process again.

Clearing neurotransmitters from the synaptic cleft

Neurotransmitters are removed either through enzymatic breakdown or by being taken back up into the presynaptic neuron for reuse. This return process is called reuptake.

The video uses serotonin as an example: some antidepressant medications inhibit its reuptake, leaving more serotonin available in the synaptic cleft for longer.

Speakers and sources featured

• Rafaela Rocha — professor and neuroscience master’s graduate; the sole speaking presenter.
• The video also refers viewers to her illustrated “neuromaps” collection and another video on neurotransmitters. No other presenter or source speaks in the subtitles.