Summary
Highlights
Synapses are thousand times thinner than paper and more numerous than grains of sand on a beach. They are the meeting points between two neurons, responsible for turning the nervous system's structure into a functional system. With hundreds to thousands of trillions in the brain, each synapse acts like a tiny computer, capable of adaptation and change, enabling learning and memory. They are also linked to psychiatric disorders and the effects of illicit drugs.
The nervous system uses two communication settings: electrical and chemical synapses. Electrical synapses are immediate, like a group text, sending ion currents directly between nerve cells through gap junctions. This speed is crucial for synchronized actions, like the heart. However, they lack control. Chemical synapses are slower but more precise, using neurotransmitters to deliver messages to specific recipients.
Despite the speed of electrical synapses, chemical synapses are more abundant due to their greater control. If all synapses were electrical, the nervous system would be in perpetual 'group text' mode, leading to constant and exhausting stimulation, essentially causing death. Chemical synapses convert signals from electrical to chemical and back again, allowing for modification, amplification, inhibition, or splitting of impulses.
A chemical synapse involves a presynaptic neuron sending a signal through its terminal, containing vesicles filled with neurotransmitters. The postsynaptic neuron receives these neurotransmitters in its receptor region, typically on a dendrite or cell body, across a synaptic cleft. This process involves the release, diffusion, and reception of neurotransmitters.
When an action potential reaches the presynaptic terminal, it opens voltage-gated calcium channels, releasing calcium ions into the neuron's cytoplasm. This causes synaptic vesicles to fuse with the membrane, releasing neurotransmitters into the synaptic gap. These neurotransmitters bind to receptors on the postsynaptic neuron, opening ion channels and converting the chemical signal back into an electrical one, which can be either excitatory (depolarizing) or inhibitory (hyperpolarizing).
Hundreds of neurotransmitters exist, influencing various bodily functions, mood, and alertness. They bind to receptors for milliseconds before degrading or being recycled. Reuptake is a process where neurotransmitters are re-absorbed by the sending neuron. Drugs, both legal and illegal, exploit this mechanism by exciting or inhibiting neurotransmitter production, release, or reuptake, or by mimicking neurotransmitters.
Cocaine targets serotonin (mood, appetite), dopamine (pleasure, emotion, attention), and norepinephrine (fight or flight). Normally, these neurotransmitters are reabsorbed after delivering their messages. Cocaine blocks the reuptake of these chemicals, especially dopamine, leading to accumulation in the synapse, causing euphoria but also paranoia and jitters. Prolonged use depletes neurotransmitter supplies and can lead to a loss of receptors, requiring more of the drug to feel normal.
Understanding how things can go wrong with synapses highlights their critical role in bodily functions. Healthy synapses maintain a balance of excitation and inhibition, knowing when to use electrical and chemical messengers. This intricate system demonstrates the precise 'etiquette of electrical messaging' essential for a healthy nervous system.