Understanding Synapses

Overview of Synapses

Synapses are the tiny communication links between neurons.
Neurons form the structure of the nervous system; synapses turn it into a functional system.
Synapses are the junctions that allow electrical messages to be converted and transmitted between neurons.

Human brain contains 100 billion neurons, each with 1,000 to 10,000 synapses.
Total synapses in brain range from 100 to 1,000 trillion.
Synapses enable learning, memory, and are linked to psychiatric disorders and drug addictions.

Electrical Synapses:
- Send ion currents through gap junctions rapidly.
- Allow synchronized actions among cells, e.g., heart muscle cells.
Chemical Synapses:
- Use neurotransmitters to send signals across synaptic gap.
- Offer control and selectivity over message transmission.

Presynaptic and Postsynaptic Neurons:
- Presynaptic neuron sends signals via axon terminal.
- Postsynaptic neuron receives signals with receptor regions.
Signal Transmission:
- Electrical signal -> Chemical signal -> Back to Electrical.
- Neurotransmitters diffuse across synaptic cleft.
Excitatory vs. Inhibitory Neurotransmitters:
- Excitatory: Depolarize postsynaptic neuron, closer to action potential.
- Inhibitory: Hyperpolarize postsynaptic neuron, further from action potential.
Neurotransmitter Lifecycle:
- Released neurotransmitters quickly degrade or recycle.
- Reuptake: Diffuse and reabsorb by presynaptic neuron.

Drugs manipulate neurotransmitter release, uptake, and mimicry.
Cocaine example: Blocks reuptake of serotonin, dopamine, norepinephrine.
- Leads to euphoria, paranoia, and jitteriness.
- Depletes neurotransmitter supply leading to adverse effects.
- Long-term use causes brain to adjust by reducing receptors.