Transmission of Action Potential Between Cells–synapse: Study Notes

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Transmission of action potential between cells–synapse

Snapse

• Synapse is the point of communication between two neurons or between a neuron and a target cell, like a muscle or a gland.
• At the synapse, the firing of an action potential in one neuron—the presynaptic, or sending, neuron—causes the transmission of a signal to another neuron—the postsynaptic, or receiving neuron—making the postsynaptic neuron either more or less likely to fire its own action potential.
• Inside the axon terminal of a sending cell are manysynaptic vesicles that are membrane-bound spheres filled with neurotransmitter molecules.
• There is a small gap between the axon terminal of the presynaptic neuron and the membrane of the postsynaptic cell, and this gap is called the synaptic cleft.

Type of Synapse

• Electrical Synapses:
  • Connect nerve cells directly through gap junctions.
  • Allow messages to pass quickly without losing strength.
  • Common in some animals for synchronizing rapid movements.
• Chemical Synapses:
  • Most synapses in vertebrates are chemical.
  • The axon terminal has sacs filled with neurotransmitters.
  • Calcium influx triggers neurotransmitter release.
  • Neurotransmitters bind to receptors on the receiving cell, altering its electrical state.
  • Depending on the receptor type, the cell can be excited or inhibited.
  • Neurotransmitters are removed by enzymes, reuptake, or glial cell uptake.

Type of Neurotransmitter

Neurotransmitters can be divided into two types: excitatory and inhibitory.

• Excitatory Neurotransmitters:
  • Make the receiving cell more likely to generate an electrical signal by causing depolarization (Na+ enters, K+ leaves).
  • Acetylcholine is a common example (effects vary by receptor).
  • Biogenic amines, such as epinephrine, norepinephrine, dopamine, and serotonin, are mainly found in the CNS.
  • Norepinephrine affects the autonomic nervous system, while dopamine and serotonin influence sleep, mood, attention, and learning.
  • Imbalances in these neurotransmitters are linked to disorders like Parkinson's disease and schizophrenia.
• Inhibitory Neurotransmitters:
  • Make the receiving cell more negative, creating an inhibitory postsynaptic potential (IPSP).
  • Potassium (K+) flows out, or chloride (Cl-) enters, making the cell more negative than its resting state.
  • Examples include GABA, glycine, glutamate, and aspartate.

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