Introduction to Neurotransmission and Potential

Neurons and Synaptic Transmission

Presynaptic and Postsynaptic Neurons

• Presynaptic Neuron: The neuron that sends a signal. Contains vesicles filled with neurotransmitters, which are signaling molecules released from the neurons.

• Vesicles: Membrane-bound sacs containing neurotransmitters ready to be released.

• Postsynaptic Neuron: Receives signals from the presynaptic neuron. Contains receptor proteins embedded in its membrane that bind neurotransmitters.

• Dendrites: The part of the postsynaptic neuron primarily responsible for receiving input.

Synaptic Transmission Process

1. Action Potential in Presynaptic Neuron: Initiates at the axon terminal, leading to depolarization.

2. Opening Voltage-Gated Calcium Channels: Caused by action potential depolarization; these channels are permeable to calcium ions.

3. Calcium Influx: Calcium moves into the presynaptic neuron, triggering vesicles containing neurotransmitters to fuse with the presynaptic membrane and release their contents into the synaptic cleft.

4. Neurotransmitter Bind to Receptors: Neurotransmitters bind to receptors on the postsynaptic neuron, activating them. This results in local changes in membrane potential.

Local and Graded Potentials

• Local (Graded) Potentials: Small changes in membrane potential that are initiated by neurotransmitter binding, can vary in size and direction (positive or negative), and do not travel far. They can be classified as:

  • Excitatory Postsynaptic Potential (EPSP):

  • Makes neuron less negative (closer to threshold, about -55 mV).

  • Caused by ions like sodium (Na) or calcium (Ca²+).

  • Inhibitory Postsynaptic Potential (IPSP):

  • Moves neuron further from threshold (more negative).

  • Caused by potassium (K extsuperscript{+}) eflux or chloride (