chemical synapses

Overview of Chemical Synapses

  • Video titled "Chemical Synapses" discussing nervous tissue and signal generation.

  • Topics include graded potentials, action potentials, and nerve impulse conduction.

  • Key focus on how neurons communicate with other neurons and target cells, including muscles at the neuromuscular junction.

Learning Objectives

  • Describe events related to signal transduction at a chemical synapse.

  • Reference: Saladin's textbook, pages 451-457.

Types of Synapses

Electrical Synapses

  • Discussed briefly; involves cells close together.

  • Plasma membranes connected by connexons (gap junctions).

  • Electrical signals transmitted quickly (e.g., in cardiac muscle).

Chemical Synapses

  • Two cells (neuron and target cell) come close but do not touch.

  • Action potential reaches synaptic terminal, altering membrane potential.

  • Opens voltage-gated calcium channels at the synaptic terminal.

Sequence of Events at Chemical Synapses

  • Action Potential Arrival: Triggers opening of calcium channels.

  • Calcium influx: Calcium enters the synaptic terminal.

  • Neurotransmitter Release: Synaptic vesicles fuse with plasma membrane via exocytosis, releasing neurotransmitters into the synaptic cleft.

  • Target cell interaction: Neurotransmitter diffuses to receptors on postsynaptic neuron.

Neurotransmitter Actions

  • Binding to receptors can:

    • Generate postsynaptic potential.

    • Induce action potential in the postsynaptic neuron or inhibit signal generation.

Key Neurotransmitters

Acetylcholine

  • Small molecule with a chain of four carbons.

  • Functions at neuromuscular junction; cannot cross plasma membrane, acts on membrane receptors.

Catecholamines

  • Include norepinephrine, epinephrine (adrenaline), and dopamine.

  • Share structural features: benzene ring with hydroxyl groups and amine group.

  • Epinephrine and norepinephrine act as neurotransmitters and hormones; released during stress (adrenaline rush).

  • Dopamine linked to reward pathways; influences feelings of euphoria and potential psychotic episodes.

Other Neurotransmitters

  • Serotonin: Distinct structure, related to mood disorders, function in gut and blood clotting.

  • GABA: Most prevalent inhibitory neurotransmitter in the brain.

  • Peptides and Purines: Larger molecules, e.g., oxytocin (peptide), ATP (purine) can act as neurotransmitters.

  • Endocannabinoids: Derived from fatty acids, serve in neurotransmission.

  • Gaseous neurotransmitters: E.g., nitric oxide, involved in signaling.

Conclusion

  • The video concludes by stating the next topic will be integration of signals within nervous tissue.