Roles of Synapses

Summation

• Temporal Summation: Involves one presynaptic membrane feeding into one postsynaptic membrane. Helps filter out low-level stimuli by requiring multiple stimuli for neurotransmitter release sufficient to trigger postsynaptic depolarization.
  • Example: Filter out the sensation of wearing clothes.
• Spatial Summation: Involves several presynaptic membranes feeding into one postsynaptic membrane, allowing for convergence. This enables impulses from more than one neuron to trigger an action potential in a single postynaptic neuron if all are activated simultaneously.

Convergence and Divergence

• Synapses allow for convergence (impulses from multiple neurons converge into a single neuron) and divergence (a single neuron's impulses are conveyed to multiple neurons).

Types of Synapses

• Excitatory Synapse: Increases membrane's potential towards threshold, potentially triggering an action potential.
• Inhibitory Synapse: Decreases membrane's potential away from threshold, reducing the chance of an action potential.

Key Roles and Functions

• Ensure Transmission in One Direction: Due to the specific arrangement of calcium channels, vesicles, and neurotransmitter receptors.
• Permit Memory and Learning: Synaptic activities contribute to brain functions like memory, learning, and decision-making.
• Filter Out Low-Level or Background Stimuli: Both temporal and spatial summation contribute to this, preventing constant response to minor stimuli.
• Prevent Fatigue and Overstimulation: By regulating the conditions under which action potentials are triggered.
• Allow Amplification of Many Low-Level Stimuli: Especially in the context of spatial summation.

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