NeuroScience Exam Notes (Some main topic)

Receptors and Synaptic Transmission

  • Receptor Types: Nicotinic Acetylcholine (ACh) receptors are ionotropic (ligand-gated ion channels); Muscarinic ACh receptors are metabotropic (G-protein coupled).

  • Synaptic Delay: Time between presynaptic action potential (AP) and postsynaptic potential.

    • Electrical synapses: no delay.

    • Directly-gated chemical synapses: <0.5 \text{ ms}.

    • Indirectly-gated chemical synapses: >0.5 \text{ ms}.

  • Inhibition:

    • Presynaptic: Reduces neurotransmitter release via calcium channel modulation at axoaxonic synapses.

    • Postsynaptic: Produces IPSPs by opening potassium or chloride channels at axosomatic/axodendritic synapses.

Action Potentials and Membrane Potentials

  • Action Potential (AP) Initiation: Most likely at the axon hillock due to high density of voltage-gated sodium channels; requires local potential to reach threshold (−55 mV-55 \text{ mV}).

  • Resting Membrane Potential (RMP): Primarily driven by non-gated potassium channels; kept stable by the Na+/K+ pump maintaining ion gradients.

  • AP Height: Influenced by the external sodium concentration (gradient for sodium influx).

  • Nodes of Ranvier: Exposed gaps in myelinated axons, concentrated with voltage-gated ion channels for saltatory conduction.

  • After-Hyperpolarization (AHP): Membrane becomes more negative than RMP after an AP, due to prolonged opening of voltage-gated potassium channels.

Glial Cells and Nerve Conduction

  • Myelin-Producing Glia:

    • Oligodendrocytes: In the CNS, myelinate up to 1515 different axons.

    • Schwann Cells: In the PNS, myelinate a single axon.

  • Conduction Velocity:

    • Unmyelinated axon: Diameter×0.5 m/sDiameter \times 0.5 \text{ m/s}.

    • Myelinated axon: Diameter×5 m/sDiameter \times 5 \text{ m/s}.

  • MS Functional Recovery: Occurs via migration of voltage-gated sodium channels into previously myelinated areas, not remyelination.

Neurotransmitter Deactivation

  • Mechanisms:

    • Diffusion: Minor mechanism for all neurotransmitters.

    • Enzymatic Breakdown: Primary for Acetylcholine (ACh) via acetylcholinesterase.

    • Active Reuptake: Primary for most other neurotransmitters (e.g., GABA, glutamate, serotonin) back into the presynaptic terminal.

  • SSRIs (Selective Serotonin Reuptake Inhibitors): Block the active reuptake of serotonin, thereby increasing its concentration in the synaptic cleft to treat mood disorders.