Chattahoochee Technical College 11

  • Action Potential: Energy needed to trigger a reaction, characterized as an all-or-nothing response.

  • Key Players:

    • Neurotransmitters: Key role in signaling, specifically acetylcholine in muscle cells.

    • Ions: Sodium (Na+) initiates action potentials, while calcium (Ca2+) and potassium (K+) play significant roles in muscle contraction and neuronal signaling.

  • Mechanism of Action:

    1. Sodium Influx: Sodium ions enter the neuron, triggering a depolarization when the membrane potential reaches -55mV (threshold).

    2. Calcium Release: The influx of sodium causes calcium to be released from the sarcoplasmic reticulum in muscle cells, enabling muscle contraction.

    3. Action Potential Propagation: After reaching a peak positive potential, potassium channels open, repolarizing the cell and eventually allowing it to return to resting potential (approx. -70mV).

    4. Hyperpolarization: Neurons can hyperpolarize below -70mV to ensure a complete reset to prevent immediate firing (refractory period).

  • Graded Potentials vs. Action Potentials:

    • Graded Potentials: Variable signal strength that may not reach the threshold; can summate but typically return to resting potential.

    • Action Potentials: Fixed intensity occurring once the threshold is reached at -55mV, leading to full depolarization and subsequent repolarization.

  • Excitatory vs. Inhibitory Signals:

    • Excitatory Postsynaptic Potential (EPSP): Caused by neurotransmitters like glutamate, bringing the membrane closer to the threshold.

    • Inhibitory Postsynaptic Potential (IPSP): Caused by neurotransmitters like GABA, moving the membrane potential further from the threshold, often by allowing chloride ions into the cell.

  • Synaptic Transmission: The space between neurons (synaptic cleft) allows neurotransmitters to transmit signals. Acetylcholine is a key neurotransmitter in muscle signaling, while in nerve-to-nerve communication, glutamate (excitatory) and GABA (inhibitory) are crucial.

  • Summary of Key Ions: Na+ and K+ are critical for depolarization and repolarization in neurons, while Ca2+ is essential for muscle contractions, and Cl- contributes to inhibitory effects.