A

8.2 (part 2) - Electrical Nature of Nerves

8.2 NERVOUS SYSTEM

  • Topic covers the basics of the nervous system and homeostasis's role within it.

ELECTRICAL NATURE OF NERVES

  • Nerve Transmission: Nerves transmit messages through electrical impulses.

    • Components of Nerve Cell:

      • Soma (cell body)

      • Axon (long projection that conducts impulses away from the cell body)

      • Axon Terminal (end point of an axon where neurotransmitters are released)

    • Action Potential:

      • The direction of travel of action potential includes states: Depolarized, Repolarizing, Resting.

Nerve Activation Phases

  • Illustrates the phases of nerve activation including resting and depolarization stages.

    • Phases:

      1. Resting Stage

      2. Depolarization Phase

      3. Repolarizing Phase

      4. Undershoot (hyperpolarization)

Resting State of Neuron

  • Ion Concentration:

    • High concentration of Sodium (Na+) outside the neuron.

    • High concentration of Potassium (K+) inside the neuron.

  • Na+/K+ Pump:

    • Maintains ion concentrations; critical for resting state.

  • Membrane Potential:

    • Defined as electrochemical charge separation across a nerve cell membrane.

    • Resting Membrane Potential is approximately -70mV.

Sodium-Potassium Pump Process

  1. Cytoplasmic Na+ binds to the sodium-potassium pump.

  2. Na+ binding stimulates phosphorylation by ATP.

  3. Phosphorylation causes the protein to alter its shape, expelling Na+.

  4. Extracellular K+ binds to the protein, leading to the release of the phosphate group.

  5. Loss of phosphate returns the protein to original shape.

  6. K+ is released; Na+ sites are ready for binding again.

Action Potential Phases

  • Triggering Action Potential:

    • Action potentials occur when threshold potential (-55mV) is reached.

    • All-or-None Principle:

      • Action potentials either occur fully or not at all, irrespective of the stimulus strength.

    • Phases of Action Potential:

      1. Depolarization (Na+ channels open, Na+ enters neuron)

      2. Repolarization (Na+ channels inactivate, K+ channels open, K+ exits neuron)

      3. Hyperpolarization (membrane potential becomes more negative; K+ channels close)

  • Refractory Period:

    • During this time, Na+ and K+ channels are closed, and the resting membrane potential is re-established without new impulses occurring.

Myelinated Nerve Impulse

  • Saltatory Conduction:

    • Action potential occurs only at Nodes of Ranvier, allowing for rapid message transmission.

Multiple Sclerosis (MS)

  • A condition caused by an immune attack on the nervous system, affecting myelin with symptoms related to:

    • Vision (loss, double vision)

    • Fatigue

    • Cognitive impairment

    • Motor function (muscle spasms, atrophy)

    • Sensory issues (heightened pain, reduced touch)

Synapse Structure and Function

  • Definition:

    • A synapse is the junction between two neurons, or between a neuron and an effector.

  • Neurotransmitters:

    • Chemicals that transmit signals between neurons (ex. Acetylcholine, Dopamine).

    • Can either excite or inhibit the postsynaptic neuron.

  • Signal Transmission:

    • Upon signal arrival, neurotransmitters bind to receptors on the postsynaptic cell, opening ion channels and potentially triggering an action potential if threshold is met.