Psych Lectures 1-30

Neuron Communication

Neuronal Membrane Structure

  • The neuronal membrane is surrounded by two types of fluids:

    • Extracellular Fluid: Found outside the membrane.

    • Intracellular Fluid: Located within the membrane, encompassing the cytoplasm.

  • This membrane acts as a barrier, separating interstitial fluid components from intracellular fluids.

Charge Differences Across Membrane

  • The two fluids exhibit different charge properties:

    • Intracellular Fluid: Typically negatively charged ions.

    • Extracellular Fluid: Contains positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-).

  • Charge distribution causes ions to flow from areas of high concentration to low concentration:

    • Positively charged ions move toward negatively charged areas (and vice versa).

Passive vs. Active Transport

  • Passive Transport:

    • Does not require energy input.

    • Example: Diffusion allows particles to move from higher to lower concentration areas without energy expenditure.

  • Active Transport:

    • Requires energy to move particles from lower to higher concentration areas, against the concentration gradient, typically through protein pumps.

  • Specific Example: Cardiac muscle cells require active transport for sodium and potassium ions to maintain proper function.

Neuron Action Potentials

  • Neurotransmitter Communication:

    • A neurotransmitter binds to receptors on an adjacent neuron, enabling sodium ions to flow in, changing the internal charge from negative to positive.

  • Threshold of Excitement:

    • Once the internal neuron potential reaches a critical level (threshold), it triggers an action potential, an electrical signal that propagates along the axon.

  • The sequence of events:

    1. Impulse travels down the axon to the axon terminals.

    2. Signal transmission occurs through synaptic connections.

    3. The membrane undergoes repolarization and can experience hyperpolarization if the potential dips below resting levels.

Action Potential Dynamics

  • At resting state, the membrane has more positive ions outside than inside, making it polarized.

  • Key Mechanisms of Action Potential:

    1. Voltage-gated Sodium Channels: Open in response to membrane depolarization, allowing Na+ to enter the neuron, further depolarizing the membrane.

    2. Repolarization: After Na+ influx, sodium channels close, and potassium channels open, allowing K+ to exit, restoring the internal negativity.

    3. Pump Action: The sodium-potassium pump restores initial ion concentration (3 Na+ out, 2 K+ in), requiring ATP energy.

Neurotransmitters and Psychological Disorders

  • Neurotransmitter systems influence psychological disorders:

    • Antagonists: Block neurotransmitter activity, as seen in schizophrenia treated with dopamine antagonists.

    • Reuptake Inhibitors: Example: SSRIs (Selective Serotonin Reuptake Inhibitors) prevent serotonin from being reabsorbed, increasing its availability and efficacy, used commonly for depression.

Neuroplasticity

  • The capacity of neurons to change and adapt; essential for learning, as synaptic connections are modified based on experiences.

Hemispheric Specialization

  • Left and Right Hemisphere Functions:

    • Left Hemisphere: Dominant in language processing, analysis, and logical reasoning.

    • Right Hemisphere: Handles visual-spatial tasks, face recognition, and emotional understanding.

  • Split Brain Studies:

    • Severing the corpus callosum to study independent hemisphere function; demonstrates separate cognitive processing abilities.

Conclusion

  • Understanding neuron communication is crucial for appreciating how signals transmit across the nervous system and how various factors can influence mental health and cognitive functions.