Intro_Biopsychology (1)

Introduction to Biopsychology

• Instructor: Cassio Campello de Menezes, MD, MAMHC, LAC, Adjunct Instructor at Caldwell University.

What is Biopsychology?

• Definition of Psychology: Derived from Greek words 'psyche' (mind) and 'logos' (reason), it signifies the reasoned study of the mind.

• Biopsychology: Focuses on the brain's role in producing behavior and mental processes.

  • The mind is a product of the brain's electrical and neurochemical activity.

  • The mind and brain are interconnected; their relationship underpins biological psychology.

  • The mystery of how the brain creates the mind is still unresolved.

Importance of Biopsychology

• Biopsychology is considered a fundamental discipline within the broader field of neuroscience.

  • Neuroscience encompasses the comprehensive study of the nervous system, from molecules to behavior.

Brain, Neurons, and Synapse

• Weight of Adult Brain: Approximately 3.5 pounds.

• Composition: Comprised of individual autonomous cells mainly neurons, which process and transmit information.

  • The human brain houses around 100 billion neurons.

  • Neurons connect through synapses, which are tiny gaps between them.

  • Communication among neurons relies on neurotransmitters.

Historical Perspectives on Brain Function

• Galen (c. 130–200 AD): Proposed that an animated spirit resided in the brain's ventricles, each with distinct mental functions.

  • This theory persisted for over 1,500 years.

• René Descartes (1596–1650): Suggested that most behaviors are mechanical and reflexive rather than governed by spirits.

• Luigi Galvani (1791): Discovered the presence of electricity in nervous tissue, challenging Galen’s theory.

Advances in Understanding Neurons

• Camillo Golgi (1875): Developed the first staining technique to visualize individual neurons.

  • This enabled Santiago Ramón y Cajal to depict various brain regions and discover synapses.

• Otto Loewi (1921): Conducted experiments proving that synaptic transmission is chemical.

• John Z. Young (1936): Discovered a giant neuron in squid.

• Hodgkin and Huxley (1952): Explained the mechanism of action potentials.

Structure of Neurons

• Key components:

  • Dendrites: Receive signals.

  • Soma (Cell Body): Contains the nucleus.

  • Axon: Transmits impulses away from the soma, insulated by myelin sheath which speeds up transmission.

  • Node of Ranvier: Gaps in the myelin where action potentials are regenerated.

  • Axon terminals: Release neurotransmitters into synapses.

Neuronal Communication

• Neurotransmitter release occurs when an electrical impulse (action potential) reaches the axon terminals.

  • Process:

    • Presynaptic neuron releases neurotransmitters into synapse.

    • These bind to receptors on the postsynaptic neuron, leading to changes in its membrane potential.

  • If the postsynaptic neuron is sufficiently excited (past -15 mV), it generates its own action potential.

Membrane Potential and Action Potentials

• Resting Potential: A neuron's membrane potential at rest, typically -70 mV.

  • Maintained by unequal ion distribution and sodium/potassium pumps.

• Depolarization: Occurs when sodium ions flood into the neuron, changing the membrane potential significantly.

  • Initiated at axon hillock when threshold (-55 mV) is reached.

Action Potential Generation

• Phases:

  • Depolarization: Sodium channels open; rapid influx of Na+ ions increases internal voltage.

  • The interior briefly becomes positively charged (overshoot) followed by repolarization when K+ ions exit.

• Saltatory Conduction: In myelinated neurons, action potentials jump between nodes of Ranvier, speeding transmission.

Neurotransmitter Activation

• Upon arrival at the axon terminal, action potentials trigger calcium channels to open.

  • This initiates exocytosis, releasing neurotransmitters into the synaptic cleft.

  • Neurotransmitters have to be deactivated (through reuptake or degradation) to prevent prolonged action.

Classification of Neurotransmitters

• Important Types:

  • Acetylcholine: Learning and muscle action.

  • Dopamine: Pleasure and reinforcement.

  • Serotonin: Mood regulation.

  • GABA: Inhibition, calming effect.

  • Endorphins: Pain relief and euphoria.

Receptor Mechanisms**

• Receptors can either be ionotropic (directly linked to ion channels) or metabotropic (indirectly linked via signaling cascades).

• Receptors follow a lock-and-key mechanism, binding specifically to their respective neurotransmitter.

Role of Glial Cells

• Functionality: Support and maintain neuronal activity and health.

  • Astrocytes: Provide structural support and maintain blood supply.

  • Oligodendrocytes: Form myelin for insulation of axons in the CNS.

  • Microglial cells: Act as the primary immune defense in the brain.