Biological Bases of Psychology

PSYC 1013 - Chapter 3: Biological Bases of Psychology

Chapter Overview

  • Overview of main topics covered in the chapter:

    • Neurons and how they function

    • The nervous system: Components and divisions

    • Brain structures and their function

    • Endocrine system

    • Heredity and behaviour

Neurons

  • Definition: The basic component of the entire nervous system.

  • Quantity: The human brain contains approximately 86 billion neurons with around 100 trillion connections between them.

  • Synapses: Neurons are separated from each other by synapses, which are tiny gaps where communication occurs between neurons.

Structure of Neurons

  • Dendrites:

    • Function: Receive incoming information from other cells.

    • Description: They're the receiving portion of a neuron and have many branches to increase surface area for receiving signals.

  • Cell Body (Soma):

    • Function: Contains the nucleus which produces proteins and neurotransmitters.

    • Importance: Critical for cell function and metabolic processes.

  • Axon:

    • Function: Long, thin fiber transmitting signals away from the cell body to other neurons, muscles, or glands.

    • Axon Terminal: The end of the axon where the neuron releases chemicals to influence the activity of other neurons. Contains synaptic vesicles filled with neurotransmitters.

  • Myelin Sheath:

    • Description: A fatty, insulating substance that wraps around the axon.

    • Function: Helps protect the neuron and speeds up the transmission of electrical impulses.

Synapses

  • Definition: The gap between neurons through which information is exchanged.

    • Presynaptic Neuron: The sending neuron that releases neurotransmitters.

    • Postsynaptic Neuron: The receiving neuron that accepts the neurotransmitters.

Types of Neurons

  • Sensory Neurons:

    • Function: Receive input from sensory organs (e.g., eyes, ears, skin) and send information to the brain.

  • Motor Neurons:

    • Function: Send output from the brain to muscles and organs, enabling movement.

  • Interneurons:

    • Function: Process and relay information between sensory and motor neurons within the brain.

    • Quantity: Thousands of times more numerous than sensory or motor neurons, reflecting their critical role in neural processing.

Communication Between Neurons

  • Mechanism: Neurons communicate through both electrical and chemical signals.

    • Electrical Signals: Messages propagated within the neuron; occur when the neuron is at rest or during action potential.

Neurons at Rest: Resting Potential

  • Ion Movement: Involves three types of ions: Chloride (-), Potassium (+), and Sodium (+).

    • Polarization: The neuron is polarized with a negative charge inside and a positive charge outside, stemming from a higher concentration of negatively charged ions inside compared to positive ions outside.

Neurons in Action: Action Potential

  • Action Potential: A neural impulse generated when incoming messages are strong enough to reach activation threshold.

    • Ion Activity: Sodium ions rapidly enter the neuron during depolarization, propagating the electrical signal.

    • All-or-None Law: If the activation threshold isn't reached, the impulse does not occur.

After Firing: Refractory Period

  • Absolute Refractory Period: After firing, the neuron temporarily cannot fire again.

    • Hyperpolarization: The electrical state becomes even more negative as chloride ions enter and positive ions exit.

    • Return to Resting Potential: Neurons need to return to resting potential to be prepared for the next impulse.

Synaptic Transmission Process

  • Neurons communicate through chemical messengers called neurotransmitters.

  • Following an action potential, neurotransmitters are released into the synapse and bind to receptors on the next neuron.

Eight Steps of Synaptic Transmission

  1. Synthesis: Neurotransmitters are synthesized in the neuron.

  2. Transportation & Storage: Neurotransmitters are transported to the axon terminal for storage in vesicles.

  3. Release: Action potential triggers the release of neurotransmitters into the synapse.

  4. Binding: Neurotransmitters bind to receptor sites on the dendrites of the receiving neuron.

  5. Deactivation: Neurotransmitters are broken down or removed from the synapse after they have fulfilled their purpose.

  6. Autoreceptor Activation: Some neurotransmitters bind to autoreceptors on the original neuron to reduce further release.

  7. Reuptake: Leftover neurotransmitters are reabsorbed into the presynaptic neuron.

  8. Degradation: Excess neurotransmitters are broken down to prevent overactivity in the synapse.

Hebbian Learning Rule

  • Proposed by Donald Hebb, this principle states that individual neurons do not influence behavior; rather, it is the networks or assemblies of neurons that do.

  • Hebbian Learning Rule: