Biological Foundations of Behavior: Neurons, Neurotransmission, and Brain Structure

Chapter 3: Biology pt. 1

Brain Mapping Techniques

Understanding the structure and function of the brain is essential in psychology. Modern imaging techniques allow researchers to observe both the anatomy and activity of the brain in living humans.

• Magnetic Resonance Imaging (MRI): Uses strong magnetic fields and radio waves to produce detailed images of the brain's structure. MRI is non-invasive and provides high-resolution images of brain anatomy.

• Functional MRI (fMRI): Measures changes in blood oxygenation (the BOLD signal) to infer neural activity. fMRI allows researchers to observe which brain areas are active during specific tasks or in response to stimuli.

• Application: These techniques are widely used in research on self-regulation, addiction, and neurodevelopmental disorders.

Neuroscience Research Example

Research labs, such as the one led by Zu Wei Zhai, investigate the development of self-regulation and its neural basis, especially in at-risk youth. They use neurocognitive test batteries and both structural and functional MRI to explore the etiology of substance and behavioral addictions.

• Key Methods: Structural and functional MRI, large epidemiological datasets, and neurocognitive assessments.

• Focus: Understanding how brain development relates to behavior and risk for addiction.

Neurons and Neural Communication

Structure and Function of Neurons

Neurons are the primary cells of the nervous system, specialized for communication. The human brain contains approximately 86 billion neurons, interconnected by trillions of synapses.

• Neuron Anatomy:

  • Dendrites: Receive information from other neurons, muscles, or glands.

  • Cell Body (Soma): Contains the nucleus and organelles; responsible for cell maintenance and integration of signals.

  • Axon: Transmits electrical impulses away from the cell body toward other neurons or effectors.

  • Myelin Sheath: Fatty covering that insulates most axons, increasing the speed of information transmission.

  • Terminal Buttons: Branches at the end of the axon that release neurotransmitters into the synapse.

• Neural Circuits: Clusters of neurons work together to process specific types of information.

Neurotransmitters and Synaptic Transmission

Neurons communicate via chemical messengers called neurotransmitters (NTs). These substances are released from the axon terminals of one neuron and bind to receptor sites on the dendrites of another neuron, transmitting signals across synapses.

• Synapse: The tiny gap between neurons where neurotransmitters are released and received.

• Transmission Process:

  1. An electrical signal (action potential) travels down the axon.

  2. At the terminal button, synaptic vesicles release neurotransmitters into the synaptic cleft.

  3. Neurotransmitters bind to receptors on the postsynaptic neuron, influencing whether it will generate its own action potential.

  4. After binding, neurotransmitters are either broken down by enzymes or taken back up by the presynaptic neuron (reuptake).

• Types of Neurotransmitters: Examples include serotonin and dopamine, each with specific roles in mood, motivation, and behavior.

• Excitatory vs. Inhibitory: Some neurotransmitters increase the likelihood of the postsynaptic neuron firing (excitatory), while others decrease it (inhibitory).

Electrical and Chemical Signaling

Neural communication involves both electrical and chemical processes:

• Within Neurons: Information is transmitted electrically via action potentials along the axon.

• Between Neurons: Communication occurs chemically through neurotransmitter release at synapses.

Myelination and Neural Efficiency

Myelination is the process of encasing axons with a myelin sheath, which begins prenatally and continues into young adulthood. Myelination increases the speed and efficiency of electrical signal transmission along the axon.

• Example: Myelinated nerve fibers conduct impulses much faster than unmyelinated fibers, which is crucial for rapid responses and complex cognitive functions.

Neurogenesis and Plasticity

The brain is capable of neurogenesis (creation of new neurons) and plasticity (the ability to change and adapt in response to experience or injury).

• Plasticity: The nervous system can reorganize itself, especially during development or after injury. For example, if one hemisphere is damaged, the other may compensate for lost functions.

• Enriched Environments: Neurons in enriched conditions show more branching and synaptic connections than those in deprived environments.

Brain Structure and Organization

Brain Hemispheres

The human brain is divided into two hemispheres (left and right), each responsible for different functions but highly interconnected.

• Left Hemisphere: Typically associated with language, logic, and analytical tasks.

• Right Hemisphere: More involved in spatial, creative, and holistic processing.

• Plasticity Example: In cases of early brain injury, one hemisphere can sometimes take over functions normally performed by the other.

The Four Lobes of the Brain

The cerebral cortex is divided into four main lobes, each with specialized functions:

Lobe	Main Functions
Frontal Lobe	Planning, decision-making, voluntary movement, speech production (Broca's area)
Parietal Lobe	Sensory processing (touch, temperature, pain), spatial orientation
Temporal Lobe	Auditory processing, language comprehension (Wernicke's area), memory
Occipital Lobe	Visual processing

• Cerebral Cortex: The outer layer of the brain, responsible for higher-order functions such as perception, thinking, and language. It makes up about 80% of the brain's volume.

Additional info:

• Action potentials are governed by the movement of ions (e.g., Na+, K+) across the neuron's membrane, following the all-or-none law.

• Neurotransmitter imbalances are implicated in various psychological disorders (e.g., depression, schizophrenia).