PSY1BNA Week 2 - Lecture Notes

Week 2: Cell Biology

Course: PSY1BNA

Institution: La Trobe University, Australia

Lecture Overview

Part 1: Introduction to how we study cells in the brain, highlighting techniques used in cellular observation and the historical evolution of these methodologies.

Parts 2 & 3: Examination of the basic and specialized structures of a typical neuron, including detailed descriptions of their roles, functionalities, and importance in neural communication.

Part 4: Classifying neurons and glial cells, explaining their characteristics, functions, and significance in maintaining overall brain health and function.

Learning Outcomes

• Understand how scientists use various techniques to study brain cells, including modern imaging methods and classical histological techniques.

• Identify and describe the basic components of all cells, with a focus on neurons, including their unique structures and functions.

• Recognize specialized neuronal structures, such as dendrites and axons, and understand the mechanisms of how information is transmitted through neurons, including neurotransmitter activities.

• Classify different types of neurons and glial cells and explain their support roles in neural activity, as well as their impact on neurological health and disease.

Readings

• Breedlove, S.M., & Watson, N.W. (2023). Behavioral Neuroscience (10th ed.). Sinauer Associates, Inc.Access the readings as specified, ensuring to focus on recent advancements in the field.

Introduction to Cell Biology

• All tissues and organs are composed of cells, which serve as the fundamental unit of life. The functionality of organs is greatly influenced by the specialized functions of their constituent cells.

• The nervous system largely consists of nerve cells (neurons) that are essential for processing and transmitting information throughout the body.

Key Facts about Nervous System Cells

• The human brain contains approximately 80-90 billion neurons along with a comparable number of glial cells, highlighting the complexity and density of neural networks.

• Neurons:

  • Sense environmental changes through receptors.

  • Transmit information between neurons via electrical impulses and neurochemical signals.

  • Command bodily responses, directly influencing actions and reflexes.

• Glial Cells:

  • Insulate, support, and nourish neighboring neurons, playing critical roles in maintaining homeostasis and forming myelin.

Structure of Neurons

• Neurons are comprised of a cell body and specialized structures that facilitate both the processing and communication of information.

• The integration of signals from various sources allows neurons to contribute to complex processing within the brain.

Challenges in Studying Brain Cells

• Neurons are often very small, requiring thin sections to be prepared for microscopic observation, which poses challenges for visualization and analysis.

• Fresh brain tissue can appear uniform, complicating the differentiation and identification of various cell types during study.

• The advent of the compound microscope marked a significant turning point in the ability to scrutinize and document cellular structures in detail.

Early Techniques in Histology

• Tissue Fixation: Formaldehyde is utilized to harden brain tissue, preserving cellular structures for study.

• Microtome: A device used to cut ultra-thin sections of tissue, facilitating detailed microscopic examination.

• Staining Techniques: Special stains such as the Nissl stain are employed to highlight specific cellular structures, effectively allowing for differentiation of neurons from other cell types by visualizing cell nuclei.

Historical Discoveries in Neuroscience

• Golgi Stain (1873): This stain highlights a small subset of neurons completely, enabling the visualization of their complex structures, which was revolutionary for understanding brain architecture.

• Cajal's Neuron Doctrine: Proposed that neurons communicate through direct contact rather than as part of a continuous network, affirming the individuality of neurons and advancing the understanding of neural circuits.

• The Electron Microscope proved instrumental in clinching evidence of neurons as distinct units rather than interconnected networks, thus validating Cajal's findings.

Key Knowledge on Neurons & Glial Cells

• Familiarity with the basic roles of neurons and glial cells, the major components of neurons, and methodologies for studying these cells.

• Understanding historical theories that laid the groundwork for modern neurobiology, including the functional implications of these theories.

The Prototypical Neuron

• Soma: Contains cytoplasm and organelles, surrounded by a membrane embedded with specialized proteins that facilitate signal reception and metabolic functions.

• Cytoplasmic Organelles: Sites for protein synthesis and modifications include:

  • Ribosomes: Responsible for the synthesis of proteins that serve various cellular functions.

  • Rough and Smooth Endoplasmic Reticulum: Involved in protein modification and lipid synthesis, respectively, essential for cell membrane production and metabolite synthesis.

  • Golgi Apparatus: Functions in packaging proteins for transport to different parts of the cell or for secretion.

  • Mitochondria: Known as the powerhouse of the cell, they generate adenosine triphosphate (ATP), providing energy necessary for neuron function.

Cytoskeleton in Neurons

• The cytoskeleton is crucial for maintaining the neuron’s shape and transportation of materials within the cell, consisting of various filamentous structures:

  • Microtubules: Give structure and facilitate intracellular transport.

  • Neurofilaments: Provide support and stability to neuronal architecture.

  • Microfilaments: Involved in the movement and stability of the neuron terminal.

Specialized Neuronal Structures

• Axon: Composed of:

  • Axon Hillock: The initial segment where action potentials are generated.

  • Axon Proper: The middle region that propagates the electrical signals.

  • Axon Terminal (or Bouton): The endpoint that connects with other neurons at the synapse, facilitating neurotransmitter release.

• Axonal transport is crucial as proteins synthesized in the soma travel down the axon to support its functions. Neurotransmission occurs at the synapse, with neurotransmitters transmitting signals to adjacent cells.

• Dendrites: The branched extensions that collect incoming signals from synapses. They play a key role in neuroplasticity, adapting in size and shape to reflect learning and memory processes.

Classification of Neurons

• Classification is based on several factors, including shape, number of neurites, and functional connections:

  • Structural Types: Unipolar, bipolar, and multipolar neurons.

  • Functional Classes: Primary sensory neurons, motor neurons, and interneurons, each serving distinct roles in the nervous system.

Glial Cells

• Different types of glial cells include:

  • Astrocytes: The most abundant glial cells that regulate the extracellular environment, influence synaptic transmission, and are involved in the formation of synapses.

  • Myelinating Glia: These include oligodendrocytes and Schwann cells that provide the myelin sheath, which enhances the speed of nerve impulse transmission.

  • Microglia: Act as the primary immune defense for the central nervous system by removing debris through phagocytosis.

  • Ependymal Cells: Produce cerebrospinal fluid, which cushions and nourishes the brain and spinal cord.

Clinical Importance of Glial Cells

• Understanding glial cells is crucial, as conditions such as brain tumors, edema after injury, the role of microglia in Alzheimer’s disease, and demyelination in multiple sclerosis highlight their significance in neurological health.

Key Understandings

• Comprehensive classification of neurons based on their structural and functional attributes, as well as neurotransmitter utilization patterns. Understanding different types of glial cells and their unique functions is vital for grasping brain physiology and pathology.