EXAM 1 PSYCH 243

Contributions of Key Scientists in Neuroscience

Historical Perspectives

• Aristotle: Proposed that the brain was merely a cooling mechanism for the heart, which he believed was the center of intellect, reflecting the ancient view of the heart's importance in cognition.

• Galen: Conducted dissections of animal brains, leading to the conclusion that the cerebrum is responsible for processing sensations while the cerebellum controls movement, laying groundwork for future neuroanatomy.

• Descartes: Introduced the concept of mind-body dualism, suggesting that the mind and body are separate entities, and theorized that movement was controlled by fluid in the brain's ventricles, influencing later philosophical and scientific thought.

Advancements in Neuroscience

• Bell and Magendie: Their work established that the dorsal roots of spinal nerves carry sensory information while the ventral roots carry motor information, a fundamental discovery in understanding the nervous system's organization.

• Franz Joseph Gall: Developed phrenology, positing that different brain regions correspond to specific personality traits, which, despite being discredited, sparked interest in the localization of brain functions.

• Darwin: Proposed that behaviors, like physical traits, evolved through natural selection, influencing the field of comparative neuroscience and the study of behavior in different species.

Nissl vs. Golgi Stains

Staining Techniques in Neuroscience

• Nissl Stain: Utilizes basic dyes to stain the nuclei and surrounding material in neurons, allowing researchers to distinguish between neurons and glial cells, and study brain cytoarchitecture.

• Golgi Stain: Employs silver chromate to visualize the complete structure of a small percentage of neurons, revealing both the soma and neurites (axons and dendrites), providing insights into neuronal morphology.

Functions of Neuronal Organelles

Key Organelles and Their Functions

• Nucleus: Houses DNA, which directs gene expression and is crucial for the synthesis of proteins necessary for neuronal function.

• Mitochondria: Responsible for generating ATP through cellular respiration, providing the energy required for various cellular processes.

• Rough Endoplasmic Reticulum (Nissl bodies): Synthesizes membrane-bound and secretory proteins, essential for neurotransmitter release and membrane maintenance.

Additional Organelles

• Smooth Endoplasmic Reticulum: Assists in protein folding and regulates internal calcium levels, which are vital for neurotransmitter release and signal transduction.

• Golgi Apparatus: Modifies, sorts, and packages proteins for transport to their final destinations, playing a key role in neuronal communication.

Functions of Neuronal Parts

Structural Components of Neurons

• Soma: Contains the nucleus and organelles; integrates signals received from dendrites and is essential for maintaining cell health.

• Axon: Transmits electrical signals over long distances, crucial for communication between neurons.

• Axon Hillock: The site where action potentials are initiated, acting as a trigger zone for signal propagation.

Dendrites and Their Role

• Dendrites: Receive synaptic inputs from other neurons, playing a critical role in integrating information and determining neuronal output.

Cytoskeleton: Function & Components

Role of the Cytoskeleton in Neurons

• Function: Provides structural support to the neuron and facilitates intracellular transport, essential for maintaining neuronal integrity and function.

• Microtubules: Large, hollow tubes made of tubulin, crucial for axonal transport of organelles and proteins, ensuring proper neuronal function.

• Neurofilaments: Provide structural stability to the neuron, helping maintain its shape and resilience against mechanical stress.

Additional Cytoskeletal Components

• Microfilaments: Composed of actin, involved in changes to cell shape and motility, playing a role in synaptic plasticity and growth cone dynamics.

Neural Membrane and Ion Regulation

Membrane Proteins and Their Functions

• Ion Channels: Allow specific ions to pass through the membrane, crucial for generating action potentials. Example: Voltage-gated sodium (Na⁺) and potassium (K⁺) channels are essential for neuronal excitability.

• Ion Pumps: Maintain ionic gradients across the membrane. Example: Sodium-potassium pump (Na⁺/K⁺ ATPase) is vital for restoring resting membrane potential after action potentials.

• Receptors: Detect neurotransmitters and initiate cellular responses. Example: AMPA and NMDA glutamate receptors are key players in synaptic transmission and plasticity.

Axonal Transport: Function and Necessity

Mechanisms of Axonal Transport

• Anterograde Transport: Moves materials from the soma to the axon terminal using kinesin motor proteins, essential for delivering proteins and organelles needed for neurotransmission.

• Retrograde Transport: Transports materials from the axon terminal back to the soma using dynein motor proteins, important for recycling materials and signaling pathways.

Neuron Classification

Types of Neurons

• Based on Number of Neurites: Neurons can be classified as unipolar, bipolar, or multipolar, reflecting their structural complexity and functional roles.

• Dendritic Structure: Neurons can be stellate (star-shaped) or pyramidal (pyramid-shaped), influencing their connectivity and function.

• Connections: Neurons are categorized as sensory, motor, or interneurons based on their roles in the nervous system.

Additional Classification Criteria

• Axon Length: Golgi Type I neurons have long axons, while Golgi Type II neurons have short axons, affecting their functional reach.

• Gene Expression: Neurons can be classified based on neurotransmitter usage, such as cholinergic neurons that release acetylcholine, influencing their roles in signaling.

Neurons vs. Glia: Anatomical & Physiological Differences

Comparison of Neurons and Glial Cells

• Neurons: Excitable cells that transmit electrical and chemical signals, forming the primary communication network in the nervous system.

• Glia: Support cells that provide insulation, nutrition, and structural support to neurons, playing critical roles in maintaining homeostasis and supporting neuronal function.

Types of Glial Cells

• Astrocytes: Found in the CNS; regulate the extracellular environment and neurotransmitter levels, contributing to the blood-brain barrier.

• Oligodendrocytes: Located in the CNS; produce myelin, which insulates axons and enhances signal transmission.

• Schwann Cells: Found in the PNS; myelinate axons, facilitating rapid conduction of action potentials.

• Microglia: Act as immune cells in the CNS, responding to injury and disease.

• Ependymal Cells: Line the ventricles of the brain and help circulate cerebrospinal fluid, contributing to the brain's homeostasis.