Psych 202 Lecture 3

Page 1: Final Exam and Quiz Announcement

• The format of the final exam is still under consideration, but it is likely to be an in-person and closed-book exam to maintain the integrity of the testing process. Specific details regarding the format, duration, and coverage of the exam will be communicated as the date approaches.

• The university aims to consolidate exams into fewer sessions for security and logistical efficiency. This may impact how exams are scheduled and conducted.

• Neuroanatomy quiz details will be communicated through Canvas, the university's online learning management system. Students are encouraged to check Canvas regularly for updates.

• The quiz will be available starting on Monday and can be accessed over one week, allowing ample time for students to complete it at their convenience. Students can take the quiz at any time within that week, enabling flexibility in scheduling.

Page 2: Quiz Structure

• The quiz will have specific time constraints to ensure it is completed within a reasonable period. The anticipated time limit will be discussed in advance to allow students to prepare adequately.

• The design of the test is intended to be completed within half of the given time to minimize time-related stress for students, thereby allowing them to focus better on the content.

• Important topics that will be covered during lab sessions will serve as a primary resource for quiz preparation, ensuring students have hands-on experience and understanding of the material covered.

Page 3: Introduction to Neurophysiology

• This section provides a foundational understanding of how neurons function and communicate. A brief yet comprehensive overview emphasizes the principles without delving too deeply into complex equations, focusing instead on core concepts.

• Learning objectives in this section concentrate on crucial aspects of neuron structure, including resting membrane potential, excitatory and inhibitory potentials, and the mechanisms and significance of action potentials.

Page 4: Neuron Structure and Function

• Neurons are composed of three main parts: dendrites, which receive signals from other neurons; the cell body containing the nucleus; and the axon, which transmits signals to other neurons or muscles.

• Communication between neurons occurs at synapses, where neurotransmitters are released and bind to receptors on dendrites, influencing the neuron's activity.

• Action potentials, the electrical signals that propagate along the neuron, are generated at the axon hillock when the neuron reaches a certain threshold, integrating various incoming signals and determining firing output.

Page 5: Myelination and Action Potential

• Axons are often coated with myelin, an insulating sheath that speeds up the transmission of action potentials. The nodes of Ranvier, gaps in the myelin sheath, are critical for the regeneration of these action potentials, enhancing signal transmission efficiency.

• Different glial cells play distinctive roles in myelination: oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS) are key players in neuronal insulation and support.

Page 6: Role of Glial Cells

• Astrocytes are a type of glial cell that provides crucial structural support to neurons and helps regulate metabolism and neurotransmitter communication. This support is essential for maintaining overall brain health.

• They play a vital role in forming the blood-brain barrier, which regulates what substances can enter the brain, thus protecting it from potentially harmful agents in the bloodstream.

Page 7: Membrane Biophysics

• This section focuses on the three key ions: sodium (Na+), chloride (Cl-), and potassium (K+), which are essential for establishing the resting membrane potential.

• The resting membrane potential represents the negative electrical charge inside the cell (typically around -70 mV) compared to the outside, a critical factor in neuronal excitability and signal propagation.

Page 8: Action Potentials and Resting Potential

• A comprehensive overview of the resting membrane potential is crucial as it sets the stage for neuronal firing, enabling communication between neurons.

• It is important to understand the changes in membrane potential, particularly at the axon hillock, where action potentials are initiated, leading to the transmission of signals.

Page 9: Ion Movement and Forces

• Inside the cell, large negatively charged molecules, often proteins, significantly contribute to maintaining the negative membrane potential.

• Ions move based on two primary forces: diffusion gradients, which drive ions from high to low concentration, and electrostatic pressures, which influence ion movement based on charge, creating a delicate balance within the cellular environment.

Page 10: Sodium and Potassium Dynamics

• The concentration of sodium ions is higher outside the neuron, and they are driven into the negatively charged interior of the cell, which is essential for the excitability of neurons.

• As sodium enters the cell, potassium ions tend to diffuse out, but this process is countered by the negatively charged internal environment, which creates electrostatic pressures that balance the movements of these ions.

Page 11: Summary of Ion Concentrations

• The concentrations of various ions across cell membranes are essential for neuronal function. For example, typical values might reflect sodium at about 145 mM outside the cell and 12 mM inside, potassium around 5 mM outside and 140 mM inside, while chloride concentrations vary based on cellular context.

Page 12: Restoring Balance with Sodium-Potassium Pump

• The sodium-potassium pump is an essential mechanism that maintains resting membrane potential by actively transporting sodium ions out of the cell and potassium ions into the cell. This process is crucial for restoring ionic balance after action potentials and ensuring proper neuronal function.

• The continuous action of this pump is vital for maintaining the neuron's resting potential and overall excitability.

Page 13: Channel Dynamics

• Ion channels regulate the flow of specific ions when they open, leading to changes in the overall excitability of the neuron.

• These channels can be triggered by neurotransmitter release at synapses, resulting in excitatory or inhibitory post-synaptic potentials (PSPs) that influence neuronal signaling and firing patterns.

Page 14: Integration of Signals

• Neurons continuously integrate excitatory and inhibitory inputs from various sources, and this modulation plays a crucial role in determining overall firing potential.

• The dominance of inhibitory input helps stabilize neuronal activity, preventing excessive excitation that could lead to detrimental effects in neural circuits.

Page 15: EPSP and IPSP Dynamics

• Understanding temporal and spatial summation is essential for grasping how neurons fire; they require a considerable excitatory input to overcome any inhibitory signals and reach the threshold for generating action potentials.

• This interplay between excitatory post-synaptic potentials (EPSPs) and inhibitory post-synaptic potentials (IPSPs) is fundamental in determining neuron firing outcomes.

Page 16: Action Potential Overview

• An action potential is initiated when a neuron reaches a specific threshold level, resulting in a rapid influx of sodium ions and depolarization of the cell membrane.

• A detailed illustration typically accompanies this section, demonstrating the generation and propagation of action potentials along the axon.

Page 17: Action Potential Mechanism

• Voltage-gated sodium channels are integral to initiating action potentials at the axon hillock, allowing sodium ions to flood into the cell, which is a critical step in the action potential mechanism and leads to significant ionic exchanges that propagate the signal.

Page 18: Graded vs. Action Potentials

• This section discusses the differences between graded potentials and action potentials, particularly how graded potentials vary in amplitude depending on stimulus strength, whereas action potentials are all-or-nothing events that must reach a threshold to occur.

Page 19: Role of Potassium Channels

• After an action potential is generated, potassium channels contribute to repolarizing the cell by allowing potassium to flow out, bringing the cell back to its resting potential. This section also describes the overshoot phase that occurs post-depolarization, illustrating the dynamic changes in membrane potential.

Page 20: Nodes of Ranvier and Faster Transmission

• This section emphasizes the essential roles of myelination and the nodes of Ranvier, which together facilitate the rapid conduction of action potentials along axons, ensuring efficient and effective neuronal communication.

Page 21: Conclusion of Lecture

• A recap of the lecture content is provided, reiterating the importance of upcoming labs for practical application and deepened understanding of neurophysiological concepts.

• Students are encouraged to engage with the material actively and to seek clarification on topics of uncertainty as they prepare for assessments.