BIOL2P03 Cell Biology Lecture 7 Part 2 2024 PDF

Cell Biology: Principles of Cell Function BIOL2P03 - Winter 2024 Lecture 7 - Membrane Transport Chapters 11 & 12: Membrane Transport and Excitable Cells Testable Material: Slides 4-18 ole-brain functional imaging at cellular resolution using light-sheet microsco...

Cell Biology: Principles of Cell Function BIOL2P03 - Winter 2024 Lecture 7 - Membrane Transport Chapters 11 & 12: Membrane Transport and Excitable Cells Testable Material: Slides 4-18 ole-brain functional imaging at cellular resolution using light-sheet microsco James Ackm Chapters 11 & 12: Ion Channels (Non-gated) Chapters 11 & 12: Ion Channels Chapters 11 & 12: Ion Channels & Membrane Potential Leak channels are largely Concentration responsible for setting the resting membrane -ve potential ▫ Resting membrane potential refers to the membrane potential of a V Electrical cell in the absence of any stimulus ▫ Typically -70 mV ▫ True for all animal cells +ve http://www.bem.fi/book/03/03.htm Excitable Cells Chapters 11 & 12: Na+ (Sodium) Ions Na+ (sodium) is another very important ion that can move across the plasma membrane through transporters, pumps and ion channels Na+ is more concentrated outside of the cell than inside of the cell ▫ Na+ will enter the cell down its concentration gradient when allowed ▫ Makes the membrane potential more positive ▫ Equilibrium potential of approximately +60 mV Na+ -ve +ve Extracellular Intracellular http://cellularlifeprocesses.weebly.com/transport. Chapters 11 & 12: Ca2+ (Calcium) Ions Ca2+ (Calcium) Ions are very important signalling molecules ▫ Involved in neuronal communication, exocytosis, gene expression, muscle contraction, etc. Similar to Na+, Ca2+ is more concentrated outside of the cell than inside Will enter the cell down its concentration gradient when allowed Makes the membrane potential more positive Chapters 11 & 12: Excitable Cells Excitable cells are specialized cells that possess gated ion channels that open in response to specific stimuli, which include: ▫ Changes in voltage ▫ Stretching of the membrane ▫ Presence of extracellular or intracellular signalling molecules (ligands) Ion fluxes rapidly alter the membrane potential ▫ Depolarization = membrane potential becoming more positive ▫ Hyperpolarization = membrane potential becoming more negative Examples of excitable cells include neurons, muscle cells and endocrine cells Chapters 11 & 12: Excitable Cells Voltage-gated Ion Channels Sensitive to changes in membrane potential ▫ Voltage sensor changes the conformation of the channel to allow ions to pass Typically in response to depolarization Voltage sensor Chapters 11 & 12: Excitable Cells Action Potential An electrical event produced in excitable cells through the co- ordinated activation of voltage-gated Na+ and K+ channels Chapters 11 & 12: Excitable Cells Action Potential Initial stimulus depolarizes membrane potential to the threshold Voltage-gated Na+ channels rapidly open Chapters 11 & 12: Excitable Cells Action Potential Voltage-gated K+ channels are also activated, but they take longer to open than Na+ channels Na+ channels have time-dependent inactivation Voltage sensor http://courses.washington.edu/conj/membrane/nacha Chapters 11 & 12: Excitable Cells Action Potential Na+ channels inactivate at around the same time that K+ channels open K+ rapidly leaves cell Ion Permeability Na+ enters K+ leaves Chapters 11 & 12: Excitable Cells - Neurons Neurons are excitable cells present in many animal species Allow for rapid communication between targets and the integration of information from multiple sources Consist of dendrites, a cell body, an axon and axon terminals Axon terminal Cell body Dendrites Axon Chapters 11 & 12: Excitable Cells - Neurons Action potential can self-propagate along axon ▫ Maintains original magnitude to axon terminal https://www.boundless.com/ biology/textbooks/boundless- biology-textbook/the-nervous- system-35/how-neurons- communicate-200/nerve- impulse-transmission-within-a- Chapters 11 & 12: Excitable Cells - Neurons Axon terminals contain voltage-gated Ca2+ channels at high density Action potential depolarizes the axon terminals, activating these Ca2+ channels, allowing Ca2+ to enter Elevations in intracellular Ca2+ levels promotes neurotransmitter release through a process known as exocytosis functional calcium imaging at cellular resolution using spinning disc confoc Ryan functional calcium imaging at cellular resolution using spinning disc confoc Ryan