Module 1: Physiology of Neurons and Muscle PDF

BIO304: Physiology of Neurons and Muscle- Module 1 Dr. Rita Kumari, [email protected] BIO304: Physiology of Neurons and Muscle- Module 1 Today's Plan Module 1 : What is Nervous System? Let's try to define nervous syste...

BIO304: Physiology of Neurons and Muscle- Module 1 Dr. Rita Kumari, [email protected] BIO304: Physiology of Neurons and Muscle- Module 1 Today's Plan Module 1 : What is Nervous System? Let's try to define nervous system Animals without "Nervous system" Defining the nervous system How information flow in the nervous system? Challenges associated with understanding the nervous system Readings: From Neuron to Brain, Chapter 1 pgs. 1-15 Module 1: What is a nervous system? Who need nervous system? A living organism exhibits the following fundamental characteristics: Organized structure Requires energy Responds to stimuli Adapts to environmental changes Capable of reproduction Stimuli: Any change in the external or internal environment of an organism that provokes a physiological or behavioral response in the organism. Module 1: Let's try to define nervous system What exactly is the nervous system? It is a network of specialized cells called neurons that can receive and transmit information. This system is unique to animals. Is a brain necessary for a nervous system to function? Many invertebrates do not have centralized neural structures. For example, jellyfish and sea anemones possess nerve nets that effectively manage behaviors and responses to environmental cues. (credit: OpenStax Biology, e: modification of work by Michael Vecchione, Clyde F.E. Roper, and Michael J. Sweeney, NOAA; credit f: modification of work by NIH) http://molecular-ethology.bs.s.u-tokyo.ac.jp/labHP/E/EResearch/11.html Glutamate triggers long-distance, calcium-based plant defense signaling.Science361,1112-1115(2018).DOI:10.1126/science.aat7744  Module 1: Let's try to define nervous system Are neurons really required? Neurons are the cells that can generate electrical impulses Even bacteria1 and plant2 cells can generate electrical impulses 1. Prindle, A., Liu, J., Asally, M. et al. Ion channels enable electrical communication in bacterial communities. Nature 527, 59–63 (2015). https://doi.org/10.1038/nature15709 2. Glutamate triggers long-distance, calcium-based plant defense signaling.Science361,1112-1115(2018).DOI:10.1126/science.aat7744 Module 1: Let's try to define nervous system Is the formation of synapse crucial? Synpases: locations of cell-to-cell contact that allow chemical communication between cells Many synaptic genes originated in single- celled eukaryotes long before the emergence of animals Module 1: Animals without "Nervous system" Placozoans are free-behaving animals that do not have synapses or a "nervous system." Pausing behavior is contagious Adjacent animals pause after one animal initiates a pause Indirect evidence for secretion of a signaling molecule, since animals need not be in contact with each other Images and text courtesy to Prof. Senatore Module 1: Defining the nervous system Defining the nervous system becomes challenging when considering animals like Trichoplax. However, for this course, we will use the following definition: 1. Nervous System Composition: The nervous system consists of a network of specialized cells that sense information from: The external environment (light, chemicals, temperature, gravity, touch) The internal environment (internal states, signals from other cells) 2. Neuronal Function: Neurons propagate information along axons and dendrites through electrical impulses: Graded potentials Action potentials 3. Synaptic Communication: Neurons communicate with each other via chemical and electrical synapses. 4. Generating Outputs: The nervous system integrates sensory information to produce behavioral and physiological responses, such as: Muscle contraction and movement Heart rate, digestion, temperature regulation Feeding, courtship, locomotion Module 1: How information flow in the nervous system? Electrical Recording Techniques  Module 1: How information flow in the nervous system? Magnetic Resonance Imaging MRI Machine: Circular tunnel through which the patient moves. Uses powerful magnets (up to 10,000 gauss or 1 Tesla in hospitals). Higher power magnets (up to 100,000 gauss or 10 Tesla) provide better spatial resolution. Principle of the Technique: Detects and quantifies the movement of water molecules. Differentiates between gray and white matter. Utilizes the brain's heterogeneous tissue composition for imaging. Benefits: Differentiates between various tissue types. Suitable for visualizing small or detailed structures. Can replace CT scans for certain applications.. Drawbacks: Loud, unsuitable for patients with metal implants, potential burns from old tattoos. https://openbooks.lib.msu.edu/introneuroscience1/chapter/imaging-the-living brain/#:~:text=The%20functional%20magnetic%20resonance%20imaging,specific%20parts%20of%20the%20brain. Module 1: How information flow in the nervous system? Let's examine how information flows through neural circuits by using visual processing in the retina as an example: Module 1: How information flow in the nervous system? Light Receptor cells in the retina have special proteins in Rod and cone cells (photoreceptors) that detect light to trigger a change in voltage across the cell Here, light is converted membrane into an electrical signal in the receptor cells Module 1: How information flow in the nervous system? Light Electrical signals travels to synapses , where they trigger the release of chemicals (neurotransmitters) that bind neurotransmitter receptors on post synaptic Bipolar cells Chemical synapses convert electrical signals into chemical signals Module 1: How information flow in the nervous system? The neurotransmitter receptors on Bipolar cells produce graded Light electrical responses Stronger light → more Neurotransmitter (NT) secretion by receptor cell More NT → stronger change in membrane voltage (depolarization) of the Bipolar cell Module 1: How information flow in the nervous system? Graded responses reach Bipolar cell nerve terminals Light which synapse onto Ganglion cells Neurotransmitters are secreted again Bind to NT receptors on Ganglion cells to once again trigger graded electrical responses Module 1: How information flow in the nervous system? Light When graded depolarization is strong enough, excitable neurons (like Ganglion cells) generate action potentials (APs) All or none electrical responses that travel very fast along nerve fibers (e.g., axons) Module 1: How information flow in the nervous system? Graded vs. action potentials Images courtesy to Prof. Senatore Module 1: How information flow in the nervous system? Action potentials arise when graded potentials activate voltage-gated sodium (NaV) and potassium (KV) channels Unlike graded potentials, APs don’t dissipate All-or-none electrical impulses that can travel up to 120 m/s along axons! Module 1: How information flow in the nervous system? Graded vs. action potentials NaV channels drive membrane depolarization, while KV channels drive repolarization/hyperpolarization Some key action potential functions in neurons: Transmit signals along axons Trigger pre-synaptic Ca2+ influx at nerve terminals, through voltage- gated calcium channels, causing the regulated release of neurotransmitters (exocytosis) (NMJs) Images courtesy to Prof. Senatore https://theory.labster.com/muscle-contraction/ Module 1: How information flow in the nervous system? Graded vs. action potentials Key function in muscle Driving contraction: Skeletal muscle, cardiac and smooth muscle Key function in endocrine cells Driving secretion of hormones (exocytosis): promotes growth and maintain homeostasis https://www.healthdirect.gov.au/hormonal- system-endocrine https://www.zmescience.com/medicine/genetic/scientists engineer super mice/ Module 1:Challenges associated with understanding the nervous system As biologists, we often think of biological systems in genetic and chemical terms: i.e., reactions and interactions involving DNA, RNA, proteins, membrane lipids, However, the movement of electrical signals through neural structures requires understanding some core principles in physics: i.e. e., current, voltage, resistance/conductance, capacitance, In this course we aim to integrate these two ways of thinking about biological systems, to better understand how our own nervous system operates And by extension, how disease states emerge at the intersect between molecular biology and electrophysiology Module 1:Challenges associated with understanding the nervous system To understand the nervous system, we will use the knowledge of: Cell to Cell Communication – In a living organism, cells must pass information to one another to coordinate their activities through cell signaling. Structure and Function – Structure and function (from the molecular level to the organ system level) are intrinsically related to each other. The functions of molecules, cells, tissues, or organs are determined by their form (structure), and function can alter structure. Systems Integration – Organ systems work together; understanding the functions of the organism require a consideration of how multiple entities (cell, tissues, organs, and organ systems) interact with one another to sustain the life of the organism. Core principles in physics – The transport of “stuff” (ions, molecules, fluids, and gas) is a central process at all levels of organization in the organism, and a simple model describes such transport, other important concepts includes resistance, electrochemical gradient, molecular charge, current etc. Recommended reading: Available on course Quercus page End of Module 1