Communication Within A Neuron PDF

Communication Within A Neuron  Group Members ATTIQA SIDDIQUE 007325/MSCP/F24 ALEENA KHAN 0073251/MSCP/F24 LAIBA IKRAM 006272/MSCP/F24 ALISHBA SHER 007354/MSCP/F24 HAJRA JAVED 008503/MSCP/F24 AMBER MASOOD 008502/MSCP/F24 Communi...

Communication Within A Neuron  Group Members ATTIQA SIDDIQUE 007325/MSCP/F24 ALEENA KHAN 0073251/MSCP/F24 LAIBA IKRAM 006272/MSCP/F24 ALISHBA SHER 007354/MSCP/F24 HAJRA JAVED 008503/MSCP/F24 AMBER MASOOD 008502/MSCP/F24 Communication Within a Neuron  Communication Neurons, the fundamental Within units of the nervous system, a communicate through a process involving both electrical andNeuron chemical signals. Communication within the neurons occurs through electrical signals and between the neurons occurs through chemical signals.... These movements create electrical currents, which help send the signal.. This action potential happens due to changes in the axon’s membrane, allowing certain substances to move in and out of the axon. An action potential is the electrical signal that travels along the axon. Neuron Neurons have a long part called the axon that carries messages from Communication Within a the cell body to the terminal buttons.  Sensory Neurons Imagine how your body reacts when A touch you sensory neuronhot, something in like youra skin hot detects the painful heat. Its dendrites stove. (branch-like parts) sense the heat, and the Here's the step-by-step Neural process: neuron sends a signal through its axon to the spinal cord. Communication Overview:  Motor Neurons Interneurons The interneuron sends a signal through At the end of the its axon to thesensory motor neuron,exciting neuron, it. the terminal buttons The motorneurotransmitters. release neuron’s terminal Neural buttons These release neurotransmitters neurotransmitters Communication that make your muscle contract, exciteyour an interneuron (athe pulling hand away from Overview: connecting hot neuron) stove to protect you in the from spinalharm. further cord.  instance, imagine holding a hot Inhibitory casserole The pain signal increases the activity of excitatory with thin potholders. Synapses neurons, telling your hand to pull away. You feel the heat and your Meanwhile, your brain sends an reflex tells inhibitory signal you to drop it. But to the spinal cord that prevents your hand from letting go of the casserole. your brain prevents you from doing so because dropping it Excitatory signals tell your hand to drop the dish. would make a mess. Inhibitory signals from the brain tell you to hold on until you safely place the casserole down.  Working of Neurons While we explained the process with just a few neurons, in reality: Dozens of sensory neurons detect the heat. Hundreds of interneurons and motor neurons are involved in. moving your hand. Thousands of brain neurons send inhibitory signals to override the reflex.. Measuring This section explains how scientists study the electrical activity of axons and the process of an action potential. Let’s break Electrical it down step by step. Potentials of Axons Giant Squid Axon: Scientists use the Why Use axon of a squid, which is about 0.5 mm a Squid in diameter, making it much larger than human axons and easier to study. Axon? Purpose in the Squid: This axon helps the squid escape danger by controlling a rapid contraction of its body, pushing water out to propel it away. Tools Neededelectrodes: to Measure Electrical Activity Microelectrode: A tiny glass electrode filled with a conductive liquid like potassium Wire Electrode: Placed in seawater around chloride, inserted into the axon. The the axon to detect electrical charges. microelectrode is extremely fine (less than 0.001 mm) to avoid damaging the axon.. Membrane Potential Once the microelectrode is inside the axon, we find the inside of the axon is negatively charged Resting compared to the outside. Potential: This is The voltage difference is -70 like stored millivolts energy (mV), called in a battery, the resting potential. waiting to be used.. A device called a voltmeter measures voltage Visualizing differences. the Voltage For better visualization, scientists use an oscilloscope, which graphs voltage changes over time. Vertical Axis: Shows voltage (strength of charge). Horizontal Axis: Shows time (how the voltage changes). When the axon is at rest, the oscilloscope shows a straight line at -70 mV.. To study what happens when the axon is "disturbed": Disturbin g the Scientists use an electrical stimulator, This reduces the negative charge inside Resting which applies positive charges inside the axon. the axon, a process called depolarization. Potential  How Depolarization Scientists apply increasingly strong stimuli to the axon, one atWorks a time. The first few weak stimuli cause small depolarizations but don’t reach the threshold for an action potential. When a strong enough stimulus is applied, it hits the threshold of excitation, causing a reversal in charge. The inside of the axon becomes positive, and the outside becomes negative. This rapid reversal is called the action potential. After the action potential, the membrane potential quickly returns to normal (-70 mV) but briefly overshoots, becoming more negative than usual. This is called hyperpolarization. After the The entire process of depolarization, action Action potential, and recovery happens in just 2 milliseconds (msec). Potential  The action potential is The Action Potential the message the neuron sends from the cell body to the terminal buttons. It is triggered only when the threshold of excitation is reached (enough depolarization occurs). This process ensures the signal travels along the axon efficiently. At rest, the axon has a negative charge (-70 mV) inside. A strong enough stimulus causes depolarization, leading to an action potential. The action potential is a reversal of charge that travels down the axon as the neuron’s signal. Tools like microelectrodes, voltmeters, and oscilloscopes help scientists study these electrical changes.  MEMBRANE POTENTIAL  MEMBRANE POTENTIAL The difference in electrical charge across cell membrane. Electrical charge occurs as a result of two opposing forces:. 1. The force of diffusion The electrostatic Pressure.  MEMBRANE POTENTIAL 1. The Force (CONT…) of Diffusion The molecules move from regions of high concentration to the regions of low. concentration. For example; Diffusion of Potassium ions. K+ and Sodium ions Na+  thems The MEMBRANEelves rate POTENTIAL evenl (CONT…) of y move throu ment ghout of the. molec medi ule Atis um in differ propo whic ent rtiona h temp l to they eratur the are e, temp dissol move eratur. ved. ment e. of ions disru pts MEMBRANE POTENTIAL The Force of Electrostatic Pressure (CONT…) Electrostatic pressure is the force that pulls oppositely charged particles toward each other. Ions with same kind of charge repel each other (+ repels + and - repels -). Ions with different charges attract each other (+ and – attract). MEMBRANE POTENTIAL (CONT…) Organic ions (A⁻) Ions In Extracellular and Intracellular fluids Potassium ions (K⁺) Sodium ions (Na⁺)  Two types of fluids; Intracellular fluids (fluids within cell) Chloride ions (Cl⁻) Extracellular fluids (fluids surrounding the cell)  Several ions are present in these fluids which are  No ion Force of channels diffusion Organic Anions (A⁻) Potassium Ions (K⁺) Present inside the Present in high No force of cell, cannot move concentration inside diffusion and outside the cell. the cell The electrostatic Electrostatic pressure Pressure Force of Diffusion Force of Sodium Ions (Na⁺) Chloride Ions (Cl⁻) Present in high Diffusion Present in high concentration concentration. outside the cell. The Electrostatic Pressure The Electrostatic Pressure MEMBRANE POTENTIAL (CONT…) Sodium Potassium Transporters  ACTION POTENTIAL  Action Potential Definition “ Rapid electrical change in a neuron caused by ion movement across the membrane”.. Key Players: Sodium (Na⁺): Pushed into the cell by diffusion and electrostatic pressure. Potassium (K⁺): Moves out of the cell during the process to restore balance. Sodium-Potassium Pump: Keeps intracellular Na⁺ levels low by actively pumping: 1) Na⁺ out of the cell. 2) K⁺ into the cell. Mechanism: Step 1: Membrane becomes briefly permeable to Na⁺ → Na⁺ rushes in.(sodium channels open ) Step 2: Membrane becomes permeable to K⁺.→ K⁺ exits. (potassium channels open) Results in a rapid change and reset of membrane potential. Ion Channels: Protein molecules with "pores" that open or close to allow ion flow. Permeability depends on the number of open channels. Giant Squid Axon Example: Hundreds of sodium channels per square micrometer. A tiny patch can pass 100 million ions/second per channel. Ion Channels  DEPOLARIZATION Movements of Ions During the Action Potential REFRACTORY PERIOD REPOLARIZATION. HYPERPOLARIZATION.  Movements of Ions During the Action Potential The movements of ions during the action Figure 2 potential. The fig.1 shows the:  Opening of Na+ channels at the threshold of excitation  Refractory condition at the peak of the action potential  Resetting when the membrane potential returns to normal.. Figure 1  Movements of Ions During Reduces membrane potential to the Action Potential threshold of excitation , triggering sodium channels to open.. DEPOLARIZATI Voltage-dependent sodium channels open → Na⁺ rushes in due to diffusion and electrostatic pressure. The influx of Na⁺ causes a rapid shift in membrane potential. from -70 mV to +40 mV.  Movements of Ions During the Action Activates voltage-dependent Potential potassium channels. (K⁺). HIGHER DEPOLA These channels are less sensitive and open later than sodium channels..  Movements of Ions During When the the actionAction potential reaches its peak (approximately 1 Potential msec), sodium channels become refractory at +40mv. REFRACTORY Na⁺ channels become blocked and cannot reopen until the membrane reaches its resting potential, stopping Na⁺ entry..  Movements of Ions During Voltage-dependent potassium channels the Action Potential fully open.. REPOLARI The inside of the axon is positively charged, driving K⁺ out of the cell via diffusion and electrostatic pressure. Membrane potential starts returning. toward resting value (-70 mV).  Movements of Ions During thepotential As the membrane Action returns to Potential normal, the potassium channels begin to close. stopping K⁺ outflow. REPOLARI Sodium channels reset, allowing readiness for the next depolarization..  The membrane potential overshoots, Movements of Ions During dropping temporarily below -70 mV the Action Potential This occurs due to the accumulation of K⁺ ions outside. HYPERPOLARI the cell. Sodium-potassium transporters remove excess Na⁺ and retrieve lost K⁺ to restore balance.. The membrane potential gradually returns to its resting value of -70 mV.  Point to Ponder ! Action potentials increase Na⁺ Na⁺ diffuses into the axoplasm, ions in the squid axon by causing negligible concentration 0.0003%. changes. The total ion influx is minimal, Long-term, transporters prevent making sodium-potassium Na⁺ buildup that would disrupt transporters unimportant short- axon function term. Conduction of Action Potential  Once an actionAll or non law Action potential potential is maintains the same triggered, it either size as it travels happens fully or not down the axon. at all. An action potential splits and continue It travels one way, along each branch from the soma to without diminishing the axon terminals. in size.  Experiment on Squid Axon The electrode is used to stimulate the axon to trigger an action potential. Other electrodes are placed at various distance along the axon and are connected to oscilloscopes. Observation: The action potential remains constant in size as it travels down the axon.  Rate Law Weak Low firing rate(fewer action Stimuli potential per second) Strong High firing rate (Many action Stimuli potential per second)  Process of Conduction in Axons  Schwann cells  Myelin Sheath: (PNS) and Insulates the oligodendrocytes  Electrical axon, created (CNS) tightly wrap disturbance by Schwann around the axon, travels cells (PNS) or preventing any passively oligodendrocyt space between through es (CNS). the axon and the myelinated  Nodes of myelin. areas. Ranvier: Gaps  Weakens in the myelin  Myelinated axons slightly but is where the only interact with strong enough axon is extracellular fluid to trigger a exposed to at the nodes of new action extracellular Ranvier, where the potential at fluid. axon is exposed. the next node.  Saltatory Conduction  Saltatory Conduction: Action potentials "hop" from node to node.  Advantages of Saltatory Conduction: Faster Speed: The signal jumps faster from node to node, speeding up communication. Energy Efficiency: Because less sodium enters the axon and less has to be pumped out, myelinated axons use less energy.  Difference between occurrence of conduction in Myelinated vs Unmyelinated axons Myelinated Axons Unmyelinated Axons Present Absent Myelin Sheath Present Absent Nodes of Ranvier Saltatory Continuous Conduction conduction (action conduction (action Method potential jumps potential moves between nodes) smoothly along Speed of axon) Conduction Faster Slower Energy Efficiency More efficient (less Less efficient (more sodium pumped sodium enters axon)  Relationship between the size of axon and the speed of conduction  Squid axon (unmyelinated): 500 µm diameter, 35 m/sec conduction  Larger axon speed. diameter = faster  Cat axon conduction. (myelinated): 6 µm  Large, diameter, same unmyelinated axons speed as squid axon (e.g., squid) can due to saltatory transmit signals conduction. quickly, even  Fastest myelinated without myelin. axon (20 µm  Myelinated axons diameter): 120 with smaller m/sec (432 km/h). diameters can achieve the same or faster speeds Size & Speed through saltatory relationship conduction.