Action Potential 2023 (PDF)

Do something boring! https://www.instagram.com/reel/C0ByaXVrO he/?igsh=MTgwb2dvenhqbG93Yw%3D%3D The Nerve Impulse Chapter 8.2 Nerve Impulses SBI4U0 - 9.2 An Electrochemical Event! Nerve Impulse/ Action Potential Neurons communicate with...

Do something boring! https://www.instagram.com/reel/C0ByaXVrO he/?igsh=MTgwb2dvenhqbG93Yw%3D%3D The Nerve Impulse Chapter 8.2 Nerve Impulses SBI4U0 - 9.2 An Electrochemical Event! Nerve Impulse/ Action Potential Neurons communicate with other neurons, muscles, and glands via electrical signals. These electrical signals are called nerve impulse or action potential. Hodgkin & Huxley discovered AP in 1940s using an axon from a Giant Squid! The membrane at rest Cells have a specific charge across the membrane The distribution of anions (Cl-, proteins) & cations (Na+, K+, Ca 2+) throughout the cell and extracellular fluid determine the charge. Neuron is -ve on inside & +ve on outside ECF Resting Potential A neuron that is not transmitting a signal is said to be at its resting potential (Po). The inside of the neuron is negatively charged relative to the outside because of the large, negatively charged molecules in the cytoplasm. The Na-K pump maintains concentration gradients for both sodium and potassium ions. The pump works against the gradient by pumping out 3Na+ while pumping in 2K+. Action Potential When nerves are stimulated, they must be excited from their resting potential (-70mV) to their action potential (+40mV). Watch: https://youtu.be/oa6rvUJlg7o When a sufficiently large stimulus reaches the membrane, an action potential is generated.  Action Potential Absolutely Relative Refractory Refractory repolari ation Membrane Potential (mV) lariz zation depo -55 threshold potential resting potential stimulus hyperpolarization Failed initiations: action potential is an “all or none” response. Stimulus must reach threshold potential for the neuron to fire. Watch: Threshold Action Potential Stimulus: stimulus opens some voltage gated Na+ channels. Na+ inflows. Depolarization: If enough Na+ inflows, membrane potential reaches the threshold and AP is triggered Repolarization: K+ channels open, K+ flows out. Na+ channels are closed. Hyperpolarization (refractory period): K+ channels slow to close, potential goes below P0 – Resting Potential (Po): Na+/K+ pump maintains gradient Propagation of AP In myelinated axons, only Nodes of Ranvier have Na+/ K+ channels, so action potentials appear to ”jump”. This jumping is known as saltatory conduction. In unmyelinated neurons, AP travels continuously along the axon. Membrane becomes depolarized in a local area, this causes adjacent Na+ channels to open and depolarize. Membrane that previously underwent depolarization enters refractory period.  Multiple Sclerosis Treatments for MS Chemotherapy Most treatments focus on suppressing the immune system so that immune cells do not continue Anti-inflammatory drugs to attack neurons. (steroids) Physical therapy autologous hematopoietic stem cell transplantation (AHSCT)  Graded Potential When a small region is depolarized Signal transmitted over a small distance b/c it fades out within few millimeters. All cells can generate graded Po BUT neurons, muscles cells, and some endocrine/immune systems can generate AP.