PeerWise PeerWise Activity We will have a total of 7 activities on 7 different topics Our first topic would be Membrane Potentials Go to Lesson 3 on Sakai Week 2 Follow the link to review a short video with guidelines on PW Register to PW details on Lesson 3 PeerWise Activity 1 Write at least 1 multiple choice question Post it on the PW site including the correct answer and detailed explanations 2 Answer at least 1 of your peer s question 3 Give feedback to at least 1 of your peers Your only resource your brain Writing higher order PW questions is positively correlated with improved performance in higher order exam questions At least 1 of your 7 PW activities should include writing a higher order question Fundamentals of the nervous system General Organization CNS and PNS PNS subgroups The basic units the cells Neurons Glial cells Neurophysiology Resting graded and action potentials Neural interactions Learning objectives To describe the different ion channels To explain what determines and maintains the membrane potential To predict the effects of ion flow on local membrane potential Ion channels Leak channels Ion channels allow ions to move through the PM But what drives them to move ECF Cytosol Let s start with K There is a concentration of K in the cytosol than in the ECF K K Will the chemical gradient drive K in out K leaves the cell via K leak channels due to the chemical gradient Negatively charged proteins cannot leave the cell As K is leaving an electrical gradient starts to pick up driving K back in Note we measure potential as inside compared to the outside cytosol compared to ECF Poll Na is found in higher concentrations in the ECF compared to the cytosol Na Na Poll What is the resting membrane potential K Na K Na Na impact on the membrane potential is much lower than K since the membrane is much less permeable to Na The Resting membrane potential is mainly dependent on the K electrochemical gradient and it is negative What creates the chemical gradient in the first place K Na K Na The restores the chemical gradients and therefore maintains the resting membrane potential All this is achieved by a movement of only a fractions of the ion involved K Na K Na 0 006 of the K actually move Summary The membrane is much more permeable to K than to Na The electrical gradient counteracts the chemical gradient and the ions reach equilibrium The K Na pump maintains the chemical gradient and is essential to create and maintain a negative resting membrane potential Learning objectives To describe the different ion channels To explain what determines and maintains the membrane potential To predict the effects of ion flow on local membrane potential Ion channels 1 Leak channels 2 Chemically ligand gated channels Can be ion specific or not e g the Ach receptor at the neural muscular junctions is permeable to all both Na and K 3 Voltage gated channels Ion selective Gates can open and close at different speeds 4 Mechanically gated channels Found in sensory receptors The Membrane is Polarized Depolarization Making the cell less polarized Hyperpolarization Making the cell more polarized How can we depolarize a cell A stimulus Example A chemical stimulus Cell body Axon Dendrites Sodium channels opening leads to depolarization 70 mV Generation of a A short range change in a membrane potential upon a stimulus On a notecard Answer the following question In two separate experiments researchers increase the sodium concentrations in the ECF In cell 1 they increase it more that Then they stimulate the sodium ligand gated channels to they do in cell 2 open up Will the local membrane potentials in cell 1 be identical to the one in cell 2 Explain No limit to the number of channels or ligand molecules Na Na Na Control 1 2 The graded potential is with a stronger stimulus Think about a membrane with 50 channels Stimulating them with 4 ligand molecules or 40 will make a difference A graded potential can spread locally Cations will move towards a negative charge The site next to the original depolarization event will also depolarize creating another graded potential l a i t n e t o p e n a r b m e M A Graded local potential A short range change in membrane potential upon a stimulus Graded potentials spread locally but die out Who said you have to depolarize A stimulus can lead to hyperpolarization l a i t n e t o p e n a r b m e M What are the molecular mechanisms by which a stimulus can lead to hyperpolarization Discuss this in groups for a few minutes determine a reporter for the group Graded local potentials Proportional to the stimulus size Act locally starting from the stimulus site Attenuate with distance Spread in both directions Take place in many types of cells Action potentials do are NOT Proportional to the stimulus size Act locally Attenuate with distance Spread in both directions Take place in many types of cells Learning objectives To contrast between local and action potentials To explain the uni directionality of action potential transport To predict the propagation of the action potential in experimental conditions To contrast between propagation in unmyelinated and myelinated axons