Lecture 2 PHCL2610 Nervous System PDF

Lecture 2 PHCL2610 Nervous System Ana Maria Oyarce Ph.D. Department of Pharmacology – HEB280C Office hours: TBD or by appointment Phone: (419)383-1919 Email: [email protected] 1  Topics  Electrical Si...

Lecture 2 PHCL2610 Nervous System Ana Maria Oyarce Ph.D. Department of Pharmacology – HEB280C Office hours: TBD or by appointment Phone: (419)383-1919 Email: [email protected] 1  Topics  Electrical Signals  Channels  Resting Membrane Potential Material Vander’s Human Physiology 16th Edition. Copyright 2023 Chapter 6. Section B: Membrane Potentials 2  Neuronal Communication Neurons communicate using specific signals Cell-cell communication happens by either electrical activity or the release of neurotransmitters 3 Why Electrical Signals in Neurons are Important? Electrical signals, action potentials or nervous impulses are used by neurons to transmit information to other neurons or other cells Action potentials play a central role in cell–cell communication An action potential travels the length of the axon and activates cell communication from one cell to another by either electrical activity or the release of neurotransmitters Important to know 1. What do we need to create an action potential? 2. How is the action potential created and propagated? 3. How does the communication between cells happen? 4  Electrical Signals in Neurons Important to know for following discussions Neurons at rest have a resting membrane potential (RMP) Activated neurons produce an action potential (AP) Production of RMP and AP in neurons depends on the concentration of ions inside and outside the neurons (potential) Because the lipid bilayer of the plasma membrane is a good insulator, the movement of ions happens through ion channels present in the membrane Different ion channels open or close in response to specific stimuli  Types of Ion Channels They are present in the plasma membrane Classification based on how the channel is activated → two types of channels Leak or passive (non-gated) channels They randomly open and close Gated channels They open and close in response to a stimulus 6  Leak or Passive Channels Permeability to ions is high They alternate between open and close position Leak channels in neurons is K+, Na+ and Cl-→ most relevant is K+ Present in all cells In neurons they are in dendrites, cell bodies and axons 7  Gated-Ion Channels  There are three main types of gated channels based on how they get activated  Ligand-gated channels Mechanically gated channels Voltage-gated channels 8  Ligand-Gated Channel Binding of a ligand or molecule (neurotransmitter, hormones and ions) to the channel increases the channel permeability to an ion In dendrites and cell bodies of neurons mainly concentrated at the synapse 9  Mechanically-Gated Channels Mechanical stimulus such as vibration, touch, pressure and tissue stretching changes the conformation (shape) of the receptor → activation of the channel In auditory receptors, receptors in internal organs and skin receptors 10  Voltage-Gated Channels They get activated in respond to a change in the membrane potential Each channels has a particular ion selectivity and voltage dependence (Examples: Na+, K+ and Ca2+ channels) Essential for the generation and propagation of action potentials in axons Present along the axon on unmyelinated axons, Node of Ranvier (myelinated axons) and axon hillock 11  Membrane Potentials  Resting membrane potential (RMP) → potential (voltage) difference across the cell membrane when the cell is at rest (no stimulation or activation)  Action potential (AP) a brief reversal of the membrane potential following activation of the neuron 12  Resting Membrane Potential RMP is due to different ion concentrations across the plasma membrane RMP in neurons is typically −40to −90 mv → negative charges inside of the neuron and positive charges outside the cell RMP depends on the distribution of ions inside vs outside of cell → mainly K + and Na+ Inside the neuron: K+ is high charge is balanced by negatively charged ions and proteins Outside the neuron: Na+ is high Na+ is balanced by high Cl- 13 Why an Electrical Potential is Generated? 14  Why an Electrical Potential is Generated?  Similar situation happens with other ions → important is Na+ 15  Equilibrium potential (electrochemical potential generated at equilibrium) can be predicted by the Nernst Equation  Numbers represent the membrane potential at which each ion comes to equilibrium (equilibrium potential for the ions) 16 Several Ions Contribute to The Membrane Potential It mainly depends on distribution of K+, Cl- & Na+ Goldman Field Equation is used to describe the membrane potential It considers concentrations of ion inside/outside cell & permeability (p) of membrane to each ion Rule: The membrane potential at any time is closest in value to the equilibrium potential for the ion to which the membrane is most permeable (K+ in neuron) Em (neuron)= -70 mv 17  Resting Membrane Potential The magnitude of the RMP depends on: 1. Differences in specific ion concentrations inside and outside of the cell 2. Differences in membrane permeability to the different ions number of open channels for an ion All cells in the rest state have a resting membrane potential  Em (skeletal muscle) = -90 mv  Em (neuron) = -70 mv  Em (RBC) = -7 mv to -14 mv 18 How is the RMP Produced and Maintained? Production of the RMP Leak K+ and Na+ channels are opened The neuron is highly permeable to K +  K+ leaks out of the cell  Na+ is less permeable and small amount leaks into the neuron Maintenance of the RMP Na+ pump is involved Neuron must compensate for K + and Na+ leaks Transport 3 Na+ out and 2 K+ in using hydrolysis of ATP 19