Neurophysiology PDF

NEUROPHYSIOLOGY study of chemical and electrical signals in neurons  INTRA-CELLULAR TRANSMISSION ▪ Intra-cellular communication: signals travel WITHIN cells/neurons ▪ Information is received – dendrites as soon as dendrite...

NEUROPHYSIOLOGY study of chemical and electrical signals in neurons  INTRA-CELLULAR TRANSMISSION ▪ Intra-cellular communication: signals travel WITHIN cells/neurons ▪ Information is received – dendrites as soon as dendrite info touches it is converted into electrica signa ▪ Integrated and processed – cell body/axon hillock ▪ Transmitted/conducted – axon ▪ Action potential = rapid electrical signal that travels along the axon  INTER-CELLULAR TRANSMISSION Synapses ▪ Inter-cellular communication: signals travel BETWEEN cells/neurons ▪ A neurotransmitter is a chemical messenger between neurons → released at synapse I floot through to dendrites INTRA-CELLULAR COMMUNICATION: THE NEURON AT REST  NEURONS HAVE MEMBRANES both have water as their base ▪ Membrane = phospholipid bilayer ▪ Surrounded by fluid (mainly water) on both sides → intra-cellular fluid/cytosol and extra-cellular fluid MEMBRANE PROTEINS ARE EMBEDDED IN THE BILAYER memb assist in rane protein transport : or out as binding site  IONS ARE DISSOLVED IN THE INTRA/EXTRA-CELLULAR FLUID ▪ Ions are charged molecules (e.g. NaCl dissolves into Na+, Cl-) ▪ Cation = positive charge loss e- ▪ Anion = negative charge goin er ▪ When ions move across the membrane, can generate an electrical signal ▪ Ion channels & Ion Pumps can flow in ↳ requires a ions energy to either direction move in both wo energy direction  HOW DO IONS MOVE ACROSS THE MEMBRANE? ▪ 1. Diffusion – ions move from regions of high concentration to low concentration (DOWN the concentration gradient) off that particular neuron  ION CONCENTRATIONS IN NEURONS AT REST ▪ Higher concentration outside: * know numbers → Cations: Na+, Ca++ → Anion: Cl- ▪ Higher concentration inside: → Cations: K+ → Negatively charged proteins ▪ Selective ion channels · only allow specific ions to cross &  CLASS QUESTION At rest, the concentration of Na+ ions is _______ inside the neuron compared to outside the neuron A. Higher B. Lower C. The same Answer: B? HOW DO IONS MOVE ACROSS THE MEMBRANE? ▪ 2. Electrostatic pressure – ions move across an electric field because they are charged ▪ Membrane voltage differential → Inside of the cell is more negatively- charged than the space immediately outside the cell rest Diff. at / / L I -  HOW DO IONS MOVE ACROSS THE MEMBRANE? ▪ Opposite charges attract, like charges repel ▪ Selective ion channels: → Cations move into the cell C → Anions move out of the cell bC inside of cell more negative · /  ELECTROCHEMICAL GRADIENT ▪ Chemical driving force → concentration ▪ Electrical driving force → opposite charges attract ▪ These two forces can collaborate or oppose one another  ECF ICF & # E  D - W E electrica Forceona  & E C ↓ we don't know which would win wo equation  electrica gradient neurons generate specific HOW ARE THE ION CONCENTRATION GRADIENTS GENERATED/MAINTAINED? by using pumps to move ions against gredient * constantly working ▪ Sodium-Potassium pump I uses → “Pump” proteins expend energy energy 1 ATD to move ions against their gradient → Na+/K+- ATPase pump molecule used → Moves 3 Na+ ions out and 2 K+ ions in for every energy molecule if pump stopped working out the but ion channels stayed pump sodium closed ? cell would have is the inside of the n e u ron (? Why build up moving out (t) ions then It into the pump · more a re you moving in 700 muan chennek open I no pump cell Chemical I ↳ will go back to equilibrium gradient  MEMBRANE POTENTIAL IN NEURONS AT REST ▪ Resting membrane potential (RMP) Cell at rest no inputs → Rest/resting means in the absence of any other external input → -60 to -70 mV (more negative inside than outside) HOW IS THE RESTING MEMBRANE POTENTIAL GENERATED/MAINTAINED? ▪ K+ Channels At rest = always open: help maintain negative charge → open (K+ can flow in either direction) → allow positively-charged K+ ions to leave cell down concentration & potessium enonnel gradient → creates a negative charge inside cell allows K + to leave makes cell even D more negative h [k ] + HOW IS THE RESTING MEMBRANE POTENTIAL GENERATED/MAINTAINED? Eventually reach equilibrium: K ▪ - Kt out + in = chemical and electrical driving forces are equal, but opposite → -60 to -70 mV RMP · K+ channels should never be closed INTRA-CELLULAR COMMUNICATION: ACTION POTENTIALS  ACTION POTENTIALS ⑭ intra 60mV will - - switch - to(t) extra inside of ▪ Action potentials are brief (transient) membrane will become + 201 + 40 instantaneously then goes bock but large changes in the membrane down and jets more (1 to 801-9p then back to -60mV potential quick flip of potential membrane ▪ For an instant, the inside of the membrane becomes positively-charged inside of (t) then membrane very quickly book to c)  ACTION POTENTIALS ▪ Action potentials triggered in the axon hillock ▪ Conducted along the axon ↓ Heree of  Channels open/closing - HOW IS AN ACTION POTENTIAL GENERATED? ▪ Ion channels can open/close for many reasons: → a ligand/chemical can bind a receptor → temperature-sensitive → voltage-sensitive When sits membrane at + 20 mv channels may a time sensitivity open/close ▪ Ions flow into/out of cell, alters membrane potential ? actionsa→ anions flows into cell - hyperpolarization (cell becomes MORE negative) (-) ; hyperpolarization more two &→ cations flows out of cell - hyperpolarization hyper ? (t ; hyperpolorization more S→ anions flows out of cell - depolarization (cell becomes LESS negative) two action ? () ; depolarization more thercoua→ cations flows into cell - depolarization ? more (H) ; depolarization  all steps generated PARTS OF AN ACTION POTENTIAL in membrane hillock of exon ▪ Stimulus causes a small depolarization of the neuron to the Threshold (#1) voltage (-40 to -55 mV) → Action potential triggered if axon hillock decides yes cases → All-or-none small depolarization to the neurons threshold ▪ Depolarization (#2) is when the interior of the cell becomes positive ▪ Repolarization (#3) is when the membrane potential becomes negative V axon hillock decision / saying nu Stimulus  PARTS OF AN ACTION POTENTIAL ▪ Hyperpolarization (#4) is when the membrane potential undershoots the RMP → Refractory period – neuron cannot westepump generate another action potential ato HOW we + until it returns to RMP al ? D S tota ▪ Resting State (#5) is when the m membrane returns to RMP ▪ Information encoded by number of action potentials, not size & if you have a week stimulu it will couse less # of action potentials ↳ strong stimul will - generate oc tion more potentials WHAT IS GOING ON DURING THE DIFFERENT PARTS OF ACTION POTENTIAL?  RESTING MEMBRANE POTENTIAL AND THRESHOLD ▪ RMP is -60 to -70 mV → K+ channels are open → Na+ channels are closed ▪ Small depolarizing stimulus causes depolarization membrane potential becomes less & comes from cell body/some negative and approach threshold potential (-40 mV)  So 40 - 78 & - & + Some V-goted Net VOLTAGE-GATED Na + this change only charnes happens at exo r hillock CHANNELS the rest of the cell is of RMP OPEN/ACTIVATE ▪ At threshold: → Voltage-gated Na+ channels open/activate (because of change in membrane voltage) → Na+ ions rush into the cell + Nat/k pump puts more Not outside the cell. Cell is (-1s0 → Membrane potential becomes ↓ Not wants to run im positive depolarization both electrically and chemically influenced  VOLTAGE-GATED Na + CHANNELS INACTIVATE Not channel * to close begin ▪ After 1 millisecond, the Na+ channels inactivate they system are on a timer Stoy → Inactivation = channel closed and closed temporarily unable to open again until are they unlocked again → No more Na+ entering cell → Absolute refractory period & Not channels a re already open/inactivated fire of another ac tion potent impossible , So it is to  VOLTAGE-GATED K + CHANNELS OPEN/ACTIVATE ▪ As membrane depolarizes, voltage- gated K+ channels slowly open/activate → “Delayed-activating” K+ channels → K+ flows out of cell & inside the cell is positive → Membrane hyperpolarizes Slower to open/close → Relative refractory period ↳ Not channels have reset even overshoot Would take m o re during this period. be due to already of a bump to re-open Not chennes Slow → Voltage-gated K+ channels close becoming m o re ( t closure but other K+ channels stay open → Na+ reset voltage activated reset when membrane voltage more  CLASS QUESTION Which number corresponds to when Na+ ions enter the neuron? Answer: 2? 2 between 1-2 when Not activated ↳ so ore K+ chemes  SUMMARY ▪ Membrane voltage potentials ▪ Overview of an action potential ▪ Concentration gradient ▪ Electrical forces ▪ Electrical forces ▪ Pumps ▪ Pumps ·  SUMMARY ▪ Membrane voltage potentials ▪ Overview of an action potential ▪ Concentration gradient ▪ Electrical forces ▪ Electrical forces ▪ Pumps ▪ Pumps