Module 3 - Neural Physiology - Fall 2024 PDF

1 MODULE 3 – NEURAL PHYSIOLOGY  FACULTY OF HEALTH KINESIOLOGY AND HEALTH SCIENCE MODULE 3 – NEURAL PHYSIOLOGY HH/KINE 2011 - HUMAN PHYSIOLOGY I...

1 MODULE 3 – NEURAL PHYSIOLOGY  FACULTY OF HEALTH KINESIOLOGY AND HEALTH SCIENCE MODULE 3 – NEURAL PHYSIOLOGY HH/KINE 2011 - HUMAN PHYSIOLOGY I Fall 2024 MODULE 3 – NEURAL PHYSIOLOGY Dr. Paris [email protected] 2 MODULE 3 – NEURAL PHYSIOLOGY MODULE 3.1 MODULE 3.2 INTERCELLULAR COMMUNICATION THE PERIPHERAL NERVOUS SYSTEM FOCUS ON NEURAL FOCUS ON THE SOMATIC SYSTEM COMMUNICATION Human Physiology, Nelson 4th Edition Human Physiology, Nelson 4th Edition Chapter 2, Pages 54-83 Chapter 3, Page 92 Chapter 4, Pages 141-142 and 187-203 For Nelson 5th edition, see Chapters 2-6 (find the sections relevant to lecture content) 3  MODULE 3.2 THE PERIPHERAL NERVOUS SYSTEM FOCUS ON THE SOMATIC SYSTEM MODULE 3.1 – NEURAL PHYSIOLOGY MODULE 3.1 INTERCELLULAR COMMUNICATION FOCUS ON NEURAL COMMUNICATION Human Physiology, Nelson 4th Edition Chapter 2, Pages 54-83 Learning objectives In this module you will learn the principles of neural communication between cells. We will discuss the concept of membrane potential, including separation of charges, ion permeability, and concentrations. This is important in order to better understand membrane potential in nerve and muscle cells as well as the behaviour of ions due to polarization and electrical signals. We will also discuss graded potentials, action potentials, signal propagation along nerve fibers, synapses and neuronal integration. 4  The plasma membrane resting potential The plasma membranes of all living cells are polarized electrically. This separation of charge creates a MODULE 3.1 – NEURAL PHYSIOLOGY ‘membrane potential'. Think of this as the ‘potential’ for ion movement across a ‘membrane’ due to charge-charge attractions or repulsions. It is a ‘potential’ because ion movement may be restricted by membranes. This principle is the basis of cellular communication in nervous and muscle tissues. Atractive forces between Sions without restriction Key factors regarding membrane potential: : + + +they would freely mix Extracellular fluid O - - - -+ + + (ECF) ✓ It is a separation of charge across a membrane - - ++ = 14 charge that gives ✓ Difference in the relative number/concentration of - b +8 + potential to work cations (+ ions) and anions (- ions) in the intracellular fluid (ICF) and extracellular fluid (ECF) Selective ✓ Difference in permeability of key ions - ✓ Therefore, ion movement (and hence ‘membrane Intracellular fluid (ICF) potential’) is influenced by both ion concentration and membrane permeability panioncrosseane) Plasma Membrane ✓ Membrane potential is measured as the Volt or restrictive the flow of ions millivolt (mV) 5 · MODULE 3.1 – NEURAL PHYSIOLOGY The movement of ions across a membrane + + + Extracellular fluid are determined by: - - - -+ + + - - [+34 ✓ Concentration gradient + Move from ‘high to low’ ✓ Electrical gradient (electrical charges) Opposites attract, similar charges repulse - ✓ The combined effects of concentration and 2 - 34 Intracellular fluid driving electrical gradients = the electrochemical forces gradient but Plasma perm ✓ Membrane permeability (restrictions to is what Membrane determines movement) what passes 6  EXAMPLE 1: (assume maximal permeability in this example) MODULE 3.1 – NEURAL PHYSIOLOGY Electrical neutrality Equal number of negative and positive charges on both sides => No potential. a ponet flowastherea EXAMPLE 2: Unequal charges on either side polarized membrane  Excess of positive charges in the left compartment  Electrical forces are now unequal  Consequence…..? A membrane potential has been generated 7  In biological cells, there are many ions in the ICF and ECF, but there are a greater concentration of ions located in a thin layer along the outer and inner surface of a cell membrane. is cone sep of charges MODULE 3.1 – NEURAL PHYSIOLOGY or S polarization rest of cell this area cause the to only , neutral Important points: electrically is ✓ The ECF and ICF are neutral. The net charge of cations (+) is balanced by the net charge of anions (-). ✓ The membrane itself is not charged along membrane C - 8  The magnitude of the potential (mV) depends on the number of opposite NET charges that are separated… MODULE 3.1 – NEURAL PHYSIOLOGY ✓ A membrane potential exists because of unequal + and – on both sides ✓ Magnitude of potential: C > B > A net diff of 16 charges 12 charges 6 charges = more potential to do work +2 still net change + + "t" + + + - - + more ++ 2 polarized - - - still + + = ++ = + 2 - - = - z more + 2 + - T - - + -- net diff is same membrane potential - + the same ‘Net’ Magnitude 9 *Net magnitude of the potential is similar in these 3 situations*  normal cell separation However, all cells have a membrane potential y otions Non-excitable cells and excitable cells have a ‘resting membrane potential’ that is relatively MODULE 3.1 – NEURAL PHYSIOLOGY constant. Excitable cells are nerve cells or muscle cells that can produce rapid and transient changes in their resting membrane potential when excited => Electrical signal (communication). I flow of ions that allows rapid change Recall….membrane potential depends on differences in concentration and permeability of key ions. Key ions are sodium (Na+), potassium (K+) and negatively charged intracellular proteins (A-) ⑥ more perm toK+ than + Nd outside Inside - both ICF &ECF -in ↑ ↓ ↓ ↑ Sodium / Potassium C-charge) d in IC Space. entirely The membrane is impermeable to A- but contribute to making 10 inside more of cell hey than outside  How do K+ and Na+ cross the plasma membrane? Ions such as Na+ or K+ are water-soluble and therefore cannot diffuse across the lipid-rich plasma MODULE 3.1 – NEURAL PHYSIOLOGY membrane… These ions can move passively through protein channels (leak channels) specific Always open , very ↑ bette ↑ (Table: Typical neuron) 11  Imagine a membrane in the following situation that would be permeable to K+ only: MODULE 3.1 – NEURAL PHYSIOLOGY Plasma membrane The concentration gradient tends to more " " more" " push K+ out of the cell (Green - arrow) + as it pushes more K ECF ICF + &+ - + Conc - The outside of the cell becomes K+ + - +electrical - K + more positive as K+ ions move out down their concentration gradient > range+ - cannot cross The membraneBis impermeable nembrane to + - A- large proteins (A ) => This makes - + - the ICF more negatively charged + - than the ECF Eventually, K+ efflux will begin to reverse the electrical gradient. This will tend to move K+ back into the cell (blue arrow). An equilibrium is reached where 12 there is no net movement of K+ (Table: Typical neuron)  Plasma membrane ECF + - ICF MODULE 3.1 – NEURAL PHYSIOLOGY + - K+ + + - - K + No further NET movement of K+ + - when the inward electrical gradient exactly counterbalances the + - outward concentration gradient. + - + - - 90 mV At this point, the membrane potential (inside cell relative to is the equilibrium potential for outside of cell ( potassium. In neurons, this value (EK+) is (-90) mV. When the potassium equilibrium potential (-90 mV) is reached: The plasma membrane has a potential No net movement of K+ across the membrane S justelecticalgradiea balance conc gradient A large concentration of K+ still exists inside the cell Why -90mV and not another value? The stable inequality of K+ on either side is due to the net 13 influence of all charges, K+ permeability in either direction and K+ concentration differences  Plasma membrane Potassium equilibrium potential (-90) mV ECF + - ICF Why (-90) and not (+90)? MODULE 3.1 – NEURAL PHYSIOLOGY + - => Convention. (-90) mV means that the K+ + + - - K + membrane potential has an amplitude of 90 mV with the inside of the cell being + - charged negatively relatively to the + - outside. + - How do we measure this (-90) mV? + -  With a micro-voltmeter measuring with one electrode inside the cell and the other one outside. 14  How do we measure this (-90) mV?  Using the NERNST equation. > - helps determine EQB potential MODULE 3.1 – NEURAL PHYSIOLOGY The Nernst equation E = 61 log Co Ci E: equilibrium constant for the ion in mV 61: constant Co: concentration of the ion outside the cell Ci: concentration of the ion inside the cell For K+: E = 61 log10 5 mM 150 mM EK+ = - (90) mV 15  What about the sodium (Na+)? The theoretical final charge difference that would exist if Na+ Plasma membrane reached its equilibrium potential (this does not refer to BEFORE movement) MODULE 3.1 – NEURAL PHYSIOLOGY " more" - more "I' ECF - + ICF ↑ conc - + No further NET movement of Na+ -Conc + Na+ - + Na+ + 65 when the outward electrical a · enough Nat gradient exactly counterbalances - electrical + the inward concentration gradient. - + - A- At this point, the membrane potential + is the equilibrium potential for - + sodium (ENa+) at (+65) mV. 16  What about the sodium (Na+)? The theoretical final charge difference that would exist if Na+ Plasma membrane reached its equilibrium potential (this does not refer to BEFORE movement) MODULE 3.1 – NEURAL PHYSIOLOGY Initially, the concentration and electrical ECF - + ICF gradient tends to push Na+ into the cell - + (green arrow) - + Na+ - + Na+ As before, the membrane is impermeable to large proteins (A-) => This makes the ICF - + more negative than the ECF - + The inside of the cell becomes more - + A- positive as Na+ ions move in down their - + electrochemical gradient Eventually, Na+ will equilibrate (blue arrow) with more positivity inside than outside (see ‘-’ ‘+’ in diagram). An equilibrium is eventually reached where there is no net movement of Na+ (ENa+) 17  - 90mV + 65 mV In a living cell, neither K+ or Na+ exist alone inside or outside of cells… … both will affect the membrane potential. To what degree? MODULE 3.1 – NEURAL PHYSIOLOGY The greater the permeability of the plasma membrane for a given ion, the greater is the tendency for that ion to drive the membrane potential toward the ion’s own equilibrium potential! Rate of leak dictates membrane.. Nat make it weg as + more resting polential is more permeable -> cell e leaves Kt than Nat so It can leak to faster (more kt leak chancels) The membrane at rest is 50-75 times more permeable to K+ than Na+ => K+ passes it more rapidly => K+ influences the resting membrane potential to a much greater extent than Na+ does. EK+ = -90 mV which means K+ naturally tends to equilibrate at balance (efflux) that would make the inside more negative than the outside. ENa+ = +65 mV which means Na+ naturally tends to make the inside more positive than the outside (influx). The net resting membrane potential of a neuron is usually -70 mV. This value is a net effect of EK+ ENa+, the relative 18 permeability of both ions, A- and other ion equilibria ↳ strongly driven by in a perm ofIt than Nat MODULE 3.1 – NEURAL PHYSIOLOGY How do K+ and Na+ cross the plasma membrane? lleak Channels)  Passive transport through specific ion channels -actively  Active transport = The Sodium-Potassium Pump transports ions Using ATP The passive ion movements are responsible for 80% of the resting membrane potential. The Na+/K+ pump is responsible for the remaining 20%. But first…how do changes in membrane potential occurs across the structure of an excitable cell (neuron or muscle cell)? 19  (structure of cell dictates function) Principles of Neural Communication MODULE 3.1 – NEURAL PHYSIOLOGY Neural and muscle cells => transient and rapid changes in their membrane potentials. Excitable tissues Electrical signals For neural cells or neurons, this can be a way to: Receive a signal. Initiate/elaborate a message. Transmit a message. & Neural communication 20  Notion of depolarization / hyperpolarization MODULE 3.1 – NEURAL PHYSIOLOGY Polarization = Charges are separated across the membrane. There is a membrane potential ( 0 mV). > - Dec amount of paurization Depolarization = Reduction in the magnitude of the negative potential The membrane is less polarized than under resting conditions. Less charges are separated than under resting conditions => Movement in the positive (+) direction or upward. (the inside is less negative…) Y (closer to zero inside) 21 2.18  charges back to after depolarization (-70 MV) Sinc separation : rest returning Repolarization = The membrane returns to resting membrane potential value after having been depolarized => Movement in the negative direction or downward. MODULE 3.1 – NEURAL PHYSIOLOGY Hyperpolarization = Increase in the magnitude of the negative potential => The membrane is more polarized than under resting conditions = Downward movement, more charges are separated across the membrane. ↳inseparationchuyesbuteapotential charges I separating further going more charge separation & G ↓ in potential ↑ in potential 22 2.18  The plasma membrane has a resting potential. When resting potential changes, Electrical signals are generated > - in mm There are two forms of electrical signals:  The graded potentials (short-distance signals) MODULE 3.1 – NEURAL PHYSIOLOGY  The action potentials (over long distances)  Note: If graded potentials become large enough, they can Graded potentials trigger action potentials (we will come back to this idea). What is a graded potential? - making it closer to 0  Local changes in the membrane potential.  Short distance signals (small areas of a cell membrane change their potential)  Graded potentials can have various magnitudes and durations ↳ greater potential E magnitude through mechanical touch receptors 23  closed e rest : Triggering of a graded potential open in response binding it to triggering event schemical  They usually result from a specific- triggering that are either chemical (usually a neurotransmitter…see later) or mechanically gated channels (for example, ‘touch’). mechanically MODULE 3.1 – NEURAL PHYSIOLOGY > - deform physically channel & open them  This starts with an opening of gated Na+ channels => Inward movement of Na+ ions down its electrochemical gradient.  Whenever a graded potential occurs, Na+ is typically the first ion to flow between the place of origin of the potential and adjacent regions of the membrane that are still at the resting potential. - 2.ganat -Nat nat - Nat Nat = 24 q localized change  The stronger the triggering event, the more gated channels that open, the greater the positive charges entering the cell, and the larger the depolarizing graded potential at the point of origin. Also, the longer the duration of the triggering event, the longer the duration of the graded potential. MODULE 3.1 – NEURAL PHYSIOLOGY · The strength of thissering event open small Jab openmoreennels : is : amount of now long it lasts weak gated channels # touch what determines of gated channels that open 25  localized every A graded potential is generated at a specific point on the plasma membrane. Neurotransmitters typically trigger a graded potential at the ‘beginning’ of a neuron or where a neuron touches a MODULE 3.1 – NEURAL PHYSIOLOGY muscle fibre (see this in later sections). The example below shows a graded potential where a gated channel for Na+ is located. At this moment, the entire plasma membrane is at its resting potential. > - 1-70Mas T 26  Triggering event => Temporarily depolarized region = ACTIVE AREA (now becomes more positive inside the cell) MODULE 3.1 – NEURAL PHYSIOLOGY ↳ closes once triggering event finishes (temporary) + more - 70my localized - The surroundings = INACTIVE AREA Key Point: The active and inactive areas have (still at the resting potential). opposite charge differences across the membrane. 27 This is the beginning of a CURRENT.  By convention, the direction of CURRENT flow is always designated by the direction in which the positive charges are moving MODULE 3.1 – NEURAL PHYSIOLOGY also attraction repulsion but > membrane of+ charges that sit along - ↓ tranverse a - mm Y only more a couple distances can't travel long as they 28  The graded potential is decremental - mas of great potential continuously dec along membrane = Its magnitude along the neuron progressively decreases. COMMUNICATION PHYSIOLOGY weaker Reason? Leaking of charge-carrying ions across parts of the membrane. = signal as you loose potential – NEURAL – NEURAL > - mag is weaker as your loosing 2.1 3.1 Nat along memb MODULE MODULE 70 mV - 55 mV = 15 mV change 5 mV change 29 Learning Objectives By the end of this section, you should be able to: – Describe the key stages in the generation of the action potential – Understand the physiological mechanisms underlying the shape of the action potential – Explain the differences between graded potentials and action potentials, with reference to ion channels and membrane permeability – Describe the action of the Na-K pump and its role in maintaining concentration gradients  Action potentials: how electrical signals are propagated MODULE 3.1 – NEURAL PHYSIOLOGY from rest Action potentials changing membrane potential - by changing perm to allowions to flow Very different from graded potential. Brief - rapid - large amplitude (100 mV) electrical gradient > - has huse chase The membrane potential REVERSES: The inside becomes more positive than the outside (not simply less negative than the outside as can occur for the graded potential). Signal is propagated through the entire membrane = NOT DECREMENTAL => Thus, they do not decrease in amplitude. They are long distance electrical signals. (Example: toe) effector organ , to I same amp from generation to compared graded where polential is after a few mm gone Action potentials can be excitable cells such as neural cells and muscle cells (also some endocrine or immune cells. A graded potential can generate an action potential if it reaches a sufficient magnitude. Glocalized initiate 30 events that can help action potentials MODULE 3.1 – NEURAL PHYSIOLOGY - needs to be reached to initiate action potential - (initial depolarizing) > - 31  Triggering event MODULE 3.1 – NEURAL PHYSIOLOGY Membrane depolarization from the resting potential of -70mV (graded potentials are building) fairly T sor graded potentials Caringgarda ifenougha N - reach Depolarization is slow (graded than TP you can potentials) until it reaches the threshold potential (-55 to -50 mV) 32 MODULE 3.1 – NEURAL PHYSIOLOGY => Explosive depolarization change membrane potential = Upward deflection (to +30. event clarge depolarization mV). The potential reverses. a potent > - repolorination Repolarization is as rapid as depolarization. This is followed by hyperpolarization (-80 mV). Other terms: The reversion period (‘reversing’ the potential above 0 mV) is also called the overshoot (0 to +30 mV). The rapid change in potential from threshold to peak and then back to the resting potential = ACTION POTENTIAL The action potential is also referred to as a spike. When an excitable membrane is triggered Always the same duration (1 msec in a nerve cell) to undergo an action potential, we say it 'fires'. 33  passive Channels cleak) Changes in membrane permeability during the generation of the action potential · Gated Channe's (mechanicall , chem , The key to an action potential is the change in membrane permeability to ions voltage ( MODULE 3.1 – NEURAL PHYSIOLOGY Rapid fluxes of Na+ and K+ ions down their concentration gradients and through voltage- gated channels. - openinresponsetovotu re reached The voltage-gated K+ channels are simple with only one activation gate. ↳ Threshold potential is reached= opened 34  Two differences between zu Na+ and K+ voltage-gated channels: Quick when TP reached Both 1) Na+ channels are much faster to respond to change in the membrane voltage / potential. MODULE 3.1 – NEURAL PHYSIOLOGY 2) Na+ channels have in their cytosolic region an activation and an inactivation gates. & Rest ↑ inactivates Nat Channel earlier thanactivation a TP is reached 1 - 55mV) 35  How do these channels (Na+ and K+) open? MODULE 3.1 – NEURAL PHYSIOLOGY * leak channels are open yall time At resting potential (-70 mV), all Na+ voltage-gated channels are CLOSED and Na+ channels are in the configuration with the inactivation gate open (but activation gate closed) ↑ Nat 7 In response to a triggering event, the membrane starts to depolarize toward the threshold (remember…graded potentials). The change in voltage (charge) opens the activation gate of nearby Na+ channels. ↳ reaching TP ↓ Nat " more" - Recall: Both the electrical and the concentration gradients are in favour of Na+ movement into the cell I responsible for action 36 potential  Na+ Inward movement of Na+ ions => greater depolarization of the membrane MODULE 3.1 – NEURAL PHYSIOLOGY Opening of more voltage-gated Na+ channels => Positive feedback cycle. inc + charge within cell membrane - 55 mV causes more to voltage gates open = Nat influx 37 more Nat into cell depolarization = furter  Na+ Once the threshold potential is reached (-55 to -50 mV) => EXPLOSIVE MODULE 3.1 – NEURAL PHYSIOLOGY increase in Na+ permeability as many Na+ channels open (symbolized PNa+) => The membrane is now 600 times more permeable to Na+ than to K+ => The membrane potential is reversed and voltage gated opening channel > - + 30 peak tends to get closer (+30 mV) to the Na+ e pic , equilibrium potential (+60-65 mV) enters At the peak of the action potential => The inactivation gates of the Na+ S channels now fully Once TP is reached , it close the channels. o 30 my sit only 38 starts veryyy slowly closing so we &30 mv as they all membrane permability al cause abrupt dec in close  threshold How do Na+ channels close? -begains at When they open rapidly => This initiates the closing process => The inactivation gate can now bind to MODULE 3.1 – NEURAL PHYSIOLOGY its binding sites within the channel. This closing process is slow compared to the opening one. The delay (0.5 msec) => allows for Na+ to enter the cell and reach a peak. Is abrupt & 30 mu stop The channel remains in its inactivated configuration until the membrane potential is back to its resting value. + 30 mu When you repolarize > to - state the resting , ball will stop blocking & activate again - G cannot open again even if voltage changes 39  to threshold potential In response K+ MODULE 3.1 – NEURAL PHYSIOLOGY inactivate gate ↑ closing channel Simultaneously with the closing process of the Na+ channels, the voltage-gated K+ channels SLOWLY start to open. K+ leaves the cell and counteracts the increased positivity inside from the Na+ influx. ) reverses ↳ as KT leaves Triggering signal: Initial depolarization to threshold (same trigger for the Na+ channel opening, but slower). Nat activation gate I. Opening 2. Begain closing inactivation gate is 3 At +30. mV inactivation ball , open closed K + voltage gates 40  SUMMARY: AT THRESHOLD 1- 50--55mV potential  Rapid opening of voltage-gated Na+ channels => Na+ influx until inactivation gate closes MODULE 3.1 – NEURAL PHYSIOLOGY  Slow closing of the Na+ channel inactivation gates => Peak; prevents the action potential from increasing further and exceeding +30 mV  Slow opening of voltage-gated K+ channels (reverses polarity, returns membrane potential towards resting) The K+ permeability is increased to about 300 times => Outward K+ movement down it’s concentration gradient Nation and electrical gradient at peak (now +30mV) · Note that at the peak, the inside is more positive than the outside. This repels K+ ions from inside the cell thereby forcing them outside. This is opposite to the electrical chemt electrical gradient gradient at the resting potential. - > Both out of cell at this are pushingIt time = rapid repolarization, dec mem perm Hyperpolarization: Due to the relatively slow closing of K+ channels. 41 ↳ extra + leaking Idip below resting potential)  loss of per mem + 30 mV is reached - · inactivation of Nat Channels - a closed to reach rapid Both channels of close opening resting potential ;I take longer to Nat b kind of permeable Hyperpolarization MODULE 3.1 – NEURAL PHYSIOLOGY = so cells are still slowkt localized graded ~ trigger- > potential - - - - - - reset channels (depolarization > - dictated by leak channels J voltage nat , k+ 42  Important! An action potential occurs ONLY when the triggering stimulus AND the current that is generated via the opening of Na+ channels (graded potentials) are sufficient to reach the threshold MODULE 3.1 – NEURAL PHYSIOLOGY potential. 70-15 Such triggering stimuli are also named threshold stimuli. 15 mr1 than resting (-55mv) Threshold of most excitable membranes: about 15 mV less negative than the resting potential. What would it be for a neural cell with a resting potential of -70 mV? What if the initial depolarization is lower than the threshold? too weak to T AP trisser  The positive feedback cycle does not start... no action potential!  Such weak depolarization is called a sub-threshold potential  The stimulus is named a sub-threshold stimulus What if the initial depolarization reaches the threshold?  An action potential is generated samea se - have  All action potentials have similar amplitude regardless of how long it took to reach threshold  Once the threshold is reached => All-or-None law (An example: a gun cannot be fired ‘softly’. Once the trigger is pulled, it fires completely. 43 44 MODULE 3.1 – NEURAL PHYSIOLOGY tre  If all action potentials have the same magnitude, how do we integrate the magnitude of the stimulus? E.g. light touch versus pinch? firing of neurons that MODULE 3.1 – NEURAL PHYSIOLOGY to see if its stimulus Key Point…Frequency > - grade weak strong Crate of AP) , 45  limit to the # of action Refractory period potentials that can be produced T MODULE 3.1 – NEURAL PHYSIOLOGY During the action potential, a second stimulus, no matter how strong it is, will NOT generate a second action potential => This region of the plasma membrane is in its absolute refractory period. (Voltage- gated Na+ channels are open or just recently inactivated). if channel closed already open , is or -& channel Ap cannot be generated Following this period is the > - following when cell reaches resting potential Relative refractory period: A · can respond to change in voltage second action potential can be generated if the stimulus is stronger than usual (occurs during hyperpolarization).>cannotreaa - it ou can generate but wont have signal or anything We will see later that the absolute · need stronger Stimulus refractory period is important for the One-way propagation of the salused : cannot respond to further ⑭ input , even if voltage changes that may usually action potential…it prevents cause Ap to happen signals from going backwards. 46  Restoration of concentration gradients MODULE 3.1 – NEURAL PHYSIOLOGY When the action potential is completed, the resting membrane potential is restored through leak channels This process is rapid: almost the same amount of time as the depolarization period of the action potential. HOWEVER, the concentrations of Na+ and K+ has been altered across the membrane… maintains -cone gradient Restoring the original concentration of Na+ and K+ occurs through the Na+/K+ ATPase pump. # &Nat(everytime 2 + wa Ap happens · constant Imbalance to return that helps restingstateas are and wer St gradient St RMP = leak channels - · All other channel is closed - 80 my 47  The Sodium-Potassium Pump closs of ions across membrane) The pump counterbalances the rate of passive leakage. MODULE 3.1 – NEURAL PHYSIOLOGY to maintain it -against conc gradients ECF ↑ [] 3 Na+ When 2 K+ are pumped back into the cell, 3 Na+ are pumped out.  Concentration gradients are maintained.  This is a primary active transport = Requires energy (ATP) for providing the energy required for the conformational change of the transporter (‘ATPase’ pump) [34 2 K+  This active movement of ions also results in 2 positive charges sent ICF back into the cell vs 3 positive charges sent out. This transport is not electrically neutral since there is a net transfer of 1 positive charge out of the cell for each molecule of ATP hydrolyzed. (make inside neg more " more" -  The pump is therefore critical for restoring the normal chemical 48 concentration MODULE 3.1 – NEURAL PHYSIOLOGY - O > - Phosphorylate protein Using ATP EXf O Bindsto O CleavePhosphatesa b ICf state- 49 50 MODULE 3.1 – NEURAL PHYSIOLOGY Learning Objectives By the end of this section, you should be able to: – Describe the structure and function of nerve cells – Explain the differences in the mechanism between contiguous and saltatory conduction – Understand the process of nerve cell communication across a chemical synapse – Describe the integration and mechanisms of excitatory and inhibitory post synaptic potentials  Propagation of Action potential cell more along - Remember, action potentials are long distance signals. MODULE 3.1 – NEURAL PHYSIOLOGY This signal should be transmitted from one cell to another, along a specific pathway. : nerves = ↑ specializedI complexicity - receive in putfromotheras located : resp for AP in - channels Inc voltage gated are hillick - =potentials generation of graded >