Physiology 1 Lecture 11 - Membrane Potentials PDF

PHYSIOLOGY 1 Lecture 11 Membrane Potentials  Membrane Potentials Objectives: Student should know – 1. The basic principals of electricity – 2. Membrane channels – 3. Electrical-chemical gradient – 4. Factors that determine resting membrane potential – 5. Io...

PHYSIOLOGY 1 Lecture 11 Membrane Potentials  Membrane Potentials Objectives: Student should know – 1. The basic principals of electricity – 2. Membrane channels – 3. Electrical-chemical gradient – 4. Factors that determine resting membrane potential – 5. Ion concentrations inside and outside cell – 6. Ohm’s law, Nernst equation, Goldman equation – 7. Polarity - role  Membrane Potentials A. The body as a whole is electrically neutral B. All of the cells of body have an electrical potential across their membrane (Voltage difference) known as the membrane potential C. Membrane potentials develop because of differing ion concentrations between the inside and outside of the cell Membrane Potentials  Membrane Potentials Principals of electricity - Potential difference is determined by the difference in charge between two points 1. Units of electrical potential are in volts (V) or for biological system millivolts (mV) 1 V = 1000mV 2. Voltage is always measured between two points (Potential difference)  Membrane Potentials B. Current - flow of electrical charges from one point to another 1. Like charges repel unlike attract 2. Ions tend to move from areas of greater concentration to areas of least concentration 3. Movement of a positive ion from one side of a membrane to the other implies a negative charge is left behind  Membrane Potentials C. Current Flow Ohm’s Law - I = E / R, R = resistance I = current flow, E = electrical potential – 1. Cell - Aqueous solution + good conductor (Ions and water) – 2. Lipid membrane - A few charged groups can not carry current - high electrical resistance - good insulator – 3. ECF and ICF - both have low electrical resistance  Membrane Potentials Resting Membrane Potential – 1. By convention - ECF (outside of the cell) is assigned a voltage of zero – 2. Polarity of the membrane is stated in terms of the sign of the excess charge inside of the cell  Membrane Ion Channels Types of Channels – 1. Leak channels - Open all of the time - slow leak of ions a. Sodium, potassium & chlorine b. Membrane 75% more permeable to K+ than Na+ c. Accounts for 95% of the resting membrane potential Membrane Ion Channels 2. Na+K+ATPase Pump a. Unequal transport of positive ions makes the ICF more negative than it would be from diffusion alone - 2 K+ inside and 3 Na+ to outside b. Electrogenic pump c. Accounts for 5% of resting membrane potential  Membrane Potentials Ion Gradients The ion gradients have two forms. – 1. Chemical Concentration Gradient – 2. Electrical concentration gradient – (Charge buildup and charge differential) – Together these form what is known as the electrochemical  Resting Membrane Potential 1. In all cells a potential difference across the membrane exists – a. Inside is negative (Na+K+ATPase) – b. Membrane potentials usually within -40 to -90 mv 2. A cell with a resting membrane potential is said to be polarized 3. Both the inside and the outside of the cell are electrically neutral  Resting Membrane Potential B. Factors that determine the resting membrane potential – Selective permeability of the of the plasma membrane – Leak channels – Na+K+ATPase pump – Differences in ion concentrations Membrane Potentials IONS INSIDE OUTSIDE Na+ 14 140 K+ 140 4 Cl- 4 108  Resting Membrane Potential 2. Many substances are in the cell but the mobile ions Na+, K+, Ca+ + and Cl- play the most important roles 3. ECF - Cl- helps to balance Na+ ICF - Proteins (Neg charge) balance K+  Resting Membrane Potential 4. Selective membrane permeability – a. At rest - Slightly permeable to Na+, 75 times more permeable to K+, and freely permeable to Cl- – b. K+ moves down it’s concentration gradient more easily & faster than Na+ – c. Movement of a K+ out leaves a negative charge behind  Resting Membrane Potential d. Why no equilibrium? – Na+K+ATPase pump - stabilizes resting membrane potential by maintaining diffusion gradients for Na+ and K+ – Concentration gradient – Limit to ability of Na+K+ATPase pump c. Cl- Movement out = movement in - no contribution to membrane potential  Equilibrium Potential Equilibrium potential or electrochemical potential at which ion movements in both directions across the membrane are exactly balanced (net movement = zero) 1. Ion flux = 0 implies no net ion movement 2. The value of the equilibrium potential (Nernst potential) for any ion depends on the concentration gradient across the  Equilibrium Potential 4. The greater the concentration gradient the greater the equilibrium potential 5. The equilibrium potential for one ion can be different in magnitude and direction from those of other ions 6. Given the ion concentration gradient the Nernst potential for any ion can be calculated. The Nernst equation is used to determine the electrochemical potential for any ion across the biological  Equilibrium Potential Nernst Equation E(x) = RT/ZF log [x]inside/[x]outside R = Gas constant T = Temp. degrees Kelvin Z = Charge on ion (Valance) F = Faraday’s constant Membrane Potentials Nernst Equation - Examples  Membrane Potentials Resting Membrane Potential In reality a living cell contains a great number of ionic species. Most of these can and do move in and out of the cell others such as proteins can not without help. The net movement of all ionic currents across the membrane determines the resting membrane potential.  Membrane Potentials Resting Membrane Potential At rest the membrane potential is not changing, then the sum of all currents must equal zero. Thus I Na+ +I K+ +I Cl- +…=0  Membrane Potentials Resting Membrane Potential Therefore g [Em -ENa+] + g K+[Em - EK+] Na+ + g Cl-[Em - ECl-] + … = 0  Membrane Potentials Resting Membrane Potential Solving for Em yields the Goldman equation which gives the resting membrane potential  Membrane Potentials Resting Membrane Potential Goldman Equation Em = [gNa+/(gNa+ + gK+ + gCl- )] E Na+ + [gK+/(gNa+ + gK+ + gCl- )] E K+ + [gCl-/(gNa+ + gK+ + gCl- )] E Cl- +… Thus the resting membrane potential is a summation of all of the ion potentials times their  Membrane Potentials Resting Membrane Potential Since K+ conductance is almost 75 times that of Na+. The resting membrane potential is much closer to the Nernst’s potential for K+ than it is to the Nernst’s potential for Na+. Why would K+ conductance predominate?  Excitable Cells A. Nerve and muscle cells are excitable (Em < -40 mV) – 1. Electrochemical impulses are transient and rapid changes in Em – 2. Two forms of electrochemical impulses B. Electrochemical signals – 1. Graded potentials - short distance – 2. Action potentials - long distance z REFLEXES z SUPERFICIAL REFLEXES  CRANIAL REFLEXES z SUPERFICIAL REFLEXES  SPINAL REFLEXES z SUPERFICIAL REFLEXES z TENDON OR DEEP REFLEXES z THANKS FOR LISTENING!  Muscle Physiology Dynamics of Muscle Contraction  Thick and Thin Filaments A. Muscle movement (=contraction) occurs at the microscopic level of the sarcomere. B. Sliding Filament Mechanism 1. Actin (thin) myofilament slides along the myosin (thick) myofilament. 2. Z lines that form the boundary of the sarcomere move toward each other along the length of the muscle. =this causes the muscle to shorten (=contractibility). The Neuromuscular Junction Muscle Cell Parts 1. Sarcolemma = the muscle membrane 2. Sarcoplasm = the muscle cytoplasm 3. Sarcoplasmic reticulum = organelle responsible for protein production.  This contains high amounts of Ca+2 ions.  Sarcomere Parts 1. Z lines: boundary of the sarcomere. 2. I Band: region of only actin myofilaments. 3. H Zone: region of only myosin myofilaments. 4. A Band: region of both actin and myosin. 5. M-Line: The exact midpoint of the sarcomere. The Sarcomere  Muscle Contraction—10 Steps 1. A nerve impulse enters the presynaptic terminal (nerve) of the neuromuscular junction. 2. The impulse causes Ach to be released from the synaptic vesicles in the axon terminal. 3. Ach diffuses across the synaptic cleft and opens Na+ channels in muscle membranes. 4. Na+ enters the muscle cell and depolarizes it. 5. “T” tubules carry impulses into the sarcoplasmic reticulum and releases Ca2+ ions. 10 steps of Muscle Contraction 6. Ca +2 enters the individual muscle fibrils and binds to troponin molecules on tropomyosin strands moving the strand and exposing the binding sites. 7. Myosin binds to actin forming crossbridges that ATP can bind to. 8. ATP breaks down, releasing energy, causing cross bridges to pull actin strand. 10 steps of muscle contraction 9. Another ATP binds to myosin cross bridge for the recovery stroke. (bend, attach, and pull) on the actin strand. 10. When the action potential ends Ca +2 ions are pumped back into the sarco. retic. Tropomyosin covers the binding sites and myosin can no longer bind. The thin filament showing what happens when Calcium binds. 1. Calcium binds to the troponin complex. 2. Tropomyosin moves exposing the binding sites. 3. Now exposed so the heads of the thick myosin filament can bind to the actin. Read the step- The Myosin Cross-Bridge Formation wise captions explaining how the cross- bridge process works. Identify: 1. Working stroke 2. Recovery stroke 3. Cross Bridge. 4. ATP + ADP Homeostasis  Glossary Maintain – keep up. Constant – the same. Internal – inside the body. External – outside the body Environment – surroundings of the body. Stimuli – events in the environment that influence behavior  What is Homeostasis? Body cells work best if they have the correct Temperature Water levels Glucose concentration Your body has mechanisms to keep the cells in a constant environment. What is Homeostasis? The maintenance of a constant environment in the body is called Homeostasis  Why is it necessary? Homeostasis Organism may live in variable environment – Heat, Food, Water, etc. Cells live in STABLE, closely REGULATED environments. Uncontrolled changes disrupt ORGANIZATION – Cell death, dead organism  Homeostasis Homeostasis Maintaining a consistent, regulated internal environment Maintained by “feedback”  External Stimuli Phototropism – the need to grow toward light Fight/Flight – nerves release chemicals in our body (adrenaline) during stressful moments.  Internal Stimuli Feedback – Fever = Body fighting illness – Goosebumps = Drop in temperature – Vomiting = Poison/stomach flu – Sweating = Overheated/rise in temperature – Dry tongue = dehydrated 02 April 2009 AnimalForm&Function.ppt 8  Internal & External Stimuli Thermoregulation, Endothermal = “warm blooded” generate internal heat, regulate temperature Mammals Ectothermal = “cold blooded” produce little heat, body temperature conforms to environment Reptiles AnimalForm&Functio 02 April 2009 9 n.ppt  Controlling body temperature All mammals maintain a constant body temperature. Human beings have a body temperature of about 37ºC (or 98.6ºF). E.g. If your body is in a hot environment your body temperature is 37ºC If your body is in a cold environment your body temperature is still 37ºC What mechanisms are there to cool the body down? 1. Sweating When your body is hot, sweat glands are stimulated to release sweat. The liquid sweat turns into a gas (it evaporates) To do this, it needs heat. It gets that heat from your skin. As your skin loses heat, it cools Sweating The skin  What mechanisms are there to cool the body down? 2. Vasodilation Your blood carries most of the heat energy around your body. There are capillaries underneath your skin that can be filled with blood if you get too hot. This brings the blood closer to the surface of the skin so more heat can be lost.  This means more heat is lost from the surface of the skin If the temperature rises, the blood vessel dilates (gets bigger). What mechanisms are there to warm the body up? 1. Vasoconstriction This is the opposite of vasodilation The capillaries underneath your skin get constricted (shut off). This takes the blood away from the surface of the skin so less heat can be lost.  This means less heat is lost from the surface of the skin If the temperature falls, the blood vessel constricts (gets shut off). What mechanisms are there to warm the body up? 2. Piloerection This is when the hairs on your skin “stand up”. It is sometimes called “goose bumps” or “chicken skin”! The hairs trap a layer of air next to the skin which is then warmed by the body heat The air becomes an insulating  Controlling Glucose levels Your cells also need an exact level of glucose in the blood. Excess glucose gets turned into glycogen in the liver This is regulated by 2 hormones (chemicals) from the pancreas called: Insulin Glucagon Glycogen If there is too much glucose in the blood, In s u lin Insulin converts some of it to glycogen Glucose in the blood Glycogen If there is not enough glucose in the blood, Glucagon Glucagon converts some glycogen into glucose. Glucose in the blood  Diabetes Some people do not produce enough insulin. When they eat food, the glucose levels in their blood cannot be reduced. This condition is known as DIABETES. Diabetics sometimes have to inject insulin into their blood. They have to be careful of their diet.  Glucose levels rise after a Insulin is Glucose meal. produced and Concentration glucose levels fall to normal again. Normal Time Meal eaten  Glucose levels Glucose rise after a Concentration meal. Diabetic Insulin is not produced so glucose levels stay high Time Meal eaten Glycogen The glucose But there is in Glucose the blood to no insulin concentration increases. convert it into rises to glycogen. In s u lin dangerous levels. Glucose in the blood  Controlling water levels The control of water levels is carried out by the KIDNEYS. It is closely linked to the excretion of urea. Urea is a waste product that is made when the LIVER breaks down proteins that are not needed by the body. Urea contains the element Nitrogen.  The kidneys The kidneys “clean” the blood of waste products and control how much water is kept in the body. The waste products and water make up urine which is excreted via the ureter. “Dirty” blood enters the kidney through the renal artery. Then, several things happen to clean the blood... 1. Filtration Blood enters the tubule area in a capillary. The capillary forms a small “knot” near the kidney tubule. The blood is filtered so all the small particles go into the tubule. The capillary then carries on to run next to the tubule. The kidney tubule now contains lots of blood components including: Glucose: Ions: Water: Urea: 2. Reabsorb sugar The body needs to have sugar in the blood for cells to use in respiration. So all the sugar is reabsorbed back into the capillary. 2. Reabsorb sugar The body needs to have sugar in the blood for cells to use in respiration. So all the sugar is reabsorbed back into the capillary. 3. Reabsorb water Water and ions are the next to be absorbed. It depends on how much is needed by the body. 3. Reabsorb water Water and ions are the next to be absorbed. It depends on how much is needed by the body.  Reabsorbing water If you have too If you have too little water in your much water in your blood, you will blood, you will produce very produce very dilute concentrated urine. urine. (very little water in (lots of water in it) it)  5. Excrete the waste Everything that is left in the kidney tubule is waste: All the urea Excess water This waste is called urine. It is excreted via the ureter and is stored in the bladder. Renal vein The “clean” blood leaves the kidney in the renal vein. Ureter  Summary of urine production Urea is a waste product made in the LIVER Water content of the body is controlled in the KIDNEYS Urea, water and other waste makes up URINE. Urine travels down the URETER and is stored in the BLADDER Urine is excreted through the URETHRA.  Movie Time Now go to Brain Pop and observe Homeostasis in action  http://www.brainpop.com/health/bod ysystems/homeostasis/ ID – mcmath Password – tigers Search – Homeostasis Start Homework –  This powerpoint was kindly donated to www.worldofteaching.com http://www.worldofteaching.com is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching.