PSL 250 Week 3 Physiology Lecture notes
PSL 250 Week 3 Physiology Lecture notes PSL 250
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This 16 page Class Notes was uploaded by Ren K. on Sunday September 18, 2016. The Class Notes belongs to PSL 250 at Michigan State University taught by Dr. Patrick Dillion in Fall 2015. Since its upload, it has received 13 views. For similar materials see Introductory Physiology in Physiology at Michigan State University.
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PSL 250 Lecture 5 Membrane transport Diffusion across membranes ● Driven by chemical or electrical gradients. ● Simple diffusion, channels and carriers. ● Diffusion goes in all directions; net diffusion will always go from high concentration to low concentration. Hydrophobicity ● Fats, hormones, steroids and gasses cross the easiest through capillaries. ● The fluidity allows 8 microns RBCs to deform through 7 micron capillaries which enhances oxygen transport. ○ RBC’s = red blood cells. ● Blood supply goes twice through 2 cycles in 1 minute. ● The presence of cholesterol gives them ‘toughness’ and when the membrane is squeezed, because it's tight up against it, oxygen can cross the membrane wall easily. ● Pneumonia water forms around the area of the capillaries prevents oxygen from entering red blood cells. The water in there prevents the movement of the RBC’s, reduces the rate of oxygen transport. Size ● Negative charge is responsible for membrane potential brain to work, muscles to contract. ● Smaller molecules move easier. Fick's law ● Applies to diffusion anywhere in the body or perfume diffusion through a room. ● Rate of diffusion, Q, Q = PA△C/△x /MW ● P = permeability hydrophobicity, hydrophilicity ● Hydrophilic molecules are slow in many phases, in some the rate of diffusion is 0. ● A area ● △ c/ △ x = concentration gradient ● MW = molecular weight (size) ● Example: ○ Emphysema lungs slowly start shrinking over time due to contaminants like tar, smoking etc. ○ Oxygen gradient from lungs to blood vessels which allows the person to breathe. ○ 20 % oxygen in environment, but for those who have emphysema it isn’t sufficient to breathe. ○ Carry oxygen tanks to breathe not 20% but 100% oxygen, increase concentration gradient by a factor of 5 which helps keep them alive for a while to compensate for the loss of area in the lungs. ● ALL play a role in diffusion. ● Increase molecular size = decrease diffusion rate ● Other 3 increase diffusion rate. Ion channels ● Ions are very water soluble which means they have to move by using channels or carrier mechanisms. ● There are different types of ion channels for different ions Na+, K+, Ca++, Cl. ● Almost all cells have chloride channels allowing Na+ to go to where the ion gradient is located. ● There is an electric charge associated to cells inside cells is always negatively charged and the outside positive charge. ● The Sodium concentration is inward. ● The positive charge on sodium is going to be attracted to the charge on the inside of cells. ● Calcium is the same way. Very little calcium on the outside because it is attracted to the positive interior. ● Most are electrically inward. Outlier = potassium, which is electrically outward. ● High concentration is inside, while the low concentration is outside. Osmosis ● The diffusion of water. ● Water moves from high concentration (low solute concentration) to low water concentration. (high solute concentration). ● Semi permeable membranes allow water to cross but nothing else. ● More water on one ‘side’ than the other. Move from high to low concentration of water. ● Swelling that occurs in injury has swelling because of osmosis, i.e. a broken barrier causing water diffusion in cells. Carrier transport ● Protein molecules change shape in the membrane and move molecules across it. ● Energy for transport may come from the concentration gradient or from ATP. ● Avoid the hydrophobic environment created by phospholipids. ● Concentration gradient drives movement of the carrier molecules. ● Or ATP causes movement. Carrier that is phosphorylated has characteristics of the carrier that the phosphate does not have, helps carry out carrier transport. Specificity ● Each carrier transports a specific molecule or type of molecule. ● Exception: carriers that move sugars ● A family of glucose carriers can carry other sugars as well. In some cases molecules that start as glucose can move other types of sugars. Vitamin c is one of these, as it is similar to glucose but our body isn’t able to synthesize it on our own that is why it is called a Vitamin. ● There are 20 amino acids in you with three basic types negative, positive and neutral. ● Families carry different types of amino acids only specific amino acids will be carried by specific families. ● There are 1000 different types of carriers. ● Most commonly carriers carry a type of molecule rather than a specific type of molecule. Saturation ● There are only a limited number of carriers in each cell. ● There can only be a certain amount of students enrolled in a course before it becomes full max capacity. ● Same concept When all carriers are being used the rate will be at the maximum. ● Particularly kidneys! ● Filtrate in the kidneys filtering out the bad, while taking back the good. ● If concentration keeps going up from low to high = the higher concentration, the higher the rate of diffusion i.e. you can keep going up indefinitely. ● But if you use a carrier at a certain point you will reach a transport maximum where you cannot transport any more no matter how high the concentration gets. ● Example: ○ Type 2 diabetes typically found in the obese. ○ Once their blood sugar rises, their kidneys filter sugar out of their bloodstream, and carriers pull it back in. ○ The normal concentration of sugar is 5 ppm. ○ Urine will be glucose free if it's at 7 ppm, and the rising blood sugar remains undetectable in urine. ○ If your glucose concentration is higher than 3 times normal for example if you have 20 ppm, only 15 ppm could be absorbed which results in a urine output with high sugar concentration. ● All carriers have a transport maximum. Facilitated diffusion ● We distinguish carriers by the system that they use to carry. ● If they use ATP, we call it facilitated diffusion. ● No ATP is used to move down diffusion gradient. ● Molecules bind to one side, while the carrier reorients molecules leaving them on the opposite side, with the movement going from high to low concentration. ● The protein squeezes the solute out, popping out the molecule. Then the protein gets phosphorylated and the process starts again. ● Pumps use ATP to move ions against the concentration gradient. ● The movement is from low to high concentration with ATP. ● Ions move from high to low. ● Bind from high affinity side to low affinity side unlikely to bind because protein has changed. Na k ATPase ● Nak ATPase moves Na+ out of cells, moves K+ into cells keeping the concentration of K+ high inside cells, while keeping Na+ high outside of cells. ● This creates gradients that allow electrical signaling. ● Occurs in all animal cells. ● Sodium moves out of the cell and moves potassium inside, allows muscles to move, to think and function. ● This creates a gradient that allows electrical signaling that let us live. ● Without this = no life. Secondary active transport ● Carrier has 2 binding sites at the agonist and Na+ energy of the Na+ gradient moves from the outside to the inside with SAT. ● Cotransport agonist in or counter agonist out. ● Na+ transports some glucose and amino acids in this way. ● In some tissues, ions drive SAT. PSL 250 Lecture 7 Neurons: Action Potentials Action Potentials ● Longest muscles hamstrings, with cells that are over a foot long. ● For a hamstring cell to work, you need to have an electrical signal that functions in a long range situation. 15 to 20 mV more than resting potential is the activation range. ● Activated by graded potentials. ● AP’s do not degrade over time and distance. ○ Tsunami can carry over hundreds of mile AP’s only stop when they reach the end of a cell. VoltageGated Channels ● VoltageGated channels will open when the membrane reaches a particular voltage. ● Turned on when membrane potential reaches a particular voltage 1520mV more than at rest. ● All vgated channels open together, causing action potential. ● Enter inactivated state soon after opening, making the refractory period. ● Don't send by size to signify strength of the signal but by frequency. ○ Slap example would show strength by sending more signals, that bro, you just got pimp slapped by college debt. ● Voltage gated sodium channels have three states open, closed or they’re closed and unopenable. ● This refractory period limits how often APs can occur within a cell. ○ This allows your heart to actually fill up with blood. ● The largest amount of contractions your large muscles can have is 5 contractions per second. ● Different tissues have different refractory periods. Phases of the AP ● Controlled by different open channels. ● ● Depolarization to threshold. (Firing level) 1 ○ Chemical or mechanical gated Na+ channels open. ○ Na+ enters down gradient. ○ T = threshold ○ At t, all v gated Na+ channels open. ○ TTX blocks fast V gated Na+ channels. ■ TTX = neurotoxin, naturally occurring. ● AP Spike 2 ○ Since all vgated Na+ channels open together, all APs in one neuron are identical. ○ Na+ enters, rapid depolarization to +20 mV ○ Doesn’t reach Na+ equilibrium potential because some Vgated K+ channels also open. ● Repolarization 3 ○ Vgated Na+ channels close after 12 msec. ○ K+ channels still open, K+ leaves, membrane potential falls. ● Hyperpolarization 4 ○ Voltage goes below resting because extra K+ channels are still open. ● Return to Resting Potential 5 ○ Extra K+ channels close. Neural structure ● Receive and pass on signals. ● Two trillion cells in brain half are neurons. ● Neurons are 10 microns long your brain has lots of small neurons, but your peripheral ones are much longer. Dendrites ● Receive neurotransmitter from other neurons. ● Many branches. ● No action potential here, only graded potential. ● Axon hillock is where sodium channel first opens. Cell body ● Cell organelles, nucleus. ● Axon hillock at the beginning of the axon, has a high density of Vgated Na+ channels. ● Action potential starts here. Axons ● Very long carry AP away from cell body. ● Speed of AP variable, increasing with increasing diameter and with myelin. Myelin Nodes of Ranvier ● Cells surround axon and wrap layers of membrane. ● Electrically insulates axon preventing electrical loss to the IF. ● Example: ○ White matter has myelin sheep, with layers and layers of the cells wrapping around the axon. ● The layers of membrane serve the same purpose as an insulator around a wire. ● Increases AP speed. ● Called saltatory conduction not for salt, but from the word jump. ● A jump for APs, 3 times faster to 10 times faster for the myelin. ● The presence of myelin significantly increases the APs speed Refractory period ● After vgated Na channels close they are unopenable for a time (30200 msec) ● No new APs during this time, limiting the AP frequency. ● AP can only travel along the axon in one direction, and they can’t go back. Frequency of APs ● We are limited to 30 APs a second, excluding your heart. ● Information is passed by the frequency, not the size of action potentials. ● More APs create a stronger signal input to CNS (Central Nervous System) PSL 250 Lecture 8 Synapses Synaptic structures ● Neurons are connections between synapses and something else. ● Most commonly between neurons and other neurons, but often a neuron can be paired with others tied with the release of hormones, heart, musculatory system. ● Neurons never physically touch each other, the gap is filled by the synapse. ● The gap is physically filled by the chemical reaction which binds to the other cell. ● Electrical within the cell, and chemical between them. ● Every time you learn something you don’t gain more brain cells you gain more synapses. Presynaptic Neuron ● End of axon synaptic knob, terminal button. ● Some of neurons get over 10000 synapses inputting into one single cell. ● Most of synaptic interactions are on the dendrites. ● Receive AP down Axon. ● AP opens Ca++ channels. Vesicles ● Contain neurotransmitters. ● Increase of Ca++ triggers merger with cell membrane, NT dumped into cleft, diffuses to postsynaptic membrane. Postsynaptic Cell ● A postsynaptic cell has receptors for Neurotransmitters from presynaptic neurons. ● Receptors connected to ion channels. ● When NT binds to receptor, channels open. Excitatory Postsynaptic Potentials EPSPs ● NT binds and Na+ channels open. ● Na+ enters and causes depolarization, ● One EPSP is not sufficient to reach threshold. ○ Never sufficient. It produces ½ mV. Inhibitory Postsynaptic potentials IPSPs ● K+ or Cl channels opened by NT ● K+ leaves or Cl enters down their electrochemical gradient. ● Membrane potential is more negative, meaning it is less likely to reach the threshold. Grand Postsynaptic Potential GPSPs ● Sum of all EPSPs and IPSPs occurring at any one time ● Reach threshold Yes; fire AP ● Most neurons are inhibited by IPSPs most of the time Axon Hillock ● It is located at the junction of the cell body and the axon. ● High density of VGated Na+ channels ● AP starts here. Oneway Conductance ● NT is only released from presynaptic neuron, receptors only on postsynaptic neuron. ● Information only goes in one direction. ● Synapse onto the axon example Acupuncture. Temporal Summation ● EPSPs from the same neuron close in time are additive they may sum to reach threshold. Spatial summation ● EPSPs from different neurons are additive in the same direction. ● IPSPs in one direction, while EPSPs are in the opposite. ● The sum of these may reach threshold. ● Some neurons receive synapses from 1000’s of other neurons. Convergence ● Multiple synapses into a single neuron. ● Anatomical basis for spatial summation can be inhibitory or additive. Divergence ● Each axon has many synaptic knobs (terminal buttons) to other neurons. ● An AP in one neuron delivers neurotransmitter to all its divergent neurons at the same time. PSL 250 Lecture 9 Intercellular communication Communication types ● Communication between cells over short and long distances. ● Combinations of electrical and chemical activity. Paracrines ● Where a chemical released from one cell, has an effect on the cell next to it. ● Local hormone. ● Released in relatively small amounts. ● Nitric Oxide Important in control of blood flow. Neurotransmitters ● Specific, each neuron has only one type of NT ● Variable neural cell length NTs work locally as its is released. ● NTs released by exocytosis synapse cell to cell. ● Neural to neural, muscle, endocrine cells. ● Rapid removal : diffusion, digestion, reuptake. Endocrine ● Hormones released from endocrine tissue (endothelial origin) ● Broad effects hormones released into blood. ● Goes everywhere. ● Effect depends on target cell receptor. Neurohormones ● Released from neurons into the blood. ● Functions as other hormones receptor dependent. Hydrophilic Hormones ● Cannot cross the membrane. ● Easily travel everywhere. ● Rely on membrane receptor activation. ● Membrane proteins produces second messengers. ● Hydrophilic hormones first messenger send an enzyme producing a second messenger within the cell. Second messengers ● Made at membrane ● Internal activation mechanism started by hydrophilic hormone (1st messenger) ● Only cells with receptors respond. cAMP ● ATP cAMP activates kinases, add phosphate to molecules ● Kinase cascades amplifies signals. PSL 250 Lecture 6 Membrane Potential Voltage ● The separation of charge in your cells is located right along the membrane. ● All cells have a negative charge inside compared with interstitial fluid. ● The opposite charges line up along the membrane. ● The MP is always in the mV range. ● The charge forms a layer along the plasma membrane. Resting membrane potential ● Resting membrane potential = voltage across cell membrane when the cell is not activated. ● MP is determined by what ion channels are open sodium channels and potassium channels. ● K+ dominates at rest (most open channels) ● Some Na+ contribution (few open channels) ● Chloride follows sodium, doesn’t determine membrane potential it just goes along with sodium. ● Changing the number of sodium channels lets us move a muscle, think a thought = open a sodium channel. Concentration ● Na+ is 150 mm in ECF, 15 mM in ICF in muscle ● K+ is 5 mM in ECF, 150 mM in ICF in muscle. ● Protein is 0 in ECF, 65 in ICF in muscle. ● The intracellular concentration of Na+, K+ and protein are different in different cell types. ● A = protein in the intracellular fluid. ● Outside is the same in every location of cells its constant. ● Different cell types have different types of concentrations of potassium and sodium. ● However, generally rule still applies lots of Na+ outside lots of K+ inside. Permeability ● Determined by the number of open channels. ● The number of open K+ or Na+ channels determines ion diffusion. ● Different open number in different cell types produces different resting MP. NaK ATPase ● Also referred as the sodium pump although it also pumps potassium. ● This enzyme creates the gradients and restores them after ions diffuse across the membrane this is the ion pump’s activity. ● Term ends in ase = always will be an enzyme. Equilibrium Potential ● Limits on K+ and Na+ ● What voltage balances chemical gradient? ● Only open channels determine MP. ● Whatever the voltage would have to be, to balance the ion gradient = equilibrium potential. ● +60_________________70______90mV ● Na+______________most K+_____K+ ● all_______________Few Na+_____all ● Solutions would tell you that 90 would perfectly balance the tendency of potassium to leave the cell. ● For your brain cells, neurons = 70mV K+ Diffusion at Rest ● At rest, K+ channels are open, K+ diffuses out. ● When K+ leaves, the positive charge leaves. ● Intracellular protein A with a negative charge, is trapped in cell. ● Na+ channels are mostly closed, little Na+ diffusion. ● Balance between pumps NaKATPase ions are leaking through the channels. ○ Boat with leaks in it ions are the leaky water. ○ Pumping rate of water leaving the boat = rate of water leaving the boat = equilibrium. Pump Leak balance ● There is a balance between the pump and diffusion (channel) activity. ● Since ions constantly diffuse down their gradients through channels, a constant input of ATP energy into ion pumps is needed to maintain the gradie . Resting MP changes ● Membrane potential is capable of changing including nerve and muscle cells. ● Changing membrane potential is important in all aspects of physiology. ● MP is always negative at rest. ● MP magnitude decreases (gets less negative) during depolarization. ● MP increases (gets more negative) during hyperpolarization. ● MP returning to resting potential is repolarization. ● Most positive a cell can already be +60. Depolarization ● The membrane potential is less negative as from 70 to 60 mV ● Depolarization is caused by closing potassium channels or opening sodium channels. ● It's not only sodium or potassium it's the ratio between them. ● MP moves toward Na+ equilibrium potential. ● Na+ channel opening is more common. Hyperpolarization ● The MP gets more negative (as from 70 to 80 mV) ● This is caused by K+ channels opening, and Na+ channels closing. ● MP moves toward K+ equilibrium potential. ● Most of the time in your brain, most signals in brain produces hyperpolarization turns itself off, inhibiting itself. ● Work to keep your brain from keeping your brain from sending any signals, so when you do send out a signal your brain knows to pay attention to it. Graded potentials ● Triggered by agonists or by physical force. ● Local event occurring at membrane, producing a local electrical response. All events are variations on graded potentials. ● Example: ○ A pond is perfectly still, and then some jerk throws a pebble into the pond disturbing it which produces a ripple which fades away. ● That's how graded potentials work, working exclusively in a local area within the cell itself. ● Example: ○ A lightwave hits your eye, something touches your skin. ● A channel opens, and ions pass through. All of your senses use sodium channels and many of your brain cells do as well. ● Size of the graded potential is proportional to the side of the stimulus. ● Spreads to adjacent areas , but decays rapidly over time and distance. ● Sodium rushes insides of the channel, making it positive and the electrical activity on the local level becomes positive on the inside and negative on the outside. ○ Hard slap and a soft touch slap causes many of the sodium channels to open up, vs less sodium channels opening up with less stimulus. ● Both graded potentials and action potentials are simple exponential decay processes. ● Graded potentials can only carry a signal over short distances decaying rapidly over time and distance. ● Occur in many cell types receptors, neurons and muscles. ● In neurons and muscles, GPS needed to reach the threshold of Action Potentials. ● Action potentials are what is necessary to transmit signals long distance. ● Action potentials are a big electrical response need to have something to turn it on. ● Graded potential response is necessary to have the Action potentials response occur.