Week One, Two, Three Notes
Week One, Two, Three Notes Bio385
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This 10 page Class Notes was uploaded by Marisa Loken on Sunday February 14, 2016. The Class Notes belongs to Bio385 at University of Wisconsin - Stevens Point taught by Dr. Sepsonwol in Winter 2016. Since its upload, it has received 36 views. For similar materials see Human Physiology in Biology at University of Wisconsin - Stevens Point.
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Date Created: 02/14/16
Physiology notes: Weeks One and Two Book/Lecture/Lab Notes - Levels of organization o Chemical level o Cellular level o Tissue level o Organ level o Body system o Organism - Tissues o Cells of similar structure and specialized function combined o Four primary tissues Muscle smooth, cardiac, skeletal Nervous send signals through body Epithelial protection (skin), lines digestive tract Connective connects tissues - Organ o Body structure that integrates different tissues and carrier at a specific function - Body system o Collections of organs that perform similar functions o Combine to form the organism o 11 total body systems: Nervous system Muscular Circulatory Digestive Endocrine Respiratory Reproductive Urinary And three others… - Homeostasis o The maintenance of a dynamic steady state in an internal environment o Each cell helps maintain the internal environment shared by cells o Factors maintained homeostatistically: Temperature pH (to acidic or basic, proteins die) oxygen and carbon dioxide nutrient concentration colume and pressure concentrations of water, salt, and other electrolytes (cell size) concentration of waste products o negative feedback a change in controlled variable triggers a response that drives the variable in the opposite direction of the initial change example is temperature o positive feedback amplifies the initial change moves the system away from the set point uncommon example is childbirth - Major functions of cell membrane proteins o Transport Protein pores and gated channels Carrier proteins Sodium Potassium ATPase enzyme proteins o Recognition Surface glycoproteins as markers Antigen recognition receptors on immune cells o Signal reception Surface protein receptors for hormones, nerve transmitters and other factors: physical stimuli o Attachment Protein junctions attach cell to cell Adhesion proteins stick cell to surface for crawling (wbc’s) anchoring (tendon to bone) association of cells into tissues o Generation of electrical potentials Separation of charge/ions causes a voltage to develop; especially important in explaining actions of nerve, muscle and hair-cell membranes o Membrane attached enzymes Associated with receptor or carrier proteins or alone o Cell shape, structure Proteins in the shapes of rods, tubes and fibers can form an elaborate framework inside the cell membrane, called the cytoskeleton that gives the cell its shape - Sodium Potassium ATPase Pump o The Sodium Potassium ATPase pump transports three sodium out of the cell for every two potassium pumped in o Cell loses more positive charge than it gains o Primary role of the pump is to actively maintain sodium and potassium concentration gradients o Only make a small direct contribution to resting membrane potential - Equilibrium potentials o Potential that would exist at equilibrium for a given ion o Two opposing factors Concentration gradient Electrical gradient o Potassium acting alone would establish an equilibrium potential of -90mV Attracted to inside of cells negative charge o Sodium acting alone would establish an equilibrium potential of +60 mV When inside reaches +60mV, Sodium gets pushed out o Equilibrium potentials are determined using the Nernst Equation - Resting Membrane Potential o RMP is 25 to 30 times more permeable to Potassium than Sodium - Excitable Cells o Neurons and muscle cells can rapidly and transiently alter their membrane permeability - Membrane Electrical States o Depolarization Decrease in potential, membrane less negative o Repolarization Return to resting potential; membrane more negative o Triggering event A triggering event triggers a change in the membrane potential by altering membrane permeability 4 types of gated channels Voltage-gated channels open in response to membrane potential change Chemically gated channels open by something binding to them Mechanically gated channels Thermally gated channels - Permeability o If a substance can cross the membrane, the membrane is permeable to the substance o Two properties determine permeability Lipid solubility Particle size - Permeation through lipid bilayer o Gases can actively pass through o Steroids can pass through o Small uncharged polar molecules slowly (water, glycerol) o Will not cross Large uncharged polar molecules (sucrose, glucose) Ions (sodium potassium) - Passive Transport o No energy required o Down concentration gradient o Rules of Passive Transport: Passive transport does not require added energy (uses thermal) The membrane must be selectively permeable to a given substance Molecules may move in both directions (bidirectional) during passive transport Molecules, ions, or atoms ALWAYS move from higher concentration to lower concentration The movement of each species of particle by passive transport is considered separately. The rate of passive diffusion of a particular substance is proportional to the permeability factor and to the difference in concentrations on each side of the membrane o Three types: Simple diffusion Osmosis Facilitated diffusion o Simple Diffusion Diffusion is the movement of molecules from high concentration to law concentration Unassisted and passive Uniform spreading out of molecules due to random intermingling Occurs until equilibrium is reached o Osmosis Similar to passive transport How water moves - Iso-osmotic Solution o No net movement of water into or out of the cell o If a solution is iso-osmotic, the cell neither swells nor shrinks, but remains the same volume o **0.29 moles of dissolved particles/liter - Ion Channels o Ions move across the membrane through channels o Specific to the type of ion passing through o Ions move through channel Down their concentration gradient Down electrical gradient - Fick’s Law of Diffusion o Concentration of gradient of substance, rate of diffusion goes up o Surface area of the membrane, goes up o Lipid solubility, rate of diffusion goes up o Molecular weight of substance, rate of diffusion goes down o Distance (thickness of membrane), rate of diffusion goes down - Osmosis o Is the process of water moving passively down its own concentration gradient to an area of higher solute concentration o Water channels aquaporins 4 types, important in kidneys o Definitions Pure water 100% water, 0% solvent Solute 90% water, 10% solvent Hydrostatic pressure Pushing pressure, opposes water Osmolarity Total number of solute particles per liter Moles and osmoles o Osmole 1 mole of solute particles 1 mole glucose = 1 osm/L 1 mole NaCl = 2 osm/L - Osmotic Pressure o The pressure required to stop osmosis o “pulling pressure” - Tonicity o The effect a solution has on a cell volume o An isotonic solution has the same concentration of solute as normal body cells (300 m Osm/L) o Hypotonic Below normal concentration of solutes (expand) o Hypertonic Above normal concentration of solutes (shrink) - Facilitated Diffusion o Requires a carrier protein o Assisted membrane transport o The carrier moves the particle down the concentration gradient Carriers are bidirectional, flows to where concentration is higher o Passive o Example: Glucose Binds to carrier protein, changes conf. so binding site is exposed to lower concentration: ejected into cell - Assisted Membrane Transport o Carrier mediated transport characteristics Specificity Saturation Transport maximum Competition Amino acids compete for carrier proteins - Active Transport o Energy is required o Area of low to high concentration o Against concentration gradient o 2 types: Primary active transport Requires direct use of ATP Examples: Na+/K+ pump Secondary Active Transport Driven by an ion concentration gradient Two types: o Symport Driving ion down concentration gradient Helps other ion o Antiport Opposite direction Sodium usually - Membrane potential o The plasma membranes of all cells are polarized electrically o The separation of opposite charges across the plasma membrane o When anions and cations are equal on both sides, no potential o When excess positive ions, positive potential o Electrically negative charges on both sides separate to make neutral o Magnitude of potential More charge has more membrane potential (number of separated ions) o Nonexcitable cells and excitable cells at rest is constant Nonexcitable ranges from -40 to -80 o Measured in millivolts (mV) o Typical resting membrane potential is -70mV o -90mV (skeletal muscle) o Influenced by the permeability of a few important ions Sodium, potassium, large anions (negative proteins) - Na+/K+ ATPase Pump o The pump transports 3 Na+ out of the cell for every 2 K+ it pumps in o Cell loses more positive charge than it gains o Primary role of the pump is to actively maintain Na+ and K+ concentration gradients o Only makes a small direct contribution to the resting membrane potential - Equilibrium potentials o Is the potential that would exist at equilibrium for a given ion o 2 opposing factors: Concentration gradient Electrical gradient o K+ acting alone would establish an equilibrium potential of -90 mV Attracted to inside the cell’s negative charge o Na+ acting alone would establish an equilibrium potential of +60 mV When inside reaches +60mV, Na+ gets pushed out o Equilibrium potentials are determined using the Nernst Equation - Graded Potential (GP) o Flow is between the active area and adjacent inactive area o Flow is passive o The magnitude of a GP varies directly with the magnitude of a stimulus o Example Postsynaptic potential, endplate o Die out over a short distance (decramental) o Summation Sum together at cell body, triggers AP - Action Potential (AP) o An AP is a brief, rapid, large, change in membrane potential o Occur when an excitable cell membrane is depolarized to threshold potential o At threshold, changes in Na+/K+ permeability are initiated o During resting potential, Na+ ions enter the cell along a concentration gradient and a long electrical gradient - Voltage Gated K+ Channels o Voltage gated K+ channels have one activation gate o Can exist in 2 conformations: Closed/open - Voltage Gated Na+ Channels o Activation gate (sliding door) o Inactivation gate (ball and chain) o Can exist in three conformations: Closed but capable of opening Open (activated) Closed and not capable of opening - Activation Potential Propagation o An action potential generates a new AP in the area next to it o AP’s propagate in one direction o AP’s do not diminish as they propagate (non-decremental) - Action Potentials o Very few K+ and Na+ actually cross the membrane during an AP - Refractory Periods o The Na+/K+ pump gradually restores the ions that moved during the ATP o After an AP the membrane enters its refractory period o Refractory periods endure one way propagation of AP’s - Action potentials o All or none o Variable strength of stimuli are coded by varying the frequency of action potentials, not their size - Two types of AP Propagation o Continuous conduction In unmyelinated fibers o Salutatory conduction Myelinated fibers - Continuous propagation o Slow conduction velocity o The AP spreads along every patch of membrane down the axon o Accomplished by local current flow - Myelin o Thick layer of lipids that cover the axon o Acts as an insulator to prevent leakage of current o Myelin farming cells are Schwann cells and digodendrocytes Schwann Cells in PNS Oligos in CNS o Between the myelinated regions are the nodes of Ranvier No voltage gated channels in myelinated regions - Saltatory Conduction o Myelinated axons o 50 times faster than continuous conduction o The impulse (axon potential) “jumps” from node to node - Synapses o The junction between neurons o 2 types: Electrical synapses Neurons connected directly by gap junctions Less common (5-10% in nervous systems) Important in hippocampus of brain Chemical synapses Neurotransmitters (nts) are transmitted across the junctions separating neurons More common o Chemical Synapse A junction between the axon terminal of one neuron and the dendrites or cell body of a second neuron First neuron is presynaptic neuron Second neuron is postsynaptic neuron - Dendrites electrical activity enters - Axon electrical activity leaves o Myelinated (wrapped in myelin sheath) - All cells have sodium – potassium pumps o Sodium out (low concentration) 10x o Potassium (high concentration) 30x o Negatively charged proteins stay in cell Anion o Sodium channels always closed - **like charges repel, opposite attract o Potassium leaves, cell gets negative - Resting potential o Due to movement of potassium (K+) ions, the only ion that can freely cross the membrane when cell is at rest - Stimulus o Something that activates sodium channels o If too many channels open, pumps have hard time More passive transport makes cell positive - Depolarization becomes more negative - Threshold o Stimulus no longer required o Charges coming in are the stimulus o Goes from threshold to depolarization (runaway) o K+ leaves cell negative, Na+ leaves cell more positive o When Na+ becomes to high, gate closes and opens K+ channels - Conduction instant electrical activity - Propagation movement of action potential down a nerve o Can cause Na+ channels to open to start new action potential - Wrap of myelin leaves gaps between – leave nodes of Ranvier - Insulator – does not allow charges to cross - MS/ALS associated with demyelination Muscles - 50% weight muscle - Muscle types o Striated muscle Skeletal cardiac o Unstriated muscle Smooth o Voluntary muscle Skeletal o Involuntary muscle Cardiac Smooth **autonomic nervous system - Skeletal Muscle o A single skeletal muscle cell is a muscle fiber Large, elongated, and cylindrically shaped Multinucleated Fibers extend entire length of muscle Lots of mitochondria - Myofibril o Muscle fibers composed of myofibrils o Each myofibril made of regular arrangement of Thick filaments myosin Thin filaments actin - One sarcomere is one functional unit - Z line thick protein disk - H zone only thick filament present - Thin actin - Z Z are one sarcomere - A band (thick filament length) - I band thin to thin (no thick filament present) - Myosin o Component of thick filaments o Consists of 2 identical subunits Two tails Two heads Heads form cross bridges between thick and thin filaments Actin binding site Mosin ATPase site o Need energy o Cross bridges project from each thick filaments in 6 directions - Actin o Thin filaments consist primarily of actin o Actin interacts with the myosin cross bridges - Regular proteins o Tropomyosin Lies alongside groove of actin spiral Covers myosin sites blocking cross bridge binding o Troponin Made of 3 polypeptides units One binds to tropomyosin One binds to actin One binds to calcium - Sliding filament mechanism o Thin filament on each side of the sarcomere side inward over stationary thick filaments o As all sarcomeres shorten, entire fiber shortens
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