Chapter 4: Diffusion, Membranes, and Neurons - Physiology PDF

Chapter 4 · Diffusion · Simple diffusion · a result of random movement · Continues until a uniform distribution is achieved key in maintaining homeostasis · Diffusion-magnitude...

Chapter 4 · Diffusion · Simple diffusion · a result of random movement · Continues until a uniform distribution is achieved key in maintaining homeostasis · Diffusion-magnitude & direction · · flux the # of particles crossing per unit time · · Concentration dependent · net flex Determines t loss of molecules gain · Depends on : · · temp. · molecule size · Surface area · meelium · Diffusion equilibrium next flux · O =  · Diffusion · Diffusion & distance numerous collisions prevent distance travel long · Glucose few seconds 10cm-11 = 10Mm A - , yes Diffusion time increases to the proportionately · square of distance Diffusion through membranes · 1000 1 000 000 slower typically through membranes - · , , Fick diffusion equation magnitude described by the · 5 PA(Co-Gi) · = · P = Diffusion Constant (MPC) = Rate & which A surface area = molecules pass · C concentration through membrane = Diffusion through Membranes · the lipid bilayer non-polar uspoloatility · nonpolar constants · Can dissolve of membrane in hydrophobic region · · O2 CO2 , , Steroid hormones diffusion ions through protein channels · · ion channels only Slightly larger · Diameter then ion Selective-diameter , charge · Role of ion movement · membrane potential separation of charges across the plasma membranes · · provides an electrical force that influences the movement of ions Like attract; (t) to 7) charges repel opposites interior 2 , movement depends electrochemical gradient · a · Concentration Charge ·  of ion movement Regulation · ion channels exist in closed state may an open or - · Channel gating of process opening+ closing channels · times per second may occur many · 3 factors control Binding in gatingeinle · 1. = ligand- gated 2. 3. changes charge = Voltage gated physically deforming membranes mechanically gated = mediated transport systems · membrane proteins known as transporters · more molecules that are · and / or large polar · mediated transport · Characteristics · typically specific Binding to sp Site ·. · Can in either direction occur · Speed depends fewer then (1000X) than ion channels an : (bridge vs Ferry 1. Saturation of site 2 #. of transporters. 3 Speed of transformers conformational change Saturation is possible · · unlike simple diff. · Facilitated diffusion still going down hill · no energy · · GLUTs · Glucose specific transporters Cell would peimpermeable to glucose ·  Constant gradient exists · different types · different · genes , cells affinity insulin affects some types · · Recruits to PM from vesicles · Active transport moves substance against conc gradient · a pumps · exhibit specificity+ saturation · energy required supplied by : · Primary active transport. 1 2 secondary active transport. Primary active transport · transporter hydrolyzes ATP · · referredto "ATPase" enzyme a Covalent modulation alters conformation transporter Nat/K ATPase + · - · one of the best studied · others : · Case · Hase H /"-ase + ·  Secondary Active transport · movement of an ion down gradient coupled to transport · a uses the instead of ATP 2 energy in the gradient binding sites - 1 ion- Nat 2 Usually Molecule.. Transported matinence of gradient relies on primary active transport · 10-40 % of of to Nat all uses under resting goes gradient · energy types : · 1 Co-transport. (symport. 2 Counter-transport Cantiport) Both are used in both cells · Osmosis · net diffusion of 120 across PM aguaporins · membrane proteins that · facilitate H2O movement types a # differ · in cells especially important in · Kidney force tubules Driving · pure H20 = 55. 5M in a IM M 54 5 glucose solution = ·. Depends on # , NOT nature of the molecules · IM glucose 1Maa regardless of size · = , · ionization means XL 1M 5 M NaCl solution glucose sol = ·.. · Osmolarity total solute conc ina solution -. higher Osmolarity less H20 ·  Semipermeable requires a membrane · · Vol. Changes only occur in the presence of a SPM Osmotic pressure · to of 120 Pressure nessicary prevent inflow · increases with osmolarity · BP · · Osmosis - Cell volume non-penetrating solutes · can't · the PM cross · Nat + Cl ions-outside K+ + solutes organic · · intracellular fluid typically 300 mOsm · · extracellular ? fluid tonicity · determined · by come. of NPS PS do notContribute · penetrating solutes · · no impact on osmosis iso osmotic hypo osmotic hyper osmotic · , Ex · 300 mOsm glucose (NP) + 100mOsm urea (P) hyperosmotic · · 100 mOsm NaCI (NP) + 100 mOsm urea (P) isosmotic ·  endocytosis · Pinocytosis · Cell drinking · ions , nutrients , small molecules · All cells Phagocytosis · Pseudopods · bacteria engulfed phagosomes · endocytosis + ectocytosis · Receptor mediated endocytosis · · Receptor dependent Can be up or down Regulated · Clathrin coated pit · ex hormoness factors , growth serum proteins · , exocytosis ·. 1 Replaces PM (Plasma Membrane) 2 enables, release of PM impermeable molecules peptide hormones · usually triggered by calcium Conc increase ·. · epithelial transport 2 types ·. Paracellular transport 1 2 Transcellular. transport · Water ions are actively transported · · H20 via Osmosis · Roles Reabsorptin fromKidneyas nes  Chapter 6 nervous Overview System · · Divisions · Central (CNS) · Perifenl (PNS) · neurons units of the · 86 billion nervous system in the brain or so · Release neurotransmitters Serve integrators · as Receive from 100's 1000's of other neurons input a · minimal mitosis · Structure of Neurons (longest Cells) Cell body · nucleus ribosomes other organelles · , , · Processes · Dendrites highly brunched · · some cells have to 400 ,000 up ofthe info along with all body receive most · · Dendritic Spines · Ribosomes · Axons Carries from c. b away ·. · Few microns to over a meter · initial Segment Chillock) trigger Zone · · Collaterals · Axon terminal · Varicosities  · structure of Neurons Many20-200 axons covered by myelin of modified PM layers · formed CNS by oligodendrocytes in · each 40 up to Myelin forming Cells · Oligodendrocytes-CNS · · Schwann Cells-PNS · Nodes 5mm,regular interest Myelin speeds signal conduction · Axonal transport · Organelles Btwn + materials must be transported cell body a axon terminals · as far Im · as Components · Scaffolding · of microtubules kinesins dyneins · + typesAntero · (Kinesin) grade most common · Cell axon terminals bodytonutrients Enzymes ( vesicles · , , · Retrograde (dynin terminals to cell body Factors RecycledVesiclepes growth · , tetanus  · Functional Classes of Neurons · 3 classes. Afferent Toward CNS (1) 1 - 2 efferent CNS (10) away from -.. interneurons Within INS (200 000) 3 - , · Afferent neurons Sensors & then~ peripheral ends signals to the brain spinal cord or mostly outside CNS · Central + peripheral process · · efferent neurons · Call bodies & dendrites are inside CNS nerves bundles of aff ↓ eff Neurons :. (typically). · interneurons CNS entirely in · · 99 % of all neurons # involved varies · None in some reflexes millions in complex processing Synapse · Junction btwn 2 · neurons highly specialized Alters the chemical & electrical activityof another · · Neurotransmitters Neuron to neuron · neuron to muscle or gland Btwn an axon t a dendrite or cell body Pre-a Post-synaptic neurons · signals from 1000's One neuron recie may · · Glial Cells 90 % 50 % of nervous Cells system · neurons take up more space 90% of brain a spinal chord Sourced CNS tra · many Oligodendrocytesmylein a · covering Astrocytes Removes 1 + + Neurotransmitters Promotes blood/brain barrier · Guide neurons development during · microglia like macrophage · Perform immune functions · ependymal cells · Line fluid · cavities in the brain ↓ spinal cord (PNS) typesSatellite · · Cells · Cover cell body · Regulate ECF Similar to astrocytes · · Schwann Cells Produce myelin sheath ·  Neuronal growth & Regulation · · Stem cells · differentiation Processes that become atons/dendrites Growth cones · Assist in finding the correct route · Direction Glial cells · cell adhesion molecules · Neurotrophic factors Family of proteins · + guid typicallyaxons released by the target all growing form upon arrival Synapses · Sensitive development during · 50-70 % of neurons undergo apoptosis · early plasticity · nearly of infant brain can be removed no visual Stimulation (1-2) (much older Language · Changes New after maturity synapses associated with learning Minor production of new neurons · · Neuronal Repair · Repair if... Damage outside CNS +ll body undamaged Sequence of events Segment separated from theCell body degenerates · new forms growth cone (Imm per day · CNS injuries Crushing injuries leadto loss of nearby oligodendrocytes no effective with severed axons regeneration · occurs  Neuronal growth - Regulation · ofchem + physiology is governed by laws physics · chargLike Repel li · = · Opposite Attract · = Potential to do work · electrical potential · potential difference · Units +mV 0001 V · = , · Resistance hindrance to electrical movement - Ohm's law T VR (I Current ; V Voltage ; R resistence) · = = = = = as resistance increases current drops (lipids ( - · Resting membrane potential · All cells have a charge difference across membrane · · Outside is reference inside negative · - 5+o 100 MV - · Generally - 40 to -90 in neurons oppositely charged ions collect near membrane Only small fraction of total ions · a · equilibrium Potential Magnitude of RMP depends · on : 1. Difference in ions concentration 2. Membrane permeability · equilibrium potential ion flows through until Stopped by E. charge Charge difference & that P point = ·. · Herst equation · Describes EP. for. a particular ion blog Conson s · Fion = z valance of the ion · = · for Sodium : Enalog GO · contribute manyions to overall charge · "fixed anions" When multiple open & ion channel types are once all ions must be · , considered Goldman-Hodgkin-Katz (GHK) equation · P[Na ]o + P[x -] P(k ]o + + + : Um · = Cel log P[K ] ; + P[Nat] ; + P[CI]o + Relative ion permeability K 1 ; Na =. 04 ; Cl 45 · = =. So the RMP of neurons is - 70mV Close to the E. for K + 790). P · Membrane is most permeable to K + of equilibrium Potential Origin · electrogenic Pump · establishes gradient · · Diffusion of ions Depends · membrane perm on · Balance of diffusion a pump  · Graded potentials & Action Potentials excitability · Some cells have channels that can be ion opened · Neurons & muscle cells terms : Depolarized Cell becomes less than RMP negative : · Overshoot : inside of all positive · Repolarization Return to RMP : RMP Hyper polarization : more negative than · Graded potentials Graded potentials : changes in membrane potential confined to small region of PM · · events Channels open ions flow many occur in depolarizing hyper polarizing · a or direction channels Depending · an Magnitude may vary · · Decremental diminishes from site of initiation : · Summation total effects of several events in sequence : · Action Potentials Large 70Changes in Membrane potential · · to- 30 Mr + · Rapid-few milliseconds Several hundred per Second · Longdistance communication · · Voltage Gated Channels chain") gate )"ballt · Nat Faster innactivation = , · K + = Slower - Action Potential Mechanism · initial depolarization · Critical threshold · Positive Feedback halted Nat inactivation gates · & · K + Channels · K+ Repolarizes membrane Brief after hyper polarization · Ke + channels slow to · close · threshold stimuli typically · 15 mV lessrun the RMP ( 55mV · · Subthreshold potentials · Don't reach threshold (-56mb) · All or None · Stronger Stimuli don't mean Stronger AP.. s · Magnitude coded by #per unit time · Disruption · Novocaine · Tetrodotoxin Refractory Periods · · Absolute refractory period Voltage gated Nat channels are open a inactivated inactivation gate · Relative Refractory period · Another A P possible but only with stronger Stimulus ·.. hyperpolarization · Limits # of A P.. typical neurons is 100's per See. · · Determines direction  A P. Propagation ·. · Local depolarization causes change in adjacent membrane Can forward only more · Refractory period Speed Larger diameter-faster · · Myelin Myelin prevents movementof ions · AP only occur & nodes of Ranvier ·. · Saltatory (to leap) conduction · A P.. appears to jump · Faster 6 5 m/s (Imi/hr) in small non-mylinated (4see ·. , 100m/s (225mi/hr) in large diameter myelinated ( O2sed ·. · Action Potential initiation Receptor potential-type of graded potential used by sensory neurons · Synaptic potential Graded potential generated by Synaptic input : - · Pacemaker potential : · Spontaneous change in neuror's membrane potential Continuous changes in membrane potential · occur · Functional Anatomy of Synapses 100 trillion CNS Synapses in · types · theshold excitatory : Closer to · Stabilized inhibitory · : Convergence + divergence · 1000's I cell may converge · on I cell effect may many ·  types electrical-Gap junctions · · Cardiac muscle now known to be Relatively wide spread in the nervous system. Chemical 2 : · Axon terminal Synaptic vesicles · · post synaptic density Synaptic deft · · 10-20nm · neurotransmitter · Cotransmitter · Mechanism of neurotransmitter Release Prior to A P. arrival. vesicles are docked · Active Zones SNARE Proteins Soluble fusion · N-ethylmaleimide-sensitive attachment protein receptors Ca + · channels Open t Ca flows in · Leads to reside fusion · Binds to Synaptotagmins Leads to Share Complex Conformation change · 2 Vesicle fates fusion · · Kiss & run fusion · Activation of post synaptic Cell A fraction bird to receptors · Receptor types · Tonotropic Receptors · ion channels · metabotrophic Receptors Second messengers · Delay · · abt 0 2 millisec.. · transient actively transported back into presynaptic membrane diffuse away transformed into inactive substances 2 types of chemical Synapses : · excitatory inhibitory · excitatory · Depolarization · typically opens nonselective Nat &k channels · + creates epsp (excitatory post synaptic potential Graded potential inhibitory Synapse · · hyper polarizing IPSP (inhibitory post synaptic potential) · may just stabilize the membranee its RMP AP Lessens the Likely Good of an.. · Mechanism · K + channels Closer to k+ E P.. (90mV) Cl-channels · Stabilizes R MP... if Cell actively regulates &I may lead to hyper polarization  · Synaptic integration A single EPSP.. typically not enough · 5 mV vs · MP is the Result of the synapses active & a moment Perhaps 1000's 100's of which are active & · , any given time · temporal summation. Stimuli occur in rapid succession · Spatial Summation 2 inputs occur in the same area neutralization Synapse impacts a certain area of the P S.. Cell · initial segments more sensitive to EPSP's higher density of Nat channels · Location of a synapse initial segment-greater Voltage change · · out branch of dendrite : less Voltage change Post Synaptic potentials · · Last longer than APs.. multiple A P 's may fire.. A p 's nearly always occur.. in bursts Synaptic Strength · enormous variability occurs in · post synaptic pot. · Ca - release not constant May build up bturn Signals · Axo-axonic Synapse · impact · · Presynaptic inhibition · presynaptic facilitation · mechanism Alter Ca + · levels ; Affect neurotransmitter Synthesis · Anto receptors  Synaptic Strength-Postynaptic Mechanisms · · Different receptor types + Manytypes greater subtype - is influence than others may have opposite effects · # of Receptors Present Up and down Regulation of receptor #'s · is likely · Receptor desensitization Synapses Drugs t diseases - most neurologically active drugs alter Synapse Neurotransmitter Synthesis · Storage · Release · Receptor activation Agonist& antagonist · · tetanus (Clostridiumtetani Destroys SNARE Proteins · impacts inhibitory neurons · Botulism (Clostridium botulinum) Also destroys SNARE Proteins · · targets excitatory synapses that activate skeletal muscles · Calciseptine neurotoxin from black mamba blocks Cat channels Prevents NT release 1st discovered specific Ca't blocker neurotransmitterses a neuromodulators Neuro modulators alter the effectiveness ofthe synapse the modify postsynaptic's cell's response tend Change the presynaptic cell's Synthesis , release or , re-uptake · to be slower hours or days · · neurotransmitters influence ion channels that control · EPSP IPSP, milliseconds · · Distinctionturn Neurotrans is not clear · always neurotransmitterse & neuromodulators acetlycholine · - PNS & in the brain major neurotrans In ·. · Cholinergic neurons - Release ACh AcetyIcholinesterase · Located on pre-a post synaptic membranes taken up into membrane presyn ·. · Sarin L receptor types · · Nicotinic receptors : ion channels Nat +k + dominates = depolarization important in attention , learning , reward pathways · muscarinic Alter the · activity of enzymes + ion channels Atropine is an MR agonist