Excitable Celle

Anode

Attracts negative ions. Positive electrode. Membrane potential will be larger. Membrane hyperpolarises --> decreases/prevents depolarization.

Katode

Attracts positive ions. Negative electrode. Placed outside cell --> create negative area on outside of membrane --> membrane potential will be more positive: depolarization --> cause Na+ channels to open. Excitatory electrode

Hjertemuskulaturens længde spændingsdiagram

Changes in filament overlap account only partly for changes in sarcomere length. Less than L0: increase in muscle length increases the Ca2+ sensitivity of myofilaments --> increase of active tension. Passive tension: cardiac muscle stiffer --> stretched beyond L0: passive tension increases to high levels

Tonisk (statisk) adaptation

Changes in stimulus are much quicker than adaptation - adaptation will set sensitivity that equals average stimulus intensity. Informs continuously on impact size.

Fasiske (dyanmisk) adaptation

Changes in stimulus strength are slower than adaptation, adaptation make impulse frequency more sensitive for seed which stimulus changes strength. Informs on occurred influential changes.

Dense bodies

Composed of actin filaments. Correspond roughly to z line. Held in position by intermediate filaments: desmin and vimentin.

Sliding filament theory

Contraction --> muscle shortening accompained by sarcomere shortening. A band unchanged but widths of I band and H zone decrease. Degree of overlap between thick and thin filaments increases.

Common features in function of all sensory receptors

Converting of absorbed energy to receptor potential (generator potential) in modtagedelen and transformation of receptorpotential to impulse in axon (afsenderdelen) with a frequency that increases with stimulus strength.

Tærskelsværdi

Depolarization --> increase possibility for voltage sensitive Na channels activates and influx of Na --> drives K+ out of cell through leak channels. After certain depolarization (point of no return) - point cannot be stopped: Na+ ind larger than K+ out. Current of K = current of Na = træskesværdi. Depolarized cellmembrane over tærskelsværdien --> action potential.

Adækvat stimulus

Determined by modtagerdelen - the stimulusform/energi that receptor is specifically sensitive for

Frank-Starling mekanismen

Diastole: ventricular pressure and intraventricular volume in relaxed heart: passive length-tension curve. Systole: Max pressure during contraction. Increase ventricular filling pressue will increase end-diastolic volume --> increase output. Øget fibrelængde, øger kontraktionskraften = stretch of hjertevæv increases binding of calcium to TnC. Relative positions of filaments optimized. Myocardial stiffness prevents stretch over optimal length.

Difasisk aktionpotential

Difference between A and B. Go negative and then positve. Not a real represenation of what happens extraceullarly on surface. Only one AP

Termination of synaptic transmission

Diffusion, enzymatic deactivation and reuptake.

nerveimpulsen

Electrical signal (action potential) that goes undiminished through axons entire length.

Triad

Extracellular Ca2+ not required for contraction. T-tubule: contains DHPRs which are L-type Ca2+ channels. Entry through DHPRs not required for E-C coupling. SR contains: SERCA (transports calcium back into ER) , RyR (calcium release channel in SR membrane) and calsequestrin (calcium binding protein). Triad: Consists of T-tubule flanked on either side of terminal cisterns of SR. Contains RyRs and DHPRs which are mechanically linked.

Elastic elements

Force generated by skeletal muscle transmitted to bone through elastic elements (tendons). Must be stretched before force can be transmitted. Causes delay between activation of actin-myosin cross-bridges and development of force.

Passive tension

Force required to stretch relaxed muscle. Active tension is difference between total tension and passive tension. Optimal length is length when tension is maximal.

Inhibitoriske neurotransmittere med iontrope receptorer

GABA, glycin

Excitatoriske neurotransmitter med ionotrope receptorer

Glutamat (primary), acetylcholin (nikotin-rec.), serotonin

Calcium Induced Calcium release

Heart muscle. Sarcolemma: DHPRs (L-type Ca2+ channels) causes influx of Ca2+ which activates RyRs in SR which causes further release of Ca2+.

Spændingsfølsomme natriumkanaler

Inactivating gate and activating gate (voltage sensitive). Activation: both open --> Na goes in cell: membrane potential goes positive close to Na ligevægtspotential (+40-+50), Inactivation: I is closed. I closes slower than A opens. Deactivation: MP negative, A and I closed. Deinactivation: I: opens.

Grunde til at axonmembrane bliver refraktær

Inactivating of spændingsafhængige natrium kanalerner, hyperpolarisering, shunt på grund af høj kaliumkonduktans.

Summation

Increase frequency of AP. Force from second twitch will be added to force from first. Second stimulus rereleases Ca2+ from SR before all Ca2+ dissociates from TnC and thus TnC remains Ca2+ bound for longer period. Gives contractile elements more time to stretch series elastic elements and thus generatre more force.

Excitatorisk neurontransmission

Increases chance for postsynpatic neuron goes to AP. Vendepotential > tærskel. Erev more positive than AP threshold. Erev when end plate current become outward instead of inward. Inward at first due to influx of Na but as Vm becomes more positive, efflux. When EPC = 0 = Erev.

Cylinderformet celle

Inner and membrane resistance determines how much of current remains in cell and how much goes out. Voltage difference decreases long get away from origin: curve. Spændingen fallen to 37 = længekonstanten lambda.

AMPA

Iontrope glutamate receptor. K out, Na+ in. Cation-ion selective - fast.

NMDA

Iontrope glutamate receptor. Slower-gating, nonselective cation channels. Permeable for Ca2+ and blocked by Mg2+. Negative Vm: Mg2+ lodges in power and blocks current flow. Conducts current outward better than inward.

Nikotinerge acetylcholinreceptor

Iontropic receptor. 5 subunits: alpha, beta, gamma, delta, epsilon. Each receptor consists of minimum 2 alpha and 3 of the others. Binding of two ACh-molecules induces conformational change of pore and channel opens. Permeable for Na+ and K+. At NMJ.

K+ kanaltyper som er væsentlige for kontrol af fyringsfrekvensen

KD: forsinkede K+ kanaler: secures quick completion of each impulse. Ka: quick inactivating K+ channels: secures possibility for low frequency by halting depolarizations speed. Kc: Ca2+ activating K+ channels: helps adaptation.

Længde-spændings kurven

L0: optimal length: max number of cross-bridges can form. 2,2 to 3,65 µm per sarcomere: reduced overlap between thick and thin filaments decreases number of cross-bridges can form - active force decrease. Less than 2,0 µm: force declines because filaments overlap in wrong orientation. Active force generated by muscle is proportional to number of attached cross-bridges.

Hastigheds-belastingsdiagrammet for glat muskulature

Larger the phosphorlyation of RLC --> larger strength/force.

Ionotrope receptorer

Ligand-gated ion channels. Ligands are neurotransmitters. Receptors composed of 4-5 subunits whose arrangement defines central-gated pore. Binding of ligand --> conformation change --> opens channel. Fast synaptic responses.

Long-term depression

Long-lasting decrease in efficacy of transmission at excitatory synpase. 1) Glutamate activates AMPARs 2) AMPARs --> inward current --> depolarization 3) depolarization relieves Mg2+ blockade in NMDARs 4) Ca2+ influx 5) Ca2+ activates CAM 6) CAM activates calcineurin 7) calcineurin activates PP1 8) AMPARs removed

Long-term potentiation

Long-lasting increase in efficacy of transmission at excitatory synapses. 1) Glutamate molecules 2) activate AMPARs --> current --> depolarize cell 3) Depolarization --> relieves Mg2+ blockade of NMDARs 4) influx of Ca2+ 5) Ca2+ binds to CaM 6) Activates Ca2+/Cam dependent protein kinase (CAMKII) 7) CAMKII phosphorylates AMPARs --> increases conductance and causes insertion of AMPARs

Celle membranen

Membrane can function as electrical condensator. Thickness of membrane is same and therefore capacity dependent of cells surface area. Resistant (R) dependent on how many open ion channels

Relative refraktærperiode

Membrane depolarizes --> Na channels gradually deinactivate. Only some Na channels open --> need stronger stimulation of Na current in cell to override K efflux. Tærskel higher than normal because 1) fewer Na+ channels open 2) membrane is hyperpolarized 3) Ka conductance is increased. Amplitude will be less.

Motorisk enhed

Motorisk neuron og de muskelfibre (10-100) neuronet innerverer.

Isometrisk muskelkontraktion

Muscle cannot shorten but force is varying.

Isotonisk muskelkontraktion

Muscle shortens with load. Concentric. Constant force.

Tykke filamenter opbygning - skelet

Myosin II. Two heavy chains and two pairs light chains - myosin essential light chain and myosin regulatory light chain. Two globular heads. Many myosin molecules align to form thick filament.

Ligevægtspotential

Na+, K+, Cl- concentrations inside cell different than outside. Conductance of ion (possibility of ion passing through channels). K+ highest conductance. Nernst equation.

Repolarisering/hyperpolarisering

Na--> ligevægtspotential Na+ close reached --> inactivate Na channels --> slowly opening voltage sensitive Ka+ channels --> brings back toward K+ ligevægtspotential = repolarising. Influx of Ca2+ activates Ca-dependent K channels --> membrane potential reaches -90= hyperpolarsering. Hyperpolariseringen deinaktiverer natrium-kanalerne og kaliumkanalerne deaktiveres and hvilepotential goes to -70mV. Natrium og kaliumkanaler klar til at generere nyt aktionspotential.

Glat muskulatur

Nonstriated. Located in walls of hollow organs. Unger voluntary control. Sarcomere not in register. Dense bodies. Lack troponin: Ca2+ binds to calmodulin --> Ca2+ calmodulin complex binds to protein light chain kinase (MLCK) --> phosphorylates RLC (switch in myosin) --> binding between actin and myosin. MLCP: catalyzes de-phosphorylation of RLCs.

Phasic/tonic smooth muscle

Phasic: are excitable: activation of contraction triggered by APs or changes in Vm. Depolarization --> opens L-type voltaged Ca2+ channels --> Ca2+ triggers RyRs. Tonic: not normally generate AP. Have L-type Ca2+ channels but do not have voltage-gated Na+ channels. Small resting Vm and some Ca2+ channels already open. Small changes in Vm alter number of open Ca2+ channels and thus alter Ca2+ concentration. Contracted a little all the time and activated by prolonged stimulus.

Monofasiske AP

Place two electrodes far away from each other or AP stopped between first and second electrode. In lab: permanent depolarization with KCl.

Leak kanaler

Potassium. Open constant. Make it that potassium has largest conductance - membranepotential most influenced on postassium ligevægtspotential.

Synaptiske transmission er stokastisk

Probability of release of vesicle in presynpase < 1. Probability that synaptic transmission leads to AP <1.

Kapacitet

Property of thin isolating layer - cell membrane. Ability to hold charges of opposite sign separate. Measured in farad (F) and represented with C. Capacity (number of charges kondensator can store) dependent between distance between plates and plates surface area.

Eletriske synapser

Quick, bi-directional (transmission in both directions). Allow currently flow directly from one neuron to another. Only 3-4nm separation. Connected by gap junction. Instantaneous transmission. Synchronization.

Spændingsafhængige kaliumkanaler

Reacts slower on changes in membrane potential. First opened when Na channels inactivates. Wants to go towards K ligevægtpotential -90mv.

Metabotrobe receptor

Receptor: G-protein-coupled receptor (GPCR). Neurotransmitter binds to receptor --> GDP on alpha subunit is exchanged for GTP. Terminated when alpha hydrolyzes GTP --> GDP. Sends intracellular messengers that either open/close ion channels.

Rekrutering

Recruit more than one motor unit.

Sarkomerets opbygning

Region between two adjacent Z lines. I bands: thin. A: thick. M line. H zone: where no actin.

Absolut refraktærperiode

Right after AP: all voltage Na channels inactivated --> no Na+channels over membrane no matter how strong stimulus.

Opladning af membranen

Send current over membrane --> current begin with going over lipid layer and charge it. Kondensator fills up with charge on each side - charge oppose each other more and more --> charges go through resistor (ion channels). Membrane completely charged - current run through resistance. Current between modstand: V = R X I: Ohms law.

Multi unit vs. single unit

Single-unit: smooth muscles cells electrically connected to one another by gap junctions. Allows depolarization to propagate from cell to cell: act in coordinated fashion - syncytium. Ex: gastrointestinal, blodkar, uterus, blæren. Multi unit: individual myocytes act independently. Ex: iris, visse blodkar

Kemiske synapser

Slower, one direction. Uses neurotransmitters that generate electrical/biochemical signals in post synpatic cells. Presynaptic terminal contains synaptic vesicles. Synaptic cleft 20-40nm wide. 99% of all synapses.

Alt eller intet loven

Stimulus is strong enough so that Na+ influx through voltage dependent Na channels greater than Ka+ efflux through Ka+ channels --> action potential. Ion conductance and electrochemical gradient determines AP size.

Spatial summation

Summation of inhibitory/exhibitory post synaptic potential affected by length constant. Large length constant means inputs from distant synapses can sum effectively.

SNARE-komplekset og synpatotagmin

Synaptotagmin: protein on SV acts as Ca2+ sensor. Binds with Ca2+ -->> triggers fusion between SV and PM.

Neuromuskulære endeplades struktur

Terminale axon hvori ACh syntetiseres (mitokondrier, vesikler), den præsynpatiske membran, den synaptiske spalte og endelig den postsynaptiske membrane, der er tæt fosynet med ACh følsomme receptorer.

Konduktans

The ease at which electrical charges in electrical field move. Marked with G. G = 1/R (modstand).

Tau

Theoretical max charging. Charging has reached 63% of max value. Specific for a given cell. Capacity has memory and therefore after charging does not immediately drop to zero. Tau is charging fallen to 37% after termation.

sensorisk receptor

A biological transducer that converts physical or chemical energy to electrical energy in form of membrane potential changes. Modtagerdel: receptormembrane Afsenderdel: affent, sensorisk axon.

Sensory neuron mediates information to CNS inside frequency area of

3Hz- 300 Hz: distance between action potentials

Tværbrocyclus

1) Increase Ca2+ --> myosin bind to actin 2) Power stroke: myosin head rotates by 45 degrees when Pi is released causing filament sliding. 3) ADP released 4) ATP binding and cross-bridge detachment 5) ATP hydrolyzed: myosin head returns to 90 degrees.

Cross-bridge cycling - glat muskulatur

1) Rise in Ca2+ 2) MLCK activates: phosphorylates RLC 3) myosin bind to actin: form actin-myosin cross-bridge 4) Pi dissociates from myosin head 5) Myosin head rotates: produces force 6) ADP released 7) ATP bound: cross-bridge detachment 8) ATP hydrolyzes to ADP and Pi: new cycle can begin. As long as RLC phosphorylated: cross-bridge cycle continue. If cross-briges still attached when myosin RLC dephosphorylated: detachment of cross-briges will be slowed --> tonic contraction.

Different places where adaptation can occur

1) undenfor receptorcellen: regulate what proportion of stimulus energy that reaches receptor membrane. 2) in modtagerddelen: regulate how much of stimulus energy is absorbed or relationship between absorbed energy and GP. 3) i afsenderdelen: regulate relationship between amplitude and resulting impulse frequency.

Et stof er neurotransmitter hvis

1. Present in neurons (not necessarily vesicles) 2. Released as result of action potential activity 3. Activates receptor in postsynaptic cell.

Calcium regulerer tværbrocyklus - glat

AP --> Ca2+ from extracellular or SR --> calcium combined with calmodulin to form complex with MLCK. MLCK+calmodulin calcium complex catalyzes phosphorylation of myosin RLC --> initiates mysoin-actin interaction. Dephosphorylation of RLC through MLCP. Activation of PKA reduces calcium sensitivty and activation of ROK increases Ca2+ sensitivity.

Depolarisering af cellen

AP created by Electrical stimulation: membrane potential opens voltage sensitive Na+ channels. Or with local depolarization with influx of Na (local response)

Tynde filamenter opbygning - skelet

Actin. Tropomyosin. Troponin: TnT links troponin to tropomyosin: TnC where Ca2+ binds: TnI inhibitory role

Pharmacomechanical coupling

Activation of smooth muscles by agonists - neurotransmitters or hormones. Agonist binds to GPCR to trigger signaling cascade: IP3 and DAF. Binds to ROC on plasma membrane which causes influx of Ca2+

Temporal summation

Affected by time constant which determines temporal persistence of subthreshold change in Vm. Larger tm --> synaptic response will last longer --> sum with later synaptic input to generate larger resultant response.

Refraktærperiode

After AP depolarization --> voltage dependent channels inactivated. Channels must be repolarized in order for channel to be deinactivated and create new AP.

Inhibitorisk neurotransmission

Decreases chance for postsynaptic neuron goes to AP. Vendepotenital < Tærsklen. 1. Opens Cl- channels --> hyperpolarisering: increases distance from tærsklen. 2. increasing conductance maintains membrane potential under tærsklen - shunting.

Calcium regulation in heart

DHPRS: t-tubule/sarcolemma, Ca2+ in. Ryr: Ca2+ in from ST. PMCA: Ca2+ out through ATP to extracellular. NCX: 3 Na+ in for 1 Ca2+ out of cell. SERCA: located in SR, uses ATP to pump Ca2+ back into SR.

Skeletmuskulaturens opbygning

Tværstribet, individuelt innerverede fibre. Consist of thick and thin filament arranged in a sarcomere. Titin holds thick filament to Z line.

Hjertemuskulaturens opbygning

Tværstribet. Lots of mitochondria and blood vessels. T rør ligger på niveau med z-linjene. Intercalated discs: desmosomes, fokale adhæsioner, gap junctions (funktionel syncytium)

Bipolær stimulation

Two electrodes: current from one electrode to the other. Current runs where there is least resistance.

Kondensator

Two metal plates close to each other separated by isolating media. Add current - positive to one and negative to other. Plates hat can be charged with charges called kondensator. Positive charges on one and negative on the other creates spændingsforskel - electrical potentiall energy between to plates. Spændingsforskel = charges/ capacity (V = Q/C). Membrane functions as electrical Kondensator.

Adaptation i en sansereceptors afsenderdel

Under AP: Ca2+ channels creates increase in [Ca2+]i in microdomain around Ca channels. Period between AP: decrease in [Ca2+]i by diffusion from microdomain. Normalization for Ca2+ takes longer than time between AP. Increase impulse activity --> increase [Ca2+]i --> increase K+ current because of Ca-afhængige Kc channels: hyperpolarized between AP. Adaptation completed when distance between AP large enough that has ligevægt between influx of Ca2+ under AP and efflux between Aps. Depends on Kc and spændingsfølsomme Ca2+ kanaler.

Kalcium stigninger i glatte muskelceller

Vm følsomme Ca2+ channels: spædningshængig kalcium influx. Ligand aktiveret kalcium-influx: ROC. Kalcium-induceret kalcium frigørelse: RyR. Receptor-induceret kalcium-frigørelse: G-protein koblede receptorer/

Membranpotential

Vægtet gennemsnit of single ions ligevægtspotenitale in proportion to their conductance over membrane. Millman-equation.

Excentrisk muskelkontraktion

Ydre kraft større end muskelkraften kan forlænge musklen.