B05 - Function and Regulation at Medizinische Universität Wien

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Study with flashcards and summaries for the course B05 - Function and Regulation at the Medizinische Universität Wien

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

What is the difference in contractility, excitability, extensability & elasticity?

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

Explain muscle contraction cycle in skeletal and cardiac muscle cells! What is needed therefore?

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

Explain the similarities and differences of skeletal and cardiac muscle action potentials!

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

How does extracellular Ca2+ affect muscle strength in skeletal & cardiac muscle cells?

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

Describe the mechanism of cardiac pacemaking!

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

Discuss the differences between skeletal and cardiac muscle excitation-contraction coupling!

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

Explain the term “refractory period” and give examples!

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

Shortly explain the different types of skeletal muscle contraction.

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

Describe the mechanisms underlying the Bayliss effect!

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

List the physical properties of blood.

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

How does red blood cell count affect blood viscosity? Why is this relevant?

Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

Discuss the reasons for a faster sedimentation rate of red blood cells!

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Exemplary flashcards for B05 - Function and Regulation at the Medizinische Universität Wien on StudySmarter:

B05 - Function and Regulation

What is the difference in contractility, excitability, extensability & elasticity?

  • Contractility = ability of muscle to shorten → generates a pulling force;
  • Excitability = capacity of muscle to respon to a stimulus;
  • Extensibility = muscle can be stretched to its nromal resting length and beyond to a limited degree;
  • Elasitcity = ability of muscle to recoil to originial resting length after stretched;

B05 - Function and Regulation

Explain muscle contraction cycle in skeletal and cardiac muscle cells! What is needed therefore?

Needed: ATP + Ca2+!! Contraction is Ca-dependedn!! if Ca is accumulating → higher force possible;


  1. Without ATP the myosin head is really strongly binding to the actin at the actin binding site. (45°) This bound is very rigid and cannot be broken that easily (e.g. rigor mortis) ->

  2. In the presence of ATP the muscle gets "softend" -> ATP binds to the myosin head and therefore, releases the myosin head from the actin ->

  3. Myosin head functions as a ATPas & Mg2+ helps to hydrolyze ATP into ADP + Pi (but its still attached to the myosin head)! -> the angle changed to 90°; now the troponin complex blocks the binding to actin until enough Ca2+ is available -> Ca2+ is freeing the binding site from the troponin molecule & triggers contraction->

  4. Pi gets released (ADP stays at the myosin head) -> the angle changes to 50° and the myosin head can bind to actin again ->

  5. Now ADP gets also released ant the starting conformation is reached again (45°); if there is enough ATP present, the cycle will start again;

B05 - Function and Regulation

Explain the similarities and differences of skeletal and cardiac muscle action potentials!

  1. Skeletal Muscle Action Potential: fast influx of Na+ into the cell -> when the threshold is reached depolarization of the membrane + overshoot to about +30mV (= equilibrium potential of Na) -> no more Na+ can enter the cell; now the slower K-Channels open their gates -> Efflux of K+ out of the cell = repolarization starts due to loss of charges inside the cell -> Hyperpolarization and refractive period -> resting membrane potential is reached again;

  2. Cardiac Muscle Action potential: threshold is also reached by a fast influx of Na+ into the cell -> depolarization starts until about +70mV (= equilibrium potential of Na within cardiac muscle cells) -> nor more Na+ can enter the cell & the slower K-Channels open their gates -> PARTIAL (!) repolarization until voltage gated Ca-Channels open their gates -> strong influx of Ca2+ into the cell, which keeps the plateau level alive for about 300ms -> even stronger efflux of K(ir) leads to complete repolarization;

B05 - Function and Regulation

How does extracellular Ca2+ affect muscle strength in skeletal & cardiac muscle cells?

  • Cardiac Muscle:  the strength of contraction depends to a great extent on the concentration of calcium in the extracellular fluids (in fact, if the heart is placed in a calcium-free solution it will quickly stop beating);

  • Skeletal Muscle: in contrast, the strength of contraction is hardly affected by moderate changes in extracellular concentrations (because contraction is caused almost entirely by Ca2+ released from the SR);

B05 - Function and Regulation

Describe the mechanism of cardiac pacemaking!

The spontaneous diastolic depolarization within the SA-node is caused by a so-called "funny current (IF)". It is called this way because it is the only channel that opens at hyperpolarization state (all other channels are closed!) =>  HCN4 = hyper polarization-activated cNMP gated channel that is non-specific for cations (K+ & Na+) this means: the channels are activated by hyperpolarization where binding of cNMP causes a higher sensitivity for voltage (opening occurs already at lower hyper polarization states) à this causes the influx of Na+ à stimulus for reaching the threshold; this can be seen within the scheme of an action potential of the heart: they never reach a stable linear RMP as they would do within a skeletal muscle cell! This is how the heart is able to contract on its own without any external stimuli.

B05 - Function and Regulation

Discuss the differences between skeletal and cardiac muscle excitation-contraction coupling!

  1. Skeletal muscle excitation-contraction coupling: key principle = direct coupling of the voltage gated calcium channel that acts as a voltage sensor within the sacrolemma to the calcium-release channel within the SR -> when the voltage gated Ca-channel gets activated a plug-like thing is pulled out of the Ca-release channel -> Ca2+ influx into the cell -> Ca2+ binding to troponin complex and thereby moving it away from the actin-binding site -> myosin can bind to actin -> muscle contraction;

  2. Cardiac muscle excitation-contraction coupling: key principle = calcium induced calcium release! The sakrolemma gets depolarized by an cardiac action potential -> voltage gated Ca-Channels are opened & influx of Ca2+ into the cell -> exactly this Ca2+ induces Ca-releasing Channel within the SR to release Ca2+ -> binding to troponin complex and thereby moving it away from the actin-binding site -> myosin can bind to actin -> muscle contraction;

B05 - Function and Regulation

Explain the term “refractory period” and give examples!

Refractory period is a period immediately following a stimulus during which further stimulation has no effect, unless it is not strong enough.

-> skeletal muscle cells have a really short refractory period, therefore, more contractions can be triggered within a shorter time period -> skeletal muscle is tetanizable!

-> cardiac muscle has due to the long plateau of cardiac AP a longer refractory period -> cardiac muscle is not tetanizable (really important that only the primary pacemaker can trigger AP within the heart);

B05 - Function and Regulation

Shortly explain the different types of skeletal muscle contraction.

  • Isotonic Contraction: Contraction of muscle with length change at constant force;
    → if muscle tension is higher than the load → muscle shortens = concentric contraction (moving the load upward); → if muscle tension is lower than the load → muscle lengthens = eccentric contraction (moving load downwards);

  • Isometric contraction: contraction of muscle without length change (depending of muscle diameter) à no movement (holds the weight in stable position);

B05 - Function and Regulation

Describe the mechanisms underlying the Bayliss effect!

Bayliss effect = auto-regulation of smooth muscle tissue within blood vessel at increasing pressure levels; if pressure increases over a certain point some resistance vessels begin to contract and thereby decreasing their diameter -> volume that flows through the vessel is kept constant!

Mechanism: inside the vessel we have some G-coupled receptors that recognize changes in surface tension and react by conformational change -> this triggers a cascade that includes second messengers & DAG -> opening of unspecific Cation-Channels (TRPC6) within the membrane of the smooth muscles -> influx of cation -> depolarization -> influx of Ca2+ -> increased phosphorylation of MLC within the smooth muscle cells -> contraction of the vessel (= vasoconstriction);

B05 - Function and Regulation

List the physical properties of blood.

  • Suspension: ~ 5 millions erythrocytes / µL → separation by gravity
  • Erythrocyte sedimentation rate (ESR) = measure of suspension stability (the faster the less stable) —> (non-specific) diagnosis marker of inflammation - high speed of separating = inflammation;
  • 4.5 - 5x more viscous than water (viscosity depends on shear forces!)
  • pH: 7.4 (slight differences between venous & arterial blood)
  • Temperature: 38°C
  • Volume: 8% of body weight (male: 5-6L; female: 4-5L)

B05 - Function and Regulation

How does red blood cell count affect blood viscosity? Why is this relevant?

Our blood is up to 50% composed of red blood cells, therefore they are the most relevant for blood viscosity → the more red blood cells, the higher the viscosity. This is relevant due to the fact that viscosity depends on shear forces. A weak heart isn't able to find the strength for pumping high-viscous blood —> stock in blood flow → coagulation of red blood cells → stroke / MCI;

B05 - Function and Regulation

Discuss the reasons for a faster sedimentation rate of red blood cells!

Faster Sedimentation rate = less stability of suspension; this is an indirect marker for inflammation;

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