Muscle Physiology

Question 1

Structure of skeletal muscle

Answer 1

-made up of sarcomeres which make up muscle fibres.
- sacromeres are made up up actin,myosi,troponin,tropomyosin protein

Question 2

Thin filaments

Answer 2

-made up of actin, troponin and tropomyosin

Question 3

Thick filaments

Answer 3

• made up of myosin

Question 4

Cross-bridge cycling

Answer 4

• controlled by action potentials
• myosin heads binds via the actin-myosin binding site
• mysosin pulls the actin filaments torwards the centre of the filaments, The power stroke is fueled by the hydolyses of ATP to ADP and phosphate which cause a conformational change to myosin head
  -ATP binds to myosin heads causing the dissociation of the actin-myosin complex
• ATP is hydrolysed
• a cross bridge forms and the myosin head bind to the new position on actin

Question 5

Role of troponin c

Answer 5

Allows troponin to bind to calcium

Question 6

Role of troponin T

Answer 6

Allows troponin to binds to tropomyosin

Question 7

Role of troponin I

Answer 7

Allows troponin to bind to ATP

Question 8

How is the cross-bridge cycle dependent on the Ca2+

Answer 8

-in a low calcium environment tropomyosin blocks the actin-myosin binding site
- in high calcium environments. Calcium binds to tropomyosin causing a conformational changing exposing the actin-myosin binding site

Question 9

Role of transverse tubules

Answer 9

• in the membrane of muscles
• increases the surface area of the membrane
• allows action potential to be be penetrated deeper in the meme table which allows to be closer to the sacroplasmic reticulum which has lots of stored calcium

Question 10

Triad structure

Answer 10

• has the T-tubule with sarcoplasmic reticulum on each side

Question 11

The effect of action potential on muscle movements

Answer 11

• signal transduction lead to action potential trigger in the muscle fibre
  -AP propagated down the sacromela and T-tubules
• leads to the depolarisation of t-tubules sensed by Dihydropyridine receptors (DHPR) which are voltage-gated channels
• caused the release of calcium by ryanodine receptors from the SR into the cytoplasm
  -initiated the cross-bridge cycling and contraction
  -CA2+ is pumped back into SR by SERCA terminating crossbridge cycling

Question 12

Factors which influence the force of contraction

Answer 12

• frequency of action potentials. The higher the frequency the higher the force in contraction
• number and size of motor units activated. Can be increased with training and leads to higher force of contraction

Question 13

what is meant by cardiac muscle is a syncytium

Answer 13

• the heart is made up of two syncytium which are clusters of cardiomyocytes
  -allows electrical impulses to travel through the heart which is crucial for the synchronized contraction of the heart chambers (atria and ventricles), leading to the effective pumping of blood through the circulatory system
  -contains a gap junction which allows the propagation of action potentials from cell to cell

Question 14

what is meant by absolute refractory period of the cardiac muscle

Answer 14

-nearly all the NA+ channels are in the inactivated state.

Question 15

what is the relative refractionary period of the cardiac muscle

Answer 15

• NA+ channels are recovering from inactivation and excitability returns towards normals a the number of channels in the inactivated state decreases

Question 16

refactionary periods of cardiac muscle

Answer 16

• they are longer compared to skeletal muscle because the long refractory period of cardiac muscle cells is a crucial adaptation to ensure the orderly and rhythmic contraction of the heart, preventing potential issues of overstimulation. This feature contributes to the stability and efficiency of the cardiac cycle.

Question 17

what is striated muscle?

Answer 17

-skeletal muscle and cardiac muscle= complicated structures

Question 18

difference between the mechanisms of contraction in cardiac muscle and in skeletal muscle

Answer 18

-skeletal muscles has mechanically coupled ryanodine receptors whereas in cardiac muscle they are ligand-gated and open as a result of increased calcium which then releases more calcium
-skeletal muscle have an all of nothing contraction whereas cardiac muscle is controlled by graded calcium meaning The more calcium available, the stronger the contraction therefore the heart can adapt to the body physiological needs

Question 19

frak-starling law of the heart

Answer 19

• the amount of strech of the cardiac muscle determines the amount of force generated during contraction-more streach=more force
  -Stretching the muscle fibers enhances the sensitivity of the muscle to calcium ions.

Question 20

Beta one adrenoreceptors involement of the intropy of the heart

Answer 20

-When the sympathetic nervous system is activated, such as during the “fight or flight’ noradrenaline is released which binds to beta-1 adrenergic receptors on the surface of cardiac muscle cells.
- this activates adenylate cyclase in turn, catalyzes the conversion of AT to cAMP
- cAMP activates (PKA), an enzyme that phosphorylates various proteins involved in the contractile process. which increases calcium levels

Question 21

postive drugs for intropic pharmaceuticals

Answer 21

• B-adrenoceptor aagonist e.g. adrenaline and noradrenalibe

Question 22

negative drugs for intropic pharmaeceuticals

Answer 22

-calcium channel blockers and B-adrenoreceptors antagonist

Question 23

Functions of smooth muscle

Answer 23

• regulating blood pressure
  -hair standing on end-piloerection

Question 24

Smooth muscle composition

Answer 24

• thin filaments are longer in smooth muscle so can contract and relax to a greater extent
• shorter thick filaments
• gap junction present for electrical and chemical communications
• dense body’s they provide ridged filaments for the filaments to attach too
• have abnormally high levels of NA+ and CA2+

Question 25

Action potential as a mechanism for contraction in smooth muscle

Answer 25

• contraction are not highly dependent on membrane potentials therefore can be a diverse range of membrane potentials that can cause a concentration including no action potentials

Question 26

does smooth muscle have a sacroplasmic reticulum ?

Answer 26

-smooth muscle has a lack of sacraplasmic reticulum

Question 27

Contraction regulation of smooth muscle by calmodulin

Answer 27

-Ca2+ influx from extracellular sources
- Ca2+bind to calmodium forming a complex. This causes a conformational change of activates myosin light chain kinase (MLC)
- this converts ATP to ADP
-ADP attached to myosin heads and cross-cycling cycle begins

Question 28

Regulation of smooth muscle relaxation

Answer 28

• stimulis activates cAMP or cGMP. this activates MLCP. myosin light chain phosphorylasewhich rremoves phosphate from the myosin heads
  -causes dissociation of actin-myosin interactions

Question 29

Pharmacological control of smooth muscle contraction

Answer 29

-stimulation of increased Ca2+
-agonist of ligand-gated channels
-increased sensitivity to ca2+ by manipulation of MLC-kinase and MLC-phosphate activity

Question 30

Pharmacological control of smooth muscle relaxation

Answer 30

-Reducing intracellular Ca2+- by using Calcium channel blockers (e.g. dihydropyridines such as nifedipine)
- Or Drugs and agonists of Gαs coupled receptors that activate potassium channels
- Inhibiting cross-bridge cycling- by Guanylyl cyclase activators (e.g. nitric oxide, nitrates)
- or cGMP phosphodiesterase inhibitors (e.g. sildenafil/Viagra