Myocyte Contraction Coupling Flashcards
Syncytium meaning
each muscle cell is joined to the next by intercalated disk
What are intercalated disks made of
desmosomes and gap junctions
What is the function of gap junctions
propagate electrical activity
Where do gap junctions exist between
myocytes
What are desmosomes
mechanical links
What are the structural units of muscle
sarcomeres
What filaments form cross bridges in muscle
actin and myosin
What does the degree of overlap of contractile proteins determine
strength of contraction
Describe the relationship between overlap and strength of contraction
as overlap increases strength of contraction increases
Process of what muscles is a calcium dependant process
skeletal and cardiac muscle
Describe one unit of sarcomere
region lying between two Z lines
What is the importance of the sarcomere unit
determines strength of contraction in myocytes in terms of heart beat
What are ryanodine receptors
calcium channels
What is the function of ryanodine receptors
calcium induced calcium release
What does calcium influx cause in muscle
contraction
Where does calcium come from in cardiac cells
extracellular fluid
How does calcium enter the cardiac cells from the extracellular fluid
L type calcium channels
What is the most important L type calcium channel
Cav1.2
Where are ryanodine receptors present
sarcoplasmic reticulum
What have a physical mechanical link in cardiac cells
Cav1.2 and ryanodine receptors
What do you need for cardiac contraction in terms of channels
both ryanodine receptors and L type channel function
Where is SERCA2a found
sarcoplasmic reticulum
What type of transporter is SERCA2a
ATPase
What is the function of SERCA2a
pump calcium against its conc grad into sarcoplasmic reticulum
What is NCX1
sodium calcium exchanger
What does NCX1 exchange
sodium in for calcium out
What type of transporter is PMCA
ATPase
What is the function of PMCA
moves calcium out and hydrogen ions in
Where is MiCa located
mitochondrial membrane
Describe the driving force for mitochondria and calcium
strong driving force for mitochondria to take up calcium
What is an important calcium store in muscle cells
mitochondria
What is the potential inside mitochondria
-160mV
What does decreased calcium levels cause
cardiac relaxation
What does the strength and velocity of contraction depend on
myocyte and muscle
What are myocytes
sensitive contractile proteins to Ca2+
What is the pre load
end diastolic volume
What changes at myocyte level
pre load EDV, and afterload arterial pressure
What is the main concept of muscle
passive and active tension
Describe passive muscle tension
tension generated at a set sarcomere length without sitmulation
Describe active muscle tension
tension generated by stimulation of the muscle at set sarcomere length
Definition of isometric
held at a specific length, tension changes
Describe the sarcomere when it is bunched up
no cross bridges
What is the effect on contraction at shorter sarcomere lengths
strength of contraction not as effective
What sarcomere length is specific to cardiac muscle
2.2um
Describe increasing sarcomere length on tension in cardiac muscle (passive)
as length increases the tension increases
What type of tension in cardiac muscle increases with more sarcomere protein overlap
passive
Describe the proteins in stretch cardiac muscle
closer
What does increased tension in stretch cardiac muscle activate
stretch activated Ca2+ channels - more Ca2+ entry from ECF
What is Starling’s law
mechanical energy set free on passage from resting to contracted state depends on length of fibres
What is EDV
end volume in the ventricles at the end of a filling phase
What EDV play a role in
determining strength of contraction
What is diastole
passive
What is systole
active
How can you calculate velocity of shortening
tension transducer, measure iso-volumetric contraction phase and ejection phase
What happens during the iso-volumetric contraction phase of shortening
muscle is set to fixed length, muscle is stimulated, tension increases
Describe the isotonic phase of contraction
disengage the screw, muscle shortens, lifts weight from table
What is a measure of the velocity of shortening
the speed at which the muscle lifts the weight from the table
Describe isotonic contraction
tension remains constant but length of muscle can change
What is the relationship between load weight and afterload
when muscle lifts a heavy load the afterload is slower
What is the relationship between velocity of shortening and weight
as weight increases, velocity of shortening also increases
If there is a large volume and low arterial pressure describe the contraction
strong and fast contraction
If there is a low volume and low arterial pressure describe the contraction
weaker and fast contraction
If there is low volume and high arterial pressure describe the contraction
weak and slow contraction
What is the relationship between HR and contracted
as HR increases contraction also increase
Why does increasing HR increase contraction
increased calcium release from sarcoplasmic reticulum
