Cardiac muscle Flashcards
Features of cardiac muscle
Striated
Highly organised thick and thin filaments
Contracts unidirectionally
Synsitial- if one cell contracts all cells contract as they are linked by gap junction
Heart-propels blood
Involuntary- regulated by ANS
What are the three types of muscle cells
Pacemaker cells
Conducting cells
Contracting cells
Traits of pacemaker cells
Small, pale, few organelles
Little myosin and actin
Drives activity of the heart
Grouping of cells in SAN and AVN
Traits of conducting cells
Not nerves they are modified muscle cells- make up bundle of his
Purkji fibres
Moves electrical signal around the heart
Little actin and myosin
Traits of contracting cells
Makes up walls of atria and ventricles
Contract the heart
High levels of actin and myosin
Pathway of conduction
An AP is generated in the SAN due to an influx of Ca ions into a cell through slow voltage gated channels, this causes a slower depolarisation spike. Cells are linked by gap junctions an AP in one cell will spread across the whole atria causing it to contract. It doesn’t spread over ventricles. Ap will spread to AVN and depolarise AVN. AVN is attached to bundle of his, AP moves down bundle of his to apex of the heart and spread up the wall of the heart through purkji fibres and makes contact with contractile cells. Passes through ventricles and causes ventricles to contract.
What is the slowest part of conduction and why
Conducting cells because of chemical synapse.
Why is it important that there is a contraction delay
Blood can effectively be pumped out of the heart
Why is SAN important for initiation
AVN takes longer to reach threshold
Will the heart continue to beat is SAN fails
Yes but also AVN is connected to atria and bundle of his which means the pumping action will be ineffective
Plateau potiential
Stable membrane potiential and if stimulated causes rapid depolarisation due to opening of voltage gated sodium channels. If we inactivate fast sodium channels, no more sodium will enter cell and depolarises membrane
Transverse section of cardiac muscle
Single central nucleus
Lots of ct
Longitudal section of cardiac muscle
Striated
Branched fibres
Single central nucleus
Smaller cells
What is an extended refractory period
Action potientials in nerve and muscle cells happen over a long period of time
Mechanical summation
When there is multiple action potientials in a twitch then the action potiential is summed together.
What would happen if u done mechanical summation in the heart
You would die, as you need separate contractions to propel blood from the heart as you need a relaxation stage.
What sets up heart rate
Activity of pacemaker cells
What happens when the activity of SNS is increased
Increased heart rate
Rapid opening of sodium channels
What neurotransmitter slows down heart rate
Acetylcholine
Excitatory contraction
Calcium diffuses into the cell as part of the AP and can drive heart to contract. AP spread over contractile cells causes opening of IC calcium channels and Ca released into intracellular membrane. On the sacroplasmic reticulum there is also calcium gated channels, so when Ca enters the cell as part of AP as well as binding to troponin it can also bind to calcium gated channels on the sacroplasmic reticulum which causes calcium to be released.
Three ways to increase intracellular calcium
Outside of the cell
Diffusion across the membrane
From sacroplasmic reticulum
Factors affecting stroke volume
Starlings law of the heart- increased stretch of the ventricular muscle due to increase in diastolic filling leads to increases force of contraction
Length tension relationship
At rest- cardiac muscle fibres are at a suboptimal length
Stimulation- has a greater force of contraction and goes to full optimal length. This allows an extra reserve of contraction for when we need to use it.
Optimal length= resting length= most able contraction
Starlings law
Describes length tension relationship which describes the overlap of thick and thin filaments not expelling all of the blood in the heart which equals death.
