L26 - cardiac muscle Flashcards
describe how cardiac muscle cells are arranged
- interconnecting electrically coupled cells which act in a syncytium
- cardiac cells separated from each other but still electrically coupled
1% of cardiac cells are?
non contractile
structure of cardiac muscle cell
- composed of branched interconnecting cardiomyocytes
- striated cells
- electrically connected via intercalated disc
what are the 2 types of electrical activity of cardiac muscle cells?
- pacemaker potential
- prolonged cardiac action potential
what is heart rate regulated by?
catecholamines
what is the functional unit of cardiac muscle?
sarcomere
cardiomyocytes (cardiac cells) are connected by intercalated discs, what does this allow?
allows them to work as a single functional syncytium
describe the intercalated discs that connect the cells
- interdigitating folds: infold at end of cells to increase SA of cell to cell connection
- mechanical junctions: fascia adherens & desmosomes
- electrical junctions: gap junctions
describe the fascia adheres (type of mechanical junction between intercalated discs)
- couple the membrane to the actin cytoskeleton (contractile apparatus) of the cells
- aids transmission of contractile force between cells
describe the desmosomes (type of mechanical junction between intercalated discs)
- provide strong structural support between cells
- makes sure cells can withstand contractile forces of heart
describe the electrical junctions for the intercalated discs
- gap junctions electrically couple cytoplasm of neighbouring cells
- coupling allows ions to move between cells
- so cardiac A.P can spread
- so heart muscle goes under depol
structure of gap junctions
- hexamer made of connexions
- forms gap junction of 12 subunits
what does the gap/electrical junction serve as?
a low resistance pathway between cells
what is cell-cell conductance?
electrical coupling
how many gap junctions represent gap junction plaque?
5-500
blood supply in cardiac muscle
- needs continuous supply of oxygen
- rich capillary supply
- short diffusion distances for oxygen and waste products
excitation contraction coupling
- actin-myosin based contraction
- fundamental unit is sarcomere
- calcium initates contraction
- regulated by troponin-tropomyosin compelex
cardiac pacemaker cells
- not by nerve stimulation like skeletal muscle
- but by specialised cells called pace maker cells
- which spontaneously generate A.P
- primary pacemaker cells in SAN (upper right atrium next to superior vena cava)
pacemaker A.P
- Na+ enters via funny channel
- calcium enters by t type calcium channel
- more ca2+ enters by L-type calcium channel
- K+ leaves by voltage gated potassium channel
cardiac action potential
- na enters by voltage gated na channel
- ca2+ enters by L type calcium channel
- K+ leaves by voltage gated k channel
calcium induced calcium release
- L type ca channels open during cardiac A.P
- small amount of ca enter cell + triggers ryanodine receptor calcium channel in sr membrane to open
- ca released from sr + binds to troponin, so formation of cross bridge happens
- calcium goes back into sr by sarcoplasmic reticulum calcium ATPase (SERCA)
- na/ca exchanger exchanger removes calcium out of cell
- membrane depolarised by k channels at end of A.P
troponin I
inhibitory
Troponin C
calcium binding
Troponin T
tropomyosin binding
what are troponin?
skeletal and cardiac muscle isoforms
what is used to detect myocardial infarction?
cardiac troponins (they are fragmented and released into blood when heart muscle is damaged)
genetic cardiomyopathies
- dilated cardiomyopathy (DCM) caused by mutations in genes
- DCM causes dilation of left ventricle, contractile failure, loss of myofibrils etc
