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Flashcards in Lecture 27 Deck (14):

What is the structure of cardiac muscle?

A striated (hence possesses Z lines) and branching muscle type, has only a single nuclei. Cardiac muscle cells are joined by intercalated discs which involve connection by gap junctions (electrical connection) and desmosomes (mechanical connection), these intercalated discs are not straight line of connection, rather their shapes can vary.


What are the four chambers of the heart?

left atrium (upper left), right atrium (upper right), left ventricle (lower left) and right ventricle (lower right).


Where are the pacemaker cells found?

In the sinoatrial node of the right atrium.


Describe the process of co-ordinated heart contraction

The pacemaker cells undergo spontaneous action potentials, this signal travels to cells in the atrioventricular node. From there the septum is depolarised and this leads to the depolarisation of the apex and bundle of his (an area at the bottom of the heart). From there purkinje fibers are stimulates and the ventricles depolarise until fully depolarised. Because the cells are continuous due to gap juncitons they will all act at once.


Why is the heart thought of as having its own 'mini nervous system?

Because its function is regulated by the acting of a central group of cells (the pacemaker cells).


What are the two types of smooth muscle and what is the main difference?

The two types are single unit smooth muscle (gap junctions allow the cells to all act together) and multi unit smooth muscle (no gap junctions hence cells act independently.)


Where would you find multi unit smooth muscle, where would you find single unit smooth muscle?

multi: pili muscles of the skin, eye muscles and blood vessels.
Single: digestive, urinary and reproductive tracts.


how does smooth muscle slow or speed up blood flow?

By constricting or relaxing the blood vessels, this is done by either relaxing the smooth muscle (allowing the blood vessel to widen and hence more blood flow), or by contracting the smooth muscle (constricting the blood vessel and hence lowering blood flow).


How does smooth muscle get excited?

Ca2+ ions bind with calmodulin, this complex then activates the myosin light chain kinase (MLCK). This MLCK will activate MLC which can then activate the myosin-actin cross bridge. This is regulated by the myosin filament rather than the actin filament as is the case in the other muscle types.


What is the structure of smooth muscle cells?

a non striated, mono nucleate cell with actin and myosin organised in many different directions.


What do the multiple directions of myosin and actin allow for in smooth muscle cells?

large length changes and sustained tension, though a weaker force it can act in many directions.


Which of the three muscle cell types have T-tubuli?

skeletal and cardiac.


What is similar about how cardiac muscle and some smooth muscle cells are controlled?

All cardiac tissue is spontaneously controlled by pacemaker cells, smooth muscle can also be controlled by pacemaker cells (also by nerves).


What are the relative contraction and impulse speeds for the three muscle types?

fast for skeletal, slow for cardiac and very slow for smooth.