PSC1002/L06 Electrical Activity & Muscle Contraction Flashcards
How are cardiac muscle cells similar to skeletal muscle cells? (2)
Have T-tubules and sarcoplasmic reticulum
Have sarcomeres made of troponin, myosin, actin, tropomyosin and troponin
What is the role of action potential?
Elevate cytoplasmic [Ca2+]
What is the role of elevated cytoplasmic [Ca2+]?
Generate contraction response
What does the term ‘autorhythmic’ mean?
Provided with oxygen and kept moist, the heart retains its beat
What are the 2 groups of myocytes and their functions?
Conducting cells/system - fast spread of AP
Work cells - generate force
Where does initiation of heart beat occur?
Sino Atrial Node (SAN) - right atrium
What 2 ways can spread of excitation occur?
By specialised ‘conducting fibres’ in atria and ventricles
Cell to cell, via gap junctions
What does the term ‘syncytium’ mean?
Work cells ‘stuck’ together by intercalated discs to function
How are the atria and ventricles separated electrically?
By a fibrous, non-conducting layer between them
What is the function of the bundle of His?
Forms a communication point between atria and ventricles
Describe depolarisation in SAN cells. (4)
Slow initial depolarisation phase - more cations leak in than out, causing slow depolarisation
Full depolarisation phase - at threshold, VG Ca2+ channels open
Repolarisation phase - Ca2+ channels close & VG K+ channels open, causing K+ outflow
Minimum potential phase - K+ channels remain open & membrane hyperpolarises, nonspecific cation channels open
How does the cardiac action potential differ from skeletal AP?
Cardiac APs last much longer
Describe the ionic basis of electrical activity in a ventricular muscle cell. (4)
Rapid depolarisation phase - VG Na+ channels activate and Na+ enter cell
Initial repolarisation phase - Na+ channels inactivated , some K+ channels open, some K+ leak out
Plateau phase - Ca2+ channels open, Ca2+ enter as K+ exit ‘trigger Ca2+’
Repolarisation phase - Na+ & Ca2+ channels close as K+ continue to exit
What is the role of trigger Ca2+?
Leads to muscle contraction through calcium-induced calcium-release (CICR)
What is force of contraction proportional to?
Number of active crossbridges
How much calcium is bound to troponin C, dependent on CICR
