cardiovascular system - cardiac muscle Flashcards
striated muscle
due to alternating patterns of dark and light (in relation to thick and thin filaments and their overlapping)
-skeletal muscle
-cardiac muscle
branching in cardiac muscle
represents the junctions between individual cells (singular myocyte)
cardiac muscle
-centralised nuclei
-branching
intercalated discs
the connections between myocytes
skeletal muscle
-nuclei on periphery of the cell
-no branching
importance of intercalated discs
-forms mechanical couple between adjacent cells
-when cells contract, lots of mechanical activity is generated
-this needs to be transmitted from once cell to the other
intercalated discs in detail
-proteins called DESMOSOMES
-they allow myofilaments to couple once cell to the next
-one sarcomere mechanically coupled to adjacent sarcomere via desmosome
gap junctions within intercalated disc
-are membrane pores
-allow ions + electrical activity to pass from one cell to the next
T-tubule
-invaginations within muscle wall
-allows electrical activity to penetrate deep into the tissue
importance of T-tubule
increases SA of muscle cell for electrical coupling (much like microvilli for S.intestine)
mitochondria
source of oxidative phosphorylation, krebs cycle and electron transport chain
sarcoplasmic reticulum
calcium storing organelle
thick filament
-chain of myosin molecules
-diameter: 11 nm
thin filament
-polymerised chain of actin molecules
-diameter: 6 nm
A band
-myosin + actin
-section containing thick filament and some of thin filament
-tends to represent width of thick filament
M band
-myosin only
-region that has thick filament but NO thin filament
-widens during contraction
-shortens during relaxation
I band
-actin only
-region of thin filament that does NOT overlap with thick filament
Z band/line
- composed of a-actinin
-limit of the sarcomere
-distance between Z lines will alter dependent on degree of relaxation or contraction
importance of narrow sarcomere limit
-usually between 1.8-2.2 microns
-degree of overlap determines how many cross bridges form between thick/thin filament
-cross bridges generate mechanical activity/force for contraction
how does the sarcomere generate force ?
-myosin head (thick) and actin binding site (thin) interact together
-form cross bridges that generate mechanical activity
sliding filament mechanism
-calcium binds the thin filament
-ATP is consumed by the thick filament
-myosin ATPase on myosin head hydrolyses ATP to form the cross bridges
-combination of ATP hydrolysis and calcium binding help force to be generated
role of ATP hydrolysis
-when ATP binds to myosin ATPase on the myosin head it causes separation between the thick and thin filament
-hydrolysis of ATP causes conformational change with myosin head, causing it to move backwards
-initial dissociation of phosphate group, leaves ADP bound to myosin head
-causes rebinding of myosin head and actin binding site
-finally, the power stroke that generates the mechanical activity is associated with dissociation of ADP molecule from myosin head
Ca2+ in muscle contraction
-Ca2+ binds troponin C
-(three troponins: C, I & T)
-they form a complex with the protein tropomyosin
-this complex causes a conformational change in tropomyosin’s position
-which allows the myosin binding sites on actin to become available for cross bridges to form
importance of Ca2+ in muscle contraction
-Ca2+ is needed to generate contractile activity
-even if ATP hydrolysis occurs, without Ca2+ tropomyosin will not be in the correct position for cross bridges to be able to form
