cardiovascular system - cardiac muscle

Question 1

striated muscle

Answer 1

due to alternating patterns of dark and light (in relation to thick and thin filaments and their overlapping)
-skeletal muscle
-cardiac muscle

Question 2

branching in cardiac muscle

Answer 2

represents the junctions between individual cells (singular myocyte)

Question 3

cardiac muscle

Answer 3

-centralised nuclei
-branching

Question 4

intercalated discs

Answer 4

the connections between myocytes

Question 5

skeletal muscle

Answer 5

-nuclei on periphery of the cell
-no branching

Question 6

importance of intercalated discs

Answer 6

-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

Question 7

intercalated discs in detail

Answer 7

-proteins called DESMOSOMES
-they allow myofilaments to couple once cell to the next
-one sarcomere mechanically coupled to adjacent sarcomere via desmosome

Question 8

gap junctions within intercalated disc

Answer 8

-are membrane pores
-allow ions + electrical activity to pass from one cell to the next

Question 9

T-tubule

Answer 9

-invaginations within muscle wall
-allows electrical activity to penetrate deep into the tissue

Question 10

importance of T-tubule

Answer 10

increases SA of muscle cell for electrical coupling (much like microvilli for S.intestine)

Question 11

mitochondria

Answer 11

source of oxidative phosphorylation, krebs cycle and electron transport chain

Question 12

sarcoplasmic reticulum

Answer 12

calcium storing organelle

Question 13

thick filament

Answer 13

-chain of myosin molecules
-diameter: 11 nm

Question 14

thin filament

Answer 14

-polymerised chain of actin molecules
-diameter: 6 nm

Question 15

A band

Answer 15

-myosin + actin
-section containing thick filament and some of thin filament
-tends to represent width of thick filament

Question 16

M band

Answer 16

-myosin only
-region that has thick filament but NO thin filament
-widens during contraction
-shortens during relaxation

Question 17

I band

Answer 17

-actin only
-region of thin filament that does NOT overlap with thick filament

Question 18

Z band/line

Answer 18

• composed of a-actinin
  -limit of the sarcomere
  -distance between Z lines will alter dependent on degree of relaxation or contraction

Question 19

importance of narrow sarcomere limit

Answer 19

-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

Question 20

how does the sarcomere generate force ?

Answer 20

-myosin head (thick) and actin binding site (thin) interact together
-form cross bridges that generate mechanical activity

Question 21

sliding filament mechanism

Answer 21

-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

Question 22

role of ATP hydrolysis

Answer 22

-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

Question 23

Ca2+ in muscle contraction

Answer 23

-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

Question 24

importance of Ca2+ in muscle contraction

Answer 24

-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