Excitation Coupling

Question 1

What is excitation contraction coupling

Answer 1

Linkage between excitation of the muscle fibre membrane and the onset of contraction

Question 2

role of transverse tubules

Answer 2

• Action potential is propagated from the end plate along the surface of the muscle fibre (sarcolemma)
• Action potential is propagated into the fibre down the T-tubule membrane
• Depolarisation of the T-tubule membrane is ‘signalled’ to the membrane of the terminal cisternae

Question 3

what two compartments is calcium recycled between

Answer 3

– Sarcoplasmic reticulum/terminal cisternae – Cytoplasm

Question 4

what are the two types of junctional foot proteins

Answer 4

– Dihydropyridine receptor protein (DHPR)
• L-type voltage-gated calcium channel in the T- tubule membrane
– Ryanodine receptor protein (RYR)
• Calcium release channel in the SR

Question 5

Dihydropyridines blocking drugs

Answer 5

Nifedipine

Question 6

what is Nifedipine used to treat

Answer 6

Used to treat (smooth muscle)
– Hypertension
– Migraine
– Atherosclerosis

Question 7

Ryanodine muscle relaxant

Answer 7

– Dantrolene

Question 8

what is Dantrolene used to treat

Answer 8

– Muscle spasm

• Malignant hyperthermia

Question 9

what is malignant hypothermia

Answer 9

• Severe reaction to commonly used anaesthetics and depolarising muscle relaxants
• First manifestations of MH occur in the operating room
• Fatal if untreated

Question 10

what are symptoms of malignant hypothermia

Answer 10

Symptoms
• Muscle rigidity
• High Fever
• Increased acid levels in blood and other tissues
• Rapid heart rate

Question 11

what is the underlying cause of malignant hypothermia

Answer 11

• Point mutations in the gene coding for RyR1

Question 12

what is SERCA

Answer 12

SERCA – Sarcoplasmic Endoplasmic Reticulum Calcium ATPase

Question 13

What activates SERCA

Answer 13

The increase in intracellular calcium concentration activates a Ca2+ ATPase (calcium pump) in the SR membrane

Question 14

What is the role of SERCA

Answer 14

Active transport of calcium from the cytoplasm into the SR (2 Ca2+ ions per molecule ATP hydrolysed)
• [Ca2+]decreasesto<10-7M-RELAXATION

Question 15

Role of calsequestrin

Answer 15

Stores calcium at high concentrations in the terminal cisternae to establish a concentration gradient from the SR to the cytoplasm

Question 16

Pacemaker cells

Answer 16

• Specialised muscle cells
• Unstable resting potential
• Undergo automatic rhythmical depolarisation

Question 17

parasympathetic neurotransmitter action and innveration

Answer 17

acetyl choline
slows rate
localised to pacemakers

Question 18

Sympathetic neurotransmitter, action, innervation

Answer 18

nor-adrenaline, increases rate and strength, diffuse

Question 19

What happens on the release of calcium

Answer 19

The increase in intracellular calcium concentration from < 10-7 M to > 10-5 M is the KEY event which ultimately leads to force generation through the interaction of actin and myosin filaments

Question 20

what percentage of calcium enters through the DHPR L-type calcium channel to induce CICR

Answer 20

25%

Question 21

what percentage of calcium enters through the calcium sensitive calcium release RYR protein in the SR

Answer 21

75%

Question 22

Relaxation in cardiac muscle

Answer 22

• Requires a decrease in cytoplasmic Ca2+ concentration from
>10-5 M to < 10-7 M
• Ca2+ ATPase in sarcoplasmic reticulum is activated
• Ca2+ ATPase in the cell membrane pumps out the trigger Ca2+
• Na+:Ca2+ exchange in the sarcolemmal membrane (3:1)

Question 23

what is the role of the sodium calcium exchanger

Answer 23

helps pump calcium outside of the cell, key cause of arythmias as if too much sodium is being pumped in there is an AP triggered when there shouldn’t be