Lecture 2: Heart Muscle – Specialized Structure & Function

Question 1

What muscle arrangement allows heart squeezing?

Answer 1

Spiral muscle arrangment, squeezes from bottom up for greatest efficiency

Question 2

What are the features of cardiac muscle?

Answer 2

Striated, mono nucleated, intercalated discs attaching one myocyte to the next

Question 3

What do intercalated discs contain?

Answer 3

Desmosome and gap junctions

Question 4

What do desmosomes do?

Answer 4

Transfer force from cell to cells and act as glue to keep myocytes together

Question 5

What do gap junctions do?

Answer 5

Spread electrical signal/ions between cells

Question 6

What are the dimensions of a cardiomyocyte?

Answer 6

100 microns long and 20 microns wide

Question 7

Why does a cardiomyocyte have lots of mitochondria?

Answer 7

Constantly slowly contraction so needs lots of energy to maintain this action

Question 8

What is force development proportional to?

Answer 8

Myofilament overlap

Question 9

Where on the length tension curve does heart muscle always sit?

Answer 9

Ascending curve - more stretch = bigger contraction

Question 10

What does EDV indicate?

Answer 10

How stretched the muscle is

Question 11

What is skeletal muscle predominantly made up of and why?

Answer 11

Myofilaments - force development in short bursts

Question 12

What is cardiac muscle predominantly made up of and why?

Answer 12

Mitochondria (35%) - slow acting and constantly producing force

Question 13

Draw the cardiac EC coupling diagram:

Answer 13

IMAGE

Question 14

What happens in cardiac EC coupling?

Answer 14

• Calcium enters during AP plateau
• Moves through l-type channels in t tubules
• Calcium dependent calcium release from RYR on SR
• Calcium released, binds to troponin c, alters tropomyosin and myosin and actin can bind
• Cross bridge cycle

Question 15

How does cardiac muscle relaxation occur?

Answer 15

80% of calcium pumped back into SR via SERCa2 ATPase, 19% pumped out via Na/Ca exchanger (3 Na in, 1 Ca out), 1% pumped out via SL ATPase

Question 16

How long is cardiac muscle contraction?

Answer 16

300msec

Question 17

What is the fuzzy space?

Answer 17

A restricted diffusional region between SL and SR

Question 18

What happens if the L-type channel and the SR release channel are misaligned?

Answer 18

Heart failure (no contraction)

Question 19

What happens if the calcium release channel is leaky or hypersensitive to calcium?

Answer 19

Arrhythmia (excessive contractions)

Question 20

How many plateaus in cardiac AP?

Answer 20

One plateau

Question 21

How does excitation occur in cardiac muscle?

Answer 21

Gap junction

Question 22

What kind of metabolism does cardiac muscle have?

Answer 22

Oxidative

Question 23

What type of RYR receptor does cardiac muscle have?

Answer 23

2

Question 24

What happens if the fuzzy space gets wider?

Answer 24

Ischemia

Question 25

What does junctophilin do?

Answer 25

Tethers SL to SR

Question 26

How much capacity does the heart recover after MI and why?

Answer 26

1/3 - because junctophilin is broken and channel widens - reducing contractions

Question 27

What type of troponin is in cardiac muscle?

Answer 27

C1