Cardiac muscle

Question 1

Features of cardiac muscle

Answer 1

Striated
Highly organised thick and thin filaments
Contracts unidirectionally
Synsitial- if one cell contracts all cells contract as they are linked by gap junction
Heart-propels blood
Involuntary- regulated by ANS

Question 2

What are the three types of muscle cells

Answer 2

Pacemaker cells
Conducting cells
Contracting cells

Question 3

Traits of pacemaker cells

Answer 3

Small, pale, few organelles
Little myosin and actin
Drives activity of the heart
Grouping of cells in SAN and AVN

Question 4

Traits of conducting cells

Answer 4

Not nerves they are modified muscle cells- make up bundle of his
Purkji fibres
Moves electrical signal around the heart
Little actin and myosin

Question 5

Traits of contracting cells

Answer 5

Makes up walls of atria and ventricles
Contract the heart
High levels of actin and myosin

Question 6

Pathway of conduction

Answer 6

An AP is generated in the SAN due to an influx of Ca ions into a cell through slow voltage gated channels, this causes a slower depolarisation spike. Cells are linked by gap junctions an AP in one cell will spread across the whole atria causing it to contract. It doesn’t spread over ventricles. Ap will spread to AVN and depolarise AVN. AVN is attached to bundle of his, AP moves down bundle of his to apex of the heart and spread up the wall of the heart through purkji fibres and makes contact with contractile cells. Passes through ventricles and causes ventricles to contract.

Question 7

What is the slowest part of conduction and why

Answer 7

Conducting cells because of chemical synapse.

Question 8

Why is it important that there is a contraction delay

Answer 8

Blood can effectively be pumped out of the heart

Question 9

Why is SAN important for initiation

Answer 9

AVN takes longer to reach threshold

Question 10

Will the heart continue to beat is SAN fails

Answer 10

Yes but also AVN is connected to atria and bundle of his which means the pumping action will be ineffective

Question 11

Plateau potiential

Answer 11

Stable membrane potiential and if stimulated causes rapid depolarisation due to opening of voltage gated sodium channels. If we inactivate fast sodium channels, no more sodium will enter cell and depolarises membrane

Question 12

Transverse section of cardiac muscle

Answer 12

Single central nucleus
Lots of ct

Question 13

Longitudal section of cardiac muscle

Answer 13

Striated
Branched fibres
Single central nucleus
Smaller cells

Question 14

What is an extended refractory period

Answer 14

Action potientials in nerve and muscle cells happen over a long period of time

Question 15

Mechanical summation

Answer 15

When there is multiple action potientials in a twitch then the action potiential is summed together.

Question 16

What would happen if u done mechanical summation in the heart

Answer 16

You would die, as you need separate contractions to propel blood from the heart as you need a relaxation stage.

Question 17

What sets up heart rate

Answer 17

Activity of pacemaker cells

Question 18

What happens when the activity of SNS is increased

Answer 18

Increased heart rate
Rapid opening of sodium channels

Question 19

What neurotransmitter slows down heart rate

Answer 19

Acetylcholine

Question 20

Excitatory contraction

Answer 20

Calcium diffuses into the cell as part of the AP and can drive heart to contract. AP spread over contractile cells causes opening of IC calcium channels and Ca released into intracellular membrane. On the sacroplasmic reticulum there is also calcium gated channels, so when Ca enters the cell as part of AP as well as binding to troponin it can also bind to calcium gated channels on the sacroplasmic reticulum which causes calcium to be released.

Question 21

Three ways to increase intracellular calcium

Answer 21

Outside of the cell
Diffusion across the membrane
From sacroplasmic reticulum

Question 22

Factors affecting stroke volume

Answer 22

Starlings law of the heart- increased stretch of the ventricular muscle due to increase in diastolic filling leads to increases force of contraction

Question 23

Length tension relationship

Answer 23

At rest- cardiac muscle fibres are at a suboptimal length
Stimulation- has a greater force of contraction and goes to full optimal length. This allows an extra reserve of contraction for when we need to use it.
Optimal length= resting length= most able contraction

Question 24

Starlings law

Answer 24

Describes length tension relationship which describes the overlap of thick and thin filaments not expelling all of the blood in the heart which equals death.

Question 25

Why does the heart sit at a suboptimal length

Answer 25

More blood can be put into the heart, then more blood can be expelled.

Question 26

Where is adrenaline from

Answer 26

Adrenal glands

Question 27

What happens when adrenaline is applied

Answer 27

Calcium permeability changes so more calcium is released from the sacroplasmic reticulum so if there is more intracellular calcium then more cross bridges will be formed this increase in cross bridges will form a stronger and faster contraction.