Muscle Contraction

Question 1

What is Cardiac Muscle Tissue?

Answer 1

Found in the heart. Involuntary contractions controlled by the electrical conduction system of the heart.

Question 1

What is Smooth Muscle Tissue?

Answer 1

Involuntary contractions and found in the walls of internal organs (e.g. blood vessels)

Question 2

What are the characteristics of muscle fibres (cells)?

Answer 2

Excitable (Muscle excitation is triggered by the depolarisation of membranes), Contractile, Extensible and Elastic

Question 3

How is Cardiac Muscle different to Skeletal muscle?

Answer 3

Smaller cells, Single Nucleus, Branched muscle cells which are joined to other cardiac muscle cells so make cell membrane to cell membrane contact (intercalated discs). They are activated by other cardiac cells.
Skeletal muscles have no cell membrane to cell membrane contact as each end is connected to tendons. Skeletal muscle cells also have multiple nuclei.

Question 4

What are the thick and thin muscle filaments called?

Answer 4

Thick = myosin
Thin= actin

Question 5

Why do we have non contractile proteins?

Answer 5

Nebulin= Regulation of Contraction
Titin= Stabilises Thick myosin filament
Dystrophin= membrane stabiliser

Question 6

Why is the resting length of the Sarcomere long?

Answer 6

This means that there is a lot of space for over lap of the thin and thick filaments so more cross bridges can form and therefore there can be more force generated.

Question 7

What is the importance of calcium ions in forming cross bridges?

Answer 7

Calcium ions bind to troponin which then shifts the tropomyosin causing a conformational change in the shape which exposes the active sites on the actin molecules available so the myosin heads can bind.

Question 8

What are the steps to muscular contraction?

Answer 8

1. Myosin cross bridge attaches to the actin myofilament and pulls on the actin filament to contract the muscle.
2. ATP binds to myosin head changing the shape of the myosin so it detaches from the actin filament
3. ATP is hydrolysed into ADP which releases the energy required for myosin to return to its original position.
4. Myosin head then binds again to new position on the actin filament.

Question 9

Where are calcium ions found in a muscle cell?

Answer 9

In the Sarcoplasmic reticulum

Question 10

How are calcium ions made available to bind to troponin?

Answer 10

Depolarisation of the membrane causes the sarcoplasmic reticulum to release Calcium ions into the cytoplasm.

Question 11

How do you stop the muscle from contracting?

Answer 11

Remove Calcium ions from the cytoplasm. This is done via a calcium ion pump which transports them back into the sarcoplasmic reticulum

Question 12

What is an end plate potential?

Answer 12

This is when a nerve impulse travels down a motor neurone to the end plate of the motor neurone which releases neurotransmitters across the neuromuscular junction which then bind to the muscle fibres at that part to cause depolarisation of the membrane.

Question 13

What happens if the threshold depolarization is met of the end plate potential?

Answer 13

This triggers the rest of the membrane to generate action potential which then moves down the sarcolemma (cell membrane)

Question 14

Are motor units connected to 1 or multiple muscle fibres?

Answer 14

One motor unit is connected to multiple muscle fibres which, if the threshold is met, means that multiple muscle fibres are recruited to perform a particular action

Question 15

What are Cardiac muscle cells excited by?

Answer 15

A pacemaker cell or an adjacent muscle cell.

Question 16

What are the sources of calcium ions in skeletal muscle and cardiac muscle?

Answer 16

One source of Calcium ions in the SR in Skeletal Muscle.
2 sources of calcium ions in Cardiac muscle- SR (75%) and transmembrane (25%)

Question 17

What are differences between striated muscle and smooth muscle? And what triggers smooth muscle tone?

Answer 17

Smooth muscle is non striated. Thin and Thick filaments are not arranged in sarcomeres.
Free calcium binds to calmodulin (not troponin).
Calcium-calmodulin then activates myosin light chain kinase (MLCK).
This enzymes phosphorylates myosin light chains in the presence of ATP.
MLC are found on the myosin head. This leads to cross bridge formation.

Question 18

What are the 3 basic sources of ATP?

Answer 18

1. Creatine Phosphate- first few seconds of exercise
2. Anaerobic glycolysis- first minute
3. Aerobic respiration

Question 19

What is a reason why muscle cells are red? What is the advantage of having this?

Answer 19

This is because they have an internal pigment called myoglobin. Myoglobin has a much higher affinity for oxygen than haemoglobin which means that more oxygen is available for aerobic respiration to provide ATP for muscle cells.

Question 20

What is the difference between endomysium and perimysium?

Answer 20

Endomysium is connective tissue that surrounds a single muscle fibre
Perimysium is a sheath of connective tissue that surrounds multiple muscle fibres.

Question 21

What is the importance of intercalated discs in cardiac muscle?

Answer 21

They allow electrical activity to spread between cardiac muscle fibres to allow synchronized contraction of the heart.

Question 22

In smooth muscle cells, where is the nucleus usually found and what shape is it?

Answer 22

Usually found centrally in each cell and are long

Question 23

What causes smooth muscle to have a smooth appearance (not striated)?

Answer 23

Actin and myosin are arranged irregularly in smooth muscle, resulting in these fibres appearing uniform and smooth under a microscope, rather than striated

Question 24

What does the force of the muscle produced, depend on?

Answer 24

The number of cross bridges formed and therefore the concentration of intracellular calcium ions.

Question 25

What does it mean by B-adrenergic activation having an inotropic effect on cardiac contraction?

Answer 25

This increases the intracellular cAMP concentration which means that in each relaxation phase, more Calcium ions are taken up by the SR instead of being released extracellular so the next contraction will release more calcium ions so more cross bridges will form so the rate of contraction will be stronger.

Question 26

How does the EDV in the Ventricle affect the force of the contraction?

Answer 26

The higher the EDV the larger the length of the sarcomere so the stronger the force of the muscle contraction as more cross bridges can form.

Question 27

What is the maximal point in the length tension relationship?

Answer 27

This is where the Z discs get so far apart that there is very little overlap of the actin and myosin filaments resulting in a decreasing force of contraction.

Question 28

What is the Frank Starling relationship?

Answer 28

The larger the EDV in the ventricle the greater the stroke volume as sarcomeres stretch more so more cross bridges form so an increase in the force of contraction.

It all depends on the volume of blood left in the ventricle at the end of diastole.