Cardiac Muscle

Label this image to show the structure of cardiac muscle.

Label this diagram of a cardiac muscle fibre.

What organelle in a cardiac muscle fibre do the myofilaments bind to?

T-tubules are organelles independent to the sarcolemma.

Where do T tubules occur?

Why do the T-tubules and the sarcoplasmic reticulum form 'diads' in conjunction with one another?

What name is given to the brick wall-like structure of the cardiac muscle whereby the myocytes fuse to share nuclei and sarcoplasm?

Which comparison between skeletal and cardiac muscle is correct?

The cardiac action potential has the same graph plot as a nervous action potential.

During which phase of a cardiac action potential can another beat not be produced?

It is impossible for the heart to produce another beat during the relative refractory period.

Why is it important that the cardiac muscle have a long refractory period in which another twitch cannot be generated?

Cardiac muscle requires an influx of calcium into the cytosol for contraction to occur.

T-tubules make the process of calcium movement more homogenous - they ensure calcium moves across the myocyte evenly to initiate even contraction.

Why do T-tubules ensure more rapid movement of calcium throughout the myocytes?

What name is given to Ca2+ channels on the sarcoplasmic reticulum which release Ca2+ into the cytosol?

The L-type calcium channels, also known as DHP receptors, are voltage-activated and are found on the T-tubules.

Fill in the blanks below to describe the process of calcium-induced calcium release which takes place in cardiac muscle. 1. Action potential arrives at [blank_start]L-type[blank_end] calcium channel in [blank_start]T-tubule[blank_end]. 2. Calcium channel opens and allows movement of calcium across the [blank_start]dyadic cleft[blank_end] - the gap between the T-tubular membrane and the terminal cisternae of the sarcoplasmic reticulum. 3. Calcium binds to [blank_start]ryanodine[blank_end] receptors on the sarcoplasmic reticulum, causing them to open. 4. Calcium moves out of sarcoplasmic reticulum and binds to muscle filaments to initiate [blank_start]contraction[blank_end].

What moves calcium from the sarcoplasm into the sarcoplasmic reticulum to refill its stores and relax the cardiac muscle?

What is required for the formation of actin-myosin crossbridges in striated muscle? Check all that apply.

In the absence of ATP, what would occur in striated muscle?

Reduced calcium concentration reduces the tension of a striated muscle fibre.

Change in overlap of the myofilaments is the key factor in explaining the length-tension relationship in cardiac muscle.

Longer sarcomeres have greater myofilament overlap but they also have...

The length-tension relationship of sarcomeres forms the cellular basis of the Frank-Starling law of the heart. The Frank law states that the peak [blank_start]systolic[blank_end] pressure of the heart is directly related to diastolic [blank_start]fibre length[blank_end]. The Starling law states that cardiac output is directly related to [blank_start]filling pressure[blank_end].

Increasing the frequency of stimuli to the heart decreases the tension of the sarcomeres.

In a failing heart, [blank_start]SERCA[blank_end] is down-regulated and the Na+/Ca2+ [blank_start]exchanger[blank_end] is elevated. This means that there is [blank_start]more[blank_end] calcium extrusion between heartbeats and that there is [blank_start]less[blank_end] calcium cycling through the sarcoplasmic reticulum. This means that increasing frequency of stimuli [blank_start]decreases[blank_end] tension of the sarcomere.

This graph shows the cardiac action potential. Label it to show which ions are increasing/decreasing in the different phases and the different channels that open/close.

What is the calcium transient?

Why can tetany occur in skeletal muscle as a result of multiple action potentials in quick succession?

Fill in the blanks to describe depolarisation-induced calcium release in skeletal muscle. 1. The [blank_start]L-type[blank_end] calcium channel on the T-tubules is [blank_start]voltage[blank_end] sensitive. 2. The receptor detects a change in [blank_start]potential[blank_end] as the [blank_start]action potential[blank_end] passes. 3. The receptor 'pulls the plug' of [blank_start]calcium[blank_end] release channels in the [blank_start]sarcoplasmic reticulum[blank_end].

Why does calcium sensitivity increase tension?

What is the Treppe/staircase effect?