Muscle Physiology

Question 1

Three types of muscles tissue

Answer 1

Skeletal

Smooth

Cardiac

Question 2

How do skeletal muscle fibres contract

Answer 2

1. ADP Bound myosin head is cocked and ready to bind to actin
2. In the presence of Ca2+ it binds to troponin which exposes binding sites on actin for myosin to bind
3. The bound myosin rotates its head producing a power stroke
4. ADP is released and ATP is bound to the myosin which causes it to detach from actin

Question 3

Type 1 vs type 2a vs type 2b muscle fibres

Answer 3

Type 1 fibres are slow twitch, meaning they are suited for situations which require long-term sustained contractions. They create ATP through oxidative metabolism, which is efficient (30 molecules of ATP per glucose molecule) but requires a rich supply of oxygen. Accordingly they have large amounts of myoglobin (an oxygen binding protein) to facilitate oxygen delivery. Because they use oxidative metabolism, which in the presence of sufficient oxygen supply can supply enough energy to sustain contraction they are fatigue resistant (hence suited for long-term contractions). Examples of muscles with lots of type 1 fibres include the soleus muscle in the leg, required for posture

Type Iia fibres are fast-twitch. They utilise both oxidative and anaerobic metabolism. Anaerobic is less efficient (2 ATP molecules per molecule of glucose) but is much faster. These fibres can contract faster and provide more power than slow twitch fibres and because they have some oxidative metabolic capacity are relatively fatigue resistant

Type Iib (sometimes called Type IIx) fibres are fast twitch and rely entirely on anaerobic metabolism. As such they appear white because they do not contain large amounts of myoglobin or mitochondria. They are also easily fatigable. Anaerobic respiration will provide energy quickly, but is much slower. Examples of muscles with high fast twitch fibre content include those which move the eye

Question 4

Where does the initiation of cardiac action potential begin

Answer 4

Sino-atrial node

Question 5

What is the role of SERCA2

Answer 5

Moves calcium back into the sarcoplasmic reticulum

Question 6

Role of RyR1

Answer 6

When RyR is activated when an action potential reaches the t-tubule, calcium flows into the cell

Question 7

How does depolarisation wave spread in the heart

Answer 7

Via gap junctions

Question 8

Role of t-tubules

Answer 8

Increase surface area for ion transfer between extracellular and intracellular fluid