Question

How do you distinguish between a skeletal muscle and a cardiac muscle?

Answer 1

Hint: Both skeletal muscle and cardiac muscle are types of striated muscle. Functionally, however, both are very different. Skeletal muscle is attached to our skeleton and is involved in movement. Cardiac muscle is found exclusively in the heart, responsible for pumping blood through our bodies.

Complete answer:
Structurally, skeletal muscle is striated with nuclei located along the periphery of the cell, and unbranched. The sarcomeres are very abundant, with triads at junctions containing the T-tubules. Contraction of skeletal muscle depends on the binding of Ca$^{2+}$ to troponin C which exposes the myosin binding site. The type of movement of skeletal muscle is voluntary.

Cardiac muscle is also striated, but the cell nuclei are in the centre, cells are branched. They have much less sarcomere, with a single terminal cistern per dyad. The contractile mechanism is similar to that of skeletal muscle, but cardiac muscles are involuntary. There are several intercalated discs which are absent in skeletal muscle.
Functionally, skeletal muscle can carry out both aerobic and anaerobic respiration, and experiences muscle fatigue rapidly. Cardiac muscle, with high levels of oxygenation and numbers of mitochondria, is dependent on aerobic respiration, and does not experience muscle fatigue.

Note: Skeletal muscle has another characteristic in that not only does it undergo hypertrophy in response to increased load, it is also able to carry out repair and renewal of muscle tissue. Cardiac muscle does undergo hypertrophy, but can carry out little to no renewal, so damage during a heart attack is permanent.