The tissue in a heart that assumes the function as the pacemaker is the node:

1. that depolarizes to reach threshold at the fastest rate
2. that has the most negative resting membrane potential
3. with the largest store of glucose and energy
4. that has the longest refractory period
5. all of the answers are true

Determine which of the following best explains why cardiac muscle is incapable of tetanus, a sustained contraction characteristic of skeletal muscle?

1. An action potential in the cardiac muscle cell has a plateau period of slow calcium entry that produces a long refractory period.
2. A cardiac muscle cell could never produce enough energy to supply ATP for more than a 0.1 second contraction.
3. Cardiac muscle cells have intercalated discs so communication between cells would prevent tetanus.
4. Cardiac muscle cells are innervated by autonomic neurons, while skeletal muscle cells are controlled by somatic motor neurons.