lct 32 - cardiac muscle

How is cardiac muscle structurally different from skeletal muscle?

Branched, single central nucleus, intercalated discs, electrically coupled

Why is the cardiac AP longer than in skeletal muscle?

Due to a plateau phase caused by sustained Ca²⁺ influx via L-type channels

Why can’t cardiac muscle undergo tetanus?

AP and twitch overlap in time, preventing summation/tetany—essential for heart function

What triggers contraction in cardiac muscle?

Ca²⁺ influx (ICaL) triggers Ca²⁺ release from SR (calcium-induced calcium release)

How is Ca²⁺ removed after contraction in cardiac muscle?

SR Ca²⁺ ATPase, Na⁺/Ca²⁺ exchanger, sarcolemmal ATPase, and mitochondrial uptake

What initiates the heartbeat?

The SA node generates pacemaker potentials via slow Ca²⁺ and Na⁺ influx

How do sympathetic and parasympathetic nerves affect HR?

Sympathetic (NA): ↑ HR; Parasympathetic (ACh): ↓ HR

What is the Frank-Starling Law?

More stretch = more force of contraction (due to optimal actin-myosin overlap)

How does increased HR increase contraction strength?

Less time to clear Ca²⁺ between beats → more cytosolic Ca²⁺ → stronger contraction

How does noradrenaline affect stroke volume?

↑ L-type Ca²⁺ entry, ↑ SR Ca²⁺ storage → stronger, shorter contractions