L4 - Cardiac & Smooth Muscle Flashcards
what is tetanus/tetany?
sustained muscle contraction
what does the size of motor units determine?
how precise the control is on the muscle
how is force of contraction increased?
smaller motor units are recruited first, the more force needed, the more motor units recruited
how is force of contraction increased?
smaller motor units are recruited first, the more force needed, the more motor units recruited
what is isotonic muscle contraction?
constant tension + muscle length changes
what is isometric muscle contraction?
constant length and tension
where is striated cardiac muscle distributed?
across atria on top and ventricles on the bottom
what is the cardiac ‘pacemaker’?
sinoatrial node - capable of spontaneous depolarization (action potentials)
why are cardiac action potentials longer than skeletal?
prevent heart from going into tetany (heart must keep pumping!)
how does a cardiac action potential spread?
via coupled cells - gap junctions - through the atria and into the ventricles
why are there no motor units in heart contraction?
all or nothing, no half recruitment like with motor units
what does smooth muscle in particular lack?
no sarcomeres or troponin (calmodulin is the Ca+ binding protein)
what is essential for smooth muscle contraction?
extracellular Ca++ and sarcoplasmic reticulum Ca++
when do smooth muscle contractions occur?
in response to stimuli such as hormones and stretch (GIT)
what is smooth muscle contraction?
mechanism of actin/myosin interaction with cross-bridge formation
