Assignment task:
1) Temporal summation also known as wave summation occurs mainly in skeletal muscles before the repolarization (repolarization step that follows the depolarization causing the release of calcium from SR). Why is that?
Is it because when the release of calcium occurs the sarcolemma has already repolarized so it can be stimulated again which then propagates the AP through the T tubules and causes more calcium to be released for a longer contraction and more forceful contraction? But if this processed occured after repolarization or during, less calcium would be present in the sarcoplasm so less force of contraction and shorter duration of contraction. Is what I explained correct?
2) Motor unit recruitment and tetanus
Are they different because with motor unit recruitment the force of contraction increases and its a recruitment of more motor neurons whereas with tetanus it is mostly the same neuron or different neurons stimulating the same myofiber one after the other with brief relaxation in between contraction (unfused) or no relaxation (fused). Is that correct?
3) Connective tissues are described as mostly extracellular matrix and cells that secrete material. Cartilage is a dense connective tissue.
My question is if cartilage is a connective tissue it should have cells such as chondrocytes derived from fibroblast with collagen, elastin fibers and ground substance. However, in my biology book it states that chondrocytes secrete cartilage. So is cartilage the connective tissue? If yes, why does chondrocyte secrete it?