1. Describe the organization of skeletal muscle.
  1. Skeletal muscle is made up of individual muscle fibers that are the "building blocks" of the muscular system in the same sense that the neurons are the building blocks of the nervous system. Most skeletal muscles begin and end in tendons, and the muscle fibers are arranged in parallel between the tendinous ends, so that the force of the contraction of the units is additive. (Really, these are my OWN words! I swear I didn't copy!) Each muscle fiber is a single cell, multinucleated, long, cylindric, and surrounded by a cell membrane, the sarcolemma (figz 3-1, 3-7, 6-9, 1-1, 94-34, 10004-1a. I guess I am copying. This is from Lang's Review of Medical Physiology.). The muscle fibers are made up of myofibrils, which are divisible into individual filaments. The filaments are made up of contractile proteins. OK, enough bull. Here's the handout.
  1. Describe the morphological changes which occur in the sarcomere during contraction.

When theactin-myosin complex contracts, the z lines come closer to each other, and the I band gets shorter. The A bands are the myosin; they stay the same.

  1. What is the function of Ca2+ ions in contraction and relaxation.

-* Upon contraction, Ca2+ ions stored in the sarcoplasmic reticulum are released into the sarcoplasmic reticulum where they bind to troponen C. This is a trimeric protein that has four binding sites for Ca2+. Binding of all four Ca2+ ions causes troponen to release the inhibition of actin activation of the myosin ATPase.

-* On relaxation (Ahhhhhhhhhhhhh) the Ca2+ ATPase pump in the membrane of the sarcoplasmic reticulum sequesters 2Ca2+ for every ATP.

  1. What is the most important component involved in excitation-contraction coupling?

Dr. Ruth? I'm not sure on this one, but I might also say the sarcomere. (If any of you find some handout one-liner related to this, please let me know.)

  1. List the main protein constituents of skeletal muscle.

Actin, myosin, troponin, tropomyosin, phinaminamyosin

6. What is the importance of the connective tissue components of muscle?

The epimysium (covers the whole enchilada), perimysium (divides muscle into fascicles), and the endomysium (covers a single fiber) are arranged to give a muscle its pretty little shape.

  1. Where is the transmitter, acetylcholine, stored?

In the synaptic vesicles of the nerve supplying the fibril. (SHH! Don’t' tell anyone!)

  1. Why are there no gap junctions in adult skeletal muscle?

Because they have the t-tubule system to conduct the impulse.

  1. What roles do mitochondria, the T-system and the SR play in muscle function?

Mitochondria provide the ATP that binds to the myosin head and causes its release from actin. The t-system is a continuation of the sarcolemma that forms invaginations into the cell. It is associated with the sarcoplasmic reticulum terminal cisternae that surrounds the myofibrils at the A-I junction. ACh depolarizes the t-tubule membrane enough to activate a voltage-gated Ca2+ channel relay down the tubule.

  1. What component surrounds each myofibril?

Survey Says!. Sarcoplasmic reticulum!

  1. What is the important difference between the SR and the T-system?

The SR is an organelle and the t-system in the membrane, Fred.

  1. What is the nature of the innervation in skeletal muscle?

Each muscle cell synapses with only one axon.

  1. Why is it called the "sliding filament model" of muscle contraction?

Actin and myosin slide past each other when the sarcomere shortens.

  1. Do sarcomeres really contract?

SIR! They shorten! SIR!

  1. What is notable about the ultrastructure of smooth muscle?

Smooth muscle has no striations. In fact it really doesn't look like anything. I'm not even sure that it's there at all.

  1. Is there a basal lamina in smooth muscle?

Sure is! In fact, the little buggers make it themselves! It consists of a proteoglycan-rich material. Individual cells and bundles of cells are surrounded a basil lemona.

  1. Compare cardiac and skeletal muscle in terms of:
  1. Sarcoplasmic reticulum

Cardiac is less organized and does not divide myofibrils into discreet units. Its t-tubules occur at the z-line instead of the A-I junction. T-tubules associate with only a single expanded external cistern.

  1. Myofibrils

Cardiac myofibrils branch and are connected to adjacent cells with intercalated disks. SEX!SEX!SEX! Wake up!

  1. Position of nuclei

Skeletal muscle nuclei are flat and located near the edge of the cell. Cardiac muscle nuclei are more round and more centered in the cell.

  1. Number of nuclei

Skeletal muscle cells are multinucleated. Cardiac aren’t.

  1. T-system

Diad in cardiac, triad in skeletal.

YOU HAVE BEEN BRIEFED

  1. What is the main function of intercalated disks?

They contain GAP junctions that allow the action potential to spread between cells.

19. Are there myoneural junctions in cardiac or in smooth muscle?

No.

20. Is there a Ca2+-storing equivalent compartment in smooth muscle?

They have calveoli. They are surface-associated vesicles involved in uptake and release.

21. What is the function of gap junctions in smooth or cardiac muscle?

They serve to conduct the impulse from cell to cell.

22. Does cardiac muscle have troponin and tropomyosin?

YUP, sure does. Just like skeletal muscles.

23. Is there a Ca2+-binding protein in smooth muscle?

YUP, calmodulin binds Ca2+ to regulate the phosphorylation of the myosin muscle.

24. What is the function of a muscle spindle?

It has intrafusal fibers that detect the amount of tension in the muscle. They aid in proprioception (knowing where your body and limbs are in space in relation to each other). There's a 50 cent word if I've ever used one!

25. Where would you find myoepithelial cells?

Around ducts and glands.