Muscle Tissue

Review Questions: What are the three types of muscle tissue? From which embryonic germ layer are they derived? What are the special characteristics of skeletal muscle tissue (e.g. what features enable them to contract under voluntary control)? What are the functions of skeletal muscles? Is a muscle (e.g. Deltoid) considered a tissue or an organ? Justify your answer.

Organization of Skeletal Muscle (macroscopic anatomy) What do the following prefixes mean: peri-, endo-, epi-, myo-, and sarco-? Describe how a muscle attaches to a bone, as shown in this figure. Why is there such a large connective tissue component to skeletal muscles?

What is the functional unit of contraction in a muscle fiber? Circle and/or label one in this diagram. What is a myofibril? Internal organization of a muscle cell: = myosin = actin What are cisternae and what chemical is stored within the cisternae of muscle cells? Each t-tubule is an extension of the ________________.

Organization of Myofilaments in a Sarcomere A Sarcomere within a Myofibril

Energy Metabolism in Muscle Cells (pages 165 & 166 in the course packet) 1.The phosphagen system 2.Aerobic cellular respiration 3.Fermentation (anaerobic metabolism) What molecule serves as the energy source for fermentation? Where does the muscle cell get these molecules?

Energy from food molecules ATPase breaks the last phosphate bond, releasing energy –leaves ADP (adenosine diphosphate) and P i ATP synthase catalyzes the addition of the terminal phosphate group back onto ADP Name the two locations where ATP synthesis takes place in a cell. The ATP cycle

Phosphagen System (Creatine Phosphate) Can cells store ATP? Can cells store CrP? Name the enzyme that controls these reactions. Where would you find this enzyme, and why?

Anaerobic ATP Synthesis (Fermentation) Which source of fuel molecules is more important, and why? What are the consequences of lactic acid production? What is the relationship between lactic acid in the blood and “oxygen debt”? Why is anaerobic muscle work more powerful than aerobic muscle work?

Write the summary equation for aerobic cellular respiration. What are the benefits of aerobic cell metabolism? What substrate(s) are available for aerobic energy metabolism? … for anaerobic metabolism? Aerobic Cellular Respiration What’s wrong with this figure?!

Summary: Energy Metabolism in Muscle Cells

Motor Units: The functional unit of movement How many muscle cells are in motor unit 1? How many neurons in motor unit 1? What is the functional classification of the neuron in motor unit 1? Describe at least two ways that these neurons controlled.

The Neuromuscular (Myoneural) Junction The appropriate term to describe an axon branch (as shown in these figures) is ___________________. The appropriate stimulus for skeletal muscle cells is _____________________. The specialization of the sarcolemma that contains receptors for acetylcholine (ACH) is called ___________________.

K + is often allowed to “leak” out of the cell. How does the Na-K pump contribute to the “potential”? Why is the cell membrane described as “polarized”? The Transmembrane Electrochemical Potential

The Action Potential At time 0, does the membrane begin to depolarize or repolarize? Unlike the graded potentials that get larger with increasing stimulus strength (e.g. at the motor end plate), the action potential is an all-or-none* response. Will a stronger stimulus produce a larger action potential? Explain. Give an example of where a graded potential would take place.

Differentiate between the absolute refractory period and the relative refractory period. Why is the refractory period important in muscle cells? Why is the refractory period important in neurons? Refractory Period from L. = “stubborn”

Chemical Synapses The calcium channels on the synaptic terminal are -gated. The sodium channels on the post- synaptic membrane are -gated. The ion channels involved in the propagation of the Action Potential are -gated.

Vesicle Transport in Exocytosis

Events at the Neuromuscular Junction Is the release of neurotransmitter active transport or passive transport? Is the influx of Na + ions by active transport or passive transport? How does the influx of Na + ions change the transmembrane electrochemical potential?

Are the calcium channels in cisternae voltage-gated or chemically-gated? Besides Ca +2, what must also be present in order for myosin to bind to actin? Study the outline beginning on page 170 in your packet.

Muscle fiberMotor neuron Nucleus

SarcolemmaMyofibrils Sarcoplasmic reticulum (SR) T-tubule SR Cistern (a portion of the sarcolemma is peeled away in this view)

Action potential reaches synaptic terminal of motor neuron

New AP generated at motor end-plate and propogated down T- tubules

Myofibrils (relaxed)Sarcomere (Sarcolemma and other structures not shown)

Myofibrils (contracted)Sarcomere

Sarcomere (relaxed) Actin (thin filaments) Myosin (thick filaments)

Sarcomere (contracted) Actin (thin filaments) Myosin (thick filaments)

Actin (thin filament) Myosin (thick filaments) Myosin heads

ActinMyosin head ADP and phosphate Protein complex Note that ATP is hydrolyzed at this point, but still attached to myosin head.

Calcium ion Myosin-binding sites (exposed) Protein complex ADP and phosphate

ActinMyosin head ADP and phosphate

ActinMyosin head PiPi AD P 1.Release of P i initiates the power stroke. 2.At the end of the power stroke, ADP is released. 3.A new ATP is required for myosin to release its hold on actin.

ActinMyosin head ATP ATP binds to the myosin head, causing it to detach from actin.

ActinMyosin head ADP and phosphate When the ATP is broken down to ADP and phosphate, the myosin head extends.

ActinMyosin heads The sequence repeats as long as calcium ions are present. The combined work of many myosin heads causes the actin filaments to slide past the myosin filaments.

Actin Myosin heads Protein complex When the action potentials stop, calcium ions are pumped back into the ER, the myosin-binding sites on actin are again blocked, and the muscle relaxes.

Actin MyosinCalcium Sarcomere (Ca +2 in green)