Anatomy and Physiology

Week 3 Summary


Muscle Tissue


1.         Know the basic characteristics of smooth, skeletal and cardiac muscle


2.         Know the gross anatomy of a skeletal muscle

a.         Individual fibers are surrounded by endomysium

            b.         Multiple fibers are bundled as fascicles

            c.         Fascicles are bound by collagen sheath

                        i.          Perimysium

            d.         Epimysium then surrounds all fascicles of an entire muscle

            e.         Deep fascia binds muscles into functional groups


3.         Know the microscopic anatomy of skeletal

a.         A bands—dark bands

b.         I bands—light bands

c.         H band (within A band)

d.         M line

e.         Z disc (membrane)

                        i.          Midline in I band


4.         Know the ultrastructure and molecular composition of actin, myosin and associated regulatory proteins


Sliding Theory of Contraction


A.        During relaxed state

1.         Ca2+ concentration in sarcoplasm is low

a.         Ca2+ is stored in sacroplasmic tubules

2.         Troponin-tropomyosin complex attached to actin filament

            a.         Tropomyosin positioned to block myosin binding sites on actin filament

3.         ATP and inactive ATPase bound to myosin head

            a.         Low energy configuration

                        i.          Binding to actin is not possible

B.        Events during contraction

1.         Nerve impulse (afferent signal) from motor neuron generates action potential in nerve cell

            a.         AP propagated along sarcolemma and down T tubules

2.         Myosin ATPase activated

            a.         ATP splits

                        i.          High energy myosin-ADP complex

3.         AP causes release of Ca2+ from sarcoplasmic reticulum

4.         Ca2+ binds to troponin

            a.         Molecular shape of troponin changes

i.          Tropomyosin is removed from binding site of mysosin on the actin filament

            b.         Myosin attaches to actin

5.         Contraction: Potential energy stored in high-energy configuration is used to pivot myosin head

            a.         Myosin head bends as it pulls on actin

            b.         ADP and inorganic phosphate are released from myosin

6.         New ATP attached to myosin head

            a.         Cross bridge simultaneously detaches

            b.         Following death, no ATP and muscle fibers cannot relax

                        i.          Rigor mortis

7.         If no new impulse, Ca2+ is pumped back into sarcoplasmic reticulum (SR)

            a.         Relaxation occurs

8.         If Ca2+ present from additional impulse, cycle repeats

            a.         Myosin head “steps” to next binding site on actin


Muscle Function


1.         Know how to describe the following:

            a.         Motor unit

            b.         Muscle twitch

            c.         Graded muscle responses

                        i.          Stimulus frequency

                        ii.         Stimulus strength

            d.         Motor unit summation

            e.         Treppe


2.         Know the various sources of ATP for muscle metabolism


3.         Know the three types of lever systems


4.         Know how to characterize muscles based on fascicle organization


Axial and Appendicular Muscles


1.         For all of the muscles discussed in class, know:

            a.         Regional organization

            b.         Actions

            c.         Origins

            d.         Insertions