BIO210 Weekly Guide #5

 

AXIAL MUSCULATURE;

MUSCLE HISTOLOGY & PHYSIOLOGY

After completing this laboratory you should be able to:

 

1)   Identify the muscles of the neck, thorax, abdomen, and back, providing the origin, insertion, and actions or each

 

2)   Recognize, fully classify, and functionally characterize samples of muscle tissues in microscopic sections

 

3)   For each type of muscle tissue, describe its distinguishing properties and state where in the body it could be found

 

4)   Describe anatomical basis of neural control of skeletal muscle

 

5)   Explain the cellular mechanism of excitation/contraction coupling

 

6)   Diagram the the cycle of interactions of the sliding filament theory, including the roles of ionic calcium and ATP

 

7)   Describe the cellular and mechanical bases for temporal recruitment, summation, tetany/tetanus, isometric contraction, isotonic contraction, fatigue, and recovery.

 









Gross Anatomy List

Guide to Gross Anatomy Guide to Histology Guide to Physiology

 

Outline

 

I. Skeletal Muscle Naming  {FAP 11-1, 11-4, Table 11-1}

     A. Shape

           e.g. deltoid, pectineous, piriformis

     B. Relative size or length

           e.g.  major, vastus, brevis

     C. Fiber orientation

           e.g. rectus, obliquus    

     D. Location or underlying bone

           e.g. pectoralis, temporalis

     E. Relative position

          e.g. medialis, inferior

     E. Origin and insertion

           e.g. sternocleidomastoid, coracobrachialis

     F. Action

           e.g. supinator, flexor, levator, adductor

     G. Other

           e.g. sartorius

 

II. Intrinsic Axial Musculature {FAP 11-5, Tables 11-8 to 11-10; APL Figs 10.2 to 10.9}

      *  Note: some "extrinsic" muscles of the trunk and "intrinsic" muscles of the head

                    will be studied in later labs with the appendages and the head

     A. Back and Posterior Neck

            transversocostal

                 sacrospinalis (erector spinae)

                      regions and columns

                      thoracolumbar fascia

                 semispinalis capitis

                 splenius capitis

            transversospinal

            suboccipital triangle (deep postural)

            ligamentum nuchae

     B. Anterior Neck

            superficial

                 sternocleidomastoid

                 platysma

            deep

                 scalenes

                 suprahyoid and infrahyoid groups

     C. Thoracic

             external intercostals

             internal intercostals

             transverse thoracis

             diaphragm

     D. Abdominals

             anterior abdomen

                 external oblique abdominis

                 internal oblique abdominis

                 transverse abdominis

                 abdominal aponeurosis

                 inguinal ligament and inguinal canal

                 rectus abdominis

                     linea alba 

                     tendinous incriptions/insertions

             posterior abdomen and pelvis

                 quadratus lumborum

                 iliopsoas

                 levator ani              

 

III. Muscle Structure

     A. Skeletal Muscles

             locations

             substructure and ["bundling"]  {FAP 10-2, 10-3; APL Fig. 11.5}

                    whole muscle - [epimysium]

                    fascicles   [perimysium]

                    fibers = cells  [endomysium and sarcolemma]

                          T-tubules

                    myofibrils   [sarcoplasmic reticulm]

                          SR cisternae

                    microfilaments

                          actin and myosin

             skeletal muscle fibers

                   multinucleate

                   peripheral nuclei

                   striations

             the sarcomere {FAP 10-3 to 10-5; APL Fig. 11.5, 11.6}

                    "structural & functional unit of muscle"

                        actin and myosin domains

                        A bands and M line - myosin "thick" filaments

                        I bands and Z line - actin "thin" filaments

                        relaxed vs. contracted appearance

                        relationship to T-tubules and SR cisternae

                    series vs. parallel arrangements

             the neuromuscular junction (NMJ) 

                        {FAP 10-4, Spotlights 10-9 to 10.13; APL Figs 11.7, 11.8}

                    structure

                         motor axon terminals

                         motor end plate

                         postsynaptic membrane

                    motor units and motor pools

       B. Cardiac Muscle  {FAP 10-8; APL Fig 5.10}

             locations

             cardiac muscle fibers

                   branched fibers

                   single, central nucleus

                   striations

                   intercalated disks

       C. Smooth (Visceral) Muscle  {FAP 10-9; APL Fig 5.10} 

              locations

              smooth muscle fibers

                   unbranched, spindle-shaped cells

                   single, central nucleus

                   non-striated

 

IV. Muscle Physiology

     A. Skeletal Muscle Physiology {FAP 10-3, 10-4}

             actin and myosin fine structure  {FAP Spotlight 10-11}

                   myosin

                   actin, tropomyosin, troponin

             the contraction cycle - the "sliding filament" theory 

                                               {FAP Spotlight 10-11; APL Fig 11.9}

                 molecular sequence

                 role of intracellular free Ca++

                 role of ATP {FAP 10-6}

                       ATP binding, hydrolysis, and release

                       creatine and arginine phosphate 

                 role of oxygen

                       mitochondria

                       hemoglobin and myoglobin

                       oxidative vs. glycolytic

             excitation-contraction coupling  {FAP Spotlight 10-12}

                 sequence of events

                      motor axon APs and end-plate potentials

                      neurotransmitter (ACh) release

                      ACh binding and postsynaptic depolarization

                      AP spread and T-tuble invasion

                      Ca++ release from SR

                      Ca++ binding to troponin

                      A-M interaction and contraction cycles

                      Ca++ resequestration

                      ACh enzymatic breakdown

                 additional considerations

                      AP vs. twitch timecourse

                      tetanus and neurotoxins

                      rigor mortis

       B. Skeletal Muscle Mechanics

               muscle tension   {FAP 10.5; APL Fig 11.10}

                     the twitch

                           single fiber twitch

                           recruitment

                           summation and tetany

                     whole muscle contraction

                           isometric contraction

                           isotonic contraction

                           series elastic components and phases of contraction

                     length vs. tension

                             sacromere corollary

                           resting muscle length and tone

               fiber metabolic types  {FAP 10-7, Table 10-2}

                     slow-twitch oxidative

                     fast-twitch oxidative

                     fast-twitch glycolytic

                     muscle mixtures

               exercise effects  {FAP Fig 10-20}    

                     energy reserves, fatigue, exhaustion, and recovery

                     growth

               skeletomuscular levers

                     lever types/arrangements

                         type 1   FPL

                         type 2   PLF

                         type 3   PFL

                     low and high "gear" muscles

       C. Comparisons Between Skeletal, Cardiac, and Smooth Muscle  {FAP 10-8, 10-9,

            Table 10.3}

                fiber size and shape

                nucleus(i)

                strength vs. speed of contraction

                length vs. tension revisited

                excitation - neurogenic vs. myogenic

                syncytial?

 

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Gross Anatomy List   

          

Back & Posterior Neck Muscles: {APL Fig 10.2 to 10.9}

       Sacrospinalis (Erector Spinae)                                   

               regions:               columns:                                     

                  iliolumborum       spinalis (medial)                                 

                  thoracis               longissimus (intermediate)                                                           

                  cervicis                iliocostalis (lateral)                      

                  capitis

       Splenius Capitis

       Semispinalis Capitis

       Occipital (suboccipital) Triangle:

               Rectus Capitis Posterior Major

               Rectus Capitis Posterior Minor

               Obliquus Capitis Superior

               Obliquus Capitis Inferior

 

Anterior Neck Muscles:

       Sternocleidomastoideus 

       Suprahyoid Group               

       Infrahyoid ( Anterior Rectus ) Group  

       Platysma      

       Scalenes            

      

Thoracic Muscles:                                     

       External Intercostals 

       Internal Intercostals 

       Transverse Thoracis  

       Diaphragm  

                                                                                                

Abdominal Muscles:

       External Oblique Abdominis  

       Internal Oblique Abdominis  

       Rectus Abdominis                                   

       Transversus Abdominis                            

       Quadratus Lumborum

       Iliopsoas (Iliacus and Psoas Major)

       Levator Ani

 

Related Structures:

       Ligamentum Nuchae                              Aponeurosis

       Thoracolumbar Fascia                            Tendinous Inscriptions             

       Inguinal Ligament                                   Inguinal Canal

       Umbilicus                                                 Linea Alba

 

KEY:           Know location, action, origin, & insertion (for muscles)

               Know location & action (for muscles)                         

               Not responsible for

 

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Guide to Gross Anatomy

Muscles of the Back {FAP Figs 11-11, 11-12; APL Figs 10.4, 10.9}                                                                        

 

The superficial back muscles will be dealt with along with the extremities upon which they act.  The deep (intrinsic) back muscles fall into two groups - the more superficial transversocostal muscles and the deep transversospinal muscles.

 

a)   The transversocostal muscles turn laterally as they ascend and collectively the muscles form a muscle group called the sacrospinalis (for its location) or erector spinae (for its function).  It is sheathed in the thoracolumbar fascia, a dense layer of connective tissue.

 

 -   Study the sacrospinalis (erector spinae) group on the models and charts.  What is the major function of this group?

 

b)     The transversospinalis muscles are smaller, more distinct muscles which turn medially as they ascend.  Study the text figures to get some idea of their numbers, actions, and distributions.  Because they are difficult to find and view in our models, we will not deal with them in this course.

 

Muscles of the Neck {FAP Fig. 11-5, 11-10 to 11-14; APL Fig. 10.2, 10.3}                                                                    

 

a)   The ligamentum nuchae (nuchal ligament) is a prominent midline structure of the posterior neck.  It is formed from the fused supraspinous ligaments of the cervical vertebrae.  In quadruped animals it holds the head up.  The human head is fairly well balanced on the atlas and the ligamentum nuchae helps maintain this balance.  It also serves as a surface for attachment of the superficial muscles of the upper back and posterior neck.

 

-      What lever type (I, II, III) is the atlantooccipital joint?       

 

b)   The more superficial posterior neck muscles are essentially a continuation of the erector spinae.  We will study the two most rostral, which attach to the occipital bone and move the head.  Study the origins, insertions, and actions of the:

 

                            splenius capitis                                    semispinalis capitis

  

c)   The suboccipital triangle is a deep muscle group of the posterior neck.  They have very impressive names for such little muscles.  Study the origins, insertions, and actions of the:

 

                       rectus capitis posterior major                      obliquus capitis inferior

                       rectus capitis posterior minor                      obliquus capitis superior

 

-    Note that these muscles define the three sides of a triangle, thus the group name.             

 

-    Note also that these are small postural muscles, rather than large "prime movers" of the head.

 

d)   Study the sternocleidomastoideus muscle on the models and charts.  This and the trapezius (next week) are the superficial lateral neck muscles. 

 

-         Note that the sternocleidomastoideus is named for its origins and insertion.  What are the actions of this muscle?

       

e)   The platysma is a broad flat very superficial muscle that defines the contours of the anterior neck and lower face.

 

 -   Notice that its origins and insertions are diffuse and principally from fascia and other muscles, rather than from bony prominences.

 

-    The sternocleidomatoideus muscles originate ventrally, but are they ventral or dorsal flexors of the neck and head?

       

f)    The suprahyoid and infrahyoid groups have the collective actions of raising and lowering the hyoid bone and base of the tongue during swallowing.

 

g)    The scalenes are a set of three muscles on each side which connect the transverse processes of the middle cervical vertebrae to the first two ribs.  They are auxiliary respiratory muscles, and the gaps between them provide passage for structures traveling laterally from the thoracic cavity to the upper extremity.

 

Muscles of the Thorax  {FAP Figs. 11-12, 11-14; APL Figs. 10.5, 10.6}                                                                                

 

a)   Study the origins and insertions of the internal and external intercostal muscles.  Note that there are 11 pairs of these muscles. 

 

-    Based on the direction in which the fibers run , which muscle set lifts and expands the thorax (inspiration)? Which depresses and contracts the thorax (expiration)?

 

b)   Study the fan-shaped transverse thoracis muscle which radiates across the posterior surface of the sternum and costal cartilages and aids in forced expiration.

 

c)   Study the domed-shaped diaphragm, the principal muscle involved in relaxed inspiration.  Note that it forms the boundary between the thoracic and abdominal cavities.  Its origin is around the periphery - the xiphoid, ribs 7-12 and their costal cartilages, and the lumbocostal arches.  Its insertion is upon itself in a central tendon.

 

 -   What are the principal structures passing through each of the three large openings in the diaphragm?

 

 -   How does the diaphragm change shape as it contracts?  How does this increase the size of the thoracic cavity?

 

d)    Virtually every other muscle that originates or inserts on the rib cage  can serve as a "auxiliary" respiratory muscle if its other attachment point is stabilized.  These muscles only aid respiration under extreme circumstances, such as active physical exertion or respiratory distress.

 

-    Think of examples from this week's and next week's muscles.

 

Muscles of the Abdomen & Pelvis  {FAP Figs. 11-12, 11-13; APL Fig. 10.7}                                              

 

a)   The anteriolateral abdominal muscles have three major functions: containment of the abdominal organs, respiration, and flexion of the lumbar spine.  Study the origins, insertions, and actions of these muscles:

 

                       external oblique abdominis              transversus abdominis

                       internal oblique abdominis               rectus abdominis

 

-    Pay particular attention to the direction in which the fibers of each muscle run. How does the crisscrossing of fiber directions strengthen the lateral abdominal wall?

 

b)   Note that the fiber directions of the external and internal oblique abdominis muscles parallel those of the external and internal intercostals, and that the thoracic and abdominal muscle fibers intermingle with each other across the boundary between the thorax and abdomen.

 

c)   How could these abdominal muscles aid in respiration?  If you are having trouble with this question, do the following:

 

-    First breathe so that only your chest expands and contracts (thoracic breathing).              What muscles are you using? 

 

-     Now breathe so that only your abdomen expands and contracts (abdominal breathing).  What muscles are you using now?

 

-    Which method is generally recommended for singing?  Why?

 

-    Which method is more readily available in the late stages of pregnancy?  Why?

 

d)  On the models study the location of the inguinal ligament. 

 

-    From the aponeurosis of which abdominal muscle is it formed? Between what two           bony prominences of the pelvis does it run? 

 

e)   The inguinal canal is a roughly tube-like structure that passes deep to the inguinal ligament.  At each end is an inguinal ring formed from a split in the aponeuroses.  The internal inguinal ring opens into the abdominal cavity, while the external inguinal ring opens into the scrotum or labia.  We will return to the inguinal canal several times in this course.

 

-    What passes through this canal in the male?  In the female?

 

-    What is an inguinal hernia?  Is this more likely to happen in a male or a female (think about howcompressible the structures running through the inguinal canal are in each)?

 

f)   An aponeurosis is a broad, flat, tendinous sheet.   The aponeuroses of the anterior abdominal muscles fuse at the midline into a structure called the linea alba. 

 

-    Notice that the relationship of the rectus abdominis to the medial aponeuroses of the other three muscles changes at the level of the umbilicus.

 

-    Where is the bulk of the muscle mass of the external oblique, internal oblique, and transverse abdominis muscles located, medially or laterally?

       

g)   Study the rectus abdominis muscles in the models. 

 

-    Notice that the muscle is broken up into discrete masses separated by the "tendinous inscriptions".

 

-    For what action are the right and left rectus abdominis muscles synergists (same   action)?  For what action are they antagonists (opposing action)?

 

-    The rectus abdominis changes “levels” at the umbilicus, diving from within the internal oblique aponeurosis to behind it.  This discontinuity creates a weak spot in the abdominal wall.  What do you suppose an umbilical hernia is?

 

h)   Study the origin and insertion of the quadratus lumborum in the posterior abdominal wall. 

 

-    For what action is each quadratus lumborum muscle a synergist with the ipsilateral (same side) rectus abdominis?  For what action is it an antagonist?

 

i)    The floor of the pelvic cavity is formed by the levator ani muscle anteriorly, the coccyx posteriomedially, and the coccygeus muscle posteriolaterally. 

 

-         Study the levator ani on the models and trace its origins and insertions on a skeleton.

 

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Guide to Histology

 

Muscle  {review APL Unit 5 Exercise 5-3, Fig 5.10}

 

Muscle is the third primary tissue type that we will study.  It has the following structural properties:

 

       1)     It is primarily cellular.

       2)     It is vascular.

       3)     It is specialized for excitability and contractility.

 

There are three principal types of muscle:

 

       1)     skeletal muscle

       2)     cardiac muscle

       3)     smooth muscle

 

The functional properties of muscle derive from the modification of general cellular organelles, especially the cytoskeletal elements.   If you like cell biology, this would be a good time to review the sliding filament theory of skeletal muscular contraction.

 

a)   Skeletal Muscle {APL Exercise 11-1; Fig 11.6}

      Skeletal muscle may be recognized in longitudinal section by the straight, unbranched fibers and prominent striations, and in cross section by the large cell size, stippled appearance of the sarcoplasm, and peripheral, flattened nuclei.

 

-    On cross section of the tongue muscle slide, note the peripheral nuclei and the large, uniform diameter cells which have a "flagstone" appearance.  Because these are elongated cells, the plane of section often does not cut through the nucleus of most cells.  Identify the delicate endomysium separating muscle fibers, the thicker perimysium bundling muscle fascicles, and the dense epimysium (if possible) wrapping the entire muscle.

 

-    On longitudinal section, note the striations and multiple peripheral elongated nuclei. What produces the striated appearance?

 

-   Where in the body is skeletal muscle found?

 

b)   Skeletal Muscle Fine Structure  {APL Exercise 11.1; Fig 11.6, 11.7}

 

      Work through APL Exercise 11.1 using the teased skeletal muscle slide, the neuromuscular junction (NMJ) slide, and the NMJ model  

 

-    On the teased muscle fiber slide use high power and/or oil immersion to try to identify the A bands, I bands, H zone, Z line, and M line on individual sarcomeres.  What structure feature of the sarcomere does each of these represent?  Again, note the peripheral nuclei of these multinucleated fibers (cells).  What is the functional significance of their location around the circumference of the fiber?  How does this compare to the muscle fiber model?

 

-   Use APL Figs. 11.4 & 11.5, as well as the the skeletal fiber model of the to identify the following "bundling" features of a typical skeletal muscle.  Note that the model depicts a short  section of a single skeletal muscle cell.:

 

            epimysium                                   whole muscle

            perimysium                                  muscle fascicle

            endomysium & sarcolemma         muscle fiber

                    note T- tublule of the sacrolemma

            sarcoplasmic reticulum                 myofibril

                    note cisternae                     

 

-   There is something seriously wrong with the NMJ model below the level of myofilaments.  Can you tell what it is?

 

-    Compare the NMJ slide with the NMJ region of the skeletal fiber model, using APL Fig 11.7 as a guide.  Can you see the axon terminal boutons and motor endplates?

 

c)   Cardiac Muscle   {APL Exercise 11.3; Figure 11.12}                                                          

      Cardiac muscle may be recognized in longitudinal section by the branched fibers and       prominent striations, and in cross section by the variance in cell size, the stippled sarcoplasm, and the central nuclei.

 

-    On cross section note the central nuclei and variance in cell size.  Again, for many cells you will not see the nucleus, because it lies out of the plane of  section.

 

-    On longitudinal section note the branching pattern.  Identify intercalated discs which are also unique to cardiac muscle.

 

-    Where in the body is cardiac muscle found?

 

 d)  Smooth (or Visceral) Muscle  {APL Exercise 11.3; Figure 11.12}                                  

      Smooth muscle may be recognized in longitudinal section by the lack of striations, the indistinct cell borders, and the relatively large, plump, cigar shaped nuclei.  In cross section it may be recognized by the small cell size, relative to cardiac and skeletal muscle, and the relatively large, central nuclei.

 

-    On cross section, note the large central nuclei, circular to oblong cross-sections through the cells, the small but varied cell diameters, and the fine endomysial connective tissue network between the cells.  Because these are relatively short, spindle shaped cells, you should see the nucleus of most cells.

 

 -   On longitudinal section, note that the cells are small and indistinct with only one nucleus per cell, with interspersed fibroblast nuclei.  There are no striations in smooth muscle. Why

 

-    Where in the body is smooth muscle found?

 

-    Now compare skeletal, cardiac, and smooth muscle in longitudinal and cross-sections, until you are sure that you can tell them apart.  See the "Hints - Tips" on APL page 221 if you are having trouble..

 

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Guide to Physiology

  

Skeletal Muscle Contractile Cycle 

 

Use APL Figures 11.8 and 11.9 to work through excitation-contraction coupling in skeletal muscle cells, including:

 

a)  the sequence of events at the neuromuscular junction (NMJ) associated with a single twitch - from presynaptic arrival of an action potential to acetylcholine release at the motor endplate, to generation and spread of a postsynaptic action potential, to calcium release from the sarcoplasmic reticulum, to initiation of fiber contraction, to termination of the contraction.

 

b)  the sequence of four steps constituing a single contraction cycle in a sarcomere.

 

Be sure that you thoroughly understand and can distinguish the roles of intracellular calcium, ATP, actin, myosin, and the troponin and tropomyosin actin subunits.

 

 

Skeletal Muscle Dynamics

 

Use the APL Exercise 11.3 Procedure 2 to investigate the length-tension relationship for skeletal muscles.  Note: our dynamometer is a bit different than the one diagrammed in APL, so pay close attention to the instructions below.

 

a)  Pick an arm.  Flex your elbow to 90 degrees.  Fully pronate your forearm, as in the diagram.  Grasp the dynamometer as if you were grasping a door knob.

 

b)  Set the red "memory" needle to the lower end of the "0" range.

 

c)  Flex your wrist as close to 90 degrees as you can.  Squeeze the bulb as hard as you can for three seconds ( a slow count to 3).

 

d)  Record the red needle psi reading next as "Fully Flexed"

 

e)   Rezero the red needle and straighten your wrist (stay pronated, elbow at 90 degrees!).

 

f)  Squeeze the bulb as hard as you can for three seconds ( a slow count to 3).

 

g)  Record the red needle psi reading next to "Extended"

 

h)  Rezero the red needle and hyperextend your wrist as far back as you can (stay pronated, elbow at 90 degrees!).

 

i)  Squeeze the bulb as hard as you can for three seconds ( a slow count to 3).

 

j)  Record the red needle psi reading next to "Hyperextended"

 

                     Data Table:

Wrist Position

Tension (psi)

Fully Flexed (short)

 

Extended (middle)

 

Hyperextended (long)  

Produce a wee line plot of tension (psi) as a function of wrist position or the relative starting length of the muscle(s).  Note that you are using primarily the common flexor muscles of the forearm, wrist, and fingers, which are shortest when the wrist is hyperflexed and longest when the wrist is hyperextended.

                     Plot of tension (y-axis) as a function of relative length (x-axis):

 

 

-    Do your results agree with your expectations, and/or the relationship shown in APL Fig. 11.11 and FAP Fig. 10-14?

 

-    Can you explain your results in terms of the relative overlap of actin and myosin microfilaments  in each of the three positions?

 

-    What is the "natural" resting position of your wrist?  Is this the position in which you can generate the greatest grip tension?  Does that make good "design sense to you?

 

-    Perform the comparable experiment with your toes as you hyperdorsiflex, relax, and hyperplantarflex your ankle.  You won't be able to use the dynamometer, but you should be able to get a good sense of your relative toe-gripping force in each position.  Again, does the natural, resting, standing position of the ankle correspond to the greatest toe tension?

 

Isotonic vs. Isometric Contraction 

 

Perform each of the following two exercises while seated in a chair:

 

a)  Grasp a dumbell in one hand.  Supinate your forearm.  Starting with your elbow at 90 degrees, lift the dumbell by flexing your elbow.  Try to keep your wrist straight.

 

b)  Put the dumbell down.  Slide your chair over to one of the seating cutouts under a counter.  Supinate your forearm and slide your hand under the countertop.  Starting with your elbow at 90 degrees, try to lift the countertop by flexing your elbow.  Try to keep your wrist straight.  Note: the countertop will not move, so don't hurt yourself.

 

 -   Which condition more closely matches an isometric contraction of your biceps?  Which condition more closely matches an isotonic contraction?  What do isometric and isotonic mean, anyway?

 

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