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.
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?
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
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.
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..
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?
Be sure that you back to top=