LAB T O P I C 3 1
Investigating the Properties of Muscle and Skeletal Systems
Supplies
You should be able to describe in your own words
the following concepts:
Preparator's guide available on WWW at
http://www.mhhe.com/dolphin
Equipment
Compound microscopes
Intellitool Setups (Batavia, IL)
Physiogrip and software
Isolated, square wave stimulator
Computer
Sliding filament theory of muscle contraction
How a nerve impulse causes a muscle to contract
Basic structure of bone
As a result of this review, you most likely have
questions about terms, concepts, or how you will do
the experiments included in this lab. Write these
questions in the space below or in the margins of the
pages of this lab topic. The lab experiments should
help you answer these questions, or you can ask your
instructor during the lab.
Materials
Fetal pig
Dissection pans and instruments
Millipedes, spiders, crabs, or insects
Bird skeleton
Human skeleton
Frog skeleton
Fresh beef long bones split longitudinally
Dry long bones
Prepared slides
Skeletal muscle, longitudinal
Smooth muscle section
Cardiac muscle, longitudinal
Bone
Hyaline cartilage
Tendon
Earthworm, cross section
Neuromuscular junction (demonstration)
Student Prelab Preparation
Before doing this lab, you should read the introduction
and sections of the lab topic that have been scheduled
by the instructor.
You should use your textbook to review the
definitions of the following terms:
antagonistic muscles
appendicular skeleton
axial skeleton
endoskeleton
exoskeleton
extensor
flexor
hydrostatic skeleton
31-1
pelvic and shoulder girdles
sarcomere
smooth, cardiac, and
skeletal muscle
summation
tetany
threshold effect
twitch
Objectives
1. To compare the microanatomy of skeletal muscle to
that of smooth and cardiac muscle
2. To investigate the surface muscles in the fetal pig
3. To investigate the physiological concepts of
threshold, recruitment, and temporal summation
during muscle contraction
4. To view examples of hydrostatic skeletons and
exoskeletons
5. To observe the microanatomy of bone
6. To compare the endoskeletons of several vertebrates
Background
Simple small organisms, such as bacteria, algae, protozoa,
and sponges, are capable of movement without muscle systems. They use cilia or flagella to move through their aqueous environments. All higher animals, whether aquatic or
terrestrial, depend on muscle systems for movement and on
nervous systems to control that movement. These muscle
systems are also intimately associated with the skeletal system, which converts muscular contraction into effective
movement and locomotion.
417
Figure 31.1
Antagonistic muscle arrangements in
human limb. Contraction of human biceps flexes the forearm,
while contraction of the triceps extends the forearm.
Origins
Scapula
Origins
Flexors:
Biceps
brachii m.
Extensors:
Long head of
triceps brachii m
Brachialis m.
Lateral head of
triceps brachii m
Medial head of
triceps brachii m
Insertion
Creek
Radius
Ulna
During contraction, actin and myosin filaments interact
with each other, shortening the muscle in much the same
manner as a deck of cards is aligned after it is shuffled (see
fig. 31.4). The force for movement comes from the interaction of the filaments themselves rather than from a shortening of the filaments.
Along with skeletal muscle, two other types of muscle
tissue are found in animals. They function in movements
within the body, rather than in movement of the body from
one location to another. Smooth muscle tissue, also called
involuntary muscle, is found in the gut, blood vessels,
pupil, and reproductive system. Cardiac muscle is found in
the heart.
An integral part of any animal's locomotory system is
its skeleton. While the word skeleton usually brings to mind
the bony endoskeleton of vertebrates, other types of skeletons occur in the animal kingdom. Hydrostatic skeletons
are found in earthworms and other soft-bodied invertebrates in which the pressure of internal fluids gives shape
and allows the organism to move. Exoskeletons are found
among such diverse animals as nematodes, arthropods,
molluscs, and corals. This tough outer covering protects the
organism and supports it in an upright position while allowing for muscle attachment and movement.
Skeletons reflect adaptations to an organism's environment and lifestyle. Frogs and birds not only have limbs
modified to fit their environments, but also have bones that
show either thickening or shortening to fit their forms of locomotion. Consider the skeletal adaptations of a human,
horse, bat, and seal to their respective forms of locomotion.
Careful study of the skeleton by the trained observer can reveal much about an animal, because skeletons are excellent
examples of the biological principle that form reflects function. Skeletons serve many other functions besides locomotion. They protect soft tissue, serve as a reservoir for calcium and phosphate, and are sites of blood cell formation.
Skeletons are often the only parts of animals that survive from the past as fossils. Because the muscles attach to
the skeleton, it is possible to see which muscles might have
been highly developed and to speculate about how an extinct animal lived on a day-to-day basis.
Muscles are nearly always found arranged as antagonistic pairs. As a result, contraction of one member of the
pair causes an action, while contraction of the second member restores the body to its original position. In earthworms,
the longitudinal and circular muscles in the body wall are
antagonists. Contraction of the circular muscles elongates
the segments by forcing the fluid of the hydrostatic skeleton forward and back in each segment, but contraction of
the longitudinal muscles shortens the segments, leading to
an increase in girth. In antagonistic pairs, neuronal activity
is such that the contraction of one antagonist is usually accompanied by the relaxation of the second.
Figure 31.1 shows the antagonistic arrangement of
human muscles associated with an internal skeleton. Muscles that increase the angle between two bones at a joint are
called extensors. Flexor muscles are antagonistic to extenwmmmmmmmmmffmmmmmt
sors and decrease the angle between two bones. StraightenYou will study the anatomy and properties of
ing your elbow is extension and bending it is flexion.
and compare several types of skeletal systems
About 80% of the mammalian body mass is muscle.
Most of this is skeletal muscle (sometimes called striated
or voluntary muscle). Skeletal muscle is characterized by
a high degree of cellular organization. Muscle proteins,
Muscular System
consisting mostly of actin and myosin, occupy most of the
cytoplasm of the cell. These proteins are arranged in a seMicroscopic Anatomy of Muscle
ries of parallel filaments. Many cylindrical muscle cells
make up a muscle, and the contractile proteins in these Ty Obtain prepared slides of smooth muscle, cardiac muscle,
fibers are arranged in such a way that it gives a striated
and a longitudinal section of skeletal muscle. Compare the
microscopic pattern to the muscle.
tissues on your slide to figure 31.2.
418
Investigating the Properties of Muscle and Skeletal Systems
31-2
Figure 31.2
Three Types of Muscle, (a) Smooth muscle
has spindle-shaped cells, each with one nucleus (t) Skeletal
muscle cells are cylindrical and have many nuclei, (c) Cardiac
muscle is unique to the heart. Its striated cells join at connections
called intercalated disks. The cylindrical cells branch. Cardiac
and skeletal muscle cells are striated due to the orderly
organization of contractile proteins.
Smooth muscle (a)
Smooth Muscle Observe the smooth muscle slide first.
Note the shape of individual cells, the presence of nuclei,
and the absence of filament organization in the cytoplasm.
These muscle cells are spindle shaped, and their actin and
myosin are not organized in parallel arrays. Smooth muscle
is innervated by the autonomic nervous system and is not
under voluntary control. It responds to various hormones. Its
response is characterized by slow, rhythmic contractions. In
some cases, contractions arise spontaneously in smooth
muscles and are propagated along the length of the organ.
Sketch two or three examples of smooth muscle cells.
Nucleus
-Muscle
fiber
H
10 jam
Skeletal muscle (b)
10 nm
Cardiac muscle (c)
D- Skeletal Muscle Now examine the slide of skeletal
muscle under the medium-power objective and compare its
organization to that of smooth muscle. Note the substantial
differences. Identify the individual cylindrical fibers that
run the length of the tissue specimen on the slide. Find a
very thin area of the section that is only one fiber thick and
Nucleus
examine it under high power. On the periphery of each
fiber, you will see several nuclei. Each skeletal muscle
Muscle
fiber is multinucleated because it is formed by the fusion
fiber
of numerous smaller, uninucleated cells during embryonic
development. Thus a muscle fiber is really a composite of
several smaller cells. Though probably not visible, several
mitochondria are also present in this peripheral cytoplasmic
area. The central area of the cell consists of many parallel
fibers called myofilaments running lengthwise in the cell.
These fibers give a cross-banding appearance to the cytoplasm. Draw two or three of these cells.
Nucleus
10 urn
31-3
Muscle
fiber
Intercalated
disk
Investigating the Properties of Muscle and Skeletal Systems
419
To understand how your drawing relates to the strucFigure 31.3
Scanning electron micrograph showing
ture of a whole muscle, such as the biceps in your upper
axon ending at the neuromuscular junction on a muscle cell.
arm, look at figure 31.4. What most people call a muscle
contains thousands of muscle fibers arranged parallel to one
another and surrounded by a sheath of connective tissue.
Within a single muscle cell are many myofibrils, which
Axon
consist of contractile units called sarcomeres joined end to
end (fig. 31.4). Each sarcomere contains two types of filamentous proteins. Actin is the protein in thin filaments and
myosin is the protein in thick filaments. The actin filaments
at each end are anchored in the Z discs, which mark the
ends of the sarcomere. The myosin filaments are suspended
between and surrounded by actin filaments. It is the interdigitation of these filaments and the areas of overlap that
create the alternating light and dark banding patterns that
you saw on your slide of skeletal muscle.
During contraction, the thin filaments slide toward the
middle over the thick filaments, pulling the Z discs inward
and shortening the overall length of the sarcomere. Because
this process is repeated simultaneously in each sarcomere,
Neuromuscular
junctions
muscle cells can dramatically shorten.
In recent years, research has revealed the molecular
mechanisms involved in muscle contractions. When a nerve
impulse arrives at the neuromuscular junction, it causes
the release of a chemical called acetylcholine (fig. 31.3). It
depolarizes the muscle cell membrane and triggers an acLook at a slide of cardiac muscle through your comtion potential in the muscle cell. As the action potential
pound microscope. Would you say that it is similar to
moves along the muscle cell, it penetrates to the interior of
the cell via the T tubule system (fig. 31.4). Membrane de- & smooth muscle or to striated muscle? Why?
polarization at the Z disks causes the sarcoplasmic reticulum to release calcium ions into the sarcomere. The calcium ions allow the actin to react chemically with the
myosin filaments. This pulls the actin filament over the surface of the myosin filament. The coordinated effect of the
interaction between actin and myosin is the shortening of
the muscle.
Look at the demonstration slide of a neuromuscular
A junction that is available in the lab. What do you find interV esting about this slide?
Use your 43x objective and look closely at one muscle
fiber. Move the slide so that you can follow a single fiber
for some distance. You should find two things in cardiac
muscle that are different from what you saw in striated
muscle. What are these differences?
Cardiac Musc/e
4>As the name implies, cardiac muscle is found in the heart,
where it makes up the mass of the heart wall along with connective and nervous tissue. It is capable of rhythmic contraction which can be modulated by the pacemaker of the heart.
The contraction of heart muscle is not under voluntary control.
420
The actin and myosin components in cardiac muscle
are found in interdigitating linear arrays, as in skeletal muscle, but the fibers are capable of spontaneous contraction,
as in smooth muscle. The muscle cells are shorter than in
Investigating the Properties of Muscle and Skeletal Systems
31-4
Figure 31.4
Skeletal muscle structure and function. A muscle fiber or cell contains many myofibrils, consisting of sarcomeres.
When the myofibrils of a muscle fiber contract, the sarcomere shortens as the actin filaments move toward the center of the
sarcomere and Z discs move closer.
bundle of
muscle fibers
T tubules
nucleus
sarcoplasmic
reticulum
calcium
storage sites
sarcoplasm
skeletal
muscle
fiber
one myofibril
A muscle fiber has
many myofibrils.
sarcolemma
A myofibril has
many sarcomeres.
cross-bridge
myosin
actin
31-5
Investigating the Properties of Muscle and Skeletal Systems
421
skeletal muscle, often branch, and are joined end to end by
tight junctions, called intercalated disks, which electrically couple the cells and allow contraction to spread from
cell to cell independent of the nervous system.
6
Starting at the head, identify the major muscles indicated in figure 31.5.
1. The latissimus dorsi is a broad muscle running obliquely
around the sides of the thoracic region. It originates on the
vertebrae and inserts on the proximal end of the humerus.
The latissimus dorsi is involved in moving the foreleg.
Fetal Pig Superficial Muscles
2. The trapezius originates on the occipital bone of the
skull and from the first ten vertebrae and inserts on the
scapula or shoulder blade. This broad muscle draws the
scapula medially. When this muscle contracts, how
does the leg move?
This dissection may be done by students or by the instructor as a demonstration, depending on the time available and
the emphasis of the course on gross anatomy.
Three terms are used to describe the anatomical orientations of muscles: origin, belly, and insertion. The origin
is the end attached to the less mobile portion of the skeleton. The belly is the central part of the muscle, and the insertion is the end of the muscle attached to the freely moving part of the skeleton. Tendons are fibrous connective
tissues that connect muscles to the skeleton.
If your fetal pig is not already skinned, skin it—being
careful not to tear away muscle as you remove the skin.
Use a probe or finger to separate the two. Under the skin,
there may be adipose (fat) tissue, which should be removed
to reveal the muscles. When the skin is removed, dry the
carcass with paper towels to improve viewing. In young
fetal pigs, the muscles are not fully developed and are often
tightly connected to the skin so that they are torn during
skinning. Identification will be difficult.
Figure 31.5
The major muscles of the fetal pig.
Deltoideus
Latissimus dorsi
Trapezius
Tensor fasciae latae
Gluteus medius
Biceps femoris
Position of
gastrocnemius
Brachiocephalic
Sternocephalicus
"
'
Transversus
Tendon to
gastrocnemius
Internal oblique'
422
Investigating the Properties of Muscle and Skeletal Systems
31-6
•
§-*>
«
3. The brachiocephalic muscle extends obliquely as a
flat belt from the back of the skull (the occipital bone)
to the foreleg (distal end of the humerus). It is involved
in moving the leg anteriorly.
4. The sternocephalic is a long muscle below the
brachiocephalic muscle. It controls the flexing of the
head. It originates on the sternum and inserts on the
mastoid process of the skull by means of a long tendon.
Remove the parotid salivary gland to see the tendon.
5. The brachialis is a small muscle located in the angle
formed by the flexed foreleg. It originates on the
humerus and inserts on the ulna. What is its function?
13. The biceps femoris is a large muscle making up most of
the back half of the thigh. It originates on the pelvis and
inserts on the lower femur and upper part of the tibia.
14. The gastrocnemius is the large muscle of the calf,
originating on the lower end of the femur and attaching
to the heel by means of the Achilles tendon. Its action
extends the foot. The soleus muscle lies close to the
gastrocnemius and has a similar function.
15. The digital flexors and extensors originate on the tibia
and fibula and insert on the metatarsals. What are their
functions?
6. The deltoid is a broad shoulder muscle originating on
the scapula and inserting on the humerus. It aids in
flexing the humerus.
7. The extensors are several muscles in the lower foreleg
that extend and rotate the wrist and digits.
8. The triceps (brachii) is a large muscle making up
practically the entire outer surface of the forelimb. It
originates on the humerus and inserts on the proximal
end of the ulna. When it contracts, the forelimb extends.
9. The external oblique muscles make up the outer wall of
the abdomen and run obliquely from the ribs to a ventral
longitudinal ligament along the ventral midline.
Contraction of these muscles constricts the abdomen.
10. The internal oblique fibers lie just under the external
oblique muscle and run almost at right angles to them.
Contraction of these fibers also results in abdominal
constriction.
1 1 . The tensor fasciae latae is the most cranial of the
thigh muscles. It originates on the pelvis and continues
ventrally as a thin, triangular muscle until it becomes a
sheet of connective tissue called the fasciae latae,
which inserts on the kneecap and extends the leg.
12. The gluteus medius is a thick muscle covered by the
tensor fasciae latae in the hip region. If the overlying
muscle is removed, its origin on the hip and insertion
on the femur can be seen. What action does it cause?
16. The peroneus muscles have origins and insertions
similar to digital muscles. They are involved in moving
the whole foot.
31-7
Physiology of Muscle
This part of the lab may be performed by the instructor as a
demonstration or by students working in groups of four or
more, depending on the time and equipment available.
Overview of Experiment
In this section of the lab, you will investigate four properties of human muscles: threshold stimulus, recruitment,
temporal summation, and tetany. You will use special
equipment and software that allows a computer to collect
and analyze data. The experimental subject(s) will be a volunteer member(s) of your class. Anyone who has heart
problems or does not wish to participate directly in this experiment should not be a subject. They can operate the
computer or record notes during the experiment.
To do this experiment, you need to make adjustments
to four major pieces of equipment—a stimulator, a transducer, an interface unit, and a computer running special
software. A stimulator is an electronic device that produces a pulse of electricity that can be varied by volts
(strength), duration of the pulse (length), and frequency
(number of pulses per second). The transducer is a device
that converts the movement of a trigger in a pistol handle
into an electrical resistance that can be recorded. The interface is a box that connects various cables together into a
single lead that is connected to a port of your computer.
The software allows your computer to record raw data
from the transducer and process the data, converting it into
graphical displays. Before you start investigating the biology of muscle, this equipment must be calibrated.
Investigating the Properties of Muscle and Skeletal Systems
423
the deflection of the trace on the computer screen as recruitment occurs?
Use the same setup as before. Be sure to use NEW
from the FILE menu to select a new data file.
Start with the previously determined threshold voltage
and record a twitch. Slowly increase the voltage and continue recording twitches. Continue this procedure until a
maximum height of contraction is reached and further increments of stimulus intensity do not evoke stronger contrac& tions. What is the voltage at which no further increase in
strength of contraction occurs?_
Turn off the stimulator.
If excitable cells exhibit an all-or-none response when
exposed to a threshold stimulus, explain why the height of
contraction increased with stimulus strength above the
threshold? (Hint: Consider the phenomenon of recruitment.)
Temporal Summation and Tetany
far in your investigations of muscle you have used a low
frequency of stimulation. In this section, you will investigate the effects of increasing frequency of contraction on the
strength of muscle contraction. With increasing frequency
of contraction, there is insufficient time for the muscle to
relax before the next stimulating impulse arrives. Consequently, the contractions begin to summate with a new contraction starting in a partially contracted muscle. This phenomenon is called temporal summation, and when the
muscle is fully contracted and cannot relax between stimuli,
tetany occurs. What would you hypothesize is the effect on
the strength of muscle contraction? State your hypothesis.
Once this base is established, gradually increase the
frequency of stimulation over a 10-second interval. Can
you see individual contractions at low frequencies?
At higher frequencies?
What happens to the strength
of contraction as the frequency of stimulation increases?
If the strength of contraction is so strong that the trigger reaches the end of its travel, stop the experiment and
change the spring in the Physiogrip to a stronger one. Erase
the previous trace from memory in the computer and repeat
the experiment.
When the strength of contraction no longer increases
with increasing frequency of stimulation, stop the experiment and turn off the stimulator.
Analyze the data that you have collected in the following way. First, print a copy of the screen by choosing
PRINT from the FILE menu. This will provide a record for
any report that you may have to write.
From the FILE menu, select ANALYZE and then DISPLACEMENT. You should see a record of the contractions
on the screen and at the top should be a series of hash
marks indicating how often a stimulus was given. Using the
ANALYZE cursor, determine the frequency of stimulation
just before temporal summation started.
What is the value in number per second?
Now
repeat this measurement at the point where tetanic contraction was reached. What is the frequency of stimulation that
results in tetany?
Measure the height of an individual twitch at the beginning of this experiment. What is it?
Now measure the height of contraction reached in
tetany. What is it?
What is the percent change due to tetany?
Skeletal Systems
Skeletal systems support and protect an animal and make locomotion possible. In some animals, especially those with
endoskeletons, the skeleton is a storage site for calcium and
phosphate ions needed in metabolism. Three types of skeletal
systems are found in the animal kingdom: hydrostatic (sometimes called hydraulic), exoskeletons, and endoskeletons.
Types of Skeletons
Hydrostatic Skeletons
Test your hypothesis, using the following procedure.
Choose NEW from the FILE menu to create a new data
file. Turn on the stimulator. Have the subject grasp the
Physiogrip and put a slight pressure on the trigger to raise
the baseline a few millimeters. Set the stimulus parameters
to 10 msec duration, frequency to 1 per sec in continuous
mode, and a voltage that gives a single contraction.
426
Many soft-bodied invertebrates, such as roundworms,
cnidarians, and annelids, do not appear to have specialized,
differentiated skeletal systems. However, close examination reveals that the body wall muscles act on the incompressible fluids in the body cavity and intracellular spaces
to facilitate very effective movement and support. Such
skeletal systems are called hydrostatic skeletons.
Investigating the Properties of Muscle and Skeletal Systems
31-10
Obtain a microscope slide of a cross section of an
earthworm. Look at it first under the low-power objective
and note the general anatomy of the animal by comparing
the slide to figure 21.9.
The external surface of the earthworm is covered by a
highly flexible cuticle secreted by the underlying cells of
the dermis. The fibrous proteins of the cuticle protect the
worm and help maintain its form. Some cells in the dermis
secrete mucus, which lubricates the passage of the earthworm through the soil and also maintains a moist surface
through which respiratory gases are exchanged.
Note that the body wall is made up of two layers of
muscles: an outer circular set and a featherlike inner longitudinal set. Since the longitudinal set runs parallel to the
long axis of the body, it will appear in cross section in the
slide. Also note the well-developed body cavity, which is
filled with fluid in live animals.
What happens to the worm's shape when the circular
muscles contract? (Consider the effects of both the muscles
and internal fluids.)
Exoskeletons
Exoskeletons are characteristic of several animal phyla. In
addition to supporting the animal, exoskeletons prevent
water loss, protect the organs, and serve as points of attachment for muscles. Animals in the phylum Arthropoda,
which includes crayfish, insects, spiders, and millipedes,
have a well-developed exoskeleton composed of a complex
polysaccharide called chitin combined with proteins to
give flexibility. Several examples of these animals should
be available in the laboratory.
Look at an insect through your dissecting microscope
and note the segmentation of the exoskeleton. The head
and thorax are composed of several fused body segments.
In insects, the thorax bears the walking legs and wings. The
segments should be clearly visible in the abdomen.
An insect's exoskeleton is made up of hardened plates
called sclerites. In the head and thorax, the sclerites are
rigidly joined to one another along suture lines. In the abdomen, the dorsal and ventral sclerites are enlarged and
joined to one another by pleural membranes, which correspond to thin, reduced vestiges of the lateral sclerites. Similar membranous areas are found between adjacent dorsal or
ventral sclerites. These thin, flexible areas allow the animal
to expand, contract, and curl its abdomen. Flexible membranous areas are also found between the joints of the various appendages.
What happens to the worm's shape when the longitudinal muscles contract? (Consider the effects of both the
muscles and internal fluids.)
The body cavity of the earthworm is divided into compartments, corresponding to each segment, by cross walls
called septa. These prevent fluids from "sloshing" from
one end of the worm to the other and allow earthworms to
make a variety of movements with fine gradations.
Although they are not part of the hydrostatic skeleton,
you should note the spinelike setae in the body wall. Muscles attached to each seta extend or retract them. When extended they project into the soil and anchor the worm. Describe how you think an earthworm could crawl forward
using its setae, circular muscles, and longitudinal muscles.
Endoskeletons
Defined as an internal supporting system of hardened material, endoskeletons are highly characteristic of vertebrates.
Cartilage and bone make up the vertebrate endoskeleton.
You will start your study of endoskeletons by examining
the structure of bone.
Bone Structure
xamine a fresh beef femur that has been cut longitudinally
in half. The central shaft of a long bone such as this one is
called the bone's diaphysis, while the enlarged ends are the
bone's epiphyses (fig. 31.8). Though difficult to observe in
31-11
Investigating the Properties of Muscle and Skeletal Systems
427
Figure 31.8
Structure of a bone: (a) a bone in partial longitudinal section; (b) scanning electron micrograph of cancellous
(spongy) bone; (c) scanning electron micrograph of Haversian canal (HC) systems in compact bone. Canals allow blood vessels to
pass into bone. Bone cells are located in the lacunae (La), (c) From R.G. Kessel and R.H. Kardon. Tissues and Organs: A Text-Atlas of
Scanning Electron Microscopy. 1979. W.H. Freeman and Co.
Epiphyseal disks
Articular cartilage
— Proximal
epiphysis
Spongy bone
Space occupied by
red marrow
Compact bone
Medullary cavity
— Diaphysis
Yellow marrow
(b)
Remnant of
epiphyseal disk
Spongy bone
Compact bone
Periosteum —
- Distal
epiphysis
(a)
Femur
older bones, a narrow zone of cartilage, the epiphyseal
disk (growth center) of the bone, separates the epiphysis
from the diaphysis.
The rounded projection from the upper end of the bone
(fig. 31.8a) is called the head, and it articulates with the acetabulum, a depression where all three pelvic bones intersect. Condyles (rounded, articular prominences) are located
on the lateral and medial sides of the distal end of the
femur. With which bone(s) do they articulate?
428
Find the periosteum, the tough connective tissue layer
surrounding the diaphysis. The surfaces of the condyles are
covered by a glassy smooth articular cartilage, which,
along with synovial fluid, reduces frictional erosion between articulating bones at the joints. Residues from the
ligament that held the joint together may also be visible.
On the outer surface of the bone, find the narrow
ridges called crests and the small, round, elevated tubercles,
where muscles attach by tendons to the bones. The surface
of the bone is perforated by openings called foramina
(sing, foramen) that allow blood vessels and nerves to penetrate the bone.
The center of the bone is a hollow chamber called the
medullary cavity. It is filled with marrow. Red marrow is
where new red blood cells are formed, but in older animals
much of the marrow is fatty yellow matter, which no longer
produces blood cells.
Investigating the Properties of Muscle and Skeletal Systems
31-12
Compare the structure of the bone in the diaphysis with
that in epiphysis. Compact bone is very dense, whereas
spongy bone has many interior cross braces. Spongy bone
is less dense than compact bone.
Microanatomy of Bone
V4>Obtain a prepared slide of ground bone and examine it
under low power. Using figure 31.8c as a guide, find a
Haversian canal. These canals allow nerves, blood vessels,
and lymphatics to penetrate bone. Note the chambers,
called lacunae, arranged in concentric circles around the
canal. Osteocytes, mature bone cells, line in these spaces
and are responsible for depositing and removing calcium
salts. Their activity is regulated by hormones. Note the
canaliculi that radiate from the lacunae. They are transportation networks and allow osteocytes to extend their cytoplasm and form intimate contact with the bone matrix.
Figure 31.9
(a) Skeleton of frog (ventral view), including
(b) ventral view of pectoral girdle.
Vomerine teeth
Sphenethmoid
Squamosal
Maxillary
Mandible
Orbit
Phalanges
Metacarpals
Carpal
Episternum
Suprascapula
Scapula
Radioulna
Sacral vertebra
Comparative Vertebrate Endoskeletons
The vertebrate skeleton has two components: the axial
skeleton, consisting of the skull and vertebral column; and
the appendicular skeleton, which includes the pelvic and
pectoral girdles as well as the bones of the appendages.
Skeletal Comparisons
the laboratory, you will observe the skeletons of three
vertebrates: a frog, a bird, and a human (figs. 31.9-31.11).
The task before you is to determine how these skeletons are
similar and how they are different. For the differences, you
should offer explanations of how these differences correlate
with locomotion or life style. For each skeleton you should
be able to quickly identify the axial and appendicular skeletons. Then you should be able to find and identify the bones
listed below.
Axial skeleton
Skull
cranium (fused bones encasing brain and sense
organs) consisting of the following major bones:
frontal
parietal
temporal
occipital
facial bones consisting of the following major bones:
zygomatic
maxilla
mandible (lower jaw), the only movable bone in
skull
Vertebral column, which supports and protects the
spinal cord. Cartilaginous discs are found between
the vertebrae in living animals. The vertebral
column is divided into five regions:
cervical vertebrae (neck)
thoracic vertebrae (on which the ribs articulate)
lumbar vertebrae (abdominal region)
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Tibiofibula
Astragalus"!
Calcaneumf
Metatarsals
Phalanges
(a)
Suprascapula
Episternum
Clavicle
Scapula
Glenoid fossa
Coracoid
Sternum
Xiphoid process
(b)
Investigating the Properties of Muscle and Skeletal Systems
429
Figure 31.10
Skeleton of a bird.
**
Parietal
Supraoccipital
Frontal
Orbit
Atlas
Nasal
Cervical vertebrae
Maxilla
Premaxillary
Metacarpals
Mandible
Phalanges
Hyoid apparatus
Radius
Ulna
Humerus
Scapula
Rib
Clavicle
Coracoid
Ilium
Caudal vertebrae
Ischium
Pubis
Tarsometatarsus
Phalanges
sacral vertebrae (enclosed by pelvic girdle)
caudal vertebrae or tail (coccyx in human)
Ribs (attached and floating)
Sternum
Xyphoid process
Appendicular skeleton
Pectoral girdle consisting of:
clavicle (collarbone)
scapula (shoulder blade)
coracoid
Forelimbs consisting of:
humerus (long bone of lower limb)
radius (long bone of lower limb, which forms a
pivot joint with the ulna and is also part of the
hinge joint of the elbow)
ulna (other long bone of lower arm, forming hinge
joint at elbow)
430
Investigating the Properties of Muscle and Skeletal Systems
carpals (small bones of wrist)
metacarpals (bones of palm)
phalanges (finger bones)
Pelvic girdle consisting of:
ilium
ischium
pubis
Hind limbs consisting of:
femur (long bone of thigh)
patella (kneecap)
tibia (larger of two long bones of lower limb)
fibula (smaller long bone of lower limb)
tarsals (bones of ankle)
calcaneus (heel bone)
metatarsals (slender foot bones)
phalanges (toe bones)
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Figure 3 1 . T l
Human skeleton.
Occipital
bone
Skull—
Shoulder
girdle
Clavicle
-Scapula
Costal
cartilages
Pelvic
girdle
Coxa—
bone
Phalanges
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Investigating the Properties of Muscle and Skeletal Systems
431
Compare a bird skeleton and a human skeleton. List w
List the skeletal differences between a frog and a
five skeletal differences associated with locomotion and exhuman that are associated with locomotion.
plain how each is involved in locomotory movement. Differences will include fusions, increase in size, reduction in
size, but not the appearance of new bones.
3. Both recruitment and temporal summation lead to
greater force of muscle contraction. Explain what is
happening in both of these phenomena.
4. Describe the structure of a bone, such as the humerus,
at the macroscopic and microscopic levels.
5. Describe the major common features of skeletons
found in all vertebrates.
6. "Form reflects function" is a statement that applies to
the skeletal system. How does the form of the
vertebrate skeleton relate to the means of locomotion
in a frog compared to a human? In a bird compared to
a human?
Learning Biology by Writing
Write a lab report that describes your experiments with
human muscles. It should have three sections in the results:
Determining threshold
Demonstrating motor unit recruitment
Demonstrating temporal summation and tetany
The discussion section should describe how recruitment and summation are important in graded responses
such as are used in sports or playing a musical instrument.
Your instructor may ask you to answer the Lab Summary and Critical Thinking Questions that follow.
Critical Thinking Questions
Internet Sources
The disease rickets affects the human skeletal system.
Use GOOGLE to search the WWW to learn what this
disease is. Where is it common? Is it found in the
U.S.? How can it be treated?
Lab Summary Questions
1. What evidence do you have that smooth, cardiac, and
skeletal muscle cell are different? Describe. Give
examples of where you would find each in your body.
2. Describe the all-or-none response in muscle cells. How
is it possible for us to have graded responses in our
muscles if muscle cells respond in an all-or-none
manner to stimuli?
432
Investigating the Properties of Muscle and Skeletal Systems
1. About 99% of the body's calcium is found as
calcium phosphate salts in bone tissue. The calcium
in plasma is in an ionic form, Ca++. Although the
level of Ca++ in the blood and tissues is closely
regulated by parathyroid hormone and calcitonin,
imbalances in Ca++ can occur. What effect would an
elevated Ca++ concentration have on muscle activity?
What effect would a Ca++ deficiency have on muscle
activity?
2. As can be seen in figure 31.10, the skeleton of a bird
is modified for flight. Aside from the size and
arrangement of the bones in the skeleton, what other
feature of its bones might affect the ability of a bird
to fly?
3. How do scientists deduce the appearance of hominids
or dinosaurs when all they have to study are a few
bone fragments?
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