Spaulding, Kelsey
October 11, 2013
A&P Lab
Muscle
Laboratory Report
1. Pre-lab assignment? (10 points)
2. Cat cadaver dissection quality (5), completeness (5) and identification of muscles
(30) posed by TA during the lab. (40 points)
3. Skeletal muscles work in antagonistic pairs. For example, one muscle provides
flexion while the other operates extension. Select three pairs of muscles that you
dissected in lab and list the location, origin, and insertion of these muscles. Next,
provide the actions performed by these muscles and why having antagonistic pairs
is important to their function. (10 points)
a. Muscles can only pull, not push. In order to allow movement of an animal,
many muscles work in antagonistic pairs. The biceps brachii and triceps
brachii are an example of this. The biceps brachii’s origin is at the
supraglenoid tubercle of the scapula and the insertion is at the radial
tuberosity. The triceps brachii has three heads, the long, lateral, and
medial head. The long head’s origin is at the caudal border of the scapula,
the lateral head’s origin is at the lateral surface of the humerus, and the
medial head’s origin is at the medial surface of the humerus. All three
heads have a point of insertion at the olecranon process. The biceps
brachii flexes the elbow and extends the shoulder, where the triceps
brachii extends the elbow. Although the biceps brachii can pull the
forelimb towards the body of the cat as the elbow flexes, the triceps
brachii is what allows a cat to extend the elbow back towards the ground.
Another example of an antagonistic pair is the coroacobrachialis and
supraspinatus. The coroacobrachialis’ origin is at the coracoid process of
the scapula and the point of insertion is the proximal shaft of the humerus.
The supraspinatus’ origin is at the supraspinous fossa of the scapula and
the insertion is at the greater or lesser tubercule of the humerus. The
coracobrachialis flexes the shoulder joint, where the supraspinatus extends
the shoulder joint. These two muscles work as an antagonistic pair to
allow use of the shoulder joint. The last example of a antagonistic pair that
I have is the semimembranosus and sartorius. The semimembranosus’
origin is at the ischial tuberocity and the insertion is at the posterior
surface of femur and tibia. The sartorius’ origin is at the ilium and the
insertion is at the knee. The semimembranosus extends the hip, where the
sartorius flexes the hip, working as an antagonistic pair.
4. Describe the steps from the beginning to the end of muscle contraction, be sure to
begin with the neural signal traveling down the motor neuron and end with the
factors that cause contraction to cease. You can use hand drawn images to
demonstrate what happens if this helps you. (10 points)
a. First an action potential runs into the motor neuron, causing a
depolarization of neuromuscular junction. There are calcium ions released
into the terminal button of the nerve, causing a release of acetylcholine
into the synapse. The acetylcholine binds to the ligand-gated nicotinic
acetylcholine receptors on the motor end plate and allows an influx of
sodium. With the change in voltage, voltage-gated ion channels open and
allow more sodium to come into the cell. This causes a depolarization of
the sarcolemma, and the acetylcholine degrades. The depolarization allows
an action potential to be spread down the t-tubules, activating the
sarcoplasmic reticulum to release calcium into the sarcolemma. The
calcium binds to troponin C and induces a conformational change in the
troponin group that moves it away from the binding site of the myosin
head to the actin. Actin and myosin then create a cross-bridge that
generates force, allowing for contraction. ATP then breaks the crossbridge, removing the ADP and inorganic phosphate present and freeing
the myosin head. The myosin head is then phosphorylated and is cocked
for the next contraction. Once the action potential has ceased, the
sarcoplasmic reticulum pumps the calcium back inside through
calsequestrin, removing the calcium from the sarcoplasm.
5. Name the three major muscle fiber types discussed in your lab/lecture and
describe the color, contraction speed, and oxidative capacity of each fiber type.
Additionally, give an example of a motion/action where each type of fiber would
be used. (10 points)
a. The first type of muscle fiber is type 1, which is red, has a slow
contraction speed, and is aerobic with a high oxidative capacity. This type
of muscle fiber is found in the postural muscles. Type 2A is intermediate
in color, has a moderate contraction speed, is both anaerobic or glycolytic
(medium oxidative capacity), and is found in the legs of marathon runners,
as it is slow to fatigue. Type 2B is a white muscle fiber with a fast
contraction speed. It is anaerobic and glycolytic (low oxidative capacity)
and is found in the leg muscles of sprinters.
6. Describe what causes rigor mortis in muscles post-mortem, be sure to explain the
biochemistry. Hint: ATP!! (5 points)
a. After the myosin head attaches to the actin filament, the muscle contracts.
In a person who is alive, ATP is used to detach the myosin heads from the
actin filament in order to allow the myosin head to recock and attach to the
next G actin globule. When a person dies, they stop metabolizing ATP.
Without ATP, the myosin head stays attached to the actin filament and the
muscle stays contracting, causing rigor mortis.
7. Describe the function of each of the following muscle proteins and why they are
important to normal muscle function: actin, myosin, troponin, tropomyosin, titin,
and nebulin. (10 points)
a. Actin – contractile protein; used for contraction, create force and tissue
movement; binds to myosin head.
b. Myosin – contractile protein; used for contraction, create force and tissue
movement; head binds to binding sites on actin and pulls the actin towards
the M-line, shortening the sarcomere.
c. Troponin – regulatory protein; made of three subunits, TnT, TnI, and TnC;
keeps tropomyosin in a position to block myosin binding sites; when
bonded by calcium, has a conformation change, taking tropomyosin with it
to allow for myosin-actin binding.
d. Tropomyosin – regulatory protein; double-stranded and each protein
covers seven myosin binding sites of the actin filament at rest; moved by
troponin.
e. Titin – structural protein; extends from the Z line to the M line and
anchors thick filaments to the Z and M lines; provides stabilization; elastic
and returns muscle to resting length after stretching.
f. Nebulin – structural protein; anchors thin filaments and connects
myofibrils to each other throughout the muscle cell
8. Where is the Psoas major muscle and what it its function/action? Why is this
muscle important in livestock animals used for consumption? (5 points)
a. The Psoas major muscle flexes and rotates the thigh at the hip and flexes
the vertebral column. The origin is from the lumbar vertebrae and the
insertion is on the femur. This muscle is known as the “tenderloin” or
“filet mignon,” which is a tender cut of meat that comes from livestock
used for consumption.