Lab 7 The Muscular System BIO201L
Student Name: Gloria Arajulu
Access Code (located on the lid of your lab kit): AC-OF2X1AP
Pre-Lab Questions
1. How do banding patterns change when a muscle contracts?
During muscle contraction, the banding patterns change due to the thick
filaments being pulled towards the center of the sarcomere. The actin slides past the myosin
which changes the appearance of band thickness without changing the size of the
myofilaments.
2. What is the difference between a muscle organ, a muscle fiber, myofibril
and a myofilament?
- Muscle Organ: A muscle organ refers to a whole muscle made up of multiple bundles of
muscle fibers, blood vessels, nerves, and connective tissue
- Muscle Fiber: A muscle fiber is a single muscle cell, also known as a muscle cell, responsible
for muscle contraction.
- Myofibril: Myofibrils are long, thread-like structures within muscle fibers that
consist of protein filaments (myofilaments) and are responsible for muscle contraction.
- Myofilament: Myofilaments are the smallest protein filaments within myofibrils,
consisting of actin and myosin, which slide past each other during muscle contraction.
3. Outline the molecular mechanism for skeletal muscle contraction. At what point is ATP
used and why?
Ca2+ is released from storage in the sarcoplasmic reticulum -> Intracellular Ca2+
binds with troponin -> Tropomyosin changes positions and exposes the myosin binding sites
on the actin-> myosin heads bound to ADP and P attach to actin and forms cross-bridges ->
ADP and P are released, which alter the shape of the myosin head and cause a sliding motion
moving actin towards the center of the sarcomere -> ATP binds to myosin -> Myosin ATP
hydrolze ATP into ADP and P, which provide energy to return the myosin head to it’s
original position -> ADP and Premain bound to the myosin head -> Ca is pumped back into
the sarcoplasmic reticulum.ATP is used as chemical energy that is converted into mechanical
energy
4. Explain why rigor mortis occurs.
Rigor mortis occurs after death due to the depletion of ATP (adenosine
triphosphate), which is the energy source required for muscle relaxation. Without ATP, the
myosin heads in the muscle cells remain bound to actin filaments, causing the muscles to
become stiff and rigid. This stiffness typically starts to develop a few hours after death, peaks
around 12-24 hours, and gradually dissipates over the next 1-2 days as the muscle tissues
begin to decompose. Rigor mortis is a natural post-mortem process and helps forensic
investigators determine the time of death in certain cases.
.
Experiment 1: Tendons and Ligaments
,Lab 7 The Muscular System BIO201L
Post-Lab Questions
1. Label the arrows in the slide images below based on your observations from
the experiment.
, Lab 7 The Muscular System BIO201L
A- Chondrocytes
B- collagen
C- nucleus
D- skeletal muscle fibers
E- nuclei
F- collagen fibers
Student Name: Gloria Arajulu
Access Code (located on the lid of your lab kit): AC-OF2X1AP
Pre-Lab Questions
1. How do banding patterns change when a muscle contracts?
During muscle contraction, the banding patterns change due to the thick
filaments being pulled towards the center of the sarcomere. The actin slides past the myosin
which changes the appearance of band thickness without changing the size of the
myofilaments.
2. What is the difference between a muscle organ, a muscle fiber, myofibril
and a myofilament?
- Muscle Organ: A muscle organ refers to a whole muscle made up of multiple bundles of
muscle fibers, blood vessels, nerves, and connective tissue
- Muscle Fiber: A muscle fiber is a single muscle cell, also known as a muscle cell, responsible
for muscle contraction.
- Myofibril: Myofibrils are long, thread-like structures within muscle fibers that
consist of protein filaments (myofilaments) and are responsible for muscle contraction.
- Myofilament: Myofilaments are the smallest protein filaments within myofibrils,
consisting of actin and myosin, which slide past each other during muscle contraction.
3. Outline the molecular mechanism for skeletal muscle contraction. At what point is ATP
used and why?
Ca2+ is released from storage in the sarcoplasmic reticulum -> Intracellular Ca2+
binds with troponin -> Tropomyosin changes positions and exposes the myosin binding sites
on the actin-> myosin heads bound to ADP and P attach to actin and forms cross-bridges ->
ADP and P are released, which alter the shape of the myosin head and cause a sliding motion
moving actin towards the center of the sarcomere -> ATP binds to myosin -> Myosin ATP
hydrolze ATP into ADP and P, which provide energy to return the myosin head to it’s
original position -> ADP and Premain bound to the myosin head -> Ca is pumped back into
the sarcoplasmic reticulum.ATP is used as chemical energy that is converted into mechanical
energy
4. Explain why rigor mortis occurs.
Rigor mortis occurs after death due to the depletion of ATP (adenosine
triphosphate), which is the energy source required for muscle relaxation. Without ATP, the
myosin heads in the muscle cells remain bound to actin filaments, causing the muscles to
become stiff and rigid. This stiffness typically starts to develop a few hours after death, peaks
around 12-24 hours, and gradually dissipates over the next 1-2 days as the muscle tissues
begin to decompose. Rigor mortis is a natural post-mortem process and helps forensic
investigators determine the time of death in certain cases.
.
Experiment 1: Tendons and Ligaments
,Lab 7 The Muscular System BIO201L
Post-Lab Questions
1. Label the arrows in the slide images below based on your observations from
the experiment.
, Lab 7 The Muscular System BIO201L
A- Chondrocytes
B- collagen
C- nucleus
D- skeletal muscle fibers
E- nuclei
F- collagen fibers
