Transcript What is a muscle fiber (cell)

March 22, 2016

Journal: When you are kicking a ball,
what muscles are the agonists and what
are the antagonists?

HAND IN YOUR LAB REP
Muscle Anatomy
Macroscopic
Anatomy
- Tendons connect
the muscles to bone
and are made up of
numerous fascicles
all clustered
together
surrounded by
epimysium
-Fascicle: a bundle
of muscle fibers
all put together
surrounded by
perimysium
-Muscle fiber
(muscle cell): a
cluster of
myofibril
surrounded by
endomysium
-Myofibrils: long
proteins chains
that make up
muscle cells
- Myofilaments:
filaments within
the myofibrils
Muscle Coverings
Deep Fascia –surrounds the muscles;
allows for communication and
connection between muscles
 Epimysium - under the fascia;
decreases the friction between muscles
 Perimysium –groups muscle fibers into
bundles
 Endomysium –encloses a single muscle
fiber

What is a muscle fiber (cell) made out of?
Microscopic Anatomy:
• Cell membrane - sarcolemma.
• Multiple nuclei and mitochondrion are
found within the cell
• Cytoplasm, called sarcoplasm, is almost
completely filled with long protein chains
called myofibrils.
What does each myofibril look like?
Myofibril Structure
• Each myofibril has an alternating light (I) and
dark (A) band.
• Each light I band has a darker midline called a Z
line.
• Each dark A band has a lighter central area called
the H zone.
• Middle area of the H zone
is called the M-line.
• One Z line to another Z line
is called a Sarcomere.
Let’s take a closer look at a Sarcomere
• Composed of long proteins called myofilaments.
2 Types:
1.Thick (myosin) filament – filled with myosin
protein heads (act like hands).
2.Thin (actin) filament – made of a protein called
actin which allows myosin heads to grab onto it.
Let’s take a closer look at Myosin
Let’s take a closer look at Actin
Macroscopic Anatomy of Skeletal Muscle
Review
4
7
1
6
5
2
3
March 24, 2016
How do muscles work?
Contraction & Relaxation
“The
Sliding Filament
Theory”
Shortening of
sarcomeres = muscle
shortening
1. Nervous system tells a muscle to contract by
releasing a chemical messenger acetylcholine (Ach)
into the synaptic cleft
2. This causes sodium ion channels to open
and sodium rushes into the muscle fiber and
excite the muscle producing muscle action
potential.
3. Increased sodium levels inside the muscle
fiber causes the Sarcoplasmic Reticulum
(SR) to release calcium into the sarcoplasm.
SR is a specialized organelle in muscle cells
used to store calcium.
4. The presence of calcium causes ATP to
interact with the actin and myosin filaments
by changing their shape.
5. Myosin heads make crossbridges to actin
filaments which pulls the sarcomeres
together, contracting the muscle.
6. When an enzyme removes the chemcial
messanger ACh from receptors on the
sarcolemma, ATP detaches myosin heads
and calcium is pumped back into the SR and
the muscle relaxes
What happens to our muscles when we die?
Ca+2 leaks out and muscle contract – no ATP
to release contraction = Rigor Mortis