1. Topic 7-3: Skeletal Muscle Fibers
By: Kaylee Wade & NiKaya DeWald

2. What it is Skeletal muscle fibers
Diameter of 100 micrometers
Length of up to 60 cm
A multinucleate containing hundreds of nuclei

3. Structures Sarcolemma- another name for the plasma membrane
Sarcoplasm- another name for cytoplasm
Transverse tubules (t tubules)- openings scattered across the surface of the sarcolemma which lead into a network of narrow tubules
Used for contraction

4. Myofibrils
These are branches of t tubules that circle cylindrical structures
1-2 micrometers in diameter
Length is the entire length of a muscle fiber
Bundles of thick and thin myofilaments also protein filaments (actin/myosin)

5. Sarcoplasmic Reticulum
A specialized form of Smooth ER
They have terminal cisternae
Which expand in chambers of the SR
The triad are transverse tubule sandwiched between terminal cisternae

6. Sarcomeres Microfilaments organized into repeating functional units
There are approx. 10,000 arranged end to end in a myofibril
They lay side by side which causes the appearance of bands under a microscope
Z lines- thin filaments at either end of the sarcomere and are attached to interconnecting proteins
M lines- made of proteins that connect the central portions of each thick filament to its neighbors
A band- area containing thick filament
I band- area containing thin filament

7. Thick & Thin Filaments
Active site- area capable of interacting with myosil
Tropomyosin- a protein that covers thin filaments
Troponin- a molecule that holds tropomyosin in place
Thick filaments
Are composed of head and tail of myosin molecules
Oriented away from the center of the sarcomere
Heads project outwards
Calcium allows for active sites to start the contraction

8. Sliding Filaments & Cross Bridges
Sliding Filament Theory- Binding the myosin heads of the filaments to active sites of the thin filaments allows for movement
Cross Bridges- when myosin heads interact with thin filaments during contraction
It pulls the heads towards the center of the sarcomere
“Attach, pivot, detach, return” is the basic motion

9. Checkpoint Questions 4. Describe the basic structure of a sarcomere
A. Attached end to end as repeating functional units
5. Why do skeletal muscle fiber appear striated when viewed through a light microscope?
A. Because they are situated side by side
6. Where would you expect the greatest concentration of calcium ions to be in a resting skeletal muscle fiber
A. the Terminal Cisternae