Which type of muscle tissue is the only voluntary type in the human body?
Skeletal muscle
What is voluntary muscle?
Muscle that is controlled consciously
What are the functions of skeletal muscle?
Skeletal muscle contracts to move parts of the body. Most skeletal muscles are attached to two bones across a joint, such that when contracted the muscle brings parts of those two bones closer to each other.
- produce movement
- maintain posture and stabilize joints
- control excretion (elimination of urine and feces) and swallowing
- produce heat
- support and protect internal organs
Describe the organization of skeletal muscle
- consists of muscle tissue and connective tissue
- connective tissue surrounds the muscle tissue and attaches the ends of each muscle to bone
What are the three layers that connective tissue in skeletal muscle is categorized as?
- Epimysium
- Perimysium
- Endomysium
Describe epimysium
- the layer of connective tissue that surrounds an entire muscle and is continuous with the tissue that becomes the tendon
Describe perimysium
- the layer of connective tissue surrounding a bundle of muscle fibers (fascicle) within a muscle
Describe endomysium
- the layer of connective tissue that surrounds the individual muscle cells (muscle fibers) within a muscle bundle
What is another word for myofiber/what is a myofiber?
A muscle cell
What is a myofiber vs myofibril vs myofilament?
Muscle cells (myofiber) –>
has many myofibrils –>
that contain numerous myofilaments
List the features of a muscle cell (there is 6 to list)
- Sarcolemma
- Nuclei
- Myofibril
- Myofilament
- Sarcoplasmic reticulum
- T-tubules
What is the sarcolemma?
- found in a muscle cell
- the cell membrane surrounding the muscle cell
- beneath it are the nuclei, myofibrils, and the sarcoplasm (cellular fluid)
Explain the nuclei of skeletal muscle cells
- multinucleated (they have more than one nucleus)
- these nuclei are located towards the outside of the myofiber
What are myofibrils?
- the structural units of the muscle cell
- contain the contractile myofilaments
What are myofilaments?
The contractile units of the muscle cell
What is the sarcoplasmic reticulum?
- surrounds each myofibril
- this is where the muscle stores calcium, which is necessary for muscle function
What are T-tubules?
- Transverse tubules (T-tubules)
- extensions of the sarcolemma that surround the myofibrils
- they transmit nerve stimulation to the sarcoplasmic reticulum within the cell
How are myofilaments organized?
- they are organized into repeating structural units AKA sarcomeres
- one sarcomere spans from one Z line to the next
How does contraction occur in sarcomeres?
When shortened, the sarcomeres cause contraction of the muscle. each unit consists of actin and myosin
Describe the structure of a sarcomere
It consists of thick and thin myofilaments
- thick = myosin
- thin = actin
Skeletal muscle has a striated appearance due to the arrangement of action and myosin into organized sarcomeres that form distinct lines and bands.
(look at an image, in mod3, section2, page 5 or online)
Z-line in the middle of actin filaments
M-line in the middle of myosin filaments
A band of myosin
I band of actin
What happens when muscles contract (actin & myosin)? + what would this look like on a micrograph
The actin and myosin filaments slide over each other, which shortens the sarcomere.
This increases muscle tension grossly resulting in the movement of structures.
**Basically in a micrograph, all the thick black bands in the middle look like they disappear (since the filaments are sliding over each other)
Why does the sarcomere appear to have light and dark bands?
- Due to the overlap of thick and thin filaments
- The I-band is light because that area only consists of thin filaments (actin). The Z-line in the middle is dark because it contains an abundance of structural protein
- The A-band is dark because it consists of thick filaments (myosin) and is even darker towards the sides because it is overlapping with actin, thus that area has both thick and thin filaments. The M-line in the middle is an abundance of structural protein that creates a dark line.
