Skeletal Muscle Structure And Function - Lecture 8 Flashcards
What are the 3 main types of muscles in the human body
- smooth - these muscles mainly line hallow organs and are not under voluntary control
- cardiac - these muscles are located only in the heart. It generates force to pump blood around the body and is not under voluntary control
- skeletal - these muscles applies force to the bones to control posture and body movements. And is mostly under voluntary control
What does not under voluntary control mean
Happening automatically
Whatbis the primary job for skeletal muscle fibres
Develop force!
And is important for both movement and posture, eg: if you were to take away the skeletal muscle you would fall because the skeleton would not be able to hold itself
How do the skeletal muscles develop force
By contracting ( shortening )
What are the secondary jobs that a skeletal muscle has
- support and protection for soft internal organs
- provides voluntary control over major openings ( allow passage of substances in and out of the body )
- converts energy into heat, which is used to maintain core temperature, eg: shivering
What are individual muscle cells called
Fibres and they gather into bundles called fascicles
What do the fascicles do
They are further bundled into muscles, we want this structure because our goal is to develop force by shortening. The muscle is set up so that it’s almost identically in the same direction, so we can get the most contraction possible
What do fibres, fascicles and muscles contain
Many blood vessels ( has to burn a lot of ATP and produce a lot of energy so the muscles can work, so to do this we need a constant supply of oxygen, glucose, sugars) and nerves ( we need some way for the brain and the muscles to know when to contract ) , and they are wrapped around in connective tissue.
Why are they fibres sheathed in connective tissue
By wrapping the fibres in connective tissue they are able to protect one another, so they can rub against each other but not loose their shape
What do all of the connective tissues do
They gather together to form tendons, which connect muscle to bone
What is a muscle fibre comprised of
Bundles of myofibrils, which are made of repeating units called SARCOMERES
What are sarocomeres made of
Contractile proteins or myofilaments
- actin ( thin filaments )
- myosin ( thick filaments )
SARCOMERES get shorter as it contracts
And therefore it has a striped / strained appearance
How do we know when do contract
We need to signal the skeletal muscles to make it contract
What are sarcolemma
This is where the muscle fibres are lined up and it plays a critical role I’m muscle contraction
What are transverse tubules and its job
Tube like extensions of the sarcolemma, its job is to conduct electrical signals ( action potentials ) deep into the core of the fibre
What is sarcoplasmic reticulum (SR) and its job
This is an extensive membrane network associated with the T tubules ( they are yellow ) at regular intervals . The job of the SR is to take up and store calcium ( Ca2+ ) while the muscle is relaxed and then to release calcium into the cytoplasm when the muscle contracts
What is EC - coupling
This is a well organised process aimed to transform the electrical stimulation of the sarcolemma into muscle contraction
What is the voltage- gated sensor (DHPR)
Receives signals from the t tubules and interacts with the ryanodine receptors
What is the ryanodine receptors
A passive calcium channel on the SR that can open to allow Ca2+ out into the cell, this is what happens after the voltage gated sensor.
What is the SR calcium -ATphase ( SERCA )
This is an active pump burns ATP to produce energy to move Ca2+ back into the SR against the concentration gradient . This removes the calcium from the cell, stopping the signalling event and allowing the muscle to relax
In the EC - coupling where is the signal coming from
Nerves running throughout the muscle and we see this coming down the plasma membrane/ sarcolemma. And we want this deep into the cell so the signal moves down the transverse tubules
How is the DHPR activated
By the signal moving through the transverse tubules
What is the last step of the EC - coupling process
Calcium diffuses throughout the cell, activating myofilaments and causing a contraction
What happens at cellular level
Skeletal muscle fibres are organised into SARCOMERES comprised of myofilaments, which give the muscle its striated appearance. They also have critical signalling components, including T tubules and sacoplasmic reticulum
What event of EC- coupling would contribute to relaxation of a muscle cell
The SERCA pump moves calcium into the SR
