Skeletal Muscle Structure and Function Flashcards
Name the 3 types of muscle in the body
Smooth, cardiac, skeletal
Where is smooth muscle commonly found?
Lining hollow organs (e.g. gut, blood vessels)
Where is cardiac muscle found in the body and what is its function?
In the heart, generates force to pump blood around the body
What types of muscle are not under voluntary control?
smooth and cardiac muscle
What is the function of skeletal muscle?
Applies force to bones to control posture and body movement
When is skeletal muscle not under voluntary control?
In an emergency situation, when the brain takes over (e.g. eyes close involuntarily if something flies towards them)
What is the primary function of skeletal muscle?
To develop force by contracting (shortening)
What are muscle cells referred to as?
Muscle FIBRES
Name 3 secondary roles of skeletal muscle
- Support and protection for soft internal organs (ab muscles)
- Provides voluntary control over major openings (toileting)
- Converts energy to heat which is used to maintain core temperature (shivering)
Individual muscle cells (fibres) are gathered into…
…fascicles
Fascicles are gathered into bundles called…
…muscles
Why do muscles have parallel organisation?
Because it allows contraction in one axis, therefore movement in one axis
= most energy efficient
How is the organisation of muscle fibres described?
Parallel organisation
What 2 structures (not muscular) are found in high numbers within/around fibres, fascicles, and muscles?
Nerves and blood vessels
What is the function of the blood vessels around muscle fibres?
Blood vessels allows for transport of nutrients and glucose into cells, and waste products out
What is the function of the nerves around muscle fibres?
Nerves connect brain to muscles. There are lots so that the brain can interact with lots of parts of muscle at same time = greater control
Name the connective tissue used to connect muscle to bone
Tendons
What is the function of a tendon?
Connect muscles to bones and allows force to be transferred to bone = movement
True or false:
Muscle fibres can contain more than one nuclei?
True - muscle fibres can contain hundreds or even thousands of nuclei!
A muscle fibre is comprised of bundles of…
…myofibrils
Myofibrils are made of repeating units known as…
…sarcomeres
Describe what a sarcomere is
A sarcomere is one contractile unit within a muscle fibre
What are sarcomeres made up of?
Contractile proteins/myofilaments
Name 2 types of myofilaments
Actin and myosin
True or false: myosin is the thinner of the myofilaments?
False: myosin is the thicker of the two types of microfilament
What is the purpose of muscle signalling?
To regulate the activity of the force- producing elements
What is the special name for the cell membrane of a muscle fibre?
The sarcolemma
What are transverse (t-) tubules?
Tube-like extensions (invaginations) of the sarcolemma that extend deep into muscle fibre
What is the role of t-tubules?
To conduct electrical signals (action potentials) deep into the core of the fibre
What membrane network is associated with the T tubules?
The sarcoplasmic reticulum (SR)
Describe the role of the SR
To take up and store calcium (Ca2+) while the muscle is relaxed, and then to release calcium into the cytoplasm when the muscle contracts
Define Excitation-Contraction Coupling (EC-coupling)
The pairing of a signalling event (excitation of the muscle cell) with a mechanical event (contraction of the muscle cell)
When a signalling event in the muscle cell is paired with a mechanical event, this is known as…
Excitation-Contraction Coupling (EC-coupling)
What 3 proteins are involved in muscle cell excitation?
- Voltage-gated sensor (DHPR)
- Ryanodine receptor (RyR)
- SR Calcium-ATPase (SERCA)
Where is the voltage-gated sensor (DHPR) found and what is its function?
The DHPR sits in and receives signals t-tubules and interacts with RyR
Where is the ryanodine receptor (RyR) found and what is its function?
The RyR is a passive calcium channel on the SR that can open to allow Ca2+ out of the SR and into the cell
Where is the SR Calcium-ATPase (SERCA) found and what is its function?
The SERCA is found on the surface of SR, further from t-tubule. It is an active calcium pump that uses ATP to move Ca2+ back into the SR against its concentration gradient, ending the excitation.
What is the first step of the excitation process?
Signal moves along and down into t-tubules
What is the second step of the excitation process?
DHPR is activated by electrical signal
What is the third step of the excitation process?
DHPR interacts with RyR
What is the fourth step of the excitation process?
RyR opens, Ca2+ moves out of SR
What is the fifth step of the excitation process?
Calcium diffuses throughout cell, activating the myofilaments and causing a contraction
What is the first step of the relaxation process?
SERCA senses rise in intracellular Ca2+
What is the second step of the relaxation process? What is the effect of this?
SECRA burns ATP to produce energy, then pumps calcium back into SR (against conc. gradient.
This removes calcium from the cell, stopping the signal and allowing the muscle to relax
