Lecture 8 Skeletal Muscle Flashcards
Where is skeleton muscle found/ connected to ?
Usually connected to skeletal system by tendons (made from collagen)
What type of control is skeletal muscle under?
Under conscious control
What are 6 functions of skeletal muscle?
- Movement - by pulling on bones to make skeleton move
- Maintain posture
- Support for soft tissues
- Control of ‘openings & exits’ - e.g. conscious control of urination, defecation, swallowing
- Maintenance of body temperature - muscles use energy & some is converted into heat
- Nutrient reserve
Gross pathology of skeletal muscle (8)
- Blood vessel
- Perimysium
- Epimysium
- Muscle fibre (cell)
- Fascicle (wrapped by perimysium)
- Endomysium (between fibres)
- Tendon
- Bone
Features of skeletal muscle fiber (4)
- Several myoblast cells fuse early in development to form a muscle fiber
- Multinucelate - nuclei located under sarcolemma (plasma membrane)
- Long (extends length of skeletal muscle)
- Striated (striped) appearance because of aligned sarcomeres
What are myofibrils?
- A muscle fibre contains many myofibrils
- Myofibrils are compromised of many myofilaments (thick & thin filaments) arranged into sarcomeres
What are myofibrils surrounded by?
Myofibrils are surrounded by sarcoplasmic reticulum (endoplasmic reticulum) which stores Ca2+
What do T-tubules do?
T-tubules are continuous with sarcolemma & they transfer action potentials to the myofibrils
What are the names of the thin & thick filaments in myofibrils ?
Thin filament = actin
Thick filament = myosin
What is the M-line in sarcomeres?
Middle line
It attaches thick filaments together
What is the A band in a sarcomere?
Dark bands
Contain myosin + actin
What is I band in sarcomere?
Light bands
Contain only actin
What is H band in sarcomere?
Contains only myosin
What is Z line (Z disc) in sarcomere?
Joins adjacent sarcomeres (alpha actinin)
What is zone of overlap in a sarcomere?
Region where actin & myosin overlap
How does a sarcomere contract ? (2)
- Sliding filament model of contraction
- Thick filaments (myosin) interact with thin filaments (actin) & pull the thin filaments towards M line
What happens to the sarcomere during contraction?
Sarcomere shortens
But contraction does not change length of the actin of myosin filaments
What is Titin?
Prevents over- extension of sarcomere
Regulation of muscle contraction
How does the contraction cycle end? (4)
- Acetylcholine (ACh) broken down in synaptic cleft
- Calcium no longer released from sarcoplasmic reticulum
- Calcium ions are pumped from cytoplasm, back into sarcoplasmic reticulum
- Calcium detached from the troponin complex on actin, so tropomyosin covers myosin binding sites, preventing muscle contraction
