Ultrastructure of Muscle Cells Flashcards
What are the three main types of muscle?
Skeletal
Cardiac
Smooth
What is skeletal muscle?
Striated muscle
Under voluntary control from somatic nervous system
What is cardiac muscle?
Striated muscle
Only in heart
What is smooth muscle?
Non-striated muscle
Under involuntary control from autonomic nervous system
What is the sarcolemma?
Cell membrane of skeletal muscle
What are T tubules?
Invaginations of sarcolemma that conduct charge when cell depolarised
What is the sarcoplasmic reticulum?
Specialised endoplasmic reticulum of skeletal muscles
What is the endomysium?
Thin layer of connective tissue surrounding muscle fibre
What is a fascicle?
Group of muscle fibres?
What is the perimysium?
Thin layer of connective tissue surrounding fascicle
What is the epimysium?
Thick layer of connective tissue surrounding whole muscle
What forms the striated appearance of skeletal muscle fibres?
Organisation of 2 contractile protein
- Actin (thin filament)
- Myosin (thick filament)
What is a sarcomere?
Functional unit of contraction in a skeletal muscle fibre
What are the sections of a sarcomere?
Z line = where actin filaments anchored M line = where myosin filaments anchored I band = contains only actin filaments A band = length of myosin filament, may contain overlapping actin filaments H zone = contains only myosin filaments
How are the sections of a sarcomere organised?
MHAZI
- M line inside H zone
- H zone inside A band
- Z line inside I band
- I band connects with A band
What does the sliding filament model describe?
Mechanism of skeletal muscle contraction
To what do the heads of myosin bind?
Sites on actin filament
With which two regulatory proteins is actin associated?
Troponin
Tropomyosin
What is the role of tropomyosin?
Blocks myosin head binding sites on actin
What is the role of troponin?
Binds tropomyosin to actin
What are the three parts of troponin?
Troponin I = binds to actin filament
Troponin T = binds to tropomyosin
Troponin C = can bind Ca ions
How does excitation-contraction coupling work?
- Depolarisation at neuromuscular junction > conducted down T tubules > Ca released from sarcoplasmic reticulum into sarcoplasm
- Ca binds to troponin C > troponin changes conformation > move tropomyosin away from myosin head binding sites of actin
- Myosin head binds to actin > forms crosslink > power stroke occurs as myosin head pivots in rowing motion, moving actin past myosin towards M line
