Chapter 13 Muscles Flashcards
What are the 3 types of muscles?
Skeletal muscle
Cardiac muscle
Involuntary/smooth muscle
What is the function and structure of skeletal muscle?
Conscious movement
Short contraction times, rapid contraction
Multinucleated, very regular, and very striated
What is the function and structure of cardiac muscle?
Involuntary and myogenic
Intermediate speed and contraction
Uninucelated stands, light striated, not very regular- interconnected
What is the structure and function of smooth/involuntary muscle?
Non-striated and non-regular arrangement
Slow and longer contraction
Uninucleated a bit of a mess
How does skeletal muscle form and why?
Many embryonic muscle cells fuse, forming long muscle fibres with shared cytoplasm and multiple nuclei
This is so there are no point of weakness, such as the point between muscle cells
What is the sarcolemma? What is the sarcoplasm? What is the sarcoplasmic reticulum? What are T-tubules?
Muscle cell membrane
Muscle shared cytoplasm
Muscle endoplasmic reticulum
Deep in foldings of the sarcolemma
What is the composition of muscles in order?
Myofibril
Sarcomeres
Myocyte
Fascicle
Muscles
What is the protein arrangement of a myofibril?
Between Z lines= myosin and actin
Actin strands
Then myosin under
See diagram
What are the different muscle bands and zones?
Light/I band- only actin
Dark/A band- contains myosin and some actin
H zone- only myosin
Z lines- protein structures marking a sarcomere
What happens to each of the muscles zones during contraction? What enables a muscle to contract?
H zone shortens
Z lines move closer together, so the sarcomere gets shorter
Light band shorter, dark band the same length
Contraction occurs when many sarcomeres contract in the same direction at the same time
What is the structure of myosin?
A large protein molecule with small myosin heads attached to it. They are hinged and can flex
There is a site for ATP/ADP and for actin
What is the structure of actin?
A large protein molecule in two main strands
Each head has a myosin binding site
Associated with tropomyosin which blocks these sites. It is held in place by another molecule called troponin
What occurs at a neuromuscular junction?
Depolarisation of the synaptic bulb causes the opening of Ca2+ channels in the cell membrane, allowing the ions to diffuse in. They bind to motor proteins causing conformational changes which allow the movement of secretory vesicles containing acetylcholine to move to the cell surface membrane.
The neurotransmitter diffuses across the synaptic cleft following exocytosis. It binds to ligand gated sodium channels, causing conformational changes which open them, enabling Na+ to diffuse into the muscle
The Na+ travel deep within the T-tubules, causing depolarisation of the sarcoplasmic reticulum. This stimulates the opening of Ca2+ channels, allowing Ca2+ to diffuse out of the sarcoplasmic reticulum into the sarcoplasm
What is the sliding filament theory (following depolarisation of the sarcoplasmic reticulum)?
1) Ca2+ diffuses through the channels from the sarcoplasmic reticulum into the sarcoplasm
2) Ca2+ bind to troponin, causing a conformation change, which pulls tropomyosin along. This exposes the actin-myosin binding sites. The myosin heads bind to the binding sites, forming an actin-myosin cross bridge
3) The myosin heads flex, pulling the actin filaments along and ADP is released
5) ATP can now bind to myosin heads, causing the myosin heads to detach
6) Ca2+ activate ATPase, catalysing the hydrolysis of ATP into ADP and phosphate, which the energy released used to move the myosin head back into its original position
7) The process can repeat with more binding
Why does the sarcomere shorten, linking to sliding filament?
The myosin heads flex towards the M line, on either side
This pulls the actin together and so shortening the sarcomere
