Muscle 1 Flashcards
What are the 2 types of Muscle?
Smooth and striated
What two subtypes make up striated muscle?
Skeletal (voluntary muscle and diaphragm)
Cardiac
What does smooth muscle make up?
Blood vessels, airways, uterus etc
What makes up each skeletal muscle fibre?
Each fibre is a large multinucleic cell packed with protein pushing the nulcei to the edge
How do skeletal muscle fibres form?
In Utero from mononucleate myoblasts
What encases the bundles of fibres that make muscles?
A connective tissue sheath
What connects muslce tbone?
Tendons
What cells replace injured skeletal muscle cells?
Satellite Cells
Why cant muscles fully recover from injury and what is done to compensate?
Theres a limited supply of satellite cells
Other fibres undergo hypertrophy to compensate for the damaged fibres.
What is a myofibril?
Every muscle fibre is packed with protein in the form of myofibrils that are like lon chains of myosin and actin filaments.
What is the sarcomere?
The sarcomere is the repeating unit of the myofibril
How are actin and myosin filaments arranged in the myofibrils?
The thick myosin filaments are arranged in triangles and the thin actin filaments in hexagons. This way every myosin filament is evenly surrounded by 6 actin filaments.
What binds myosin and actin filaments together?
Cross bridges on the myosin fliament
What happens to the filaments when muscle contracts?
The cross bridges drag the actin filament along, sliding the two filament types along eachother.
What binds to myosin cross-bridges?
They have actin binding sites and ATP binding sites.
What are the 4 steps of the cross-bridge cycle?
[Ca2+] in the cell rises and the energized cross-bridge binds to actin.
The cross-bridge moves draggin the actin along and releases ADP + Pi (products of the last cycle)
ATP binds to the myosin causing the cross-bridge to detach
Hydrolysis of the ATP energizes the cross-bridge ready for the next cycle.
What are the two accessory proteins wrapped around actin?
Troponin and Tropomyosin
What is the function of tropomyosin?
Tropomyosin partially covers the myosin binding site preventing random connection of cross-bridges (rnadom muscle contraction).
What is the function of troponin?
Troponin hlds tropomyosin in position and when bound to by Ca2+ it pulls away the tropomyosin allowin contraction.
What and where is the sarcoplasmic reticulum?
The muscle cells internal store of calcium ions
Its a spread of fine tubules throughout the whole cell to allow rapid and even dispersion of calcium throughout the cell.
How is calcium taking rapidly back into the sarcoplasmic reticulum after contraction?
By Ca2+ATPase (calcium pump)
Why cant calcium be allowed to remain in the cell any longer than necessary?
It is highly toxic and in fact rapid release of Ca2+ is how cells commit suicide.
What makes up a motor unit?
A motor neuron attached to many muscle fibres by neuromuscular junctions.
What makes muscle fibres able to withstand damage to to motor neurones?
Muscle fibres from a motor neuron can be spread throughout a muscle and multiple motor neurons are often linked to different fibres in a muscle.
Define tension and load
Tension is the force exerted by muscle
Load is the force exerted on muscle
Define isometric contraction
Contraction with a constant length. E.g. a weightlifter holding a weight above his head
Define iostonic contraction
Contaction with shortening length. E.g. runnin
Define Lenghtening contraction
Contraction with increasing length. E.g. The muscles on the back of the leg when sitting down
What is a twitch contraction?
When a single AP is fired and causes a muscle fibre to contract slightly and suddenly. Often used for studying muscles and motor neurons
What is the latent period of a twitch contraction?
The time before excitation contraction starts (i.e. the time for the signal to travel and signal tranduction to occur)
What is contraction time?
The time between the start of tension and peak tension
What effects contraction time?
Type of muscle fibre
[Ca2+]
Load
How does load affect contraction?
As the load increases the contraction velocity decreases as does the distance shortened.
How is Isometirc contraction differnt in terms of latent period and contraction time?
Isometric contraction has a longer contraction event but a shorter latent period.
