Muscles Flashcards
What are the 3 types of muscles?
Smooth
Skeletal
Cardiac
Describe the structure of skeletal muscle?
Individual cells make up muscle fibers Fibers wrapped in CT sheaths Blood vessels in gaps between fibers Fibers contain myofibrils Striated
What are tendons made from?
CT
Continuation of the sheath covering muscle fibres
Describe the structure of a myofibril.
Sarcomere - repeating unit Z lines - boundary of sarcomere Thin actin filaments Thick myosin filaments Titin filaments
What are the purpose of titin filaments?
Guide for myosin filaments
Ensures actin + myosin filaments slide over each other
Describe what happens in contraction, in terms of actin, myosin, titin filaments, and the distances between them.
Titin shorten
Distance between actin filaments decreases
Distance between adjacent myosin filaments decreases
Describe the cross-bridge cycle.
4
1) Calcium released into sarcomere - [Ca2+] up - cross bridge binding sites on actin filament open - CB binds to actin
2) Cross bridge moves - ADP + Pi (from step 4) released
3) ATP binds to myosin - cross bridge detaches from actin
4) ATP hydrolyses energises cross bridge - ready to bind to actin
How does Calcium regulate the cross bridge cycle?
Tropomyosin + Tropinin on actin filaments
Cross bridge binding site blocked by tropomyosin - held in place my troponin
Ca2+ binds to troponin binding site - change in shape - pulls tropomyosin away - opens CB binding site
Why is the sarcoplasmic reticulum important in the cross bridge cycle?
Storage/release of Ca2+ into myofibrils
Why are transverse tubules present around myofibrils?
Takes surface depolarisation by motor neurone and channels it deep into the muscle fibres
Coordinated contraction
Why must Ca2+ be removed from the myofibril actively?
If [Ca2+] remained high, cross bridge binding site would remain open and muscle would not be able to relax
Remove Ca2+ = tropomyosin restores blocking action
What is the difference between isometric and isotonic twitches?
Isometric - shorter latent period but longer contraction event
Isotonic - longer latent period but fast contraction event
Describe what summation of contractions is?
Rapid repeated AP’s
Maintains high [Ca2+]
Cross bridge binding sites remain open
Constant stimulus (fused tetanus)
Sum of the length-tension relationship of muscle contraction.
Too stretched = not enough overlap = less tension
Too squashed = interference between filaments
Muscle length for optimal tension = optimal length
Why does summation not occur in cardiac muscle?
Heart muscles must relax in between strokes or you’ll bloody die wont you
Why do muscles fatigue?
Stops ATP from being used up
This stops muscles from not being able to activate new cross bridge cycles
Why does intense anaerobic exercise impact muscle function?
Anaerobic ∴ Substrate level phosphorylation ∴ lactic acid
Acidifies contractile proteins
Less effective
Explain why long periods of low intensity exercise causes blood glucose and muscle glycogen levels to drop.
Aerobic ∴ oxidative phosphorylation ∴ CAC
Uses glucose ∴ glycogen broken down in muscles
= Drop in levels
What are the 3 types of muscle fibres and their resistances to fatigue?
1 - Slow oxidative - resistant
2a - Fast oxidative - mod resistance
2b - Fast glycolytic - fatigues quickly
Highlight the main differences between oxidative and glycolytic muscle fibres.
Oxidative have more mitochondria, more vascularisation, contain myoglobin (and are red) and have low diameters
Glycolytic have few mitochondria. less vascularisation, more glycolytic enzymes (+ glycogen) and have a larger diameter
When an increased load is applied to a muscle, what is the order of recruitment of different muscle fibre types?
Slow oxidative (1) Fast oxidative (2a) Fast oxidative (2b)
What is the difference between disuse atrophy and denervation atrophy?
Denervation = nerve/nmj damage ∴ disuse ∴ cells waste away
Disuse = muscles not used (broken limb, prolonged bed rest etc) ∴ cells waste away
What is hypertrophy?
Increase in muscle mass
Aerobic and anaerobic exercise cause hypertrophy in different ways, describe them?
Aerobic = more mitochondria + more vascularisation + increase in diameter
Anaerobic = increase in diameter + increase in glycolysis
In terms of the nervous system, how is smooth muscle different from skeletal muscle?
Smooth muscle innervated by the ANS
Skeletal is innervated by SNS
Why does smooth muscle not have striations?
Actin and myosin filaments not in regular arrangement in smooth muscle
Describe the filament arrangement in smooth muscle.
Diagonally across cells
Less ordered
Anchored to membranes by dense bodies
Describe the cross bridge mechanism for contraction of smooth muscles.
[Ca2+] up ∴ binds to calmodulin
Calmodulin binds to Myosin Light chain kinase
Kinase phosphorylates X-bridges with ATP
X bridges bind to actin filaments
Contraction
What enzyme is used to relax smooth muscle after it has contracted?
Myosin light chain phosphotase
Phosphorylated cross bridges may be dephosphorylated when still bound to actin.
Explain how this is beneficial to some parts of the body that contain smooth muscle.
Lower rate of ATP splitting
∴ slower cross bridge cycle
This means tension can be maintained without using up fuck tons of ATP
Useful in muscles that need to stay open for long periods of time such as blood vessel walls
All muscle types require Calcium ions
What are the two main sources of Cytosolic Ca2+, and what muscle types are they used more in?
Sarcoplasmic reticulum - more SR in skeletal muscle
Extracellular Ca2+ - brought in using VGCC’s
Out of smooth and skeletal muscle, which has a faster Ca2+ removal process?
Skeletal
Smooth muscles maintain a constant degree of tension…
How?
Always Ca2+ present in cytosol at a level that causes some contraction
Skeletal muscle has lots of transverse tubules cutting about in the fibres whereas smooth muscle doesn’t
SMOOTH muscle can be contracted in a more controlled way due to this
How?
Transverse tubules carries signal deep into muscle fibre
1 AP releases enough Ca2+ to saturate tropinin sites ∴ big action triggered (all or nothing)
In smooth muscle, less TT’s so the amount of calmodulin activated etc depends on the nummber of APs that reach the cell
∴ smooth muscle contraction is graded
What is tetanus?
Sustained muscle contraction with no/reduced relaxation
What is the name given to the gap between the action potential firing, and beginning of contraction?
Latent period
What is the name for the force exerted on a muscle?
Load
What is the force exerted by a muscle?
Tension
What is the name for contraction with constant length?
Isometric
Contraction with a decreasing length.
What is the name for this?
Isotonic
When you sit down, some of your muscles contract, but increase in length.
What is the name given to this?
Lengthening
