Muscles Flashcards by Michael Alcorn

What are the 3 types of muscles?

Smooth
Skeletal
Cardiac

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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

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What are tendons made from?

Continuation of the sheath covering muscle fibres

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Describe the structure of a myofibril.

Sarcomere - repeating unit 
Z lines - boundary of sarcomere 
Thin actin filaments 
Thick myosin filaments 
Titin filaments

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What are the purpose of titin filaments?

Guide for myosin filaments

Ensures actin + myosin filaments slide over each other

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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

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Describe the cross-bridge cycle.

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

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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

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Why is the sarcoplasmic reticulum important in the cross bridge cycle?

Storage/release of Ca2+ into myofibrils

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Why are transverse tubules present around myofibrils?

Takes surface depolarisation by motor neurone and channels it deep into the muscle fibres

Coordinated contraction

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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

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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

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Describe what summation of contractions is?

Rapid repeated AP’s
Maintains high [Ca2+]
Cross bridge binding sites remain open
Constant stimulus (fused tetanus)

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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

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Why does summation not occur in cardiac muscle?

Heart muscles must relax in between strokes or you’ll bloody die wont you

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Why do muscles fatigue?

Stops ATP from being used up

This stops muscles from not being able to activate new cross bridge cycles

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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