Flashcards in Muscle Deck (28):
What are the three types of muscle?
Skeletal, smooth and cardiac
What muscle types are regarded as striated?
Skeletal and cardiac
What structures attach bones to muscle?
What happens when skeletal muscle cells are injured?
Satellite cells replace injured cells
Hypertrophy of surrounding fibres
What is meant by hypertrophy of muscle cells?
The packing in of more protein (actin and myosin filaments)
What changes occur to the sarcomere during muscle contraction?
Actin slides over myosin filaments, moving closer to M line.
This reduces the width of the H band and the I band
What molecules block the binding sites on actin filaments?
Tropomyosin partially blocks binding sites. Troponin holds the tropomyosin in the blocking position.
What effect does calcium have on the blocking of myosin binding sites?
Calcium binds to troponin, altering its shape. Troponin pulls away from tropomyosin which can move away from the binding site.
The exposed binding site can now bind myosin heads.
What is the role of the sarcolplasmic reticulum?
Storage of calcium ions
What is the role of transverse tubules?
Conduction of signal deep into the muscle tissue.
What are the components of a motor unit?
Motor neuron and muscle fibre
What is meant by an isometric contraction?
Contraction with constant length
What is meant by an isotonic contraction?
Contraction with shortening length
What is meant by a lengthening contraction?
Contraction with increasing length
E.g. sitting down
For what two mechanisms in muscle contraction is ATP required?
1. Detachment of myosin heads from actin filaments to allow a new cycle to begin and contraction to be furthered.
2. Pumping of calcium ions back into the sarcoplasmic reticulum to end contraction.
What factors can cause fatigue in high intensity, short duration exercise?
1. Increased [K+] causing depolarisation
2. Increased [lactic acid] to acidify proteins
3. Increased [ADP+ Pi] to delay detachment of myosin heads from actin filaments, so inhibiting cross bridge cycle.
What factors cause fatigue in low intensity, long-term exercise?
1. Decreased [blood glucose]
2. Decrease muscle glycogen
What two factors need to be considered in the characterisation of skeletal muscle fibres?
1. Whether the fibre is short or fast shortening
2. Whether oxidative or glycolytic ATP forming pathways are used
What is meant by a fast shortening muscle fibre?
Contains myosin with high ATPase activity
What is meant by a slow shortening muscle fibre?
Contains myosin with low ATPase activity
What are the features of skeletal muscle fibres which use oxidative ATP forming pathways?
1. Red in colour
2. Small diameter
3. High vascularisation
4. Blood vessels contain myoglobin
5. Many mitochondria present for oxidative phosphorylation
What are the features of skeletal muscle fibres which use glycolytic ATP forming pathways?
1. White in colour
2. Larger diameter
3. Lesser blood supply
4. Contains many glycolytic enzymes and glycogen
5. Few mitochondria
What type of skeletal muscle fibre is most resistant to fatigue?
What type of skeletal muscle fibre is least resistant to fatigue?
In muscle contraction, what is meant by 'recruitment'?
The increased activation of motor units, as a result of increased load.
Describe the smooth muscle cross bridge cycle.
Calcium binds to Calmodulin
Calcium-calmodulin complex binds to myosin light chain kinase
This can then phosphorylate cross bridges, which can then bind to actin, allowing contraction.
How does smooth muscle contraction differ from skeletal muscle contraction?
Smooth muscle contraction can be graded.
The number of actin binding sites exposed depends on the number of Action Potentials which act on the muscle cell.