What are the 4 steps of muscle contraction?
- Attachment of myosin head to thin filament
- Movement of the cross-bridge producing tension
- Detachment of the myosin head and thin filament
- Energising of the head so it can repeat the cycle
What type of collagen is predominant in tendons?
Type 1 collagen
What are the 4 sources of ATP in skeletal muscle?
- Dephosphorylation of phosphocreatine
- Oxidation of free fatty acids from the blood
- Aerobic metabolism of carbohydrates (glucose)
- Anaerobic metabolism of carbohydrate (glycogen stores)
Which muscle fibres are the most resistant to fatigue?
Type 1 and Type 2a
What neurotransmitter is released at the neuromuscular junction?
Where is the site of most muscle strains or "pulls"?
The myotendinous junction
How many polypeptide chains make up a collagen fibre?
3 polypeptide chains woven into a triple helix.
What is a consequence of an Achilles' tendon rupture?
There is substantial weakness in plantarflexion of the foot.
How can muscle contractions vary in strength?
- Number of motor units recruited
- Frequency of motor unit activation changes
What collagen type is predominant in ligaments?
- Type 1 collagen
- Small amounts of type 3 .
What proteins make up the thin filaments of a muscle?
What is the main function of the fibrillar collagens?
To provide tensile/mechanical strength to a tissue.
Describe oxidative muscle fibres.
- Contain lots of mitochondria so have high capacity for oxidative phosphorylation
- Rich blood supply of oxygen and fuel
- Contain large amounts of myoglobin which allows greater rates of oxygen diffusion into the cell.
What are the main fibril-associated collagens (FACIT)?
- Type 9
- Type 12
- Type 14
- Type 16
- Type 19
Define eccentric contraction.
A contraction where the muscle is lengthening despite the contraction mechanism being activated
How many heads does each myosin molecule contain, and what is their function?
2 heads; extend from the molecule and form cross-bridges with actin
How does central fatigue affect muscle activity?
The cerebral cortex fails to send excitatory signals to the muscle, therefore the muscle will not function
The "psychological" barrier to exercise.
What is a motor unit?
A single motor neurone and the muscle fibres it innervates
Which collagen connects the basal laminae of the skin to the connective tissue underneath?
What happens to pyruvate in the muscle under intense exercise? (anaerobic respiration)
It is converted to lactate
What enzyme catalyses the dephosphorylation of phosphocreatine?
Define isotonic contraction.
Where the muscle shortens while the load on the muscle remains constant
During muscle contraction which zones/bands of the sarcomere become shorter?
- H zone
- I band
Why are type 1 fibres referred to as red muscle fibres?
They contain a large amount of myoglobin
How are collagen molecules assembled into fibres?
In a quarter staggered arrangement
What type of receptor does ACh bind to on the motor end plate?
What ion initiates the binding of the cross-bridges between actin and myosin and where does it come from?
Ca2+; from the sacroplasmic reticulum when an action potential is conducted down the T-tubules from the motor end
Besides type 1 collagen, what other types of collagen are present in tendons?
- Type 3
- Type 5
What is a motor neurone pool?
All the motor units that completely supply 1 muscle
What are the main fibrillar collagens?
- Type 1
- Type 2
- Type 3
- Type 5
- Type 11
What is the function of elastin within the tendon?
- Provides elastic properties to the tendon
- Stores energy during movement
What is the motor end plate?
The part of the muscle fibre that is directly under the terminal portion of its axon
What physical sign develops when there is chronic partial denervation of a muscle?
Fasciculations in the affected muscle are seen
The side chains of which amino acids covalently link to strengthen the collagen fibril?
What can cause chronic partial denervation of a muscle?
Poliomyelitis - destroys motor neurones
Motor neurone disease
What is the function of a retinaculum?
It is a band of fibrous tissue that holds tendons in place, usually near a joint to prevent bowstringing.
What happens to the tendon in "wrap-around" regions?
- The tendon develops fibrocartilage, with significantly higher proteoglycan content than the tendon
- This develops to resist the compressive forces placed on the tendon by the bone.
What happens to tendons due to exercise?
- Increase in collagen fibril size
- Increased strength
- Increased stiffness
What are the 3 types of muscle fibre?
- Type 1
- Type 2a
- Type 2b
What are the functions of a ligament?
- Provide muscle attachment
- Hold down soft tissue
- Prevent over-stretching due to rich nerve supply
- Hold bones together and limit movements between bones.
Which collagen is the found in the majority of basement membranes?
Type 4 collagen
What stabilises the structure of the collagen triple helix?
H-bonds between each molecule
Define isometric contraction.
When a muscle develops tension but does not shorten or lengthen
Where are the cell bodies found for lower and upper motor neurones?
- Lower motor neurones = spinal cord
- Upper motor neurones = cerebral cortex (motor area)
What are the functions of proteoglycans in tendons?
They regulate the size of the collagen fibrils
They bind water to resist compression
What is the enthesis?
It is a specialised area of fibrocartilage where the tendon inserts into the bone.
How is the myotendinous junction adapted for the transfer of power from the muscle to the tendon?
The tendon digitates into the muscle, which provides a greater surface area for force transfer
Where does Ca2+ bind in order to move tropomyosin from the myosin binding site on actin
It binds to troponin
Where is ATP utilised in the cross-bridge cycle of muscle contraction?
It is used to energise the myosin head after it has dissociated from the thin filament
How is Ca2+ removed from the sarcoplasm after a muscle contraction?
It is actively pumped back into the sacroplasmic reticulum
What is a muscle cramp?
- A painful, strong contraction caused by ischaemia or metabolic disturbances
- Abnormally high numbers of AP are fired from the motor nerve during a cramp.
The process of increasing the number of motor units that are active in a muscle at any given time.
What happens to muscle during low intensity, long duration training?
- Increase in mitochondria
- Increased number of capillaries surrounding muscle fibres.
What are the 4 main macromolecules found in the ECM
Which muscle fibres type is referred to as slow twitch, and what is the cause for the "slowness"?
Type 1; it contains myosin that has a slower maximal rate at which it can hydrolyse ATP, therefore limiting the rate of cross-bridge formation.
Which muscle protein is present in the thick filaments under microscopy?
What makes up 55% of the wet tendon weight?
Name an inhibitor of the nicotinic receptor on the motor end plate.
Curare; used for poison arrowheads
What is the function of the enthesis?
It dissipates the compressive forces of the tendon reducing the risk of wear and tear injuries.
What process is caused by the fall in ATP concentration in cells following death leading to stiff muscles.
How does tropomyosin regulate muscle contraction?
When there is no need to contract there is very little Ca2+ present in the sarcoplasm.
In this situation, tropomyosin occludes the myosin-binding site on the actin molecule.
When Ca is present, the tropomyosin changes shape and this site becomes free
What factors can cause peripheral fatigue of a muscle?
- Contraction failure; APs not propagated along fibre
- Lactic acid build up; H interferes with muscle proteins
- ATP hydrolysis producing more H
- Build up of ADP & Pi inhibiting cross-bridge formation
How are the collagen fibres arranged within a ligament, and how does arranged assist in the ligament's function?
The collagen is wound in a spiral which prevents rotation of the ligament in either direction.
What happens to muscle in short duration, high intensity training?
- There is hypertrophy of fast-glycolytic fibres
- Increased synthesis of glycolytic enzymes
What are the functions of tendons?
- Allows muscle belly to be far from site of action
- Eliminates the need for long muscle bellies and provides focus
- Can change direction of muscle pull
- Acts as a spring
- Holds other tendons in place
What type of contraction is most associated with muscle strains?
Eccentric muscle contractions
What is the order of recruitment of muscle fibres?
- 1st; slow oxidative fibres (type 1)
- 2nd; fast oxidative (Type 2a)
- 3rd; fast glycolytic (Type 2b)
Define glycolytic fibres.
- Few mitochondria, but high levels of glycolytic enzymes and glycogen
- Relatively poor blood supply
- Contain little myoglobin so termed white fibres
- Type 2b
What protein is attached to the ends of the myosin molecule and provide elasticity to the muscle?
The elastic protein titin