Muscle in Health and Disease Flashcards
How many % of total body mass is muscle?
How many % of the total body water is in muscle?
40%
80%
What does muscle store? (4)
Intracellular ions such as potassium
Water
Calcium
Glucose
What is another role of muscle?
Important for heat production
Describe a muscle cell.
Multi-nucleate, 10cm long and 10-100mm in diameter.
Peripheral nuclei
What is a muscle fibre formed of?
Formed by the fusion of many individual cells (up to 200) together into a muscle fibre.
When might a muscle cell nucleus be central (rather than peripheral)?
When it has undergone damage that required repair, so it is regenerating. It will move to the periphery once it is repaired.
What two contractile proteins are muscle fibres made up of?
Actin and myosin
What is the endomysium?
Surrounds each individual myocyte
What is the perimysium?
Surrounds a bundle of muscle fibres, grouping them together
What is the epimysium?
Surrounds the entire muscle.
Motor neurons initiate contraction of muscle - how?
They cause the release of Ach from synapse terminal which activates the nicotinic Ach receptors on fibre and initiates contraction.
What is a muscle unit?
A single motor neuron innervates 5-200 muscle fibres - this is a muscle unit.
What happens if you lose a single motor neuron?
All the muscle fibres/whole unit innervated by that motor neuron are affected and they atrophy as they are no longer innervated. They become small, angulated muscle fibres.
Why are all the fibres in a motor unit the same fibre type?
Because the fibre type is determined by the primary motor neuron that innervates the unit.
How does loss of a motor neuron cause grouping and enlargement?
The loss of a motor neuron puts out stress signals to the NMJ on neighbouring fibres, causing remaining motor axons to sprout to innervate de-innervated fibres. This means that the motor units are enlarged (made up of more fibres) and the fibres become grouped (when it should be a haphazard arrangement of fast/slow fibres and scattered). The re-innervated fibres may switch from their old phenotype to a new one determined by this new motor neuron.
What is infantile hypotonia often called?
What is it?
Floppy baby syndrome
Decreased muscle tone due to congenital fibre type disproportion.
What do the fibres look like on biopsy (in infantile hypotonia)?
Most fibres are small and round with a few massively hypertrophic fibres
Why do type 2 fibres stain dark with ATPase stain?
Type 2 fibres are (small) fast-contracting fibres, that use mixed aerobic and anaerobic metabolism. The more ATP you have, the quicker you can contract the muscle (i.e. fast fibres have lots of ATP) and this stain demarks fibres with lots of ATPase versus those with less, so they appear dark.
Why do type 1 fibres stain pale with ATPase stain?
Type 1 fibres are (large) slow-contracting fibres, that use mainly aerobic metabolism. The more ATP you have, the quicker you can contract the muscle (i.e. slow fibres don’t have a lot of ATP) and as this stain demarks fibres with lots of ATPase versus those with less, they appear pale.
There are two types of infantile hypotonia. How are these differentiated?
Need ATPase stain to tell the difference
One type - type 1 fibres are normal/larger than normal and type 2 are small.
Other type – type 2 fibres are normal/larger than normal, type 1 are small
Sarcopenia - what is this?
Loss of muscle
What is the rate of muscle loss after age of 50?
What about if you are physically inactive?
0.5 – 1%
3% - 5%
What is the difference in muscle loss between men and women?
No difference
Why don’t people with sarcopenia lose weight?
The muscle is replaced with fat.
