Muscle Mechanics

Question 1

what is a preload?

Answer 1

a weight the muscle feels when it’s in its relaxed state.

Question 2

What is the Length Tension relationship ?

Answer 2

When a muscle contracts isometrically, the tension developed depends on the initial length of the muscle before it contraction

this initial length-tension relationship curve is constructed by varying the muscle length at rest and measurign the isometric tension when the muscle is maximally stimulated at that length

initial length is determined by the preload with the ‘stop’ removed

Question 3

what is the ‘optimal length’ for muscle tension?

Answer 3

optimal length is the length at which tension devleopment is maximal - skeletal muscle is usually near optimal length naturally -

Question 4

describe the relationship between the length tension relationship and COPD ?

Answer 4

lung hyperinflation (COPD) reduces diaphragm force

• COPD cuases trapping of air and the lung volume actually gets larger than other patients and the diaphragm is a skeletal muscle - init’s normal position the diaphragm pushes down and flattens sucking air into the lungs - however in it’s hyperinflated state the diaphragm is hyperextended meaning the ‘length’ of the muscle is no longer at optimal in the length-tension relationship curve

therefore the force of breathing decreases

Question 5

what does the clsotridium tetani infection cause?

Answer 5

cuases Tetanus

• the toxin blocks inhibitory synapses in the central nervous system so that there is increased activity of the motor nerves to skeletal muscle - stimulating the muscle at higher frequences so as it twitches, another action potential happens and there is no refractory period - sums the forces building up like resonance

Question 6

how many times can a muscle be activated per second?

Answer 6

the action potential of skeletal muscle cells has a duration of 5ms

therefore the muscle can be activated more than 200 times per second theoretically

Question 7

what is the ‘staircase phenomenon’?

Answer 7

when a muscle is stimulated repetitively at a frequency below that which causes summation, there is a progressive increase in the tension developed with each twitch until a max is reached (warmin up effect)

• various attempts to explain this phenomenon but the best one may be that the increase termperature increases the rate at which muscles can act and the tropomyosin complex may be binding calcium to a good extent

Question 8

what are the two types of smooth muscle?

Answer 8

multiunit

visceral (single unit)

Question 9

what types of multiunit smooth muscles are there?

Answer 9

• ciliary muscle
• iris
• piloerector muscles
• large arteries and veins
• arteriovenous shunt vessels

Question 10

what are some types of visceral smooth muscle?

Answer 10

• intestine
• uterus
• bladder
• ureters
• ducts of exocrine glands
• precapillary sphincters
• small blood vessels