Lecture 8: muscle mechanics

Question 1

how is the length tension relationship constructed?

Answer 1

• it is constructed by varying the muscle length at rest and then measuring the isometric tension when the muscle is maximally stimulated at that length

Question 2

Describe the length tension curve of skeletal muscle

Answer 2

• as the length of the sarcomere is shorter, the tension is low
• as the sarcomere gets stretched - it gets to a point in which the tension produced is maximal - optimal length
• skeletal muscle is usually near the optimal lnegth

Question 3

what is an isolated contraction of a skeletal muscle called and how is it developed?

Answer 3

• a single AP from a motor neuron will produce a single contraction in the muscle fibres innervated by the motor neuron
• the isolated contraction is called a** twitch**

Question 4

what does clostridium tetani infections cause and how do they do this?

Answer 4

• clpstridium tetani infections cause tetanus - where there uncontrollable spasms of the muscle
• the toxin blocks inhibitory synapses in the CNS - which causes increased activity of the motor nerves to the sksletal muscle

Question 5

what is twitch summation?

Answer 5

• if a muscle fiber is restimulated before it has completely relaxed, the** second twitch is added onto the first twitch**, resulting in a summation

Question 6

what is a tetanus in terms of muscle contractions?

Answer 6

• if a muscle fibre is stimulated so rapidly that it does not have time to relax between all the stimuli - a maximal sustained contraction known as a tetanus occurs

Question 7

compare unfused tetanus and complete tetanus contraction

Answer 7

• summation can lead to unfused tetanus - the **stimuli are far enough apart **to **allow muscle to relax slightly **between stimuli
• summation can also lead to complete tetanus- muscle reaches steady contraction - doesnt relax until fatigue hits

Question 8

how long does the action potential of a skeletal muscle last for?

Answer 8

• 5 milliseconds

Question 9

if a skeletal muscle AP lasts for 5ms, how many times can a muscle be activated per second?

Answer 9

more than 200 times per second

Question 10

Describe the staircase phenomenon (treppe) with regards to muscle contraction

Answer 10

• when a muscle is** stimulated repetitvely** at a frequency** below which causes summation, there is a progressive increase in the tension **developed with each twitch **until a max twitch is developed **