Control of Muscle Tension (Nursing)

by Jasmine Clark

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    00:01 So now let's discuss how we control muscle tension or the strength of a muscle contraction.

    00:08 The strength of a muscle contraction is going to depend on how many motor units are activated.

    00:14 What is a motor unit? A motor unit consists of a somatic motor neuron and the muscle fiber that it innervates.

    00:23 So think back to the neuromuscular junction.

    00:28 For weak muscle contractions, we usually only activate a few motor units.

    00:34 For stronger muscle contractions however, we generally recruit more motor units.

    00:41 So now let's look at other factors that might affect muscle tension.

    00:46 Another factor that can control the tension of a muscle contraction is the twitch.

    00:53 The twitch is the brief contraction of all the muscle fibers in a muscle unit in response to a single action potential.

    01:01 During the twitch you have the latent period, where there is no tension at all.

    01:08 This is followed by the contraction period, where you have the most tension.

    01:14 This is then followed by a relaxation period as we then prepare to go through another contraction.

    01:23 During part of the relaxation period, there is also a refractory period.

    01:28 During the refractory period which is not pictured here, you are unable to start another contraction.

    01:38 So, how do we get stronger contractions? Wave summation is a process in which we can get a stronger contraction by increasing the frequency of twitches.

    01:53 Increasing or adding on or summating each twitch can lead to a stronger contraction.

    02:00 There are two ways to increase the strength of a contraction.

    02:05 An unfused tetanus, we are going to continuously have muscle contractions happening over and over but in between each contractions there's a small period of rest.

    02:20 In fuse tetanus, there is so many contractions happening back to back that there is no rest period and it looks like a complete peak, as you can see in the diagram.

    02:33 So now let's put it all together.

    02:35 We just talked about several different factors that can influence the strength of a muscle contraction.

    02:41 This includes the size of a motor unit, where you have smaller units they were going to lead to weaker contractions and larger units leading to stronger contractions.

    02:55 As well, we can recruit more motor units and this can also increase the strength of a contraction.

    03:04 Third, sarcomere length also plays a role by increasing the potential for myosin heads to attach to the actin filament.

    03:14 And then lastly we discuss the frequency of the stimulation of the muscle fiber, including fused and unfused tetanus.

    03:24 Did you know that even at rest, the skeletal muscles exhibit a small amount of tension at all times.

    03:32 This is referred to as tone or muscle tone.

    03:36 Tone is established by alternating involuntary action of small groups of motor units in a muscle.

    03:43 When a muscle has no tone, it is referred to as flaccid.

    About the Lecture

    The lecture Control of Muscle Tension (Nursing) by Jasmine Clark is from the course Musculoskeletal System – Physiology (Nursing).

    Included Quiz Questions

    1. The size of the motor unit
    2. Width between the I bands
    3. Recruitment of motor units
    4. Sarcomere length
    5. Frequency of stimulation
    1. Latent period, contraction period, relaxation period, and refractory period
    2. Initiation period, refractory period, contraction period, and termination period
    3. Refractory period, latent period, contraction period, and termination period
    4. Contraction period, latent period, initiation period, and refractory period

    Author of lecture Control of Muscle Tension (Nursing)

     Jasmine Clark

    Jasmine Clark

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