Control of Muscle Tension (Nursing)

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.