How does muscle fiber move during relaxation/contraction?
I am confused about what happens to a muscle when it contracts an relaxes. Question 10 on the review asks the term for lengthened muscle fibers, and you state the answer is relaxed and contract is when they are shortened.
In the quiz question 3 asks what happens when a muscle is relaxed and I said lengthen like on the review questions and the answer was when they are stretched. and it states that muscles don’t always shorten when they contract. Can you please explain?
Thanks so much for getting in touch and bringing this to my attention! It is unclear, so I will do my best to clarify it. Part of this comes down to muscles as a tissue vs. muscle protein fibers.
In the audio review, the “relaxed = lengthen” refers to the sarcomere unit, the functional unit of muscle, and its protein fibers. (I will update the course to better clarify this). This section of the course talks about it, but here’s a quick highlight:
Shortened Sarcomere = Contraction
Long Sarcomere = Relaxation
In the quiz, this is more referring to muscles as a whole tissue. And in that case, contraction refers to tension rather than muscle tissue length.
This is going to go beyond what you need for the TEAS, but here’s more details on muscle contraction (rather than sarcomere, the functional unit of muscle):
When muscles contract (when they do action), they can either shorten or elongate. In what’s called eccentric contraction, the muscles lengthen when they do work.
An example of this type of contraction is pushing down. You very likely will not see eccentric contraction on the TEAS, but you do need to know that lengthen can signal contraction. In addition, some muscles can contract without changing length.
I know it’s confusing because contraction makes it sound like something is only getting shorter.
— Contraction, when referring to muscles, instead means that there’s tension.
— Stretch, on the other hand, is more associated with relaxed muscle.
— Release of tension would be a better way to describe a relaxed muscle, but stretch is the best option out of the answers.
— But for sarcomere (muscle fibers), shortened = contraction.
I hope this helps clarify things for you, and again, I’ll update the course to better clarify this.
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