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03.03 Skeletal Muscle

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Overview

    1. Gross structure of skeletal muscle
      1. Epimysium
        1. WFCT around every muscle
        2. Blends with tendon
        3. Holds fascicles together
      2. Perimysium
        1. WFCT surrounds groups of cells called fascicles
      3. Endomysium
        1. Collagen fibers which surround individual muscle cells
      4. Pathway for BV’s and nerves to get to cells
        1. Epimysium → perimysium → endomysium → cell

Nursing Points

General

      1. Ultrastructure of skeletal muscle
        1. Sarcolemma = cell membrane
        2. Sarcoplasm = cytoplasm
          1. Mitochondria—ATP formation
          2. Myofibrils
            1. Contractile units
            2. Made of myofilaments
              1. Thick filaments (myosin)
              2. Thin filaments (actin, tropomyosin, troponin)
            3. Banding patterns
              1. Dark band = A band
              2. Light band = I band
              3. Create cross striations
            4. Microscopic structure of myofibrils
              1. A band includes thick filaments
              2. I band includes thin filaments
              3. Bands separated by Z line
              4. H zone (M line in center)
                1. Light region in the middle of the A band
                2. No thin filaments
              5. A band is dark because it contains thick AND thin filaments
              6. I band is light because it had NO thick filaments
              7. Sarcomere
                1. Smallest unit of muscle contraction (ultrastructural)
                2. Between 2 adjacent Z lines
        3. T-system (transverse)
          1. System of open tubules
            1. Begin as pores in sarcolemma
            2. Long tubule into sarcoplasm
              1. Between myofibrils
            3. Function
              1. Transfer an action potential from sarcolemma to myofilaments
        4. Sarcoplasmic reticulum
          1. Close system of tubules in sarcoplasm
            1. Reticular network (central)
            2. Sarcotubules extend laterally from network
            3. Terminal cysternae (lateral sacs) at the ends
            4. Function:
              1. Regulation of Calcium within sarcoplasm
        5. “Triads”
          1. Central T-tubule
          2. 2 lateral cysternae

References
Betts, J.G., et al. (2017). Anatomy and physiology. Houston, TX: OpenStax, Rice University. Retrieved from https://openstax.org/details/books/anatomy-and-physiology?Book%20details

Study Tools

Video Transcript

In this lesson, we’re going to take a look at the gross structure and function of skeletal muscle.

To get started let’s look at the overall structure of skeletal muscle. At the base level, you have an individual muscle cell that is surrounded by collagen fibers. This is called the endomysium. As individual muscle cells become bundled together they are surrounded by white fibrous connective tissue and they are call fascicles. These fascicles are covered by this white fibrous connective tissue and we call this the perimysium. As all of those bundles of fascicles come together they form the actual whole skeletal muscle. This muscle is surrounded by the White fibrous connective tissue, and that blends with the tendon that attaches to the bone. This white fibrous connective tissue holds the fascicles altogether, and it’s called the epimysium. Now I’m sure you’re wondering how blood and nerves get to all of those individual muscle cells. Well starts from the outside and moves in. You have the epimysium, they move into the perimysium, they move further into the end of my team, and then they go to the cell and provide the nutrients and remove waste.

So let’s start with the basic unit of a muscle cell. You have the sarcolemma which is the cell membrane, and you have the sarcoplasm which is essentially the muscle cell cytoplasm. Then you have this thing called the myofibril which is the contractile unit of skeletal muscle. You have the six elements which are known as myosin, and then you have the thin filaments which are known as actin tropomyosin and troponin. You also start to get these banding patterns, which are the light and dark bands. The dark band is known as the a band, and the light band is known as the iban. When you have this alternating powder of dark and light bands you get the striated colors of skeletal muscle.

Okay so what’s in a myofibril? Let’s start with the band. Give it a band and then I van. And a van has thick filaments, so that’s myosin. The iban has the thin filaments, so that Acton, troponin, and tropomyosin. Now what happens is during muscle contraction the sarcomere, which is the functional unit shortens and you have this overlapping of these band. This overlap occurs in the H Zone, along that the M line. The whole sarcomere itself is separated by the Z discs or Z lines, and it is the functional unit and the smallest unit of muscle contraction.

Now that we’ve gotten that out of the way, let’s look at the T system. The T system is the transverse system, and what happens is the sarcolemma which is the cell membrane, needs to get information inside of it. And the way that says this is to these long tubules in the sarcoplasm. What happens is as the nurse comes in and sends an action potential from the nervous system to the muscle cells it’s transferred through this tube system. The signal is sent from the outside of the cell membrane all the way down to the myofilaments and causes the muscle contraction.

So now that you understand how it gets in the outside of the cell down into the myofilaments, we need to look at the structure of something called the sarcoplasmic reticulum and Triads. Now the sarcoplasmic reticulum is the closest mm of tubules inside the sarcoplasm. So this is the tubules in the cytoplasm of the muscle cell. There is a central network of reticulum call the reticular Network here and this goes out to the circle tubules which extend laterally so away from the middle. At the end you has something called terminal cisternae. The whole purpose of the sarcoplasmic reticulum is to regulate calcium within the sarcoplasm, and it does this with calcium channels. In each section you’ll have something called a Triad. The Triad consists of a central t-tubule and two lateral cisternae on each side.

Okay so let’s recap. All of the layers of muscle have connective tissue. You have the endomysium, perimysium, and epimysium. The myofibrils are the Contractile units of the muscle cell, and they consist of the sarcolemma, sarcoplasm Anna and the contractile filaments myosin, Acton, tropomyosin, and troponin. Myofibrils structure. This is your iban, you’re a band, your H Zone with your in line, and the Z disc which go from each end of the sarcomere. The T system is the tubules system which allows Action potentials to go from the neuron all the way to the inside of the cell. The sarcoplasmic reticulum is a system of tubules that regulate calcium in the sarcoplasm with calcium channel.

That’s it for a lesson on skeletal muscle and all the components to go into it. Make sure you check out all the resources attached to this lesson. Now, go out and be your best selves today, and as always happy nursing

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