Structure of Skeletal Muscles Flashcards
What are the 7 structures of a skeletal muscle?
- Epimysium.
- Perimysium.
- Fasiclcle.
- Endomysium.
- Muscle fiber.
- Sarcolemma.
- Myofibril.
What is the Epimysium?
A connective tissue sheath that -
- Enwraps the entire muscle.
- Enables muscle to retain structural integrity when contracting + lengthening.
- Keeps muscles separate from each other.
What is the Perimysium?
A connective tissue sheath that -
- Enwraps the fascicles.
- Allows the nervous system to recruit fibres housed within the fascicle with greater specificity.
What is Fascicle?
A bundle of skeletal muscle fibres surrounded by the perimysium.
What is the Endomysium?
Connective tissue sheath that -
- Enwraps individual muscle fibres.
- Surrounds + supports the cell’s extracellular matrix.
What is the Muscle Fibre?
- Muscle fibre is composed of many fibrils.
- Gives the cell its striated appearance.
What percentage of muscle fibre is occupied by water?
75%.
What percentage of muscle fibre is occupied by protein?
20%.
What 2 proteins make up the 20% of muscle fibre space?
- Myofibrillar (15%)
- Non myofibrillar (5%)
What are Myofibrillar proteins (15%)?
- Proteins involved in contraction.
What are Non Myofibrillar proteins (5%)?
- Are enzymes.
What is the Sarcolemma?
- Is the cell membrane covering each muscle fibre.
- Consists of elastic properties.
- Needs to have elasticity to withstand tensile load + not rupture.
What is the Myofibril?
- Give the fibre its structure and function.
- Myofibrils are suspended in the sarcoplasm + run the length of the fibre.
- Are made up sarcomeres connected in series.
Outline the 4 steps on how connective tissue structures permit ‘Force Transmission’ to produce movement.
- When a muscle contracts tension is created.
- Tension is transferred sequentially through each connective tissue layer to the tendon.
- Force is concentrated at the myoconnective junction.
- Force is transferred to the periosteal layer of the bone, which pulls on it + creates movement.
Where are Nuclei found in a muscle fibre?
- Found at the periphery of the fibre in the space between the myofibrils + sarcolemma.
Where is there a higher Myonuclei density in the muscle fibre?
Motor end plate.
Why is it important muscle fibres have multiple nuclei?
- More nuclei support the theory of Hypertrophy.
- It supplies the muscle with protein allowing it to grow.
Outline the layered structure of the Sarcolemma.
- Phospholipids.
- Membrane-bound receptors + transport molecules.
- Structural proteins that anchor the cytoskeleton to the extracellular matrix.
What is the Basement Membrane?
- Found external to the Sarcolemma.
- Anchors the fibre.
- Supports cell development + regernation.
- Helps mechanotransduction to occur.
What is the Basement Membrane also referred to as?
Basal lamina.
What is the Sarcoplasm?
- The cytoplasm of muscle fibres.
- Densely packed with myofibrils.
- It suspends myofibrillar proteins + organelles.
What percentage of space does the Sarcoplasm take up of a muscle fibre?
9%.
List 4 contents found in the sarcoplasm.
- Ions.
- Enzymes.
- ATP.
- Glycogen.
What percentage of the intracellular space of the muscle fibre does mitochondria occupy?
5-6%.
What 2 things will an increase in the size + density of mitochondria lead to?
- This will support energy production which can be used for muscular contraction.
- There will be a greater concentration of enzymes to aid reactions in Oxidative Phosphorylation.
What are Peripheral Mitochondria?
- Located closer to the periphery of the cell.
- Support active transport.
What are Inter-Myofibril Mitochondria?
- Extend inwards towards the centre of the cell.
- Provides energy for muscular contraction.
What is the Sarcoplasmic Reticulum?
- Stores, releases + retrives calcium ions.
- Calcium is fundamental for contraction.
What are Transverse tubules?
- Invaginations of the sarcolemma that extends inwards towards the centre of the cell.
- Stay close to the sarcoplasmic reticulum which is important for excitation-contraction coupling.
What is Terminal cisternae?
- A region close to the sarcoplasmic reticulum.
- Surrounds the transverse tubules.
- Stores calcium ions which is fundamental for excitation-contraction coupling.
What is the T-Tubule + Sarcoplasmic Reticulum mechanism?
- Allows communication between the outside of the cell membrane (SR) and deep in the muscle fibre.
- Signals would not be transmitted without these invaginations.
How many T-tubules does a skeletal muscle have for each Sarcomere?
2.
What percentage of the intracellular space do myofibrils occupy within the muscle fibre?
85%.
What is the Sarcomere?
- The smallest functional unit within the skeletal muscle.
- Made up of contractile + structural proteins.
Why is the Sarcomere regarded as a ‘Functional unit’?
- Contraction of sarcomeres leads to the contraction of muscle fibres, which leads to the contraction of the entire muscle.
What proteins does the sarcomere consist of?
- Myosin Filament (Thick)
- Actin Filament (Thin)
What are Z discs?
- Located on the edge of the sarcomere.
- Structural proteins.
- Support + define the area of the sarcomere.
What is the H zone?
The distance between actin filaments.
What is the A band?
The length of the myosin filament.
What is the I band?
The distance from the edge of myosin to the z-line.
What is the structure of the Myosin (Thick) filament?
- Made up of 2 myosin heavy chain molecules + 2 myosin light chain molecules.
- Consists of a tail, hinge + head region.
What are the 2 binding sites located at the head region of the ‘myosin heavy chain molecule’?
- Actin binding site.
- ATP binding site.
What is the Actin Binding site?
- Important for binding strokes + contracting the sarcomere.
What is the ATP Binding site?
- Important for energizing the binding strokes.
What is located at the hinge region of the ‘myosin light chain molecule’?
- Regularoty protein.
What do the heads of the ‘myosin heavy chain molecules’ contain?
- ATPase.
Outline the importance of ATPase.
- Will break down ATP into ADP + a free phosphate ion.
- This releases energy to power the contraction.
What is the structure of the actin (thin) filament?
- Made up of 2 actin chains.
- Troponin + Tropomysoin span the actin chain.
What is the functions of ‘Troponin’ and ‘Tropomyosin’?
- Both will shield actin binding sites so when at rest our sarcomeres aren’t contracting.
What is Titan, and what is its function?
- A structural protein.
- Provides elasticity.
- Stabilizes myosin.
- Assists eccentric muscular contractions.
What are satellite cells?
- When load is applied these cells will donate nuclei to the muscle fibre.
- Allows muscle fibre to grow more protein.
- Leading to muscular hypertrophy.
