Unit 3.2: Skeletal Muscles Flashcards
What are the characteristics of skeletal muscles? How are they attached to bones?
Responsible for positioning and movement of the skeleton
Attached to bones via tendons
What are tendons composed of?
Dense regular connective tissue (collagen)
What is the structure of skeletal muscles?
Outer connective tissue: epimysium Contains bundles of: Fascicles Which are covered by perimysium Fascicles contain muscle fibres Which are covered by endomysium Muscle fibres contain myofibrils
What does the cytosol of muscle fibres contain?
Many glycogen granules (energy storage) and mitochondria (ATP synthesis)
What is the structure of a muscle fibre?
Long, cylindrical cell
Has several hundred nuclei
What is the cell membrane of the muscle fibre called?
Sarcolemma
What is the ER of muscle fibres called?
Sarcoplasmic reticulum
What is associated with the SR?
Transverse tubules (T-tubules)
What is characteristic of the t-tubule’s lumen?
It is continuous with the ECM
What is closely associated with t-tubules?
Terminal cisternae
What do terminal cisternae do?
They sequester (store) Ca2+
What is a triad?
One t-tubule with flanking terminal cisternae
What do t-tubules allow?
Rapid AP diffusion into the muscle fibre
What are the muscle equivalents of: Muscle cell Cell Membrane Cytoplasm Modified ER
Muscle cell ———– Muscle fiber
Cell Membrane —– Sarcolemma
Cytoplasm ———— Sarcoplasm
Modified ER ———- Sarcoplasmic reticulum
What protein occupies most space in a muscle fibre?
contractile structures
What are the different proteins found in a muscle?
- Contractile proteins: Actin and Myosin
- Regulatory proteins: Tropomyosin and Troponin
- Accessory proteins: Titin, Nebulin, others
What do myofibrils have under light microscope?
Striations
What is one repeated pattern of striations called?
Sarcomere
What is a sarcomere made of?
- Z-line (disks)
- I band (isotropic): reflects light uniformly
- A band (anisotropic): scatters light unevenly
- H zone (part of the A band)
- M-line
What causes striations?
The organization of the protein components of the myofibrils
What is the structure of myosin?
Consists of 2 coiled protein molecles that have 2 important parts: head and tail region
Head and tail are stiff and are joined by a flexible hinge
What makes up a thick filament?
250 myosin molecules join
How are myosins arranged in the cell?
Heads are at the ends
What are the subunits of actin?
G-actin (globular actin)
What is the structure of actin?
G-actin subunits polymerize to form chain called f-actin
2 f-actins twist together to form a thin filament
What does the coiled f-actin associate with?
Regulatory proteins troponin and tropomyosin
What do the regulatory proteins do?
Regulate muscle contraction
forms the completed thin filament
What is it called when myosin heads interact with actin filaments?
Crossbridges
What are Z-lines?
Disks
Site of attachment for thin filament
One sarcomere is made of 2 Z disks and the filaments between them
What are I band?
This is a region containing only thin filaments
Z-disc runs through th emiddle of an I band, thus each half of the I band is part of a different sarcomere
What is the A band?
Region containing both thick and thin filaments
They overlap at the edge of the A band
Center is only thick filaments
What is the H zone?
Part of the A band, it contains ONLY thick filaments
What is the M line?
Site of attachment for thick filaments
M line is the center of the sarcomere
What would cross sections of the muscles will show you?
One thin filament surrounded by 3 thick
One thick filament surrounded by 6 thin
What proteins allow for proper alignment within a sarcomere?
- Titin - elastic protein, largest known protein, stretches from Z-disc to M-line and stabilizes position of contractile filaments
- Nebulin - non-elastic, attaches to Z disc and helps to align actin filaments in the sarcomere
