Skeletal Muscle Flashcards
How is skeletal muscle formed
Fusion of myoblasts to form multi-nucleated cells - muscle fibres
Where are the nuclei of muscle fibres
At the edge of the fibres just beneath the plasma membrane (plasmalemma)
Appear alongside the pink-stained fibre
What forms the striations of skeletal muscle
Myofibrils lie in parallel with one another and are joined side by side with the sarcomeres in register
Endomysium
Specialised connective tissue between muscle fibres
Permysium
Bundles of muscle fibres are bound together to form fasciculi by a sheath of connective tissue
Epimysium
Groups of fasciculi are bound together to form muscles by more connective tissue
Myofibrils
A linear series of sarcomeres connected by Z lines
2 major contractile proteins of sarcomere
Myosin
Actin
Myosin
Bipolar thick filaments
What is the maximum amount of shortening of the sarcomere
30%
Extrinsic work
Thin actin filaments slide deeper within the A band bringing the Z lines closer together and shortening the sarcomere
Intrinsic work
Shortening of the sarcomere is minimal but tension within the muscle increases
Function of titin
Maintaining the structural integrity of the myofibrils
Which part of the sarcomere is darker staining
A bands
Which part of the sarcomere is lighter staining
I band
Khonheim’s fields
A refractory optical feature
A slightly oblique cut involving more than one band of the sarcomere
What stain is commonly used to resolve the bands of a sarcomere
Iron haematoxylin
3 types of muscle fibres
Type 1
Type 2A
Type 2B
Type 1 muscle fibres
Slow twitch
Oxidation in terms of energy supply
Fatigue resistant
Where are type 1 muscle fibres found in highest numbers
Postural muscles
Type 2A muscle fibres
Fast twitch
Use a mixture of oxidative and glycolytic processes to obtain energy
Moderately fatigue resistant
Type 2B muscle fibres
Fast twitch
Dependent on glycolytic processes for energy
Fatigue sensitive
Where are type 2B muscle fibres predominantly found
Sprint muscles
Structure of type 1 muscle fibres
Large mitochondria that lie in rows between myofibrils
Fat droplets alongside mitochondria - use as a source of triglyceride for production of ATP
Structure of type 2 muscle fibres
Fewer and smaller mitochondria
Large reserves of glycogen
Mysium
Connective tissue that connects muscles to bone
Sharpey’s fibres
Numerous small collagen bundles that surrounds the muscle fibres
What do the collagen bundles of Sharpey’s fibres merge with
Fibrous periosteum of bone and collagenous matrix of bone itself
Examples of Sharpey’s fibres
Origins of rotator cuff muscles on the blade of the scapula
Advantage of Sharpey’s fibres
Spreads force of the muscle over a wide area
Advantage of Tendons
Exert force over a smaller, more defined area
Example of tendons
Tendinous insertions of the rotator cuff muscles on the head of the humerus
What composes tendons and aponeuroses
Condensed parallel bundles of collagen fibres interspersed with fibroblasts
What happens at the end of muscle
Fasciculi split becoming smaller but more numerous
Connective tissue between becomes more prominent
Structure of tendon
Continuation of the peri and Epimysium of the muscle which becomes highly condensed to form tough inelastic bands
Structure of muscle spindles
A small number of muscle fibres (intrafusal fibres) isolated from the surrounding extrafusal fibres by a connective tissue sheath
Intrafusal fibres
Have nerve fibres wound around them
Function of muscle spindles
Relay information about the degree of contraction of the surrounding muscle
Which muscles have more muscle spindles
Muscles with fine movements with small motor units have more than larger motor units concerned with course movements
Are bundles of muscle fibres in the tongue small or large
Generally quite small
What do small fascicles denote
Smaller motor units
- greater the level of fine movement and control
Are all skeletal muscle anchored to bone
No - some are interconnected by fibrous connective tissue eg a raphe
Dystrophin
Binds actin to the plasmalemma of muscle cells
Mechanism of muscular dystrophy
Dystrophin fails to bind actin successfully to the plasmalemma causing weakness in the muscles
What is the major protein of Z lines
Alpha actinin-
(60% lipid which electrostatically binds the proteins together)
Which type of collagen composed tendons and Sharpey’s fibres
Type 1
How is a torn tendon repaired
Tearing causes inflammation which stimulates the fibroblasts to synthesise actin and collagen
Approximately how many actin filaments are there to each myosin filament in a sarcomere
6 (hexagonal close packing) - each actin filaments also interacts with another adjoining myosin filament
To what are the actin filaments within a sarcomere attached
Nebulin
Tropomyosin
Nebulin function
Binds actin to Z line
Tropomyosin function
Orients actin with respect to myosin
What prevents a sarcomere being stretched beyond its normal limits
Non-contractile proteins - titin and nebulin
What is a motor unit
A group of muscle fibres that receive a nerve supply from the same axon and therefore respond identically to stimulation
Golgi tendon organs
Reside close to or within tendons and monitor tension within the muscle
Muscle types
Smooth muscle
Skeletal muscle
Cardiac muscle
Other contractile cells - pericytes, myo-fibroblasts, myo-epithelial cells
Where is skeletal muscle found
Skeletal muscles
Larynx
Diaphragm
Syncytium
Myoblasts fused to form multi-celled syncytium
Fascicles
Muscle fibres clumped together
Dimensions of a muscle fibre
50-60 um diameter
Up to 10cm in length
T-tubules
Convey Ca2+ into the cytoplasm
Skeletal muscle overview
Voluntary muscle
Elongated fibres
Striated cytoplasm
Mutlinucleate
Nuclei at edges
Non-branching
Is skeletal muscle branching
No
Structure of a sarcomere
Z line
I band
A band
H zone
M line
Which type of muscle fibre are richer in ATPase
Type 1
Type of nerve fibres in a muscle spindle
Gamma efferent
What do fibroblasts synthesise
Collagen
