Anatomy of skeletal muscles Flashcards
Definition of myofibre
Skeletal muscle fibre
Definition of myonucleus
Nucelus in syncytial muscle fibre
Definition of myofibril
Rodlike structure of many sarcomeres in series
Definition of myogenesis
Process of making skeletal muscle
Definition of myoblast
Proliferative cell committed to making skeletal muscle
Definition of myocyte
Mononucleated differentiated muscle cell
Definition of myotube
Immature muscle fibre with centrally located nuclei
Definition of satellite cell
Resident stem cell of skeletal muscle
Definition of prime mover
Agonist in muscle movement, concentric contraction such as gravity
Definition of antagonist
Opposite agonist/prime mover
Definition of synergist
Complements prime mover action either with same movement of by acting as fixator of intervening joint
Definition of fixator
Movement that stabilizes position through isometric contraction
Function of skeletal muscle
Force generation for movement, breathing
Force generation for postural support
Heat production
Metabolism
Type of muscles
Skeletal muscle
Cardiac muscle
Smooth muscle
Properties of skeletal muscle
Striated
SNS, voluntary
Multinucleated, unbranched
Properties of cardiac muscle
Striated
ANS, involuntary
Branched, joined by intercalated discs
Properties of smooth muscle
Not striated
ANS, involuntary
Not branched, spindle single cells
Characteristics of muscle fibres
1 fibre=1 muscle cell
40-100um in diameter, cms long
Larger for power, smaller for coordination
Myonuclei on periphery, controls syncytial cell
Cytoplasm packed with myofibrils and mitochondria
Structures and properties of skeletal muscles and tendons
Move skeleton
Muscles attach to skeleton by tendon
Endo, peri and epimysium merge with dense CT of tendon at myotendinous junction
Tendons transmit muscle force to bone
Tendons made of collagen, strong and stiff
Muscle arrangements
Generate force by contracting
Only pull in antagonistic pairs
Flexors and extensors
Types of contraction
Isotonic (dynamic)
Isometric
Isotonic (eccentric)
Isotonic (dynamic)
Concentric muscle shortens during force production
Isometric
Muscle exerts force without changing length
Pulling against immovable object
Postural muscles
Isotonic (eccentric)
Muscle produces force but length increases
General structures and connective tissue in skeletal muscle
CT holds fibres in position in skeletal muscle Epimysium Perimysium Endomysium Vessels and nerves embedded in CT
Epimysium
Tough outermost layer, surrounds entire muscle
Perimysium
Surrounds muscle fibre bundles, create fascicle
Endomysium
Surrounds each fibre with fascicles
Architecture and shape of skeletal muscles
Circular Fusiform Flat parallel Bipennate Unipennate Digastric Multipennate Convergent Tendinous intersections Thin parallel
Formation of skeletal muscle
Myoblasts fuse into myotubes to form syncytial cells
Satellite cells and properties
Type of stem cell on muscle fibre surface, dormant in mitosis, but can self renew, maintain stem cells population
Can be activated, enter cell cycle, become my oblasts
Myoblasts proliferate, differentiate, become new myonuclei
Myonuclei cannot divide
Importance of satellite cells
Muscle growth after birth
Muscle maintenance
Muscle hypertrophy
Muscle repair and regeneration
Composition of myofibrils
Sarcomere, contractile unit of skeletal muscle
Myofibrils made up of 2 protein filaments
Myosin and actin
Sarcomere organisation
H bands, myosin only
A band, length of myosin
Z, center of actin
I band, actin only
What happens when the sarcomere contracts
Z lines move closer together
I and H bands narrow
A band does not change
Subtypes of muscle fibres
According the speed of contraction
Speed of contraction depends on myosin heavy chain isoform
T1 slow
T2 fast IIa, IIb, IIx
Metabolic properties of fast fibres
Found in white fibres, small amount of myoglobin
Metabolic properties of slow fibres
Found in red fibres, large amount of myoglobin
Fibre specification
I slow oxidative
IIa fast oxidative
IIb fast glycolytic
Iix super fast glycolytic
Fibres in 1 motor unit
All the same
How are muscles innervated
Myofibre innervated from 1 motor neuron
Nerve in contact with NMJ on fibre membrane
1 neurone contacts motor unit (many fibres)
Motor unit size increases degree of muscle control
Muscle circuit diagram
Motor neurone to muscle
Muscle to sensory afferent neurone to dorsal root
Dorsal root in spinal cord to motor neurone
What happens when you don’t use your muscles
Mature muscles normally grow by hypertrophy
Skeletal muscle fibres cannot self renew
New fibres replaced by satellite cells, activated in repair
Ability to repair/build muscle decreases with age
Can be replaced by adipose, fibrous tissue, impedes function
Definition of aponeurosis
Large flat tendon
Definition of raphe
Tendons between small groups of muscle that have fused together
Definition of intermediate tendon
Tendon that breaks up digastric muscle
Describe a 1st class lever
Force is on one side of the pivot, weight is on the other side of the pivot
Pivot=top of spine
Weight=head
Force=splenius capitus
Muscle that can pull your head back (splenius capitus)
Describe a 2nd class lever
The force is more distal from the pivot than the weight
Pivot=ball of foot
Weight=body weight
Force=calves
The calf muscles. 2nd class levers often used for power
Describe a 3rd class lever
The weight is more distal to the pivot than the force
Pivot=elbow
Weight=arm
Force=bicep brachii
3rd class levers used more for control than power
