Physiology, drugs and disease
Muscle Structure and Function
FdSc FISM
Year 2
Janis Leach
15/01/10
Objectives
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Define 3 types of muscle tissue
Describe the functions of muscle
Outline the structure of muscle
Explain the sliding filament theory
Types of muscle tissue
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Skeletal muscle
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Cardiac muscle
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Voluntary muscles – attachments to bones
Involuntary muscle only present in the heart
Smooth muscle
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Involuntary muscle found in walls of hollow organs
Functions
 Movement
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Skeletal muscle contracts and exerts force
on the skeletal system
Cardiac muscle allows the pressure to
pump blood around the body
Smooth muscle in the walls of blood
vessels maintains BP
Functions
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Postural maintenance
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Skeletal muscles maintain posture
Joint Stability
 Skeletal
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muscles contribute to joint stability
Heat Generation
 Muscles
produce heat during contraction
 Critical in maintaining normal body
temperature
Structure of muscle
Structure
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Epimysium
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Fascicles
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Bundles of muscle cells
Perimysium
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Whole muscle wrapped in connective tissue
Surrounds the bundles
Endomysium
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Each muscle fibre surrounded by sheath of
tissue – gives strength and elasticity
Muscle cell
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Skeletal muscle cells are very large compared
to other cells
Muscle cells or fibers are long cylindrical
cells with multiple oval nucleui arranged just
below the sarcolemma or plasma membrane.
Myofibrils (contractile elements of the
muscle cell)
Muscle cell
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Note the alternating dark and light bands in
the muscle fiber that consist of even smaller
contractile units called sarcomeres (muscle
segemen). The sarcomere is the smallest
contractile unit of a muscle fiber
Myofibrils
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thick filament  myosin
thin filament  actin
Myosin - Each filament within a scaromere
contains  200 myosin molecules.
Actin - Also has several regulatory proteins
Sliding filament theory
Huxley’s sliding filament theory of muscle
contraction
 Muscle cells shorten because their sarcomeres
shorten. As the length of the sarcomeres
shortens, the myofibrils shorten resulting in a
shortening of the cell as a whole.
 The thick or thick filaments do not change
length during shortening.
Sliding filament theory
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As name of the theory suggests the
change in the length of the sarcomere is
due to the sliding of the filaments.
The overlap of the thick and thin filaments
changes during shortening with the thin
filaments sliding toward the centre of the
sarcomere.
Contraction of skeletal muscle
•During contraction the
cross-bridges between
the myosin and actin
filaments
pull
them
towards one another this
increases the overlap
and pulls the Z lines
towards one another.
Motor unit
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Consists of motor neuron and all the muscle
fibres that it supplies
It is the functional unit of skeletal muscle
1 motor unit can supply 2000 muscle fibres
Precise movements – 1 unit will supply 2 or 3
fibres
Non precise – 1 will supply hundreds
A single motor unit will cause weak contraction
of the entire muscle.
Task
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Describe the sliding filament theory in
your own words
Explain what a motor unit is