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41 elements of muscle structures, Recruitment of Motor units - Coggle…
41
elements of muscle structures
composition of muscle fibers
Contractile proteins
Single muscle contains many
fascicles
:
groups of muscle fibers surrounded by
connective tissues
Cell:
Muscle fiber
Cell membrane:
Sarcolemma
Cytoplasm:
Sarcoplasm
Content:
Myofibrils
– contractile structure
of a muscle fiber
Other contents include: ribosomes,
glycogen, mitochondria
Myofibrils are made up of thick and thin
myofliments
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contractile unit
Z Discs
serve as boundaries for
Sarcomere
and link the thin filaments
together
Bands
or
Zones
help to identify the arrangement of thick and thin filament in
a sarcomere
A band
(anisotropic) – length of
the thick filament and the
overlapping area of the thin
filament
H zone
length of the thick
filament with out overlap
M Band
connection at the
center of myosin filaments
I band
(isotropic) – length of
the thin filament without
overlap
Cross-bridge interaction
Muscle
contraction
Initiated by arrival of nerve impulse at motor end plate
Evokes an electrical impulse
Action
potential
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Types of Muscle Contraction
Isometric contraction:
Length of sarcomere is constant
Concentric contraction:
Thin myofilaments are pulled
towards the thick filaments
Cross-bridges are formed, broken and reformed
Active shortening of muscle fibre
Eccentric contraction
(Lengthening contraction):
Thin myofilaments are pulled away from
the thick filaments
Cross bridges are broken, reformed and broken again
motor unit
Organisation
Consists of Alpha motor neuron and all the muscle fibers it
innervates
Motor axon leaves through the ventral root
All cell bodies are in the ventral horn of the spinal cord
Axons extends from cell body to muscle fibers, divides into few ends or as many as thousands of small branches
Size of the motor unit is determined by
-Number of muscle fibers
-Size of motor nerve axons
The contraction of entire muscle
is the result of
many motor units firing
asynchronously and
repeatedly
Magnitude of contraction affected by
Changing number of activated motor units
Frequency of activation
Motor units may vary according to
Size of neuron cell body
Diameter of the axon
Number of muscle fibers
Type of muscle fibers
muscle structure
muscle tissues
(contractile)
has the ability to develop
tension in response to stimuli
Chemical
Electrical
Mechanical
connective tissues
(noncontractile).
develop tension in response
to passive loading
are often called striated muscles
muscular connective tissue
Recruitment of Motor units
Size principle of motor unit recruitment strategy
In isometric muscle action:
Motor units with small cell bodies and fewer motor fibers are recruited first,
and as force increases large motor units are recruited
This recruitment strategy is based ultimately on the force required for motion
Energy conserving
Recruitment strategy may also be based
Nature of the task
Multitask muscles will be recruited differently for the motion
Eg: flexion and supination by biceps brachii
Type of muscle action
Small distal muscles tend to rely on increased frequency
Proximal muscles rely on recruitment of additional muscles
(isometric, concentric and eccentric)