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Muscle
Readings: Ch. 14, pp. 255-278
• Three different type of
muscles in human
– Smooth (visceral) muscles
– Cardiac muscle
– Skeletal muscle
• Function of muscle
– Movement of limb
– Posture maintenance
– Heat production (chemical Æ
mechanical E conversion)
– Protection of organs
– Pressure alteration
• Basic muscle
characteristics
– contractility--capacity to
shorten by stimulationÎ
Tension
– extensibility--capacity to
lengthen
– elasticity--ability to return to
original state after
lengthening or shortening
Structure of Muscle
• Active Tissue
– Excitable muscle fibers (tissues) and their cross-bridge
– Contractile part : muscle
• Passive structure
– Non-excitable tissue : tendon
– connective tissue that organizes muscle fibers and binds them
together
BASIC MUSCLE FUNCTION
!
Readings: McGinnis Chapter 14
Excitable (_____) muscle tissues -- muscle fibers:
actin/ myosin elements and their linkage
(cross bridges)
Non-excitable (_____) tissues -- connective
tissue that organizes muscle fibers and binds
them together
How Muscle Force is Generated:
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Active vs. passive muscle tissues...
Muscles convert chemical energy into
________________
Muscles are internal motors of human body
responsible for all movements of skeletal system
Muscles can only ____; they cannot ____
Muscles must cross a joint to create motion
Our focus--skeletal (striated) muscle
!
Actin/Myosin arrangement:
Myosin - _____ filaments or myofibrils
Actin - ____ filaments
Basic muscle characteristics:
!
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_________--sensitive to stimulation
_________--capacity to shorten
_________--capacity to lengthen
_________--ability to return to original state after
lengthening or shortening
Basic muscle structure:
!
There is considerable variation in size, shape,
structure depending on function, e.g., need for
power, ROM, fast movement, postural control, or
precise movement.
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Muscle actions:
Sliding Filament
Theory
!
Concentric --
active muscle
that _______
against
resistance
Steps:
1. Myosin filament forms
x-bridge to actin
e.g., biceps brachii during elbow flexion in a
standing biceps curl
2. Myosin pulls actin
!
3. x-bridge releases
Eccentric -- active muscle that _________
against a resistance
e.g., biceps brachii
during elbow
extension in a
standing biceps curl
4. Myosin ready for
another x-bridge
formation
Myosin
Actin
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!
Isometric ("same length") or static -essentially __________ in overall muscle
length during activation
!
It is important to remember that when a
muscle is activated, the only thing it can try to
do is _________ (i.e., tries to bring the origin
and insertion closer together)
Relates to directionality of cross-bridge
function.
!
______________- rate at which MUs are
stimulated. To increase force, NS
recruits MUs more frequently (e.g., from
10 Hz to 25 Hz).
Muscle architecture
C
Physiological ______________ area:
greater area, greater force producing
ability
Fiber orientation...
Factors affecting muscle force production:
!
Excitation factors - role of nervous system
C Motor unit recruitment
__________ (MU) = a motor neuron
and all muscle fibers it innervates.
When a motor neuron is activated, all
of its muscle fibers are activated and
contribute to force production.
To increase force, nervous system
(NS) recruits _________.
Lower
_____
_____
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CSA
Force
Shortening
Higher
_____
_____
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!
Muscle Mechanics
Force - Velocity Relationship
Force production is a function of the number of
____________ formed at any given time.
Force-Length Relationship
active and passive components...
Concentric - _____________________,
lower potential to form cross-bridge
attachments, lower F producing potential
Eccentric - greater forces can be sustained
by muscle under __________ conditions
compared to concentric and isometric
"Directionality" of cross-bridge function takes _____ force to break attachment
under eccentric conditions.
Active component - related to ___________
overlap: # cross-bridges formed at any given time
Passive response - related to ____________
response: a very stiff rubber band
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Muscle length
• Force production is a function of the # of cross-bridges
formed at any given time.
<Length – Tension Relationship>
Interaction of the actin and myosin filaments with each other and the Z
disks determine the magnitude of active tension developed in a sarcomere.
Muscle Temperature
Value of warm-up: primarily affects
_______________; has the effect of
increasing force and power potential at any
given velocity
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