Download Properties of Muscle Fibers

PROPERTIES OF MUSCLE FIBERS
LEARNING OBJECTIVES
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By the end of this presentation, the students should be able to understand:
Types of muscle fibers.
Properties of muscle fibers.
Functions of muscles.
Stimulus and properties of stimuli.
Effects of multiple stimuli on muscle fibers.
Properties of smooth muscle and cardiac muscle fiber.
MUSCL
ES
SKELETAL
SMOOTH
CARDIAC
STRIPED,
STRIATED,
SOMATIC,
VOLUNTARY.
PLAIN,
UNSTRIPED,
NON-STRIATED,
VISCERAL,
INVOLUNTARY.
STRIATED,
BRANCHED,
INVOLUNTARY.
PROPERTIES OF MUSCLE FIBRES
 Contractility
 Ability of a muscle to shorten with force
 Excitability
 Capacity of muscle to respond to a stimulus
 Extensibility
 Muscle can be stretched to its normal resting length and beyond
to a limited degree
 Elasticity
 Ability of muscle to recoil to original resting length after
stretched
FUNCTION OF MUSCLES
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Produce movement
Maintain posture
Stabilize joints
Generate heat
NERVE STIMULUS TO MUSCLES
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a)
b)
c)
d)
Skeletal muscles must be stimulated by a nerve to contract (motor
neuron).
Motor unit
One neuron.
Muscle cells stimulated by that neuron
Smooth muscles are innervated by autonomic fibers.
Cardiac muscle fibers are regulated by pacemaker activity from the
SinoAtrial Node (SAN).
TYPES OF STIMULUS
 Electrical- commonly used in labs
 Mechanical
 Thermal
 Chemical
 Electro-magnetic
QUALITY OF STIMULUS
 Strength of stimulus- subminimal, minimal (threshold), submaximal,
maximal and supramaximal
 Duration of stimulus
MUSCLE TWITCH
 Muscle contraction in response to a stimulus that causes action
potential in one or more muscle fibers
 Phases
 Lag or latent
 Contraction
 Relaxation
CONTRACTION OF A SKELETAL MUSCLE
 Muscle fiber contraction follows “all or none” principle.
 All or None response
An individual muscle fiber exhibits contraction of an uniform intensity
once their particular threshold has been reached
FACTORS AFFECTING CONTRACTION
a) Strength of stimuli- summation
b) Effect of multiple stimuli:
i) beneficial effect
ii) summation
iii) clonus
iv) tetanus
v) treppe
vi) fatigue
c)
Effect of temperature
MUSCLE RESPONSE TO STRONG STIMULI
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Muscle force depends upon the number of fibers stimulated
More fibers contracting results in greater muscle tension
Muscles can continue to contract unless they run out of energy
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Muscle force depends upon the number of fibers stimulated
More fibers contracting results in greater muscle tension
Muscles can continue to contract unless they run out of energy



Muscle force depends upon the number of fibers stimulated
More fibers contracting results in greater muscle tension
Muscles can continue to contract unless they run out of energy
FATIGUE
 Def: it is a decrease in the performance due to continuous and prolonged activity
 Site of fatigue: CNS is the first site of fatigue even though the muscle itself can
undergo fatigue.
 Nerve is indefatigable
MUSCLE FATIGUE AND OXYGEN DEBT
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When a muscle is fatigued, it is unable to contract
The common reason for muscle fatigue is oxygen debt
Oxygen must be “repaid” to tissue to remove oxygen debt
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Oxygen is required to get rid of accumulated lactic acid
Increasing acidity (from lactic acid) and lack of ATP causes the muscle to
contract less
MULTIPLE MOTOR UNIT SUMMATION
A whole muscle contracts with a small or large force depending on number of motor
units stimulated to contract
MULTIPLE-WAVE SUMMATION
 As frequency of action potentials increase, frequency of contraction
increases
 Action potentials come close enough together so that the muscle does
not have time to completely relax between contractions.
TREPPE OR STAIR CASE EFFECT
 Graded response
 Occurs in muscle rested for prolonged period
 Each subsequent contraction is stronger than previous until all
equal after few stimuli
TYPES OF MUSCLE CONTRACTIONS
 Isotonic contractions
 Myofilaments are able to slide past each other during
contractions
 The muscle shortens
 Isometric contractions
 Tension in the muscles increases
 The muscle is unable to shorten
III. CONDUCTIVITY
 Velocity of action potential conduction across skeletal muscle is
5m/sec
 In nerves it is up to 120m/sec
 Conduction is along the sarcolemma and moves along the T-tubules
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MUSCLE TONE
 Some fibers are contracted even in a relaxed muscle
 Different fibers contract at different times to provide muscle tone.
 The process of stimulating various fibers is under involuntary or
reflex control
EFFECTS OF AGING ON SKELETAL MUSCLE MASS
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Increased time for muscle to contract in response to nervous stimuli
Reduced stamina
Increased recovery time
Loss of muscle fibers
Decreased density of capillaries in muscle
MUSCLE ATROPHY
 Weakening and shrinking of a muscle
 May be caused
 Immobilization
 Loss of neural stimulation
MUSCLE HYPERTROPHY
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Enlargement of a muscle
More capillaries
More mitochondria
Caused by
 Strenuous exercise
 Steroid hormones
MUSCLE TONUS
 Tightness of a muscle
 Some fibers are always contracted
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TETANY
 Sustained contraction of a muscle
 Result of a rapid succession of nerve impulses
TETANUS
REFRACTORINESS
RIGOR MORTIS
 Stiffening of the body beginning 3 to 4 hours after death
 Deteriorating sarcoplasmic reticulum releases calcium
 Calcium activates myosin-actin cross-bridging and muscle contracts,
but can not relax.
 Muscle relaxation requires ATP and ATP production is no longer
produced after death
 Fibers remain contracted until myofilaments decay.
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