Title: MUSCLE TISSUE
1MUSCLE TISSUE
2POSTURE / MOVEMENT
- Stable posture results from a balance of
competing forces. - Movement occurs when competing forces are
unbalanced. - Force generated by muscles is the primary means
for controlling the balance between posture and
movement.
3MUSCLE AS A SKELETAL STABILIZER
- Muscle generates force to stabilize the skeletal
system. - Muscle tissue is coupled to the external
environment and internal control mechanisms
provided by the nervous system allow it to
respond to changes in the external environment. - Whole muscles consist of many individual muscle
fibers. - Muscle adapts to the immediate (acute) and
repeated long-term (chronic) external forces that
can destabilize the body. - Fine control surgery
- Large forces dead-lift
4Types of Muscle Tissue
- Skeletal muscle tissue
- Cardiac muscle tissue
- Autorhythmicity - pacemaker
- Smooth muscle tissue
5Functions of Muscle Tissue
- Producing body movements
- Stabilizing body positions
- Storing and moving substances within the body
- Sphincters sustained contractions of ringlike
bands prevent outflow of the contents of a hollow
organ - Cardiac muscle pumps nutrients and wastes through
- Smooth muscle moves food, bile, gametes, and
urine - Skeletal muscle contractions promote flow of
lymph and return blood to the heart - Generating heat - thermogenesis
6Properties of Muscle Tissue
- Electrical excitability
- Produces electrical signals action potentials
- Contractility
- Isometric contraction tension without muscle
shortening - Isotonic contraction constant tension with
muscle shortening
7Properties of Muscle Tissue
- Extensibility ability of a muscle to stretch
without being damaged - Elasticity
- Ability of a muscle to return to its original
length
8Connective Tissue Components
- Fascia a sheet of fibrous CT that supports or
surrounds muscles and other organs - Superficial fascia (subcutaneous layer)
separates muscle from skin - Deep fascia holds muscles with similar
functions together - Epimysium outermost layer encircles whole
muscles - Perimysium
- Surrounds groups of 10 100 individual muscle
fibers separating them into bundles called
fascicles
9Connective Tissue Components
- Endomysium
- Separates individual muscle fibers within the
fascicle - Tendon
- All 3 CT layers may extend beyond the muscle to
form a cord of dense regular CT that attaches
muscle to the periosteum of bone - Aponeurosis
- A broad, flat layer of CT
10(No Transcript)
11BASIC COMPONENTS OF MUSCLE
12MUSCLE SIZE
- Whole muscles are made up of many individual
muscle fibers. - These fibers range in thickness from 10 to 100 µm
and in length from 1 to 50 cm. - Each muscle fiber is an individual muscle cell
with many nuclei. - The individual muscle fibers contract, which will
ultimately result in contraction of the entire
muscle.
13Nerve and Blood Supply
- Skeletal muscles are well supplied with nerves
and blood vessels - Neuromuscular junction the structural point of
contact and the functional site of communication
between a nerve and the muscle fiber - Capillaries are abundant each muscle fiber
comes into contact with 1 or more
14TWO TYPES OF PROTEINS IN MUSCLE
- Contractile proteins
- Actin and myosin
- Shorten the muscle fiber and generate active
force - Referred to as active proteins
- Noncontractile proteins
- Titan and desmin
- Titan provides tensile strength
- Desmin stabilizes adjacent sarcomeres
- Make up the cytoskeleton within and between
muscle fibers - Referred to as structural proteins
15Sarcolemma, T Tubules, and Sarcoplasm
- Sarcolemma the plasma membrane of a muscle cell
- T (transverse) tubules Propogate action
potentials extend to the outside of the muscle
fiber - Sarcoplasm cytoplasm of the muscle fiber
- Contains myoglobin protein that binds with
oxygen
16Myofibrils and Sarcoplasmic Reticulum
- Myofibril the contractile elements of skeletal
muscle - Sarcoplasmic reticulum (SR) encircles each
myofibril stores CA2 (its release triggers
muscle contractions)
17(No Transcript)
18Atrophy and Hypertrophy
- Muscular atrophy wasting away of muscles
- Disuse
- Denervation
- Muscular hypertrophy an excessive increase in
the diameter of muscle fibers
19Filaments and the Sarcomere
- Filaments structures within the myofibril
- Thin
- Thick
- Sarcomere basic functional unit of a myofibril
- Z discs separate one sarcomere from the next
20(No Transcript)
21MYOFIBRIL ELECTRON MICROGRAPH
22Filaments and the Sarcomere
- A band predominantly thick filaments
- Zone of overlap at the ends of the A bands
- H zone contains thick, but no thin filaments
- I band thin filaments
- M-line middle of the sarcomere
23Muscle Proteins
- Contractile proteins generate force
- Myosin
- Actin
- Regulatory proteins switch contraction on and
off - Structural proteins
24(No Transcript)
25Sliding Filament Mechanism
- Muscle contraction occurs because myosin heads
attach to the thin filaments at both ends of the
sarcomere and pull them toward the M line. - The length of the filaments does not change
However, the sarcomeres shorten, thereby
shortening the entire muscle.
26(No Transcript)
27RELAXED CONTRACTED MYOFIBRILS
28(No Transcript)
29POWER STROKE OF CROSSBRIDGE CYCLING
30Role of Ca2 in Contraction
- An increase in calcium ion concentration in the
cytosol initiates muscle contraction and a
decrease in calcium ions stops it.
31(No Transcript)
32MAJOR SEQUENCE OF EVENTS UNDERLYING MUSCLE FIBER
ACTIVATION
- 1. Action potential is initiated and propagated
down a motor axon. - 2. Acetylcholine is released from axon terminals
at neuromuscular junction. - 3. Acetylcholine is bound to receptor sites on
the motor endplate. - 4. Sodium and potassium ions enter and
depolarize the muscle membrane. - 5. Muscle action potential is propagated over
membrane surface. - 6. Transverse tubules are depolarized, leading
to release of calcium ions surrounding the
myofibrils. - 7. Calcium ions bind to troponin, which leads to
the release of inhibition of actin and myosin
binding. The crossbridge between actin and
myosin heads is created. - 8. Actin combines with myosin adenosine
triphosphate (ATP), an energy-providing molecule. - 9. Energy is released to produce movement of
myosin heads. - 10. Myosin and actin slide relative to each
other. - 11. Actin and myosin bond (crossbridge) is
broken and reestablished if calcium concentration
remains sufficiently high.
33Rigor Mortis
- After death the cellular membranes become leaky.
- Calcium ions are released and cause muscular
contraction. - The muscles are in a state of rigidity called
rigor mortis. - It begins 3-4 hours after death and lasts about
24 hours, until proteolytic enzymes break down
(digest) the cross-bridges.
34Neuromuscular Junction (NMJ)
- Muscle action potentials arise at the NMJ.
- The NMJ is the site at which the motor neuron
contacts the skeletal muscle fiber. - A synapse is the region where communication
occurs.
35Neuromuscular Juntcion (NMJ)
- The neuron cell communicates with the second by
releasing a chemical called a neurotransmitter. - Synaptic vesicles containing the neurotransmitter
acetylcholine (ach) are released at the NMJ. - The motor end plate is the muscular part of the
NMJ. It contains acetylcholine receptors. - The enzyme acetlycholineesterase (AChE) breaks
down ACh.
36(No Transcript)
37Production of ATP
- 1. From creatine phosphate.
- When muscle fibers are relaxed they produce more
ATP than they need. This excess is used to
synthesize creatine phosphate (an energy rich
compound).
38Production of ATP
- 2. Anaerobic cellular respiration.
- Glucose undergoes glycolysis, yielding ATP and 2
molecules of pyruvic acid. - Does not require oxygen.
39Production of ATP
- 3. Aerobic cellular respiration.
- The pyruvic acid enters the mitochondria where it
is broken down to form more ATP. - Slower than anaerobic respiration, but yields
more ATP. - Utilizes oxygen.
- 2 sources of oxygen.
- Diffuses from bloodstream.
- Oxygen released from myoglobin.
40Muscle Fatigue
- Muscle fatigue is the inability of a muscle to
contract forcefully after prolonged activity. - Central fatigue a person may develop feelings
of tiredness before actual muscle fatigue.
41Oxygen Debt or Recovery Oxygen Uptake
- Added oxygen, over and above resting oxygen
consumption, taken in after exercise. - Used to restore metabolic conditions.
- 1. To convert lactic acid back into glycogen
stores in the liver. - 2. To resynthesize creatine phosphate and ATP in
muscle fibers. - 3. To replace the oxygen removed from hemoglobin.
42Motor Units
- A motor unit consists of the somatic motor neuron
and all the skeletal muscle fibers it stimulates. - A single motor neuron makes contact with an
average of 150 muscle fibers. - All muscle fibers in one motor unit contract in
unison.
43(No Transcript)
44MOTOR UNIT
45Twitch Contraction
- A twitch contraction is the brief contraction of
all the muscle fibers in a motor unit in response
to a single action potential. - A myogram is a record of a muscle contraction and
illustrates the phases of contraction.
46(No Transcript)
47Refractory Period
- A period of lost excitability during which a
muscle fiber cannot respond to stimulation.
48Motor Unit Recruitment
- The process in which the number of active motor
units increases. - The weakest motor units are recruited first, with
progressively stronger units being added if the
task requires more force.
49Muscle Tone
- Even at rest a muscle exhibits a small amount of
muscle tone tension or tautness. - Flaccid when motor units serving a muscle are
damaged or cut. - Spastic when motor units are over-stimulated.
50Isotonic and Isometric Contractions
- Concentric isotonic activation (contraction) a
muscle shortens and pulls on another structure. - Eccentric isotonic activation the length of a
muscle increases during contraction. - Isometric activation muscle tension is created
However, the muscle doesnt shorten or lengthen.
51Types of Skeletal Muscle Fibers
- Slow oxidative (SO) fibers.
- Smallest of the fibers.
- Least powerful.
- Appear dark red much myoglobin and many
capillaries. - Resistant to fatigue.
52Types of Skeletal Muscle Fibers
- Fast oxidative-Glycolytic (FOG) fibers.
- Intermediate in diameter.
- Appear dark red much myoglobin and many
capillaries. - High level of intracellular glycogen.
- Resistant to fatigue.
53Types of Skeletal Muscle Fibers
- Fast Glycolitic (FG) fibers.
- Largest in diameter.
- Contain the most myofibrils, therefore more
powerful contractions. - Appear white low myoglobin and few capillaries.
- Large amounts of glycogen anaerobic
respiration. - Fatigue quickly.
54TWITCH CLASSIFICATIONS
- Slow twitch - Muscle fibers innervated by small
motor neurons have twitch responses that are
relatively long in duration and small in
amplitude. - Classified as S (slow) due to slower contractile
characteristics. - Associated fibers are classified as SO fibers due
to their slow and oxidative histochemical
profile. - Fast twitch muscle fibers associated with
larger motor neurons have twitch responses that
are relatively brief in duration and higher in
amplitude. - Classified as FF (fast and easily fatigable).
- Associated fibers are classified as FG due to
their fast twitch, glycolytic profile. - Intermediate
- Classified as FR (fast fatigue-resistant).
- Associated fibers are classified as FOG due to
utilization of both oxidative and glycoltyic
energy sources.
55MOTOR UNIT TYPES
56Distribution and Recruitment of Different Types
of Fibers
- Most skeletal muscles are a mixture of all three
types. - The continually active postural muscles have a
high concentration of SO fibers.
57Distribution and Recruitment of Different Types
of Fibers
- Muscles of the shoulders and arms are used
briefly and for quick actions, therefore they
have many FG fibers. - Muscle of the legs support the body and
participate in quick activities, therefore they
have many SO and FOG fibers.
58MUSCLE MORPHOLOGY
- Muscle morphology describes the basic shape of
the muscle. - The shape will influence the ultimate function of
the muscle. - The two most common forms are fusiform and
pennate.
59FUSIFORM PENNATE MUSCLE FIBERS
- Fusiform
- Fusiform muscles have fibers running parallel to
one another and the central tendon (i.e. biceps
brachii). - Pennate (Latin feather)
- Pennate muscles possess fibers that approach
their central tendon obliquely. - Pennate muscles have a greater number of muscle
fibers and generate larger forces. - Most muscles in the body are considered pennate.
- Subdivisions
- Unipennate
- Bipennate
- Multipennate
60MUSCLE SHAPES
61FEATURES THAT AFFECT THE FORCE THROUGH A MUSCLE
ON THE TENDON
- Physiological cross-sectional area
- The amount of active proteins available to
generate a contraction force - With full activation, the maximal force potential
of a muscle is proportional to the sum of the
cross-sectional area of all its fibers. - A thicker muscle generates greater force than a
thinner muscle of similar morphology. - Pennation angle
- Pennation angle refers to the angle of
orientation between the muscle fibers and tendon.
62PENNATION ANGLE DEGREE OF FORCE
- If muscle fibers attach parallel to the tendon
the angle is defined as 0 degrees (essentially
all the force generated is transmitted across the
joint). - If the pennation angle is greater than 0 degrees,
then less of the force produced is transmitted
through the tendon. - A muscle with a pennation angle of 0 degrees
transmits 100 of its contractile force
(theoretically). - A muscle with a pennation angle of 30 degrees
transmits 86 of its contractile force. - Most human muscles have pennation angles that
range from 0 to 30 degrees.
63PENNATION ANGLE VECTOR OF FORCE
64PENNATE VS. FUSIFORM
- In general, pennate muscles produce greater
maximal force than fusiform muscles of similar
volume. - Orienting muscle fibers obliquely to the central
tendon allows for more total muscle fibers into a
given length of muscle. This increases the
physiological cross-sectional area and therefore
the force.
65PASSIVE TENSION
- There are noncontractile elements of the muscle
and tendon. - These noncontractile elements are referred to as
parallel and series elastic components of muscle. - Series elastic components are tissues that lie in
series with active proteins. - Parallel elastic components are tissues that
surround or lie in parallel with the active
proteins. These are the extracellular connective
tissues (epimysium, perimysium, and endomysium). - Stretching the whole muscle by extending the
joint elongates both the parallel and series
elastic components, generating a spring like
resistance, or stiffness, within the muscle. - This resistance is referred to as passive tension.
66PARALLEL SERIES ELASTIC COMPONENTS
67PASSIVE TENSION CONTINUED
- The passive elements within a muscle begin
generating passive tension after a critical
length at which all of the relaxed (i.e. slack)
tissue has been brought to an initial level of
tension. - Tension progressively increases after this until
the muscle reaches very high levels of stiffness. - Eventually, the tissue ruptures or fails.
- At very long lengths the muscle fibers begin to
lose their active force-generating capability
because there is less overlap among the active
proteins that generate force. The additional
passive tension becomes very important.
68PURPOSE OF PASSIVE TENSION
- Passive tension helps with movement and joint
stabilization against the forces of gravity,
physical contact, or other activated muscles. - Stretched muscle tissue stores potential energy
which can be released to augment the overall
force potential of a muscle. - The elasticity from the passive tension can serve
as a damping mechanism that protects the
structural components of the muscle and tendon.
69PASSIVE LENGTH-TENSION CURVE
70ACTIVE TENSION
- Muscle tissue generates force actively in
response to a stimulus from the nervous system. - The sarcomere is the fundamental active force
generator within the muscle fiber. - The sliding filament hypothesis explains how the
actin and myosin filaments can contract and exert
their force. - Each myosin head attaches to an adjacent actin
filament, forming a crossbridge. - The amount of force generated within each
sarcomere depends on the number of simultaneously
formed crossbridges. The greater the number of
crossbridges, the greater the force generated
within the sarcomere.
71ACTIVE LENGTH-TENSION CURVE
- The amount of active force depends upon the
instantaneous length of the muscle fiber. - A change in fiber length- from either active
contraction or passive elongation- alters the
amount of overlap between actin and myosin. - The ideal resting length of a muscle fiber (or
individual sarcomere) is the length that allows
the greatest number of crossbridges and therefore
the greatest potential force. - As the sarcomere lengthens of shortens from its
resting length, the number of potential
crossbridges decreases so that lesser amounts of
active force are generated.
72CROSSBRIDGE
73ACTIVE LENGTH-TENSION CURVE
74LENGTH-FORCE (LENGTH-TENSION)
- The ideal resting length of the muscle fiber
allows for the optimum length-force relationship. - While the phrase length-force is more
appropriate, the term length-tension is used
instead due to its wide acceptance in the
physiology literature.
75TOTAL LENGTH-TENSION CURVE OF MUSCLE
- The active length-tension curve, when combined
with the passive length-tension curve, yields the
total length-tension curve of muscle. - The combination of active force and passive
tension allows for a large range of muscle forces
over a wide range of muscle length.
76TOTAL LENGTH-TENSION CURVE
77ISOMETRIC MUSCLE FORCE
- Isometric activation of a muscle produces force
without significant change in its length. - This occurs when the joint over which an
activated muscle crosses is constrained from
movement. - Constraint can occur from a force produced by an
antagonistic muscle or from an external source. - Isometrically produced forces provide stability
to the joints and the body as a whole.
78MAXIMAL ISOMETRIC FORCE AS AN INDICATOR OF A
MUSCLES PEAK STRENGTH
- Maximal isometric force of a muscle is often used
as a general indicator of a muscles peak
strength and can indicate neuromuscular recovery
after injury. - A muscles internal torque generation can be
measured isometrically at several joint angles. - The magnitude of isometric torque differs
considerably based on the angle of the joint at
the time of activation, even with maximal effort. - The internal torque produced isometrically by a
muscle group can be determined by asking an
individual to produce a maximal effort
contraction against a known external torque. - It is important that clinical measurements of
isometric torque include the joint angle so that
future comparisons are valid.
79DYNANOMETER
- A dynamometer is an instrument used to measure
force, moment of force (torque), or power. - In the fields of rehabilitation, therapy,
kinesiology, and ergonomics, force dynanometers
are used to measure back, grip, arm, or leg
strength in order to evaluate physical status,
performance, or task demands.
80HAND DYNANOMETER
81RESISTING A FORCE
- The nervous system stimulates a muscle to resist
a force by concentric, eccentric, or isometric
activation. - During concentric activation, the muscle shortens
(contracts). The internal (muscle) torque
exceeds the external (load) torque. - During eccentric activation, the external torque
exceeds the internal torque. The muscle is
driven by the nervous system to contract but it
is elongated in response to a more dominating
force (an external force or an antagonistic
muscle). - During isometric activation, the length of the
muscle remains nearly constant, as the internal
and external torques are equally matched.
82MODULATING FORCE THROUGH CONCENTRIC AND ECCENTRIC
ACTIVATION
- During concentric and eccentric activations, a
very specific relationship exists between a
muscles maximum force output and its velocity of
contraction (or elongation). - Concentric activation
- A muscle contracts at a maximum velocity when the
load is negligible. - As the load increases, the maximum contraction
velocity of the muscle decreases. - Eventually, a very large load results in a
contraction velocity of zero (i.e. isometric
state). - Eccentric activation
- A load that barely exceeds the isometric force
level causes the muscle to lengthen slowly. - Speed of lengthening increases as a greater load
is applied. - There is a maximal load level the muscle cannot
resist, beyond which the muscle uncontrollably
lengthens.
83RELATIONSHIP BETWEEN LOAD AND MAXIMAL SHORTENING
VELOCITY
84FORCE-VELOCITY CURVE
85POWER WORK
- Power, or the rate of work, can be expressed as a
product of force and contraction velocity. - A constant power output of a muscle can be
sustained by increasing the load (resistance)
while proportionately decreasing the contraction
velocity, or vise versa. switching gears on a
bike - Positive work
- A muscle undergoing a concentric contraction
against a load is doing positive work on a load. - Negative work
- A muscle undergoing eccentric activation against
an overbearing load is doing negative work. - A muscle can act as either an active accelerator
of movement against a load while the muscle is
contracting (i.e. concentric activation) or as a
brake or decelerator when a load is applied and
the activated muscle is lengthening (i.e.
eccentric activation). - The quadriceps muscles act concentrically when
one ascends the stairs and lifts the weight of
the body (positive work). The quadriceps perform
eccentrically as they lower the body down the
stairs in a controlled fashion (negative work).