Download Muscle Tissue

MUSCLE TISSUE
Dr. Michael P. Gillespie
POSTURE / 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.

MUSCLE 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

T YPES OF MUSCLE TISSUE
Skeletal muscle tissue
 Cardiac muscle tissue


Dr. Michael P. Gillespie

Autorhythmicity - pacemaker
Smooth muscle tissue
4
FUNCTIONS OF MUSCLE TISSUE
 Producing
Dr. Michael P. Gillespie
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
5
PROPERTIES OF MUSCLE TISSUE

Electrical excitability

Dr. Michael P. Gillespie

Produces electrical signals – action potentials
Contractility
Isometric contraction – tension without muscle shortening
 Isotonic contraction – constant tension with muscle shortening

6
PROPERTIES OF MUSCLE TISSUE
Extensibility – ability of a muscle to stretch without being
damaged
 Elasticity

Dr. Michael P. Gillespie

Ability of a muscle to return to its original length
7
CONNECTIVE TISSUE COMPONENTS
 Fascia
– a sheet of fibrous CT that supports or
surrounds muscles and other organs
Dr. Michael P. Gillespie
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
8
CONNECTIVE TISSUE COMPONENTS
 Endomysium

Dr. Michael P. Gillespie
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
9
Dr. Michael P. Gillespie
10
BASIC COMPONENTS OF MUSCLE
Dr. Michael P. Gillespie
11
MUSCLE 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.

Dr. Michael P. Gillespie
12
NERVE 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

Dr. Michael P. Gillespie
13
TWO 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
Dr. Michael P. Gillespie

Titan provides tensile strength
 Desmin stabilizes adjacent sarcomeres

Make up the cytoskeleton within and between muscle
fibers
 Referred to as “structural” proteins

14
SARCOLEMMA, 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
Dr. Michael P. Gillespie

15
MYOFIBRILS AND SARCOPLASMIC RETICULUM
Myofibril – the contractile elements of skeletal muscle
 Sarcoplasmic reticulum (SR) – encircles each myofibril – stores
CA2+ (its release triggers muscle contractions)

Dr. Michael P. Gillespie
16
Dr. Michael P. Gillespie
17
ATROPHY AND HYPERTROPHY

Muscular atrophy – wasting away of muscles
Disuse
 Denervation

Muscular hypertrophy – an excessive increase in the diameter
of muscle fibers
Dr. Michael P. Gillespie

18
FILAMENTS AND THE SARCOMERE

Filaments – structures within the myofibril
Thin
 Thick

Dr. Michael P. Gillespie
Sarcomere – basic functional unit of a myofibril
 Z discs – separate one sarcomere from the next

19
Dr. Michael P. Gillespie
20
MYOFIBRIL ELECTRON
MICROGRAPH
Dr. Michael P. Gillespie
21
FILAMENTS 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

Dr. Michael P. Gillespie
I band – thin filaments
 M-line – middle of the sarcomere

22
MUSCLE PROTEINS

Contractile proteins – generate force
Myosin
 Actin

Dr. Michael P. Gillespie
Regulatory proteins – switch contraction on and off
 Structural proteins

23
Dr. Michael P. Gillespie
24
SLIDING 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.

Dr. Michael P. Gillespie
25
Dr. Michael P. Gillespie
26
RELAXED & CONTRACTED
MYOFIBRILS
Dr. Michael P. Gillespie
27
Dr. Michael P. Gillespie
28
POWER STROKE OF CROSSBRIDGE
CYCLING
Dr. Michael P. Gillespie
29
ROLE OF CA2+ IN CONTRACTION

An increase in calcium ion concentration in the cytosol initiates
muscle contraction and a decrease in calcium ions stops it.
Dr. Michael P. Gillespie
30
Dr. Michael P. Gillespie
31
MAJOR SEQUENCE OF EVENTS
UNDERLYING MUSCLE FIBER
ACTIVATION










Dr. Michael P. Gillespie

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.
32
RIGOR MORTIS
 After
Dr. Michael P. Gillespie
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.
33
NEUROMUSCULAR 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.

Dr. Michael P. Gillespie
34
NEUROMUSCULAR JUNTCION (NMJ)
 The
Dr. Michael P. Gillespie
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.
35
Dr. Michael P. Gillespie
36
PRODUCTION OF ATP

1. From creatine phosphate.

Dr. Michael P. Gillespie
When muscle fibers are relaxed they produce more ATP than they
need. This excess is used to synthesize creatine phosphate (an energy
rich compound).
37
PRODUCTION OF ATP

2. Anaerobic cellular respiration.
Glucose undergoes glycolysis, yielding ATP and 2 molecules of
pyruvic acid.
 Does not require oxygen.

Dr. Michael P. Gillespie
38
PRODUCTION 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.

Dr. Michael P. Gillespie
Diffuses from bloodstream.
 Oxygen released from myoglobin.

39
MUSCLE 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.

Dr. Michael P. Gillespie
40
OXYGEN DEBT OR RECOVERY OXYGEN UPTAKE
 Added
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.

Dr. Michael P. Gillespie
oxygen, over and above resting oxygen
consumption, taken in after exercise.
 Used to restore metabolic conditions.
41
MOTOR 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.

Dr. Michael P. Gillespie
42
Dr. Michael P. Gillespie
43
MOTOR UNIT
Dr. Michael P. Gillespie
44
TWITCH 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.

Dr. Michael P. Gillespie
45
Dr. Michael P. Gillespie
46
REFRACTORY PERIOD

A period of lost excitability during which a muscle fiber cannot
respond to stimulation.
Dr. Michael P. Gillespie
47
MOTOR 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.

Dr. Michael P. Gillespie
48
MUSCLE 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.

Dr. Michael P. Gillespie
49
ISOTONIC AND ISOMETRIC CONTRACTIONS
 Concentric
Dr. Michael P. Gillespie
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 doesn’t shorten or lengthen.
50
T YPES 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.

Dr. Michael P. Gillespie
51
T YPES 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.

Dr. Michael P. Gillespie
52
T YPES OF SKELETAL MUSCLE FIBERS
 Fast




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.
Dr. Michael P. Gillespie

Glycolitic (FG) fibers.
53
TWITCH CLASSIFICATIONS

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.



Dr. Michael P. Gillespie
“Slow twitch” - Muscle fibers innervated by small
motor neurons have twitch responses that are
relatively long in duration and small 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.
54
MOTOR UNIT TYPES
Dr. Michael P. Gillespie
55
DISTRIBUTION AND RECRUITMENT OF DIFFERENT
T YPES OF FIBERS
Most skeletal muscles are a mixture of all three types.
 The continually active postural muscles have a high
concentration of SO fibers.

Dr. Michael P. Gillespie
56
DISTRIBUTION AND RECRUITMENT OF DIFFERENT
T YPES 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.

Dr. Michael P. Gillespie
57
MUSCLE 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.

Dr. Michael P. Gillespie
58
FUSIFORM & PENNATE MUSCLE
FIBERS

Fusiform

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
Dr. Michael P. Gillespie

Fusiform muscles have fibers running parallel to one
another and the central tendon (i.e. biceps brachii).

59
MUSCLE SHAPES
Dr. Michael P. Gillespie
60
FEATURES 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 crosssectional area of all its fibers.
 A thicker muscle generates greater force than a
thinner muscle of similar morphology.

Dr. Michael P. Gillespie

Pennation angle

Pennation angle refers to the angle of orientation
between the muscle fibers and tendon.
61
PENNATION 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.

Dr. Michael P. Gillespie
62
PENNATION ANGLE & VECTOR OF
FORCE
Dr. Michael P. Gillespie
63
PENNATE 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.

Dr. Michael P. Gillespie
64
PASSIVE TENSION





Dr. Michael P. Gillespie

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.
65
PARALLEL & SERIES ELASTIC
COMPONENTS
Dr. Michael P. Gillespie
66
PASSIVE 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.

Dr. Michael P. Gillespie
67
PURPOSE 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.

Dr. Michael P. Gillespie
68
PASSIVE LENGTH-TENSION CURVE
Dr. Michael P. Gillespie
69
ACTIVE TENSION




Dr. Michael P. Gillespie

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.
70
ACTIVE 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.

Dr. Michael P. Gillespie
71
CROSSBRIDGE
Dr. Michael P. Gillespie
72
ACTIVE LENGTH-TENSION CURVE
Dr. Michael P. Gillespie
73
LENGTH-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.

Dr. Michael P. Gillespie
74
TOTAL 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.

Dr. Michael P. Gillespie
75
TOTAL LENGTH-TENSION CURVE
Dr. Michael P. Gillespie
76
ISOMETRIC 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.

Dr. Michael P. Gillespie
77
MAXIMAL ISOMETRIC FORCE AS AN
INDICATOR OF A MUSCLE’S PEAK
STRENGTH




Dr. Michael P. Gillespie

Maximal isometric force of a muscle is often used as a
general indicator of a muscle’s peak strength and can
indicate neuromuscular recovery after injury.
A muscle’s 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.
78
DYNANOMETER
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.

Dr. Michael P. Gillespie
79
HAND DYNANOMETER
Dr. Michael P. Gillespie
80
RESISTING A FORCE



Dr. Michael P. Gillespie

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.
81
MODULATING FORCE THROUGH
CONCENTRIC AND ECCENTRIC
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).


Dr. Michael P. Gillespie

During concentric and eccentric activations, a very
specific relationship exists between a muscle’s
maximum force output and its velocity of contraction
(or elongation).
Concentric activation
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.

82
RELATIONSHIP BETWEEN LOAD
AND MAXIMAL SHORTENING
VELOCITY
Dr. Michael P. Gillespie
83
FORCE-VELOCITY CURVE
Dr. Michael P. Gillespie
84
POWER & WORK




Negative work



A muscle undergoing a concentric contraction against a load is doing
positive work on a load.
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).
Dr. Michael P. Gillespie

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
85