Learn about how our muscle functioning everyday. And check out the muscle roles!! Simple notes, Simple slides for the beginner person who's attracted to science.

1. MUSCULAR SYSTEM
OBJECTIVE:
•Identify
the basic behavioral
properties of the
musculotendinous unit
•Structure
of skeletal muscle
•Change
in muscle length with
tension development
•Factors
affecting muscular
force generation
1

2. BEHAVIORAL PROPERTIES OF THE
MUSCULOTENDINOUS UNIT


Four behavioral properties of muscle tissue:
 Extensibility
 Elasticity
 Irritability
 The ability to develop tension
These properties are common to all muscle,
including the cardiac, smooth, & skeletal muscle
of human beings.
2

3. Extensibility & Elasticity
The properties of extensibility & elasticity are
common to many biological tissues.

Extensibility – the ability to be stretched or to
increase in length.

Elasticity – the ability to return to normal length
after a stretch.
Muscle’s elasticity returns it to normal resting
length following a stretch & provides for the
smooth transmission of tension from muscle to
bone.
3

4. Two major components of the elastic behavior of muscle:
 Parallel elastic component (PEC)
 Passive elastic property of muscle derived from the
muscle membranes.
 Series elastic component (SEC)
 Passive elastic property of muscle derived from the
tendons.
 Act as a spring to store elastic energy (EE) when a
tensed muscle is stretched.
 Contractile component
 Muscle property enabling tension development by
stimulated muscle fibers.
 Membranes & tendons are respectively parallel to &
in series (or in line) with the muscle fibers.
4

5. Parallel Elastic Component
Contractile
Component
Series
Elastic
Component
5

6. The elasticity of human skeletal muscle is believed
to be due primarily to the SEC.
 When a tensed muscle is stretched, the SEC
causes an elastic recoil effect
 The stretch promotes subsequent forceful
shortening of the muscle
 This pattern of eccentric contraction followed
immediately by concentric contraction is known
as the stretch-shortening cycle.
This phenomenon contributes to effective
development of concentric muscular force in
many sport activities.
6

7. The stretch-shortening cycle also promotes
storage & use of elastic energy (EE) during
running, particularly with the alternating eccentric
& concentric tension present in the gastrocnemius.
Both SEC & PEC have a viscous property that
enable muscle to stretch & recoil in a timedependent fashion.
When static stretch of a muscle group is maintained over
time, the muscle progressively lengthens, increasing joint
range of motion
 After a group has been stretched, it does not recoil to
resting length immediately, but shortens gradually over time

7

8. 8

9.  Extensibility
 Elasticity
 Irritability
 The
ability to develop tension
9

10. Irritability & the Ability to Develop Tension
Irritability- The ability to respond to a stimulus.
Stimuli affecting muscles are either:
 Electrochemical – action potential from the
attaching nerve.
 Mechanical – an external blow to a portion of a
muscle.
Muscle
stimulus
Develop tension
• The ability to develop tension is the one behavioral characteristic
unique to muscle tissue.
• Development of tension = contraction (eccentric or concentric)
10

11. STRUCTURAL ORGANIZATION OF
SKELETAL MUSCLE
Approximately 434 muscles in the human body (4045% of the body weight of most adult).
About 75 muscle pairs are responsible for body
movements & posture, with the remainder involved
in activities such as eye control & swallowing.
11

12. Structure of Skeletal Muscle (muscle fiber)
Epimysium
Bone Epimysium
Perimysium
Endomysium
Tendon
(b)
Perimysium Fascicle
(a)
Muscle fiber
in middle of
a fascicle
Blood vessel
Fascicle
(wrapped by perimysium)
Endomysium
(between individual
muscle fibers)
Muscle fiber
(single muscle
cell)
12

13. Epimysium
 The outermost layer that surround the entire
muscle.
Perimysium
 Connective tissue surround individual bundles of
muscle fibers (inward from the epimysium).
Fascicle
 Individual bundle of muscle fibers.
Endomysium
 Connective tissue surrounded for each muscle fiber
within the fasciculus.
13

14. Sarcolemma
◦ The cell membrane surrounding the muscle fiber cell.
Myofibrils
◦ Numerous threadlike structure that contain the
contractile proteins (protein filaments)
 Myosin – thick filaments composed of the protein.
 Actin – thin filaments composed primarily of the
protein.
Sarcoplasmic reticulum
◦ The storage sites for calcium, which plays an
important role in muscular contraction.
Sarcomeres
◦ Myofibrils further subdivided into individual segments.
14

15. Small part of one myofibril enlarged to
show the myofilaments
responsible for the banding pattern. Each
sarcomere extends from
one Z disc to the next (basic structural unit of
muscle fiber).
Enlargement of one sarcomere
(sectioned lengthwise). Notice the
myosin heads on the thick filaments.
M line
Bisect each sarcomere (middle)
A band
Contain thick, rough myosin filament, each of
which is surrounded by thin, smooth actin
filaments
I band
Contain only thin actin filaments
Z lines (disc)
Attachment of thin actin filaments
H zones
Center of A bands, contain only thick myosin
15

16. Part of a skeletal
muscle fiber (cell)
A band
I band
Z disc
Myofibril
I band
H zone
Z disc
M line
Sarcolemma
Sarcolemma
Triad:
• T tubule
• Terminal
cisternae
of the SR (2)
Tubules of
the SR
Myofibrils
Mitochondria
16
Figure 9.5

17. Motor Units
Composed of a single motor neuron & all fibers
innervated by it.
Typically, there is only 1 end plate per fiber.
A single mammalian motor unit may contain from
less than 100 to nearly 2000 fibers, depending on
the type of movements the muscle executes.


Movements that are precisely controlled (eyes, fingers) produced
by motor units with small numbers of fibers
Gross, forceful movements (gastrocnemius) result of the activity
of large motor units
17

18. Spinal cord
Motor Motor
unit 1 unit 2
Axon terminals at
neuromuscular junctions
Nerve
Motor neuron
cell body
Motor
Muscle
Motor end
plate
neuron
axon
Muscle
fibers
Axons of motor neurons extend from the spinal cord to the
muscle. There each axon divides into a number of axon
terminals that form neuromuscular junctions with muscle
fibers scattered throughout the muscle.
18
Figure 9.13a

19. Fiber Types
Slow twitch fiber (ST)
◦ A fiber that reaches peak tension relatively
slowly.
Fast twitch fiber (FT)
◦ A fiber that reaches peak tension relatively
quickly.
◦ Fast-twitch Oxidative Glycolytic
◦ Fast-twitch Glycolytic
19

20. SKELETAL MUSCLE FIBER CHARACTERISTICS
CHARACTERISTIC
TYPE 1
SLOWTWITCH
OXIDATIVE
(SO)
TYPE IIA
FAST-TWITCH
OXIDATIVE
GLYCOLYTIC
(FOG)
TYPE IIB
FASTTWITCH
GLYCOLYTIC
(FG)
Contraction speed
Slow
Fast
Fast
Fatigue rate
Slow
Intermediate
fast
Diameter
Small
Intermediate
Large
ATPase concentration
Low
High
High
Mitochondrial concentration
High
High
Low
Glycolytic enzyme
concentration
Low
Intermediate
High
20

21. FT
ST
Twitch
tension
Time
21

22. Fiber Architecture
Two categories of muscle fiber
arrangement
◦ Parallel fiber arrangement
 Pattern of fibers within a
muscle in which the fibers
are roughly parallel to the
longitudinal axis of the
muscle.
 E.g. sartorius, rectus
abdominis, biceps brachii.
22

23. Pennate fiber arrangement
 Pattern of fibers within a
muscle with short fibers
attaching to one or more
tendons (lie at an angle).
 E.g. tibialis posterior,
rectus femoris, deltoids
23

24. SKELETAL MUSCLE FUNCTION
When an activated muscle develops tension, the
amount of tension present is constant throughout
the length of the muscle, & at the sites of the
musculotendinous attachments to bone.
The tensile force (stretching force) developed by
the muscle pulls on the attached bones & create
torque at the joints crossed by the muscle.
24

25. Torque (Tm ) produced
by a muscle at the
joint center of
rotation is the product
of muscle force ( Fm )
& muscle moment arm
( d⊥ ).
25

26. The torque exerted
by the biceps brachii
(Fb) must counteract
the torques created
by the force
developed in the
triceps brachii (Ft),
the weight of the
forearm & hand
(wtf), & the weight
of the shot held in
the hand (wts).
26

27. Recruitment of motor units
The CNS exerts an elaborate system of control that
enables:
◦ Matching of the speed & magnitude of muscle
contraction to the requirements of the movement
so that:
 Smooth, delicate, & precise movements can be
executed.
Slow twitch (ST) motor units generally have low
thresholds & are relatively easy to activate.
Fast twitch (FT) motor units are supplied by nerves
more difficult to activate.
27

28. Change in Muscle Length with Tension
Development
When muscular tension produces a torque larger than
the resistive torque at a joint, the muscle shortens,
causing a change in the angle at the joint.
Type of contraction;
◦ Concentric
◦ Eccentric
◦ Isometric
28

29. Concentric



Eccentric
Isometric
Contraction involving shortening of muscle
Resulting joint movement is in the same direction
as the net torque generated by the muscle.
A single muscle fiber is capable of shortening to
approximately one-half of its normal resting
length.
29

30. Concentric





Eccentric
Isometric
When opposing joint torque exceeds that
produced by tension in a muscle, the muscle
lengthens.
When a muscle lengthens as it is being stimulated
to develop tension.
The direction of joint motion is opposite that of
the net muscle torque.
The eccentric tension acts as a braking
mechanism to control movement speed.
E.g. without the presence of eccentric tension in
muscles, the forearms, hand, & weight would drop
uncontrolled because of the force of gravity.
30

31. Concentric


Eccentric
Isometric
Muscular tension is developed but no change in
muscle length.
Opposing torque at the joint crossed by the
muscle is equal to the torque produced by the
muscle (with zero net torque present),
◦ Muscle length remains unchanged & no
movement occurs at the joint.
31

32. SKELETAL MUSCLE FUNCTION
Recruitment of motor units
 Change in muscle length with tension
development
 Roles assumed by muscles

32

33. Roles Assumed by Muscles

Agonist

Antagonist

Stabilizers

Neutralizer
33

34. Agonist



Prime mover.
When a muscle contracts & causes movement of a
body segment at a joint.
E.g.
◦ During the elbow flexion phase of a forearm
curl, the brachialis & the biceps brachii act as
the primary agonist, with the
brachioradialis, extensor carpi radialis longus, &
pronator teres serving as assistant agonist.
34

35. Antagonist




Muscle with actions opposite those of the agonist
act.
Opposers by developing eccentric tension at the
same time that the agonists are causing movement.
Agonists & antagonists are typically positioned on
opposite sides of a joint.
E.g.
◦ During elbow flexion when the brachialis & the
biceps brachii are primary agonists, the triceps
could act as antagonists by developing resistive
tension.
35

36. Stabilizers


Stabilizing a portion of the body against a
particular force.
◦ The force may be internal, from tension in other
muscles, or external, such as the weight of an
object being lifted.
E.g.
◦ The rhomboids act as stabilizers by developing
tension to stabilize the scapulae against the pull
of the tow rope during water skiing, or on tugof-war event.
36

37. Neutralizer



Neutralizers muscle prevent unwanted accessory
actions that normally occur when agonists develop
concentric tension.
E.g.
◦ When the biceps brachii develops concentric
tension, it produces both flexion at the elbow &
supination of the forearm. If only elbow flexion
is desired, the pronator teres act as a
neutralizer to counteract the supination of the
forearm.
Performance of human movements typically
involves the cooperative actions of many muscle
groups acting sequentially & in concert.
37

38. Factors Affecting Muscular Force
Generation
The magnitude of the force generated by muscle
is also related to:
Velocity of muscle shortening
Length of the muscle when it is stimulated
Period of time since the muscle received a
stimulus
Factors affecting:
Force-Velocity relationship
Length-Tension Relationship
Electromechanical Delay (EMD)
38

39. Force-Velocity Relationship for muscle tissue
When the resistance (force) is negligible, muscle
contracts with maximal velocity.
 As the load progressively increases, concentric contraction
velocity slows to zero at isometric maximum.
 As the load increases further, the muscle lengthens
eccentrically.
Maximall
y
activated
muscle
FVR does NOT imply that it is impossible to move a
heavy resistance at a fast speed.
 The stronger a muscle, the greater the magnitude of
maximum isometric tension
FVR also does NOT imply that it is impossible to move
a light load at a slow speed.
39

40. Length-Tension Relationship
The total tension present in a stretched muscle is
the sum of the active tension provided by the
muscle fibers & the passive tension provided by
the tendons & muscle membranes.
Total tension = active tension (muscle fibers) + passive tension (tendons &
muscle membranes)
Within the human body, force generation capability
increases when the muscle is lightly stretched.
 Parallel-fibered muscles produce maximum tensions at just
over resting length.
 Pennate-fibered muscles generate maximum tension at
between 120% & 130% of resting length.
 This phenomenon is due to the contribution of the elastic
components of muscle (primarily the SEC), which add to
the tension present in the muscle when the muscle is
stretched.
40

41. Electromechanical Delay (EMD)
When a muscle is stimulated, a brief period of time
elapse before the muscle begins to develop tension.
ED- time between the arrival of neural stimulus and
tension development by the muscle
41

42. EMD where the period of time is believed to be needed
for the contractile component of the muscle to stretch
the SEC.
During this time, muscle laxity is eliminated.
Once the SEC is sufficiently stretched, tension
development proceeds.
Researchers have found shorter EMDs produced by
muscles with high percentages of FT fibers as compared
to muscles with high percentages of ST fibers.
42

43. Muscular Strength, Power & Endurance
Muscular Strength
The maximum amount of force a muscle can
produce in a single effort
Muscular Power
The product of muscular force and the
velocity of muscle shortening
Muscular Endurance
The ability of a muscle to exert a sub-maximal
force repeatedly over time
43

44. What is the effect of muscle temperature (warm up) ?
The speeds of nerve and muscle functions increase.
Normal body temperature
Elevated body temperature
velocity
With warm-up, there is
a shift to the right in
the force-velocity
curve, with higher
maximum isometric
tension and higher
maximum velocity of
shortening possible at a
given load.
force
44

45. Common Muscle Injuries
Strains - overstretching of muscle tissue
Contusions - compressive forces sustained during impacts
Cramps - electrolytes imbalance, deficiencies in calcium & magnesium,
dehydration
Delayed-Onset Muscle Soreness (DOMS)
◦ occurs after some period of time following
unaccustomed exercise.
◦ arises 24 – 72 hours after participation in a long or
strenuous bout of exercise.
45