Transcript Ch9_ MusclesPartIII

The Muscular System
Skeletal Muscle Tissue
And Muscle Organization
Chapter 9 Part III
Alireza Ashraf, M.D.
Professor of Physical Medicine & Rehabilitation
Shiraz Medical school
Levels of Functional
Organization in a
Skeletal Muscle
Fiber
Muscle Fascicle
Muscle Fiber
Myofibril
Sacromere
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Orientation of the SR, T Tubules,
and Individual Sacromeres
Fig 9.9
Fig 9.6
Thin and Thick Filaments
Changes in the appearance
of a sarcomere during
contraction of a skeletal
muscle fiber
During a contraction, the A
band stays the same width,
but the Z lines move closer
together and the I band
and H band are reduced in
width
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Fig 9.8
The Effect of Sarcomere Length on Tension
9.9
The Orientation of the Sarcoplasmic Reticulum, T
Tubules, and Individual Sarcomeres
A triad occurs where a T tubule encircles a sarcomere between 2
terminal cisternae
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9.10
The Neuromuscular Synapse
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9.11
The Events in Muscle Contraction
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9.12 The Arrangement of Motor Units in a Skeletal Muscle
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Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Organization of Skeletal Muscle Fibers

Most muscle fibers contract and shorten to the same
degree
- variations in skeletal muscle fiber organization can affect the
power, range, and speed of movement

Muscle fibers of each fascicle bundle lie parallel to
one another

Organization of the fascicles and the relationship
between the fascicles and associated tendon can vary

4 different patterns of fascicle arrangements
produce:
Parallel, Convergent, Pennate, and Circular muscles
Contraction – muscle
gets shorter but body
increases in diameter
Fig 9.14
Fascicles are parallel to the long axis of the muscle (most muscles)
 Firm attachment by a tendon extends from the free tip to a movable
bone of the skeleton – flat bands with aponeuroses; spindle shaped
with cordline tendons; have a central body, belly or gaster (‘stomach)

Fig 9.14
Muscle fibers cover a broad area, but all fibers come together
at a common attachment site and pull on a tendon, a tendinous
sheet, or a raphe (band of collagen fibers)
 Fibers on opposite sides of the tendon pull in different

Unipennate –
all muscle cells are on
the same side of the
tendon
Fig 9.14
Pennate muscles have 1 or more tendons that run through the
body, fascicles form an oblique angle to the tendon
 Have more fibers than a parallel - generates more tension
than a parallel muscle of the same size

Fig 9.14
Bipennate Muscle – muscle fibers on both sides of
the tendon
Fig 9.14
Multipennate – triangular deltoid muscle covers the superior
surface of the shoulder joint
Fig 9.14
Sphincter, fibers are concentric around an opening or recess
 Contraction – opening diameter decreases; guard entrances
and exits of internal passageways (digestive and urinary tracts)

Muscle Terminology (Table 9.2)

Origin – remains stationary

Insertion – moves
- commonly the origin is proximal to the insertion

If the muscle extends from a broad aponeurosis to
a narrow tendon:
Aponeurosis = origin

Tendon = insertion
If there are several tendons at one end and just
one at the other:
Multiple = origins
Single = insertion
Muscle Movement

Almost all skeletal muscles either originate or insert
on the skeleton

When a muscle moves a portion of the skeleton,
that movement may involve:
abduction, adduction, flexion, extension, circumduction,
rotation, pronation, supination, everison, inversion,
dorsiflexion, plantar flexion, lateral flexion, opposition,
protraction, retraction, elevation, and depression (review
pages 210-212)
Muscle Actions
There are 2 methods of describing actions:

The first references the bone region affected:
- example, the biceps brachii muscle is said to perform
‘flexion of the forearm’

The second method specifies the joint involved:
- example, the action of the biceps brachii muscle is
described as ‘flexion of the elbow’
Primary Actions
Muscles can be grouped according to their primary
actions into 3 types:

Prime movers (agonists) – muscles chiefly
responsible for producing a particular movement

Synergists – muscle contracts to assist the prime
mover in performing that action
- if a synergist stabilizes the origin of the agonist, it is called
a fixator

Antagonists – muscles whose actions oppose that
of the agonist
- if the agonist produces flexion, the antagonist will produce
extension
Muscle Terminology
Specific body regions
- brachialis
 Shape of the muscle
- trapezius
 Orientation of muscle
fibers
- rectus, transverse,
oblique

Specific or unusual
features
- biceps (2 origins)
 Identification of origin
and insertion
- sternocleidomastoid
 Primary functions
- flexor carpi radialis
 Reference to actions
- buccinator

Levers and Pulleys

The muscle force, speed, or direction of movement
- produced by its contraction can be modified by attaching
the muscle to a lever
- the applied force is the effort produced by the contraction
- the effort is opposed by a resistance (load or weight)

A lever is a rigid structure – board, crowbar, or
bone
- that moves on a fixed point or fulcrum

In the body each bone is a lever and each joint a
fulcrum; levers can change
1) direction of an applied force
2) distance and speed of movement produced by a force and
3) the strength of a force
Levers and Pulleys:
A Systems Design for Movement

First-class levers –seesaw
- fulcrum lies between the applied force and the resistance

Second-class levers - characteristics include:
- the force is magnified
- the resistance moves more slowly and covers a shorter
distance

Third-class levers – characteristics include:
- speed and distance traveled are increased
- the force produced must be great
Levers and Pulleys

Although every muscle does not operate as
part of a lever system, the presence of levers
provides speed and versatility far in excess of
what we would predict on the basis of muscle
physiology alone
Levers and Pulleys: A Systems Design for Movement
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Levers and Pulleys: A Systems Design for Movement
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Levers and Pulleys: A Systems Design for Movement
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Levers and Pulleys: A Systems Design for Movement
Figure 9.16
Anatomical Pulleys
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Aging and the Muscular System

Skeletal muscle fibers become smaller in
diameter and less elastic

Tolerance for exercise decreases

The ability to recover from muscular injuries
decreases
Figure 9.17
The Life Cycle of Trichinella spiralis