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The Muscular System
Skeletal Muscle Tissue and Muscle
Organization
Chapter 9
Alireza Ashraf, M.D.
Professor of Physical Medicine & Rehabilitation
Shiraz Medical school
The Muscular System

Skeketal Muscle, Cardiac Muscle, Smooth Muscle

Share 4 basic properties:
1) Excitability – respond to stimulation by either the
nervous system or to circulating hormones
2) Contractility – ability to shorten actively and exert
a pull or tension harnessed by CT
3) Extensibility – ability to contract over a range of
resting lengths
4) Elasticity – ability of a muscle to rebound toward
its original length after a contraction
Skeletal Muscle Functions

Contractile organs directly or indirectly attached to
bones

Functions include:
1) Produce skeletal movement: muscle contractions
pull on tendons and move the bones
- effects range from simple motions to highly coordinated
movements of swimming, skiing, or typing
2) Maintain posture and body positions: contraction
of secific muscles
– involves the contraction of muscles that stabilize joints,
without constant muscular contraction, we could not sit
upright without collapsing or stand without toppling over
Skeletal Muscle Functions
3) Support soft tissues: the abdominal wall and the
floor of the pelvic cavity consist of layers of skeletal
muscle
- support the weight of visceral organs and protect internal
tissues
4) Regulate entering and exiting of material:
openings or orifices, of the digestive and urinary
tracts are encircled by skeletal muscles
- provide voluntary control over swallowing, defecation, and
urination
5) Maintain body temperature: muscle contractions
require energy some is converted to heat
- heat lost by contracting muscles maintains our body temp
Anatomy of Skeletal Muscles

Epimysium (mys = muscle) - outer layer of dense
irregular CT connected to the deep fascia:
- surrounds the entire skeletal muscle and separates the
muscle from surrounding tissues

Perimysium - CT fibers that surrounds each fascicle:
- divides the muscle into a series of internal compartments
each containing a bundle of muscle fibers called fascicles
- collagen and elastic fibers, BVs and nerve supply

Endomysium – surrounds each skeletal muscle fiber
- binds each muscle fiber to its neighbor and supports the
capillaries that supply each individual fiber
- consists of a network of reticular fibers with scattered
myosatellite cells that function in repair of damaged muscle
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig 9.1
Structural Organization of Skeletal Muscle
Tendons and Aponeuroses

CT fibers of the all 3 are interwoven, those of the
perimysium blend into the epimysium

At each end of the muscle, collagen fibers often
converge
- form a fibrous tendon that attaches muscle to bone,
skin, or another muscle
- tendons resemble thick cords or cables those that form
flattened sheets are called aponeuroses

Tendon fibers are interwoven into the periosteum
and matrix of associated bone
- provides an extremely strong bond to withstand muscle
contractions
Nerves and Blood Vessels

3 CT layers contain the nerves and BVs that supply
the muscle fibers

Called voluntary muscles because their contractions
can be controlled
- provided by the nerves of the nervous system

Nerves, bundles of axons, penetrate the epimysium
- branch through the perimysium and enter the endomysium
to innervate individual fibers

Neuromuscular synapse or myoneural junction
– site of chemical communication between a synaptic
terminal of the neuron and a skeletal muscle fiber
Skeletal Muscle Innervation
Fig 9.2
Each muscle fiber is stimulated by a nerve fiber usually located
midway along its length
- the synaptic terminal of the neuron is bound to the motor end
plate (specialized area of the muscle cell membrane)
- entensive vascular supply delivers oxygen and nutrients

Microanatomy of Skeletal Muscle
Fibers

Sarcolemma (sarkos = flesh + lemma = husk)
- cell membrane of a skeletal muscle fiber surrounds the
cytoplasm, or sarcoplasm

Skeletal muscle fibers differ from the ‘typical’ cell:
- very large, a fiber from a leg muscle can have a 100 um
diameter and a length equal to that of the entire muscle
- are multinucleate, during development groups of
embryonic cells or myoblasts fuse together to form fibers
- deep indentations called transverse tubules or T tubules in
the sarcolemmal surface form a network of narrow tubules
that extend into the sarcolemma to help stimulate and
coordinate muscle contractions
Fig 9.3
The Formation and Structure of a Skeletal Muscle
Development of a
skeletal muscle fiber
Sarcomere Structure
Fig 9.4
Levels of Functional
Organization in a
Skeletal Muscle
Fiber
Muscle Fascicle
Muscle Fiber
Myofibril
Sacromere
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig 9.8
The Effect of Sarcomere Length on Tension