Ch 9: Skeletal Muscle Tissue
and Organization
main objectives:
1) Describe the distinguishing characteristics
of the different muscle tissues
2)
Discuss the organization of skeletal muscle
3)
Explain the micro-anatomy of a skeletal
muscle fiber
4)
Describe the fascicle arrangement in
different types of muscle
5)
Review general muscle terminology
Muscle tissue vs. Muscle as an organ
One of the 4
primary tissue
types
How many
subtypes?
Made up of _____
tissue types.
> 700 skeletal
muscles
Word roots:
sarco
mys
Function of Skeletal Muscles
1.
Skeletal movement
2.
Posture and body position
3.
Support of soft tissues
4.
Guarding of entrances & exits
5.
Maintenance of body temperature
Gross Anatomy
Each skeletal muscle is wrapped by 3 concentric layers of
connective tissue.
Epi-, Peri-, and Endomysium
Are interwoven - Go over into tendon
Distinguish between:
Tendon
Aponeurosis
Ligament
Function:
Protection
Blood supply
Innervation
Fig 9-1
Nerve and Blood Vessel Supply
Skeletal muscles are rich in nerves
and blood vessels
Chemical communication at Synapsis
(neuromuscular junction)
Synaptic terminal of axon meets motor end
Fig 9-2
plate of muscle cell
Coiled capillaries are able to adapt to
changes in length of muscle fiber
Microanatomy of Skeletal Muscle Fibers
Some vocabulary:
Skeletal muscle fiber or
myofiber
Sarcolemma
Sarcoplasm
Sarcoplasmic reticulum
Myofibril
Myofilaments
Fig 9-3
Myofilaments
Myofiber ( 100µm)
Myofibrils (

1-2 µm)
Myofilaments
Actin & Myosin
Sarcomeres
Thick and Thin Filaments are organized in
repeating functional units = ______
Each myofibril has linear arrangement of
~ 10,000 sarcomers
Banded appearance (striation) due to arrangement
of thick and thin filaments
Interaction of thick and thin filaments
responsible for skeletal muscle fiber contraction
Sarcomere
Structure
Z - line
I - band
= LIght band
A- band
= dArk band
Thin Filament: Actin
F-actin
G-actin
Thick Filament: Myosin
Development of Myofibers from
Myoblasts
Some Myoblasts do not fuse
satelite cells in endomysium
regeneration of muscle
Motor Units
= All muscle fibers that are controlled by a
single motor neuron
The lower the ratio of muscle fibers to neurons,
the more precise the movement can be!
Few cases 1: 1 relationship. Where?
Most cases: many muscle fibers (up to
2,000) : 1 motor neuron. Where?
Fig 9-12
Muscle Control
Muscle tone = Resting tension of skeletal
muscles (continuous contraction of some motor units to
maintain some muscle tension)
Recruitment or Multiple motor unit
summation
Maximal tension production: ?
Muscle Hypertrophy vs. Atrophy
Hypertrophy due to anaerobic exercise
Leads to increased muscle size - how?
Atrophy if supply of myofilaments exceeds
demand. Muscle fibers become smaller and
weaker.
Eventual death of muscle fibers is irreversible!
Importance of Physical Therapy
Three Types of Muscle Fibers
1) Fast (or White) Fibers
Fast contraction after nervous stimulation
Large diameter
large glycogen reserve
few mitochondria
densely packed myofibrils
Fatigue fast due to mainly anaerobic
respiration
2) Slow (or Red) Fibers
Slower but continuous contraction for
extended periods
Smaller diameter (~ half)
contain myoglobin
more capillaries
more mitochondria
Do not fatigue as fast due to ?
Fig 9-13
3) Intermediate Fibers
Have attributes inbetween fast and slow
types
Most skeletal muscles contain mixture of
fiber types. Proportion of fast to slow depends
on ___________?
One motor unit only contains one fiber type
Eye, hand: ____ fibers dominate
Back, calf: ____ fibers dominate
Organization of Skeletal Muscle Fibers
Effect of individual muscle contraction
determined by:
1. arrangement of muscle fibers
2. way of attachment to skeletal system
Bundles of muscle fibers =
Muscle fibers within 1 fascicle are parallel
4 types of fascicle organization
Parallel Muscels
Majority
Spindle shaped with
cord-like tendons
Some flat bands with
broad _____ on each
end
Examples: ?
Convergent muscels
Broad origin,
pointed
insertion
Direction of pull
can be varied:
versatility!!
Example
Pennate Muscles: Unipennate
One or more tendons
run though muscle
body
Fascicles in oblique angle
to tendon
Can generate more
tension
Example
Pennate Muscles:
Example
Bipennate &
Multipennate
Example
Circular Muscles
= Sphincters
Concentric fibers
adjust opening
Examples: orbicularis
occuli and oris
Muscle Terminology
Origin
Insertion
stationary
moves
Possible: multiple origins
Types of Actions
 flexion, extension
 adduction, abduction
 elevation, depression
 rotation,
circumduction
 pronation, supination
etc. . . . .
Grouping of Muscles according to
Primary Action
Agonist = Prime Mover
Antagonist (action opposes agonist)
Synergists = Assistants of prime mover
Naming of skeletal Muscles
Orientation of fibers
Size & shape
Location
Action
Origin & / or insertion
Specific features
Use muscle name to help identify its location,
appearance and function!