Muscular System
Intro to Muscles
1. Nearly half our weight
comes from muscle
tissue
2. There are 650 different
muscles in the human
body
Three Main Functions
1. Responsible for body
movement
2. Responsible for body
form and shape
(posture)
3. Responsible for body
heat and maintaining
body temperature
4 Characteristics of a Muscle
1. CONTRACTILITY – the capability or quality of
shrinking or contracting
2. EXCITEABILITY– the ability to respond to
certain stimuli by producing impulses
3. EXTENSIBILITY – the ability to be stretched.
4. ELASTICITY – ability of muscle to return to its
original length when relaxing.
Types of Muscle
● Skeletal – striated, voluntary, multinucleated, long and run parallel
to eachother, found on bones
● Smooth – non-striated, involuntary, single nucleus, tapered, found
in many organs, contract using peristalsis
● Cardiac – striated, involuntary, 1-2 nuclei, long and branched, found
in heart, contain intercalated discs, rhythmic contractions
The word
“striated” means
striped. Skeletal
muscle appears
striped under a
microscope.
Muscles and Muscle Fiber Structure
•
Individual muscles are separated by FASCIA, which also
forms tendons
**Tendonitis – inflammation of the tendons
•
Muscle fibers (cells) are arranged in bundles called
FASCICLES
• EPIMYSIUM = outermost layer, surrounds entire muscle.
• PERIMYSIUM = separates and surrounds fascicles
(bundles of muscle fibers)
• ENDOMYSIUM = surrounds each individual muscle fiber
This model of the muscles uses
straws to represent fibers.
Green = endomysium
Yellow = perimysium
Blue = epimysium
Muscle Layers
Epimysium
Perimysium
Endomysium
It is important to remember the hierarchy
Wrapped in
EPIMYSIUM
MUSCLE
Wrapped in
PERIMYSIUM
FASCICLES
Wrapped in
ENDOMYSIUM
MUSCLE FIBERS
MYOFIBRILS
FILAMENTS
ACTIN (light)
MYOSIN (dark)
Muscles / Cells
Sarcolemma = muscle fiber membrane
Sarcoplasm = inner material surrounding
fibrils (like cytoplasm)
Myofibrils = individual threads within
muscle fiber made of myofilaments
Nucleus
Sarcolemma
Mitochondrion
Sarcoplasm
Myofibril
Myofibrils are made of
ACTIN = thin filaments
MYOSIN = thick filaments
Myofilaments ACTIN (thin) and MYOSIN (thick)
-- form dark and light bands
 A band = dArk • thick (myosin)
 I band = lIght • thIn (actin)
SLIDING FILAMENT THEORY (MODEL) - theory of
how muscle contracts
This occurs as the thin filament (actin) slides past the thick
filaments (myosin)
Explanation of Skeletal Muscle and Sliding Filament Theory
Start at 1:40
http://www.youtube.com/watch?v=mejCXr7p37U&spfreload=10
How Muscles Work with the Nervous System
NEUROMUSCULAR JUNCTION - where a nerve
and muscle fiber come together
Neuromuscular Junction
• Motor neurons stimulate muscle fibers to contract
• Motor neuron secretes neurotransmitter known as
ACETYLCHOLINASE
• One motor neuron connected to muscle fibers make up a
motor unit
Energy Source
-ATP is produced by CELLULAR RESPIRATION; occurs in
the mitochondria
-Creatine phosphate increases regeneration of ATP
* Only 25% of energy
produced during cellular
respiration is used in
metabolic processes - the
rest is in the form of HEAT.
- maintains body
temperature.
Other Terms
1. All-or-None Response
2. Motor Unit
3. Recruitment
4. Muscular Hypertrophy
5. Muscular Atrophy
6. Muscle Cramp
7. Origin & Insertion
8. Strain
9. Sprain
10. Hernia
1. All-or-None
Response
Fibers do not contract partially, they either do or
don't
2. Motor Unit
The muscle fiber + the motor neuron
3. Recruitment
•
More fibers contract as the
intensity of stimulus increases
4. Hypertrophy
- muscles
enlarge (working out or certain
disorders)
5. Atrophy - muscles become
small and weak due to disuse
Cardiomyopathy
6. Muscle Cramp
- a sustained involuntary
contraction
7. Origin and Insertion
Origin = the immovable end of the muscle
Insertion = the movable end of the muscle
8. Strain – tear in
muscles/tendons from
excessive use
9. Sprain – tear in
ligaments
10. Hernia – protrusion of an
organ or tissue through a weak
muscle or opening
11. Ligaments vs. Tendons
Ligaments – bone to bone
Tendons – muscle to bone
Treatments (R.I.C.E.)
1. Rest
2. Ice
3. Compression
4. Elevation