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MUSCLE
Types of Muscle
●Skeletal – striated & voluntary
●Smooth – involuntary
●Cardiac - heart
The word
“striated” means
striped. Skeletal
muscle appears
striped under a
microscope.
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I Kinds of muscle tissue
A. smooth (visceral)
1) common in many invertebrates and in the viscera of
vertebrates
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2) single nucleus
– 3) slow contraction
3-180 sec.
– 4) involuntary
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as in peristalsis ( wave-like contractions of muscle (intestine)
B. Cardiac
1) heart
2) involuntary
3) contractions last 1-5 sec
heart beat
C. Skeletal ( striated)
1) makes up 40% of body weight
2) multinucleated
3) voluntary
4) mostly in limbs & body wall
5) fast reaction .1sec to react
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II Connections
A. individual
1) origin
(a) end attached to the more stationary part of skeleton
2) insertion
(a) end attached to the element moved by contraction
B. as whole
1) tendon (cord-like)
(a) muscle to bone
2) aponeuroses ( sheet-like)
(a) muscle to muscle or bone
C. sites of attachment
1) bone
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2) cartilage
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3) connective tissue
Muscles and Muscle Fiber Structure
Muscles are composed of many FIBERS that are
arranged in bundles
called FASCICLES
III. Structure
A. Connective tissue Covering
1) fascia
(a) layers of connective tissue
that separates an individual
skeletal muscle from adjacent
muscle
Individual muscles are separated by
FASCIA, which also forms tendons
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2) epimysium
(a) layer of connective tissue that closely surrounds a
skeletal muscle
3) perimysium
(a) separates muscle tissue into small compartments
(fascicles)
4) endomysium
(a) encloses muscle fibers within fasicle
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
Muscle Fiber
Endomysium
Perimysium
Epimysium
Epimysium
Perimysium
Endomysium
Muscles / Cells
Sarcolemma = muscle fiber membrane
Sarcoplasm = inner material surrounding
fibers (like cytoplasm)
Sarcoplasmic Reticulum - transport
Myofibrils = individual muscle
fibers, 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)
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B. Fibers
– 1) a single cell that contracts in response to stimulation and then relaxes
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when the stimulation ends
– 2) thin elongated cylinders ( encased in a membrane (sarcolemma))
– 3) inside these fibers are myofibrils which enclose 2 types of protein
filaments
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(a) myosin - thick
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(b) actin - thin
– 4) the arrangement of these give skeletal muscle it’s striations
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actin & myosin form a number of repeating sections within a myofibril.
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Each section is known as a sarcomere; the functional unit of the
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muscle.
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(a) striation pattern
1. I bands
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2. Z lines
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Light bands of thin actin
Apprear in center of I bands
3. A bands
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Dark bands of myosin
Protein troponin and tropomyosin
Associated with actin filaments
It is important to remember the hierarchy
fasicles
myofibrils
myofilaments
actin
myosin
How Muscles Work with the Nervous System
NEUROMUSCULAR JUNCTION - where a nerve
and muscle fiber come together
MOTOR END PLATE - folded area where muscle
and neuron communicate
SYNAPTIC CLEFT - gap between the neuron and
motor end plate
SYNAPTIC VESICLES - where neurotransmitters
are stored
*these are released into the cleft
and tell the muscle to contract
IV. Contraction
A. Motor Unit – a motor neuron and all of the muscle fibers
it innervates.
1.The CNS sends a signal (electrical impulse) down the
axon of a neuron.
2. At the axon terminal, neurotransmitters are released;
ACh- acetylcholine
3. Neurotransmitters cross the synapse carrying electrical
impulses from the nerve to the muscle.
4. ACh stimulates the muscle to start contraction
5. Once stimulated muscle fibers innervated by the nerve
will contract if stimulus is strong enough or not at all if not.
“All or nothing Law” – No partial contraction.
Motor Unit or Neuromuscular Junction
1. Neuron
3. Vesicle
2. Sarcolemma (or motor end plate)
4. Synapse
5. Mitochondria
The neurotransmitter that cross the gap is
ACETYLCHOLINE
ACH is broken down by CHOLINESTERASE
The neurotransmitter that crosses the gap is
ACETYLCHOLINE.
This is what activates the muscle.
Acetylcholine is
stored in vesicles
B. Sliding Filament Theory- Actin & Myosin
filaments slide past one another shortening
sarcomeres. Muscle fiber shortens
1. Stimulus begins when ACh is released @
neuromuscular junction.
2. The sarcoplasmic reticulum around the
myofibril releases Ca+²
3.When Ca+² concentration rises, binding sites on
actin open.
4.Cross bridges from myosin attach & pull on actin
– sliding it
5. ATP binds to cross bridge releasing it from
actin.
6. Ca+² & ATP keep the cycle going as long as
they are present
* When sarcomeres shorten, the thick and
thin filaments do not change length. Rather,
they slide past one another.
SLIDING FILAMENT THEORY (MODEL)
The theory of how muscle contracts is the sliding filament
theory. The contraction of a muscle occurs as the thin
filament slide past the thick filaments.
What is needed
ATP
Calcium
Myosin & Actin
Acetylcholine
Cholinesterase
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C.Contraction requires energy
1) attached to the actin filament is ATP ( adenosine triphosphate)
(a) only enough ATP in muscle for a 10 sec contraction then must use
Glycolysis
(b) Glycolysis – early phase of cell respiration
(c) Cellular respiration is the conversion of glucose into ATP (our
energy source)
(d) glucose is the sugar we get from our food
2) Glycolysis
C6H12O6 + 6O2  6CO2 + 6H2O + ATP
(a) 2 types
1. aerobic (with Oxygen)
19 times more efficient than without Oxygen (34 units of ATP)
2. anaerobic (without Oxygen) – Glycolysis is usually
2 units of ATP
used when Oxygen can’t be supplied fast enough by the blood to
keep up with the demand
Energy Source
-ATP is produced by CELLULAR RESPIRATION
which occurs in the mitochondria
-Creation phosphate increases regeneration of
ATP
* Only 25% of energy
produced during cellular
respiration is used in
metabolic processes - th
rest is in the form of
HEAT.
- maintains body
temperature.
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D. Oxygen Debt
1. During Strenuous Exercise ATP can be used faster than it is produced.
Oxygen is used to synthesize ATP for contraction.
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E. Athletics
1) blood doping
(a) extracting red blood cells and storing until approx. 24 hrs before
activity
(b) illegal in athletics since 1986
distance runners, skaters, etc.
(c) military
1993 special forces at FT Bragg
1998 Australian defense forces
scientist in study believed it increased endurance & alertness
2) altitude training
(a) high altitude (>5000ft) training can lead to an increase in rbc
(b) the atmospheric pressure is less decreasing the oxygen hemoglobin
saturation. To make up for this the kidneys secrete a hormone(EPO)
that stimulates rbc production in the marrow
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E. Reserve
1) ATP can be used faster than it is produced during strenuous exercise
2) muscles must build up a reserve supply
(a) fibers store excess ATP on myosin filaments
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2. Lactic Acid is a byproduct and accumulates when oxygen debt occurs
can lead to muscle cramping.
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(b) ATP combines with creatine to form creatine phosphate
1. creatine is a natural material that body secretes
2. often taken as a supplement by athletes and body builders
* helps supply energy by increasing formation of ATP
* can cause asthmatic symptoms and possibly kidney damage
F. Steroids
1) promote
signs of masculinity
increased synthesis of muscle proteins
2) drawbacks
organ damage
males- hair loss, breast development, stunted height,
females- deepening of voice, hair growth, male physique
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V. Interaction of skeletal muscles
A. Skeletal muscles usually function in groups
1) prime mover– muscle that does the majority of work
2) synergist– muscles that assist the prime mover
3) antagonist– a muscle that causes the opposite reaction of a prime
mover
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B. All or None
1) a muscle either contracts or doesn’t ( can’t partially contract)
C. Summation
1) force of several combined contractions are added together
(a) whenever stimuli happen very frequently the muscle might not be
able to relax
1. this sustained contraction is tetanic
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VII. Kinds of Contractions
A. Isotonic
1) muscle shortens and there is movement
B. Isometric
1) tension with no movement
C. tonic
1) long sustained contraction
D. twitch
1) short rapid response to a stimulus
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VIII. Effects of Muscular exercise
A. size change
1) atrophy- shrinking of muscle (lack of use)
2) hypertrophy – increase in muscle size ( use)
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B. respiration
1) rate increase
(a) supply more Oxygen to muscles
C. circulation
1) concentration of RBC increases
(a) oxygen
D. heart rate
1) increase
(a) body demanding more blood
E. blood pressure
1) increases
(a) need for more blood to muscles
F. body temperature
1) increases
(a) 60% of energy is given off as heat
H. urine production
1) decreases
(a) need for extra water (dehydration)
Location of Muscles
A. Origin – immovable or fixed end of muscle. Head
muscle. Most proximal end
B. Insertion – movable end of muscle on other side
of joint
* Muscles may have more than one origin or
insertion
eg. Biceps Brachii – 2 origins
* During Contration: insertion is pulled towards
origin.
Interaction
1. Agonist (Prime mover) muscle primarily responsible for
producing action.
eg. Abducting arm- Deltoid contracts
2. Synergists – assist the prime mover by contracting also.
3. Antagonist – resist prime movers action and cause
movement in opposite direction.
Eg. Biceps / triceps
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IX. Naming muscles
A. direction of fibers
1) rectus III
(a) rectus abdominus( stomach)
2) oblique ///
(a) external oblique( ribs)
B. location
1) temporalis
(a) temporal bone
C. relative size
1) maximus, minimus, longus, brevis, major, minor
(a) gluteus maximus
(b) gluteus minimus
D. number of origins
1) biceps
(a) 2 origins
E. shape
1) trapezius
(a) trapezoid shape
F. origin and insertion
1) sternocleidomastoid
(a) attached to sternum, clavicle, & mastoid process
G. action
1) flexor digitorum
(a) flexes digits
Other Terms
●1. Threshold Stimulus
●2. All-or-None Response
●3. Motor Unit
●5. Recruitment
●6. Muscle Tone
●7. Muscular Hypertrophy
●8. Muscular Atrophy
●9. Muscle Fatigue
●10. Muscle Cramp
●11. Oxygen Debt
1. Threshold Stimulus
Minimal strength required to cause a
contraction
Motor neuron releases enough acetylcholine to
reach threshold
2.All-or-None Response
Fibers do not contract partially, they either do
or don't
3. Motor Unit
The muscle fiber + the motor neuron
4. Recruitment
more and more fibers contract as the
intensity of the stimulus increases
5. Muscle Tone
Sustained contraction of individual
fibers, even when muscle is at rest
6. Hypertrophy
- muscles enlarge (working out or
certain disorders)
7. Atrophy - muscles become small and weak due to
disuse
8. Muscle Fatigue - muscle loses ability to
contract after prolonged exercise or strain
9. Muscle Cramp - a sustained involuntary
contraction
10. Oxygen Debt
oxygen is used to create
ATP, -- not have enough oxygen causes Lactic
Acid to accumulate in the muscles → Soreness
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*See Magic School Bus
11. Origin and Insertion
Origin = the immovable
end of the muscle
Insertion = the movable
end of the muscle
The biceps brachii has two origins
(or two heads).
What is rigor mortis?
A few hours after a person or animal dies,
the joints of the body stiffen and become
locked in place. This stiffening is called
rigor mortis. Depending on temperature
and other conditions, rigor mortis lasts
approximately 72 hours. The phenomenon
is caused by the skeletal muscles partially
contracting. The muscles are unable to
relax, so the joints become fixed in place.
What is tetanus?
Tetanus causes cholinosterase to not break down the
acetylcholine in the synapse. This results in a person's
muscles contracting and not relaxing.
A tetanus shot
must be
administered
shortly after
exposure to
the bacteria.
Once you
develop
tetanus, there