Download Muscles

The Muscular System
Anatomy & Physiology
Muscles: the machines of the
body
Skeletal Muscle Characteristics
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Voluntary: move due to a conscious
decision
Striated: striped in appearance
Multinucleate: Cells long; more nuclei
More mitochondria for energy production
500+ muscles, 40-50% body weight
Skeletal Muscle Extras
Soft and fragile yet TOUGH
Exerts TREMENDOUS power
Power provided by bundles of muscle
fibers wrapped in connective tissue
Connective tissue coverings allows for
transmission of blood and nerves to
muscles & provides support
Functional Characteristics of
Skeletal Muscle
Produces movement: for locomotion,
manipulation and responding to the
external environment; also for
expressing emotions
Maintaining posture: works continuously
to fight downward pressure of gravity
Functional Characteristics of
Skeletal Muscle
Stabilizing joints: muscle tendons
stabilize and reinforce joints that have
poor articulating surfaces
Generating heat: heat is a by-product of
muscular activity; maintains normal
body temperature
Skeletal Muscle Interactions
Muscles are arranged in the body to
either work together or work in
opposition of each other
Number 1 Rule of Muscle Activity:
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MUSCLES ONLY PULL*** THEY NEVER
PUSH!
In other words, muscle contractions are
caused by SHORTENING of fibers
Skeletal Muscle Interactions
Insertion: the
movable attachment
of a muscle
Examples: biceps
tendon attachment
to radial tuberosity
Origin: the fixed,
immovable point of
attachment
Examples: biceps
tendon attachment
to greater tubercle
A muscle contraction involves a muscle’s
insertion moving toward its origin
Origins and Insertions
4 Functional Groups of
Skeletal Muscles
1.) Agonists (prime movers): a muscle
that provides the major force for
providing a specific movement
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Example: biceps brachii- prime mover of
elbow flexion
4 Functional Groups of
Skeletal Muscles
2.) Antagonists: muscles that
oppose/reverse a movement; relaxed
when the agonist is active; helps
regulate action of agonist by providing
resistance
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Can also be agonists
Example: the triceps brachii is the
antagonist to the biceps during elbow
flexion
4 Functional Groups of
Skeletal Muscles
3.) Synergists: “work together”; aids
agonist by promoting the same
movement or reducing unnecessary
movements that might occur as the
agonist contracts
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Example: biceps brachii and brachioradialis
in elbow flexion
4 Functional Groups of
Skeletal Muscles
4.) Fixators: a synergist that immobilizes a
bone or a muscle’s origin
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Example: erector spinae (muscles for posture)
All types of muscles work together to provide
smooth, coordinated and precise movements.
Any one muscle can be in any functional
group, dependant on its action
Detailed Skeletal Muscle
Deep fascia:
sheet/band of dense
connective tissue
covering muscles
Epimysium:
connective tissue
covering many
fascicles, all bound
together
Detailed Skeletal Muscle
Fascicle: a bundle of
fibers wrapped in
perimysium
Endomysium:
connective tissue
surrounding each
muscle fiber
Perimysium:
connective tissue
surrounding a
bundle of muscle
fibers
Aponeuroses:
sheetlike epimysia
that connects muscle to
each other and to
cartilage/bone
Detailed Skeletal Muscle
Tendon: cordlike
band of epimysia
connecting muscles
to bones
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Durable and able to
cross bony
projections
Small in diameter to
fit in crowded joint
spaces
Nervous Stimulation of a
Muscle Cell
Skeletal muscle cells possess unique abilities:
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Excitability: can receive & respond to a stimulus
Contractility: they can shorten
Extensibility: lengthen or stretch
Elasticity: cells return to resting form after
contracted or stretched
When a skeletal muscle contracts, it is told to
do so by the nervous system
Nervous Stimulation of a
Muscle Cell
Motor Neuron: nerve extending from spinal
cord to muscle fiber
Motor Unit: one motor neuron and all the
skeletal muscle cells it stimulates
Neuromuscular Junction: where the end of
the nerve and the beginning of the muscle
fiber meets
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Synaptic cleft: space between nerve and muscle
fiber
Motor Unit
Nervous Stimulation of a
Muscle Cell
Action Potential: an electrical current
that can cause a muscular contraction
Neurotransmitter: a chemical that
carries a signal from the nerve to the
muscle; continues the nervous
stimulation
Acetylcholine (ACh): the
neurotransmitter specific to muscles
Nervous Stimulation of a
Muscle Cell
The nervous system sends a neural
signal to the motor unit. This causes a
release of ACh into the neuromuscular
junction, where it binds to receptors on
the muscle cell. This causes an action
potential to run throughout the muscle
cell, initiating a muscle contraction.
Synaptic Cleft
Microscopic Anatomy
Microscopic Anatomy of
Skeletal Muscle
Muscle cell = muscle fiber
Sarcomere: contractile units of
myofibrils, aligned end-to-end
Myofibril: contractile proteins of muscle
cells; lie parallel along length of fiber
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Thin myofilaments: actin
Thick myofilaments: myosin
Microscopic Anatomy of
Skeletal Muscle
A band: where the myosin filaments are
aligned
H Zone: less dense portion of A band where
thin filaments don’t overlap thick filaments
Z line: separates sarcomeres; where actin
filaments attach
I band:light bands; where the actin filaments
are aligned; extends to tips of myosin
filaments
Sarcomere
Graded Responses of Skeletal
Muscle Contraction
A graded response: the degree of
muscle shortening is dependant on
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1. The speed of muscle stimulation
2. The number of muscle cells stimulated
Speed of Stimulation
Muscle Twitch: a single, brief contraction
caused by a mistake of the nervous system
Summing of Contractions: when nervous
impulses are delivered to a muscle at a rapid
rate so it can’t relax between impulses; the
contractions are summed(added) to create a
smooth, strong contraction
Tetanus: no relaxation between contractions;
smooth and sustained
Number of Cells Stimulated
Small, weak contractions: few cells
initiated
Large, strong contractions: all motor
units are active and all muscle cells
stimulated
Types of Skeletal Muscle
Contractions
Isotonic: same tone
or tension
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Myofilaments slide,
muscle shortens &
movement occurs
Types of Skeletal Muscle
Contractions
Isometric: same
length
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Muscles DO NOT
shorten
Myosin myofilaments
do not move, tension
in the fibers build
Muscle tries to move
but cannot
Energy for Muscle
Contractions
There are 3 different energy systems in the
body that provide for muscle contractions
Definitions:
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Creatine Phosphate (CP): high energy molecule
only in muscles which help replenish energy stores
Adenosine Triphoshate (ATP): energy source in the
body
Glucose: blood sugar
Glycogen: storage form of blood sugar
Energy for Muscle
Contractions
Lactic Acid: a byproduct of an anaerobic
pathway; causes muscle burning
Aerobic: using oxygen during activity
Anaerobic: not using oxygen during
activity
Energy Systems
There are 3 ways energy is utilized for
muscular activity:
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1. ATP-PC/Rapid Recovery
 Anaerobic, lasting no more than 20 seconds
 ATP production rate is rapid
 ATP stores broken down rapidly and resupplied
by creatine phosphate (transfers a phosphate
to ADP)
 More creatine stored in muscles than ATP
Energy Systems
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2. Lactic Acid/Anaerobic
 Breaks down glucose for energy without using
oxygen
 Muscles are working too fast for oxygen &
glucose to be delivered by aerobic respiration
 Results in build up of lactic acid in muscles:
promotes muscle fatigue and soreness
Lactic Acid/Anaerobic
Continued
 Muscle fatigue: when a muscle is unable to
contract even though it is still being stimulated.
 Oxygen Debt: occurs during prolonged muscle
activity; can’t get oxygen fast enough for the
muscle’s needs; lactic acid builds up leading to
fatigue; repaid by breathing deeply until the
muscles receive enough oxygen to get rid of
lactic acid and make more ATP and creatine
phosphate
Energy Systems
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3. Aerobic Respiration
 During light exercise, ATP stores are
regenerated by using oxygen
 Can last for hours if glucose supplies are
present
 Used in endurance activities
Types of Skeletal Muscle
Fibers
There are 2 different kinds:
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1. Slow twitch
 For endurance
 Speed of contraction is slow
 Uses aerobic respiration
 Low glycogen stores-more fats used
 Slow rate of fatigue
Types of skeletal muscle fibers
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2. Fast twitch
 Explosive movements for short distances
 Speed of contraction very fast
 Some aerobic, some anaerobic fibers
 High glycogen stores but fatigues quickly
The distribution of muscle fibers is not complete
until the teenage years. It varies between
muscles, within muscles and between people.