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Chapter 8
Muscles
Muscular system – typically refers to skeletal muscle
muscle (organ) – composed of muscle tissue,
connective tissue and nervous tissue
Functions of Muscles
1. Body movements
2. Maintain posture
3. Moving substances (mostly smooth)
(GI and respiratory tract)
4. Generating heat
(75% of ATP energy is lost as heat during
contraction)
5. Pump blood (cardiac)
TRIVIA!
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How many muscles are there in the human body?
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Answer: 640 Muscles
The muscles make up about 40 % of the body mass.
What is the longest muscle in the body?
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Answer: The Sartorius
The Sartorius runs from the outside of the hip, down and across to the
inside of the knee. It twists and pulls the thigh outwards.
What is the smallest muscle in the body?
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Answer: The Stapedius
The Stapedius is located deep in the ear. It is only 5mm long and thinner
than cotton thread. It is involved in hearing.
What is the biggest muscle in the body?
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Answer: The Gluteus Maximus
The Gluteus Maximus is located in the buttock. It pulls the leg
backwards powerfully for walking and running.
Skeletal Muscle Movement
• Movement – muscle move bones by
pulling not pushing.
– Synergists – any movement is generally
accomplished by more than one muscle. All
of the muscles responsible for the movement
are synergists.
– Prime Mover (agonist) = one most
responsible for the movement
– Ex. Push-up: see attachment Pushup.pdf
• Movement cont.
– Antagonists – muscles and muscle groups
working in pairs
– when one contracts the other relaxes
(extends).
– example: the biceps brachii flexes your
arm and the triceps brachii extends your
arm.
Portions of a muscle
origin
• Origin: end of the
muscle attached to the
bone that remains
stationary
belly
• Insertion: end of the
muscle attached to the
bone that moves
• Belly: the fleshy part
of the muscle between
the tendons of origin
and/or insertion
insertion
Categories of
skeletal muscle actions
• Categories
Actions
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Increases the angle at a joint
Decreases the angle at a joint
Moves limb away from midline of body
Moves limb toward midline of body
Moves insertion upward
Moves insertion downward
Rotates a bone along its axis
Constricts an opening
Extensor
Flexor
Abductor
Adductor
Levator
Depressor
Rotator
Sphincter
Naming Skeletal Muscles
Trapezius
• Shape:
– deltoid (triangle)
– trapezius (trapezoid, 2
parallel sides)
Deltoid
– serratus (sawtoothed)
– rhomboideus
(rhomboid, 4 parallel
sides)
– orbicularis (circular)
Serratus anterior
Rhomboideus
major
Muscles Named by Location
• Frontalis
(over frontal bone)
• Tibialis anterior
(front of tibia)
• Brachii
(arm)
• Lateralis
(toward outside)
tibialis
anterior
Muscles Named by Size
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maximus (largest)
minimis (smallest)
longus (longest)
brevis (short)
major (large)
minor (small)
Psoas
minor
Psoas
major
Muscles Named by
Direction of Fibers
• Rectus (straight)
–parallel to long
axis
Rectus
abdominis
• Transverse
• Oblique
External
oblique
Muscles Named for
Number of Origins
Biceps
brachii
• Biceps (2)
• Triceps (3)
Muscles Named for Origin and
Insertion
Sternocleidomastoid
originates from
sternum and clavicle
and inserts on
mastoid process of
temporal bone
insertion
origins
Muscles Named for Action
• Flexor carpi radialis
(extensor carpi radialis)
– flexes wrist
• Abductor pollicis brevis
(adductor pollicis)
– abducts thumb
• Adductor magnus
– adducts thigh
• Extensor digitorum
– extends fingers
Adductor
magnus
The 3 Types of Muscle Tissue
3 Types of Muscles
Skeletal Muscle
Smooth Muscle
Cardiac Muscle
Smooth Muscle
• Fibers are thin
and spindle
shaped.
• No striations
• Single nuclei
• Involuntary
• Contracts slowly
Smooth Muscle
• Found in the circulatory system
– Lining of the blood vessels
• Found in the digestive system
– Esophagus, stomach, intestine
• Found in the respiratory system
– Can regulate air flow
• Found in the urinary system
– Urinary bladder
Cardiac Muscle
• Cells are branched and
fused with one another
= intercalated discs
• striatied
• Each cell has a central
nuclei
• Involuntary
• Intermediate contraction
speed
Cardiac Muscle
• Healthy cardiac muscle NEVER fatigues
Skeletal Muscle
• Fibers are long and
cylindrical
• multiple nuclei
• striatied
• Voluntary
• Rapid contraction
speed
Skeletal Muscle
• Composed of striated muscle cells (muscle
fibers) and connective tissue.
– Most muscles attach to 2 bones that have a moveable
joint between them.
Connective tissue components:
- Muscle fibers (cells) are soft and surprisingly fragile
- Thousands of fibers are held together by fibrous
connective tissue – provides the strength and support
Tendon: thick dense connective tissue extension of the
fascia attaching muscle to bone
Aponeuroses – sheet-like structure of dense connective
tissue connecting muscle to muscle
Muscle Structure Terms: Outside to
Inside
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Fascia
Epimysium
Perimysium
Fascicle
Endomysium
Muscle Fiber
Myofibril
Components of a Muscle Cell
(Myofiber)
• Sarcolemma
– Cell membrane of a muscle fiber
• Sarcoplasm
– Cytoplasm of cell w/ large numbers of glycosomes (granules of
stored glycogen) and significant amounts of myoglobin
– Myoglobin
• Oxygen binding pigment (protein) related to hemoglobin
• T tubules
– Deep invaginations of membrane which allow depolarization of
the membrane to quickly penetrate to the interior of the cell
• Multiple nuclei
• Multiple mitochondria
– Produce ATP (energy) for the cell by cellular respiration
• Myofibrils
– Cylindrical organelles which contain contractile proteins
Components of a Myofibril
• Sarcomere = single contractile unit of a myofibril
– Hundreds end to end per myofibril
• Actin = thin filaments (protein)
– Filaments pulled during contraction
• Myosin = thick filaments (protein)
– Contain ATPase
– Studded w/ myosin heads
• Z disc (line) = actin attachment site
• M line = myosin attachment
• A Band = dark band of myosin (and actin
overlap)
• I Band = light band of only actin fibers
• H zone = only myosin filements
– Disappears during contraction
Muscle contraction
• A muscle cell must be stimulated by a
neuron to contract
• Motor unit = a motor neuron and all the
muscle fibers it stimulates (on ave. 150)
• Neuromusclar junction = site where a
neuron’s axon meets the muscle fiber
– DO NOT actually touch – gap between them
called synaptic cleft
• During contraction the myofilaments slide
over each other increasing overlap =
sliding filament theory
Sequence of event in muscle contraction:
1. Nerve impulse reaches end of motor neuron
2. Neurotransmitter acetylcholine (ACh) released and diffuses across
synaptic cleft
3. ACh binds with receptors on sarcolemma causing depolarization of
membrane (causes action potential)
4. Action potential travel along sarcolemma and down T tubules
5. Changes permeability of sarcoplamic reticulum, opening protein
channels allowing Ca ions to flood into sarcoplasm
6. Ca binds to actin filaments changing shape and exposing active
sites
7. Myosin heads bind to active sites forming cross bridges
8. ATP is broken down and energy released flexes the myosin head
pulling the actin filaments
9. Actin filaments are pulled toward each other shortening the
sarcomere by pulling the Z lines towards each other (H zone
disappears)
Sequence for return to resting state:
• Ach in synaptic cleft broken down
• Calcium ions pumped back into sarcoplasmic
reticulum by active transport (requires ATP)
• Active sites on actin are again covered
• Actin filaments slide back to original position
• Extra fact: Botulism blocks the release of Ach
stopping motor neuron stimulation of respiratory
muscles
Fueling Muscle Contraction:
1. Use available ATP
- Very limited supply
2. Use Creatine Phosphate
- 4-6x more abundant then ATP
- contains a high-energy phosphate bond
- can quickly convert ADP back into ATP in
mitocondria
- again supply is limited
3. Convert glucose into ATP
- using cellular (aerobic) respiration
- from blood or glycogen
- also occurs in mitochondria and requires
oxygen
34-36
Oxygen Debt:
During rest or moderate activity respiratory and
cardiovascular system supply sufficient oxygen to
muscles.
During heavy activity it cannot - eventually converts to
anaerobic respiration
Lactic acid fermentation occurs – lactic acid must be
removed by blood and reconverted in liver to glucose
(requires oxygen)
Creates oxygen debt:
= amount of oxygen required for liver to convert
lactic acid to glucose + oxygen required for muscle cells
to restock ATP and creatine phosphate
- slow to repay – may take several hours
Muscle fatigue:
- After prolonged activity muscle may lose
ability to contract = fatigue
- Usually result of high lactic acid buildup in
muscles
- Lowers pH and muscles no longer respond to
stimulus
- Lactic acid also stimulates pain receptors and
muscle soreness occurs
Benefits of exercise:
Aerobic: (lead to resistance to fatigue)
- more capillaries form around muscle
- more mitochondria and myoglobin in cells
- more metabolic enzymes produced (glycolysis)
- heart becomes stronger
- more RBC’s produced
- respiratory system increases efficiency
Resistance:
- muscle cells produce more myofilaments (increase mass)
- connective tissue increases in thickness
- capable of contracting w/ more force
- resting metabolic rate increases
Graded Responses:
• Multiple fiber summation –
– Weak signal from CNS stimulates small motor units first
– As signal strength increases, more motor units are excited =
recruitment
– more and larger motor units are activated, the force of muscle
contraction becomes progressively stronger
– Maximal tension = all possible motor unit are activated
• Frequency summation –
- in skeletal muscles, the force exerted by the muscle is controlled
by varying the frequency at which action potentials are sent to
muscle fibers
- twitch = single contraction lasting fraction of a second
- if next action potential arrives before complete relaxation the force
of twitches combines
- tetanus – sustain contraction lacks even partial relaxation
Myogram
Concentric: Force is
greater than load –
muscle shortens
Eccentric: Force is
weaker than load –
muscle lengthens
slowly
Isometric: Force is
equal to load –
Muscle length remains
same
Types of Fibers
• Slow Oxidative Fibers
– Dark red
– Large amounts of myoglobin and mitochondria
– Aerobic respiration
• Fast Glycolytic Fibers
– Low myoglobin content
– Few mitochondria
– Anaerobic movement
Typical person = 50/50
Elite sprinters – as much as 80% fast twitch
Elite marathoners – as much as 80% slow twitch