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Muscle Anatomy
Chapter 9
Muscle Structure- connective tissue
component
 1. Endomysium- delicate connective tissue
membrane that covers specialized skeletal muscle
fibers.
 2. Perimysium- tough connective tissue binding
together fascicles
 3. Epimysium-coarse sheath covering the muscle
as a whole
 4. These 3 fibrous components may become a
tendon or an aponeurosis.
Size Shape and fiber arrangement
 1. Skeletal muscles vary considerably in size, shape, and fiber
arrangement
 2. Size- range from extremely small (muscles to bones in ear)
to extremely large-(quadriceps)
 3. Shape- variety of shapes, such as broad, narrow, long,
tapering, short, blunt, triangular, quadrilateral, irregular, flat
sheets, or bulky masses.
 4. Arrangement- variety of arrangements, such a s parallel to
long axis, converge to a narrow attachment, oblique,
pennate, bipennate, or curved; the direction of fibers is
significant due to its relationship to function
Attachment of Muscles
 1. Origin- point of attachment
that does not move when the
muscle contracts.
 2. Insertion- point of attachment
that moves when the muscle
contracts
Muscle Action
 Muscle movement is a coordinated action of several
muscles; some muscles in the group contract while
others relax
 PRIME MOVER (agonist)- a muscle or group of
muscles that directly performs a specific movement
 ANTAGONIST- muscles that , when contracting,
directly oppose prime movers; relax while prime
mover (agonist) is contracting to produce movement;
provide precision and control during contraction of
prime movers.
Muscle actions continued
 SYNERGISTS-muscles that contract at the same
time as the prime movers; they facilitate prime
mover actions to produce a more efficient
movement
 FIXATOR MUSCLES- joint stabilizers
LEVER- any rigid bar free to turn about
a fixed point called a fulcrum
 In the body the bones act as a lever, joints serve as a fulcrum
and the muscles applies a pulling force on a bone lever at the
point of attachment to the bone.
Levers (p284)
Tips on Naming Skeletal Muscles
 Direction of Muscle Fibers
 rectus
 oblique
 Relative Size of Muscle Fibers
 maximus
 minimus
 longus
 Location of the Muscle
 temporalis
 frontalis
Tips on Naming Muscle
 Number of Origins
 biceps
 triceps
 quadriceps
 Location of Origin
and Insertion
 sterno
 cleido
 mastoid
Naming Muscle
 Muscle Shape
 deltoid
 Muscle Action
 flexor
 extensor
 adductor
Physiology of the Muscular System
 General Function of the Muscular system
 MOVEMENT
 HEAT PRODUCTION
 POSTURE
 Function of muscular tissue
 Excitability ( or irritability)- they can respond to regulatory
mechanisms like nerve signals.
 Contractility- Ability to contract, pull on bones and produce
movement
 Extensibility- Ability to extend or stretch to return to resting
length.
Muscle Cell overview
 Muscle cell are called fibers because they are threadlike in
shape.
 Sarcolemma is the plasma membrane of the muscle cell.
 Sarcoplasmic Reticulum-
 Network of tubules and sacs found within mm fibers
 Membrane of the SR continually pumps calcium ions from the
Sarcoplasm and stores the ions within its sacs.
 Muscle fibers contain many mitochondria and several nuclei.
 Myofibrils are numerous fine fibers packed close together in
the sarcoplasm
Sarcomere
 Segment of myofibril between two successive Z lines
 Each myofibril consists of many sarcomeres
 Contractile unit of the muscle fiber
T tubules
 Transverse tubules extend
across the sarcoplasm at
right angles to the long
axis of the muscle fiber.
 Membrane has ion pumps
that continually transport
Calcium ions inward from
the sarcoplasm
 Allow electrical impulses
traveling along the
sarcolemma to move
deeper into the cell.
Triad
 A T-tubule
sandwiched between
2 sacs of SR. Allows
an electrical impulse
traveling along Ttubule to stimulate
the release of Ca++
causing a contraction
of the mm cell.
Myofilaments
 Each myofibril contains thousands of thick and thin
myofilaments
 Four different proteins make up these myofilaments
 Myosin
 Makes up THICK filaments
 Heads are chemically attracted to actin molecules
 Myosin heads are known as cross bridges when attached to actin.
 Actin- globular protein that forms two fibrous strands twisted
around each other to form the bulk of the THIN filament.
 Tropomyosin- protein that blocks the active sites on the actin
molecules
 Troponin- protein that holds tropomyosin molecules in place
Sliding Filament Theory
 The sliding filament theory
states that when signaled
the actin filament within
each sarcomere slides
toward one another,
shortening the sarcomere
in each fiber causing
muscle contraction.
Mechanism of contraction
 When a motor neuron sends and impulse to the muscle cell
 The neurotransmitter ACETYLCHOLINE is released and
stimulates the T tubules and the impulse travels inward causing
release of Ca++.
 Ca++ binds to troponin, causing the tropomyosin to shift and
expose active sites on the actin.
Relaxation of Muscle
 Immediately after Ca ions are released the SR begins pumping
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them back into the sacs.
Ca++ ions are removed from the troponin and it shuts down the
contraction.
ATP is the energy source
Muscle cells continually re-synthesize ATP from the breakdown of
CREATINE PHOSPHATE
Aerobic respiration- adequate levels of ATP because Oxygen is
available.
Anaerobic respiration- inadequate O2 levels in cell respiration
result in lactic acid fermentation.
 See ACTIN-MYOSIN ppt
The Motor Unit= Neuromuscular
junctions (nerve meets muscle)
Muscle fiber types
 Red-slow twitch fibers (dark meat)
 Thin, slow acting ATPases, red in color due to myoglobin
 Fat metabolism, fatigue resistant- aerobic pathways
 High endurance, not much power
 White-fast twitch (white meat)
 Little myoglobin, thicker, fast acting ATPases
 Large glycogen reserves, anaerobic, fatigable fibers
 Short term, rapid, intense movements
 Intermediate-fast twitch fibers
 Fast acting, fast acting myosin, oxygen dependent, less fatigable,
Muscle fibers cont…
 Muscles contain a mixture of muscle fibers
 Sprinting- white fast twitch
 Marathon- red slow twitch
 Posture- red slow twitch
 Weight lifters- balance between red and white.
Physiology of Skeletal Muscle
Contraction
 Energy Sources
 Breakdown of ATP
 ATPADP + O2 + energy
 Energy comes from CELLULAR RESPIRATION
 Results depend on AMOUNT OF OXYGEN AVAILABLE
 Moderate activity- adequate amounts of oxygen
 Strenuous activity- not enough oxygen causing Pyruvic Acid (from the
first step of Cell respiration) to be converted to LACTIC ACID
 OXYGEN DEBT-extra oxygen that must be taken in by the body for
restorative process. Difference between the amount of oxygen needed
for totally aerobic respiration during muscle activity and the amount
actually used.
Muscle tone
Steady partial contraction present at all times
State of tension when awake
Enable muscle to react immediately
Does not produce active movement
Loss of muscle tone in paralysis, coma, atrophy, prolonged
immobilization.
Muscle fatigue
 Muscle unable to contract
 Tension drops
 Inability to generate enough ATP to power contraction
 Excessive accumulation of lactic acid and ionic imbalance
 Spasm- sudden involuntary contraction
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Clonic- alternating spasm with relaxation
Tonic- sustained
Tetanus-smooth sustained contraction
Tetany-result of low calcium, increases excitability of neurons,
convulsions may follow.
Twitch Contraction
 A quick jerk of a muscle that is produced as a result of a
single, brief threshold stimulus. 3 phases
 Latent: Action Pontential reaches sarcolemma; SR
releases Ca2+; 2ms
 Contraction: Cross-bridge formation; Ca2+, troponin;
15ms
 Relaxation: Ca2+ uptake; tropomyosin covers actin;
25ms
 All or None response- Once the muscle fiber has
been stimulated to contract the muscle fiber will
contract to its fullest extent.
Twitch Contraction
Twitch to full contraction
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How do twitches achieve whole muscle contraction?
By building tension
1.
2.
Multiple motor units are stimulated (recruited)
Stimulus from nerve arrives more frequently
Types of Muscle contractionmyography
 Single twitch contraction- seen in above slide
 Treppe
 Staircase phenomenon- strength of contraction builds after it
has contracted a few times (stronger when you get warmed up)
 Tetanus
 Results from the coordinated contractions of different motor
units within the muscle organ. These motor units fire in an
overlapping time sequence to produces a “relay team” effect that
results in a sustained contraction. This is the kind of contraction
exhibited by normal skeletal muscle organs most of the time.
 (incomplete and complete tetanus)
Muscle contraction cont…
 Muscle tone
 Tonic contraction is a continual, partial contraction in a muscle
organ. At any one moment a small number of the muscle fibers
in a muscle contract, producing a tautness of the muscle rather
than a recognizable contraction. Muscle tone. Allows muscle
to always be ready to respond when stimulated immediately.
 Muscles with less tone than normal are FLACCID
 Muscles with excess tone are called SPASTIC.
 GRADED STRENGTH PRINCIPLE- basically the number of
muscle fibers contracting are in response to the task. Ie.
Heavy object, more myofibrils contract
Isotonic vs. Isometric contraction
 Isotonic contraction is a contraction in which the tone or
tension within a muscle remains the same as the length of the
muscle changes. (P 328)
 There is actually movement- lifting weights
 Isometric contraction is a contraction where the length of
the muscle stays the same while the muscle tension increases. Ie.
Pulling up on an immovable object.
Points of Interest
 Muscle fatigue- simply muscle exhaustion. Muscle
runs out of ATP rendering myosin heads incapable of
producing the force required for continued
contraction
 Exercise effects on muscle:
 Disuse causes atrophy (wasting away). Overuse causes
hypertrophy (overgrowth)
 Strength training- increases the number of
myofilaments in each muscle fibers, increasing muscle
mass. (muscle fibers stay the same myofilaments can
increase.)
 Endurance training- lean muscle not hypertrophy.
This increases the number of blood vessels to the tissue,
increasing oxygen availability and efficiency along with
increase in mitochondria for higher ATP production.
Cardiac muscle
 Heart muscle
 Cells directly connected via intercalated
discs (pores through which ions pass)
 Allows all connected cells to contract as one
 Cardiac muscle is autorhythmic
(spontaneous generation of AP)
 Involuntary (influenced by hormones)
 Metabolism is always aerobic
Smooth muscle
 Less actin & myosin, no sarcomeres
 Contracts slowly
 No O2 debt
 Autorhythmic
 Involuntary control