The Muscular System
Objective:
 The student will become familiar with the
structure and function of the muscular
system
Question of the day:
What moves you?
Composition:
 The musclar system makes up 40-50% of
total body weight
 The muscular system is
– 75% water
– 20% proteins
 Actin and Myosin
– 5% miscellaneous carbohydrates, fats, and
inorganic salts
Terms to know:
 Myology: study of muscle
 Tendons connect bone to muscle
 Fascia
– Loose connective tissue
– Aponeurosis
 Sheet of connective tissue that connects muscle to
muscle
Function:
 The primary function of muscle is to ….
PULL
 Muscles work in opposing pairs
– While one pulls, the other relaxes
Types of muscle tissue:
QuickTime™ and a
decompressor
are needed to see this picture.
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19917.jpg
Cardiac
Striated
One centrally
located
nucleus
Skeletal
Striated
Multinucleated
Smooth
Non-striated
One centrally
located
nucleus
Involuntary
control
Automatic
rhythmic
Both
involuntary
and
voluntary
control
Involuntary
control
Slow and
sustained
Walls of the
heart
Attached to
bones
Lining the
internal
organs
Voluntary (skeletal) muscle
function:
1. Movement

Physical movement of the body
2. Posture

Maintain body position
3. Heat production


Muscles give of 65% of their energy
production as heat
Works to maintain a constant body
temperature
Smooth (involuntary) Muscle
function:
1. Movement of substances through body tubes

Ex. Peristalsis in the esophagus
2. Expulsion of stored substances

Ex. Gallbladder
3. Regulation of the size of openings

Ex. Iris of the eye
4. Regulation of the diameter of tubes

Ex. Blood vessels
Characteristics of Muscle Tissue:
1. Excitability (irritability)

Abilitiy of muscle to be stimulated to evoke
response
2. Contractility


Function of muscle as a contractile unit
Muscle’s ability to contract/shorten
3. Extensibility

The ability of a muscle to stretch
Characteristics of Muscle Tissue:
(cont.)
4. Elasticity

The ability of the muscles to return to normal
shape after being stretched or muscle
contraction
5. Conductivity

The ability to conduct an electric impulse
along the entire length of the muscle
Fascia:
 Loose connective tissue that “wraps” muscle
tissue
 Superficial fascia: subcutaneous layer that
holds skin to muscles
 Deep fascia: more fibrous than superficial
hold muscles together
Functions of Fascia:
1.
2.
3.
4.
Storehouse for water
Insulation
Mechanical protection
Houses blood vessels and nerves
Muscle Structure
QuickTime™ and a
decompressor
are needed to see this picture.
http://www.ivy-rose.co.uk/Topics/Muscles/Epimysium.jpg
 Epimyseum: tissue that wraps the entire
muscle (found deep to the fascia)
 Perimyseum: smaller units of muscle
– Holds the fascicles together
 Fascicle: collections of the smaller unit
– Group of individually wrapped fibers
 Endomysium: wrapping of the smaller unit
– Each muscle fiber (myofiber) is surrounded by a
plasma membrane individually wrapped in a
sheet of endomysium
 Sarcolemma is comparable to the plasma
membrane of a muscle fiber
 Sarcoplasm
– Liquid environment within a muscle cell that contains
calcium ions surrounding the myofibrils
 Myofibrils are made up of 2 types of filaments
(myofilaments)
– Actin and Myosin
– Adjacent myofilmaments line up with each other so that
the Z-line of one sarcomere lines up with the Z-line of an
adjacent myofibrils
 T-tubules
– Are extensions of the sarcoplasmic reticulum that run
transversely along muscle fibers
– Hold substances needed for muscle contraction
QuickTime™ and a
decompressor
are needed to see this picture.
http://www.edcenter.sdsu.edu/cso/paper
/image005.jpg
http://ab.mec.edu/abrhs/science/AnatPhys_Labs/ima
ges/sarcomere.gif
QuickTime™ and a
decompressor
are needed to see this picture.
The contractile unit of muscle:
Think about it …
 Tendons are continuous with the epimysium
surrounding the larger muscle
 Tendons connect muscle to bone
Why do we have all of this?
 All of these components are necessary to
create movement
 Muscle generates movement
 Muscle is living tissue
– Requires blood supply and nerve innervation
How do muscles create
movement?
 Well actually they don’t …
the Brain does.
Movement:
 Movement is initiated in the brain which is
part of the Central Nervous System (CNS)
with the initiation of an action potential
 The impulse travels down the spinal cord
out to the motor neuron which carries the
electrical impulse to the muscle
 Between the motor neuron and muscle is a
synapse
QuickTime™ and a
decompressor
are needed to see this picture.
What is needed to create
movement?
 Mitochondria
– Power house of the cell
– Produce energy in the form of ATP with the help
of myoglobin
 T-tubules
– extension of the sarcoplasmic reticulum
– Hold substances needed for muscle contraction
Myofilaments
 Actin and myosin
 Myosin has a hook-like binding site while
actin has a bulb shaped binding site
 These binding sites are not readily available
– The binding sites on actin and myosin are
covered by tropomyosin and troponin
 This is to keep the binding sites from attaching to one
another during a relaxed state
Sliding Filament Mechanism:
1. Brain says move
2. Impulse travels down spinal cord
3. Impulse travels out spinal nerve to periphery (the
muscle you want to move)
4. The impulse travels down the motor neuron
5. The impulse reaches the presynaptic bulb of the
motor neuron where (ACh is stored in vesicles,
the sarcolemma is semipermeable and polarized
due to Na+ and K+ ions gathering outside the
sarcollema)
6. The impulse crosses the neuromuscular
junction (NMJ) with the help of ACh

The junction of the motor neuron and muscle
fiber
7. As soon as the ACh hits the sarcolemma
the action potential is stimulated and the
permeability of the sarcolemma is changed
or depolarized.

The wave of depolarization continues down
the length of the muscle fiber.
8. Wave of depolarization releases Ca+ ions
from the sarcoplasmic reticulum



Actin and myosin have on their surface
binding sites so that the myofibrils can bind
together to create muscle contraction
Binding sites are protected by
Troponin/Tropomyosin to prevent the
myofibrils from binding to each other when the
muscle is at rest
Ca+ ions push Troponin/Tropomyosin away
from the binding sites on actin and myosin,
making the binding sites readily available for
the creation of cross-bridges
9. ATP (created by the mitochondria by/with
myoglobin) allows for a power stroke

Pushes the Z-lines of the sarcomere closer
together
10. AChE (Acetylcholine Esterase) is secreted
which destroys ACh which allows the
sarcolemma to go back to its resting state
(repolarized)
What can interfere with muscle
contraction?
 Oxygen debt: can’t get enough oxygen into
the body so we start to build up lactic acid
– Lactic acid is “poison” to the muscles
– Slows the reclaiming of Ca+ ions so the muscles
won’t fully relax
 Muscle Fatigue: is largely the result of the
depletion of oxygen and/or glycogen
Rigor Mortis
 “when muscles tighten after you die”
 When a person dies they no longer posses
oxygen so lactic acid builds up and the
sarcoplasmic reticulum breaks down
releasing Ca+ ions and the muscles contract
 Rigor can last for 12-20 hours
3 Major Energy systems for
Muscle contraction:
(Anaerobic processes)
1. Available ATP
2. Phosphagen system
3. Glycolysis
Available ATP:
 Immediate energy source
 Good for the first 5-6 seconds of energy
expenditure
Phosphagen system:
 Contained in muscles
 High energy molecule creatine-phosphate or
phospho-creatine
 Capable of delivering lots of energy in a
short period of time
 15 second energy bursts
Glycolysis:

“glucose splitting”
– Breakdown of carbohydrates (glucose =
C6H12O6)

The Liver:
– Stores glucose in the blood
– Converts stored energy into usable energy
Muscles contract to create
movement:
 The All-or-none principle states that when a
stimulus is applied a muscle fiber will
contract completely or not at all
 No such thing as a partial contraction
 Strength of contraction depends on the
number of fibers stimulated
How do muscles contact?
 EMG
(electromyogram)
find diseases that
damage muscle
tissue, nerves, or
the
neuromuscular
junctions (nmj)
QuickTime™ and a
decompressor
are needed to see this picture.
EMG output (myogram):
Types of muscle contraction:
1. Tetanous: continuous
contraction/continuous stimulation


Voluntary movement
Single contraction: twitch
2. Wave summation: staircasing effect
Types of muscle contraction (cont.)
3. Isotonic: “iso” = same


“tonic” = force
Contraction that remains at the same force
throughout
4. Isometric: “iso” = same


“metric” = length
Contraction, no movement
Types of muscle contraction (cont.):
5. Concentric: muscles shorten while generating
force

“positive” lift
6. Eccentric: the muscle elongates while under
tension due to an opposing force being greater
than the force generated by the muscle.


“negative” lift
Rather than working to pull a joint in the direction of
the muscle contraction, the muscle acts to decelerate
the joint at the end of a movement or otherwise control
the repositioning of a load.
Movement:
 Most muscles cross at least one joint
– Some cross 2 or even 3 joints
 When muscles contract they pull with equal
force from both ends
– One end of the muscle must be stable to create
movement
Terminology:
 Origin: immovable end of the muscle
– Where the muscle “starts”
 Insertion: moveable end of the muscle
– The end of the muscle that the force is applied
to
 Belly: “meaty” part of the muscle
– Where the actual muscle contraction occurs
Levers:
 The body moves through a system of levers
 Muscle pull works around these levers
 Levers also give the body a mechanical
advantage
– This means that it takes less force to create
movement therefore making the muscles job
“easier”
Classes of levers:
QuickTime™ and a
decompressor
are needed to see this picture.
http://www.biologyreference.com/images/biol_03_img0301.jpg
Group Actions:
 Agonist
– “prime mover”
– The muscle that initiates the movement
 Synergist
– Muscles that work together to generate movement
 Antagonist
– Muscles that work against the prime movers
 Fixators/Stabilizers
– Muscles that stabilize a joint or bone so that another
muscle can work more efficiently
How are muscles named?

1.
2.
3.
4.
5.
6.
7.
600-700 muscles in the body
Direction of fibers
Location
Size of the muscle
Number of heads of origin
Shape
Origins and insertions
Action
Terminology:
 Hypertrophy: muscle growth (size)
 Atrophy: muscle shrinking
 Myopathy: muscle disease
 Myoma: muscle tumor
 Myolatia: muscle softening
 Myocitis: inflammation of muscle tissue
Disorders of the muscular
system:
 Fibrosis: increase in the amout of fibrous
connective tissue where it is not supposed
to be decreasing the ability of the muscles to
contract and expand the way they’re
supposed to
 Muscular Dystrophy: disintigration of muscle
fibers can lead to complete atrophy and loss
of motor function
Disorders (cont.)
 Myesthemia Gravis: autoimmune disorder
that results in the weakening of the the
muscles caused by faulty nmj
 Abnormal contractions:
– Muscle spasm: a single muscle group does an
uncontrolled contraction
– Tonic spasm: cramp