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The Muscular System
Chapter 10
MUSCLE FUNCTION
 Movement (voluntary and involuntary)
 Supports the body (maintains posture)
 Movement of food along the digestive tract
 Regulation of blood pressure (vasoconstriction)
 Guarding entrances and exits of the body
(sphincter muscles)
 Maintaining body temperature (contracting
muscles release heat)
Contraction & Relaxation of muscles
•Muscles “pull”
bones together
•Contraction
involves
shortening of the
muscle
•Relaxation
involves
lengthening of the
muscle
3 TYPES OF MUSCLES:
• skeletal muscles
• cardiac muscles
• smooth muscles
Skeletal muscle tissue
• Associated with & attached to the skeleton
• Under our conscious (voluntary) control
• Microscopically the tissue appears striated
• Cells are long, cylindrical & multinucleated
Cardiac muscle tissue
• Makes up walls of the heart
• Unconsciously (involuntarily) controlled
• Microscopically appears striated
• Cells are short, branching & have a single nucleus
Smooth muscle tissue
• Makes up walls of organs & blood vessels
• Tissue is non-striated & involuntary
• Cells are long & tapered at one end have a
single nucleus
Anatomy of skeletal muscles
Connective tissue
Muscle fibre bundle
tendon
Muscle fibre
bundle
Skeletal
muscle
sarcolemm
a
Skeletal
muscle
fiber (cell)
Organization of Skeletal Muscles
Components of Skeletal Muscle Fibres
Component
Description
Function
Muscle fibre
single muscle cell
is responsible for muscle contractions
myoglobin
oxygen-binding pigment (similar to hemoglobin) in a skeletal
muscle fibre
stores oxygen for use during muscle
contractions
sarcolemma
membrane of a muscle fibre
surrounds the muscle fibre and
regulates the entry and exit of
materials
sarcoplasm
cytoplasm of a muscle fibre
is the site of metabolic processes for
normal cell activities; contains
myoglobin and glycogen (which
stores energy for muscle
contractions)
sarcoplasmic
reticulum
smooth endoplasmic reticulum in a muscle fibre
stores calcium ions needed for
muscle contractions
Myofibrils
organized bundles of myofilaments; cylindrical structures, as
long as the muscle fibre itself
contain myofilaments that are
responsible for muscle contractions
thick filament
fine myofilament composed of bundles of protein called
myosin (about 11 nm in diameter)
binds to actin and causes muscle
contractions
thin filament
fine myofilament composed of strands of protein called actin
(about 5 nm in diameter)
binds to myosin and causes muscle
contractions
Microanatomy of a Muscle Fiber
Microanatomy of a Muscle Fiber (Cell)
transverse
(T) tubules
sarcoplasmic
reticulum
Sarcolemma (muscle
fibre membrane)
mitochondria
myoglobin
thick myofilament
thin
myofilament
myofibril
nuclei
Muscle fiber
sarcomere
Z-line
myofibril
Thin filaments
Thick filaments
Thin myofilament
Myosin molecule of
thick myofilament
Thin Myofilament
(myosin binding site)
Thick myofilament
(has ATP
& actin
binding
site)
Sarcomere
A band
Z line
Z line
H zone
I band
Thin
myofilaments
Zone of
overlap
Thick
myofilaments
M line
Zone of
overlap
Sliding Filament Theory
• Myosin heads attach to actin molecules (at binding (active) site)
• Myosin “pulls” on actin, causing thin myofilaments to slide across
thick myofilaments, towards the center of the sarcomere
• Sarcomere shortens causing muscle fibre to contract
ATP – the energy currency of cells
ATP = adenosine triphophate
ATP molecule is made up of 1 adenosine molecule
bonded to 3 phosphate (PO43-) molecules
http://student.ccbcmd.edu/biotutorials/energy/atpa
n.html
(reversible animation ATP ---- ADP + P + Energy
http://www.youtube.com/watch?v=Lx9GklK0xQg
(short animation of phosphorylation/dephosphorylation
will start automatically on next slide)
Physiology of skeletal muscle contraction – events
at the myofilaments
Resting sarcomere
ADP
+
P
Myosin head
Active-site exposure
ADP
+ P
Sarcoplasm
Troponin
Actin
ADP
+
Ca2+
Tropomyosin
Cross-bridge formation
Ca2+
Active site
ADP
P +
Myosin reactivation
P
Ca2+
ADP Ca2+
P +
ADP
P +
Cross bridge detachment
Pivoting of myosin head
ATP
ADP
+ P
ADP + P
Ca2+
Ca2+
Ca2+
ADP
P +
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Ca2+
Ca2+
ATP
Ca2+
ADP + P
Figure 7-5
1 of 7
Resting sarcomere
ADP
+
P
Myosin head
Active-site exposure
ADP
+ P
Sarcoplasm
Troponin
Ca2+
Tropomyosin
Actin
Active site
ADP
P +
Ca2+
ADP
P +
• Calcium (Ca+2 ) gates in the sarcoplasmic reticulum (SR)
open, allowing Ca+2 to diffuse into the sarcoplasm
• Calcium will bind to troponin (on the thin myofilament - actin),
causing it to change its shape.
• This then pulls tropomyosin away from the active sites of actin
molecules, allowing myosin heads to bind to the actin.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 7-5
3 of 7
Resting sarcomere
ADP
+
P
Myosin head
Active-site exposure
ADP
+ P
Sarcoplasm
Troponin
Actin
ADP
+
Ca2+
Tropomyosin
Cross-bridge formation
P
Ca2+
Active site
ADP
P +
Ca2+
ADP
ADP Ca2+
P +
P +
• Myosin heads are “energized” by the presence of ATP at the
ATP binding site (energy is released as phosphate bond of ATP
breaks)
• Once the active sites are exposed, the energized myosin
heads hook into actin molecules forming cross-bridges
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 7-5
4 of 7
Resting sarcomere
ADP
+
P
Myosin head
Active-site exposure
ADP
+ P
Sarcoplasm
Troponin
Actin
ADP
+
Ca2+
Tropomyosin
Cross-bridge formation
P
Ca2+
Active site
ADP
P +
Ca2+
ADP Ca2+
P +
ADP
P +
Pivoting of myosin head
• Using the stored energy, the attached
myosin heads pivot toward the center of
the sarcomere
• The ADP & phosphate group are
released from the myosin head
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
ADP + P
Ca2+
Ca2+
ADP + P
Figure 7-5
5 of 7
Resting sarcomere
ADP
+
P
Myosin head
Active-site exposure
ADP
+ P
Sarcoplasm
Troponin
Actin
ADP
+
Ca2+
Tropomyosin
Cross-bridge formation
Ca2+
Active site
ADP
P +
• A new molecule of
ATP binds to the
myosin head, causing
the cross bridge to
detach from the actin
strand
Ca2+
ADP Ca2+
P +
ADP
P +
Cross bridge detachment
Pivoting of myosin head
ATP
ADP + P
Ca2+
Ca2+
Ca2+
• The myosin head will
get re-energized as the
ATP  ADP+P
P
ATP
Ca2+
ADP + P
• As long as the active sites are still exposed, the myosin head can bind
again to the next active site
Resting sarcomere
ADP
+
P
Myosin head
Active-site exposure
ADP
+ P
Sarcoplasm
Troponin
Actin
ADP
+
Ca2+
Tropomyosin
Cross-bridge formation
Ca2+
Active site
ADP
P +
Myosin reactivation
P
Ca2+
ADP Ca2+
P +
ADP
P +
Cross bridge detachment
Pivoting of myosin head
ATP
ADP
+ P
ADP + P
Ca2+
Ca2+
Ca2+
ADP
P +
Ca2+
Ca2+
ATP
http://highered.mcgraw-hill.com/olc/dl/120104/bio_b.swf
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Ca2+
ADP + P
Figure 7-5
7 of 7
Sliding Filament Theory
http://media.pearsoncmg.com/bc/bc_cam
pbell_biology_6/cipl/ins/49/HTML/sourc
e/71.html
Muscle contraction
http://highered.mcgrawhill.com/sites/0072495855/student_view
0/chapter10/animation__action_potentia
ls_and_muscle_contraction.html
Calcium and muscle contraction
If the diet is low in calcium (therefore blood
Ca2+ is low) – do muscles still contract?
If so … HOW?
Interesting fact:
After death, calcium levels inside the muscle cells rise
and the body's level of ATP drops. Inside the muscles,
myosin binds to actin and the muscles contract.
However, with no ATP to reset the crossbridges and
release the myosin, all of the muscles remain
contracted and stiff -- this state is called rigor mortis.
Key Note
Skeletal muscle fibers shorten as thin
filaments interact with thick filaments and
sliding occurs. The trigger for contraction is
the calcium ions released by the SR when
the muscle fiber is stimulated by its motor
neuron. Contraction is an active process;
relaxation and the return to resting length is
entirely passive.
Muscle contraction animations
http://entochem.tamu.edu/MuscleStrucContractswf/ind
ex.html
(step-by-step animation of the Sliding Filament Model
Energy for Muscle Contraction
Energy for Muscle Contraction con’t
Once creatine
phosphate stores are
used up, the muscle
will continue to
contract only if more
ATP can be
generated.
It obtains ATP
through the aerobic
respiration (oxidation)
of glucose (if O2 is
available)
OR fermentation
(which produces
lactic acid if no O2)
3 methods of acquiring ATP for
muscles:
• creatine phosphate (no oxygen – only enough
for 8 seconds of muscle activity)
• fermentation (no oxygen – glucose is broken
down and lactic acid is released as a by-product – 2-3 min)
• aerobic cellular respiration (oxygen
required – glucose is completely oxidized to form water +
carbon dioxide + many ATP molecules – long term energy)
Myoglobin – oxygen-carrying molecule like hemoglobin,
only found in muscle cells, can temporarily store oxygen
Should creatine be used as a supplement for
Creatine phosphate is the primary source of the muscle’s energy during exercise and
kids?
sporting events is a compound called adenosine triphosphate, or ATP. Creatine helps
regenerate the ATP our bodies use to power muscle contractions during activity
bursts.Creatine is an amino acid naturally made in the liver and pancreas, stored in
the muscle, and naturally found in milk, meat and fish. The daily requirement of
creatine is about two grams. The theory by some trainers and coaches is that if by
saturating muscles with creatine athletes will increase the muscle's creatine stores.
Athletes will then be able to regenerate ATP faster and have more energy and less
exhaustion. According to a study in July's Journal of the American Dietetic
Association, weight lifters who took supplementary creatine could do more powerful
jump squats and more bench-press repetitions because their ATP was replenished
faster.Word quickly spread that creatine was safe and effective since it seemed to
increased muscle strength and accelerated the muscle’s recovery time between bouts
of intense exercise. Therefore, creatine may work by allowing athletes to work out
harder. Creatine does nothing by itself without exercise.Once the use of creatine
became more widespread, doctors and trainers began seeing side effects. The most
common reason young athletes stop using the product is severe diarrhea and gastric
distress. Many athletes became predisposed to cramping and dehydration (even
those promoting creatine supplements encourage hydration). More scientific studies
were done that showed positive effects in the exercise laboratory, but no positive
effects with athletes in competition. Respected members of the sports medicine
community have reported muscle tears in athletes on creatine. Furthermore, taking
more than five grams per day of creatine was associated with kidney and liver
inflammation.
Oxygen Debt
Oxygen debt
occurs when the
athlete’s
muscles are
demanding
more ATP than
can be provided
-The answer is
to generate ATP
anaerobically
(creatine-P and
fermentation)
-ATP is
replenished
aerobically after
exercise ceases
Oxygen debt con’t
•Muscle tissue has the unique ability to
operate without oxygen – whereas other
tissue (ie brain tissue) cannot perform without
readily available oxygen
•Athletes train their muscles to increase the
numbers of mitochondria which increases the
aerobic respiration capability and decreases
the amount of oxygen debt necessary –
therefore less lactic acid build-up!!
When skeletal muscles contract, they may
produce two types of contractions:
 Isotonic contraction
 Isometric contraction
Isotonic contraction – as tension increases (more
motor units recruited), length of muscle changes
usually resulting in movement of a joint. The
tension (load) on a muscle stays constant (iso =
same, tonic = tension) during a movement.
(Example: lifting a baby, picking up object, walking,
etc. )
Isometric contraction – no change in length of
muscle even as tension increases. The length of a
muscle stays constant (iso = same, metric = length)
during a “contraction” (Example: holding a baby at
arms length, pushing against a closed door, core
exercises)
Anatomy of the Muscular System
•Origin
Muscle attachment that remains
fixed
•Insertion
Muscle attachment that moves
•Action
What joint movement a muscle
produces
i.e. flexion, extension, abduction,
etc.
Muscle twitch - myogram
When a muscle
receives a
stimulus (electric
impulse), it will
contract or “twitch”
Describe the actions of the myofilaments during a muscle twitch.
Sustained muscle contraction
(TETANUS)
When a muscle
is stimulated
repeatedly, it
produces a
sustained
contraction
(tetanus).
What is summation? What happens to the force of contraction during
summation?
Types of muscle fibres
Types of Muscle Fibres
Marathon runner =
mainly slow-twitch
Sprinter = mainly
fast-twitch
Complications of Muscular System
• atrophy – reduction in size, tone and power of muscles
- Inactivity (due to paralysis, injury, lifestyle) causes muscles to
atrophy
- Initially, muscle size decrease is temporary – but can become
permanent
Severe atrophy due to a
neuromuscular disorder
Hypertrophy – an increase in muscle mass –
due to high-intensity exercise or performanceenhancing drugs (anabolic steroids)
Side Effects of Anabolic Steroids…
STEROIDS AND ATHLETES
http://health.howstuffworks.com/humanbody/systems/musculoskeletal/muscle.htm
Banned Substances and Athletes
http://www.cifstate.org/health_s
afety/steroids/Steroid%20PPT%
200805.ppt
(powerpoint dealing with
banned substances and
athletes)
The Science of Steroids – Documentary
http://www.youtube.com/watch?v=YUTvaU5fXO4