MUSCLE TISSUE
Muscle Contraction
TYPES OF MUSCLE TISSUE
A. Skeletal muscle-voluntary muscle, striated with
light and dark bands, many nuclei per cell.

Found in limbs, trunk of body, jaws, face, eyes etc.
B. Smooth muscle—involuntary, visceral muscle
forms muscular layer of organs. Has one nucleus
per cell, contracts involuntarily, elongated.
Rhythmic contractions.

Digestive tract, bladder, ducts, arteries and veins.
C. Cardiac muscle-involuntary, similar to skeletalstriated but controlled by the autonomic nervous
system. Branched cells with central nuclei.
Intercalated discs assure impulses travel
between cells.

Heart muscle
SKELETAL MUSCLE COMPONENTS
MICROSOPIC ANATOMY OF SKELETAL
MUSCLE
A.
B.
C.
Muscles contain bundles of fascicles that
contain muscle fibers (cells).
Muscle fibers contain Myofibrils which
contain sarcomeres. Myofibrils play a key
role in muscle contraction.
Sarcomeres contain:
 Actin-thin filaments
 Myosin-thick filaments
 The organization between actin and
myosin create the striations we see in
muscle tissue.
THE SARCOMERE
The sarcomere is the basic unit of the muscle fiber.
A. I band- contain thin actin filaments
B. Z lines-attach to the thin actin filaments
C. A bands-thick myosin and thin actin filaments overlap
Sarcomere Shortening Video
MUSCLE CONTRACTION
The sarcoplasmic reticulum is a series of
membrane channels that surround the
myofibrils.
 The transverse tubules extend from the
sarcoplasmic reticulum
 Together these structures help activate muscle
contraction
 Neuromuscular junction

THE NEUROMUSCULAR JUNCTION
A. Connects nerve cells called motor
neurons with muscle cells at a
specialized region on the muscle called
the motor end plate.
B. Neurotransmitters-chemicals released by
the nerve cell which stimulate muscles
to contract. For muscle contraction
acetylcholine (ACh) is used.
C. Target of neurotransmitters is the
sarcomere in the muscle.
THE NEUROMUSCULAR JUNCTION
STEPS OF MUSCLE CONTRACTION
1. Action potential-electrical signal from a motor neuron
(nerve fiber) causes a change in the electrical charge of
the membrane in the nerve cell (Na+ rushes in).
2. The action potential causes a neurotransmitter
(chemical that sends signals from the nervous system)
called ACh ( acetylcholine) is released and bind to ACh
receptors on muscle cell membrane,
3. This signals the muscle fibers in the sarcoplasmic
reticulum which causes Ca++ rushes in from surrounding
sarcoplasmic reticulum.
4. Ca++ binds to a molecule called troponin on actin which
causes the shape to change.
5. Cross bridges attach and detach on actin and myosin
causing contraction of muscle. The muscle fiber shortens.
Myofilament Contraction video
6. For the muscle to relax, ACh, and Ca++ are taken up and
chemical energy ATP is needed to break actin apart from
myosin.
Threshold stimulus-minimum stimulus needed for a muscle to
contract.
All or None Response-partial contraction does not happen, the
muscle contracts when the threshold stimulus occurs. A
stronger stimulus does not affect the contraction.
WHAT IS ADENOSINE TRIPHOSPHATE
(ATP) (SEE NEXT SLIDE FOR DIAGRAM)
ATP is the source of energy for muscle
contraction/relaxation.
 Muscles store a very limited amount of ATP (4-6 sec.
worth at most).
 ATP must be regenerated if contraction is to continue
 ATP can be generated by one of three pathways….

1. AEROBIC METABOLISM/CELLULAR
RESPIRATION
• Occurs in mitochondria, requires oxygen, and involves a
complex sequence of chemical reactions.
Glucose + oxygen carbon dioxide + water+ energy
(36 ATP)
When this system is used:
• Used during prolonged, endurance activities which
maintain a constant heart rate
• As long as there is enough oxygen available relative to ATP
demand, a muscle will utilize aerobic metabolism.
• Posture, most daily movements, marathon runs, bike riding
2.) ANAEROBIC METABOLISM/GLYCOLYSIS
o
Description:
• When muscles contract vigorously, the bulging muscles compress
blood vessels within, impairing oxygen delivery.
• This pathway can occur in the absence of oxygen.
 Chemical Formula:
Glucose  lactic acid +energy (2 ATP)

When this system is used:
• When large amounts of ATP relative to available O2 are needed.
Usually for exercise about 30-40 seconds long.
• Tennis, soccer, 100 meter swim
3. ANAEROBIC METABOLISM/CREATIN
PATHWAY
1. Description:
• Utilizes the molecule creatine phosphate to regenerate ATP, after stored ATP is
depleted.
2. Chemical Formula:
Creatine phosphate + ADP Creatine + ATP (1 ATP)
3. When this system is used:
• Moblized at the beginning of exercise, before other pathways ‘kick in’.
• Creates enough energy for about 15 seconds of contraction.
• 100 meter dash, weightlifting
MUSCLE FATIGUE
Definition: the state of physiological inability to contract
Causes:
1. Occurs when ATP production fails to keep up with ATP
use.
• Deficiency of ATP, as opposed to total absence of ATP which
leads to a continuous state of contraction (rigor mortis, writers
cramp)
2. Accumulation of lactic acid and ionic imbalances also
contribute.
• decreases muscle pH
• causes burning sensation
• interferes with actin/myosin binding
SUMMARY OF MUSCLE METABOLISM
Creatine
pathway
Glycolysis
Pathway
Aerobic
pathway
Requires oxygen
no
no
yes
Amount of ATP
produced
1 ATP
2 ATP
36 ATP
Duration
15 seconds
30-60 seconds
hours
By product
creatine
lactic acid
CO2 and H2O
Advantages
• Rapid energy
• Easily
mobilized
• Quick energy • More
• Does not
ATP/glucose
require
• Waste products
oxygen
are easy to
excrete
Disadvantages
• Small amount
of creatine
available
• Small amount
of ATP
• less
ATP/glucose
• Lactic acid
produces
muscle
fatigue
• Slower
• Limited by
oxygen
FAST TWITCH VS. SLOW TWITCH MUSCLES
SPRINTER VS. MARTHONER
SLOW TWITCH/FAST TWITCH
Fast Twitch
Slow Twitch
Lighter in color-less blood
Darker in color-rich in blood
Few mitochondria
Many Mitochondria
Mostly anaerobic
Primarily aerobic
Easily fatigue
Fatigue slowly
More forceful contractions
Less forceful contractions
Increase in size with training
Don’t increase in size with
training
Sprinters
Distance runners
Analogy: birds
White meat-fast twitch, found in breast and wings, used
for flying-quick movements.
Dark meat-slow twitch, found in legs, used for walking.
MUSCLE CONDITIONS
 Muscle
cramps- (charley horse)sudden
involuntary contraction of muscles due to
injury, deficiency in calcium or phosphate,
lack of blood flow, nerve tissue damage or
dehydration.
 Muscle twitches -often cause by a single
nerve, due to fatigue, lack of water, stress
and anxiety.
 ALS-Lou Gehrig’s disease - damages motor
neurons, leads to loss of motor movement.
 Muscular dystrophy -skeletal muscle
progressively weaken.