What are functions of the
1. Gross body movement
2. Stabilizing body positions – “Tone”
3. Generate heartbeat
4. Movement substances within the
5. Regulating organ volumes
6. Producing body heat
Properties of Muscle Tissue
1. Electrical Excitability – able
to respond to stimuli and send
2. Contractility – ability to
contract forcefully, muscle
3. Extensibility – ability to
4. Elasticity – ability to return
to original length or shape
What are the 3 types of
* Voluntary control
•Location: Internal organs, blood vessels
•“Peristalsis” movement of digestive tract
cells •Usually organized into two sheet-like layers:
longitudinal and circular
Involuntary •Two types: Visceral and Multiunit
• Striated and uni-
• Branching cells
• Intercalated discs
• Only found in wall
• Large transverse
Aponeurosis, Fascia and
• Fascia – “gift
muscle body or
skin (spider webs)
• Tendons -
muscle to bone
• Aponeurosis –
flat and sheet-
muscle to CT
Skeletal Muscle Anatomy
The Muscle Fiber Structure
1. Actin (thin)
2. Myosin (thick)
Skeletal Muscle Fiber Structure
Anatomy of a Myofibril
Sarcomere: Single contracting unit within a myofibril.
Striation pattern is caused by the organization of the
• Length = Z line to Z line
• I band = only actin region Contraction: Z-line
• A band = myosin and actin region moves towards M
• H zone = only myosin region
• M line = center of H zone
Muscle Fibers Smallest
Now that you are familiar
with muscle anatomy, what
is the physiology of
How does muscle
One neuron and all
the muscle fibers it
have more motor
The Neuromuscular Junction: where the
neuron meets with the muscle fiber.
Sarcomere – smallest contracting
The Sliding Filament Theory
Now, look at how this process really works…
1. Impulse reaches synaptic
2. Calcium channels open and
3. Ca causes vesicles to
migrate to cell membrane to
(Acetylcholine = Ach).
4. Vesicles fuse with
membrane and release Ach Video
into synaptic cleft (gap).
5. Ach diffuses across the
6. Ach binds with receptor
proteins on motor end plate.
7. Motor end plate depolarizes.
8. Action potential is generated
in muscle cell.
9. Action Potential moves:
• along the sarcolemma
•down the transverse tubules
Animation •into the sarcoplasmic reticulum
10. Calcium is released from the sarcoplasmic
Binding site before and after
calcium reaches myofilaments.
Troponin/tropomyosin complex pulled away by
calcium so myosin can bind!
1. Acetylcholine esterase decomposes Ach
and removes it from synaptic gap.
2. ATP binds to myosin causing linkage to
release from actin.
3. Actin and myosin filaments slide apart.
4. Calcium ions are actively transported
back into the sarcoplasmic reticulum.
5. Muscle fiber relaxes.
How does the muscle fiber
get ATP for the
• Cell Storage
• Creatine phosphate
• Cellular respiration or
• Used when current cell
supply of ATP runs out.
(within 6 sec.)
• Cannot be used
directly as an energy
• Purpose: to transfer
stored energy to ADP
to make ATP.
• Creatine supply is
exhausted in 30 sec.
• Activities that benefit:
100 meter dash and
• With oxygen
the max amount
only in muscle
What if you run out of
Anaerobic respiration occurs by fermentation.
Fermentation produces Lactic Acid.
Lactic acid is carried to liver to be converted
back to glucose.
Low intensity or moderate exercise can recycle
the lactic acid immediately. (not a lot is
Good energy source for “stop and go” sports.
(soccer, tennis, short-term swimming)
• The amount of O2 liver cells require to
convert the lactic acid into glucose +
the O2 muscle cells require to restore
stored ATP and creatine phosphate.
• Training can speed up the process.
O2 Muscle need + O2 Liver need = Oxygen Debt
For most activities, all systems are used. It’s just
the percentages differ based on the intensity of
% Creatine % Lactic % Aerobic
Phosphate Acid Respiration
Sprint 95 3 2
Mile 15 55 30
Marathon 5 5 90
Muscle Fiber Types
Slow Twitch Fast Twitch
• Not easily fatigued • Easily fatigued
• Myoglobin – “red” • Little myoglobin – “white”
• Use in low intensity • Used in high intensity
activities – Anaerobic
activities – Endurance! Power!
• Not a lot of growth – Lean • Increase filaments with
• Lots of mitochondria use – Hypertrophy!
• Can be irreversibly
changed into slow twitch!
Genetically, most people are
50% slow, 50% fast twitch
What if the muscle
• Loss of the ability to contract
1. Lactic acid buildup, pH drops
2. Blood supply interruption
3. Lack of acetylcholine
4. Lack of ATP
• Cramps: sudden, involuntary contractions or
spasms in one or more of your muscles.
Possible causes: lack of ATP, dehydration or electrolyte imbalance
• Threshold stimulus – minimum
amount of stimulus (Ach) needed to
cause a contraction.
• All-or-None Response – a muscle
fiber will always fully contract no
matter the strength of the stimulus.
If the minimum amount of stimulus
is not met, no contraction will occur.
Muscle contractions can be
measured and recorded by:
Twitch: A single contraction of a
a) Shows a series of
the next stimulus.
Stimulus is held
there is no
• Stimulating more motor units in a muscle body to
• A greater force applied to the muscle or increase
the frequency of stimuli will cause this.
• Skeletal muscle fibers constantly being
stimulated by brain. (involuntary)
• Stretch receptors in muscles monitor muscle
• Loss of posture tone = collapse
How Do I
Do high intensity activities.
2. Use the fast-twitch muscles.
3. Eat protein for building material.
4. Maintain activity or else: atrophy
By age 80, there is a 50% decrease in muscle