Muscular System
Functions of Muscles
1. Produce movement
2. Stabilize joints
3. Maintain posture
4. Generate heat
Anatomy of a Muscle
1. Epimysium2. Perimysium3. Fascicle4. Endomysium5. Tendon6. Aponeuroses-
Muscle Categories
• Prime Mover =
(agonist) - muscle that
produces a desired
movement
• Antagonist - muscle(s)
that oppose the action
of the prime mover
Muscle Categories (cont’d)
•
Synergists: muscles that contracts at the same time as a
prime mover and assists it in carrying out its action
Brachialis helps the Biceps brachii
during elbow flexion
• Fixators: muscles that stabilize a joint to allow other
movements to take place
Rhomboids stabilize the scapulae
during elbow flexion
Origin and Insertion
1. All muscles cross at least one joint
2. Typically, the bulk of the muscle lies proximal to the joint
crossed
3. All muscles have at least two attachments:
a. the origin
b. the insertion
4. Muscles can only pull; they never push
5. During a contraction, the muscle insertion moves toward
the origin
Anatomy of a Muscle fiber
Relaxed Muscle
Contracted Muscle
Sarcoplasmic Reticulum
Muscle Fiber Anatomy
Sarcoplasmic Reticulum (SR)- ER of muscle cell; surround
each myofibril like a crocheted sweater; regulates
intracellular Ca2+ when muscle is stimulated
T-tubules- invaginations of the cell membrane
(sarcolemma); conducts nerve impulses into cell
Terminal Cisternae (TC)- ends of SR, run perpendicular
to SR; occur in pairs, release Ca2+ ions
Triad- combo of SR and TC and T-tubules
Motor Unit
A motor neuron and all
the fibers that it
activates
“All or Nothing Principle”
• When stimulated by a nerve signal, each
muscle cell contracts to the fullest extent.
There is never a partial contraction. The
strength of the muscles contraction has to do
with how many muscle cells are activated
(stimulated), not by how strong the
contraction is.
Neuromuscular Junction
Role of
Calcium in
Muscle
Contractions
Actin
The Role of Calcium in a Muscle
Contraction
What causes Rigor Mortis?
Rigor mortis is a stiffening of the body’s muscles 2-6 hours after death
proceeding from head to foot.
The body is completely stiff in 12-18 hours and will remain that way for about
2 days.
Calcium is released into the cytosol from the deterioration of the
sarcoplasmic reticulum.
This causes myosin-actin cross bridging.
But, there is no ATP produced to release the myosin heads.
Myoglobin
• An iron and oxygen binding protein synthesized by
muscles. Increases the O2 available to muscle cells.
• It has a greater affinity to oxygen than hemoglobin.
• Gives muscle reddish/brown appearance
• Important to have besides hemoglobin (Hb) because
muscle contractions can compress blood vessels and
decrease blood flow.
3 Ways to Produce ATP for Muscle
Contractions
Creatine Phosphate
•Creatine phosphate is
synthesized by the liver
and the muscles
•Its phosphate group is
used to generate ATP
ADP + P  ATP
•Very short duration
•1CP= 1 ATP
Aerobic Respiration
(Glycolysis)
•Requires oxygen
•Produces most ATP
•Slowest forming
•Moderate activity
Glucose  36 ATP +
CO2 + O2
Anaerobic Respiration
•No oxygen is present
•Glucose produces 2 ATP
•End product is lactic acid
•Short term, high intensity
exercise
Types of Muscle Contractions
• Isometric- contraction, but no movement
• Isotonic- contraction that produces movement
a. concentric- muscle shortens
b. eccentric- muscle lengthens
Isotonic
Which is concentric and
which is eccentric?
Isometric
Postural muscles
contract isometrically all
day to keep you upright
The Walking Gait
When walking, certain leg muscles contract isometrically to
keep the leg stiff as it touches the ground
Hypertrophy vs. Atrophy
Hypertrophy- enlargement of a muscle
Atrophy- shrinking of a muscle