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Bell Ringer
1. What is the best way to build muscle
WITHOUT using perfomance enhancing
drugs?
2. Would you consider supplements such as
Creatine to be a performance enhancing drug?
Why or why not?
The Muscular System
A&P Fall 2016
I. Overview of Muscle Tissues
A. Muscle Types
1. Skeletal Muscle
a. Muscle fibers are packaged together to form whole
muscles
b. Muscles are striated (have stripes)
c. Controlled voluntarily
2. Smooth Muscle
a. Found in walls of hollow organs
i. Ex. Stomach, bladder, etc
b. Has no striations
c. Involuntary control
3. Cardiac Muscle
a. Found only in the heart
b. Has striations
c. Involuntary control
B. Skeletal Muscle Functions
1. Producing Movement
a. mobility of the body as a whole
2. Maintaining posture and body position
a. continual tiny adjustments to maintain
standing or sitting posture
3. Stabilizing Joints
a. muscle tendons reinforce joints where
bones don’t fit together well
i. Ex. Shoulder joint
4. Generating Heat
a. energy used for muscle activity creates
heat
5. Protection
a. covers internal organs
II. Microscopic Anatomy of Skeletal
Muscle
A. Myofibrils
1. Ribbon-like organelles
2. Made of chains of sacromeres
a. Myofilaments are substructures that
produce light and dark banding patterns
i. Thick filaments made of myosin
protein
ii. Thin filaments made of actin protein
3. Broken into many parts
a. Z disc
i. Where sacromeres join together
b. Light I band
i. Space where no myosin protein is
present
c. Dark A band
i. Space where myosin protein is
present
d. H zone
i. Space where mysoin IS present, but
Actin is absent
e. M line
i. Located within the H zone
ii. Protein rods that hold adjacent
myosin filaments together
B. Muscle Fibers (Cells)
1. Have many ocal nuclei
2. Contain special organelles
a. Myofibrils
i. Many in each cell
ii. Take up most of the space in the cytoplasm
b. Sarcoplasmic reticulum
i. Special ER that surrounds every myofibril
3. Plasma membrane is called the sarcolemma
a. Means “Muscle Husk”
4. Each cell enclosed in Endomysium
a. A delicate connective tissue sheath
C. Fascicle
1. Formed by many muscle fibers bundled together
2. Surrounded by the Perimysium
a. Another fibrous membrane
b. Coarser and stronger than the Endomysium
D. Muscle Organ
1. Formed by many Fascicles bundled together
2. Surrounded by the Epimysium
a. Toughest membrane of all
b. Also form tendons at the end of muscles
III. Skeletal Muscle Activity
A. Stimulation & Contraction of a Single Muscle
Cell
1. The Nerve Stimulus and the Action
Potential
a. Motor Unit
i. Made of one neuron and multiple
muscle cells
ii. The nerve fiber branches into
multiple axon terminals
b. Structure of Neuromuscular Junctions
i. Space between a neuron and muscle
cell
ii. Filled with vesicles that contain
acetylcholine (ACh)
iii. Acetylcholine is a neurotransmitter
c. Action of neuromuscular junctions
i. Action potential
reaches axon terminal
of a motor neuron
ii. Calcium (Ca2+)
channels open and
Ca2+ enters the axon
terminal
iii. Ca2+ entry causes
some synaptic vesicles
to release their
contents (ACh) by
exocytosis
vi. Enzyme
acetylcholinesterase
breaks down Ach in
the synaptic cleft,
ending the process
v. ACh binds and
channels open that
allow simultaneous
passage of Na+ into the
fiber and K+ out of the
fiber (More Na+ moves
in than K+ moves out).
The passage of these
ions leads to an action
potential
iv. ACh diffuses across
the synaptic cleft and
binds to receptors in
the sarcolemma
2. The Sliding Filament Theory
a. Action potential within the sarcolemma
causes calcium ions to be released into the
cytoplasm
i. Ca2+ comes from the sarcoplasmic
reticulum
b. Release of Ca2+ triggers the binding of
myosin to actin
c. Myosin heads “walk” along actin filaments,
causing actin proteins to slide closer together
i. Neither filaments actually shorten,
they just slide past one another
B. Contraction of Skeletal Muscle as a whole
1. Graded Responses
a. The “all-or-none” rule applies to fibers
i. means a fiber will always contract
to its fullest extent when stimulated
ii. Does NOT apply to the whole
muscle
b. Whole muscle can react with different
degrees of shortening in 2 ways
i. change the frequency of muscle
stimulation
ii. Change the number of fibers being
stimulated at one time
2. Muscle Response to rapid stimulation
a. Complete Tetanus
i. muscle contractions are completely
smooth and sustained
ii. No evidence of relaxation
3. Muscle Fatigue and Oxygen Deficit
a. Muscle fatigue occurs when muscles are
exercised strenuously
i. Muscles are still being stimulated
but are unable to contract
b. Oxygen deficit most likely cause
i. body is unable to take oxygen in
fast enough
ii. Muscles do not get the amount
needed to contract
iii. Lactic acid builds up as a result
4. Types of Muscle Contraction
a. Isotonic
i. the muscle shortens during contraction
ii. Ex. Bending your knee
b. Isometric
i. the muscle does NOT shorten
ii. Ex. Straining to lift a heavy object
5. Muscle Tone
a. Some muscle fibers are still contracting
at all times
i. allows muscle to remain firm and
healthy
ii. Exercise can increase muscle tone
b. Endurance exercises
i. results in stronger, more flexible
muscles that resist fatigue
ii. Ex. Jogging or biking
c. Resistance exercises
i. increases muscle strength and size
ii. Ex. Forcing a muscle to contract