The Central Nervous System (brain) tells them how &
when to contract!
What Happens at the Neuromuscular Junction
How Skeletal Muscles are
Told to Contract: A Reflex
Arc
Sensation relayed
to the brain by
association
neuron/
interneuron
The Nerve Stimulus &
Potential
Action
• Skeletal muscles must be
stimulated by a motor
neuron (nerve cell) to
contract
• Motor unit—
one motor neuron
& all skeletal
muscle cells
stimulated by
that neuron
• Action Potential –
electrical signal sent
along neuron to
stimulate an effect
Figure 6.4a
The Nerve Stimulus & Action
Potential
• Neuromuscular junction
• Association site of axon terminal (end) of motor neuron &
muscle
Myofibrils
Neuromuscular Junction
The Nerve Stimulus &
Action Potential
• Synaptic cleft (synapse)
• Gap between nerve & muscle
• Do not make contact
• Filled with interstitial fluid
As you watch this
animation, be
listening for what
chemicals are
IMPORTANT for
the “message” of
contraction to be
passed to a
skeletal muscle
Neuromuscular Junction
Animation
Transmission of Nerve Impulse to
Muscle
• Neurotransmitter—
chemical released by
nerve upon arrival of
nerve impulse
• Skeletal muscle –
acetylcholine (ACh)
• ACh attaches
to receptors on
sarcolemma
• Sarcolemma
becomes
permeable to
sodium (Na+)
Transmission of Nerve Impulse to
Muscle
• Na+ rushes into cell, generating an Action Potential
(electrical signal)
• Once started, muscle contraction cannot be stopped
Week #7 (11/30-12/4)
Warm Up – Wed, 12/2
Have out:
Anatomy Fun Fact:
Homework:
?
-Reflex Arc
When doing resistance (weight)
training, a repetition range
between 10-15 repetitions will
improve the endurance capacity
of a muscle.
Agenda:
1.
2.
Muscles Quiz #3
Notes: Muscle Contractions/Sliding
Filament Theory
1.
Anterior Muscles
Quiz-Tues, 12/8
2.
Sliding Filament
Theory
Assignment-due
Wed, 12/2
GRADEBOOK CLOSES
FRIDAY
12/11/2015!!
Muscles to Identify Quiz #3
• Pick up 1 colored pencil
(ALL muscles will be colorcode with 1 color).
• QUIETLY take the quiz &
turn it in to the Hmwk Bin
when finished.
How Skeletal Muscles are Told to
Contract: A Reflex Arc
Step 1
Sensation relayed
to the brain by
association
neuron/
interneuron
Step 2
Step 5
Step 3
Step 4
CHECK FOR
UNDERSTANDING:
Neuromuscular Junction Goings-ons…
(whole section)
Microscopic Anatomy of Skeletal
Muscle
• Diving in to
the
smallest
doll!
A
A
Microscopic Anatomy of
Skeletal Muscle
• Sarcomere—contractile unit
fiber (cell)
• Organization of the
of a muscle
sarcomere
• Myofilaments
• Thick filaments =
• Thin filaments =
filaments
myosin filaments
actin
A
A
Microscopic Anatomy of Skeletal
Muscle
• Myofibrils are aligned to give distinct bands
• I band = light band
• Contains only thin filaments
• A band = dark band
• Contains the
length of
filaments
entire
the thick
A
A
Microscopic Anatomy of Skeletal
Muscle
• Thick filaments = myosin filaments
• Composed of the protein myosin
• Myosin filaments have heads (extensions) = 2-headed golf club
• Myosin & actin overlap somewhat (A-band)
• Thin filaments =
actin filaments
• Composed of the
• Anchored to the Z
protein actin
disc
A
A
The End
Microscopic Anatomy of Skeletal
Muscle
Skeletal Muscle Organization
B
(wrapping)
D
(wrapping)
A
(structure)
C
(structure)
E
(wrapping)
F
(structure)
G
(structure)
Name the
following
structures &
connective tissue
wrappings of
skeletal muscle.
Sarcomere Contraction animation
Microscopic Anatomy of
Skeletal Muscle
Myofilament Contraction animation
The Sliding Filament Theory of
Muscle Contraction
• BIG PICTURE:
• Activation by nerve causes
myosin heads to attach to binding
sites on thin filament (actin) =
”cross-bridge”
• Myosin heads then pull the actin
thin filament toward center of
sarcomere
• Continued action causes a
sliding of the myosin along
actin
• Result – muscle is shortened
(contracted)
Muscle Contraction at Its Finest!
• Myosin (filament & head)
• Actin (protein chain)
• Troponin complex: Ca2+
ions bind here to move
tropomyosin off of binding
site
• Tropomyosin: actin protein
blocking myosin-binding
sites
Troponin complex
Actin
Tropomyosin
Myosin
The Contraction Cycle
The Sliding Filament Theory
The Sliding Filament Theory
Troponin
complex
The Sliding Filament Theory
REVIEW:
Cycle
The Contraction
Sliding Filament Theory article & Concept Map
- As you read the
article that
tells you
experiments that led
closer to
day
skeletal muscle, be
about the first
scientists
the presentunderstanding of
looking for…
5 Golden Rules of Skeletal Muscle
Activity
Muscles & Body Movements
• Movement is attained due to a muscle moving an attached bone
• Muscles are attached to
points
• Origin
• Attachment to
• Insertion
• Attachment to
at least 2
moveable bone
immovable bone
Isotonic Contractions
• Isotonic Contraction:
• Example: lifting dumbbells
with arm
• Tension (effort) increases &
muscle fibers shorten &
lengthen
• Concentric contraction:
• Tension (effort) exceeds
resistance (weight) & muscle
shortens
• Eccentric contraction:
• Resistance exceeds tension
(effort) & muscle lengthens
(due to gravity)
Isometric Contractions
• Isometric Contraction:
• Example: pushing against a wall
• Tension (effort) never exceeds resistance
(weight)
• Muscle does NOT change length
Muscle Relaxation
• Relaxation of muscle
fibers
• Passive process
• Combo of elastic forces, opposing muscle contractions &
gravity to elongate a contracted muscle
• Elastic force: some energy used to stretch tendons in
contraction phase forces a recoil
• Opposing muscle contractions: muscles move in antagonistic
pairs
• Gravity: pulls down muscle to extended position
Rigor mortis
Within 3-4 hours after death
• Dying muscle cell membranes become more permeable
to Ca+ ions
• Promotes myosin cross-bridge binding
• After death, circulation of nutrients ends
• Without ATP, Ca+ ions are not removed & crossbridges cannot detach from
actin sites so muscles become
locked in place – “stiff”
• Rigor mortis disappears as
muscle proteins break down
several hours after death
(48-60 hours)
Effect of Exercise on Muscles
• Exercise increases muscle size, strength
& endurance
• Aerobic (endurance/
cardiovascular) exercise (biking,
jogging) results in stronger, more
flexible muscles with greater
resistance to fatigue
• Makes body metabolism more
efficient
• Improves digestion &
coordination
• Resistance (isotonic & isometric)
exercise (weight-lifting) increases
muscle size & strength
Fast vs. Slow-Twitch Muscles
• Fast Twitch Fibers
• Most skeletal muscle fibers
• Contract in 0.01 sec or less after
stimulation
• Large in diameter
• Contain densely-packed myofibrils
• Have large glycogen reserves & few
mitochondria
• Produce powerful contractions
• Fatigue rapidly
• “white muscle fibers”
Fast vs. Slow-Twitch Muscles
• Slow Twitch Fibers
• ~Half the diameter of fast fibers
• Take 3x as long to contract after stimulation
• Specialized to continue contracting for
extended periods
• Contain extensive network of capillaries &
has higher oxygen supply
• Contain red pigment myoglobin
• Contain more mitochondria than fast
fibers
• “red muscle fibers”
• Intermediate Fibers
• Contain properties of fast fibers & slow
fibers
Tetanus
• Many toxins, drugs & diseases may interfere with
occurring at the neuromuscular junction
events
• Tetanus: infection of Nervous System from potentially deadly
bacteria Clostridium tetani
– Bacteria spreads & makes poison called tetanospasmin
– Poison blocks nerve signals from spinal cord to skeletal
muscles, causing severe
muscle spasms
– Prolonged muscle
contractions,
spasms &
stiffness
– Spasms can be so
powerful that they tear
the muscles or cause
fractures of the spine
Muscular System~
Putting it ALL Together