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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
Fill in the back side of your
“Conn. Tissue Wrap. of Sk.
Muscle” wkst!
Sensation relayed to the brain by association neuron/ interneuron
The Nerve Stimulus & Action Potential• 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
End of the motor neuron (axon terminal)
MUSCLE CELL/FIBER
Synapse = space between neuron & next cell
Use your 3 different colors to identify each
region of the Neuromuscular Junction!
• Synaptic cleft (synapse)• Gap between nerve & muscle
• Do not make contact• Filled with interstitial fluid
The Nerve Stimulus & Action Potential
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
Fill in your Skeletal Muscle
Activity diagram!
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+)
End of the
motor neuron
MUSCLE CELL/ FIBER
Transmission of Nerve Impulse to Muscle• Na+ rushes into cell, generating an Action Potential
(electrical signal)• Once started, muscle contraction cannot be stopped
Complete #6 on your Skeletal Muscle Activity wkst!
Scratch out “axon terminal” on #3.
Week #7 (11/30-12/4)Warm Up – Wed, 12/2-Reflex Arc
Have out:?
Agenda:1. Muscles Quiz #32. Notes: Muscle Contractions/Sliding
Filament Theory
Homework:
1. Anterior Muscles Quiz-Tues, 12/8
2. Sliding Filament Theory Assignment-due Wed, 12/2
GRADEBOOK CLOSES FRIDAY 12/11/2015!!
Anatomy Fun Fact:When doing resistance (weight) training, a repetition range between 10-15 repetitions will improve the endurance capacity of a muscle.
Muscles to Identify Quiz #3• Pick up 1 colored pencil
(ALL muscles will be color-code 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
Sensation relayed to the brain by association neuron/ interneuron
Step 1 Step 2
Step 3Step 4
Step 5
CHECK FOR UNDERSTANDING:Neuromuscular Junction Goings-ons…
(whole section)
Complete the TOP & identify the
following structures on your
Skeletal Muscle Activity wkst!
Microscopic Anatomy of Skeletal Muscle
• Diving in to the smallest doll!
A A
Microscopic Anatomy of Skeletal Muscle
• Sarcomere—contractile unit of a muscle fiber (cell)
• Organization of the sarcomere• Myofilaments
• Thick filaments = myosin filaments• Thin filaments = actin
filaments
Identify the following structures
on your Muscle Structure wkst!
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 entire length
of the thick filaments
Identify the following structures on your Muscle
Structure wkst!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 protein actin• Anchored to the Z disc
Identify the following structures on your Muscle
Structure wkst!A A
Microscopic Anatomy of Skeletal Muscle
SARCOMERE CONTRACTION DEMO!
The End
Skeletal Muscle OrganizationName the following structures & connective tissue wrappings of skeletal muscle.
B (wrapping)
D (wrapping)
A (structure)
C (structure)
E (wrapping)
F (structure)
G(structure)
Microscopic Anatomy of Skeletal Muscle
Follow along on the BACK of your Muscle Structure
wkst!
Sarcomere 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)
Myofilament Contraction animation
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
Myosin
Actin
Troponin complex
Tropomyosin
The Contraction Cycle
The Sliding Filament Theory
The Sliding Filament Theory
Troponin complex
The Sliding Filament Theory
REVIEW: The Contraction Cycle
Sliding Filament Theory article & Concept Map- As you read the article that tells you about the first experiments that led scientists closer to the present-day understanding of skeletal muscle, be looking for…
So how was it figured out how muscle
fibers contract?
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 at least 2 points
• Origin• Attachment to moveable bone
• Insertion• Attachment to 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)
“iso” – same“ton” – weight/resistance
Isometric Contractions• Isometric Contraction:
• Example: pushing against a wall• Tension (effort) never exceeds resistance
(weight)• Muscle does NOT change length
“iso” – same“metr” – distance
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 mortisWithin 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 & cross-bridges 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 events occurring at the neuromuscular junction
• 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