1. So How Do Skeletal Muscles KNOW how to or when to contract?
The Central Nervous System (brain) tells them how & when to contract!
What Happens at the Neuromuscular Junction

2. 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

3. 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

4. The Nerve Stimulus & Action Potential
Neuromuscular junction
Association site of axon terminal (end) of motor neuron & muscle
Myofibrils

5. Neuromuscular Junction
Use your 3 different colors to identify each region of the Neuromuscular Junction!
End of the motor neuron (axon terminal)
Synapse = space between neuron & next cell
Muscle cell/fiber

6. Fill in your Skeletal Muscle Activity diagram!
The Nerve Stimulus & Action Potential
Fill in your Skeletal Muscle Activity diagram!
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

7. 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

8. 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.

9. Today in Human Anatomy... Anatomy Fun Fact: Week #7 (11/30-12/4)
Warm Up – Wed, 12/2
-Reflex Arc
Have out: ?
Anatomy Fun Fact:
When doing resistance (weight) training, a repetition range between repetitions will improve the endurance capacity of a muscle.
Homework:
Anterior Muscles Quiz-Tues, 12/8
Sliding Filament Theory Assignment-due Wed, 12/2
GRADEBOOK CLOSES FRIDAY 12/11/2015!!
Agenda:
Muscles Quiz #3
Notes: Muscle Contractions/Sliding Filament Theory 9

10. 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.

11. How Skeletal Muscles are Told to Contract: A Reflex Arc
Step 2
Step 1
Sensation relayed to the brain by association neuron/ interneuron
Step 5
Step 3
Step 4

12. CHECK FOR UNDERSTANDING: Neuromuscular Junction Goings-ons…
Complete the TOP & identify the following structures on your Skeletal Muscle Activity wkst! H A B G F D C E
(whole section)

13. Microscopic Anatomy of Skeletal Muscle
Diving in to the smallest doll! A A

14. 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

15. 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

16. 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

17. Microscopic Anatomy of Skeletal Muscle
The End
Microscopic Anatomy of Skeletal Muscle
Sarcomere contraction demo!

18. Skeletal Muscle Organization
B (wrapping)
Name the following structures & connective tissue wrappings of skeletal muscle.
D (wrapping)
A (structure)
C (structure)
E (wrapping)
F (structure) G
(structure)

19. Microscopic Anatomy of Skeletal Muscle
Sarcomere Contraction animation
Follow along on the BACK of your Muscle Structure wkst!
Microscopic Anatomy of Skeletal Muscle

20. The Sliding Filament Theory of Muscle Contraction
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)

21. Muscle Contraction at Its Finest!
Then pick up 4 different colored pencils!
Use your different colors to identify the following:
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

22. Fill in the Muscle Contraction diagram!
The Contraction Cycle
REORIENT/
COCK
BIND/
ATTACH
FLEX /
Power Stroke
RELEASE

23. The Sliding Filament Theory

24. The Sliding Filament Theory
Troponin complex

25. The Sliding Filament Theory

26. REVIEW: The Contraction Cycle
REORIENT/
COCK
BIND/
ATTACH
FLEX /
Power Stroke
RELEASE

27. So how was it figured out how muscle fibers contract?
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…

28. 5 Golden Rules of Skeletal Muscle Activity

29. 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

30. Isotonic Contractions
Is flexion a concentric or eccentric contraction?
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

31. Isometric Contractions
Example: pushing against a wall
Tension (effort) never exceeds resistance (weight)
Muscle does NOT change length
“iso” – same
“metr” – distance

32. 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

33. 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 & 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)

34. 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

35. Fast vs. Slow-Twitch Muscles
FYI
Fast vs. Slow-Twitch Muscles
Contain densely-packed myofibrils
Have large glycogen reserves & few mitochondria
Produce powerful contractions
Fatigue rapidly
“white muscle fibers”
Fast Twitch Fibers
Most skeletal muscle fibers
Contract in 0.01 sec or less after stimulation
Large in diameter

36. Fast vs. Slow-Twitch Muscles
FYI
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

37. 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

38. Muscular System~ Putting it ALL Together
Complete #10 on your
Muscle Movements, Types & Names wkst!