1. THE MUSCULAR SYSTEM
CHAPTER 8

2. Objectives To explain the structure of muscle
To list various outcomes of muscular actions
Describe how connective tissue is part of a skeletal muscle
Name the major parts of a skeletal muscle fiber, and describe the function of each

3. Introduction Muscles are responsible for all types of body movement
Use chemical energy stored in nutrients to contract
muscle tone, propel body fluids and food, generate heartbeat, and distribute heat
Types:
Skeletal
Smooth
Cardiac

4. Skeletal Muscle Attaches to bones Tendon: muscle to bone
Ligament: bone to bone
Conscious control
Come in antagonistic pairs:
flexor (bends a joint) and extensor (straightens a joint)
Contract and shorten

5. Skeletal Muscle (cont.)
Composed of:
Skeletal muscle tissue
Nervous tissue
Blood
Connective tissue

6. Connective Tissue Coverings
Fascia: layers of fibrous connective tissue that separates an individual skeletal muscle from adjacent muscles
Epimysium: layer of connective tissue that closely surrounds a skeletal muscle
Perimysium: extend inward from epimysium, separates muscle tissue into small compartments
Fascicles: bundles of skeletal fibers
Endomysium: thin covering of each fiber within a fascicle

7. Skeletal Muscle Fibers
Single cell that contracts in response to stimulation, relaxes when stimulation ends.
myofibrils divided into sections called sarcomeres
Sarcomere
functional unit of muscle contraction
contain myofilaments (alternating bands of thin (actin) and thick (myosin) protein filaments)

8. Thin Filaments (Actin)
Complex of proteins
Helix of actin molecules and tropomyosin fibers
Tropomyosin fibers secured with troponin molecules which block the spot where the myosin fiber will attach (must be moved for muscle contraction)

9. Thick Filaments (Myosin)
Each thick filament consists of many myosin molecules
consist of head, neck and tail
head binds to actin molecules

10. *Organization of filaments produces striations*

11. Neuromuscular Junction
Motor Neuron stimulates muscle contraction
Neuromuscular junction: connection between motor neuron and muscle fiber
Nerve impulse reaches end of motor neuron axon, vesicles release neurotransmitter (acetylcholine)
Neurotransmitter received by receptors on muscle cell, contraction is then stimulated
Animation

12. Skeletal Muscle Contraction
Sliding Filament Theory
Sarcomeres shorten because cross-bridges pull on thin filaments
Thin filaments slide toward M line
Width of the A band remains the same
Z lines move closer together

13. Steps of Contraction Step 1: Action Potential
Nerve action potential releases acetylcholine into synaptic cleft, opening Na+ channels
Action potential spreads across sarcolemma, releases Ca2+ into sarcoplasm

14. Steps of Contraction (cont)
Step 2: Myosin-actin binding
a. Upon stimulation, Ca2+ binds to receptor on troponin molecule
b. Troponin-tropomyosin complex changes, exposing active site of actin
2. Myosin head attaches to actin using energy from ATP, forming a cross-bridge

15. Steps of Contraction (cont.)
Step 3: Power Stroke
Side arm pivots towards M line so actin and myosin slide by each other, shortening the sarcomere
ADP and P are released

16. Steps of Contraction (cont.)
Step 4: ATP Binding, Actin-myosin release
Myosin head binds another ATP molecule
Cross-bridges detach, releasing actin

17. Steps of Contraction (cont.)
Step 5: ATP Cleavage
ATPase splits ATP and captures released energy, detached myosin head is reactivated
Cycle will repeat if Ca2+ is still available

18. Hmmmmm…..
If a muscle is contracted, what happens if a new molecule of ATP is not available?
Why does rigor mortis occur?
Place your fingers along the angle of your jaw just in front of your ear. Grit your teeth and feel what happens. What muscle is contracting?

19. Do Now:
Complete #’s 1-6 on the upper leg. Fill out the diagram and the function.

20. Steps of Contraction (all together now!)

21. Rigor Mortis Occurs 2-4 hours after death due to lack of ATP
Muscles remain contracted until the muscle tissue itself starts to deteriorate.

22. TENSION PRODUCTION The all-or-none principle
As a whole, a muscle fiber either contracts completely or does not contract at all

23. NUMBER OF MUSCLE FIBERS ACTIVATED
Recruitment (multiple motor unit summation)
In a whole muscle or group of muscles, increasing tension is produced by slowly increasing the size or number of motor units stimulated

24. MOTOR UNITS
Figure 7-8

25. NUMBER OF MUSCLE FIBERS ACTIVATED
Muscle tone
The normal tension and firmness of a muscle at rest
Muscle units actively maintain body position, without motion
Increasing muscle tone increases metabolic energy used, even at rest

26. MUSCLE CONTRACTION
A muscle fiber will contract after threshold stimulus has been reached.
Once stimulated, the entire fiber completely contracts which is called the all-or-none response.
*the extent of shortening depends on resistance.

27. MYOGRAM Twitch: single muscle contraction
Latent period: time between stimulation and response
Period of contraction: muscle is contracted
Relaxation: fiber returns to former length

29. TYPES OF GRAPHS Twitch- full contraction
Twitch summation (treppe)- stimulating the muscle before it completely relaxes
Incomplete tetanus- minimal amt. of relaxation after each stimulus
Complete tetanus- no relaxation, continuous calcium ion deposit

30. Objectives (P. 3 2/17)
To identify the stages of contraction on a myogram
To discuss the role of ATP and cellular respiration in muscle fatigue
To compare and contrast hypertrophy and atrophy
To create dance/workout routines using anatomical terms of movement

31. ATP AND MUSCLE CONTRACTION
Sustained muscle contraction uses a lot of ATP energy
Muscles store enough energy to start contraction
Muscle fibers must manufacture more ATP as needed

32. Finish the muscles of the leg (functions and diagram)
Do Now
Finish the muscles of the leg (functions and diagram)

33. MUSCLE FATIGUE
Cells undergo both aerobic and anaerobic respiration to supply ample atp (lactic acid fermentation)
Lactic acid creates an oxygen debt because the liver cells must now use oxygen to break down the lactic acid (can take several hours)
Lactic acid lowers the ph, which diminishes the muscle fibers response to stimulation
More exercise = more glycolytic enzymes = increased capacity for glycolysis= increased capacity for aerobic respiration!! … start working out ☺

34. HYPERTROPHY VS. ATROPHY
Hypertrophy- muscles respond to exercise and enlarge
Slow twitch fibers activated by low intensity exercise such as swimming or running, develop more mitochondria and capillaries, prolonging fatigue
Fast twitch fibers activated by weight lifting can produce new myofilaments & enlarge the muscle (they are still fatigable)
Atrophy- when regular exercise stops, capillary networks shrink, mitochondria decrease, actin & myosin decrease, and muscle shrinks.

35. TETANUS Caused by Clostridium tetani bacteria present in soil
Bacteria produces a neurotoxin which blocks the release of inhibitory neurotransmitters.

36. Muscle Workout/Dance Activity
Your group must come up with instructions for a workout/dance routine that can be done in the classroom. You must include at least 3 muscles from each section that we covered. Write out the instructions for the next group. They will have to do your “dance” and try to guess which muscles you focused on!

37. Happy Heart Day!!!