1. Chapter 9-Muscular System

2. The Muscular System Moves Body Parts and Maintains Posture
The muscular system produces movement and maintains posture
There are three types of muscles: skeletal, cardiac, and smooth
All muscles are excitable, contractile, extensible, and elastic
Excitable: respond to stimuli
Contractile: shorten
Extensible: stretch
Elastic: return to their original length after being shortened or stretched

3. FIGURE 6.2
Some major muscles of the body

4. Skeletal Muscles Work in Pairs
Skeletal muscles are voluntary muscles responsible for moving our body
Each muscle is attached to a bone by a tendon
The origin of the muscle remains stationary during movement while the insertion is attached to the bone that moves
Most muscles are arranged in pairs, called antagonistic pairs, that work in opposition to one another

5. FIGURE 6.1a
The antagonistic action of the triceps and biceps muscles during flexion and extension. The origins and insertions of the muscles are shown.

6. FIGURE 6.1b
The antagonistic action of the triceps and biceps muscles during flexion and extension. The origins and insertions of the muscles are shown.

7. Sacromeres Are the Contractile Units of Muscle
When skeletal muscles are viewed under a microscope, they have distinct bands called striations
They are formed by the arrangement of myofibrils within the muscle cell
Each myofibril contains groups of long myofilaments
Each myofilament is composed of myosin and actin filaments

8. FIGURE 6.3
The structure of a skeletal muscle

9. FIGURE 6.3a,b
The structure of a skeletal muscle

10. FIGURE 6.3b,c
The structure of a skeletal muscle

11. FIGURE 6.3c,d
The structure of a skeletal muscle

12. Sarcomeres Sarcomeres are the contractile units of muscle
They shorten as the actin filaments slide along the myosin filaments
Muscle contraction occurs at the molecular level
According to the sliding filament model, muscle contracts when actin filaments slide past myosin filaments

13. FIGURE 6.4
Each myofibril is packed with actin filaments and myosin filaments. When a muscle contracts, actin filaments slide past myosin filaments. Movements of the heads of myosin filaments pull actin filaments toward the center of a sarcomere.

14. FIGURE 6.5 part 1
The sliding filament model of muscle contraction. (The regulatory proteins on the actin are described in the following subsection.)

15. FIGURE 6.5 part 2
The sliding filament model of muscle contraction. (The regulatory proteins on the actin are described in the following subsection.)

16. FIGURE 6.5 part 3
The sliding filament model of muscle contraction. (The regulatory proteins on the actin are described in the following subsection.)

17. FIGURE 6.5 part 4
The sliding filament model of muscle contraction. (The regulatory proteins on the actin are described in the following subsection.)

18. FIGURE 6.5 part 5
The sliding filament model of muscle contraction. (The regulatory proteins on the actin are described in the following subsection.)

19. Sarcomeres
The myosin head attaches to the actin filament forming a cross bridge
Then it bends and swivels, pulling the actin filament toward the midline of the cell
The tropomyosin-troponin complex and calcium ions regulate muscle contraction at the actin-myosin binding sites
Contraction is triggered when a nerve impulse travels down a motor neuron until it reaches the neuromuscular junction

20. FIGURE 6.6
The availability of calcium ions controls muscle contraction.

21. FIGURE 6.6
The availability of calcium ions controls muscle contraction.

22. FIGURE 6.7
The connection between a motor neuron and a muscle cell is called a neuromuscular junction.

23. Sacromeres
At the neuromuscular junction it causes the release of acetylcholine from vesicles in the motor neuron
The acetylcholine causes changes in the permeability of the muscle cell, resulting in an electrochemical message similar to a nerve impulse

24. Muscle Contraction Depends on the Stimulation of Motor Units
A motor neuron and all the muscle cells it stimulates are called a motor unit
The strength of muscle contraction depends on the number of motor units that are stimulated
The muscle cells of a motor unit are spread throughout the muscle resulting in even, whole muscle contraction

25. FIGURE 6.8
A motor unit includes a motor neuron and the muscle cells it stimulates.

26. Myofibril Contains protein filaments – ACTIN (thin) and MYOSIN (thick)
These filaments overlap to form dark and light bands on the muscle fiber
A band = dArk • thick (myosin)
I band = lIght • thIn (actin)
In the middle of each I band are Z lines. A sarcomere is on Z line to the other

30. It is important to remember the heirarchy
myosin
myofibrils
fasicles
myofilaments
actin

31. It is important to remember the heirarchy
fasicles
myofibrils
myofilaments
actin
myosin

32. muscle fiber
myofilament
myofibrils
epimysium
muscle
sarcomere

33. myofilament
muscle
sarcomere
epimysium
myofibrils
muscle fiber

36. Muscles & Nervous System

37. Motor Unit or Neuromuscular Junction
1.  Neuron         2.  Sarcolemma   (or motor end plate)       
3.  Vesicle      4.  Synapse        5.  Mitochondria

38. The neurotransmitter that crosses the gap is ACETYLCHOLINE.
This is what activates the muscle.
Acetylcholine is stored in vesicles

39. Motor Unit
The muscle fiber  and  the motor neuron 

41. SLIDING FILAMENT THEORY (MODEL)
The theory of how muscle contracts is the sliding filament theory. The contraction of a muscle occurs as the thin filament slide past the thick filaments. The sliding filament theory involves five different molecules plus calcium ions.
The five molecules are:
myosin
actin
tropomyosin
troponin
ATP

42. Sliding Filament Handout

43. Sliding Filament Handout

44. ANIMATION OF SLIDING FILAMENT

45. Muscle Stimulation Increases the Strength of Contraction
All of the muscle cells innervated by a single neuron contract at once causing a muscle twitch
If a second stimulus is received before the muscle is fully relaxed, the second twitch will be stronger than the first due to wave summation
Taken to the extreme, a sustained powerful contraction is called tetanus
Fatigue sets in when a muscle is unable to contract even when stimulated

46. FIGURE 6.9
Muscle contraction shown graphically: (a) muscle twitch, (b) summation, (c) tetanus.

47. FIGURE 6.9
Muscle contraction shown graphically: (a) muscle twitch, (b) summation, (c) tetanus.

48. ATP for Muscle Contraction Comes from Many Sources
The ATP for muscle contraction comes from many sources
The initial source is the ATP stored in the muscle cells and then the ATP formed from the creatine phosphate reserves
When those sources are depleted, the muscles depend upon stored glycogen, which is converted to glucose and then to ATP through aerobic respiration or lactic acid fermentation

49. FIGURE 6.10
Energy sources for muscle contraction

50. Slow-Twitch and Fast-Twitch Muscle Cells Differ
Slow-twitch cells are loaded with mitochondria and therefore deliver prolonged, strong contractions
Fast-twitch cells contract rapidly and powerfully but with much less endurance. They rely on lactic acid fermentation as their source of energy and therefore tire quickly

51. FIGURE 6.11
Slow- and fast-twitch muscle cells

52. Aerobic Exercise; Resistance Exercise
Aerobic exercise increases endurance and coordination
Resistance exercise builds strength