1. Chapter 9
The Muscular System

2. Functions
Movement
Maintain posture
Respiration
Production of body heat
Communication
Heart Beat

3. Properties of Muscle Muscle fibers shorten with a force
Contractility
Muscle fibers shorten with a force
Excitability
Ability of muscle to respond to stimuli
Extensibility
Muscle can be stretched to its normal resting length and beyond to a limited degree
Elasticity
Ability of a muscle to retain its shape after stretching

4. Long cylindrical shape Attached to bones Multiple peripheral nuclei
Types of Muscle
Skeletal
Long cylindrical shape
Attached to bones
Multiple peripheral nuclei
Striated/ voluntary
40% of the body’s weight
Controlled by the nervous system

6. Types of Muscle
Smooth
Spindle shaped
Hollow organs and tubes, iris of the eye, walls of blood vessels
Single central nucleus
No Striations
Involuntary

8. Types of Muscle Cardiac Cylindrical and branched
Located ONLY in the heart
Single central nucleus
Striations
Intercalated disks
Involuntary

10. Skeletal Muscle Structure
Another name for skeletal muscle is muscle fiber (because they are elongated)
Muscle fibers develop from less mature, multinucleated cells called myoblasts (Great extra credit question!!)

11. Skeletal Muscle Cont.
Number of fibers remain constant after birth (You are born with as many as you will have for your lifetime)
Hypertrophy (enlargement) of muscle fibers result in an increase in their size (exercise!!)
A single muscle fiber can extend from one end of a muscle to another
Large muscle contain large diameter fibers and small muscle contain delicate fibers

13. Connective Tissue of the Muscle Fiber
The outermost “wrapping” of a muscle is called the epimysium.
The name means “Outside the muscle”
This covers the entire muscle

14. Connective Tissue
Within each muscle, cells are grouped into bundle called a fascicle.
Each fascicle is surrounded by a fibrous tissue called the perimysium .
Perimysium means “around the muscle”

15. Connective Tissue
Within in each fascicle, each muscle fiber (cell) is surrounded by a fine CT layer called the endomysium.
The name means “within the muscle.”

17. Epimysium (Fascicle) Perimysium Endomysium To Summarize:
The layers of CT superficial to deep.
Epimysium
(Fascicle)
Perimysium
Endomysium

18. Nerves Specialized nerve cells
Motor Neurons
Specialized nerve cells
Their cell bodies are located in the brainstem or nerve cord and their axons extend into the muscle fibers
They stimulate contraction
At the perimysium, the axons branch, each toward the center of one muscle fiber

20. Myofibril
Myofibril
Threadlike structure that extends from one end of the muscle fiber to the other
Composed of 2 proteins filaments called Myofilaments
Actin are thin (8 nanometers in diameter)
Myosin are thick (12 nanometers in diameter)
Sarcomeres are highly ordered units in which actin and myosin are organized
and hill.com/sites/ /student_view0/chapter10/anima tion__myofilament_contraction.html

22. Actin Myofilaments Actin
Each actin myofilament is composed of 2 strands of fibrous actin (F actin)
The two strands of F actin are coiled to form a double helix
Each F actin is a polymer of 200 small globular units, or monomers

24. Globular actin Globular Actin
Each has an active site that myosin attaches to during contraction
Tropomyosin is an elongated protein that winds along the groove of the F actin double helix

25. Myosin Filaments Long and shaped like golf clubs
Composed of myosin molecules
Long and shaped like golf clubs
Each myosin molecules consists of heavy myosin molecules wound together to form a rod portion and 2 heads that extend laterally.
Each myosin myofilament consists of 300 myosin molecules

27. Myosin Heads Three important properties
The heads can bind to active sites on actin molecules to form cross-bridges
The heads are attached to the rod portion by a hinge region
The heads have ATPase activity, the enzyme that breaks down ATP for energy

29. Physiology of Skeletal Muscle Fibers
Action Potentials are . . .
Electrical signals of the nervous system
Transmitted along axons to muscle fibers
Stimulates production of action potentials in muscle fibers, causing contraction

30. Types of Contraction
Isometric Contraction
Length of muscle is constant
Tension increases
Example are the muscle of posture in the spine

31. Length of muscle changes Tension is constant
Types of Contraction
Isotonic Contraction
Length of muscle changes
Tension is constant
2 types (Concentric and Eccentric)

32. Types of Isotonic Contraction
Concentric Contraction
Muscle length shortens
Tension increases
The most common contraction; lifting, walking, running, etc.

33. Types of Isotonic Contraction
Eccentric Contraction
Muscle length increases
Tension remains constant
Example is lowering a heavy object

34. Length vs. Tension
The length of muscle before stimulation influences the force of a contraction or the amount of work a muscle can do
This explains why weight lifters have a particular stance before they lift weights

35. Question?? What happens when a muscle is not stretched?
Decrease in tension because actin and myosin are already overlapping

36. Question?? What happens when a muscle is severely stretched?
Decrease in tension because actin and myosin are only overlapping in a small area and fewer connections can be made

37. Question?? When is a muscle able to perform at its peak?
When the muscle is relaxed and actin and myosin are overlapping in every possible place

38. Fatigue We have all experienced fatigue after a long work-out session
It can be due to 3 factors:
The nervous system
The muscle fibers
Neuromuscular junctions

39. Nervous System Fatigue
The most common
Called psychological fatigue
It happens when your mind “perceives” additional work as being impossible and action potentials are never sent
It can be helped with encouragement

40. Happens when ATPase is depleted
Muscle Fiber Fatigue
The second most common
Happens when ATPase is depleted

41. Neuromuscular Junction Fatigue
It is fairly rare
Happens when the release of acetylcholine is greater than acetylcholine synthesis

42. Inflammation in muscle fibers and connective tissue
Muscle soreness
Inflammation in muscle fibers and connective tissue
Built-up of lactic acid

43. There are two types of muscle fibers: slow and fast twitch
Types of Fibers
There are two types of muscle fibers: slow and fast twitch
The amount of each in humans is primarily determined by your genes

44. Slow Twitch Also called high-oxidative or Type 1 Contraction slower
Smaller in diameter
Better blood supply
Large amounts of myoglobin acts as a reservoir for oxygen
Fatigue resistant
Dark meat in chicken due to increased blood supply

45. Fast Twitch Less myoglobin Also called low-oxidative or Type 2
Contract fast
Larger diameter
Less blood supply
Less myoglobin
Fatigue happens faster
Light meat of chicken due to low blood supply

46. Fiber distribution
No clear distinction in humans
Sprinters have more fast twitch fibers
Long distance runners have more slow twitch fibers

47. Aging and the muscular system
Time to contract increases
Action Potentials sent decreases
Loss of muscle fibers after 25 years old
50% of muscle fibers gone at 80
The amount of fast-twitch fibers is greatly reduced