1. Seminar 6 The Muscular System

2. Introduction Muscular tissue enables the body and its parts to move
Movement caused by ability of muscle cells (called fibers) to shorten or contract
Muscle cells shorten by converting chemical energy (obtained from food) into mechanical energy, which causes movement
Three types of muscle tissue exist in body

3. 3 Types of muscle
Skeletal
Cardiac
Smooth

4. Parts of a Skeletal muscle
Origin—attachment to the bone that remains relatively stationary or fixed when movement at the joint occurs
Insertion—point of attachment to the bone that moves when a muscle contracts
Body—main part of the muscle

5. Microscopic Structures
Here’s the breakdown:
Muscle >bundles of fibers>individual muscle fibers>sarcomeres>myofilaments
A sarcomere is a contractile unit of a muscle fiber. Fibers contain thick myofilaments (myosin) and thin myofilaments (actin).

6. Figure 8-3, page 232

7. Sliding Filament Theory
Actin and myosin myofilaments slide past each other in a “ratchet” motion
What two things are required for this contraction to occur?

8. Motor Unit – how we get muscles to move!
Stimulation of a muscle happens by a nerve impulse .
Each muscle has specific nerves that function to make it move!!!
A motor neuron is the specialized nerve that transmits an impulse to a muscle, causing contraction
Neuromuscular Junction is the exact spot where the nerve enters the muscle

9. What are the functions of the muscular system?

10. Functions of the muscular system:
Movement
Posture
Heat production

11. Movement Prime Mover Synergist Antagonist
The main muscle responsible for a particular movement
Synergist
The muscle(s) that assist the prime mover with a particular motion
Antagonist
The muscle that works in opposition to the above

12. Posture
Tonic muscle contraction allows us to maintain good posture

13. Heat Production Requires ATP
Contraction of muscle fibers produces heat

14. Muscle Fatigue – what causes it?
Reduced strength of muscle contraction
Caused by repeated muscle stimulation without adequate periods of rest
Repeated muscular contraction depletes cellular ATP stores
Contraction in the absence of adequate oxygen produces lactic acid
What is meant by Oxygen Debt?

15. Motor Unit
Each muscle of the body has a particular nerve or several nerves that “innervate” that muscle.
The muscle and the nerve that supplies it’s innervation are known as a motor unit.

16. Types of skeletal muscle contractions
Twitch
Tetanic
Isotonic
Isometric

17. Twitch
Tetanic
Isotonic
Isometric

18. Effects of Exercise on Skeletal Muscles
Improves muscle tone
Improves posture
Results in more efficient heart and lung functioning
Reduces fatigue

19. Effects of Exercise on Skeletal Muscles
Prolonged inactivity causes disuse, called atrophy
Regular exercise increases muscle size, called hypertrophy

20. The Step Test – The question
Why do breathing and heart rate remain elevated after exercise stops?

21. The Step Test – The answer
Stored ATP is quickly depleted, and if oxygen supplies are not sufficient, muscle cells switch to energy conversion that does not require oxygen. However, this energy conversion produces lactic acid.
The “oxygen debt” is paid when labored breathing and an increased heart rate are required to remove lactic acid and replace depleted energy reserves, even after exercise has ended.

22. Step Test – 2nd question
Why would a “physically fit” person return to normal breathing and heart rate levels more quickly than an unfit person?

23. Step Test – 2nd answer
increased efficiency of the respiratory and circulatory systems
an increase in the number of blood vessels in muscles
more efficient delivery of oxygen and glucose to muscle fibers
more oxygen is available = the less “oxygen debt” there will be in the muscles.

24. Step Test – 3rd question
Aerobic training also increases the number of mitochondria in muscle fibers.
Why would this benefit the muscle contraction process?

25. Step Test – 3rd answer
Mitochondria are cellular organelles that convert glucose to ATP
Contraction of muscle cells requires ATP
an increase in the number of mitochondria in a muscle cell increases the speed with which ATP is produced in the cell.
Mitochondria = ATP

26. Body movements Figure 8-11
Rotation
Adduction and abduction
Pronation and supination
Dorsiflexion and plantarflexion

27. Exercise – Learning activity
Let’s say we want to strengthen the various muscles listed here….
Biceps brachii
Pectoralis major
Gluteus maximus
Gastrocnemius
Rectus abdominus
What exercises should we do?

28. Exercise – Learning activity
Let’s say we want to strengthen the various muscles listed here….
Biceps brachii = arm curls
Pectoralis major = push ups
Gluteus maximus = squats
Gastrocnemius = foot flexion and extension
Rectus abdominus = sit-ups

29. Muscle disorders Strain—injury from overexertion or trauma
Cramps are painful muscle spasms (involuntary twitches)
Infections
Muscular dystrophy
Myasthenia gravis

30. Review Function of the muscular system Structure of a muscle
Types of muscle tissue
How a contraction occurs
Types of contractions
How exercise affects muscle