1. Chapter 9
Muscular System

2. Function of Skeletal Muscles
The functions include movement, heat production, and posture.
Movement - contraction of muscles.
Heat production - maintains homeostasis of temperature.
Posture - maintenance of partial muscle contraction.
Allows sitting, standing

3. Muscle and Muscle Fiber Structure
A muscle is composed of many muscle fibers (muscle fiber = muscle cell). The individual muscles are separated from each other and held in place by a covering called the FASCIA. This fascia also forms TENDONS and APONEUROSES (layers of tendons) connecting muscles to bones and muscles to muscles.

4. Microscopic Structure of Skeletal Muscles
Composed of bundles of fibers, not cells.
Fibers:
Sarcolemma - plasma membrane of the muscle.
Sarcoplasma - cytoplasm of a fiber.
Sarcoplasmic reticulum – like the endoplasmic reticulum, tunnels throughout fiber.
Contains many mitochondria and several nuclei - more ATP production.

5. Microscopic Structure of Skeletal Muscles Continued
Fibers:
Myofibrils - bundles of very fine fibers that extend through the sarcoplasm.
Each myofibril is made of many protein filaments called myofilaments.

6. 2 Types of Myofilaments
Myosin -Thick filaments
Actin - Thin filaments

7. Movement
Actin and Myosin filaments are arranged in an overlapping pattern of light (“I” bands) and dark (“A” bands). In the middle of each “I” band is a line called a “Z” line. The section of a myofibril from one Z-line to the next Z-line is called a SARCOMERE. The arrangement of these sarcomeres next to each other produces the STRIATIONS of the skeletal muscle fibers.

8. Movement Continued Myosin and actin interact
Myofibrils pull toward sarcomere
Sarcomeres shorten, myofibrils shorten, muscle shortens = contraction.
All-or-None Law
contract with all force possible under conditions or do not contract at all.

9. Energy Sources ATP - Adenosine Triphosphate
Breakdown bonds between the phosphate groups provides energy for contraction.
Creatine Phosphate provides energy for the regeneration of ATP.
For more intense contractions, generation of ATP comes from food intake - Cellular respiration.
ATP is made in the mitochondria.

10. Energy Sources Continued
Only 25% of energy produced during cellular respiration is used in metabolic processes – the rest is in the form of HEAT. This is what produces our body heat and maintains body temperature. More muscle activity = more heat.

11. Connective Tissue Components
Epimysium - sheath that envelopes each muscle
Perimysium - extension of sheath between fiber bundles - like a partition.
Endomysium - extension of sheath between individual fibers.

12. Connective Tissue Components Continued
Tendon - extention of three above structures from the muscle to its other end which is continuous with the periosteum (fiberous tissue that covers bone)
Shin splints - tendon not torn because of strength, but can be pulled away from bone.
Tendon sheath - tube shaped structure, encloses certain tendons - ex. wrist, ankle
Lined with synovial fluid
Allows easy movement

13. Connective Tissue Components Continued
Deep fascia - extension from epi, peri, and endomysium of muscles and their attachment to bone.

14. Contraction Clip

17. Muscle Names Action - Flexor, extensor Direction of fibers
Reason for muscle names
Action - Flexor, extensor
Direction of fibers
Location - Femoris
Number of divisions
Shape
Points of attachment

18. Muscle Groupings Muscles are grouped according to location.
Muscles are grouped according to function.

19. Principles of Skeletal Muscle Function
Contract only if stimulated (nerves)

20. Principles of Skeletal Muscle Function Continued
Types of Contractions
Tonic - continual, partial contraction - tautness (occurs only when awake).
Isotonic - contraction remains the same, but length of muscle changes = shortens (walking, running, lifting an object).
Isometric - muscle length remains the same, muscle tension increases (push against wall).
Convulsions - abnormal, uncoordinated contractions.

21. Principles of Skeletal Muscle Function Continued
Produce movement by pulling on bones
Bones serve as levers, and joints serve as fulcrums of the levers.
Muscles move parts other than where they lie.

22. Principles of Skeletal Muscle Function Continued
Act in groups
Prime movers - contraction produces movement (primarily responsible for producing an action).
Antagonists - relaxation of muscle while prime movers are contracting.
* antagonist of a flexor is an extensor*
Synergists - contract at same time as prime, assist in movement.

23. Skeletal Muscle Contraction
Neurotransmitter must stimulate muscle - acetylcholine for muscle contraction.
ATP must be present at the same time
Decrease acetylcholine = muscle relaxation

24. Energy Sources for Contraction
           Creatine phosphate
1. contains high energy phosphate bonds
2. stores excess energy released from mitochondria
3. decrease ATP---- energy from creatine turns to ADP—ADP is coverted to ATP
4. creatine is depleted rapidly in active muscles
5. can ingest extra creatine to increase body supply.

25. Muscle Fatigue Inability of muscle to contract
Due to accumulation of lactic acid
Could coincide with cramping due to a lack of ATP

26. Rigor Mortis Partial muscle contraction after death
Can continue for 72 hours
Rigor Mortis
                        

27. Posture
  Maintenance
Muscles exert continual pull on bone in opposite direction (extensors).
2. Tonicity (elastic tension of living muscles) allows pull against gravity
a. Absent during sleep
b. Will not counteract gravity
c. Cannot sleep standing up
                        

28. Posture Continued Importance of good posture
1. Decreases work on muscles
2. Bad posture puts strain on ligaments
3. Bad posture interferes with
respiration, digestion, etc…
Posture Continued
                        

29.                         
Trapezius

30. Anterior
Muscles
                        

31. Posterior
Muscles