1. Textbook Reference: chapter 6
The Muscular System
Textbook Reference: chapter 6

2. Unit ___ Goals
Describe the characteristics and function of skeletal muscle
Differentiate between a muscle’s origin and its insertion
Identify the microscopic anatomy of skeletal muscle
Differentiate between different muscular contractions
Define the 4 functional groups of muscles
Describe how a muscle is stimulated to contract and the mechanism of muscle shortening
Identify the major muscles of the human body

3. Muscles: the machines of the body
Skeletal Muscle Characteristics
Voluntary: move due to a conscious decision
Striated: striped in appearance
Multinucleate: Cells long; more nuclei
More mitochondria for energy production
500+ muscles, 40-50% body weight

4. Skeletal Muscle Extras
Soft and fragile yet TOUGH
Exerts TREMENDOUS power
Power provided by bundles of muscle fibers wrapped in connective tissue
Connective tissue coverings allows for transmission of blood and nerves to muscles & provides support

5. Functional Characteristics of Skeletal Muscle
Produces movement: for locomotion, manipulation and responding to the external environment; also for expressing emotions
Maintaining posture: works continuously to fight downward pressure of gravity

6. Functional Characteristics of Skeletal Muscle
Stabilizing joints: muscle tendons stabilize and reinforce joints that have poor articulating surfaces
Generating heat: heat is a by-product of muscular activity; maintains normal body temperature

7. Skeletal Muscle Interactions
Muscles are arranged in the body to either work together or work in opposition of each other
Number 1 Rule of Muscle Activity:
MUSCLES ONLY PULL*** THEY NEVER PUSH!
In other words, muscle contractions are caused by SHORTENING of fibers

8. Skeletal Muscle Interactions
Insertion: the movable attachment of a muscle
Examples: biceps tendon attachment to radial tuberosity
Origin: the fixed, immovable point of attachment
Examples: biceps tendon attachment to greater tubercle
A muscle contraction involves a muscle’s
insertion moving toward its origin

9. Origins and Insertions

10. 4 Functional Groups of Skeletal Muscles
1.) Agonists (prime movers): a muscle that provides the major force for providing a specific movement
Example: biceps brachii- prime mover of elbow flexion

11. 4 Functional Groups of Skeletal Muscles
2.) Antagonists: muscles that oppose/reverse a movement; relaxed when the agonist is active; helps regulate action of agonist by providing resistance
Can also be agonists
Example: the triceps brachii is the antagonist to the biceps during elbow flexion

12. 4 Functional Groups of Skeletal Muscles
3.) Synergists: “work together”; aids agonist by promoting the same movement or reducing unnecessary movements that might occur as the agonist contracts
Example: biceps brachii and brachioradialis in elbow flexion

13. 4 Functional Groups of Skeletal Muscles
4.) Fixators: a synergist that immobilizes a bone or a muscle’s origin
Example: erector spinae (muscles for posture)
All types of muscles work together to provide smooth, coordinated and precise movements.
Any one muscle can be in any functional group, dependant on its action

14. Detailed Skeletal Muscle
Deep fascia: sheet/band of dense connective tissue covering muscles
Epimysium: connective tissue covering many fascicles, all bound together

15. Connective Wrappings of Skeletal Muscle

16. Detailed Skeletal Muscle
Fascicle: a bundle of fibers wrapped in perimysium
Perimysium: connective tissue surrounding a bundle of muscle fibers
Endomysium: connective tissue surrounding each muscle fiber
Aponeuroses: sheetlike epimysia that connects muscle to each other and to cartilage/bone

17. Detailed Skeletal Muscle
Tendon: cordlike band of epimysia connecting muscles to bones
Durable and able to cross bony projections
Small in diameter to fit in crowded joint spaces

18. Microscopic Anatomy of Skeletal Muscle
Muscle cell = muscle fiber
Sarcoplasm: cytoplasm of muscle fiber
Sarcolema: plasma membrane of muscle fiber
Sarcoplasmic reticulum: site of calcium storage used for contraction

19. Microscopic Anatomy

20. Microscopic Anatomy of Skeletal Muscle
Sarcomere: contractile units of myofibrils, aligned end-to-end
Myofibril: contractile proteins of muscle cells; lie parallel along length of fiber
Thin myofilaments: actin, tropomyosin and troponin
Thick myofilaments: myosin

21. Microscopic Anatomy of Skeletal Muscle
Z line: separates sarcomeres; where actin filaments attach
I band:light bands; where the actin filaments are aligned; extends to tips of myosin filaments
A band: where the myosin filaments are aligned
H Zone: less dense portion of A band where thin filaments don’t overlap thick filaments

22. Sarcomere

23. Nervous Stimulation of a Muscle Cell
Skeletal muscle cells possess unique abilities:
Excitability: can receive & respond to a stimulus
Contractility: they can shorten
Extensibility: lengthen or stretch
Elasticity: cells return to resting form after contracted or stretched
When a skeletal muscle contracts, it is told to do so by the nervous system

24. Nervous Stimulation of a Muscle Cell
Motor Neuron: nerve extending from spinal cord to muscle fiber
Motor Unit: one motor neuron and all the skeletal muscle cells it stimulates
Neuromuscular Junction: where the end of the nerve and the beginning of the muscle fiber meets
Synaptic cleft: space between nerve and muscle fiber
Motor end plate: highly folded sarcolema; lines synaptic cleft

25. Motor Unit

26. Nervous Stimulation of a Muscle Cell
Neurotransmitter: a chemical that carries a signal from the nerve to the muscle; continues the nervous stimulation
Synaptic Vesicles: sacs at motor end plate that holds ACh
Acetylcholine (ACh): the neurotransmitter specific to muscles
Action Potential: an electrical current that can cause a muscular contraction

27. Nervous Stimulation of a Muscle Cell
The nervous system sends a neural signal to the motor unit. This causes a release of ACh into the neuromuscular junction, where it binds to receptors on the muscle cell. This causes an action potential to run throughout the muscle cell, initiating a muscle contraction.

28. Synaptic Cleft

29. Graded Responses of Skeletal Muscle Contraction
A graded response: the degree of muscle shortening dependant on
1. The speed of muscle stimulation
2. The number of muscle cells stimulated

30. Speed of Stimulation
Muscle Twitch: a single, brief contraction caused by a mistake of the nervous system
Summing of Contractions: when nervous impulses are delivered to a muscle at a rapid rate so it can’t relax between impulses; the contractions are summed(added) to create a smooth, strong contraction
Tetanus: no relaxation between contractions; smooth and sustained

31. Number of Cells Stimulated
Small, weak contractions: few cells initiated
Large, strong contractions: all motor units are active and all muscle cells stimulated

32. Types of Skeletal Muscle Contractions
Isotonic: same tone or tension
Myofilaments slide, muscle shortens & movement occurs

33. Types of Skeletal Muscle Contractions
Isometric: same length
Muscles DO NOT shorten
Myosin myofilaments do not move, tension in the fibers build
Muscle tries to move but cannot

34. Energy for Muscle Contractions
There are 3 different energy systems in the body that provide for muscle contractions
Definitions:
Creatine Phosphate (CP): high energy molecule only in muscles which help replenish energy stores
Adenosine Triphoshate (ATP): energy source in the body
Glucose: blood sugar
Glycogen: storage form of blood sugar

35. Energy for Muscle Contractions
Lactic Acid: a byproduct of an anaerobic pathway; causes muscle burning
Aerobic: using oxygen during activity
Anaerobic: not using oxygen during activity

36. Energy Systems
There are 3 ways energy is utilized for muscular activity:
1. ATP-PC/Rapid Recovery
Anaerobic, lasting no more than 20 seconds
ATP production rate is rapid
ATP stores broken down rapidly and resupplied by creatine phosphate (transfers a phosphate to ADP)
More creatine stored in muscles than ATP

37. Energy Systems 2. Lactic Acid/Anaerobic
Breaks down glucose for energy without using oxygen
Muscles are working too fast for oxygen & glucose to be delivered by aerobic respiration
Results in build up of lactic acid in muscles: promotes muscle fatigue and soreness

38. Lactic Acid/Anaerobic Continued
Muscle fatigue: when a muscle is unable to contract even though it is still being stimulated.
Oxygen Debt: occurs during prolonged muscle activity; can’t get oxygen fast enough for the muscle’s needs; lactic acid builds up leading to fatigue; repaid by breathing deeply until the muscles receive enough oxygen to get rid of lactic acid and make more ATP and creatine phosphate

39. Energy Systems 3. Aerobic Respiration
During light exercise, ATP stores are regenerated by using oxygen
Can last for hours if glucose supplies are present
Used in endurance activities

40. Types of Skeletal Muscle Fibers
There are 2 different kinds:
1. Slow twitch
For endurance
Speed of contraction is slow
Uses aerobic respiration
Low glycogen stores-more fats used
Slow rate of fatigue

41. Types of skeletal muscle fibers
2. Fast twitch
Explosive movements for short distances
Speed of contraction very fast
Some aerobic, some anaerobic fibers
High glycogen stores but fatigues quickly
The distribution of muscle fibers is not complete
until the teenage years. It varies between
muscles, within muscles and between people.