1. The Muscular System

2. The Muscular System Myology = The study of muscles
Functions of muscle tissue:
Move the body by pulling bones
Maintain body positions by continuous muscle contraction (ex. Neck holding up the head)
Move substances within the body such as blood, reproductive cells and food.
Produce heat- muscle contraction generates thermal energy
Regulate organ volume (controls opening from the bladder, stomach, and rectum)

3. There are 3 types of muscle tissue
Skeletal
Smooth
Cardiac

4. Skeletal Muscle Characteristics
Most are attached by tendons to bones
Cells- called muscle fibers- are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by connective tissue = great force, but tires easily

5. Smooth Muscle Characteristics
Has no striations
Spindle-shaped cells
Muscle fibers have a single nucleus
Involuntary – no conscious control
Found mainly in the walls of hollow organs and structures
Slow, sustained and tireless

6. Cardiac Muscle Characteristics
Has striations
Muscle fibers branch and contain a single nucleus
Joined to another muscle cell at an intercalated disc
Involuntary
Found only in the heart
Steady pace!

8. Naming of Skeletal Muscles
Location of the muscles origin and insertion
Example: sterno (on the sternum)
Shape of the muscle
Example: deltoid (triangular)
Action of the muscle
Example: flexor and extensor (flexes or extends a bone)

9. Naming of Skeletal Muscles
Direction of muscle fibers
Example: rectus (straight)
Relative size of the muscle
Example: maximus (largest)

10. Naming of Skeletal Muscles
Location of the muscle
Example: many muscles are named for bones (e.g., temporalis)
Number of origins
Example: triceps (three heads)

15. Connective Tissue Wrappings of Skeletal Muscle
Epimysium – covers the entire skeletal muscle
Fascia – on the outside of the epimysium

16. Connective Tissue Wrappings of Skeletal Muscle
Perimysium – around a fascicle (bundle of fibers)
Endomysium – around single muscle fiber (cell)

17. Microscopic Anatomy of Skeletal Muscle
Sarcolemma – specialized plasma membrane of a muscle fiber
Sarcoplasm- cytoplasm of the muscle fiber
Sarcoplasmic reticulum – network of tubules in the muscle fiber that store calcium ions for muscle contraction
Myoglobin- pigment in the sarcoplasm that stores oxygen

18. Microscopic Anatomy of Skeletal Muscle
Myofibril- Cylindrical structure within a muscle fiber
Bundles of thick and thin filament (makes muscle striated)
I band = light band (thin)
A band = dark band (thick)

19. Microscopic Anatomy of Skeletal Muscle
Sarcomere
Contractile units of a muscle fiber which are
separated by Z discs

21. Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere
Thick myofilaments = myosin filaments= have extensions called “heads”
Thin myofilaments = actin filaments
Myosin and actin somewhat overlap
Actin are anchored at the z-disc

23. Quick Review
For cardiac, smooth and skeletal muscle, indicate if they are: striated or not; voluntary or not; multinucleated or not
2. What are the differences in shape between the different muscle cells?
3. What is the outermost connective tissue layer of skeletal muscle?
4. What are bundles of muscle fibers called?
5. What tissue layer surrounds each muscle fiber?

24. Quick Review cont…..
What is the plasma membrane of a muscle fiber called?
What is the cylindrical unit inside a muscle cell?
What are the 2 myofilaments in a muscle fiber?
What is another term for the thick band?
What is another term for the thin band?
What is the region between z-discs called?
What is the region where the actin filaments are anchored?
Where are calcium ions stored in a muscle fiber?

25. The Sliding Filament Theory of Muscle Contraction
1. Activation by a nerve causes myosin heads to attach to binding sites on the adjacent thin filament.
2. Myosin heads flex inward then reach ahead to attach to the next site of the thin filament.
3. This continued forward grabbing causes a sliding of the myosin along the actin.
4. The result is that the sarcomere shortens, thus shortening the entire muscle.
5. Myosin heads attach and detach to actin due to ATP (energy stored in mitochondria) and Ca+ (stored in sarcoplasmic reticulum).

26. Nerve Stimulus to Muscles
Neuromuscular junctions – Where motor neurons (nerve cells) and muscle fibers associate

27. Nerve Stimulus to Muscles
Synaptic cleft – gap between nerve and muscle
Nerve and muscle do not make contact
Area between nerve and muscle is filled with fluid

28. Transmission of Nerve Impulse to Muscle
Neurotransmitter – chemical released by a nerve to communicate with another nerve or muscle
The neurotransmitter for skeletal muscle is acetylcholine (ACh)
ACh attaches to receptors on the sarcolemma
Sarcolemma allows sodium (Na+) to enter the muscle fiber
Sodium rushing into the cell initiates muscle contraction by causing the release of Ca+ from the sarcoplasmic reticulum.

30. Contraction of a Skeletal Muscle
What happens if NMJs are blocked?
No muscle contraction!!
Why would someone want to purposely block NMJs?
No muscle contraction= No wrinkles!!
What is a drug that does that?
BOTOX!!

31. Botox “before” and “after”

32. What causes a muscle to relax after contraction?
The enzyme acetylcholinesterase rapidly breaks down acetylcholine in the synaptic cleft, preventing it from continuing to signal to the muscle fiber.
Ca2+ ions are transported from the sarcoplasm back into the sarcoplasmic reticulum for storage.
The actin filaments slide back to their relaxed positions

33. Muscle Fatigue and Oxygen Debt
Muscle fatigue is the inability to contract after prolonged activity.
What are some possible reasons for why this happens?
The common reason for muscle fatigue is oxygen debt
Oxygen debt is the amount of oxygen taken into the body after exercise to “repay” what was taken from the myoglobin.

34. Muscle Fatigue and Oxygen Debt
Under anaerobic (low oxygen) conditions (during exercise when not taking in enough oxygen), muscle cells go through fermentation to produce energy. This results in a build up of lactic acid in the muscles. This is a very inefficient energy producing process.
Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less.
The body uses oxygen debt to remove lactic acid and produce more ATP.

35. Muscles and Body Movements
Movement is attained due to a muscle moving an attached bone
Figure 6.12
Slide 6.30a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

36. Muscles and Body Movements
Muscles are attached to at least two points
Point of Origin –attachment to an immovable bone
Point of Insertion –attachment to a moveable bone
Figure 6.12
Slide 6.30b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

37. Types of Muscles
Prime mover – muscle with the major responsibility for a certain movement
Antagonist – muscle that opposes or reverses a prime mover
Synergist – muscle that aids a prime mover in a movement and helps prevent rotation
Flexor- bends a joint
Extensor- straightens a joint

38. Example: Biceps curl- Prime mover- Biceps brachii
Antagonistic muscle- Triceps brachii
Synergist muscle- Pectoralis major
Flexor- Biceps brachii
Extensor- Triceps brachii

40. Disorders relating to the Muscular System
Muscular Dystrophy: inherited, muscle enlarge due to increased fat and connective tissue, but fibers degenerate and atrophy
Duchenne MD: lacking a protein to maintain the sarcolemma
Myasthemia Gravis: progressive weakness due to a shortage of acetylcholine receptors