1. CHAPTER EIGHT
MUSCULAR
SYSTEM

2. FUNCTIONS:
MOVEMENT
POSTURE
HEAT PRODUCTION
PROTECTION

3. 3 TYPES OF MUSCLE TISSUE SMOOTH MUSCLE: SKELETAL MUSCLE:
Involuntary
One nucleus, no striations, tapered at ends
Digestive tract, blood vessels
SKELETAL MUSCLE:
Voluntary
Multinucleated, striations, cylindrical
CARDIAC MUSCLE:
One nucleus, striations, intercalated disks

4. SMOOTH MUSCLE

5. Characteristics Connect to form “syncytia” (similar to cardiac)
Impulses and contractions occur much more slowly than cardiac muscle, however
Cause wave-like movement, called “peristalsis”

6. Skeletal Muscle Characteristics
Long, multi-nucleated cylinders
Separated by connective tissue
Each cell stimulated by motor neuron

7. Skeletal Muscle E.M.

8. Skeletal MUSCLE

10. Cardiac Muscle Characteristics
Faintly striated, branched
Connect by intercalated discs to form a “network”
Action potential travels through all cells connected together in the “syncytium”
Function as a unit

11. CARDIAC MUSCLE

12. Type of muscle?
Skeletal

13. Type of muscle?
Cardiac

14. Type of muscle?
Smooth

15. Organization of (skeletal) muscle
Skeletal muscle fibers located in muscles
Organized into fiber bundles called fascicles (fasciculi)
Surrounded by perimysium, connective tissue layer

16. Membranes Portions of perimysium extend into the endomysium
Thin layer of CT that covers each muscle fiber
Muscle fiber (bundle)= multinucleate cell
Perimysium also extends to the CT that surrounds the muscle, the epimysium

18. Sarcoplasmic Reticulum
Each myofibril is surrounded by network of tubes and storage sacs (Transverse tubules and sarcoplasmic reticulum)
Releases Ca2+ ions when stimulated by motor neuron
Triggers contraction (more on this later…)

19. SARCOMERE Sarcomere= basic (functional) contractile unit
Separated by each other by dark Z lines/discs
Actin & myosin slide past each other as the muscle contracts
Contraction requires Ca2+ and ATP

20. Other Key Points About Sarcomeres
Z-line/disc
I Bands
Lighter areas of non-overlap between actin and myosin
Contain the Z-lines.
Dark Bands = A Bands
Areas where some overlap occurs
= “Striations” on the slide
Coincide with the length of myosin myofilaments.

21. MICROSCOPIC STRUCTURE
FIBERS: grouped into bundles (fasciculi)
= 1 cell!
Fibers contain myofibrils with:
ACTIN: thin myofilaments
MYOSIN: thick myofilaments

24. Another look…

25. Muscular System
Physiology of the Muscle

27. Myosin head “primer”…

28. Sliding filament theory
In the absence of Calcium ions…
Tropomyosin blocks access to the myosin binding site of actin.

29. When Calcium is released by the Sarcoplasmic reticulum
it diffuses into the muscles
binds to the troponin
shifting the troponin and tropomyosin

30. Myosin splits ATP and undergoes a conformational change into a high-energy state.
The head of myosin binds to actin
Forms a cross-bridge between the thick and thin filaments.

31. The energy stored by myosin is released
ADP and phosphate released from myosin.
The myosin molecule relaxes
Causes rotation of the globular head
This leads to the sliding of the filaments.

32. ATP binds to cross bridge, causing cross bridge to disconnect from actin.
Splitting of ATP leads to re-energizing/ repositioning of the cross bridge.

33. Ca2+ ions transported back to sarcoplasmic reticulum (req. ATP)
When the calcium level decreases
troponin locks tropomyosin back into the blocking position
thin filament (actin) slides back to the resting state (when ATP binds to myosin head)

34. Review of the Role of ATP
1. ATP transfers its energy to the myosin cross bridge, which in turn energizes the power stroke.
2. ATP disconnects the myosin cross bridge from the binding site on actin.
3. ATP fuels the pump that actively transports calcium ions back into the sarcoplasmic reticulum.

35. Motor Unit
Stimulation of a muscle by a nerve impulse (motor nerve) is required before a muscle can shorten
Neuromuscular junction: point of contact b/w nerve ending and the muscle fiber it innervates.
Motor unit: motor neuron + muscle cell

36. Neuromuscular Junction

38. Motor Unit

39. Muscle Stimulus
Threshold stimulus: minimal level of stimulation required to cause a muscle fiber to contract
All-or-none response: once stimulated, a muscle fiber will contract completely

40. Types of Contractions
Twitch contractions: a single contraction of a muscle fiber caused by a single threshold stimulus
Tetanic contractions: sustained and steady muscular contractions caused by a series of stimuli bombarding a muscle in rapid succession

41. Isotonic vs. Isometric Contraction
Isotonic Contraction
Produces movement at the joint
Muscle shortens
Isometric
Does not produce movement at the joint
Muscle does not shorten but tension within the muscle increases

42. Antagonist vs. Agonist Muscles
Agonistic muscles have the same action
Adductor magnus, adductor brevis
Vastus intermedius, rectus femoris
Antagonistic muscles have opposites actions (when one is fully contracted, the other must be relaxed)
Biceps brachii, triceps brachii
Forearm flexors, forearm extensors
Rectus abdominus, erector spinae

43. Strength vs. Endurance Strength training… Endurance training…
Increases number of muscle fibers’ myofilaments (causes increase in diameter)
Increases bulk of muscle (hypertrophy)
Endurance training…
Increases number of mitochondria in muscle cell