1. Muscle Tissue

2. Overview: Muscle Tissue
Types
1. Skeletal: attached to bones; striated, voluntary
2. Cardiac: forms wall of heart; striated, involuntary
3. Smooth: located in viscera; non-striated, involuntary

3. Functions of Muscle Tissue
Body movements
2. Stabilization
3. Organ composition
4. Moving substances within body
5. Generating body heat

4. Muscle Tissue Properties
Electrical Excitability: ability to respond action potential (impulse)

5. Muscle Tissue Properties
Contractility = ability to shorten and thicken, generating force to do work
Isometric contraction = muscle develops tension but does not shorten
Ex/ Postural Muscles
Isotonic contraction = the tension remains constant while the muscle shortens
Ex/ Flexing Bicep

6. Muscle Tissue Properties
Extensibility = ability to extend without damaging tissue
Elasticity = ability to return to original shape after contraction or extension

7. Skeletal Muscle Tissue

8. Skeletal Muscular Tissue
Each skeletal muscle is a separate organ composed of cells called fibers.

9. Muscle Fiber Arrangement
Made up of bundles of Fasicles
Fasicle
Bundle of muscle fibers
Muscle Fibers
Muscle Cell
Myofibrils
Bundles of Thick and Thin Filaments
Thick and Thin Filaments
Made up of muscular proteins

10. Connective Tissue Components of Skeletal Muscle

11. Connective Tissue Components
Fascia
A sheet or band of fibrous connective tissue that is deep to the skin and surrounds muscles and other organs of the body

12. Connective Tissue Components
Superficial Fascia
Separates muscle from skin
Deep Fascia
Lines the body wall and limbs and holds muscles together, allows free movement of muscles

13. Connective Tissue Components
Epimysium = covering entire muscle
Perimysium = covering fascicles
Endomysium = covering individual muscle fibers
All are extensions of deep fascia.

14. Connective Tissue Components
Tendons
Attach muscles to bones
Aponeurosis
Tendon that extends as a broad, flat layer.

15. Muscle Attachment Origin - tendons attach muscle to a stationary bone
Insertion - muscle attaches to moving bone (usually distal)

16. Microscopic Anatomy of Skeletal Muscle Fiber

17. Microscopic Anatomy of Skeletal Muscle Fiber
Sarcolemma = muscle cell membrane
Sarcoplasm = muscle cell cytoplasm
Contains
Glycogen – energy storage
Myoglobin – oxygen storage

18. Microscopic Anatomy of Skeletal Muscle Fiber
T-Tubules
Tiny depressions of sarcolemma (muscle cell membrane)
- Allows nerve impulses to reach muscle fibers

19. Microscopic Anatomy of Skeletal Muscle Fiber
Myofibrils
thin and thick filaments of muscle fiber
Sarcoplasmic Reticulum
Encircles each myofibril; stores calcium ions

20. Microscopic Anatomy of Skeletal Muscle Fiber
Myofibrils are composed of thick and thin filaments arranged in units called Sarcomeres
Motor Unit
Nerve associated with a muscle fiber

21. Microscopic Anatomy of Skeletal Muscle Fiber
Sarcomeres
Basic functional units of a myofibril; show distinct dark (A band) and light (I band) areas.

22. Microscopic Anatomy of Skeletal Muscle Fiber
1. The darker middle portion is the A band; consisting of the thick filaments with some thin filaments overlapping the thick ones.
2. The lighter sides are I bands, which consist of thin filaments only.
3. A Z disc passes through center of I band.
4. A narrow H zone in center of each A band contains thick but no thin filaments.

23. Muscle Fiber Types Slow Twitch Fast Twitch Intermediate Fibers
Called “Red Fibers”
Contain myoglobin (stores oxygen for cellular respiration)
Can contract for long periods without fatiguing
Fast Twitch
Called “White Fibers”
Contain less myoglobin
Contract rapidly; fatigue easily
Intermediate Fibers
These fibers have have the fast twitch speed associated with white fibers combined with a substantial oxidative capacity associated with red fibers

24. Muscle Proteins

25. Contractile Proteins Myosin
Main component of thick filaments; functions as motor proteins
2. Actin
Main component of thin filaments; connects to myosin for the sliding together of the filaments

26. Regulatory Proteins Switch contractions “on” and “off”.
Tropomyosin and troponin are bound to the thin filament

27. Structural Proteins
Keep thick and thin filaments in proper alignment; give myofibril elasticity and extensibility.

28. Structural Proteins
Titin = helps sarcomere return to its resting length after contraction.
2. Myomesin = forms M line
3. Nebulin = helps maintain alignment of thin filaments in the sarcomere
4. Dystrophin = reinforces sarcolemma and helps transmit the tension generated by the sarcomeres to the tendons

29. Contraction and Relaxation of Skeletal Muscle Fibers

30. Sliding Filament Theory
During muscle contraction, myosin cross-bridges pull on thin filaments, causing them to slide inward toward the H Zone
Z discs come toward each other and the sarcomere shortens but the thick and thin filaments do not change in length.
The sliding filaments and shortening of sarcomeres causes the shortening of the whole muscle fiber and ultimately the entire muscle.

31. The Contraction Cycle
At the beginning of contraction, the sarcoplasmic reticulum releases calcium ions, which bind to troponin and cause the troponin- tropomysium complex.
This uncovers the myosin- binding sites on actin.
When the binding sites are “free” the contraction cycle begins.

32. Excitation and Coupling Phase
An increase in calcium ion concentration in the cytosol starts contraction; a decrease stops it.
The muscle action potential releases calcium ions from the sarcoplasmic reticulum that combine with troponin, causing it to pull on tropomyosin to change orientation, thus exposing myosin-binding sites on actin and allowing the actin and myosin to bind together.

33. Excitation and Coupling Phase
Calcium ions remove the contraction inhibitor and allows contraction of the muscle fiber
Calcium ion active transport pumps return calcium ions to the sarcoplasmic reticulum

34. Summary: Sliding Filament Theory

35. The Neuromuscular Junction

36. The Neuromuscular Junction
Muscle action potentials arise at the neuromuscular junction (NMJ), the synapse between a somatic motor neuron and a skeletal muscle fiber.
Synapse
A region of communication between two neurons or a neuron and a target cell.

37. The Neuromuscular Junction
Synapses separate cells from direct physical contact.
Neurotransmitters bridge the gap.
The neurotransmitter at an NMJ is acetycholine (Ach).

38. Muscular Responses

39. Muscle Twitch Cycle of contraction and relaxation of a muscle fiber.
When a muscle fiber contracts, it will contract completely
Called “All-or-none” response
Latent Period
Time between stimulus and muscle contraction
Contraction Phase
Muscle contracts
Refractory Period
Relaxation phase in which muscle cannot respond

40. Sustained Contractions
Even when a muscle is at rest, its fibers maintain muscle tone.
Example: back muscles that control posture

41. Recruitment
The process of increasing the number of active motor units.
Prevents fatigue and helps provide smooth muscular contraction rather than jerky motions.
Aerobic training builds endurance and anaerobic training builds muscle strength.

42. Muscle Tone
A sustained partial contraction of portions of a relaxed skeletal muscle.
Essential for maintaining posture.

43. Striated and Involuntary
Cardiac Muscle Tissue
Striated and Involuntary

44. Cardiac Muscle Tissue
Cardiac muscle tissue is found only in the heart wall.
Fibers are arranged similarly to skeletal muscle fibers.
Connect to adjacent fibers via intercalated disks.

45. Cardiac Muscle Tissue
Contract when stimulated by own autorythmic fibers.
This continuous rhythmic activity is a major physiological difference between cardiac and skeletal muscle tissue.

46. Non-Striated and Involuntary
Smooth Muscle
Non-Striated and Involuntary

47. Smooth Muscle – Two Types
Visceral
Found in walls of hollow viscera and small blood vessels.
Multiunit
Found in large blood vessels, large airways, arrector pilli muscles, and the iris of the eye.

48. Regeneration of Muscle Tissue

49. Regeneration of Skeletal Muscle Tissue
Skeletal muscle fibers cannot divide and have limited powers of regeneration.
The number of new fibers formed is minimal.
Extensive repair results in fibrosis, the replacement of muscle fibers with scar tissue.

50. Regeneration of Cardiac Muscle Tissue
Cardiac muscle fibers cannot divide or regenerate.
Once the heart is injured, it cannot repair itself.

51. Regeneration of Smooth Muscle Tissue
Smooth muscle fibers have limited capacity for division or regeneration.
Example:
Repair of blood vessels
Vessels are composed of smooth muscle

52. Aging and Muscle Tissue
At 30 years of age, there is a progressive loss of skeletal muscle, which is replaced by fat.
There is also a decrease in maximal strength and a slowing of muscle reflexes.

53. Rigor Mortis Ca++ pumps run out of ATP Ca++ cannot be removed
Continuous contraction
Eventually tissues break down

54. Muscle Atrophy Decrease in size of muscle fibers
Disuse atrophy - bedridden individuals, casts
Denervation atrophy loss of nerves and muscle function

55. Muscular Diseases Muscular Dystrophy Myasthenia gravis
Loss of muscle fibers
Linked to young males (ages 3-5)
Lacking certain protein thus allows too much Ca+ into cell
this leads to cell death and replacement with scarring
Myasthenia gravis
autoimmune disease
antibodies bind to ACh receptors
atrophy of muscle fibers
drugs that keep levels of ACh high are used