1. PA 544 Clinical Anatomy Tony Serino, Ph.D.
Muscular System
PA 544
Clinical Anatomy
Tony Serino, Ph.D.

2. Muscular System Functions: Attributes:
Movement –generation of force and/or shortening
Maintenance of posture
Joint stabilization
Heat Generation
Attributes:
contractility, irritability, extensibility, and elasticity

3. Types of Muscle Cells Skeletal Muscle –voluntary, striated
Cardiac Muscle –involuntary, striated
Smooth Muscle –involuntary, no striations

4. Muscles wrapped with CT, that is continuous with tendon and periosteum

5. The elasticity of the CT sheaths, tendon and the muscle cells = the Series Elastic Component

6. Antagonistic Muscle Arrangement
This arrangement plus the series elastic component allows the muscle to return to its original length.

7. Skeletal Muscle Cells
Long, cylindrical, non-branching, multinucleated
mcm wide and up to 35 cm long
Voluntary, no spontaneous depolarization normally
Contractile proteins (myosin & actin) arranged in bundles called myofibrils

8. Develop as a fusion of myoblasts, which accounts for multinucleated cells, extra myoblasts remain as satellite cells.

9. Unique Muscle Cell Structures
Sarcomere

10. Each skeletal muscle cell must be innervated by a motor neuron to begin contracting.

11. Neuronal AP triggers release of ACh at neuromuscular junction (motor end plate).

12. Neuromuscular Junction (Motor End Plate)

13. Muscle Contraction Review

14. Muscles are arranged as Motor Units
Motor Unit = 1 motor neuron + all the muscle fibers it controls (innervates)
The size of the motor unit depends on the degree of control needed in that particular whole muscle.

15. Biomechanics of Force Production
Tension = force exerted on an object by a muscle
Load = force exerted on muscle by the weight of an object
Twitch = the mechanical response of a muscle to an AP
Types of Contractions:
Isometric = muscle increases tension without shortening
Isotonic = muscle shortens with no further increase in tension
Load
Tension
Bicep
Fulcrum (pivot point)
Weight of arm + object

16. Types of Muscle Fiber: each motor unit consists of only one type of muscle fiber
Slow twitch, red (oxidative) fibers (SO) –small diameter, weakest, slow ATPase, much myoglobin and mitochondria, abundant blood supply, fatigue resistant
Fast twitch, red (oxidative) fibers (FO) –medium diameter, moderate strength, fast ATPase, abundant mitochondria and myoglobin, good blood supply, moderate fatigue resistance
Fast twitch, white (glycolytic) fibers (FG) –largest diameter, great strength, fast ATPase, low amount of myoglobin or mitochondria, decreased blood supply, high in glycolytic enzymes, tire quickly

17. Cardiac Muscle
Striated, single nucleus, branched cells, connected together by intercalated discs (with many gap junctions)
Spontaneously contracts, needs no innervation, involuntary

18. Smooth Muscle
No sarcomeres, therefore, no striations, single nucleated, small spindle shaped cells
Spontaneously contracts, involuntary control, can remain contracted for long periods of time without fatiguing
Two types: Visceral (single unit) –united by gap junctions Multi-unit –needs innervations, behaves like skeletal muscle (Ex. Iris)

19. Smooth Muscle Cell

20. Visceral Smooth Muscle