The Muscular System

1. The Muscular System Part 2: Support & Movement

2. Muscle Tissue • Muscle: One of the 4 basic human tissues • Defined by its ability to contract & provide movement • Composition of muscle tissue will be discussed in next chapter • Current chapter will cover location, function, & classification

3. 3 Types of Muscle Tissue • Skeletal Muscle: • Striated - associated with unstriated muscle • Voluntary • Attaches to the bones of the skeletonMultinucleated • Smooth Muscle: • Involuntary • Found in digestive system, blood vessel walls, urinary & reproductive systems • Cardiac Muscle: • Involuntary • Only found in the heart • Has rhythmicity – will beat without outside stimulation • Sources of energy that moves blood through the blood vessels • Smooth & Cardiac Muscle are controlled by the autonomic nervous system.

5. Common Traits • Proteins Needed: • Actin • Myosin • Four Essential Ions Needed: • Calcium • Sodium • Chloride • Potassium • Common Characteristics: • Excitability • Conductivity • Contractility • Extensibility • Elasticity

6. Skeletal Muscles: Function • Functions: • Movement • Stability • Communication • Expressions, Speech • Provides primary source of body heat • Through muscle contractions – thermogenesis • Roughly 600 skeletal muscles in the human body

7. Skeletal Muscles: Properties • Contractility: Ability to forcefully contract when stimulated • Extensibility: Ability of the tissue to stretch without damage • Elasticity: Ability to return to its original shape after contraction or extension • Excitability: Ability to respond to stimuli • Action Potentials: Electrical signals prompted by neurotransmitters or by autorhythmic signals arising within the muscle tissue

8. Skeletal Muscles: Connective Tissue Components • Fascicles: Bundles of muscle fiber that make up skeletal muscles • Enveloped by connective tissue • Fascia: Thin fibrous sheet of connective tissue that surrounds muscles & provides protection • Superficial Fascia: Separates the skin from muscle; subcutaneous layer • Deep Fascia: Holds individual muscles together

10. Skeletal Muscles: Connective Tissue • 3 Types of Connective Tissue protecting muscles: • Endomysium: Layer of areolar tissue surrounding individual muscle fibers • Perimysium: Sheath of connective tissue surrounding the fascicles • Epimysium: Outer layer of connective tissue covering the entire muscle & blending into the fascia

12. Skeletal Muscles: Attachment • Collagen Fibers: Connects muscle directly to bone • Attaches using epimysium & periosteum • Tendons: Extensions of connective tissue, primarily from the deep fascia • Attaches to the periosteum of the bone

14. Skeletal Muscles: General Anatomy • Points of Attachment: • Origin: Point of attachment at the stationary end of an individual muscle. • Usually medial • Insertion: Point of attachment at the more mobile end of the muscle. • Belly: Middle region of the muscle; very thick.

16. Skeletal Muscles: Classification • Intrinsic Muscles: Entirely contained within a particular region, e.g. the tongue. • Extrinsic Muscles: Act upon a certain region, but their origin is elsewhere.

17. Skeletal Muscles: Classification • Classification based on the orientation of fascicles: 5 Types • Circular: Surround body openings; e.g. sphincter muscles • Convergent: Fan shaped; e.g. pectoralis major • Fusiform: Tapered at the ends but thicker in the middle; e.g. digrastric muscles • Parallel: Relatively long & uniform in width, look like straps with parallel fascicles; e.g. stylohyoid muscle. • Pennate: Short, feather-shaped bundles with tendons running almost the entire length; have unipennate, bipennate, multipennate forms; e.g. deltoid muscles.

18. Muscle Action & Coordination • Muscles act together as coordinated groups to produce movement • Muscles are often paired against muscles of an opposing joint. • Prime Mover or Agonist: The muscle that produces the most force. • Antagonist: The muscle that yields to the effects of the prime mover; acts opposite to it. • Synergist: A muscle that aids the prime mover and prevents unwanted movement at the joints. • Fixator: A muscle that prevents bone from moving and stabilizes the movement itself. • Example: Flexing the forearm at the elbow – biceps brachii is the prime mover & triceps brachii is the antagonist.

20. Muscle Innervation • Innervation: Every muscle fiber has a single motor neuron which innervates several other muscle fibers. • Threshold: The level of stimulus needed for the neuron to fire… It will not fire until this is reached, and will instantly fire once it is reached. • Without nerves, skeletal muscles will not move. • Atrophy: Without innervation & movement, muscles will waste away & form scar tissue.

21. Skeletal Muscle Names • Skeletal muscles are named according to their distinctive features! • Named for size, shape, action, & number of origins.

22. Skeletal Muscle Names • Named by Size: • Maximus: Largest muscles • E.g. gluteus maximus • Minimus: Smallest muscles • E.g. gluteus minimus • Longus: Long muscles • E.g. adductor longus • Major: Larger muscles • E.g. pectoralis major

23. Skeletal Muscle Names • Named by Shape: • Trapezius: Trapezoid shaped • E.g. Trapezius muscle • Rhomboid: Diamond shaped • E.g. Rhomboid major • Quadratus: Square shaped • E.g. Quadratus femoris

24. Skeletal Muscle Names • Named by Action: • Flexor: Decreases angle • E.g. flexor carpi radialis • Levator: Elevates • E.g. levator scapulae • Tensor: Makes rigid • E.g. tensor fasciae latae

25. Skeletal Muscle Names • Named by Number of Origins: • Biceps: Two origins • E.g. biceps brachii • Triceps: Three origins • E.g. triceps brachii • Quadriceps: Four origins • E.g. quadriceps femori