1. Chapter 3: Myology

2. Learning Objectives
Compare and contrast the three types of muscle tissue in the human body.
Discuss the five functions of skeletal muscle.
Compare and contrast parallel and pennate fiber arrangements and give an example of each.
Identify the six factors that make up muscle names. Give examples using each factor.
Explain the contribution of each of the five properties of skeletal muscle tissue to human movement.
Identify the major macroscopic and microscopic structures of muscle tissue and describe the function of each.

3. Learning Objectives (cont’d)
List the events that lead to a skeletal muscle contraction and identify all chemicals necessary in the process.
Discuss the factors that influence the amount of force produced by a muscle.
Compare and contrast slow twitch, fast twitch, and intermediate muscles fibers.
Compare and contrast isometric and isotonic muscle contractions.
Compare and contrast concentric and eccentric muscles contractions.
Discuss the functional interrelationships between agonist, synergist, and antagonist muscles.

4. Learning Objectives (cont’d)
Identify the major skeletal muscles of the human body.
Identify the components of a lever and give an example of each type of lever in the human body.
Identify and describe the anatomical structures of proprioception in the human body.
Define and demonstrate active, passive, and resisted range of motion.
Explain the purpose of performing active, passive, and resisted range of motion.

5. Types of Muscle Tissue Smooth Muscle (involuntary)
In walls of hollow organs, vessels, & respiratory passageways; functions in digestion, reproduction, circulation, & breathing
Has no striations (visible alternating dark & light fibers)
Cardiac Muscle (involuntary)
Makes up wall of heart; creates pulsing action to circulate blood
Unique in that electrical impulse travels from cell to cell
Skeletal Muscle (voluntary)
Connected to bones; produces movement at joints

6. Types of Muscle Tissue (cont’d)

7. Skeletal Muscle Functions
Motion: Primary function is to exert pull on bones, creating motion
Posture: Maintain upright posture against gravity
Protection: Protect underlying structures in areas where bones do not
Thermogenesis: Produce body heat
Vascular Pump: Help propel circulation of lymph & venous blood via contractions of skeletal muscles

8. Fiber Direction and Naming Muscles
Parallel Arrangements
Fibers equal in length that do not intersect
Enables entire muscle to shorten equally & in same direction; maximizes range of motion
Fusiform: thick central belly with tapered ends (brachialis, biceps brachii)
Circular: fiber arrangements surround an opening to form a sphincter; designed to contract & close passages or relax & open them (orbicularis oris, sphincter ani)
Triangular: broad at base, converging to single point; fan- shaped arrangement allows diverse actions (pectoralis major, trapezius)

9. Fiber Direction and Naming Muscles (cont’d)
Pennate Arrangements
Feather-shaped, with shorter fibers intersecting a central tendon
Maximize number of fibers in an area, cross-sectional area, & force production
Unipennate: Fibers run obliquely from one side of central tendon; look like half a feather (tibialis posterior, biceps femoris)
Bipennate: Fibers run obliquely along both sides of central tendon; look like a full feather (rectus femoris)
Multipennate: Multiple tendons with oblique muscle fibers on both sides; produce least amount of force (deltoid)

10. Fiber Direction and Naming Muscles (cont’d)
Oblique (slanting): external oblique
Rectus (straight): rectus abdominis
Location
Brachii (arm): biceps brachii
Femoris (thigh): rectus femoris
Pectoralis (chest): pectoralis major
Abdominus (abdomen): rectus abdominus

11. Fiber Direction and Naming Muscles (cont’d)
Action
Flexor: flexor carpi radialis
Extensor: extensor digitorum
Pronator: pronator teres
Size
Major/minor: pectoralis major & minor
Maximus/medius/minimus: gluteus maximus, etc.
Longus/brevis/tertius: peroneus longus, etc.

12. Fiber Direction and Naming Muscles (cont’d)
Shape
Trapezoid: trapezius
Delta: deltoid
Saw-shaped: serratus anterior
Number of Heads
Biceps (2 heads): biceps brachii
Triceps (3 heads): triceps brachii
Quadriceps (4 heads): quadriceps (4 anterior thigh muscles)

13. Skeletal Muscle Properties
Extensibility
Ability to stretch without sustaining damage
Allows muscles to lengthen when relaxed
Elasticity
Ability to return to original shape after lengthening or shortening
Maintains a specific shape & geometry in muscles despite malleable nature
Excitability
Ability to respond to a stimulus by producing electrical signals
Allows muscle to contract & function

14. Skeletal Muscle Properties (cont’d)
Conductivity
Ability to propagate electrical signals, including action potentials
Allows action potential to be transmitted along muscle cell, activating tissue & initiating muscle contraction
Contractility
Ability to shorten & thicken, thus producing force, in response to a specific stimulus
Allows force production & movement

15. Anatomy of Skeletal Muscle Tissue
Macroscopic Anatomy
Connective tissue wrappings support, protect, & separate portions of muscle & whole muscles
Fibers: individual muscle cells
Endomysium: sheath of connective tissue enveloping fibers
Fascicles: bundles of grouped muscle fibers
Perimysium: layer of connective tissue enveloping fascicles
Epimysium: layer of deep fascia enveloping bundle of fascicles
Musculotendinous junction: point where epimysium converges to form a tendon
Muscle belly: portion of muscle between tendons

16. Anatomy of Skeletal Muscle Tissue (cont’d)

17. Anatomy of Skeletal Muscle Tissue (cont’d)
Microscopic Anatomy
Sarcolemma: cell membrane; regulates chemical transport into & out of fiber
Sarcoplasm: a gelatinous substance surrounding structures within fiber; cytoplasm of muscle cells
Nuclei: structures within a fiber that contain functional information for cell & control its operations
Myofibrils: specialized contractile proteins that make skeletal muscle tissue appear striated; two filaments: thin & thick
Sarcomere: functional unit of muscle fiber; their shortening causes contraction

18. Anatomy of Skeletal Muscle Tissue (cont’d)
Microscopic Anatomy
Mitochondria: produce adenosine triphosphate (ATP), a compound that stores energy needed for muscle contraction
Transverse tubules: network of tubules that run at right angles to sarcomeres & transmit nerve impulses from sarcolemma to cell interior
Sarcoplasmic reticulum: network of fluid-filled chambers that covers each myofibril like a lacy sleeve; stores calcium ions

19. Physiology of Muscle Contraction
Steps Involved in Initiating Muscle Contraction
1. A neuron sends electrical signal (action potential) down axon
2. Signal reaches ends of axon branches, stimulates release of neurotransmitter acetylcholine (ACh)
3. ACh molecules cross synaptic cleft & bind with receptors in sarcolemma
4. A muscle action potential travels along sarcolemma & down transverse tubules

20. Physiology of Muscle Contraction (cont’d)
Neuromuscular junction

21. Physiology of Muscle Contraction (cont’d)
Sliding Filament Theory
1. Action potential travels to sarcoplasmic reticulum & releases calcium ions into sarcoplasm
2. Calcium ions bind with troponin, moving aside tropomyosin protein strands covering binding sites on actin filament
3. Myosin heads are charged with energy from breakdown of ATP
4. Energy binds myosin heads to active receptor sites on actin filament, making connections called cross-bridges
5. Ratcheting action (power stroke) occurs as myosin heads pull sarcomere together, shortening the strand
6. Myosin heads bind more ATP, providing energy needed to release hold on actin strand; process creates contractions

22. Physiology of Muscle Contraction (cont’d)
Events of muscle contraction

23. Physiology of Muscle Contraction (cont’d)
Sliding filament mechanism

24. Physiology of Muscle Contraction (cont’d)
Factors Affecting Force Production
Motor unit recruitment
Motor neuron: neuron responsible for initiating motion
Motor unit: motor neuron & all fibers it controls
Few fibers = fine movement, less power; many fibers = no fine movement, greater power
One muscle is typically composed of multiple motor units
Body can control amount of force by varying number & size of motor units recruited
Summation: process of recruiting more & more motor units

25. Physiology of Muscle Contraction (cont’d)
Motor unit

26. Physiology of Muscle Contraction (cont’d)
Factors Affecting Force Production
Cross-Sectional Area
As myofibrils become larger, muscles increase in cross- sectional area & can generate more force
Fiber Arrangement
Pennate fiber arrangements generate more total force than parallel fiber arrangements
Muscle Length
Shortened muscles have decreased ability to produce force
Muscles at resting length can produce greatest force

27. Physiology of Muscle Contraction (cont’d)
Length-tension relationship

28. Skeletal Muscle Fiber Types
Slow Twitch Fibers
Contract slowly but are resistant to fatigue
Rely on aerobic energy production
Used for long-duration activities (walking, jogging)
Fast Twitch Fibers
Contract rapidly & powerfully but fatigue quickly
Larger in diameter than slow twitch fibers due to having more myofilaments
Rely on anaerobic energy production
Used for short-duration activities (sprinting, lifting)

29. Skeletal Muscle Fiber Types (cont’d)
Intermediate Fibers
Have characteristics of both slow twitch & fast twitch fibers
May adapt to body’s demands
“Reservists” waiting to be called up when & where need arises
Distribution of Fiber Types
Intermingled & genetically determined
Those with higher concentration of slow twitch fibers have longer, leaner muscles & predisposition to endurance activities
Those with higher concentration of fast twitch fibers have larger, thicker muscles & predisposition for sprinting or body building

30. Types of Muscle Contractions
Isometric Contractions
Tension is generated in muscle, but muscle length & joint angle don’t change (pushing against an immovable object)
Used to stabilize joints
Isotonic Contractions
Change muscle length & create movement
Two types
Concentric: muscle shortens (lifting a book off a table)
Eccentric: muscle lengthens (slowly lowering book to table)

31. Muscle Relationships Agonists Synergists Antagonists
Create joint movement (prime movers)
Synergists
Assist agonist in creating movement
Stabilize, steer, or contribute to a particular joint movement
Muscles that have same action or actions are considered synergists
Antagonists
Perform opposite actions of agonist (i.e., flexion/extension)
Critical for proper posture & controlling & finishing movements

32. Muscles of the Human Body
A. Anterior view.

33. Muscles of the Human Body (cont’d)
B. Posterior view.

34. Levers in the Human Body
A. First-class levers. B. Second-class levers. C. Third- class levers.

35. Proprioception Proprioception: overall awareness of body position
Types of Proprioceptors
Muscle Spindles: distributed throughout skeletal muscle & monitor changes in tissue length
Golgi Tendon Organs: woven into connective tissue in tendons & monitor changes in muscle tension
Vestibular Apparatus: located in inner ear & provides feedback about head position
Mechanoreceptors: specialized nerve endings that deform in response to pressure & indicate position & movement of associated structures

36. Range of Motion
Range of motion: extent of movement possible at a joint
Active Range of Motion
Client moves a given body part through its possible motions independently
Passive Range of Motion
Client rests while therapist moves joint through its possible movements
Resisted Range of Motion
Client meets resistance from practitioner in attempting to produce movement at a joint