Functions of Muscular System

• movement (~75 pairs [out of 434 muscles] are responsible for movement)
• posture (as well as absorb shock)
• respiration
• heat
• communication
• constriction
• heart beat

Skeletal (our focus here) Cardiac Smooth

• Contractility - ability to contract (develop tension)

 
• Excitability (Irritability) - ability to respond to a stimulus
• either electrochemical (action potential --> depolarization, etc...) or mechanical (blow to muscle by external force)

 
• Extensibility - ability to be stretched
• Viscoelastic - having the ability to stretch or shorten over time (makes an effective stretching program necessary)

 
• Elasticity - ability to recoil to normal length
• Parallel elastic component (PEC) - passive elastic property of muscle derived from muscle membranes (epimysium, perimysium, endomysium, sarcolemma)
• Series elastic component (SEC) - passive elastic property of muscle derived from the tendons  (primarily responsible for elasticity)
• Stretch-shortening cycle - eccentric contraction followed immediately by concentric contraction (plyometrics)
• Contractile component (CC) - actual part of muscle that contracts (actin and myosin)

• tendon - connects skeletal muscle to bone
• epimysium - fibrous connective tissue around belly of skeletal muscle
• fasiculi - bundles of muscle fibers
• perimysium - connective tissue surrounding fasiculi
• endomysium - connective tissue surrounding the individual muscle fibers (muscle cell)
• muscle fiber - single muscle cell (threadlike in shape)
• sarcolemma - membrane surrounding the muscle fiber
• sarcoplasm - specialized cytoplasm of muscle fiber containing multiple nuclei and mitochondria
• myofibrils - "rod-like" structures running through the muscle fibers that contain the contractile proteins actin an myosin that give the skeletal muscle the striated appearance
• wide range of length and diameters
• actin myofilaments - contain actin with binding sites covered by tropomyosin that has strategically located sites of troponin protein on to which calcium ions have a high affinity for
• myosin myofilaments - contain globular heads

• sarcomere - smallest contractile unit of skeletal muscle
• Z disc - ends of sarcomere
• A band - beginning of mysoin to end of adjacent myosin held together at the M line
• H zone - end of one actine myofilament to the beginning of the next actin myofilament in the same sarcomere
• M line - bisects sarcomere, anchors two adjacent myosin myofilaments together (center of H zone)
• I band - area in two adjacent sarcomere that only contain actin myofilaments

• during maximal contraction:
1. Z discs come together towards A band
2. I band narrows
3. H zone disappears

• single motor neuron and all of the fibers it innervates
• twitch - response to single stimulus (<100 msec) vs. tetanus - state of muscle producing sustained maximal tension due to repeated stimulus
• summation - when rapid impulse build in an additive fashion
• electro mechanical delay (EMD) - time between arrival of neural stimulus and tension development by muscle

• slow twitch (Type I, Slow-twitch Oxidative; SO):
• longer max tension time
• lower tension
• high endurance
• fast twitch (FT, Type II):
• shorter max. tension time
• higher tension
• fatigue quickly
• sub-types:
• Type IIa (Fast-twitch Oxidative Glycolytic; FOG)
• Type IIb (Fast-twitch Glycolytic; FG)
• Type IIc (knowledge limited)

• concentric contraction: muscle length decreases
• eccentric contraction: muscle length increases
• isometric contraction: muscle length does not change

Expanded explanation of step 3 above:

Roles Assumed by Skeletal Muscles

• agonist - responsible for the joint motion (primary & assistant)
• antagonist - acts against the agonist for fine control and balance
• stabilizer/fixator - stabilizes a portion of the body against a particular force
• neutralizer - prevents unwanted accessory actions that normally occur when agonist develops concentric tension
• example: Biceps Brachii (elbow flexion & supination) vs. Pronator Teres (pronation)

• origin - most stationary end of skeletal muscle
• belly - between origin and insertion
• insertion - end of muscle with most movement

• motor unit recruitment -calcium availability, frequency of stimulation, number of motor units

• preloading - tension development prior to contraction (example: balancing a barbell)
• cross-sectional area - hypertrophy, hyperplasia?, atrophy
• velocity of contraction - concentric: faster = less force, eccentric: faster = more force

• angle of pennation
• sarcomere and muscle length
• muscle age - sarcopenia - muscular atrophy with aging due to inactivity
• fiber type - slow vs. fast
• muscle soreness (DOMS)
• muscle fatigue
• muscle temperature
• attatchments (biarticulate - active vs. passive insufficiency)
  

Muscular Strength - ability of a given muscle group to generate torque at a particular joint
Muscular Power - product of force and velocity
Muscular Endurance - ability of muscle group to exert tension over time

Chapter 6 Key Terms

active insufficiency (161)	limited ability of two joint muscle to produce force when joint position places the muscle on slack
agonist (159)	role played by a muscle acting to cause a movement
antagonist (159)	role played by a muscle acting to slow or stop a movement
concentric (158)	contraction involving shortening of a muscle
contractile component (147)	muscle property enabling tension development by stimulated muscle fibers
eccentric (159)	contraction involving lengthening of a muscle
electromechanical delay (165)	time between arrival of neural stimulus and tension development by the muscle
fast twitch fiber (152)	a fiber that reaches peak tension relatively quickly
isometric (159)	contraction involving no change in muscle length
motor unit (151)	a single motor neuron and all fibers it innervates
neutralizer (160)	role played by a muscle acting to eliminate an unwanted action produced by an agonist
parallel elastic component (146)	passive elastic property of muscle derived from the muscle membranes
parallel fiber arrangement (154)	fiber patterns within a muscle in which fibers are roughly parallel to longitudinal axis of the muscle
passive insufficiency (161)	inability of two-joint muscle to stretch to the extent required to allow full ROM at all joints crossed
pennate fiber arrangement (154)	pattern of fibers within a muscle with short fibers attaching to one or more tendons
series elastic component (147)	passive elastic property of muscle derived from the tendons
slow twitch fiber (152)	a fiber that reaches peak tension relatively slowly
stabilizer (160)	role played by a muscle acting to stabilize a body part against some other force
stretch-shortening cycle (163)	eccentric contraction followed immediately by concentric contraction
summation (152)	building in an additive fashion
tetanus (152)	state of muscle producing sustained maximal tension resulting from repetitive stimulation
viscoelastic (147)	having the ability to stretch or shorten over time