I. Organization of Skeletal Muscles
A. Characteristics of Skeletal Muscle
1. Contracts (All Muscles)
2. Excitable (Like Nervous Tissue)
a. Action Potentials
3. Extensible
4. Elasticity
5. Responsibilities
a. Locomotion
b. Maintenance of Posture
c. Body Temperature
d. Support of Soft Tissues
B. Skeletal Muscle Organization
1. Connective Tissue Coverings
a. Layers
1) Epimysium
2) Perimysium
a) Fascicles (Fasciculus)
3) Endomysium
b. Attachments
1) Tendons or Aponeuroses
a) Insertion
1] More Moveable
b) Origin
1] Usually Immoveable
c) Belly (Gaster)
2) Deep Fascia
2. Structure of a Skeletal Muscle Fiber (Cell)
a. Sarcolemma
b. Sarcoplasm
c. Transverse (T) tubule
d. Sarcoplasmic Reticulum
1) Terminal Cisternae
2) Triad
e. Sarcomeres
f. Striations
g. Multinucleate
h. Myofibrils ~ 10,000 Sarcomeres
1) Thin Filaments (Myofilaments) ~ 3000
a) Mostly Actin
(1) Z disc (line)
(a) Actinin
(2) I band
(3) Components of Strands
(a) 300-400 G Actin
individual molecules
1] Active site
(b) F-actin strand
(c) Nebulin
(d) Tropomyosin
(e) Troponin
2) Thick Filaments (Myofilaments) ~ 1500
a) Myosin
(1) A band
(a) Zone of Overlap
(b) H zone
(c) M line
(2) Myosin ~ 300 Subunits
(a) Tails
(b) Heads
1] Binding Site
2] ATPase enzyme
(c) Hinge
(d) Titin attaches to Z line
3. Clinical Applications: Muscular Dystrophies (MD)
a. Duchene’s (DMD)
1) Dystrophin Mutation
C. The Neuromuscular (Myoneural) Junction
1. Motor Neuron
a. Synaptic Terminals (Knobs)
1) Synaptic Vesicles
a) Acetylcholine (ACh)
2. Synaptic Cleft
3. Muscle Cells (Fibers)
a. Motor End Plate
1) Acetylcholinesterase (AChE)
4. Overview of Muscle Contraction
a. Action Potential (Nerve Impulse)
b. ACh release and diffuses across Synaptic Cleft
c. Binds to ACh receptors on Sarcolemma
d. Generates an Action Potential
e. Potential Spreads through Transverse Tubules
f. Sarcoplasmic Reticulum releases Calcium
g. Calcium binds to Troponin
h. Tropomyosin moves & exposes Active Sites
i. Myosin Heads attach to Active Sites
j. Thin Filament slides into H-zone/Muscle shortens
D. Naming Skeletal Muscles – Muscle Terminology
1. Specific Region (Location) of the Muscle – Review
2. Relative Position of Muscle Fibers (Fascicles)
a. Anterior/Ventral
b. Posterior/Dorsal
c. Externus/Superficialis
d. Internus/Profundus
e. Inferioris
f. Superioris
g. Lateralis
h. Medialis/Medius
i. Extrinsic
j. Intrinsic
3. Direction of Muscle Fibers (Fascicles)
a. Rectus
b. Transverse
c. Oblique
4. Nature (Number) of Origins
a. Biceps
b. Triceps
c. Quadriceps
5. Location of the Muscle’s Origin and Insertion
6. Shape of the Muscle
a. Deltoid
b. Orbicularis
c. Pectinate
d. Piriformis
e. Platyf. Pyramidal
g. Rhomboid
h. Serratus
i. Splenius
j. Teres
k. Trapezius
7. Relative Size of the Muscle
a. Magnus/Major/Maximus
b. Minor/Minimus
c. Longus/Longissimus
d. Brevis
e. Gracilis
f. Lata/Latissimus
g. Vastus
8. Other Striking Structural Features
a. Alba
b. Tendinosus
9. Action of the Muscle – Review General Actions (Joints)
a. Buccinator
b. Risorius
c. Sartorius
II. Skeletal Muscle Physiology
A. Excitable Tissue Review
1. Action Potentials – Both Neurons and Muscle Cells
2. Resting Membrane Potential -85 mV for Skeletal Muscle
3. Neurotransmitters
4. Depolarize – Peaks at +30 mV
5. Repolarize
B. Biochemical Nature of Muscle Contraction
C. Types of Muscle Contraction
1. Motor Unit
2. All-or-None Principle
3. Muscle Twitch – Single Stimulus
a. Myogram (Tracing)
1) Latent Period
2) Contraction Phase
3) Relaxation Phase
4. Myograms of Repeated (Multiple) Stimulations
a. Treppe
b. Wave (Temporal) Summation
c. Incomplete Tetanus
d. Complete Tetanus
1) Recruitment-Multiple Motor Unit Summation
e. Fatigue
5. Clinical Application: Tetanus
a. Clostridium tetani
b. Lockjaw
D. Isometric Contraction & Isotonic Contraction
1. Isometric Contraction – Tension Increases to Peak, but
Muscle Length does not change
2. Isotonic Contraction – Length of Muscle Changes, Tension is
Generated but remains constant during contraction
a. Concentric Contraction – Muscle Shortens
b. Eccentric Contraction – Muscle Lengthens
E. Fascicle Arrangement
1. Parallel
a. Fusiform
1) Body or Belly
2. Convergent
a. Raphe
3. Pennate
a. Unipennate
b. Bipennate
c. Multipennate
4. Circular or Sphincter
F. Muscles as Lever Systems
1. Components of Leverage
a. Lever – Rigid Rod – Bone
b. Fulcrum (F) – Pivot Point – Joint
c. Load (L) – Resistance
d. Applied Force (AF) – Amount of Work – Muscle Effort
2. First-Class Lever (Fulcrum between Load and Applied Force)
3. Second-Class Lever (Load between Fulcrum and Applied
Force)
4. Third-Class Lever – Most Common in Body (Applied Force
between Load and Fulcrum)
G. Electromyography – Skeletal Muscle Physiology (PhysioEx)
1. Electromyogram (EMG) – Tracing
a. Activity 1 is Practice
b. Activity 2 – Determine Latent Period
c. Activity 3 – Graded Muscle Response to Increased
Stimulus Intensity
1) Determine Threshold Stimulus
2) Determine Maximal Stimulus
3) Multiple Motor Unit Summation
(Recruitment)
d. Activity 4 – Investigating Treppe
e. Activity 5 – Investigating Wave Summation
1) Increasing Stimulus Frequency
f. Activity 6 – Investigating Tetanus
1) Incomplete Tetanus
2) Complete Tetanus
g. Activity 7 – Investigating Muscle Fatigue
(Physiological)
1) Difference between with and without rest
h. Activity 8 – Investigating Isometric Contraction
1) Passive Force
2) Active Force
3) Total Force
4) Optimum Length
i. Activity 9 – Investigating Effect of Load (Isotonic &
Isometric Contractions)
1) Effect of Load (Resistance) versus Initial
Velocity of Contraction (Shortening)
2) Effect of Starting Length versus Initial
Velocity of Contraction (Shortening)