1. Myology: the study of skeletal muscles
MUSCLES – 1A
Myology: the study of skeletal muscles

2. Ability to generate electrical impulses (action potentials)
Basic Features
Excitability
Ability to generate electrical impulses (action potentials)
Contractility
Ability to shorten (contract)

3. Functions of Skeletal Muscle
Heat production
Voluntary movement
Including speech and breathing
Maintenance of body posture
Guard body openings
Store nutrient reserves

4. Relationship of Skeletal Muscle to Bone
Muscles pull on bones
Provide a “force” (effort)
Bones serve as levers
Lever – a rigid bar (makes it easier to do work.
To carry a “load” (resistance; weight)
Joints act as fulcrums for the levers
Fulcrum = fixed point
Force (muscle)
Resistance (weight)
Fulcrum (joint)

5. Examples—seesaws, scissors, and lifting your head off your chest
First-class lever
E - F - R
Examples—seesaws, scissors, and lifting your head off your chest
Load
Effort L
Fulcrum
Load
1st class lever =
E-F-R
If the fulcrum near the load, you can lift a lot of weight a short distance! (mechanical advantage) L
Effort
Fulcrum
Fulcrum
Load
Effort

6. Second-class lever (F-R-E) Fulcrum-Load - Effort
Examples—wheelbarrow or standing on tiptoe
An uncommon type of lever in the body
Works at a mechanical advantage
effort
load
fulcrum

7. Arrangement of the elements is
Third-class lever
Effort is applied between the load and the fulcrum
Works speedily
Always at a mechanical disadvantage
Third-class lever
Arrangement of the elements is
load-effort-fulcrum.
Load
Effort
3rd class lever =
F-E-R L
Fulcrum
Load
If the fulcrum is far from the load, it’s hard to lift a lot of weight BUT you can lift the load farther! L
Fulcrum
Effort
Most skeletal muscles are 3rd-class levers
Example—biceps brachii
Fulcrum—the elbow joint
Force—exerted on the proximal region of the radius
Load—the distal part of the forearm
Example: tweezers or forceps
Effort
Load
Fulcrum
In the body: Flexing the forearm by the biceps
brachii muscle exemplifies third-class leverage. The
effort is exerted on the proximal radius of the forearm;
the fulcrum is the elbow joint; and the load is the
hand and distal end of the forearm.

8. Tendons: Muscle Attachment to Bone
Tendons attach muscle to the periosteum of bone.
One bone moves; one bone remains fixed
Origin—(head; ceps) - less movable attachment
”ceps” = cephalic, which means “head”
Biceps, triceps, quadriceps
Insertion— (tail) attachment to more movable attachment
Muscle contracting
Origin by direct attachment
Brachialis
(belly of muscle)
Tendon
Insertion by indirect attachment

9. Types of Contractions
isotonic – muscle contracts and changes length. 2 types:
eccentric – lengthening contraction
concentric – shortening contraction
isometric – muscle contracts but does not change length

10. Group Actions of Muscles
Agonist (prime mover) – muscle that causes the action
Synergist (helper) – muscle that acts with an agonist
Antagonist – muscle that causes the opposite action of the agonist
Fixator (stabilizer) – muscle that stabilizes body position
In a flexion, the biceps is the prime mover; the brachialis (not shown)is a synergist;
the triceps is an antagonist

11. SKELETAL MUSCLE
Skeletal muscle is voluntary. It is under conscious control.
“Conscious” means that the nervous system is involved in getting your muscles to move.
Neurons are the cells of the nervous system that send messages.
“Motor Neurons” send messages to skeletal muscle, telling them to move.

12. A single neuron can send messages to many muscle cells (fibers).
As more muscle fibers are recruited, the strength of the contraction will increase.
Let’s look at a single motor neuron contacting many muscle cells at once.

13. Motor Unit
a single motor neuron innervates (supplies) several hundred skeletal muscle fibers
a voluntary motor neuron is called a somatic motor neuron

14. Structure of a Skeletal Muscle
A Skeletal Muscle is an organ
Contains different tissues:
skeletal muscle
nervous
blood vessels
connective
fascia – surrounds each muscle
tendon – holds to bone
aponeuroses – broad, fibrous sheets, attach muscle to muscle or other structures.

15. Terminology Specific to Muscle Tissue
Myo and mys—prefixes meaning “muscle”
Sarco—prefix meaning “flesh”
Sarcolemma—plasma membrane of muscle cells
Sarcoplasm—cytoplasm of muscle cells
Sarcasm – flesh-eating words!

16. Structure of a Skeletal Muscle
9-4

17. Skeletal Muscle Fiber

18. Sarcomere
9-6

19. Myofilaments are thick and thin filaments
composed of actin
associated with troponin and tropomyosin
Thick Filaments
composed of myosin
cross-bridges

20. Neuromuscular Junction
Neuron transmits an action potential via a neurotransmitter
(acetylcholine)

21. Calcium binds to troponin, allows actin to bind to myosin, sliding occurs

22. Sliding Filament Theory
When sarcromeres shorten, myosin and actin filaments slide past one another
Z lines move closer together

23. RELAXATION acetylcholinesterase – breaks down acetylcholine
muscle impulse stops
Ca+2 moves back into SR
myosin and actin binding prevented

24. end