1. The Muscular System
Chapter 9

2. Anatomy of skeletal muscles

3. Anatomy of the Muscular System
Origin - Muscle attachment that remains
fixed
Insertion - Muscle attachment that moves
Action - What movement a muscle produces. Movement usually occurs at joints i.e. flexion, extension, abduction, etc.

4. For muscles to create a movement, they can only pull, not push
Muscles in the body rarely work alone, & are usually arranged in groups surrounding a joint
A muscle that contracts to create the desired action is known as an agonist or prime mover
A muscle that helps the agonist is a synergist. Some synergists act as fixators
A muscle that opposes the action of the agonist, therefore undoing the desired action is an antagonist

5. Fascicle arrangement within skeletal muscles

6. To understand how muscles move the body (their actions), you must understand the attachments of the muscles (origin & insertion), and the arrangement of fascicles within the muscle (parallel, circular, etc.)

7. To describe the actions of skeletal muscles, most of the time you describe the specific motions that occur at the moving joint
Exceptions: muscles of facial expression

8. Skeletal muscle movements
(see chap. 8 – motions occurring at synovial joints)
Flexion/extension/hyperextension
Lateral flexion (spinal joints)
Abduction/adduction (extremity joints)
Rotation – left/right (spinal joints); internal(medial)/external(lateral) (extremity joints)
Pronation/supination (proximal radio-ulnar joint)
Dorsiflexion/plantarflexion (ankle joint)
Inversion/eversion (tarsal joints)
Elevation/depression (TMJ; scapulothoracic junction)
Protraction/retraction (TMJ; scapulothoracic junction)

9. Naming of Skeletal Muscles

10. The primary tissue found within the muscular system is muscle tissue
Characteristics associated with muscle tissue:
Excitability
Contractility
Extensibility
Elasticity
- Tissue can receive & respond to stimulation
- Tissue can shorten & thicken
- Tissue can lengthen
- After contracting or lengthening, tissue always wants to return to its resting state

11. Functions of muscle tissue:
Movement – both voluntary & involuntary
Maintaining posture
Supporting soft tissues within body cavities
Guarding entrances & exits of the body
Maintaining body temperature

12. Types of muscle tissue: Skeletal muscle tissue
Associated with & attached to the skeleton
Under our conscious (voluntary) control
Microscopically the tissue appears striated
Cells are long, cylindrical & multinucleate

13. Cardiac muscle tissue
Makes up myocardium of heart
Unconsciously (involuntarily) controlled
Microscopically appears striated
Cells are short, branching & have a single nucleus
Cells connect to each other at intercalated discs

14. Makes up walls of organs & blood vessels
Smooth (visceral) muscle tissue
Makes up walls of organs & blood vessels
Tissue is non-striated & involuntary
Cells are short, spindle-shaped & have a single nucleus
Tissue is extremely extensible, while still retaining ability to contract

15. Organization of Skeletal Muscles
(cell)

16. Microanatomy of a Skeletal Muscle Fiber (cell)

17. transverse (T) tubules sarcoplasmic reticulum
Microanatomy of a Muscle Fiber (Cell)
transverse (T) tubules
sarcoplasmic reticulum
sarcolemma
terminal cisternae
myoglobin
mitochondria
thick myofilament
thin myofilament
myofibril
triad
nuclei

18. Myosin molecule of thick filaments
Muscle fiber
sarcomere
Z-line
myofibril
Thin filaments
Thick filaments
Myosin molecule of thick filaments
Thin filament

19. Thin Myofilament
Z-line
(myosin binding site)

20. Thick myofilament
M-line
(has ATP & actin binding site)

21. Sarcomere A band Z line Z line I band Zone of overlap M line
H zone
I band
Zone of overlap
Zone of overlap
M line
Thin myofilaments
Thick myofilaments

22. Sliding Filament Theory
Myosin heads attach to actin molecules (at binding (active) site)
Myosin “pulls” on actin, causing thin myofilaments to slide across thick myofilaments, towards the center of the sarcomere
Sarcomere shortens, I bands get smaller, H zone gets smaller, & zone of overlap increases

23. As sarcomeres shorten, myofibril shortens
As sarcomeres shorten, myofibril shortens. As myofibrils shorten, so does muscle fiber
Once a muscle fiber (cell) begins to contract, it will contract maximally
This is known as the “all or none” principle

24. Physiology of skeletal muscle contraction
Skeletal muscles require stimulation from the nervous system in order to contract
Motor neurons are the cells that cause muscle fibers to contract
cell body
dendrites
Synaptic terminals (synaptic end bulbs)
axon
telodendria
motor neuron
axon hillock
End bulbs contain vesicles filled with Acetylcholine (ACh)

25. Anatomy of the Neuromuscular junction
telodendria
Synaptic terminal (end bulb)
Synaptic vessicles containing Ach
Synaptic cleft
Motor end plate
of sarcolemma

26. Basic Physiology of Skeletal Muscle Contraction

27. Skeletal muscles are made up of thousands of muscle fibers
A single motor neuron may directly control a few fibers within a muscle, or hundreds to thousands of muscle fibers
All of the muscle fibers controlled by a single motor neuron constitute a motor unit

28. small motor units  precise control (e.g. eye muscles)
The size of the motor unit determines how fine the control of movement can be –
small motor units  precise control (e.g. eye muscles)
large motor units gross control (e.g. leg muscles)
Recruitment is the ability to activate more motor units as more force (tension) needs to be generated