1. The Muscular System

2. Muscles Nearly ½ of your body mass is muscle
Muscle is groups of fibers or cells bound together.
Major Functions:
Motion
Maintenance of posture
Stabilizes joints
Produces heat
By-product of muscle activity

3. Characteristics of Muscle Tissue
Contract
Ability to shorten & thicken
Extensible
Ability to be stretched/extended
Excitable or have Irritability
Can receive & respond to stimuli
Elastic
Ability to return to their original shape after contraction or extension

4. Types of Muscle Tissue Smooth Muscle Cardiac Muscle Skeletal Muscle
Wall of internal organs & blood vessels
Involuntary
Generally squeeze the organ they surround to move material
Ex. Digestive tract
Cardiac Muscle
Heart muscle – involuntary – striated
Generates & conducts electrical
impulses for rhythmic pumping
Skeletal Muscle
Allows movement – attaches to bone
Voluntary – conscious control

6. Muscle Structure Muscle is made up of fibers
Each fiber is made up of smaller units called myofibrils
Myofibrils can be divided into units called sarcomeres
Function units of muscles

7. Sacromeres Contractile units
Aligned end to end along the length of the myofibrils
Composed of smaller units called myofilaments
Two types of myofilaments
Myosin filament
Thick filament
Actin filament
Thin filaments
Arrangement of myofilaments produces the banding pattern (striations) in skeletal muscle.

9. Nerve Stimulation + Contraction
Skeletal muscles must be stimulated by nerve impulses to contract
One neuron may stimulate a few or hundreds of muscle cells
Motor Unit
One neuron & all the skeletal
muscle cells it stimulates
Nerve impulse releases a
neurotransmitter (acetylcholine)
that stimulates skeletal muscle.
Generates an electrical current
called an action potential
The action potential travels from
one end of the cell to the other
causing the muscle to contract.

10. Muscle Contraction Sliding Filament Theory
When signaled by a nerve impulse (release of Calcium ions into muscle fibers), the actin filaments slide toward one another, shortening the sacromeres & causing muscle to contract
Myosin filaments do not move but acts as anchors to help the actin filaments move.

13. Types of Muscle Contractions
Isotonic
Muscles shorten and movement occurs
force generated by a muscle while contracting, when the muscle lengthens and shortens during movement, with the force remaining constant
Isometric
Muscles do NOT shorten
muscle contraction without the muscle or joints moving
push against something that is immovable

15. Muscle Tone
Results from a state of continuous partial contraction of portion of a skeletal muscle
Essential for maintaining posture
Flaccidity is a condition of less then normal tone.
Atrophy is a decrease in size or wasting away of muscle tone
Hypertrophy is an enlargement or overgrowth

16. Building Muscle…Exercise!
Aerobic exercise results in stronger, more flexible muscles with greater resistance to fatigue
Resistance or isometric exercise thickens
fibers by adding more myofibrils
More groups of myosin & actin
Lactic Acid fermentation may occur during rigorous exercise due to low oxygen levels (oxygen debt) in the muscle cells.
Causes a buildup of lactic acid & muscle cramps

17. Producing Movement Muscles produce movement by pulling on bones
Muscles attach to bone at 2 points or more.
The Origin – attached to immovable bone
The Insertion – attached to the movable bone
When a muscle contracts, the insertion moves toward the origin
Work in opposing pairs
One pulls one side of a bone
The other “resets” the motion

19. Naming Skeletal Muscles
Named on the basis of distinctive criteria:
Direction of muscle fibers – rectus or oblique
Relative size – maximus, minimus, or longus
Location – temporalis or frontalis
Number of origins – biceps or triceps
Shape – deltoid (triangular)
Location of origin & insertion – sternocleidomastoid
Action of muscle – flexor, extensor, adductor

20. Muscles Named by Location
frontalis – frontal bone
lateralis – lateral or on the side
tibialis anterior – front of tibia
fibularis longus – near fibula
supra – above
infra – below
sub - underneath

21. Shape: Muscles Named by Shape deltoid – triangle latissimus – wide
teres - round
trapezius – trapezoid
serratus –saw-toothe
orbicularis – circular

22. Muscles Named by Size Size: maximus – largest minimis – smallest
vastus - huge
longus – longest
brevis – short
major – large
minor – small
Example: Pectoralis Major

23. Muscles Named by Direction of Fibers
Direction/Orientation:
rectus (straight) - parallel to the muscle’s long axis
ex: rectus abdominis
transversus (transverse) – at right angles to the muscle’s long axis
oblique – diagonal

24. Muscles Named for Number of Origins
biceps – two origins
ex: biceps brachii
triceps – three origins
ex: triceps brachii
quadriceps – four origins

25. Muscles Named for Origin and Insertion Points
sterno = sternum
cleiodo = clavicle
mastoid = location on the temporal bone
sternocleiodomastoid muscle

26. Muscles Named for Action
flexor carpi radialis – flexes wrist
abductor magnus – abducts the thigh
extensor digitorum – extends the digits
levator – lifts a structure

27. Muscular System Disorders
Fibrosis
Formation of fibrous tissue where it normally does not exist
Frequently occurs in damaged muscle tissue.
Fibrositis
Inflammation of fibrous tissue (ex: lumbago)
Muscular Dystrophy
Hereditary disease of muscles characterized by degeneration of individual muscle cells
Abnormal contractions
Include spasms, cramps, convulsions, & tics

28. Muscular System Disorders
Tonic seizures
involve increased muscle tone or stiffness.
Clonic seizures
rhythmic jerking which involve only one or a few twitches or jerks without any particular rhythm.
Tetanus
a medical condition characterized by a prolonged contraction of skeletal muscle fibers
Tetany
abnormal condition characterized by periodic painful muscular spasms and tremors
caused by decreased calcium, vitamin D deficiency, or alkalosis, or following ingestion of alkaline salts.

29. Muscle and Tendon Injuries
Strains
injuries from overexertion or trauma which involve stretching or tearing of muscle fibers.
often are accompanied by pain and inflammation of the muscle and tendon.
Sprain
the injury near a joint and involves a ligament
Cramps
painful muscle spasms or involuntary twitches.
Stress-induced muscle tension
may cause back pain and headaches.