1. Muscular System

2. Types of Muscle Skeletal – striated & voluntary Smooth – involuntary
Cardiac - heart
The word “striated” means striped. Skeletal muscle appears striped under a microscope.

3. Pathology Connection: Strains and Tears
Strains caused by overstretching tendons or muscles
Severity of injury can range from mild to severe
Mild: pulled muscle (slight overstretch of muscle)
Severe: complete muscle tear or complete tendon rupture

4. Pathology Connection: Strains and Tears (cont’d)
Injuries can be acute or chronic
Acute: usually resulting from trauma
Chronic: usually resulting from overuse or disease
Signs and symptoms: vary depending on severity of injury
Mild strain (no tear of muscle or tendon fibers): mild pain and possibly stiffness
Moderate strain (some tearing of muscle or tendon fibers): more intense pain, bruising, obvious weakness
Severe strain (complete tear of muscle or tendon): severe pain, swelling, extensive bruising, and often complete loss of movement

5. Pathology Connection: Strains and Tears (cont’d)
Treatment: varies with severity of injury
Strains
In first 72 hours, PRICE therapy: Protection, Rest, Ice, Compression, Elevation
After first 72 hours: gradual increase in activity and/or physical therapy, application of heat
Pain relievers (like acetaminophen or ibuprofen)

6. Muscles and Muscle Fiber Structure
Muscles are composed of many FIBERS that are arranged in bundles called FASCICLES

7. Individual muscles are separated by FASCIA, which also forms tendons

8. EPIMYSIUM = outermost layer, surrounds entire muscle.
PERIMYSIUM = separates and surrounds fascicles (bundles of muscle fibers)
ENDOMYSIUM = surrounds each individual muscle fiber
This model of the muscles uses straws to represent fibers.
Green = endomysium Yellow = perimysium Blue = epimysium

9. Muscle Layers
Muscle Fiber
Endomysium
Perimysium
Epimysium

10. Epimysium
Perimysium
Endomysium

11. Muscles / Cells Sarcolemma = muscle fiber membrane
Sarcoplasm = inner material surrounding fibers  (like cytoplasm)
Sarcoplasmic Reticulum – transport, store, and release calcium ions in the muscle cell.
Myofibrils  = individual muscle fibers,  made of myofilaments

12. Functional unit of the Muscle
Each muscle cell is elongated fiber known as muscle fiber, can be up to 12 inches in length
Several muscle fibers can be bundled together to form specific muscle segment
Each muscle fiber composed of several myofibrils

13. Nucleus
Sarcolemma
Mitochondrion
Sarcoplasm
Myofibril

14. Myofibrils are made of
ACTIN = thin filaments
MYOSIN = thick filaments

15. Functional Unit of the Muscle
Sarcomeres: functional contractile units of each fiber
Each has two types of threadlike structures called thick and thin myofilaments
Thick myofilaments made up of protein myosin
Thin myofilaments made up of protein actin
ACTIN = thin filaments
MYOSIN = thick filaments

16. Myofilaments ACTIN (thin) and MYOSIN (thick)
  form dark and light bands
A band = dArk • thick (myosin)
I band = lIght • thIn (actin)

17. Sarcomeres: functional contractile units of each fiber
Sarcomere has actin and myosin filaments arranged in repeating units separated from each other by dark bands called Z lines which give striated appearance to skeletal muscle
Z lines are borders of each sarcomere

21. It is important to remember the hierarchy
fasicles
myofibrils
myofilaments
actin
myosin

22. How Muscles Work with the Nervous System

23. The neurotransmitter that cross the gap is ACETYLCHOLINE
ACH is broken down by CHOLINESTERASE

24. The neurotransmitter that crosses the gap is ACETYLCHOLINE.
This is what activates the muscle.
Acetylcholine is stored in vesicles

25. SLIDING FILAMENT THEORY (MODEL)
The theory of how muscle contracts is the sliding filament theory. The contraction of a muscle occurs as the thin filament slide past the thick filaments.
What is needed:
ATP
Calcium
Myosin & Actin
Acetylcholine
Cholinesterase

26. Contraction of muscle causes two types of myofilaments to slide toward each other and shorten each sarcomere, and therefore entire muscle
Muscle contraction requires temporary connections of cross-bridges formed between myosin head and actin; these pull sarcomere together

27. ATP and Calcium
Energy needed for contraction and relaxation; comes from adenosine triphosphate (ATP), which help myosin heads form and break cross-bridges with actin
Calcium stored away from actin and myosin in sarcoplasmic reticulum (SR) during relaxation of muscle
During contraction, calcium released from SR and causes actin, myosin, and ATP to interact, which causes contraction; when calcium leaves muscle and returns to SR, cross-bridge attachments are broken and muscle relaxes

28. When nervous system tells muscle to contract, signal causes muscle fiber to open sodium ion channels
Sodium ions flow into muscle fiber, exciting it
When muscle becomes excited, calcium released from SR
It is calcium that causes muscles to contract
Calcium is then pumped back into SR

29. Sliding Filament Handout
(additional)

31. Energy Source -ATP is produced by CELLULAR RESPIRATION
which occurs in the mitochondria
-Creatine phosphate increases regeneration of ATP
* Only 25% of energy produced during cellular respiration is used in metabolic processes - the rest is in the form of HEAT.
maintains body temperature.

32. Other Terms 1. Threshold Stimulus 2. All-or-None Response
3. Motor Unit
5. Recruitment
6. Muscle Tone
7. Muscular Hypertrophy
8. Muscular Atrophy
9. Muscle Fatigue
10. Muscle Cramp
11.  Oxygen Debt

33. Threshold Stimulus All-or-None Response
Minimal strength required to cause a contraction 
Motor neuron releases enough acetylcholine to reach threshold
All-or-None Response
Fibers do not contract partially, they either do or don't

34. Motor Unit Recruitment Muscle Tone The muscle fiber + the motor neuron
The muscle fiber  +   the motor neuron 
Recruitment
more and more fibers contract as the intensity of the stimulus increases
Muscle Tone
Sustained contraction of individual fibers, even when muscle is at rest

35. Hypertrophy - muscles enlarge (working out or certain disorders)
Atrophy - muscles become small and weak due to disuse

36. Muscle Cramp - a sustained involuntary contraction
Muscle Fatigue -  muscle loses ability to contract after prolonged exercise or strain
Muscle Cramp  -  a sustained involuntary contraction
Oxygen Debt  -  oxygen is used to create ATP, -- not have enough oxygen  causes Lactic Acid to accumulate in the muscles → Soreness
                                           *See Magic School Bus 

37. 11. Origin and Insertion Origin = the immovable end of the muscle
Insertion = the movable end of the muscle
The biceps brachii has two origins (or two heads).

38. What is rigor mortis?
A few hours after a person or animal dies, the joints of the body stiffen and become locked in place. This stiffening is called rigor mortis. Depending on temperature and other conditions, rigor mortis lasts approximately 72 hours. The phenomenon is caused by the skeletal muscles partially contracting. The muscles are unable to relax, so the joints become fixed in place.

39. What is tetanus?
Tetanus causes cholinosterase to not break down the acetylcholine in the synapse.  This results in a person's muscles contracting and not relaxing.
A tetanus shot must be administered shortly after exposure to the  bacteria.
Once you develop tetanus, there is no cure.