0. Muscular System Overview

1. Types of Muscle Skeletal – striated & voluntary
Smooth – non-striated & involuntary
Cardiac – striated & involuntary

3. Muscles and Muscle Fiber Structure
Muscles are composed of many fibers that are arranged in bundles called FASCICLES
Individual muscles are separated by FASCIA, which also forms tendons and ligaments.

4. Muscle Layers: Epimysium, Perimysium, and Endomysium

6. ENERGY Fibers contain multiple mitochondria for energy
Most fibers have multiple nuclei

7. SARCOLEMMA Sarcolemma = muscle fiber membrane
Sarcoplasm = inner material surrounding fibers  (like cytoplasm)
Myofibrils  = individual muscle fibers  -->  made of myofilaments

8. Myofibril (Muscle fiber or cell)
Contains protein filaments
       – ACTIN (thin) and MYOSIN (thick)
These filaments overlap to form dark and light bands on the muscle fiber
A band = dArk • thick (myosin)
I band = lIght • thIn (actin)
In the middle of each I band are Z lines. A sarcomere is one Z line to the other

9. Structure of a Sarcomere (functional unit of a muscle)
Actin and Myosin filaments are arranged in an overlapping pattern of light (I bands) and dark (A bands).
In the middle of each I band is a line called a Z line.
The section of a myofibril from one Z line to the next Z line is the Sarcomere.
*The arrangement of these sarcomeres next to each other produces the striations of the skeletal muscle fibers.
Note: Each Myofibril is surrounded by a network of channels called Sarcoplasmic Reticulum. Transverse tubules pass through the fibers.

13. It is important to remember the heirarchy
myosin
myofibrils
fasicles
myofilaments
actin

14. It is important to remember the heirarchy
fasicles
myofibrils
myofilaments
actin
myosin

15. muscle fiber
myofilament
myofibrils
epimysium
muscle
sarcomere

16. myofilament
muscle
sarcomere
epimysium
myofibrils
muscle fiber

18. Muscles & the Nervous System
NEUROMUSCULAR JUNCTION - where a NERVE FIBER and muscle fiber come together. A.K.A. Myoneural junction.
MOTOR NEURON ENDINGS - nerve fiber caries the impulse that stimulates the muscle fibers
MOTOR END PLATE - specialized part of muscle fiber membrane (sarcolemma) located at the neuromuscular junction, has many folds
SYNAPTIC CLEFT - An actual "gap" or cleft which exits between the motor neuron endings and the motor end plate.
SYNAPTIC VESICLES - numerous vesicles in motor neuron endings, where neurotransmitters are stored before being released into the synaptic cleft.
NEUROTRANSMITTER - substance that is released from nerve endings into synaptic cleft. Stimulates an impulse. In this case, a "muscle impulse". One of the major neurotransmitters is ACETYLCHOLINE. This brings about muscle contractions. ACETYLCHOLINESTERASE is an enzyme that breaks down acetylcholine

20. Motor Unit or Neuromuscular Junction
1.  Neuron         2.  Sarcolemma   (or motor end plate)       
3.  Vesicle      4.  Synapse        5.  Mitochondria

21. Events in a Muscle Contraction
A nerve impulse stimulates the release of a neurotransmitter (acetylcholine) from synaptic vesicles into the synaptic cleft.
The impulse spreads across the sarcolemma and into the fiber. This impulse causes an increase in the permeability to calcium ions. The S.R. has a high conc. of Ca++.
Calcium ions diffuse into the sarcoplasm. The Ca++ causes the formation of "cross bridges" between the actin and myosin filaments.
The filaments slide between each other, and this shortens the myofibrils, which in turn shorten the muscle fibers, which shortens the muscle.
A "Calcium Pump" returns the CA++ into the S.R. (requires energy- ATP)
The enzyme Acetylcholinesterase stops the action of Acetylcholine

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

23. Motor Unit
The muscle fiber  and  the motor neuron 

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. The sliding filament theory involves five different molecules plus calcium ions.
The five molecules are:
myosin
actin
tropomyosin
troponin
ATP

28. ANIMATION OF SLIDING FILAMENT

29. Energy Source Provided by ATP from cellular respiration (mitochondria)
Creatine phosphate increases regeneration of ATP
Much of the energy forms heat, which keeps our bodies warm

31. 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

32. 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

33. 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

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

35. 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, during exercise you may not have enough oxygen    -->  this causes Lactic Acid to accumulate in the muscles
                                          

36. Origin and Insertion Origin = the immovable end of the muscle
Insertion = the movable end of the muscle
   **when a muscle contracts the insertion is moved toward the origin
The biceps brachii has two origins (or two heads).

37. 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.

38. 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.