1. Chapter 8
Muscular System

2. Introduction
Three types of muscles:
Skeletal
Smooth
Cardiac

3. Structures of Skeletal Muscle
Tissues present in skeletal muscle
Muscle, nervous, connective (including blood)
Skeletal muscle is held in place by layers of fibrous connective tissue called fascia
*fascia covers the muscle

4. Structures of Skeletal Muscle
Fascia extends beyond the end of a skeletal muscle to form a cord like tendon (muscle to bone)
When connective tissues extend beyond the muscle to form a sheet-like structure, it is called an aponeuroses
Attach to bone or to adjacent muscles

5. Structures of Skeletal Muscle
Fascicles are bundles of skeletal muscle fibers
The connective tissue that covers each muscle fiber within a fascicle is the endomysium
*the muscles are enclosed and separated into compartments by epimysium and perimysium (figure 8.1)
*blood vessels and nerves pass through layers

6. Analogy Time!
Pretend you are going to play a joke on someone and give them 100 pencils. The pencils will represent muscle fibers. First you wrap each individual pencil in tissue paper (dense tissue paper of course!). This would be endomysium. Then you take about 10 pencils in a bundle (a fascicle) and wrap them in paper (Perimysium). Then you take all the bundles and wrap them in gift wrap (epimysium). But you are going to mail this joke, so you also have to wrap it in brown paper representing the fascia.

7. Skeletal Muscle Fiber Single muscle fiber
Single cell, thin, elongated, contracts
Sarcoplasm (cytoplasm) contains
Many nuclei and mitochondria
Myofibrils (parallel)

8. Skeletal Muscle Fiber Make note of this! Myofibrils
Fundamental role in contraction
2 kinds of protein filament
Thin – actin
Thick – myosin

9. Skeletal Muscle Fiber What are sarcomeres? (figure 8.3)
Functional units of muscle contractions
1st are light bands of actin filaments which are attached to Z lines.
2nd are A bands which contain myosin filaments - overlap actin filaments.
The segment of a myofibril from one Z line to the next Z line is known as a sarcomere
Myofibrils are sarcomeres joined end to end

10. Skeletal Muscle Fibers
The network of membranous channels in the cytoplasm of muscle fibers is the sarcoplasmic reticulum. A second set of channels is the tranverse tubules which extend inward from the fibers membrane.
These channels activate muscle contraction when the fiber is stimulated.

11. Questions to Answer What is tendinitis?
What causes two of the most common forms of muscular dystrophy?
What causes muscle strain?
What is the difference in a mild form and a severe form?
*Write your answers on a piece of scrap paper

12. Labeling
Part D of “Structure of a Skeletal Muscle”

13. Neuromuscular Junction
Write these notes below “D” on page 58
Motor neurons – neurons that control effectors
Synapse – functional connection between a motor neuron and a skeletal muscle fiber
Muscle fibers and motor neurons not directly connected – a gap between them called synaptic cleft

14. Neuromuscular Junction
Neurotransmitters – chemicals released by the neurons to allow communication with the cells (tell fibers when to move)
Neuromuscular Junction – connection between motor neuron and muscle fiber

15. Neuromuscular Junction
End of Motor Neuron – rich in mitochondria and synaptic vesicles (store neurotransmitters)
Motor end plate – muscle fiber membrane is folded and contains many nuclei and mitochondria
Nerve impulse  end of motor neuron  release neurotransmitters  motor end plate  muscle contraction!

16. Skeletal Muscle Contraction “Sliding Filament Theory”
Roles of Actin and Myosin
Actin - have a binding site for the myosin cross bridges
Myosin - have cross bridges that “pull” actin for contraction
*Part B is answered by notes on page 58

17. Skeletal Muscle Contraction “Sliding Filament Theory”
Use highlighter and Figure 8.8 printout to highlight key steps
The sliding filament model gets its name from the way the sarcomeres shorten
The filaments do not change, they slide past one another
Actin slides toward the center of the sarcomere from both ends

18. Skeletal Muscle Contraction “Sliding Filament Theory”
Acetylcholine (neurotransmitter) and Calcium ions (Ca+)
Nerve impulse  motor neuron  releases acetylcholine  diffuses to muscle fiber  causes muscle impulse  allows diffusion of Ca+ into muscle fiber  binding sites open  muscle contraction begins

19. Skeletal Muscle Contraction “Sliding Filament Theory”
What are cross bridges?
formed when the projecting parts of the myosin filament that will occupy a binding site on the actin filament and pull

20. Skeletal Muscle Contraction “Sliding Filament Theory”
The action of acetylcholine is halted by the enzyme acetylcholinesterase
The enzyme decomposes the neurotransmitter

21. Skeletal Muscle Contraction
Review Handout
Write on own sheet of paper
Will finish in class tomorrow
Worth 20 points

22. Skeletal Muscle Contraction
How does ATP supply energy for muscle contraction?
ATP = stored energy
ADP + P = released energy
What do these equations mean?

23. Skeletal Muscle Contraction
How does creatine phosphate supply energy for muscle contraction?
Stores energy generated by the mitochondria much like ATP
4 to 6 times more abundant than ATP
Energy is transferred to ADP molecules, converting them back to ATP

24. Skeletal Muscle Contraction
What happens when creatine phosphate is exhausted due to heavy work? (think back to Biology)
How is commercially produced creatine used?

25. Skeletal Muscle Contraction
What substance in muscle seems able to store oxygen temporarily?
Myoglobin, a pigment, is synthesized in muscle cells and imparts the reddish-brown color of skeletal muscle tissue
It is able to combine loosely with oxygen, allowing temporary storage
*hemoglobin in red blood cells acts in the same way

26. Skeletal Muscle Contraction
Why is oxygen necessary for muscle contraction?
Cellular respiration of glucose, which supplies the energy needed for a sufficient amount of ATP
Is this process aerobic or anaerobic?

27. Skeletal Muscle Contraction
How does the muscle continue to contract in the absence of oxygen?
Anaerobic respiration
Glucose  pyruvic acid  lactic acid
Yields a much smaller amount of energy than aerobic respiration
Glucose can be synthesized from lactic acid in the liver

28. Skeletal Muscle Contraction
When do you experience oxygen debt?
Lactic acid accumulation in the liver
Oxygen debt =
amt. of oxygen liver cells require to convert lactic acid into glucose + amt. of oxygen muscle cells require to restore ATP and creatine phosphate
*repayment could take several hours
*training can help increase your bodies ability to repay its oxygen debt by increasing glycolytic enzmes, mitochondria, and capillaries

29. Skeletal Muscle Contractions
What is meant by muscle fatigue?
A muscle has lost its ability to contract
What causes it?
Interruption in the blood supply
Accumulation of lactic acid (most likely)
Lowers pH, fibers no longer respond to stimulation
Cramps are likely due to a lack of ATP

30. Skeletal Muscle Contractions
Less than half the energy released by cellular respiration is available for metabolic processes. The rest is lost as heat.

31. Steroids and Athletes Read “Topic of Interest” page 186
Class discussion on use of steroids and creatine