1. Muscular System
Muscle Contraction

2. Movement requires muscle
Three types: skeletal, smooth, cardiac
Skeletal will be our focus
Long fibrous tissue
Muscle fibers are enclosed in layers of connective tissue

5. From Largest to smallest
Muscle
Bundle of fibers called a fascicle
Muscle fiber (one cell)
Bundle of myofibrils
Filaments arranged in sarcomeres
Actin and myosin are the proteins of the myofilament

7. Terms Cytoplasm is called sarcoplasm
Inside the muscle fiber (muscle cell) are myofibrils
They contain 2 proteins: actin and myosin

8. A sarcomere The space from one Z line to the next Z line
Striations (stripes) are caused by the proteins of the myofilament
Sarcomere is the contracting unit of the muscle fiber
Z lines

9. Contraction Contractions means getting smaller
The myofibril can contract because actin and myosin move
This movement is described in the sliding filament theory

11. Sliding Filament Theory
Head of myosin attaches to the actin
This can happen only if calcium is present
Myosin head pulls the actin filament in
Makes the sarcomere shorter

13. Neuromuscular Junction
Connection between a motor neuron and a muscle

14. Neuromuscular Junction
A nerve fibers comes from the brain or spinal cord to the muscle.
The nerve and the muscle do not actually touch
The gap between them is called the synaptic cleft

15. Neuromuscular Junction
At the end of the neuron, many tiny vesicles are present
These vesicles store chemicals called neurotransmitters
The neurotransmitter will go across the gap (synaptic cleft)

16. Neuromuscular Junction
The muscle fiber on the other side of the gap is stimulated by the neurotransmitter
The muscle fiber contracts
The neurotransmitter is called acetylcholine

17. After contraction, relaxation
Acetylcholinesterase (an enzyme) destroys the remaining acetylcholine
Calcium ions are taken away
Without these actions, the muscle would stay contracted

18. Related Conditions Nerve gas works by inhibiting acetylcholinesterase
Breathing muscles cannot relax
Botulism prevents the release of acetylcholine, so muscles cannot contract

19. Related Conditions Rigor mortis Ca++ pumps run out of ATP
Ca++ cannot be removed
continuous contraction
eventually tissues break down

20. Contraction Facts
Threshold stimulus must be reached to cause a contraction
Enough acetylcholine must reach the receptors
All or none response
Either the fiber (and its motor unit) contracts or it doesn’t

21. Contraction Facts
A motor neuron comes from the brain or spinal cord and connects to a group of muscle fibers, called a motor unit. When a motor neuron transmits an impulse, all the fibers in the motor unit contract
(If threshold was reached)

22. Contraction Facts A motor unit exhibits an all or none response
How, then, can some muscle contractions be more forceful than others?
Determined by the number of motor units stimulated

23. Contraction Facts
Where does the energy come from to power muscle contraction?
ATP (adenosine tri-phosphate)
If extra energy is available, it is stored in creatine phosphate
Creatine phosphate is converted to ATP when needed.

24. Origin and Insertion
One end of a skeletal muscle is attached to an immovable end, like an anchor. This is the ORIGIN.
The other end is attached to a movable part, called the INSERTION.

25. Biceps Brachii
Two origins
Insertion

26. Contraction Facts Muscle Twitch cycle of contraction and relaxation
Contraction only lasts a fraction of a second

27. Contraction Facts Tetany is sustained contraction
Lacks even partial relaxation
Tetanus bacteria can cause this
Lockjaw

28. Contraction Facts Muscle cramps ATP depletion dehydration
ion imbalance
massage or stretching increase circulation

29. Which are You? A sprinter or an endurance performer?
Why do some people excel at one, but not the other?
Read the article and find out!

30. Use It or Lose It! Muscle inactivity will lead to weakness and wasting
Aerobic exercise will result in stronger, more flexible muscles with greater resistance to fatigue.
Resistance (isometric) exercise will result in increased size of muscles.

31. Which type should you do?
Resistance: body building; enlarges individual muscle cells.
Aerobic: endurance, increases strength in other systems as well.
YOU NEED BOTH!

32. Contraction Facts Muscle fatigue lack of carbohydrate source (glucose)
Contraction Facts
Muscle fatigue
lack of carbohydrate source (glucose)
lack of ATP to restore membrane potential
lactic acid drops pH which interferes with protein function

33. Oxygen Debt Happens later, while you are resting or sleeping
Body cannot supply muscles with enough oxygen during strenuous exercise
Muscles must switch to anaerobic respiration
This produces lactic acid, which the liver will destroy later
Oxygen debt is the amount of oxygen liver cells need to convert the lactic acid into glucose