1. MUSCULAR SYSTEM
CHAPTER 8

2. Muscles 3 types: Skeletal Smooth Cardiac
We will concentrate mostly on this one.
Smooth
Cardiac
All three are composed of more than just muscle tissue.
Example: Skeletal muscles are composed of skeletal muscle tissue, nervous tissue, blood, and connective tissue.

3. Structure of Skeletal Muscles
Why has it been hard to see some of the muscles within the cats?
They are covered with connective tissue.
There is loose connective tissue and the other type.
FASCIA - connective tissue that covers muscles.
Has two purposes:
separates individual muscles from adjacent muscles
hold muscles in position.
How does it hold muscles in position?
2 ways

4. Structure of Skeletal Muscles
TENDONS - connective tissue that connects muscles to the bone.
It is an area beyond the end of the muscle where the fascia gets very dense and compact.
APONEUROSES - associated with sheet-like muscles, connects muscle to muscle.

5. Structure of Skeletal Muscles
Muscles have multiple layers
Cylinders within cylinders
Levels of muscles, big to small:
Muscle  fascicle  muscle fiber  myofibril  filaments (page 178)
Each level of a muscle is enclosed in a layer of connective tissue
Epimysium – covers entire muscle
Perimysium – separates muscle into fascicles
Endomysium – separates fascicles into muscle fibers

6. Skeletal Muscle Fibers
What is the purpose of all the levels?
Help with contraction, all of them can work together
Skeletal muscle fiber – individual cell that contracts in response to stimulation.
Each one is a thin, elongated cylinder with rounded ends
These have different names for the cell membrane and cytoplasm
Cell membrane = sarcolemma
Cytoplasm = sarcoplasm

7. Skeletal Muscle Fibers
The sarcoplasm contains numerous threadlike myofibrils that lie parallel to one another.
Myofibrils are involved in muscle contraction.
Myofibrils contain two kinds of protein filaments.

8. Skeletal Muscle Fibers
Myosin Filaments - The “thick” filaments that are composed of protein.
Actin Filaments – The “thin” filaments that are composed of protein
What effect do these have on the appereance of muscle tissue?
The arrangement of these filaments is the reason for the striations that we see with skeletal muscles.

9. Skeletal Muscle Fibers
Striation pattern parts:
I band (light bands) – where only actin filaments are. Where they meet is known as the Z line.
A bands (dark bands) – where the thick myosin filaments are overlapping with thin actin filaments.
Usually thicker bands
H zone is in the middle
From Z line to Z line is one sarcomere.

10. Structure of Skeletal Muscle
Sarcoplasmic reticulum - network channels that run parallel to each myofibril
Transverse tubules – tubes that extend inward and pass through the fiber.
What would these be used for?
Activate muscle contraction when the fiber is stimulated.

11. Muscle activation How are muscles activated to contract?
The neuromuscular junction
Each skeletal muscle fiber is connected to an extension of a motor neuron.
The nerve fiber and the muscle meet at the neuromuscular junction.

12. Neuromuscular Junction
There is a tiny gap between the neuron and the muscle called the synaptic cleft.
How does the nerve actually stimulate the muscle with a gap there?
The neuron contains many tiny vesicles (synaptic vesicles) that store chemicals called neurotransmitters.

13. Neuromuscular Junction
When the nerve receives and impulse, the neuron releases the neurotransmitter into the synaptic cleft.
What will this cause?
Binds with a channel protein, allowing Ca+ to pass through, it is then able to enter the muscle fiber
This action stimulates the muscle fiber to contract.

14. Motor Units Does each nerve only control one muscle fiber?
NO, we have motor units.
A motor unit consists of a motor neuron and all of the muscle fibers it controls.
The number of muscle fibers in a motor unit varies considerably.
Why would that be?
The fewer muscle fibers in the motor units, the finer the movement.

15. Skeletal Muscle Contraction
Myosin has protein strands with globular parts called cross-bridges projecting outward along their length.
Think about your arm while flexing your bicep
Actin molecules, arranged together in a double twisted strand, form an actin filament.
Tropomyosin & troponin are the two proteins associated with actin filaments.

16. Skeletal Muscle Contraction
The sliding filament theory is the most widely accepted theory on how muscle contraction works.
It says that the head of a myosin cross-bridge can attach to an actin binding site and bend slightly
What will this cause?
The actin to move (or slide) with it
The head can then release, straighten itself, and combine with another binding site farther down the actin filament.
Example, arms with a meter stick
This can happen several times causing the muscle fiber to shorten dramatically

17. Skeletal Muscle Contraction
All of this binding and changing of shape will take energy, where will it come from?
ATP
The enzyme ATPase causes the breakdown of ATP to supply energy for these actions.
Acetylcholine (ACh) is a neurotransmitter that is synthesized in the cytoplasm of the motor neuron and is stored in vesicles.

18. Muscular Responses How does a muscle respond to activation?
The stimulus increases until it reaches the threshold stimulus
Threshold stimulus is the minimum strength of stimulus required to cause a contraction.
Once stimulated the muscle will respond completely. There is no partial contraction.
This is called an All-or-None Response.

19. Steps to muscle contraction
1. Nerve impulse arrives at the neuromuscular junction
2. Acetylcholine diffuses across the gap at the neuromuscular junction
3. T Tubules carry acetlycholine to sarcoplasmic reticulum, which causes cell membrane to permeable to Ca2+
4. Ca2+ binds to troponin

20. Steps to muscle contraction
5. Conformation shift - troponin pulls tropomyosin off active binding sites
6. One ATP per myosin Head releases and activates myosin
7. Actin and myosin filaments form linkages
8. Myosin cross-bridges pull actin filaments inward
9. Muscle fiber shortens and contracts

21. Isotonic and Isometric
Isotonic contractions
Contractions that shorten the muscle.
Isometric contractions
Tension in the muscle but no change in length.

22. Muscle Relaxing What happens when a muscle needs to relax?
When a muscle relaxes, the Ach is rapidly decomposed by action of an enzyme called acetylcholinesterase. (Ach-ase)
What was Ach used for in the first place?
This enzyme is present at the neuromuscular junction in the membranes of the motor end plate.

23. Muscle Relaxing
The Ach-ase stops a single nerve impulse from continuously stimulating the muscle fiber.
As this ceases, the calcium pump quickly moves calcium ions back into the sarcoplasmic reticulum.
What does this do?
The linkages will break
the troponin and tropomyosin return to the normal conformation, blocking the binding sites.
The muscle fiber relaxes.

24. Muscle Fatigue
Muscle fatigue most often occurs from an accumulation of lactic acid.
What is this caused by?
Anaerobic respiration
An interruption of the blood supply or the lack of ACh can also cause fatigue.
Muscle fatigue can cause the muscle to cramp.

25. Muscle Cramps
Cramps occur when the muscle contracts spasmodically, but does not relax completely.
The condition is due to a lack of ATP needed to move calcium or other ions, can also be caused by a lack of those ions
Why would there be a lack of ATP?
Anaerobic respiration does not produce much ATP.
Exercise stimulates new capillaries to grow within the muscles and it also causes an increase in the number of mitochondria.

26. Fast and Slow Muscles
There are two types of muscles relating to the speed of contraction.
Fast and Slow
The speed of contraction is related to the specialized function of a muscle.
Example: Eye muscles that blink are ten times faster than the muscles involved in posture.

27. Fast and Slow Muscles Slow-contracting (slow twitch) muscles
Often called red muscles
Why?
Most of their fibers contain red, oxygen-storing myoglobin.
Well supplied with blood.
Have a high respiratory capacity. They generate enough ATP to keep up with the activities. (which means they have a lot of what?)

28. Fast and Slow Muscles Fast-contracting (fast twitch) muscles
Also called white muscles.
Why?
They contain less myoglobin and have a poorer blood supply than red muscles.
White muscles contains fewer mitochondria which reduces the respiratory capacity.

29. Fast and Slow Muscles
What makes white fibers able to contract quicker?
White Fibers have more extensive sarcoplasmic reticulum.
Why does this help?
Most skeletal muscles contain both types of fibers.
Research has discovered an intermediate fiber.

30. Assignment Due Friday Pg. 210 Review Ex. #2,8,12,15,
Critical thinking #3

31. DIDN’T USE
ANY SLIDES AFTER THIS POINT, I DID NOT USE, BUT KEPT IN CASE I WANTED TO.

32. Skeletal Muscle Contraction
In the presence of calcium ions, the myosin cross-bridges react with actin filaments and form linkages with them.
This reaction between the myosin and actin filaments provides the force that shortens myofibrils during muscle contraction.

33. Skeletal Muscle Contraction
Actin accounts for about 1/4 of the total protein in skeletal muscle.
Actin molecules, arranged together in a double twisted strand, form an actin filament.
Tropomyosin & troponin are two proteins associated with actin filaments.

34. Skeletal Muscle Contraction
The tropomyosin-troponin complex blocks the binding sites on the actin molecules when the muscle is at rest.
If a high concentration of calcium ions is present, the calcium ions bind to the troponin, and this modifies the position of the tropomyosin.

35. Skeletal Muscle Contraction
The tropomyosin molecules move, exposing the binding sites on the actin filaments, and the linkages form between the actin and myosin filaments.

36. Skeletal Muscle Contraction
The sliding filament theory of muscle contraction suggests that the head of a myosin cross-bridge can attach to an actin binding site and bend slightly, pulling the actin filament with it.
Then the head can release, straighten itself, and combine with another binding site farther down the actin filament.

37. Skeletal Muscle Contraction
The enzyme ATPase causes the breakdown of ATP to supply energy for these actions.

38. Stimulus for Contraction
Acetylcholine (ACh) is a neurotransmitter that is synthesized in the cytoplasm of the motor neuron and is stored in vesicles.
A nerve impulse reaches the end of the axon, some of these vesicles release ACh into the gap between the nerve and the motor end plate.

39. Stimulus for Contraction
The ACh diffuses rapidly across the gap, combines with certain protein molecules in the sarcolemma, and thus stimulates the muscle fiber membrane.
This stimulus causes a muscle impulse that passes in all directions over the surface of the sarcolemma.

40. Stimulus for Contraction
It also travels through the sarcoplasmic reticulum and the transverse tubules.
The sarcoplasmic reticulum contains a high concentration of calcium ions compared to the sarcoplasm.

41. Stimulus for Contraction
In response to a muscle impulse, the membranes of the cisternae become more permeable to these ions and the calcium ions diffuse into the sarcoplasm of the muscle fiber.

42. Stimulus for Contraction
When a relatively high concentration of calcium ions is present in the sarcoplasm, linkages form between the actin and myosin filaments, and a muscle contracts.

43. Energy Sources of Contraction
The energy for muscle contractions comes from ATP.
The muscle has enough ATP to contract briefly. Therefore, when a fiber is active, ATP must be regenerated.
Creatine phosphate supplies the energy to change ADP back to energy rich ATP

44. Oxygen Supply and Cellular Respiration
Oxygen is transported by the red blood cells. It is loosely bound to molecules of hemoglobin.
The hemoglobin releases the oxygen in areas of the body that are low in oxygen content

45. Oxygen Supply and Cellular Respiration
Myoglobin, in the muscle cells, can store oxygen temporarily.
This reduces a muscle’s need for a continuous blood supply during a contraction.

46. Oxygen Debt
During strenuous exercise, the available oxygen supply may be used up. The body then relies on anaerobic respiration creating an oxygen debt.
Anaerobic respiration builds up lactic acid. The liver converts lactic acid back to glucose, but it takes several hours to complete the conversion.

47. Heat Production
Since muscle tissue represents a large proportion of the total body mass, it is a major source of heat.
About 25% of the energy released in cellular respiration is available for use in metabolic processes.

48. Heat Production Active muscles release large amounts of heat.
Blood transports this heat to other tissues to help maintain body temperature.

49. Smooth Muscle Smooth muscle characteristics:
Shorter than the fibers of skeletal muscle.
Single, central nucleus.
Cells are elongated with tapering ends.
Filaments are more randomly arranged than skeletal muscle.

50. Smooth Muscle
The two types of smooth muscle are multiunit and visceral.
Multiunit muscles are less organized and occur as separate fibers.
Multiunit are found in the irises of the eyes and walls of blood vessels.
They contract through motor nerve impulse or hormone action.

51. Smooth Muscle
Visceral smooth muscle is composed of sheets of spindle shaped cells held together by gap junctions.
Visceral smooth muscles are found in walls of hollow organs (ex. Stomach, intestines)
There usually will be two muscle layers, a longitudinal and a circular layer.

52. Smooth Muscle
When one fiber is stimulated, the impulse will also excite adjacent cells causing a rhythmic contraction.
Peristalsis - wavelike contraction that occurs in tubular organs.

53. Smooth Muscle Contraction
Smooth muscle contraction is similar to skeletal muscle contraction.
Smooth muscle lacks troponin. Instead it uses a protein called calmodulin to bind calcium ions.
Calcium diffuses into the cell from the extracellular fluid.

54. Smooth Muscle Contraction
Smooth muscle reacts to the neurotransmitter ACh and norepinephrine.
Some hormones cause smooth muscle contraction. (Ex. Childbirth)
Stretching smooth muscle can cause contractions. (Ex. Digesting food in the stomach)

55. Smooth Muscle Contraction
Smooth muscle is slower to contract and slower to relax.
Smooth muscle can contract for a longer time with the same amount of ATP.
Smooth muscles stretch without changing tautness while a hollow organ fills.

56. Cardiac Muscle Found only in the heart.
Striated cells joined end to end forming interconnecting branched three-dimensional network.
Each cell contains a single nucleus.
Well developed sarcoplasmic reticulum and transverse tubules.

57. Cardiac Muscle
Sarcoplasmic reticulum stores less calcium but the enlarged transverse tubules store extra calcium.
The extra calcium allows cardiac muscle to maintain a contraction longer than skeletal muscles.

58. Cardiac Muscle
Intercalated disks separate opposing ends of cardiac cells.
The disks help hold adjacent cells together and transmit the force of contraction from cell to cell.

59. Cardiac Muscle
When one portion of the cardiac network is stimulated, the impulse passes throughout the network causing the whole structure to contract as a unit.

60. Muscle Action The main muscle is the prime mover.
Muscles that contract along with the prime mover are called synergists.
Muscles opposing the prime mover are called antagonists.