1. Muscles
The movers in our body
Mrs. Sheila Taylor

2. What are muscles?
Specialized cells that use chemical energy to contract.
This contraction helps propel fluid and foods, make the heart beat, distribute heat, and of course make us move
Three major types of muscle
Skeletal
Smooth
Cardiac

4. Skeletal muscle structure
Composed of
Connective tissue
Muscle fibers
Neuromuscular junctions
Motor units

5. The connective tissue covering
Fascia – layers of fibrous connective tissue
Separates the individual muscle
Holds the muscle in place
two ways of attachment
Fibers project off the ends of the muscle creating cords called tendons, which intertwines with the periosteum
Broad fibrous sheets called aponeuroses that can attach to either bone or other muscle facia
Inner layer of tissue is called the epimysium

6. Coverings continued
Perimysium extends into the muscle from the epimysium
separates the muscle into small compartments with little bundles of muscle fibers in them
Fiber bundles are called fascicles
Each fiber in the fascicle lies in the endomysium, a thin connective tissue covering
This arrangement allows for some independent movement in the parts of the muscle and for a pathway for blood vessels and nerves to travel into the muscle

7. Skeletal Muscle Fibers
A single cell
Contracts when stimulated, and relaxes when the stimulus ends
Are thin, elongated with rounded ends, can extend the full length of the muscle
Sacrolemma is the cell membrane
Sarcoplasma is the cell cytoplasm
Has many small oval nuclei and mitochondria
Contains lots of myofibril
Actin (thin myofibril) and myosin (thick myofibril)
Lie parallel to each other
Responsible for the striated appearance of the muscle

9. Striations indepth Two main parts
I bands – light bands
Consist of actin attached to the Z lines
A bands – dark bands
Myosin filaments are overlapping the actin filaments
the H zone is the area where there is only myosin
The M line is where a protein holds the myosin in place
In the center of the H zone
The area between two Z lines is called a sarcomere
Where muscles really contract

11. A few more bits and pieces
Sarcoplasmic reticulum
Network of membranous channels that surrounds and runs parallel to the myofibril
Transverse tubules (T tubules)
Extend inward from the sarcolemma and passes to the other side
Filled with extracellular fluid
Goes between the cisternae of the sarcoplasmic reticulum
It lies on the A band
These two activate the contraction

13. Neuromuscular Junction
Each skeletal muscle fiber has its own connection with a motor neuron
This is called a neuromuscular junction
Muscle side is called a motor end plate
Plenty of nuclei and mitochondria
Sarcolemma is extensively folded
End of the nerve branches and projects into the recesses of the nerve fiber
Lots of mitochondria and vesicle filled with neurotransmitters
Neurotransmitters are released to travel to the muscle when a stimulus is received

15. Motor Unit The motor neuron has a highly branched axon
One nerve can connect to many muscle fibers
One nerve impulse equals many fibers contracting
The motor neuron and the muscle fibers are called a motor unit

17. Skeletal muscle contraction
Myosin
The molecule
Made of two twisted protein strands
Has cross bridges which are globular parts that extend outward
The filament has many molecules together
Actin
A globular structure with binding sites for the cross bridges
The filament
Many actin molecules twist together into a double helix
Troponin and tropomyosin are two proteins that wrap around the molecule chain

19. Sliding filament model
A complex action of molecules that cause actin and myosin to slide past one another, shortening the the muscle.
The myosin cross bridges attach to the binding the sites on the actin
They then bend slightly, pulling the actin filaments together
They then release and attach to another binding site and pull some more
ATP is broke down to give energy to the myosin so that it can attach to the actin another is used to release it

21. Stimulus for contraction
Nothing happens until the motor neuron is stimulated and release acetylcholine
Acetylcholine stimulates a muscle impulse which travels in all directions across the nerve fiber membrane and the T-tubules until finally reaching the sarcoplasm reticulum
Sarcoplasmic reticulum release Ca ions from the cisternae
The Ca cause troponin and tropomyosin to expose the binding sites to the myosin

23. Oxygen and muscles Myoglobin Oxygen debt
A pigment whose job is to hold onto oxygen, temporarily storing it for the muscle
Oxygen debt
If the muscle exceeds the amount of oxygen available it will uses lactic acid fermentation to get energy, this creates lactic acid
The amount of O needed to convert lactic acid back to glucose, and the amount needed to restore ATP and creatine phosphate to original amount is the debt

24. Muscle fatigue The lose of a muscles ability to contract
Possible causes
Interruption or lack of blood supply
Lack of acetylcholine
Accumulation of lactic acid (most common case)
Lowers pH so the the fiber no longer responds to the stimulus
Cramps
A sustained involuntary contraction
Both fatigue and cramps can happen at the same time

25. Heat production Skeletal muscles are responsible for our body heat
Less than half of the energy released from glucose become usable energy, the rest is heat

26. Muscle responses Threshold stimulus All-or-none response
The amount of stimulus needed for a muscle fiber to react
All-or-none response
Once it receives a threshold stimulus the fiber contracts to its fullest ability
How much the fibers shortens depends on the amount of resistance

27. A picture of a contraction
Myogram
The pattern drawn during a muscle contraction
Twitch
A single contraction that last a fraction of a second
Three zones of a myogram
Latent period – the time between the stimulation and the actual contraction
Period of contraction – when the muscle pulls at its attachment
Period of relaxation – when the muscle fibers returns to formal length

29. Two types of twitches Fast twitch Slow twitch
Fibers that are for quick strength
Glycolytic therefore easily fatigable
When using forceful exercise regularly, they will make more actin and myosin.
Slow twitch
Fibers that are used for endurance
Highly oxidative therefore fatigue resistant
When used extensively, make more mitochondria and capillary networks
Skeletal muscles are about 50% each

30. The diagram shows the structure of the muscles
The diagram shows the structure of the muscles. The inset picture (brown colored) shows you the fast and slow twitch fibers. Lighter = fast twitch / darker = slow twitch.

31. Summation
A fiber exposed to a series of stimuli eventually can only partially relax before the next stimulus
The force of the individual twitches combine
This is called summation
A tetanic contraction is a type of summation that lacks even a partially relaxation.
AKA tetanus

33. Recruiting help Muscles have many motor units
The motor units have different thresholds so they respond to different intensity of stimulation
The finer, smaller, units have a lower threshold
The larger, thicker, units have a higher one
As the increase of stimulation increase more motor units are recruited to do the job
This is recruitment
When all muscle fibers are recruited the muscle contracts at its maximal tension

35. Sustained contraction
Both summation and recruitment work together to create a sustained contraction
This is when the muscle actually works.
Muscle tone
The muscles are actually always in some level of sustained contraction
Helps to maintain posture
When lost the body collapses

36. Smooth Muscles Muscle cells Two main types Elongated and tapered ends
Have actin and myosin, but randomly arranged and organized differently , so no striations
Two main types
Multiunit smooth muscle
Visceral smooth muscle

37. Multiunit Smooth muscles
Muscle fibers are separate
Contracts only in response to a motor nerve impulse or a certain hormone
Found in the iris or walls of blood vessels

38. Visceral Smooth Muscles
Sheets of spindle shaped cells
The fibers of the muscle can stimulate each other
Once one is stimulate the stimulus can travel to the adjacent cells
This causes a rhythmicity
A pattern of repeated contraction
Cause wave like motion called peristalsis
Found in the walls of the hollow organs

40. Smooth muscle contraction
Similar to the skeletal contraction
Actin and myosin are in both
Differences
Has two Neurotransmitters
Acetylcholine and norepinepherine
Stimulates and inhibits contractions in different smooth muscle
Reacts to a number of hormones
Starts or inhibits contractions
Contracts and relaxes slower but maintains a forceful contraction longer
Can change length without sacrificing tauntness

41. Cardiac Muscle Found only in the heart
Straited and interconnected cells
Connection are three dimensional networks
Intercalated disc connect the opposing ends of the cells
Form elaborate junctions
Allows impulses to travel freely

43. Cardiac Contraction Similar to the skeletal muscle Difference
Actin and myosin creates the striations
Difference
Cisternae are smaller but the t-tubules are large, and both release Ca ions
Make for longer muscle twitches
Muscle fibers highly conductive
One member of the network is stimulates, all are – all or none response network wide
Self exciting and rythmic

44. Skeletal muscle actions
Depends on the kind of joint and the way the muscles are attached on either side of it
Attachment of the muscle
Origin – the end of the muscle attached to a relatively fixed or immovable part of the joint
Can have more than one
Head of the muscle is closest to the origin
Insertion – the end that attaches at the movable part on the other side of the joint

46. How they work together
A movement calls for more than one muscle to work
The main muscle working is the prime mover aka agonist
The muscles that help the prime mover are called the synergists
They hold the other area steady, or move them into a optimal position
The antagonists are the muscles that would move the joint in the opposite direction
They must relax so the agonist can work