1. Muscle Tissue

2. Muscle tissue is highly specialized to convert chemical energy into kinetic energy
Your movements occur through the coordinated contracting and relaxing of many muscles
When muscles contract (shorten) it causes a part of the body to move

3. There are 3 types of muscle cells
Skeletal
Smooth
Cardiac
Food moves through the intestines due to peristalsis of the smooth muscles
Your heart beats because of cardiac muscles
And your body moves because skeletal muscles pull on your bones

4. 3 Basic Muscle Types

5. The cells of smooth muscle tissue are long and tapered at each end and have one nucleus
They are arranged in parallel lines, forming sheets
Are found in the walls of blood vessels, hollow internal organs, and in the iris of the eye
Contraction of these muscles is involuntary (without your control)

6. The smooth muscles contract slower but can remained contracted for an extended amount of time because they don’t fatigue easily

7. The cardiac muscle is unique to the heart and forms the walls
These cells are tubular and have bands of light and dark (striated), and have one nucleus
The muscle cells are branched, creating a netlike structure
Like smooth muscles, cardiac muscles contract involuntary

9. Skeletal muscles are also tubular and striated
the “meat” of our bodies are composed of these muscles
The contraction of these muscles is voluntary and is controlled by the nervous system
The bodies movements is due to over 600 skeletal muscles

11. The skeletal muscles have the following functions:
Supports the body by opposing the force of gravity allowing us to stand upright
Makes our body move
Helps maintain a constant body temperature by releasing heat when using energy
Protects the internal organs and stabilizes the joints

12. Unlike smooth and cardiac muscle cells, skeletal muscles are very long and have many nuclei which maintain the normal functions of these cells
They are usually referred to as fibers rather than cells because of their structure

13. Cooperation When muscles contract, they shorten
This means that muscles can only pull
The work of a muscle is done when it contracts and when it relaxes it is in a passive state
Muscles that allow motion come in pairs
For the action of each muscle, there is another muscle that does the opposite action

15. Bundles of Fibers
Each muscle in the body lies along the length of a bone
A tough, heavy band of tissue, called a tendon, attaches each end of a muscle to a different bone
The long skeletal muscle fibers can be up to 20 cm in length
Muscle fibers are organized into many larger bundles

17. A muscle then consists of clusters of these bundles of muscle fibers
A layer of connective tissue wraps around each fiber
Another layer wraps around each bundle and another around the whole muscle itself
Blood vessels and nerves run between the bundles of muscle fibers

19. The blood provides the fibers with nutrients and oxygen required to power the contractions as well as removes cellular wastes
The nerves trigger and control muscle contractions
Most of the volume of a muscle fiber consists of many subunits called myofibrils
And each myofibril is made of even finer myofilaments

22. Muscle Contractions

23. Muscle contractions involve the coordinated action of the two types of myofilaments, actin and myosin
A thin actin myofilament consists of two strands of protein molecules that are wrapped around each other

24. A thick myosin myofilament also consists of two strands of protein molecules wound around each other but is about 10 times longer

25. When a myofilament contracts, the heads of the myosin move first
Like flexing your hand at the wrist, the heads bend backward and inward
This moves them closer to their rod-like “backbone” and a bit in the direction of the flex
Because the heads are attached at this time to an actin myofilament, the actin is pulled along with the myosin heads

27. As each myosin head flexes one after the other, the myosin walks along the actin
Each step requires ATP to provide energy that repositions the myosin head before each flex

28. The sliding of actin past the myosin is part of the sliding filament model of the muscle contraction
The actin is anchored at one end of each myofilament at a position in the muscle tissue called the Z line
Because the actin is anchored like this, its movement pulls the Z line along with it

30. As the Z lines are pulled closer together, the plasma membranes to which they are attached to cause the entire muscle fiber to contract

31. Aerobic Cellular Respiration
Aerobic cellular respiration provides most of a muscle’s ATP
The muscle fibers use glucose from fats and oxygen to produce ATP
The other products are carbon dioxide, water and heat
CO2 leaves the body at the lungs, water is absorbed, and the heat warms the body

32. About 2/3 of the heat that maintains a constant body temperature comes from the aerobic cellular respiration of the skeletal muscles throughout the body

33. Role of Calcium
When a muscle is relaxed, its myosin heads are raised and ready but not attached to actin due to another protein called tropomyosin blocking the attachment site
For a muscle to contract the tropomyosin must be moved out of the way

35. Another protein called troponin binds to the tropomyosin to form a complex regulated by calcium concentration
When calcium concentration is low, tropomyosin prevents myosin from binding to actin
When calcium concentration is raised, the complex forms and is shifted away, allowing the binding of myosin and actin

39. Muscles and Health

40. During active use, some muscles are contracting and others relaxing
Even when muscles appear to be at rest, their fibers are always contracting
This continuous low-level activity results in muscle tone
Muscle tone is important for maintaining posture
If all our muscles were to completely relax, our body would collapse

41. In general, the skeletal muscles are subject to fewer disorders compared to other organ systems
However they are vulnerable to injuries that result from sudden and intense stress placed on them and on tendons
Complete the description of the listed muscular system disorders

42. Muscles may also be impaired simply from lack of use, this is referred to as atrophy
Atrophy is a reduction in size, tone, and muscle power
If extreme atrophy occurs, the loss of muscle function is permanent
Exercise is important to strengthen muscles and allow them to use energy more efficiently

43. Create your own set of notes for slow-twitch fibers and fast-twitch fibers