1. Muscular System

2. Overview of muscle tissues
Muscle Types
There are 3 types of muscle tissue
Skeletal
Cardiac
Smooth
All muscles
Have elongated cells
Have cells that are called muscle fibers
Prefixes myo- & mys- (muscle) and sarco- (flesh) refer to muscle.

3. Skeletal muscle Accounts for almost 40% of the body’s total mass.
Skeletal muscle fibers are packaged into skeletal muscle that attach to the skeleton
Skeletal muscle fibers are
Cigar-shaped
Multinucleated
Largest of the muscle fiber types
Some up to 30 cm long

4. Skeletal muscle Also known as striated muscle Voluntary muscle
Appears to be striped
Voluntary muscle
It is under conscious control
Often activated by reflexes
Key words associated with skeletal muscles
Skeletal
Striated
Voluntary

5. What have you learned? Skeletal muscle attaches to
Muscle cells are multinucleated? TRUE or FALSE
Muscle cell are under INVOLUNTARY or VOLUNTARY control ?
Now What?
Complete the color and label pages
BONE

6. Skeletal muscle Skeletal muscle fibers are soft and fragile
Exert tremendous power because of their packaging
Thousands of muscle fibers are bundled by connective tissue called the endomysium
Connective tissue provides strength and support to the muscle
Several bundles of muscle fibers, called fascicles, are wrapped in a fibrous membrane called the perimysium
Many fascicles are bound together by a tougher “overcoat” of connective tissue called the epimysium
The epimysium blends into a strong cord-like tendon, or into a sheet- like aponeuroses
The aponeuroses attaches muscles indirectly to bones, cartilage, or other connective tissue coverings.

7. Skeletal muscle Play IP Anatomy of Skeletal muscles (IP p. 4-6)
epimysium
tendon
perimysium
Muscle Fascicle
Surrounded by perimysium
endomysium
endomysium
Skeletal muscle
Skeletal muscle fiber (cell)
Surrounded by epimysium
Surrounded by endomysium
Play IP Anatomy of Skeletal muscles (IP p. 4-6)

8. Skeletal muscle Tendons Anchor muscle to bone Provide durability
Conserve space
Composed of rough collagen fibers
Allows tendons to pass over rough bony projections instead of muscles

9. Smooth muscle Has no striations Involuntary Location
Cannot consciously control it.
Location
Walls of hollow visceral organs (stomach, urinary bladder, and respiratory passages
Propels substances along a definite tract or passage way within the body

10. Smooth muscle Key words associated with smooth muscle
Visceral
Nonstriated
Involuntary
Smooth muscle cells are
Spindle shaped
Have a single nucleus
Arranged in sheets, or layers
One running longitudinally
One running circularly

11. Smooth muscle
As the two layers alternately contract and relax, they change the size and shape of the organ.
Contraction is slow and sustained

12. Cardiac Muscle Found only in one place Is striated Involuntary control
THE HEART
Serves as a pump, propelling blood into the blood vessels and to all tissues of the body
Is striated
Involuntary control
Key words associated with
cardiac muscle
Cardiac
Striated
Involuntary

13. Cardiac Muscle
Fibers are cushioned by small amounts of soft connective tissue and arranged in spiral shaped bundles
When the heart contracts, its internal chambers become smaller, forcing the blood into the large arteries leaving the heart
Contracts at a fairly steady rate, except when in response to stimuli.

14. Muscle Functions Muscles play four important roles in the body
Produce movement
Maintain posture
Stabilize joints
Generate heat

15. Muscle Functions Producing Movement
Almost all movements of the human body are a result of muscle contraction
Enable us to respond quickly to changes in the external environment
Allow us to have facial expressions
Smooth and cardiac muscle work together to circulate blood and maintain blood pressure
Smooth muscle forces fluid (urine, bile) and other substance (food, a baby) through internal body channels

16. Muscle Functions Maintaining Posture Stabilizing Joints
Skeletal muscles work by making tiny adjustments so that we can maintain an erect or seated posture despite the downward pull of gravity
Stabilizing Joints
Skeletal muscles along with tendons are responsible for stabilizing and reinforcing joints.

17. Muscle Functions Generating Heat
Heat is a by-product of muscle activity
As ATP is used to power muscle contraction, nearly 75% is lost as heat
The heat is vital in maintaining normal body temperature
Skeletal muscle is the muscle type responsible for heat generation

18. Sites of Muscle Attachment
Bones
Cartilage
Connective tissue coverings

19. Microscopic Anatomy of Skeletal Muscle
Many oval nuclei can be seen just below the plasma membrane, the sarcolema, in muscle cells.
The nuclei are pushed aside by long, ribbon-like organelles, the myofibrils, which nearly fill the cytoplasm.

20. Myofibrils have alternating light (I) and dark(A) bands which give the cell its striped appearance.

21. The area between 2 I bands is called a sarcomere
The light I band has a midline interruption, a darker area called the Z disk
The dark A band has a lighter region called the H zone.
The banding pattern shows the working structure of the myofibrils
Myofibrils are chains of sarcomeres that lie end to end
The arrangement of myofilaments within the sarcomeres that produce the banding pattern
Make sure to discuss that myoflimants are what composes myobibrils.

22. Types of myofilaments There are 2 types of myofilaments
Thick-composed of myosin protein
Contain ATPase enzymes that split ATP to generate power for muscle contraction
Extend the entire length of the A band
The center is smooth while the ends are covered with projections, myosin heads, that are sometimes called cross bridges because they link the thick and thin filaments together during muscle contraction.
Thick filaments are also called myosin filaments
Thin filaments are also called actin filaments

23. Types of myofilaments There are 2 types of myofilaments
Thin filaments – composed of actin proteins
Are anchored to the Z disk
The I band contains only actin filaments
The area called the H zone does not have any actin filaments
It is also referred to as the bare zone.

24. Skeletal Muscle Activity
Skeletal muscle has special functional properties
Properties of Muscle
Irritability – ability to receive and respond to a stimulus
Contractibility – ability to shorten when an adequate stimulus is received
Extensibility – ability to lengthen when an adequate stimulus is received
Elasticity – ability to return to normal shape

25. The Nerve Stimulus & Action Potential
Skeletal muscle cells must be stimulated by nerve impulses to contract
One motor neuron (nerve cell) may stimulate a few muscle cells or hundreds
One neuron and all the skeletal muscle cells it stimulates are called motor units
The number of muscle cells stimulated depends on the particular muscle and the work it does.

26. Neuromuscular junction
When the nerve fiber or axon reaches the muscle, it branches into a number of axon terminals.
Each axon terminal forms a junction with the sarcolemma of different muscle cells.
Neuromuscular junction
The nerve endings and muscle tissue never touch
Filled with interstitial fluid
Called the synaptic cleft

27. Neurotransmitters
When the nerve impulses reach the synaptic cleft, a chemical, called a neurotransmitter, is released.
Acetylcholine (Ach) is the neurotransmitter that stimulates skeletal muscles
The diffusion of Ach across the synaptic cleft causes Na+ to rush into the muscle cell
The sudden rush of Na+ “upsets” and changes the electrical conditions of the sarcolemma
The “upset” generates an electrical current called an action potential
Once started, the action potential is unstoppable
The result is muscle contractions
Remind students that other neurotransmitters stimulate other organs. Also, remind students that the rush of Na+ gives the sarcolemma an excessively positive charge

28. Neuromuscular Junction

29. Sliding Filament Theory
Myosin heads attach to actin molecules (at binding (active) site)
Myosin “pulls” on actin, causing thin myofilaments to slide across thick myofilaments, towards the center of the sarcomere
Sarcomere shortens, I bands get smaller, H zone gets smaller, & zone of overlap increases

30. As sarcomeres shorten, myofibril shortens
As sarcomeres shorten, myofibril shortens. As myofibrils shorten, so does the muscle fibers
Once a muscle fiber begins to contract, it will contract maximally
This is known as the “all or none” principle