1. FROM FASCIA TO FILAMENT
ANATOMY OF A MUSCLE
FROM FASCIA TO FILAMENT

2. Connective Tissue Coverings
Skeletal Muscle- Organ Composed of muscle, nervous, circulatory and connective tissue
A Muscle is an organ with several levels of organization
Each one is covered with its own type of connective tissue to hold its position

3. Levels of Connective Tissue
Aponeuroses- large sheets of connective tissue that attach to the facia of adjacent muscles
Facia- surround each entire muscle on the outside
Extends beyond the muscle to form tendons
Epimysium- right under facia
Perimysium- separates the muscle into smaller compartments called fascicle
Endomysium- separates each fascicle into individual muscle fibers

4. Levels of Organization
Muscular System V
Muscle Group
Muscle
Fascicle (bundle of muscle fibers)

5. Levels of Organization
Muscle Fiber (from fascicle)- the muscle cell V
Myofibril
Sarcomere (from one Z line to next Z line of myofibril)
Filaments (actin and myocin)

6. Skeletal Muscle Fibers
Muscle Fiber- a cell that responds to stimuli & relaxes when stimuli ends
Actually the fusion of many cells called a myoblast
Multinucleated due to this fusion
Other cellular structures have special names due to the fiber’s unique structure
Sarcolemma- outer covering
Sarcoplasm- inner fluid
Sarcoplasmic Reticulum- nework of internal channels
Transverse Tubules- channels that lead outside
Combination of two networks activate muscle contractions

7. Skeletal Muscle Fibers
Each fiber is very dense with mitochondria
Myofibrils- parallel threadlike subdivisions in each fiber
Fundamental in muscle contraction
Actin (thin) & Myosin (thick)- two types of protein filaments
The alternating of these filaments produces muscle striations
Muscle Striations- Two Main Parts
I Bands- light bands made up of thin actin filaments directly attached to structures called Z lines
A Bands- dark bands composed of thick myosin filaments overlapping with thin actin filaments
The H Zone is the middle of the A Band consisting of the M line (thickening of the myosin filaments)
Sarcomere- segment of the myofibril that extends from Z line to Z line

8. Figure 23.1: Sarcomere microanatomy: Relaxed (above) and contracted (below):
(a) actin (b) myosin
(c) Z-line (d) H-zone
(e) I-band (f) A-band
(green, diagonal arrows) H-band and I-band which change in length during contraction, (red, vertical arrows) A-band which does not change in length.

10. NEUROMUSCULAR JUNCTION

11. Motor unit
A motor unit is a single motor neuron and all of the corresponding muscle fibers it innervates.
When a motor unit is activated, all of its fibers contract.
Groups of motor units often work together to coordinate the contractions of a single muscle;
all of the motor units that subserve a single muscle are considered a motor unit pool.

12. SKELETAL MUSCLE CONTRACTION

13. ROLE OF ACTIN AND MYOSIN
Sliding Filament Theory- Muscle contractions result in actin and myosin filaments sliding across one another
Myosin molecule- two twisted protein strands
Cross bridges- globular heads running down its length
Myosin strand- Many myosin molecules
Actin molecule- globular structures that have binding sites for the myosin cross bridges
Actin strand- many actin molecules in a helix

14. Muscle Contracts When Myosin Crossbridges Attach to Actin and the Molecule Bends
The filaments slide together because myosin attaches to actin and pulls on it
Myosin head (H) attaches to actin filament (A), forming a crossbridge
After the crossbridge is formed the myosin head bends, pulling on the actin filaments and causing them to slide:
Muscle contraction is a little like climbing a rope. The crossbridge cycle is: grab -> pull -> release, repeated over and over

15. ATP is Required for Both Contraction and Relaxation of Muscle
ATP is the energy supply for contraction
It is required for the sliding of the filaments which is accomplished by a bending movement of the myosin heads
It is also required for the separation of actin and myosin which relaxes the muscle

16. STIMULUS FOR CONTRACTION
Action potential impulse sent from CNS causing Calcium Ions to be pumped into the motor neuron
Calcium ions causes the synaptic vesicles to open
Neurotransmitter acetlycholene (Ach) is released
Ach diffuses across the junction and binds to a receptor protien in the post synaptic membrane
This depolarizes the membrane, transfers the action potential to the muscle

17. Muscle Contraction and Relaxation
The action potential is received in the muscle membrane and travels through the transverse tubules to the sarcoplasmic reticulum (SR)
In response to the impulse Ca++ ions are released from the (SR) and goes to the actin filaments
This causes the myosin cross bridges to form linkages to the actin and a muscle contraction occurs
The contraction will continue as long as ATP is present and nerve impulses cause Ach release.

18. MUSCLES ARE NATURALLY IN A STATE OF RELAXATION
When the nerve impulse stops, Ach is broken down and sent back to the nerve for recycling
Also, Ach breakdown causes the Ca++ to go back into the SR and the actin-myosin linkages are broken, thus relaxation
MUSCLES ARE NATURALLY IN A STATE OF RELAXATION

19. Figure 23.1: Sarcomere microanatomy: Relaxed (above) and contracted (below):
(a) actin,
(b) myosin,
(c) Z-line,
(d) H-zone,
(e) I-band,
(f) A-band,
(green, diagonal arrows) H-band and I-band which change in length during contraction, (red, vertical arrows) A-band which does not change in length.

20. ENERGY FOR MUSCLE CONTRACTION
Muscle contractions take more ATP than is available in fibers
Creatine Phosphate- is able to make ATP from ADP and phosphate
Stored in the mitochondria
OXYGEN SUPPLY & CELLULAR RESPIRATION
Oxygen for cellular respiration comes from red blood cells
Hemoglobin- pigment molecules in red blood cells that allows them to carry oxygen
Myoglobin- pigment in blood cells that also binds to oxygen
OXYGEN DEBT & MUSCLE FATIGUE
Oxygen Debt- During activity, oxygen is used up and anaerobic respiration occurs
Anaerobic respiration results in the production of lactic acid
Muscle Fatigue- caused by a build up of lactic acid

21. MUSCULAR RESPONSES Use single muscle fiber to observe
Threshold Stimulus- minimum strength of stimulus required to cause a muscle contraction
All-or-None Response- muscle fibers do not partially contract. Once the threshold stimulus is reached, a full contraction occurs.
Myogram- pattern a muscle contraction produces
Twitch- a single muscle contraction- 3 parts
Latent period- delay btn stimulus and response
Period of contraction- when muscle pulls
Period of relaxation- when muscle returns to original length
Summation- series of twitches that increase in strength before complete relaxation
Tectanic contraction- no relaxation between twitches

22. Recruitment of motor units- muscles are organized into motor units
Motor units are stimulated all-or none, one at a time until all the motor units for that motion are stimulated
Sustained contractions- when summation and recruitment are combined over time
Muscle tone- sustained contractions occurring continually in a resting muscle

23. SMOOTH MUSCLE

24. SMOOTH MUSCLE
Contractile mechanisms for smooth and cardiac muscles are the same as those of skeletal muscles
Smooth muscle fibers- no striations
Multiunit smooth muscle- occur as separate fibers rather than in sheets
Irises of the eyes and blood vessels
Visceral smooth muscle- sheets of spindle shaped cells- more common
Walls of hollow organs- stomach, intestine, bladder
Peristalsis- rhythmic contraction of smooth muscles
Smooth muscle- slower to contract than skeletal muscle, but can maintain contraction longer with the same amount of ATP

25. CARDIAC MUSCLE Occurs only in the heart
Striated cells joined end to end
Long contractions
Intercolated Discs- cross bands that connect opposing ends of cardiac muscle cells
Cardiac muscle cells form a network and act as a single unit when the all-or-none stimuli response occurs
Cardiac muscle is self exciting and rhythmic

26. SKELETAL MUSCLE ACTIONS
Provide body movement
Origin & Insertion
Origin- immovable end of a muscle
Insertion- movable end of a muscle
Action- movement muscle causes
Dependent on attachments and type of joint

27. INTERACTIONS OF SKELETAL MUSCLES
Skeletal muscle function in groups
Prime Mover- muscle in group that provides most of the movement
Synergists- muscles that assist the prime mover
Antagonists- muscle that resist the prime mover and move in the opposite direction