1. Introduction to Muscle
Movement is a fundamental characteristic of all living things.
Muscles cells are capable of shortening and converting the chemical energy of ATP into mechanical energy.
Types of muscle
Skeletal
Cardiac
Smooth

2. Skeletal Muscle
Has obvious stripes called striations and multiple nucleuses
Under voluntary control
Attached to the skeletal system
Responsible for movement.

3. Cardiac Muscle Striated muscle but is involuntary
Intercalated discs connect adjacent cells together

4. Smooth Muscle
Found in the walls of hollow visceral organs, such as the stomach, intestines ,bladder.
It is not striated and is involuntary

5. Characteristics of Muscle Tissue
Excitability, or responsiveness
the ability to respond to stimuli
Conductivity
the ability to produce and conduct an action potential along the cell membrane
Contractility
the ability to shorten creates movement by:
Skeletal: pulling on bones
Visceral: Movement created by visceral organs.
Extensibility
the ability to be stretched
Elasticity
the ability to recoil after being stretched

6. Connective Tissues of a Muscle
Tendon
Deep fascia
Epimysium
Perimysium
Endomysium

7. Skeletal Muscle
Each muscle is composed of various tissue types. They include muscle tissue, blood vessels, nerve fibers, and connective tissue.
The connective tissue located is important for supplying a framework for the blood vessels and nerves. They also contribute to the elastic qualities of muscle aiding in force production.
The three connective tissue sheaths are:
Endomysium – fine sheath of connective tissue surrounding each muscle fiber
Perimysium –connective tissue that surrounds groups of muscle fibers called fascicles
Epimysium – an overcoat of dense regular connective tissue that surrounds the entire muscle

8. The Muscle Fiber

9. Anatomy of a Skeletal Muscle Fiber
Each fiber is surrounded by a sarcolemma
( cell membrane around the muscle)
the sarcolemma contains voltage-gated channels able of generating an action potential
The action potential travels along the sarcolemma and dips into the center of the muscle via transverse-tubules. (T-tubules)
Sarcoplasmic reticulum (SR) (bathes the muscle fibers)
Extensions of the T-tubules which store intracellular calcium (Ca+2)
Once an action potential reaches the T-tubules Ca+2 from the terminal cysterna of SR is released into the sarcoplasm triggering a muscle contraction.

10. Myofilaments: Banding Pattern

11. Myofilaments: Banding Pattern
The thin and thick filaments overlapping forming sarcomeres.
Z disc
anchors the thin filaments and connects myofibrils to one another
Z-disc to Z disc = one sarcomere
A band
the length of the thick filaments
I band
the length of thin filaments within a sarcomere that is not overlapping with the thick filaments
H zone
the length of thick filaments within in a sarcomere that do not overlapping with the thin filaments

12. Resting Muscle
When a muscle is in a relaxed state the sarcomere is at its normal length.
The H-zone is visible.

13. Contracted Sarcomeres
Muscle cells shorten because their individual sarcomeres shorten as myosin pulls actin toward the center of the sarcomere.
pulling Z discs closer together
Notice neither thick nor thin filaments change length they overlap as sarcomeres shorten
H-zone disappears

14. Resting muscle/Contracted muscles

15. Thick Filaments
Arranged in a bundle with heads directed outward in a spiral array
Myosin heads:
Form cross bridges with actin.
Myosin contains the enzyme ATPase which hydrolyzes ATP to create movement.

16. Thin Filaments
Actin: Two intertwined strands fibrous protein containing the active site for myosin heads.
Tropomyosin : Prevents actin and myosin cross bridge formation
Troponin: a protein attached to tropomyosin that calcium binds to allowing cross bridge formation and muscle contraction.

17. The Neuromuscular Junction

18. Neuromuscular Junctions (Synapse)
Functional connection between nerve fiber and muscle cell
Neurotransmitter (acetylcholine/ACh) released from nerve fiber stimulates muscle cell
Components of synapse (NMJ)
synaptic knob is swollen end of nerve fiber (contains ACh)
junctional folds region of sarcolemma
increases surface area for ACh receptors
contains acetylcholinesterase that breaks down ACh and causes relaxation
synaptic cleft = tiny gap between nerve and muscle cells

19. Electrically Excitable Cells
Plasma membrane is polarized or charged
resting membrane potential due to Na+ outside of cell and K+ and other anions inside of cell
difference in charge across the membrane = resting membrane potential (-90 mV cell)
Stimulation opens ion gates in membrane
ion gates open (Na+ rushes into cell and K+ rushes out of cell)
quick up-and-down voltage shift = action potential
spreads over cell surface as nerve signal

20. Excitation (Steps 1 and 2)
AP opens voltage-gated calcium channels. Calcium stimulates exocytosis of synaptic vesicles containing ACh = ACh release into synaptic cleft.

21. Excitation (steps 3 and 4)
Binding of ACh to receptor proteins opens Na+ and K+ channels resulting in jump in RMP from -90mV to +75mV forming an end-plate potential (EPP).

22. Excitation (step 5)
Voltage change in end-plate region (EPP) opens nearby voltage-gated channels producing an action potential

23. Excitation-Contraction Coupling (steps 6 and 7)
Action potential spreading over sarcolemma enters T tubules -- voltage-gated channels open in T tubules causing calcium gates to open in SR

24. Excitation-Contraction Coupling (steps 8 and 9)
Calcium released by SR binds to troponin
Troponin-tropomyosin complex changes shape and exposes active sites on actin

25. Contraction (steps 10 and 11)
Myosin ATPase in myosin head hydrolyzes an ATP molecule, activating the head and “cocking” it in an extended position
It binds to actin active site forming a cross-bridge

26. Contraction (steps 12 and 13)
Power stroke = creates muscle contraction
myosin head pulls the actin over it.
With the binding of more ATP, the myosin head will detach and break the cross bridge.

27. Relaxation (steps 14 and 15)
Nerve stimulation ceases and acetylcholinesterase removes ACh from receptors. Stimulation of the muscle cell ceases.

28. Relaxation (step 16)
Active transport needed to pump calcium back into SR to bind to calsequestrin
ATP is needed for muscle relaxation as well as muscle contraction

29. Relaxation (steps 17 and 18)
Loss of calcium from sarcoplasm moves troponin-tropomyosin complex over active sites
Muscle fiber returns to its resting length

30. Motor Units A motor neuron and the muscle fibers it innervates.
Fine control
small motor units contain as few as 20 muscle fibers per nerve fiber
eye muscles
Allow for greater dexterity because of a lower neuron to muscle fiber ratio.
Strength control
gastrocnemius muscle has fibers per nerve fiber
One motor neuron controls many muscle fibers which allows for strength production.

31. Recruitment and Stimulus Intensity
Strength of muscle contraction is dependant of # of motor units recruited
Multiple motor unit summation
The harder the activity is the more motor units will be recruited.
Lifting 1 lb vs. 100 lbs
How do you explain the rapid strength gains when you first start training?

32. Muscle Twitch A single stimulus results in a single muscle twitch
Each twitch has time to recover but develops more tension than the one before (treppe phenomenon)

33. Muscle Response: Stimulation Frequency
Higher frequency stimulation generates gradually more strength
each stimuli arrives before last one recovers
temporal summation or wave summation
incomplete tetanus = sustained fluttering contractions
Maximum frequency stimulation
muscle has no time to relax at all
twitches fuse into smooth, prolonged contraction called complete tetanus

34. Isometric and Isotonic Contractions
Isometric muscle contraction
develops tension without changing length
important in postural muscle function and antagonistic muscle joint stabilization
Isotonic muscle contraction
tension while shortening = concentric
tension while lengthening = eccentric

35. Metabolism and Skeletal Muscle Fibers Types
There are 3 different types skeletal muscle fibers based histological differences, duration of a twitch and the method of ATP production
slow oxidative fibers
fast oxidative fibers
fast glycolytic fibers
Proportions genetically determined

36. Fast Glycolytic, Fast-Twitch Fibers
rich in enzymes for phosphagen and glycogen-lactic acid systems
Limited # of mitochondria and high concentration of glycogen stores makes it adapted for anaerobic metabolism
a lack of myoglobin in glycolytic fibers results in a white color
sarcoplasmic reticulum releases calcium quickly so contractions are quicker which are required for movements that produce speed and power.
extraocular eye muscles, gastrocnemius and biceps brachii

37. Slow- Twitch Fibers Slow oxidative, slow-twitch fibers
Oxidative fibers contain greater amounts of mitochondria and myoglobin which binds oxygen.
Rich blood supply and high concentration of myoglobin these fibers appear red in color.
adapted for endurance (resistant to fatigue)
Soleus and postural muscles of the back are predominantly this type.

38. Fast Oxidative Fibers Fast oxidative fibers:
characteristics of both fast and slow fibers.
have a fast twitch (use ATP quickly)
Increased mitochondria make it moderately resistant to fatigue
Usually make up 10% of fibers.
Training will make these fibers adapt to become functionally more fast or slow.

39. Cellular Adaptations to Physical Demands
Strength training: high intensity training stresses anaerobic pathways.
Increased # and size of glycolytic associated enzymes and substrates
ATP, creatine phosphate and glycogen
Endurance training: Enhance the aerobic pathways.
increased # and size of mitochondrial membranes and associated enzymes.
This will increase O2 uptake ( VO2 max) which will delay the formation of lactic acid.