1. MUSCLE PHYSIOLOGY
CHAPTER 8 CONT….

2. What are muscles? Muscle Muscle Actions
An organ composed of specialized cells that use the chemical energy stored in nutrients to contract.
Muscle Actions
Provide muscle tone
Propel body fluids and food
Generate heart beat
Distribute heat

3. 3 Types of Muscles Skeletal, smooth, cardiac SKELETAL SMOOTH CARDIAC
LOCATION
(40% of body mass)
Attached to bone
Surrounds digestive organs and blood vessels
In heart
CONTRACTIONS
Voluntary
Involuntary
involuntary
STRIATED
Yes No
yes

5. Structure of Skeletal Muscle
MUSCLE (COVERED BY EPIMYSIUM)
FASCICLES (COVERED BY PERIMYSIUM)
MUSCLE FIBERS(COVERED BY ENDOMYSIUM)
MYOFIBRILS
THICK AND THIN FILAMENTS
(MYOSIN) (ACTIN)
Fascia: layers of fibrous connective tissue that separates individual muscles and hold it in position; forms the tendon and attaches to bone’s periosteum
(aponeuroses: broad sheets of connective tissue that may attach to bone or other muscles)

7. Sarcoplasmic reticulum :
activates muscle contraction mechanism when the fiber is
stimulated.
Actin and Myosin: Protein filaments. The organization of these produces the alternating light and dark striations.
(form repeating pattern units called sacromeres.)

8. I band: light band composed of actin attached to Z lines
I band: light band composed of actin attached to Z lines. A band: dark band composed of myosin overlapping actin. H zone: has only myosin. M line: holds myosin in place.

9. Skeletal Muscle Contraction
Motor Neuron: conducts impulse from brain and brings it to the muscle fiber.
Neuromuscular Junction: connection between neuron and muscle.
Neurotransmitter: chemicals at ends of connection that stimulates fiber.

10. Stimulus for Contraction
Neurotransmitter (acetylcholine) is released at end of motor neuron.
Acetylcholine diffuses into muscle fiber.
Sarcolemma is stimulated and impulse travels deep into the sarcoplasmic reticulum.
Ca+2 ions diffuse from sarcoplasmic reticulum into sarcoplasm.

11. Sliding Filament Theory
When Ca+2 is present, actin binding sites are exposed.
Myosin cross-bridges form a link at binding site.
Myosin cross-bridges bend to pull on actin.
Linkage breaks.
Myosin cross-bridges forms to next binding site.

13. Relaxation of Muscle
Acetylcholinesterase decomposes acetylcholine and the sarcolemma is no longer stimulated.
Ca+2 is transported back to sarcoplasmic reticulum.
Linkages between actin and myosin break.
Filaments slide apart.
Muscle fiber relaxes.

14. Muscle Responses
When one muscle fiber (cell) reached its threshold stimulus and contracts it is called a twitch.
MYOGRAM
All - Or - Nothing (but muscles vary)

15. A. Normal contraction
B. Summation contraction: series of stimuli with increasing frequency.
C. Tetanic contraction: sustained contraction that lacks relaxation. (tetanus)

16. SMOOTH & CARDIAC CONTRACTIONS
Essentially same as skeletal, difference include: (pg 190)
SMOOTH
CARDIAC
Fibers can stimulate each other
2 neurotransmitters (acetylcholine & norepinephrine) and hormones for stimulation
Contracts and relaxes slowly
Produces more Ca+ in transverse tubules which makes twitches longer
Contracts as a functional unit
Single nuclei
Self-exciting, rhythmic

17. Fatigue: caused by an interruption in
Slow Twitch Fibers (fatigue resistant) & Fast Twitch Fibers (fatigable)
Normal person ½ & ½
Sprinter 80% fast twitch
Marathoner 90% slow twitch
Fatigue: caused by an interruption in
Blood supply
Lack of acetylcholine
Accumulation of lactic acid due to lack of O2
Cramp: sustained involuntary contraction from changes in extracellular fluid.
Muscle tone: Partial sustained muscle contraction
Important in maintaining posture

18. Muscle Strain: muscle fiber can be overstretched or even torn.
Muscle pull: tendon of muscle tears away from bone.
Shin splints: soreness due to straining the tibialis anterior
Rigor mortis: partial contraction that fixes joints; actin and myosin remain linked until decomposition.
Tendinitis: inflammation of tendon.
Muscle hypertrophy: forcefully exercised muscle that causes increased size and shape.
Muscle atrophy: unused muscle caused decrease in size and strength.
Muscular dystrophies: missing or abnormal dystrophin (protein that holds fibers together); muscle will weaken and degenerate.
Myoma: tumor composed of muscle tissue
Myositis: inflammation of skeletal muscle tissue

19. Botox: toxin injected into the facial skin to temporarily smooth wrinkles preventing muscles from contraction. It prevents acetylcholine from being released.
Too much can cause a frozen face
Also causes botulism which is a serious form of food poisoning

20. Muscle movements
Muscle is connected to bone or connective tissue at 2 main points.
Origin: attachment to the immovable or less movable bone.
Insertion: attachment to movable bone
Moves toward origin during contraction
Some muscles have interchangeable origins
and insertions: (rectus femoris)
Muscles can only pull (not push) as they contract.
Prime mover: muscle that has main responsibility for a movement. (biceps)
Antagonist: muscle that opposes or reverses movement. (triceps)