1. Chapter 9 Muscular System
Three Types of Muscle Tissues
Skeletal Muscle
usually attached to bones
under conscious control
striated
Cardiac Muscle
wall of heart
not under conscious control
striated
Intercalated discs
Smooth Muscle
walls of most viscera, blood vessels, skin
not under conscious control
not striated

2. Functions of Skeletal Muscle
Produce skeletal movement
Maintain posture and body position
Support soft tissues
Guard entrances and exits
Maintain body temperature
Store nutrient reserves

3. Structure of a Skeletal Muscle
organ of the muscular system
- skeletal muscle tissue
- nervous tissue
- blood
- connective tissues
fascia-tissue that surrounds the entire muscle
tendons-dense connective tissue cord that connect muscles to bones
aponeuroses-sheet-like tendon that connects muscles to bones

4. Connective Tissue Coverings
epimysium-membrane that surrounds the whole muscle
perimysium-membrane that surrounds fascicles
fascicles-groups of muscle fibers(cells)
endomysium-membrane that that surrounds individual muscle cells
muscle fibers-muscle cells
myofibrils-protein fibers inside muscle cells
thick and thin filaments

5. Skeletal Muscle Fibers
sarcolemma-cell membrane of a muscle fiber
sacroplasm-cytoplasm of a muscle fiber
sarcoplasmic reticulum-stores calcium ions
transverse tubule-carries muscle impulse from sarcolemma to searcplasmic reticulum
triad
pair of cisternae of sarcoplasmic reticulum
transverse tubule

6. Skeletal Muscle Fibers
Myofibril-proteins fibers
actin filaments-thin filaments
myosin filaments-thick filaments
sarcomere-functional unit of skeletal muscle

7. Sarcomere I bands-thin only A bands-thick and thin H band-thick only
Z lines-edge of sarcomer
M line-mid-line of sarcomere
zone of overlap-where thick and thin filaments overlap

8. Myofilaments Thin Filaments Thick Filaments composed of actin
associated with troponin and tropomyosin
Thick Filaments
composed of myosin
cross-bridges

9. Neuromuscular Junction
also known as myoneural junction
site where an axon and muscle fiber meet
motor neuron-neuron that controls a muscle fiber
motor end plate-area of muscle fiber that forms synapse (junction) with motor neuron

10. Neuromuscular Junction
Synapse-area where the neuron communicates with the muscle fiber
synaptic cleft-space between neuron and sarcolemma
synaptic vesicles-store and release neurotransmitters in neuron
neurotransmitters-chemical messengers that carry the signal across the synapse

11. Motor Unit single motor neuron
all muscle fibers controlled by motor neuron

12. Stimulus for Contraction
acetylcholine (ACh)
nerve impulse causes release of ACh from synaptic vesicles
ACh binds to ACh receptors on motor end plate
generates a muscle impulse
muscle impulse eventually reaches sarcoplasmic reticulum
and the cisternae

13. Excitation Contraction Coupling
muscle impulses cause sarcoplasmic reticulum to release calcium ions into cytosol
calcium binds to troponin to change its shape
position of tropomyosin is altered
binding sites on actin are exposed
actin and myosin molecules bind

14. Sliding Filament Model of Muscle Contraction
When sarcromeres shorten, thick and thin filaments slide past one another
H zones and I bands narrow
Z lines move closer together

15. Cross-bridge Cycling
myosin cross-bridge attaches to actin binding site
myosin cross-bridge pulls thin filament
ADP and phosphate released from myosin
new ATP binds to myosin
linkage between actin and myosin cross-bridge break
ATP splits
myosin cross-bridge goes back to original position

16. Relaxation acetylcholinesterase – rapidly decomposes Ach
remaining in the synapse
muscle impulse stops
stimulus to sarcolemma and muscle fiber membrane
ceases
calcium moves back into sarcoplasmic reticulum
myosin and actin binding prevented
muscle fiber relaxes
Rigor mortis-muscle contract and stay contracted as calcium leaks out and there is no ATP to break the cross bridges

17. Major Events of Muscle Contraction and Relaxation

18. Energy Sources for Contraction
1) Creatine phosphate 2) Cellular respiration
creatine phosphate – stores energy that quickly converts ADP to ATP

19. Oxygen Supply and Cellular Respiration
Oxygen is needed to completely breakdown glucose
myoglobin
Anaerobic Phase
glycolysis
occurs in cytoplasm
produces little ATP
Aerobic Phase
citric acid cycle
electron transport chain
occurs in the mitochondria
produces most ATP
myoglobin stores extra oxygen

20. Oxygen Debt
Oxygen debt – amount of oxygen needed by liver cells to use the accumulated lactic acid to produce glucose plus the amount muscle cells require to resynthesize ATP and creatine phosphate and restore their original conditions
oxygen not available
glycolysis continues
pyruvic acid converted to lactic acid
liver converts lactic acid to glucose
Anaerobic threshold or lactic acid threshold

21. Muscle Fatigue inability to contract after persistent, prolonged use
commonly caused from
decreased blood flow
ion imbalances across the sarcolemma
accumulation of lactic acid (most common cause)
Psychological loss of desire to continue the exercise
cramp – sustained, painful, involuntary muscle contraction

22. Heat Production muscle cells are major source of body heat
by-product of cellular respiration
muscle cells are major source of body heat
Helps maintain body temperature
blood transports heat throughout body

23. Muscular Responses Threshold Stimulus
minimal strength required to cause contraction
Recording a Muscle Contraction
myogram
twitch
latent period
period of contraction
period of relaxation
refractory period
all-or-none response

24. Length-Tension Relationship

25. Summation process by which individual twitches combine
produces sustained contractions
can lead to tetanic contractions

26. Recruitment of Motor Units
recruitment - increase in the number of motor units activated
whole muscle composed of many motor units
more precise movements are produced with fewer
muscle fibers within a motor unit
as intensity of stimulation increases, recruitment of motor units continues until all motor units are activated

27. Sustained Contractions
smaller motor units (smaller diameter axons)
- recruited first
larger motor units (larger diameter axons)
- recruited later
produce smooth movements
muscle tone – continuous state of partial contraction

28. Types of Contractions isotonic – muscle contracts and changes length
concentric – shortening contraction
isometric – muscle contracts but does not change length
eccentric – lengthening contraction

29. Fast and Slow Twitch Muscle Fibers
Slow-twitch fibers (type I)
always oxidative
resistant to fatigue
red fibers
most myoglobin
good blood supply
Many mitochondria
aerobic
Fast-twitch fatigue-resistant fibers (type IIa)
intermediate fibers
oxidative
intermediate amount of myoglobin
pink to red in color
resistant to fatigue
Fast-twitch glycolytic fibers (type IIb)
white fibers (less myoglobin)
poorer blood supply
susceptible to fatigue
Few mitochondria
anaerobic

30. Smooth Muscle Fibers Compared to skeletal muscle fibers shorter
single, centrally located nucleus
elongated with tapering ends
myofilaments randomly organized
lack striations
lack transverse tubules
sarcoplasmic reticula not well developed

31. Types of Smooth Muscle Visceral Smooth Muscle Multiunit Smooth Muscle
single-unit smooth muscle
sheets of muscle fibers
fibers held together by gap junctions
exhibit rhythmicity
exhibit peristalsis
walls of most hollow organs
Multiunit Smooth Muscle
less organized
function as separate units
fibers function separately
irises of eye
walls of blood vessels

32. Smooth Muscle Contraction
Resembles skeletal muscle contraction
interaction between actin and myosin
both use calcium and ATP
both are triggered by membrane impulses
Different from skeletal muscle contraction
smooth muscle lacks troponin
smooth muscle uses calmodulin
two neurotransmitters affect smooth muscle
acetlycholine and norepinephrine
hormones affect smooth muscle
stretching can trigger smooth muscle contraction
smooth muscle slower to contract and relax
smooth muscle more resistant to fatigue
smooth muscle can change length without changing
tautness

33. Cardiac Muscle
located only in the heart
striated muscle fibers joined together by intercalated discs
Single nucleus per cells
Cisternae are less developed and store less calcium
transverse tubules are larger
fibers branch
network of fibers contracts as a unit
self-exciting and rhythmic
longer refractory period than skeletal muscle

34. Characteristics of Muscle Tissue

35. Skeletal Muscle Actions
origin – immovable end
insertion – movable end
prime mover (agonist) – primarily responsible for movement
synergists – assist prime mover
antagonist – resist prime mover’s action and cause movement in the opposite direction

36. Body Movement Four Basic Components of Lever rigid bar – bones
fulcrum – point on which bar moves; joint
object - moved against resistance; weight
force – supplies energy for movement; muscles

37. Levers and Movement

38. Life-Span Changes
Changes in muscular system first begin to appear in one’s 40’s
myoglobin, ATP, and creatine phosphate decline
by age 80, half of muscle mass has atrophied
adipose cells and connective tissues replace muscle tissue
exercise helps to maintain muscle mass and function

39. Clinical Application Myasthenia Gravis autoimmune disorder
receptors for ACh on muscle cells are attacked
weak and easily fatigued muscles result
difficulty swallowing and chewing
ventilator needed if respiratory muscles are affected
treatments include
drugs that boost ACh
removing thymus gland
immunosuppressant drugs
antibodies

40. Clinical Application
tenanus - sustained powerful contractions of skeletal muscles throughout the body
Caused by Clostridium tetani
Lockjaw
Tetanus shot-vaccine against the toxin