1. Human Anatomy and Physiology
Chapter 9
Muscular System
9-1

2. Chapter 9 Muscular System
Three Types of Muscle Tissues
-All designed to contract
Cardiac Muscle
wall of heart
not under conscious control
striated
Skeletal Muscle
usually attached to bones
under conscious control
striated
Smooth Muscle
walls of most viscera, blood vessels, skin
not under conscious control
not striated
9-2

3. Structure of a Skeletal Muscle
organ of the muscular system
skeletal muscle tissue
nervous tissue
blood
connective tissues
fascia- tissue surrounds each muscle
tendon- attach muscle to bone
aponeuroses- attach muscle to muscle
9-3

4. Structure of a Skeletal Muscle
muscle is surrounded by epimysium
muscle is divided into fasicles by perimysium
Fasicle is divided into muscle fibers (cells) by endomysium
9-4

5. Skeletal Muscle Fiber
sarcolemma surrounds muscle fiber (muscle cell) and contains many nuclei, mitochondria, and myofibrils
sarcoplasmic reticulum contains calcium ions
muscle fiber is made of many myofibrils
are made of actin (thin) and myosin (thick)
are divided into sections called sarcomeres
9-5

6. Myofilaments Thin Filaments Thick Filaments
composed of actin (protein)
associated with troponin and tropomyosin
Thick Filaments
composed of myosin (protein)
cross-bridges
9-7

7. Sarcomere Sarcomeres are the ‘active unit’ of the cell I band A band
H zone
Z line
M line
9-6

8. Neuromuscular Junction
site where axon (end of nerve) and muscle fiber communicate
motor neuron
motor end plate
synaptic cleft
synaptic vesicles
neurotransmitters
9-8

9. Motor Unit group of muscle fibers attached to a single motor neuron
all muscle fibers controlled by motor neuron
muscle fibers act as group
9-9

10. Stimulus for Contraction
acetylcholine (ACh) neurotransmitter
nerve impulse causes release of acetylcholine from synaptic vesicles
binds to acetylcholine receptors on motor end plate
generates a muscle impulse
muscle impulse eventually reaches sarcoplasmic reticulum
9-10

11. Excitation Contraction Coupling
muscle impulses cause sarcoplasmic reticulum to release calcium ions into cytosol
calcium binds to troponin-tropomyosin complex to change its shape
position of t-t complex is altered
binding sites on actin exposed
myosin binds to actin
9-11

12. Cross-bridge Cycling myosin cross-bridge pulls actin
9-13
myosin cross-bridge pulls actin
ADP and phosphate released from myosin
new ATP binds to myosin
linkage between actin and myosin cross-bridge break
ATP splits
12. stimulus stopped, calcium pumped out, t-t complex recovers binding sites; or process keeps cycling (back to step 5 further down the actin filament)
myosin cross-bridge goes back to original position

13. Sliding Filament Theory
When sarcomeres shorten, thick and thin filaments slide past one another
H zones and I bands get narrower
Z lines move closer together
9-12

14. Relaxation motor neuron impulse stops
acetylcholinesterase released – breaks down acetylcholine
calcium moves back into sarcoplasmic reticulum
t-t complex covers binding site
myosin and actin binding prevented
9-14

15. Energy Sources for Contraction
1) Cellular respiration [ATP Production] 2) Creatine Phosphate
creatine phosphate – stores energy that quickly converts ADP to ATP
9-15

16. Oxygen Supply and Cellular Respiration
Aerobic Phase
use oxygen
citric acid cycle
electron transport chain
produces most ATP (36)
myoglobin stores extra oxygen
Anaerobic Phase
no oxygen
glycolysis
produces little ATP (2)
9-16

17. Anaerobic threshold
Anaerobic threshold- point at which there is not enough O2 and cell transitions to anaerobic respiration
oxygen not available
glycolysis continues
pyruvic acid is converted to lactic acid
liver converts lactic acid to glucose
9-17

18. Muscle Fatigue inability to contract commonly caused from
lack of oxygen/lungs at capacity or
decreased blood flow
anaerobic respiration
decrease in available ATP
accumulation of lactic acid
ion imbalances
cramp – sustained, involuntary contraction
9-18

19. Heat Production by-product of cellular respiration
muscle cells are major source of body heat
blood transports heat throughout body
9-19

20. Muscular Responses Threshold Stimulus
minimal strength required to cause contraction
Recording a Muscle Contraction
twitch- single contraction
latent period
period of contraction
period of relaxation
refractory period
all-or-none response
9-20

21. Summation process by which individual twitches combine
produces sustained contractions
can lead to tetanic contractions –sustained contraction that lacks relaxation
9-21

22. Recruitment of Motor Units
recruitment - increase in the number of motor units activated (causes stronger contraction)
whole muscle composed of many motor units
as intensity of stimulation increases, recruitment of motor units continues until all motor units are activated
9-22

23. Sustained Contractions
smaller motor units recruited first
larger motor units recruited later
produces smooth movements
muscle tone – continuous state of partial contraction
9-23

24. Types of Contractions isotonic – muscle contracts and changes length
isometric – muscle contracts but does not change length
eccentric – lengthening contraction
concentric – shortening contraction
9-24

25. Fast and Slow Twitch Muscle Fibers
Slow-twitch fibers (type I)
always oxidative
resistant to fatigue
red fibers
most myoglobin
good blood supply
posture muscles
Fast-twitch fatigue-resistant fibers (type IIb)
intermediate fibers
oxidative
intermediate amount of myoglobin
pink to red in color
Fast-twitch glycolytic fibers (type II)
white fibers (less myoglobin)
poorer blood supply
susceptible to fatigue
9-25

26. Smooth Muscle Fibers Compared to skeletal muscle fibers shorter
single nucleus
elongated with tapering ends
no striations
myofilaments randomly organized
lack transverse tubules
sarcoplasmic reticula not well developed
9-26

27. Types of Smooth Muscle Visceral Smooth Muscle Multiunit Smooth Muscle
single-unit smooth muscle
sheets of muscle fibers
exhibit rhythmicity/ peristalsis
walls of most hollow organs
Multiunit Smooth Muscle
fibers function separately
irises of eye
walls of blood vessels
9-27

28. Smooth Muscle Contraction
Resembles skeletal muscle contraction
interaction between actin and myosin
both use calcium and ATP
both depend on impulses
Different from skeletal muscle contraction
smooth muscle lacks troponin
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
9-28

29. Cardiac Muscle only in the heart
muscle fibers joined together by intercalated discs
fibers branch
network of fibers contracts as a unit
self-exciting and rhythmic
longer refractory period than skeletal muscle
9-29

30. 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
9-30

31. Life-Span Changes 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
9-65