Chapter 9 - Muscles and Muscle Tissue

1
Chapter 9 - Muscles and Muscle Tissue

• I. Overview of Muscle Tissue
• A. Muscle Types - depending on structure and
  function
• 3 types
• 1. Similarities
• a. Muscle fibers skeletal and smooth muscle
  are elongated
• b. Contraction depends on myofilaments actin
  and myosin
• c. Myo- or mys- muscle and sarco flesh
• d. Sarcolemma membrane of muscle
• e. Muscle fiber cytoplasm sarcoplasm

2
Types and Functions of Muscles

• Smooth muscle is located in the walls of hollow
  internal organs and contracts involuntarily.
  (non-striated / involuntary, visceral muscle)
• Cardiac muscle forms the heart wall and contracts
  involuntarily. (striated, involuntary)
• Skeletal muscle runs the entire length of the
  muscle and contracts voluntarily. (striated,
  voluntary)

3

• I. Skeletal muscle
• a. Striated
• b. Controlled voluntary - subject to conscious
  control
• c. Contracts in response to a signal from a
  motor neuron, they cannot initiate their own
  contraction.

4

• 2. Cardiac
• a. Striated
• b. Involuntary - no conscious control
• c. Both cardiac and smooth have multiple levels
  of control through the autonomic nervous system,
  endocrine system and sometimes spontaneous
  contraction
• 3. Smooth Muscle
• a. Nonstriated (homogeneous appearance w/o bands
  because of less organized arrangement of
  contractile fibers)
• b. Visceral organs
• c. Involuntary
• d. Slow and sustained contractions

5

• Muscle Functions
• 1. Motion and force skeletal muscles, voice,
  vessels, heart, digestion, urinary, reproductive
• 2. Posture
• 3. Stabilize joints
• 4. Heat production and homeostasis of body
  temperature muscles generate heat as they
  contract

6

• C. Functional Characteristics
• 1. Excitability or irritability ability to
  respond to a stimulus ACh, hormone, local change
  in pH
• 2. Contractility ability to shorten when
  stimulated
• 3. Extensibility ability to be stretched or
  extended
• 4. Elasticity resume resting length after
  contraction

7
Skeletal Muscle

• A. Anatomy _______________________
• 1. Connective tissue coverings from external to
  internal
• a. Epimysium surrounds entire muscle fibrous
• b. Perimysium bundle of muscle fibers grouped
  into fascicles covered by a perimysium (around
  the muscle).
• c. Endomysium within a fascicle, each muscle
  fiber is surrounded by a sheath of reticular
  fibers

8

• 2. Nerves Blood
• a. Every fiber must be attached to a nerve
  ending that controls its activity
• b. Continuous blood flow brings oxygen and
  removes wastes because contracting muscle fibers
  use huge amounts of energy
• c. Each muscle served by an artery and one or
  more veins

9

• 3. Attachments
• a. Origin more stationary end attached closest
  to the trunk
• b. Insertion more distal or mobile attachment
  moves toward origin when muscle contracts
• c. Attachments
• Direct fleshy attachments epimysium fused to
  periosteum of bone or perichondrium of cartilage
• d. Indirect attachments connective tissue
  wrappings extend as a tendon or a sheetlike
  aponeurosis to attach muscle to connective tissue
  covering of bone or cartilage or to fascia of
  other muscles.

10
(No Transcript)
11

• B. Microscopic anatomy of a skeletal muscle
  fiber
• 1. Long cylindrical cell that is multinucleate
  beneath its outer membrane
• 2. Sarcoplasm in muscles (cytoplasm) more
  stored glycogen and contains myoglobin, a red
  pigment that binds O2
• Myofibrils - when viewed at high magnification
• a.. The contractile elements of skeletal muscle
• b. 80 of cell volume - thousands of myofibrils
  in each muscle
• c. Run parallel entire length of cell
• d. Tightly packed with other organelles squeezed
  between
• e. Sarcomere repeating series of dark and
  light bands along the length of the myofibril

12
(No Transcript)
13
myofibril
14

• 6. Sarcomere
• a. Striations caused by A bands
• Overlap of actin myosin
• b. H Zone
• Myosin only
• c. M Line
• Dark line bisects H
• d. Z line midline of I bands boundary of a
  single sarcomere
• e. Thick filaments myosin
• f. Thin filaments
• actin

15

• 7. Myofilaments - actin and myosin
• a. Thick filaments - Myosin has tail and a
  globular head
• b. Cross bridges combination of arms and heads
• c. Each thick filament of myosin has 200gt myosin
  molecules
• and
• d. Thin filament of actin bears the active site
• e. Actin has tropomyosin molecules that lie on
  top of the active binding sites

http//www.tekonline.org/c-o-n-t-e-n-t-s/SCIENCE_W
ORLD/science_world.html
16

• Skeletal muscle fibers contain
• sarcoplasmic reticulum and
• T tubules
• that help regulate muscle contraction
• Sarcoplasmic Reticulum
• a. Is like the smooth ER of a cell. It wraps
  around each myofibril like lace
• b. Surrounds myofibril with terminal cisternae
  (end sacs)
• c. Role is to concentrate and sequester calcium
  ions

17

• 9. T - Tubules
• a. T tubules are continuations of the surface
  membrane of the muscle fiber
• b. Where the sarcolemma of muscle cell
  penetrates into the cell interior to form a
  hollow tubule (T tubule)
• c. That allow action potentials that originate
  on the cell surface to move into the interior the
  the cell.

18

• C. Muscle Fiber Contraction
• 1. Sliding Filament Theory - 1954 by Sir Huxley
• a Thin filaments slide past thick filaments so
  actin and myosin overlap during contraction of
  muscle
• b. Definition Overlapping fibers of fixed
  length slide past each other in an
  energy-requiring process, resulting in muscle
  contraction.
• c. A muscle can contract without shortening.
• d. Tension generated in a muscle fiber is
  directly proportional to the interaction between
  thick and thin filaments

19
(No Transcript)
20

• Molecular events
• 1) Cross bridge attachment myosin cross bridge
  attaches to actin
• 2) Working stroke as myosin head binds, it
  pivots, pulling on the actin ( high energy config
  70 degrees, low energy bent)
• 3) Cross bridge detachment new ATP attaches to
  the myosin head, the cross bridge attachment
  detaches
• 4) Cocking of myosin head hydrolysis of ATP
  provides energy to return myosin to high-energy
  position repeated over and over as sarcomere
  shortens
• 5) Each myosin cross bridge attaches and
  detaches many times during a single contraction.
  
• 6) Sliding continues as long as the calcium
  signal and ATP are present

highered.mcgraw-hill.com/CADFA
highered.mcgraw-hill.com/CADFA
21

• 2. Regulation of Contraction
• Must be stimulated by
• a nerve ending and
• must propagate an electrical current
• or
• Action potential on sarcolemma (membrane).
• Excitation-contraction coupling are the events
  linking electrical signal to contraction

22

• 3. Stimulus
• a. Neuromuscular junctionmotor neuron axonal
  endings on muscle fiber usually one per fiber.
  Each muscle fiber has 1 neuromuscular junction so
  each skeletal muscle fiber has a nerve ending

23

• 3. Stimulus
• b. Synaptic cleft space between axon terminal
  of neuron and the muscle fiber
• c. Synaptic vesicles vesicles that contain
  acetylcholine
• d. Motor end plate branching nerve terminal
  invaginates into the muscle fiber

24

• e. Calcium release causes vesicles filled with
  ACh to fuse with membrane and release ACh into
  the synaptic cleft
• f. ACh binds to receptors on motor end plate of
  muscle fiber
• g. which opens the sodium channel - which
  initiates an AP along the muscle gt
  contraction

25

• 4. Generation of Action Potentials across the
  sarcolemma
• a. Inside is negative
• b. Binding of ACh opens chemically regulated ion
  gates
• c. Depolarization is a result of ions (sodium)
  entering to make inside less negative so the
  difference between inside and outside the cell
  decreases
• d. Action potential formation
• 1) Na gates open
• 2) Depolarization wave spreads to adjacent
  sarcolemma to open Na gates
• 3) Repolarization Na gates close and K
  gates open and K diffuses out

26
(No Transcript)
27

• e. Refractory period cannot be stimulated to
  produce another AP
• f. All-or-none responseonce initiated, AP
• cannot be stopped and causes full contraction of
  the fiber muscles contract completely or not at
  all
• ALL OR NONE

28
Depolarized - difference inside and outside the
cell decreases Repolarized - return to the
resting potential of electrical
disequilibrium from uneven distribution of ions
across the cell membrane. Hyperpolarized -
membrane is more negative and the difference
increased and the cell has hyperpolarized
29

• ControlAfter release of ACh, it is destroyed by
  acetylcholinesterase (AChE)
• This prevents continuous muscle fiber contraction
  in the absence of additional nervous stimulation
• Nicotine mimics ACh but nicotinic ACh not
  destroyed by AChE
• Nerve gas prevents AChE from inactivating ACh

30
Excitation-Contraction Coupling

• What is it?
• Name the steps?

31

• Excitation-Contraction Coupling
• a. Latent period time from stimulus until
  muscle contracts
• b. Action potential starts along sarcolemma and
  down T tubules
• c. SR releases calcium ions into the sarcoplasm
  of muscle cell
• d. Calcium binds troponin and removes blocking
  action of tropomyosin, freeing the actin active
  site to bind with myosin cross bridges
• e. Myosin cross bridges attach and shorten
  sarcomere
• f. Calcium pump takes calcium back to SR for
  storage
• g. Tropomyosin again blocks actin active sites
  and muscle fiber relaxes so the calcium signal
  ends here -the end of contraction

32

• D. Skeletal Muscle Contraction
• 1. Motor unit
• a. Contains a motor neuron and all muscle fibers
  it innervates
• b. Average is 150, with a range of four to
  -several hundred muscle fibers
• c. Smaller motor units in areas of precise
  control (eye)
• d. Large, weight bearing muscles of less
  precision have larger units
• e. Muscle fibers in a single unit are spread out
  so stimulation causes contraction of the entire
  muscle

33

• 2. Twitch and Tension Development
• a. Myogram graphic recording of contraction
• b. Muscle twitch response of muscle to single
  brief threshold stimulus
• c. Latent period first few milliseconds
  following stimulation when muscle tension is
  beginning but no response on the myogram
• d. Contraction period 10-100 ms onset of
  contraction to peak tension development enough to
  overcome resistance of the load to contract
• e. Period of Relaxation 10-100 ms Ca2 back
  into SR

34
(No Transcript)
35

• 3. Graded Responses - variations in the degree
  of contraction
• a. Produced by changing speed of stimulation or
  number of motor units activated
• b. Wave Summation Tetanus
• 1) Wave summation two identical stimuli in
  rapid succession, the second twitch will be
  stronger than the first because a 2nd contraction
  occurs before the muscle has relaxed.
  Contractions are summed but still have a
  refractory period. Second stimulus before
  complete repolarization
• 2) Tetanus increase rate of stimulus until
  relaxation phase disappears sustained
  contraction
• 3) Muscle fatigue prolonged tetanus leads to
  fatigue or the muscle loses ability to contract
  due to lack of ATP.

36

• 4. Treppe
• a. Staircase effect reflecting increasing Ca2
  availability
• b. Contractions increase in strength with each
  stimulus
• c Basis for warming up for athletic events
• 5. Muscle tone relaxed muscles are always in a
  slightly contracted state - keeps muscles firm
  and ready to respond

37

• 6. Isotonic Isometric Contractions
• a. General
• 1) Muscle tension force exerted by a
  contracting muscle on an object
• 2) Load resistance to movement exerted by
  object
• b. Isotonic Contractions -
• 1) Creates force and moves a load
• 2) Concentric muscle shortens
• 3) Eccentric muscle contracts as it lengthens
• Calf muscle as you walk up a hill

38
Concentric Contraction
39

• c. Isometric Contractions
• 1) Tension develops, but muscle does not
  shorten. Tension develops because of the elastic
  elements of the muscle
• 2) Maintenance of posture, stability of joints
  while other joints move, tucking in your stomach.
  Accomplish no work
• 3) Example If you pick up weights and hold them
  in front of you, there is tension to overcome the
  load of the weight. The muscle is not
  shortening it is isometric. If you bend your
  arms and bring the weight to you shoulder,
  muscle shortens, isotonic contraction. If you
  slowly extend the arms, resisting the weight to
  pull down, it is eccentric or lengthening.
  Eccentric may cause cellular damage and lead to
  soreness.

40

• E. Where does the energy come from?
• 1. Energy for Contraction is ATP
• a. Little stored ATP

41
(No Transcript)
42
(No Transcript)
43

• e. Athletics
• 1) Sprints, weight lifting, diving, etc. rely on
  ATP and CP stores
• 2) Tennis, soccer surges or activity fueled
  almost completely by anaerobic respiration
• 3) Marathon running, prolonged activities depend
  on aerobic
• 4) Aerobic endurance time muscle can continue
  to contract using aerobic pathways
• Anaerobic threshold muscle activity can be
  continued for a long time when ATP demands are
  maintained below the anaerobic threshold
• (ATP 1-2 seconds CP 5-8 seconds, glycogen 60
  seconds aerobic metabolism 2-4 hours)

44

• 2. Muscle fatigue
• a. Physiological inability of muscle to contract
• b. Glycogen glucose exhausted
• c. Results from a relative deficit of ATP,
• d. Lactic acid buildup with resultant
  inhibition of key muscle enzymes

45

• 3. Oxygen Debt
• a. To sustain contractions during exercise, an
  oxygen debt is incurred that must be repaid after
  exercise is over.
• b. Increased breathing provides the oxygen
  required in the biochemical reactions that
• 1. restore creatine phosphate reserves
• 2. remove lactic acid
• 3. replenish depleted glycogen
• c. Increased oxygen uptake is often due to
  elevated muscle temperature and increased levels
  of epinephrine
• 4. Heat production 40 of energy released
  during muscle contraction is converted to useful
  work remainder given off as heat which has to be
  dealt with to maintain homeostasis
• surface heat radiation
• sweat

46
Athletics and Muscle Contraction

• Although all muscle fibers metabolize both
  aerobically and anaerobically, some muscle fibers
  utilize one method more than the other.
• Slow-twitch fibers produce most of their energy
  aerobically and tire only when their fuel supply
  is gone.
• Fast-twitch fibers tend to be anaerobic and seem
  to be designed for strength as their motor units
  contain many fibers.
• Can develop greater, and more rapid, maximum
  tension than slow-twitch fibers.

47
(No Transcript)
48
brief and intense
longer duration
49
Ben Johnson, 1988, Olympic gold medal 100-m
sprint.
50
Athletics and Muscle Contraction

• Muscles that are not used, or are used in only
  weak contractions can atrophy.
• Can cause muscle fibers to progressively shorten,
  leaving body parts contracted in contorted
  positions.
• Hypertrophy occurs if the muscle contracts to at
  least 75 of its maximum tension.

51

• Exercise
• Aerobic exercise increases capillaries,
• mitochondria,
• myoglobin, especially in red slow-twitch fibers,
• hypertrophy of heart,
• better metabolism,
• neuromuscular coordination,
• increases GI movement,
• better gas exchange in lungs.
• 2. Resistance exercise usually anaerobic,
  isometric with high resistance (weights)
  hypertrophy
• 3. Cross-training is best for overall fitness

52
III. Smooth Muscle

• A. Microscopic Structure
• 1. Spindle-shaped, small cells with central
  nuclei
• Not arranged orderly so no striations
• 2. Arranged in sheets or layers in vessels,
  hollow organs
• 3. Longitudinal and circular layers present in
  most of above

53

• 1. Smooth muscles lack highly structured
  neuromuscular junctions of skeletal muscle.
• Less developed SR, no T tubules
• 3. No striations no sarcomeres but thick and
  thin filaments present in a spiral arrangement

54

• B. Contraction
• 1. Smooth muscles have slow, synchronized
  contractions
• 2. Mechanism of Contraction - similar to
  skeletal
• a. Actin and myosin interact by sliding filament
  mechanism
• b. Calcium triggers contraction
• c. ATP provides energy for sliding process
• 3. Contraction is slow, sustained, and resistant
  to fatigue.

55
(No Transcript)
56

• 7. Neural Regulation
• a. Similar to skeletal Action potential, Ca
  channels open
• b. Unlike skeletal, different neurotransmitters
  have different effects (bronchioles, vessels,
  digestive, etc.)
• Chemical factors cause smooth muscle contraction
  also
• hormones,
• lack of oxygen,
• excess CO2
• low pH