Chapter 9 Muscles and Muscle Tissue J.F. Thompson, Ph.D. &
J.R. Schiller, Ph.D. & G. Pitts, Ph.D.
Slide 2
Some Muscle Terminology Myology: the scientific study of muscle
muscle fibers = muscle cells myo, mys & sarco: word roots
referring to muscle
Slide 3
Three Types of Muscle Skeletal, cardiac, and smooth muscle
differ in: Microscopic anatomy Location Regulation by the endocrine
system and the nervous system
Slide 4
Characteristics of Skeletal Muscle Attached primarily to bones
Voluntary (conscious) control (usually) Contracts quickly, tires
easily (fatigable) Allows for wide range of forces to be
generated
Characteristics of Cardiac Muscle Forms most of heart wall
(myocardium) Involuntary (unconscious) Autorhythmicity (contracts
without external stimuli) Fast contraction, non-fatigable Beats at
constant rhythm that can be modified by neural and hormonal
signals
Characteristics of Smooth Muscle Found in the walls of hollow
internal structures (digestive, respiratory, reproductive tracts,
blood vessels) Arrector pili, pupil of the eye, etc. Involuntary
(unconscious) Long, slow contractions, non-fatigable
Functions of Muscle Tissue Motion: external (walking, running,
talking, looking) and internal (heartbeat, blood pressure,
digestion, elimination) body part movements Posture: maintain body
posture Stabilization: stabilize joints muscles have tone even at
rest Thermogenesis: generating heat by normal contractions and by
shivering
Slide 11
Functional Characteristics Excitability (irritability) the
ability to receive and respond to a stimulus (chemical signal
molecules) Contractility ability of muscle tissue to shorten
Extensibility the ability to be stretched without damage most
muscles are arranged in functionally opposing pairs as one
contracts, the other relaxes, which permits the relaxing muscle to
be stretched back Elasticity the ability to return to its original
shape Conductivity (impulse transmission) the ability to conduct
excitation over length of muscle
Slide 12
Connective Tissue Wrappings of Skeletal Muscle Tissue
Superficial Fascia: "hypodermis" Deep Fascia: lines body walls
& extremities; binds muscle together, separating them into
functional groups Epimysium: wraps an entire muscle Perimysium:
subdivides each muscle into fascicles, bundles of 10-100 muscle
fibers Endomysium: wraps individual muscle fibers
Slide 13
Nerve and Blood Supply Each muscle fiber is supplied by a
branch of a motor nerve Each muscle is supplied by its own arteries
and veins Blood vessels branch profusely to provide each muscle
fiber with a direct blood supply
Slide 14
Attachments (to bone) Origin: the part of a muscle attached to
the stationary bone (relative to a particular motion) Insertion:
the part of a muscle attached to the bone that moves (relative to a
particular motion) Attachments are extensions of connective tissue
sheaths beyond a muscle, attaching it to other structures Direct
attachment: epimysium fused to periosteum
Slide 15
Attachment Structure Indirect attachment: connective tissue
wrappings gathered into a tendon or aponeurosis which attaches to
an origin or insertion on bone Tendon: cord (of dense regular
connective tissue) Aponeurosis: sheet (of dense regular connective
tissue)
Slide 16
Microscopic Anatomy of A Skeletal Muscle Fiber Muscle fibers
(cells): long, cylindrical, and multinucleate (individual muscle
cells fuse during embryonic development) Sarcolemma: the cell
membrane of a muscle fiber myoglobinSarcoplasm: the cytoplasm of a
muscle fiber, rich in oxygen-storing myoglobin protein
Slide 17
Myofibrils of A Skeletal Muscle Fiber myofilamentsMyofibrils:
bundles of contractile protein filaments (myofilaments) arranged in
parallel, fill most of the cytoplasm of each muscle fiber; 100s to
1000s per cell Sarcomeres: the repeating unit of contraction in
each myofibril
Slide 18
Organelles of A Skeletal Muscle Fiber Mitochondria: provide the
ATP required for contraction Sarcoplasmic reticulum (smooth ER):
stores Ca 2+ ions which serve as second messengers for
contraction
Slide 19
Striations/Sarcomeres sarcomeresZ discs (lines): the boundary
between sarcomeres; proteins anchor the thin filaments; bisects
each I band A (anisotropic) band: overlap of thick (myosin)
filaments & thin filaments I (isotropic) band: thin (actin)
filaments only H zone: thick filaments only M line: proteins anchor
the adjacent thick filaments
Slide 20
Myofilaments Thin filaments: actin (plus some tropomyosin &
troponin) Thick filaments: myosin Elastic filaments: titin
(connectin) attaches myosin to the Z discs (very high mol.
wt.)
Slide 21
Sarcomeres Components of the muscle fiber with myofilaments
arranged into contractile units The functional unit of striated
muscle contraction Produce the visible banding pattern (striations)
The myofilaments between two successive z discs
Slide 22
Summary of Muscle Structure
Slide 23
Myosin Protein Rod-like tail with two heads Each head contains
ATPase and an actin-binding site; point to the Z line Tails point
to the M line Splitting ATP releases energy which causes the head
to ratchet and pull on actin fibers
Slide 24
Thick (Myosin) Myofilaments Each thick filament contains many
myosin units woven together
Slide 25
Thin (Actin) Myofilaments Two G actin strands are arranged into
helical strands Each G actin has a binding site for myosin Two
tropomyosin filaments spiral around the actin strands Troponin
regulatory proteins (switch molecules) may bind to actin and
tropomyosin & have Ca 2+ binding sites
Slide 26
Muscle Fiber Triads Triads: 2 terminal cisternae + 1 T tubule
Sarcoplasmic reticulum (SER): modified smooth ER, stores Ca 2+ ions
Terminal cisternae: large flattened sacs of the SER Transverse (T)
tubules: inward folding of the sarcolemma
Slide 27
Regulation of Contraction & The Neuromuscular Junction The
Neuromuscular Junction: Where motor neurons communicate with the
muscle fibers Composed of an axon terminal & motor end plate
Axon terminal: end of the motor neurons branches (axon) Motor end
plate: the specialized region of the muscle cell plasma membrane
adjacent to the axon terminal
Slide 28
The Neuromuscular Junction: Synapse: point of communication is
a small gap Synaptic cleft: the space between axon terminal &
motor end plate Synaptic vesicles: membrane-enclosed sacs in the
axon terminals containing the neurotransmitter
Slide 29
The Neuromuscular Junction: Neurotransmitter: the chemical that
travels across the synapse, i.e., acetylcholine, ACh) Acetylcholine
(ACh) receptors: integral membrane proteins which bind ACh
Slide 30
axonal terminal motor end plate Generation of an Action
Potential (Excitation) Binding of neurotransmitter (ACh) causes the
ligand-gated Na + channels to open Opening of the Na + channels
depolarizes the sarcolemma (cell membrane)
Slide 31
Generation of an Action Potential Initial depolarization causes
adjacent voltage- gated Na + channels to open; Na + ions flow in,
beginning an action potential Action potential: a large transient
depolarization of the membrane potential transmitted over the
entire sarcolemma (and down the T tubules)
Slide 32
Generation of an Action Potential Repolarization: the return to
polarization due to the closing voltage-gated Na + channels and the
opening of voltage gated K + channels Refractory period: the time
during membrane repolarization when the muscle fiber cannot respond
to a new stimulus (a few milliseconds) All-or-none response: once
an action potential is initiated it results in a complete
contraction of the muscle cell
Slide 33
Excitation-Contraction Coupling The action potential
(excitation) travels over the sarcolemma, including T- tubules DHP
receptors serve as voltage sensors on the T- tubules and cause
ryanodine receptors on the SR to open and release Ca 2+ ions And
now, for the interactions between calcium and the sarcomere
Slide 34
The Sliding Filament Model of Muscle Contraction Thin and thick
filaments slide past each other to shorten each sarcomere and,
thus, each myofibril The cumulative effect is to shorten the
muscle
Slide 35
http://www.lab.anhb.uwa.edu.au/mb140/CorePages/Muscle/Muscle.htm#SKELETAL
This simulation of the sliding filament model can also be viewed on
line at the web site below along with additional information on
muscle tissue
Slide 36
Calcium (Ca 2+ ) The on-off switch: allows myosin to bind to
actin off on
Slide 37
Calcium Movements Inside Muscle Fibers Action potential causes
release of Ca 2+ ions (from the cisternae of the SR) Ca 2+ combines
with troponin, causing a change in the position of tropomyosin,
allowing actin to bind to myosin and be pulled (slide) Ca 2+ pumps
on the SR remove calcium ions from the sarcoplasm when the stimulus
ends
Slide 38
The Power Stroke & ATP 1.Cross bridge attachment. myosin
binds to actin 2.The working stroke. myosin changes shape (pulls
actin toward it); releases ADP + P i 3.Cross bridge detachment.
myosin binds to new ATP; releases actin
Slide 39
The Power Stroke & ATP 4. "Cocking" of the myosin head. ATP
hydrolyzed (split) to ADP + P i ; provides potential energy for the
next stroke
Slide 40
The Ratchet Effect Repeat steps 1-4: The ratchet action repeats
the process, shortening the sarcomeres and myofibrils, until Ca 2+
ions are removed from the sarcoplasm or the ATP supply is exhausted
Attach Power Stroke Release Repeat
Excitation-Contraction Coupling 1.The action potential
(excitation) travels over the sarcolemma, including T- tubules
2.DHP receptors serve as voltage sensors on the T- tubules and
cause ryanodine receptors on the SR to open and release Ca 2+ ions
3.Ca 2+ binds to troponin, causing tropomyosin to move out of its
blocking position 4.Myosin forms cross bridges to actin, the power
stroke occurs, filaments slide, muscle shortens 5.Calsequestrin and
calmodulin help regulate Ca 2+ levels inside muscle cells
Slide 43
Destruction of Acetylcholine Acetylcholinesterase: an enzyme
that rapidly breaks down acetylcholine is located in the
neuromuscular junction Prevents continuous excitation (generation
of more action potentials) Many drugs and diseases interfere with
events in the neuromuscular junction Myasthenia gravis: loss of
function at ACh receptors (autoimmune disease?) Curare (poison
arrow toxin): binds irreversibly to and blocks the ACh
receptors
Slide 44
MUSCLE CONTRACTION One power stroke shortens a muscle about 1%
Normal muscle contraction shortens a muscle by about 35% Cross
bridge (ratchet effect) cycle repeats continue repeating power
strokes, continue pulling increasing overlap of fibers; Z lines
come together About half the myosin molecules are attached at any
time Cross bridges are maintained until Ca 2+ levels decrease Ca 2+
released in response to action potential delivered by motor neuron
Ca 2+ ATPase Ca 2+ ATPase pumps Ca 2+ ions back into the SR
Slide 45
RIGOR MORTIS IN DEATH Ca 2+ ions leak from SR causing binding
of actin and myosin and some contraction of the muscles Lasts ~24
hours, then enzymatic tissue disintegration eliminates it in
another 12 hours
Slide 46
Skeletal Muscle Motor Units The Motor Unit = Motor Neuron +
Muscle Fibers to which it connects (Synapses)
Slide 47
Skeletal Muscle Motor Units The size of Motor Units varies:
Small - two muscle fibers/unit (larynx, eyes) Large hundreds to
thousands/unit (biceps, gastrocnemius, lower back muscles) The
individual muscle cells/fibers of each unit are spread throughout
the muscle for smooth efficient operation of the muscle as a
whole
Slide 48
The Myogram Myogram: a recording of muscle contraction
Stimulus: nerve impulse or electrical charge Twitch: a single
contraction of all the muscle fibers in a motor unit (one nerve
signal)
Slide 49
Myogram 1.Latent period: delay between stimulus and response
2.Contraction phase: tension or shortening occurs 3.Relaxation
phase: relaxation or lengthening
Slide 50
Muscle Twitches All or none rule: All the muscle fibers of a
motor unit contract all the way when stimulated
Slide 51
Graded Muscle Responses Force of muscle contraction varies
depending on need. How much tension is needed? Twitch does not
provide much force Contraction force can be altered in 3 ways: 1.
changing the frequency of stimulation (temporal summation) 2.
changing the stimulus strength (recruitment) 3. changing the
muscles length
Slide 52
Temporal Summation Temporal (wave) summation: contractions
repeated before complete relaxation, leads to progressively
stronger contractions unfused (incomplete) tetanus: frequency of
stimulation allows only incomplete relaxation fused (complete)
tetanus: frequency of stimulation allows no relaxation
Slide 53
Treppe: the staircase effect warming up of a muscle fiber
Slide 54
Multiple Motor Unit Summation ( Recruitment) The stimulation of
more motor units leads to more forceful muscle contraction
Slide 55
The Size Principle As stimulus intensity increases, motor units
leads with larger fibers are recruited
Slide 56
Stretch: Length-Tension Relationship Stretch (sarcomere length)
determines the number of cross bridges extensive overlap of actin
with myosin: less tension optimal overlap of actin with myosin:
most tension reduced overlap of actin with myosin: less tension
Optimal overlap: most cross bridges available for the power stroke
and least structural interference more resistance most cross
bridges/least resistance fewest cross bridges
Slide 57
Stretch: Length-Tension Relationship Optimal length - L o
maximum number of cross bridges no overlap of actin fibers from
opposite ends of the sarcomere normal working muscle range from 70
- 130% of L o
Slide 58
Contraction of a Skeletal Muscle Isometric Contraction: Muscle
does not shorten Tension increases
Slide 59
Contraction of a Skeletal Muscle Isotonic Contraction: tension
does not change Muscle (length) shortens
Slide 60
Regular small contractions caused by spinal reflexes Respond to
tendon stretch receptor sensory input Activate different motor
units over time Provide constant tension development muscles are
firm but no movement e.g., neck, back and leg muscles maintain
posture Muscle Tone
Slide 61
Muscle Metabolism Energy availability Not much ATP is available
at any given moment ATP is needed for cross bridges and Ca 2+
removal Maintaining ATP levels is vital for continued activity
Three ways to replenish ATP: 1. Creatine Phosphate energy storage
system 2. Anaerobic Glycolysis -- Lactic Acid system 3. Aerobic
Respiration
Slide 62
CrP stored in cell Allows for rapid ATP replenishment Only a
small amount available (10-30 seconds worth) Direct Phosphorylation
Creatine Phosphate System
Slide 63
Anaerobic Glycolysis Lactic Acid System Anaerobic system - no O
2 required Very inefficient, does not create much ATP Only useful
in short term situations (30 sec - 1 min) Produces lactic acid as a
by-product
Slide 64
Aerobic System -Uses oxygen for ATP production -Oxygen comes
from the RBCs in the blood and the myoglobin storage depot -Uses
many substrates: carbohydrates, lipids, proteins -Good for long
term exercise -May provide 90-100% of the needed ATP during these
periods
Slide 65
Summary of Muscle Metabolism
Slide 66
Oxygen Debt The amount of oxygen needed to restore muscle
tissue (and the body) to the pre-exercise state Muscle O 2, ATP,
creatine phosphate, and glycogen levels, and a normal pH must be
restored after any vigorous exercise Circulating lactic acid is
converted/recycled back to glucose by the liver
Slide 67
Factors Affecting the Force of Contraction 1.Number of muscle
fibers contracting (recruitment) 2. Size of the muscle 3.Frequency
of stimulation 4.Degree of muscle stretch when the contraction
begins
Slide 68
Muscle Fiber Type: Speed of Contraction Slow oxidative fibers
contract slowly, have slow acting myosin ATPases, and are fatigue
resistant (red) Fast oxidative fibers contract quickly, have fast
myosin ATPases, and have moderate resistance to fatigue Fast
glycolytic fibers contract quickly, have fast myosin ATPases, and
are easily fatigued (white)
Slide 69
Force, Velocity, and Duration of Muscle Contraction
Slide 70
Smooth Muscle Tissue When the longitudinal layer contracts, the
organ dilates and contracts When the circular layer contracts, the
organ elongates
Slide 71
Smooth Muscle Contractions Peristalsis alternating contractions
and relaxations of smooth muscles that squeeze substances through
the lumen of hollow organs Segmentation contractions and
relaxations of smooth muscles that mix substances in the lumen of
hollow organs Peristalsis Animation
Slide 72
Contraction of Smooth Muscle Some smooth muscle cells: Act as
pacemakers and set the contractile pace for whole sheets of muscle
Are self-excitatory and depolarize without external stimuli Whole
sheets of smooth muscle exhibit slow, synchronized contraction They
contract in unison, reflecting their electrical coupling with gap
junctions Action potentials are transmitted from cell to cell
Slide 73
Smooth Muscle Tissue Contracts under the influence of:
Autonomic nerves Hormones Local factors
Slide 74
Developmental Aspects of the Muscular System Muscle tissue
develops from embryonic mesoderm called myoblasts (except the
muscles of the iris of the eye and the arrector pili muscles in the
skin) Multinucleated skeletal muscles form by fusion of myoblasts
The growth factor agrin stimulates the clustering of ACh receptors
at newly forming motor end plates As muscles are brought under the
control of the somatic nervous system, the numbers of fast and slow
fibers are also determined Cardiac and smooth muscle myoblasts do
not fuse but develop gap junctions at an early embryonic stage
Slide 75
Regeneration of Muscle Tissue Cardiac and skeletal muscle
become amitotic, but can lengthen and thicken Myoblast-like
satellite cells show very limited regenerative ability Satellite
(stem) cells can fuse to form new skeletal muscle fibers Cardiac
cells lack satellite cells Smooth muscle has good regenerative
ability
Slide 76
Developmental Aspects: After Birth Muscular development
reflects neuromuscular coordination Development occurs head-to-toe,
and proximal-to-distal Peak natural neural control of muscles is
achieved by midadolescence Athletics and training can improve
neuromuscular control
Slide 77
Developmental Aspects: Male and Female There is a biological
basis for greater strength in men than in women Womens skeletal
muscle makes up 36% of their body mass Mens skeletal muscle makes
up 42% of their body mass
Slide 78
Developmental Aspects: Male and Female These differences are
due primarily to the male sex hormone testosterone With more muscle
mass, men are generally stronger than women Body strength per unit
muscle mass, however, is the same in both sexes
Slide 79
Developmental Aspects: Age Related With age, connective tissue
increases and muscle fibers decrease Muscles become stringier and
more sinewy By age 80, 50% of muscle mass is lost (sarcopenia)
Regular exercise reverses sarcopenia Aging of the cardiovascular
system affects every organ in the body Atherosclerosis may block
distal arteries, leading to intermittent claudication and causing
severe pain in leg muscles
Slide 80
Homeostatic Imbalances Muscular dystrophy group of inherited
muscle- destroying diseases where muscles enlarge due to fat and
connective tissue deposits, but muscle fibers atrophy.
Slide 81
Homeostatic Imbalances Duchenne Muscular Dystrophy: Inherited
lack of functional gene for formation of a protein, dystrophin,
that helps maintain the integrity of the sarcolemma Onset in early
childhood, victims rarely live to adulthood
Smooth Muscle Composed of spindle-shaped fibers with a diameter
of 2-10 m and lengths of several hundred m Lack the coarse
connective tissue sheaths of skeletal muscle, but have fine
endomysium Organized into two layers (longitudinal and circular) of
closely apposed fibers Found in walls of hollow organs (except the
heart) Have essentially the same contractile mechanisms as skeletal
muscle
Slide 86
Smooth Muscle Tissue No striations (no sarcomeres) Uninucleate
Spindle-shaped Involuntary May be autorhythmic May have gap
junctions
Slide 87
Series Elastic Elements All of the noncontractile structures of
a muscle: Connective tissue coverings and tendons Elastic elements
of sarcomeres Internal load: force generated by myofibrils on the
series elastic elements External load: force generated by series
elastic elements on load
![[PPT]Muscle Tissue - Austin Peay State University · Web viewLab 8 Muscle Physiology Gilbert R. Pitts, Ph.D., Joseph R. Schiller, Ph.D., and James F. Thompson, Ph.D. Lab 8 Activities](https://img.pdfslide.us/doc/110x75/5af1a6c27f8b9a8c308ec58a/pptmuscle-tissue-austin-peay-state-viewlab-8-muscle-physiology-gilbert-r-pitts.jpg)
