Download Unit II- Muscular System Physiology

Unit II
Muscular System
Homeostasis
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Maintaining Boundaries
Movement
Responsiveness
Digestion
Metabolism
Growth
Support
Skeletal
Muscle Tissue
Chapter 10
Overview of Muscle Tissue
• ‘Little mouse’ – 3 types of muscle tissue
▫ Walls of the heart (cardiac muscle tissue)
▫ Walls of hollow organs (smooth muscle tissue)
▫ Skeletal muscle makes up 40% of body weight
Homeostatic Function of Muscle Tissue
• Movement
▫ Skeletal muscle moves the body by moving the bones
▫ Smooth muscle squeezes fluids and other substances through hollow
organs
• Maintenance of posture – enables the body to remain sitting
or standing
• Joint stabilization – muscle tone
• Heat generation – muscle contractions produce heat that
helps maintain normal body temperature
Functional Features of Muscle
• Contractility – long cells shorten and generate pulling force
• Excitability – electrical nerve impulse stimulates the muscle
cells to contract
• Extensibility – can be stretched back to its original length by
contraction of an opposing muscle
• Elasticity – can recoil passively and resume its resting length
Types of Muscle
• Skeletal
• Smooth
• Cardiac
Skeletal Muscle
•
•
•
•
Longest and most slender muscle fibers
1-20 mm in length and 40-50 µm in diameter
Single-celled, Cigar-shaped, multinucleate cells
Striated
SKELETAL MUSCLE
• SKELETAL MUSCLES ARE RESPONSIBLE
FOR VOLUNTARY (CONSCIOUS)
MOVEMENT.
▫ What are they controlled by?
• Striated
• Found in limbs and body trunk
SMOOTH MUSCLES
• Spindle-shaped and have single nucleus
▫ Not striated
▫ Interlace to form sheets of smooth muscle tissue
• Not under voluntary control AKA involuntary muscle.
• Found in internal organs: stomach, intestines, and blood
vessels
• 4. Smooth muscle fibers are surrounded by connective
tissue, but the connective tissue does not unite to form
TENDONS as it does in Skeletal Muscles.
CARDIAC MUSCLE
• Found in the heart
• Striated but involuntary
• Cells contain ONE
Nucleus located near the
center, adjacent cells
form branching fibers
that allow Nerve
Impulses to pass from
cell to cell.
Anatomy of Skeletal Muscle
• Muscle Fasicles Muscle Fiber Myofibril
Sarcomere Actin and Myosin
Levels of Functional
Organization in a
Skeletal Muscle
Muscle Fascicle
Muscle Fiber
Myofibril
Sacromere
Imagine…
• Imagine a muscle fiber
as a single stalk of
spaghetti
• Several stalks of
spaghetti are bundled
together in a sheath
• Those sheaths are also
bundled together until
you have a bundle of
bundles
From Fiber to Epimysium
• One muscle fiber is wrapped in an endomysium
▫ Endo=within
▫ Myo=muscle
From Fiber to Epimysium
• Each endomysiumwrapped fiber is in turn
bundled and called a
fascicle
▫ These fascicles
wrapped in another
layer of connective
tissue called a
perimysium
 Peri=around (think
“perimeter”)
From Fiber to Epimysium
• These perimysium-wrapped fascicles are
bundled together and receive yet one more
connective tissue covering: the epimysium
▫ Epi=on top of
• The epimysium blends together into a tendon,
which in turn connects it to the bone
Exit Survey
• http://goo.gl/kvpqoH
Diagram of Part of a Muscle Fiber
Sarcolemma
Mitochondrion
Myofibril
Dark A band
Nucleus
Light I band
(b) Diagram of part of a muscle fiber
showing the myofibrils. One myofibril is
extended from the cut end of the fiber.
Figure 10.4b
Part II: Microscopic
• Muscle fiber = muscle cell
• Long thin tube with many
nuclei (multinucleate)
Microscopic Anatomy of Skeletal
Muscle
• Sarcolemma – specialized
plasma membrane
• Sarcoplasmic reticulum –
specialized smooth
endoplasmic reticulum
▫ Stores calcium (Ca2+)
Figure 6.3a
Microscopic Anatomy of Skeletal
Muscle
• Myofibril
▫ Long ribbon-like organelles that fill cytoplasm
▫ Composed of bundles of myofilaments
▫ Myofibrils are aligned to give distinct bands
 I band =
light band
 A band =
dark band
• Bands make muscle look STRIATED
Figure 6.3b
Microscopic Anatomy of Skeletal
Muscle
• Sarcomere
▫ Contractile unit of a muscle fiber
▫ From Z disc to Z disc
Figure 6.3b
Myofilaments
• The thick filaments are composed of a protein called
myosin
▫ These are classified as an ATPase
 means it is an enzyme that generates energy through
breaking down ATP
• The thin filaments are composed of a protein called
actin
▫ These anchor to the Z disc (the center of the I band)
 This is why the I band is lighter-it only contains thin
filaments!
• The thick and the thin filaments overlap and are
anchored to each other
Actin Video
Polleverywhere
Microscopic Anatomy of Skeletal Muscle
• Sarcomere organization (Section of myofibrils)
▫ Thick filaments = myosin filaments = dark band
Figure 6.3c
Microscopic Anatomy of Skeletal
Muscle
• Organization of the sarcomere
▫ Thin filaments = actin filaments = light band
 Composed of the protein actin
Figure 6.3c
Microscopic Anatomy of Skeletal
Muscle
• Myosin filaments have heads (extensions, or
cross bridges)
• Myosin and
actin overlap
somewhat
Figure 6.3d
Microscopic Anatomy of Skeletal
Muscle
• At rest, there is a bare zone that lacks actin
filaments
Figure 6.3d
What about that other stuff?
• Z disc
▫ The half-way point
right in the middle
of the I line
 Dark or light?
 LIGHT!
• There is also the H
zone and the M line
Sarcomere Structure
• A bands: full length of the thick filament
▫ Includes overlapping inner end of thin filaments
• H zone: center part of A band, no thin filaments occur
▫ A bands and I bands refract polarized light differently
 A bands—anisotropic
 I bands—isotropic
• M line: center of H zone
▫ Contains tiny rods that hold thick filaments together
• I band: region with only thin filaments
▫ Lies within two adjacent sarcomeres
Sarcomere
• Basic unit of contraction of skeletal muscle
▫ Z disc (Z line): boundaries of each sarcomere
▫ Thin (actin) filaments: extend from Z disc toward the center of the sarcomere
▫ Thick (myosin) filaments: located in the center of the sarcomere
 Overlap inner ends of the thin filaments
 Contain ATPase enzymes
Skeletal Muscle Video
Exit Survey
• http://goo.gl/M6NJ4k
Fig. 50-25b
TEM
M line
0.5 µm
Thick
filaments
(myosin)
Thin
filaments
(actin)
Z line
Z line
Sarcomere
Spinal cord
Motor Units
Motor Motor
unit 1 unit 2
Axon terminals at
neuromuscular
junctions
Branching axon
to motor unit
Nerve
Motor neuron
cell body
Motor
neuron
axon
Muscle
Muscle
fibers
(a) Axons of motor neurons extend from the spinal cord to
the muscle. There each axon divides into a number of
axon terminals that form neuromuscular junctions with
muscle fibers scattered throughout the muscle.
(b) Branching axon
terminals form
neuromuscular
junctions, one
per muscle fiber
(photomicrograph
110).
Fig 10.10
Video
• http://bcs.whfreeman.com/thelifewire/content/
chp44/4402003.html
Innervation of Skeletal Muscle
• Motor neurons innervate skeletal muscle tissue
▫ Nerve that carries signal from spinal cord to muscle
▫ Each muscle fiber connected to nerve ending that signals contraction
• Neuromuscular junction (motor end plate) – point of contact
between the nerve ending and muscle fiber
• Axon terminals (ends of axons): store neurotransmitters
• Synaptic cleft: space between axon terminal and sarcolemma
of a muscle fiber
▫ Neurotransmitter: Chemical that transmits signal across a synapse
▫ Acetylcholine: NT that diffuses across the synaptic cleft
 Binds its receptor inducing an impulse that initiates fiber contraction
Polleverywhere
What’s the difference between motor unit &
neuromuscular junction?
Motor Unit: one neuron & the
muscle fibers it controls
• Neuromuscular Junction: one
neuron and one muscle fiber.
• What are the circle like
structures in the neuron?
• What is the muscle fiber in this
picture?
Muscle Stimulation Process
1.
2.
Impulse travels down neuron
Once an impulse travels
down the neuron, where does
Calcium (Ca++) enter the
neuron?
-What does the Calcium do?
-Calcium channels open and
calcium flows into axon
terminal
Muscle Stimulation Process
• 3. Calcium signals vesicles to
release neurotransmitter.
Muscle Stimulation Process
4. Acetylcholine travels across
synaptic cleft and binds to
sodium-gated channel.
-How does this affect the muscle
fiber? What is entering the
muscle fiber?
▫ Sodium (Na+)
Muscle Stimulation Process
5. What happens to the
neurotransmitters after
sodium enters the muscle cell?
-Acetylcholine broken
down by acetylcholinesterase
and taken back up to be placed
into more vesicles
Muscle Stimulation Process
6. Muscle Impulse travels
INSIDE muscle fiber to
myofibril.
7. What is released from
Sarcoplasmic Reticulum (SR)?
Calcium
NMJ Activity
Exit Survey
• http://goo.gl/evjf3n
Physiology of Muscle Cell
Contraction
Muscle Stimulation Process: Sliding
Filament Theory
8. Ca++ released from SR
attaches to what myofilament?
- actin
- troponin/tropomyosin
Muscle Stimulation Process: Sliding
Filament Theory
9. Myosin heads attach to actin
at binding sites
Muscle Stimulation Process: Sliding
Filament Theory
10. Myosin pushes actin back
(Walk along actin)
• 11. ATP binds to myosin head
and myosin reloads
1 Myosin heads
Key:
= Ca2+
break down ATP
and become
reoriented and
energized
2 Myosin heads
ADP
P
bind to actin,
forming cross–
bridges
P
ATP
4 As myosin heads
bind ATP, the
cross–bridges
detach from actin
ATP
Contraction cycle continues
if ATP is available and Ca2+
level in the sarcoplasm is
high
ADP
ADP
3 Myosin cross–bridges
rotate toward center of
the sarcomere (power
stroke)
Polleverywhere
Mechanism of Contraction
• SR contains calcium ions – released when muscle is
stimulated to contract
▫ Ca2+ diffuse out triggering the sliding filament mechanism
 After contraction ions pumped back into SR for storage
• Contraction: controlled by nerve-generated impulses
▫ Travel along the sarcolemma of the muscle fiber
▫ Impulses further conducted by T-tubules
▫ Each impulse promotes release of calcium ions from the terminal
cisterns
Sarcolemma
\
Transverse
tubules
Terminal
cistern of SR
Muscle action potential
Ca2+ release channels open
Ca2+ release channels closed
Thin filament
Myosinbinding site on
actin
Troponin
Tropomyosin
Myosin
Key:
= Ca2+
Troponin holds tropomyosin in
position to block myosin-binding
sites on actin.
(a) Relaxation
= Ca2+ active
transport pumps
= Ca2+ release
channels
Ca2+ binds to troponin, which changes
the shape of the troponin–tropomyosin
complex and uncovers the myosinbinding sites on actin.
(b) Contraction
Sliding Filament
Mechanism
• Explains concentric contraction
▫ Myosin heads attach to thin filaments at both ends of a
sarcomere
 Then pull thin filaments toward the center of the
sarcomere
 Thin and thick filaments do not shorten
▫ Initiated by release of calcium ions from the SR
▫ Powered by ATP
1 Myosin heads
Key:
= Ca2+
break down ATP
and become
reoriented and
energized
2 Myosin heads
ADP
P
bind to actin,
forming cross–
bridges
P
ATP
4 As myosin heads
bind ATP, the
cross–bridges
detach from actin
ATP
Contraction cycle continues
if ATP is available and Ca2+
level in the sarcoplasm is
high
ADP
ADP
3 Myosin cross–bridges
rotate toward center of
the sarcomere (power
stroke)
Sliding Filament Mechanism
Thick (myosin)
filament
Thin (actin)
filament
Thin (actin)
filament
Thin (actin)
filament
Myosin
heads
Thick (myosin)
filament
Movement
Myosin
head
Thick (myosin)
filament
(a) Myosin heads attach to actin in the
thin filaments, then pivot to pull the
thin filaments inward.
(b) Transmission electron micrograph of
part of a sarcomere, showing myosin
heads attached to the thin filaments
Figure 10.7
Sliding Filament Mechanism
• Contraction changes the striation pattern
▫ Fully relaxed: thin filaments partially overlap thin filaments
▫ Contraction: Z discs move closer together
 Sarcomere shortens
 I bands shorten, H zone disappears
 A band remains the same length
Sliding Filament Mechanism
Z
I
H
A
Z
Z
I
I
1 Fully relaxed sarcomere of a muscle fiber
Z
A
I
2 Fully contracted sarcomere of a muscle fiber
• Myosin heads attach to actin in thin filaments
• Pivot to pull the thin filaments inward toward the center of the
sarcomere
Figure 10.8
Exit Survey
http://goo.gl/wMmmOt
Exit Survey 2.0
• http://goo.gl/wOSV40
Modeling Activity
• Pipe Cleaner= Actin and
Myosin
• Popsicle stick= Z-disc
• Clay= Troponin
• Foil= Tropomyosin
Mechanism of Contraction
• Two types of muscle contraction:
▫ Eccentric contraction: muscle generates force as it lengthens
 Essential for controlled movement and resistance to gravity
 Muscles act as a ‘brake’ to resist gravity
 ‘Down’ portion of a pushup
▫ Concentric contraction: muscle shortens to do work
 Sliding filament mechanism
Microscopic and Functional Anatomy
of Skeletal Muscle Tissue
• Muscle extension: muscle is stretched by a movement
opposite that which contracts it
• Muscle fiber length and force of contraction
▫ Greatest force produced when a fiber starts out slightly stretched
▫ Myosin heads can pull along the entire length of the thin filaments
The Neuromuscular Junction
Nerve
impulse
Nucleus
Myelinated axon
of motor neuron
Axon terminal of
neuromuscular
junction
Sarcolemma of
the muscle fiber
1 Nerve impulse stimulates the
release of the neurotransmitter
acetylcholine (ACh) into the
synaptic cleft.
(a)
Synaptic
cleft
Axon terminal
of motor neuron
Synaptic vesicle
containing ACh
Sarcolemma
2 ACh stimulates changes in
the sarcolemma that excite the
muscle fiber. This stimulus is
carried down the T tubules to
initiate fiber contraction.
Terminal
cisterna
of SR
Triad
Muscle fiber
(b)
Figure 10.9
Ca2+
3 Enzymes in the synaptic cleft
break down ACh and thus limit its
action to a single muscle twitch.
Effect of Exercise on Muscles
• SWBAT analyze the effects of exercise on
muscles
Types of Skeletal Muscle Fibers
• Skeletal muscle fibers are categorized according to two
characteristics
▫ How they manufacture energy (ATP)
▫ How quickly they contract
• Oxidative fibers—produce ATP aerobically
• Glycolytic fibers—produce ATP anaerobically by glycolysis
Types of Skeletal Muscle Fibers
• Skeletal muscle fibers divided into
three classes
▫ Slow oxidative fibers: red slow oxidative fibers
▫ Fast glycolytic fibers: white fast glycolytic fibers
▫ Fast oxidative fibers: intermediate fibers
• Slow Oxidative Fibers: red color due to abundant myoglobin
▫ Obtain energy from aerobic metabolic reactions
▫ Contain a large number of mitochondria
▫ Richly supplied with capillaries
▫ Contract slowly and resistant to fatigue
▫ Fibers are small in diameter
Types of Skeletal Muscle Fibers
• Fast Glycolytic Fibers: contain little myoglobin and few
mitochondria
▫
▫
▫
▫
About twice the diameter of slow-oxidative fibers
Contain more myofilaments and generate more power
Depend on anaerobic pathways
Contract rapidly and tire quickly
• Fast Oxidative Fibers: have an intermediate diameter
▫
▫
▫
▫
▫
Contract quickly like fast glycolytic fibers
Are oxygen-dependent
Have high myoglobin content and rich supply of capillaries
Somewhat fatigue-resistant
More powerful than slow oxidative fibers
Fast Twitch vs. Slow Twitch
• http://www.youtube.com/watch?v=Uxwh2IIg_
Z0
Exercise and Skeletal Muscle Tissue
• The relative ratio of FG and SO fibers is genetically determined and
helps account for individual differences in physical performance
Effect of Exercise on Muscles
• Muscle inactivity always leads to muscular
wasting
• Use it or lose it
• Regular exercise increases muscle size, strength,
and endurance
Aerobic Exercise
• Jogging or biking
• Effects to muscle cells: Increases blood supply to
muscles, individual cells form more
mitochondria and store more oxygen
• Results in stronger more flexible muscles with
greater endurance
• Aerobic exercise does not cause muscle to increase
in size
Aerobic Exercise
• Effects on Rest of Body:
▫
▫
▫
▫
▫
Improves digestion
Enhances neuromuscular coordination
Heart enlarges
Clears fat deposits
Lungs become more efficient in gas exchange
Heart Rate
• Average resting heart rate is 70 bpm
• Lowest ever recorded is 27 bpm
• Lance Armstrong 32-34 bpm
• Let’s find out ours! How do we find our pulse?
Lung Capacity
• The maximum rate of Oxygen (O2) consumption
by the body during exercise, commonly written
as VO2max, is the criterion measure of aerobic
endurance fitness.
• The measurement can be given in the units liters
of O2 per min (l.min-1) or divided by body
weight to get a score relative to a person's body
weight (ml.kg.min-1)
Lung Capacity
• The average young untrained male of about 3.5
liters/minute or 45 ml/min/kg.
• World class male endurance athletes in sports
such as cycling and cross-country skiing
typically achieved scores in excess of 80
ml/kg/min, and occasionally a few may exceed
90 ml/kg/min.
• Lance Armstrong 84.0 ml/kg/min.
• The average young untrained female will score
about 2.0 liters/minute or 38 ml/min/kg
compared to world class female endurance
athletes which a few may exceed 70 ml/kg/min.
Resistance Exercise
• Muscles are pitted against some immovable
object or form of resistance
• Effects:
▫ Results in increased number of contractile
filaments within muscle cells
 (# of muscle cells doesn’t increase but the size of
them does)
▫ Amount of connective tissue that reinforces
muscle also increases
Resistance Exercise
• Strenuous exercise can cause
slight damage to the muscle
fibers.
• It’s actually through this
process of damage and repair
that muscles become stronger.
• After exercise, we sometimes
experience stiffness or
soreness for a period of time
until our muscles have fully
recovered.
• This soreness can also be
caused by lactic acid
remaining in the muscles
Botox
Disorders of Muscle Tissue
• Muscle tissues experience few disorders
▫ Heart muscle is the exception
▫ Skeletal muscle remarkably resistant to infection
▫ Smooth muscle problems stem from external irritants
• Muscular dystrophy: group of inherited muscle destroying
disease
▫ Affected muscles enlarge with fat and connective tissue and muscles
degenerate
▫ Types of muscular dystrophy: Duchenne muscular dystrophy and
myotonic dystrophy
Disorders of Muscle Tissue
• Myofascial pain syndrome: pain caused by tightened bands
of muscle fibers
• Fibromyalgia: mysterious chronic-pain syndrome
▫ Affects mostly women
▫ Symptoms include fatigue, sleep abnormalities, severe musculoskeletal
pain, and headache
Muscle Tissue Throughout Life
• Muscle tissue develops from myoblasts
▫ Myoblasts fuse to form skeletal muscle fibers
▫ Skeletal muscles contract by the Myotube
seventh week of development
Embryonic
mesoderm cells
Myoblasts
(immature
multinucleate
muscle fiber)
Satellite
cell
1 Embryonic
2 Several
3 Myotube
mesoderm
cells undergo
cell division
(to increase
number) and
enlarge.
myoblasts
fuse together
to form a
myotube.
matures into
skeletal
muscle fiber.
Mature
skeletal
muscle
fiber
Muscle Tissue Throughout Life
• Cardiac muscle: pumps blood three weeks after fertilization
• Satellite cells surround skeletal muscle fibers
▫ Resemble undifferentiated myoblasts
▫ Fuse into existing muscle fibers to help them grow
• With increased age amount of connective tissue increases in
muscles and number of muscle fibers decreases
• Loss of muscle mass with aging
▫ Decrease in muscular strength is 50% by age 80
▫ Sarcopenia: muscle wasting