Download Exercise 12 Muscle Tissue

Exercise 14
Microscopic Anatomy,
Organization, and
Classification of
Skeletal Muscle
SKELETAL MUSCLE



Voluntary or involuntary?
Striated or not?
Multinucleate or uninucleate?
Terminology
“Myo-” or “-Mys-” = muscle
 “Sarco-” = flesh

Figure 12.1a Microscopic anatomy of skeletal muscle.
Microscopic
Anatomy


Muscle Fiber
Nuclei
Dark A band
Light I band
Nuclei
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Fiber
Figure 12.1b Microscopic anatomy of skeletal muscle.
Muscle Fiber Anatomy
• Sarcolemma
• Sarcoplasm
Sarcolemma
Mitochondrion
Myofibril
Dark
A band
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Light
I band
Nucleus
Figure 12.1c Microscopic anatomy of skeletal muscle.
• Myofibrils
– Composed of myofilaments
• Actin (thin filaments) & myosin (thick filaments)
Z disc
H zone
Z disc
Thin (actin) filament
Thick (myosin) filament
I band
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A band
I band
M line

Transverse tubules

Sarcoplasmic Reticulum (SR)
– Smooth ER
– Terminal cisternae: enlarged portion of SR
on either side of T tubule

Triad = T tubule + 2 terminal cisternae
Fig. 10-3
Fig. 10-6
Figure 12.3 Photomicrograph of muscle fibers, longitudinal and cross sections (800).
Nuclei of muscle fibers
Muscle fibers,
longitudinal
view
Muscle fibers,
cross-sectional
view
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Figure 12.1d Microscopic anatomy of skeletal muscle.
• Sarcomeres
– Organized group of myofilaments
– Contractile units, smallest functional unit of
muscle fiber
– Z-line to Z-line
M line
Z disc
Z disc
Thin (actin) filament
Elastic (titin) filaments
Thick (myosin) filament
I band: LIGHT
• midline is Z
line/disc
• Thin only
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A band: DARK
• Thick and thin
• M line in
middle
Myofilaments

Thick filaments: myosin
 “cross-bridges”
Contraction:
myosin head
changes
shape & will
grab onto
actin…and
pull it toward
M-line
Fig. 10-7
Myofilaments

Thin filaments: 3 types of protein molecules
– actin
– Tropomyosin
– Troponin
Connective Tissue Wrappings:
3 Layers
Epimysium = outer
 Perimysium = central
 Endomysium = inner

Connective Tissue Wrappings

Epimysium
– Epi = on (outside layer)
– Surrounds entire muscle
Connective Tissue Wrappings

Perimysium
– Peri = around (central layer)
– Divides muscle into compartments:
 Fascicle = bundle of muscle fibers (cells)
Fig. 10-1
Connective Tissue Wrappings

Endomysium
– Endo = inside (inner layer)
– Surrounds individual skeletal muscle
cells (fibers)
Fig. 10-1
Connective Tissues, cont.
Layers continuous & interwoven –
blend into one another
 Muscle’s ends: layers unite to form

– Bundle: TENDON
 Attach skeletal muscles to bones
 Contraction pulls the bone(s)
– Broad sheet: APONEUROSIS
 Attach skeletal muscles to bones or other
muscles
Connective tissue layers!
Muscle—covered by epimysium
 Fascicles—covered by perimysium
 Fiber (cell)—covered by endomysium
 Myofibril—covered by sarcoplasmic
reticulum
 Sarcomere—contains thick and thin
filaments

Figure 12.4 Connective tissue coverings of skeletal muscle.
Epimysium
Bone
Perimysium
Epimysium
Endomysium
Tendon
Muscle fiber
within a
fascicle
Blood vessel
Perimysium wrapping a fascicle
Endomysium
(between individual
muscle fibers)
Muscle fiber
Fascicle
Perimysium
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Blood & Nerve Supply

Muscles need lots of energy, lots of oxygen

Blood vessels supply these
– Each fiber (cell) has capillary blood supply

Contraction stimulated by nerve impulses
– Axons (nerve fibers) penetrate connective
tissue layers, & innervate individual muscle
fibers (cells)
How Muscles Contract:
DVD
Neuromuscular Junction

Junction of motor neuron & a muscle fiber

MOTOR Neuron —elongated portion =
axon
– synaptic terminals
– synaptic cleft
Neuromuscular Junction

Synaptic terminals
– synaptic vesicles
 Filled with acetylcholine (ACh)
– Neurotransmitter
– Release triggers muscle contraction
 motor end plate
– Sarcolemma, has receptors to bind ACh
Neuromuscular Junction
Fig. 10-10
“Action Potential”
Neuromuscular Junction

Motor unit = A single motor neuron &
ALL the muscle fibers it controls
Fig. 10-17
Figure 12.5 The neuromuscular junction.
Synaptic vesicle
containing ACh
Sarcolemma
Mitochondrion
Axon terminal of
motor neuron
Synaptic
cleft
Fusing
synaptic
vesicles
ACh
Sarcoplasm
of muscle fiber
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ACh
receptors
Junctional folds
of sarcolemma
Figure 12.6 Photomicrograph of neuromuscular junctions (750).
Terminal
branch of
an axon
Axon
terminal at
neuromuscular
junction
Muscle fibers
© 2014 Pearson Education, Inc.
Fig. 10-10
Fig. 10-10
Figure 12.6 Photomicrograph of neuromuscular junctions (750).
Terminal
branch of
an axon
Axon
terminal at
neuromuscular
junction
Muscle fibers
© 2014 Pearson Education, Inc.
Review Figure 12.1
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Review Figure 12.2
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Review Figure 12.3
Action
potential
Nucleus
Junctional
folds of the
sarcolemma
Part of a
myofibril
© 2014 Pearson Education, Inc.