Download chapter 9-muscle tissue

(a) Skeletal muscle
Description: Long, cylindrical,
multinucleate cells; obvious
striations.
Striations
Function: Voluntary movement;
locomotion; manipulation of the
environment; facial expression;
voluntary control.
Location: In skeletal muscles
attached to bones or
occasionally to skin.
Nuclei
Part of
muscle
fiber (cell)
Photomicrograph: Skeletal muscle (approx. 460x).
Notice the obvious banding pattern and the
fact that these large cells are multinucleate.
(b) Cardiac muscle
Description: Branching,
striated, generally uninucleate
cells that interdigitate at
specialized junctions
(intercalated discs).
Striations
Intercalated
discs
Function: As it contracts, it
propels blood into the
circulation; involuntary control.
Location: The walls of the
heart.
Nucleus
Photomicrograph: Cardiac muscle (500X);
notice the striations, branching of cells, and
the intercalated discs.
(c) Smooth muscle
Description: Spindle-shaped
cells with central nuclei; no
striations; cells arranged
closely to form sheets.
Function: Propels substances
or objects (foodstuffs, urine,
a baby) along internal passageways; involuntary control.
Location: Mostly in the walls
of hollow organs.
Smooth
muscle
cell
Nuclei
Photomicrograph: Sheet of smooth muscle (200x).
Bone
Epimysium
Tendon
Blood vessel
Figure 9.1a Connective tissue
Fascicle
(wrapped by perimysium)
sheaths of skeletal muscle:
Endomysium
(between individual
epimysium, perimysium,
and
muscle fibers)
endomysium.
Muscle fiber
Perimysium
Fascicle
Epimysium
Perimysium
Figure 9.1b Connective tissue
sheaths of skeletal muscle:
Endomysium
epimysium, perimysium, and
fiber
endomysium. Muscle
in middle of
a fascicle
Nuclei
Dark A band
Figure 9.2a MicroscopicLight I band
anatomy of a skeletal muscle
fiber.
Fiber
Axon terminal of
neuromuscular
junction
Action potential
Sarcolemma
(AP)
of the muscle
fiber
Nucleus
Myelinated axon
of motor neuron
Figure 9.8 Events at the
Neuromuscular Junction (1 of 4)
Myelinated axon
of motor neuron
Axon terminal of
neuromuscular
junction
Action
potential (AP)
Nucleus
Sarcolemma of
the muscle fiber
Figure 9.8 Events at the
Neuromuscular Junction
1 Action potential arrives at
axon terminal of motor neuron.
2 Voltage-gated Ca2+ channels
Ca2+
Ca2+
open and Ca2+ enters the axon
terminal.
Axon terminal
of motor neuron
3 Ca2+ entry causes some
Fusing synaptic
vesicles
synaptic vesicles to release
their contents (acetylcholine)
by exocytosis.
ACh
4 Acetylcholine, a
neurotransmitter, diffuses across
the synaptic cleft and binds to
receptors in the sarcolemma.
by its enzymatic breakdown in
the synaptic cleft by
acetylcholinesterase.
Junctional
folds of
sarcolemma
Sarcoplasm of
muscle fiber
5 ACh binding opens ion
channels that allow simultaneous
passage of Na+ into the muscle
fiber and K+ out of the muscle
fiber.
6 ACh effects are terminated
Synaptic vesicle
containing ACh
Mitochondrion
Synaptic
cleft
Na+ K+
Ach–
Degraded ACh
Na+
Acetylcholinesterase K+
Postsynaptic membrane
ion channel opens;
ions pass.
Postsynaptic membrane
ion channel closed;
ions cannot pass.
1 Action potential
arrives at axon terminal
of motor neuron.
2 Voltage-gated Ca2+
channels open and
Ca2+ enters the axon
terminal.
3 Ca2+ entry
causes some
synaptic vesicles
to release their
contents
(acetylcholine)
by exocytosis.
4 Acetylcholine, a
neurotransmitter, diffuses
across the synaptic cleft
and binds to receptors in
the sarcolemma.
Ca2+
Ca2+
Axon terminal
of motor neuron
Synaptic vesicle
containing ACh
Mitochondrion
Synaptic cleft
Fusing
synaptic
vesicles
ACh
Junctional
folds of
sarcolemma
Sarcoplasm of muscle fiber
Sarcolemma
Mitochondrion
Myofibril
Dark A band Light I band Nucleus
Thin (actin)
filament
Z disc
H zone
Z disc
Figure 9.2c Microscopic
anatomy of a skeletal muscle
Thick (myosin)
I band
A
band
I band
M line
fiber.
filament
Sarcomere
Sarcomere
Z disc
M line
Z disc
(actin)
Figure 9.2d Microscopic Thin
filament
Elastic (titin)
filaments
anatomy of a skeletal muscle
Thick
(myosin)
fiber.
filament
Myosin
filament
Actin
filament
I band
thin
filaments
only
H zone
thick
filaments
only
M line
Outer edge
of A band
thick filaments
linked by
thick and thin
accessory
filaments overlap
proteins
Longitudinal section of filaments
within one sarcomere of a myofibril
Thick filament
Figure 9.3 Composition of thick
and thin filaments.
Thin filament
In the center of the sarcomere, the thick
filaments lack myosin heads. Myosin heads
are present only in areas of myosin-actin overlap.
Thick filament
Thin filament
Each thick filament consists of many
A thin filament consists of two strands
myosin molecules whose heads protrude of actin subunits twisted into a helix
at opposite ends of the filament.
plus two types of regulatory proteins
(troponin and tropomyosin).
Portion of a thick filament
Portion of a thin filament
Myosin head
Tropomyosin
Troponin
Actin
Actin-binding sites
ATPbinding
site
Heads
Tail
Flexible hinge region
Myosin molecule
Active sites
for myosin
attachment
Actin
subunits
Actin subunits
Longitudinal section of filaments within one
sarcomere of a myofibril
Figure 9.3 Composition of thick
and thin filaments (1 of 3).
Thick
filament
Thin
filament
Thick filament
Each thick filament consists of many myosin molecules
whose heads protrude at opposite ends of the filament.
Portion of a thick filament
Myosin head
Figure 9.3 Composition of thick
and thin filaments (2 of 3).
Actin-binding sites
Heads
ATPbinding
site
Flexible hinge region
Myosin molecule
Tail
Thin filament
A thin filament consists of two strands of actin subunits
twisted into a helix plus two types of regulatory proteins
(troponin and tropomyosin).
Portion of a thin filament
Tropomyosin
Troponin Actin
Figure
9.3 Composition
of thick
and thin filaments (3 of 3).
Active sites
for myosin
attachment
Actin subunits
Actin subunits
Thin filament (actin)
Myosin heads
Thick filament (myosin)
Part of a skeletal
muscle fiber (cell)
Myofibril
I band
A band
I band
Z disc
H zone
Z disc
M line
Figure 9.5 Relationship ofSarcolemma
the
Triad:
sarcoplasmic reticulum and
T
• T tubule
• Terminal
cisternae
Sarcolemma
tubules to myofibrils of skeletal
of the SR (2)
Tubules of
muscle.
the SR
Myofibrils
Mitochondria
Z
Z
H
A
I
1 Fully relaxed sarcomere of a muscle fiber
Z
I
I
Z
A
I
2 Fully contracted sarcomere of a muscle fiber
Figure 9.6 Sliding filament
model of contraction (1 of 2).
Z
I
H
A
1 Fully relaxed sarcomere of a muscle fiber
Z
I
Figure 9.6 Sliding filament
model of contraction (2 of 2).
Z
Z
I
A
I
2 Fully contracted sarcomere of a muscle fiber
Latent Period of
period contraction
Period of
relaxation
Figure 9.14a The muscle twitch.
Single
stimulus
Latent period
Extraocular muscle (lateral rectus)
Gastrocnemius
Soleus
Figure 9.14b The muscle twitch.
Single
stimulus
Single stimulus
single twitch
Figure
9.15a
Muscle
response
Contraction
to changes
in stimulation
Relaxation
frequency.
Stimulus
Low stimulation frequency
unfused (incomplete) tetanus
Partial relaxation
Figure 9.15b Muscle response
to changes in stimulation
Stimuli
frequency.
High stimulation frequency
fused (complete) tetanus
Figure 9.15c Muscle response
to changes in stimulation
frequency.
Stimuli
Stimulus strength
Maximal
stimulus
Threshold
stimulus
Proportion of motor units excited
Strength of muscle contraction
Maximal contraction
Figure 9.17 The size principle of
recruitment.
Motor
unit 1
Recruited
(small
fibers)
Motor
unit 2
recruited
(medium
fibers)
Motor
unit 3
recruited
(large
fibers)
(a)
Direct phosphorylation
Coupled reaction of creatine
phosphate (CP) and ADP
Energy source: CP
CP
ADP
Figure 9.19a
Pathways
for
Creatine
regenerating ATP kinase
during muscle
activity.
Creatine
ATP
Oxygen use: None
Products: 1 ATP per CP, creatine
Duration of energy provision:
15 seconds
(b)
Anaerobic pathway
Glycolysis and lactic acid formation
Energy source: glucose
Glucose (from
glycogen breakdown or
delivered from blood)
Figure 9.19b Pathways for
regenerating ATP during muscle
activity.
Glycolysis
in cytosol
2
O2
ATP
net gain
Released
to blood
Pyruvic acid
O2
Lactic acid
Oxygen use: None
Products: 2 ATP per glucose, lactic acid
Duration of energy provision:
60 seconds, or slightly more
(c)
Aerobic pathway
Aerobic cellular respiration
Energy source: glucose; pyruvic acid;
free fatty acids from adipose tissue;
amino acids from protein catabolism
Glucose (from
glycogen breakdown or
delivered from blood)
Figure 9.19c Pathways for
regenerating ATP during muscle
activity.
O2
Pyruvic acid
Fatty
acids
O2
Aerobic
respiration
Aerobic respiration
in mitochondria
mitochondria
Amino
acids
32
CO2
H2O
ATP
net gain per
glucose
Oxygen use: Required
Products: 32 ATP per glucose, CO2, H2O
Duration of energy provision: Hours