Transcript Muscle Histology

Muscular Histology and Physiology
Photomicrograph of the capillary network surrounding skeletal muscle fibers
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Microscopic anatomy of a skeletal muscle fiber
Nuclei
Fiber
(a)
Sarcolemma
Mitochondrion
Myofibril
(b)
Dark
Light
A band I band
Nucleus
Z disc
H zone Z disc
Thin (actin) filament
Thick (myosin)
filament
(c)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Composition of thick and thin filaments
Thick filament
Tail
Thin filament
Heads
Flexible hinge region
(a) Myosin molecule
(d) Longitudinal section of filaments within
one sarcomere of a myofibril
Thin filament (actin) Myosin heads Thick filament (myosin)
Myosin head
(b) Portion of a thick filament
Troponin complex
Tropomyosin
(c) Portion of a thin filament
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Actin
(e) Transmission electron micrograph of part
of a sarcomere
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Microscopic anatomy of a skeletal muscle fiber
Z disc
H zone
Z disc
Thin (actin) filament
Thick (myosin)
filament
(c)
I band
Thin (actin) filament
Z disc
A band
Sarcomere
M line
I band
M line
Z disc
Elastic (titin)
filaments
Thick (myosin)
filament
(d)
(e)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
I band
thin filaments
only
H zone
M line
Outer edge of
thick filaments thick filaments linked
A band
only
by accessory proteins thick and thin
filaments overlap
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle
I band
A band
I band
Z disc
H zone
Z disc
M
line
Part of a skeletal
muscle fiber (cell)
Sarcolemma
Triad
Mitochondrion
Myofibrils
Myofibril
Tubules of
sarcoplasmic
reticulum
Sarcolemma
Terminal cisterna
of the sarcoplasmic
reticulum
T tubule
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Sliding filament model of contraction
Z
1
I
Z
H
A
I
Z
3
Z
2
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Z
A
Z
A
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Connective tissue sheaths of skeletal muscle
Epimysium
Tendon
Muscle fiber
in middle of
a fascicle
Epimysium
Endomysium Endomysium
(between
fibers)
(b)
Perimysium
Muscle fiber
(cell)
Bone
(a)
Perimysium
Blood
Fascicle
(wrapped by vessel
perimysium)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Blood vessel
Endomysium
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Figure 4.30
The neuromuscular junction
Myelinated axon
of motor neuron
Action
potential Axon terminal at
neuromuscular junction
Sarcolemma
of the
muscle fiber
Nucleus
(a)
Axon terminal
Axon terminal of
a motor neuron
Mitochondrion
Synaptic cleft
Ca2+
Fusing synaptic
vesicle
ACh molecules
Synaptic
vesicle
Acetic acid
T tubule
Junctional
folds of the
sarcolemma
at motor end
plate
Part of a
myofibril
(b)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Choline
Synaptic
cleft
K+
(c)
Acetylcholinesterase
Na+
Binding of Ach
to receptor opens
Na+/K+ channel
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Figure 9.7a: The neuromuscular junction, p. 290.
Myelinated axon
of motor neuron
Action
potential
Axon terminal at
neuromuscular junction
Sarcolemma
of the
muscle fiber
Nucleus
(a)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
The neuromuscular junction
Axon terminal of
a motor neuron
Mitochondrion
Synaptic cleft
Ca2+
Synaptic
vesicle
T tubule
Junctional
folds of the
sarcolemma
at motor end
plate
Part of a
myofibril
(b)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Muscle Contraction Physiology
The neuromuscular junction
Axon terminal
Fusing synaptic
vesicle
ACh molecules
Acetic acid
Choline
Synaptic
cleft
Acetylcholinesterase
K+
(c)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Na+
Binding of Ach
to receptor opens
Na+/K+ channel
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
An action potential in a skeletal muscle fiber
[Na+] [K+]
[K+] [Na+]
(a)
Na+
Stimulus
(b)
(a) Electrical conditions of a resting (polarized) sarcolemma.
The outside face is positive, while the inside face is negative.
The predominant extracellular ion is sodium (Na+); the
predominant intracellular ion is potassium (K+). The sarcolemma
is relatively impermeable to both ions.
(b) Step 1: Depolarization and generation of the action potential.
Production of an end plate potential at the motor end plate causes
adjacent areas of the sarcolemma to become permeable to sodium
(voltage-gated sodium channels open). As sodium ions diffuse rapidly
into the cell, the resting potential is decreased (i.e., depolarization
occurs). If the stimulus is strong enough, an action potential is
initiated.
(c) Step 2: Propagation of the action potential.
The positive charge inside the initial patch of sarcolemma
changes the permeability of an adjacent patch, opening voltagegated Na+ channels there. Consequently the membrane potential
in that region decreases and depolarization occurs there as well.
Thus, the action potential travels rapidly over the entire
sarcolemma.
(c)
K+
(d)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
(d) Step 3: Repolarization.
Immediately after the depolarization wave passes, the
sarcolemma's permeability changes once again: Na+ channels
close and K+ channels open, allowing K+ to diffuse from the cell.
This restores the electrical conditions of the resting (polarized)
state. Repolarization occurs in the same direction as
depolarization, and must occur before the muscle fiber can be
stimulated again. The ionic concentrations of the resting state
are restored later by the sodium-potassium pump
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
+30
Na+ channels
close
Action potential
Relative membrane permeability
Membrane potential (mV)
Action potential scan showing changing sarcolemma permeability to Na+ and K+ ions
K+ channels
open
0
Na+
channels
open
Threshold
–55
–70
0
1
2
3
4
Time (ms)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Excitation-contraction coupling
Axon terminal
Synaptic
cleft
Sarcolemma
Synaptic
vesicle
ACh
Neurotransmitter released
diffuses across the synaptic
cleft and attaches to ACh
ACh
T tubule
1 Net entry of Na+ initiates
an action potential which
is propagated along the
ACh
sarcolemma and down
the T tubules.
Ca2+
SR tubules (cut)
2 Action potential
Ca2+
in T tubule activates
voltage-sensitive
receptors, which in
ADP
turn trigger Ca2+
Pi
release from terminal
cisternae of SR
Ca2+
into cytosol.
Ca2+
6 Tropomyosin blockage
restored, blocking myosin
binding sites onactin;
contraction ends and
Ca2+
muscle fiber relaxes.
Ca2+
SR
Ca2+
Ca2+
Ca2+
3 Calcium ions bind to troponin;
troponin changes shape, removing
the blocking action of tropomyosin;
actin active sites exposed.
5 Removal of Ca2+ by active transport
into the SR after the action
potential ends.
Ca2+
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
4 Contraction; myosin heads alternately attach to
actin and detach, pulling the actin filaments toward
the center of the sarcomere; release of energy by
ATP hydrolysis powers the cycling process.
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Role of ionic calcium in the contraction mechanism
Overview
Actin
Troponin
Myosin
head
Tropomyosin
Plane of (d)
Plane of (a)
TnT
Tropomyosin
Tnl
Myosin
binding
sites
Actin
Myosin
TnC binding
site
+ Ca2+
Additional
calcium
ions
bind
to TnC
Actin
Troponin
complex
(a)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Additional
calcium
ions
bind
Myosin
head
(b)
Myosin
head
(c)
(d)
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
The cross bridge cycle
Myosin head
(high-energy
configuration)
ADP
Pi
1 Myosin head attaches to the actin
myofilament, forming a cross bridge.
Thin filament
ATP
hydrolysis
ADP
ADP
Thick filament
Pi
4 As ATP is split into ADP and Pi, the myosin
head is energized (cocked into the high-energy
conformation).
2 Inorganic phosphate (Pi) generated in theprevious
contraction cycle is released, initiating
the power (working) stroke. The myosin head
pivots and bends as it pulls on the actin filament,
sliding it toward the M line. Then ADP is released.
ATP
ATP
Myosin head
(low-energy
configuration)
3 As new ATP attaches to the myosin head, the link between
Myosin and actin weakens, and the cross bridge detaches.
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
, p. 296.
Spinal cord
Motor
unit 1
Motor
unit 2
Axon terminals at
neuromuscular junctions
Nerve
Motor neuron
cell body
Muscle
Motor neuron
axon
Muscle fibers
Muscle
fibers
Branching axon
to motor unit
(a)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
(b)
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
The muscle twitch
Latent period
Period of
relaxation
Extraocular muscle (lateral rectus)
Percentage of
maximum tension
Percentage of
maximum tension
Latent Period of
period contraction
Single 0
stimulus
(a)
20
40
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
60
80
Time (ms)
100
120
140
Single 0
stimulus
(b)
Gastrocnemius
Soleus
40
80
120
Time (ms)
160
200
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Methods of regenerating ATP during muscle activity
Glucose (from
glycogen breakdown or
delivered from blood)
CP
Glucose (from
glycogen breakdown or
delivered from blood)
O2
ADP
Glycolysis
in cytosol
Creatine
ATP
O2
2 ATP
Pyruvic acid
net gain
Released
to blood
(a) Direct phosphorylation
[coupled reaction of creatine
phosphate (CP) and ADP]
Energy source: CP
O2
Lactic acid
(b) Anaerobic mechanism (glycolysis
and lactic acid formation)
Energy source: glucose
Pyruvic acid
Fatty
acids
O2
Aerobic respiration
in mitochondria
Amino
acids
CO2
38
H2O
ATP
net gain per glucose
(c) Aerobic mechanism (aerobic cellular
respiration)
Energy source: glucose; pyruvic acid; free
fatty acids from adipose tissue; amino acids
from protein catabolism
Oxygen use: None
Oxygen use: Required
Oxygen use: None
Products:
2
ATP
per
glucose,
lactic
acid
Products: 38 ATP per glucose, CO2, H2O
Products: 1 ATP per CP, creatine
Duration of energy provision: Hours
Duration of energy provision: 15s Duration of energy provision: 30–60 s.
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Factors influencing force, velocity, and duration of skeletal muscle contraction
Large number
of muscle
fibers activated
Large
muscle
fibers
Asynchronous
tetanic
contractions
(a) Increased
contractile
force
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Muscle and
sarcomere
length slightly
over 100% of
resting length
Predominance
of fast glycolytic
(fatigable) fibers
(b) Increased
contractile
velocity
Small load
Predominance
of slow oxidative
(fatigue-resistant)
fibers
(c) Increased
contractile
duration
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Light load
Intermediate load
Heavy load
0
20
40
60
80
100
Velocity of shortening
Distance shortened
Influence of load on contraction velocity and duration
120
0
Time (ms)
Single action
potential initiated
Increasing load
(b)
(a)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Innervation of smooth muscle
Mucosa
Smooth muscle cell
Varicosities
Submucosa
Autonomic
nerve
fiber
Serosa
Muscularis
externa
Varicosity
Mitochondrion
Synaptic vesicles
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Sequence of events in excitation-contraction coupling of smooth muscle
Extracellular fluid
Ca2+
Ca2+
Plasma membrane
1 Calcium ions (Ca2+) enter
the cytosol from the ECF
or from the scant SR.
Cytoplasm
2 Ca2+ binds to and
activates calmodulin.
Activated
Inactive
3 Activated calmodulin activates
calmodulin
calmodulin
the myosin light chain kinase
Activated enzymes.
Inactive
kinase
kinase
4 The activated kinase
ATP
enzyme catalyzes transfer
ADP
of phosphate to myosin
Pi
Pi
heads, activating the
myosin head ATPases.
Activated
Inactive myosin
(phosphorylated)
molecule
myosin molecule
Thin myofilament
Pi
5 Phosphorylated myosin
Thick filament
heads form cross bridges
with actin of the thin
Pi
filaments and shortening
occurs.
Sarcoplasmic reticulum
Ca2+
6 Cross bridge activity ends
when phosphate is removed
from the myosin heads by
phosphorylase enzymes and
intracellular Ca2+ levels fall.
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.