Muscle Tissue Flashcards
1
Q
What is the function of the muscle tissue?
A
To contract and therefore it’s responsible for movement within organ systems and the body. Moreover, a change in the shape and size of internal organs.
2
Q
What is the muscle tissue characterized by?
A
Specialized elongated cells arranged in a parallel array.
3
Q
Where does the contraction force come from?
A
Actin filaments and associated proteins.
4
Q
Whats the origin of Muscle tissue and how does it form?
Embryonic orgin
A
Mesodermal origin. It differenciates by cell lengthening while synthesizing actin and myosin filaments.
5
Q
What are Myofilaments and whats the location?
A
Location: Cytoplasm
Made of: Actin (thin) and Myosin(thick) filaments.
6
Q
How does contraction occur?
A
The sliding of the actin along the myosin filament.
7
Q
What is actin and what is it composed of?
A
A thin filament composed of actin. G-actin (globular) and F-actin (fibrous).
8
Q
What is myosin and what is it composed of?
A
A thick filament composed of Myosin II. Myosin molecules are in a regular parallel array and are composed of a head and a tail. Head projects in a regular helical pattern.
9
Q
What is the difference between the appearance of striated versus smooth muscle under the LM?
A
Striated muscle: cross striation
Smooth muscle: No cross striation
10
Q
What is the morphological and functional characterization of Skeletal muscle?
A
Large elongated multinucleated fibers.
Strong quick voluntary contractions.
11
Q
What is the morphological and functional characterization of Cardiac muscle?
A
Irregularly branched cells bounded by intercalated discs.
Strong involuntary contraction
12
Q
What is the morphological and functional characterization of Smooth muscle?
A
No striation grouped fusiform cells (like fused).
Weak involuntary contractions
13
Q
Where is the skeletal muscle located and what function correlation?
A
Attached to bone (for movement)
Maintain body position and posture
Precise eye movements (extra-ocular muscles)
14
Q
Where is Visceral striated muscle located and what function correlation?
A
Morphologically identical to skeletal muscle.
Restricted to tongue, pharynx, and upper part of the esophagus.
Role in speech, breathing and swallowing
15
Q
Where is Cardiac muscle located and what function correlation?
A
Wall of heart
Base of large veins that empty into heart
16
Q
How is the skeletal muscle formed? Where is the nucleus located?
A
When the myoblast (individual muscle cell) fuse, a multinucleated syncytium is formed. It is grouped into bundles and surrounded by connective tissue. The nucleus is right under the sacrolemma.
17
Q
What is the Muscle cell membrane and external lamina?
A
Sacrolemma
18
Q
What is muscle cytoplasm?
A
Sarcoplasm
19
Q
What is muscle smooth ER?
A
Sarcoplasmic reticulum
20
Q
What is the skeletal muscle also called?
A
Muscle fiber
21
Q
What is the longitudinal section of the skeletal muscle characterized by?
A
The length varies. The cytoplasm of the muscle cell contains regular arrangments of myofibrils. Alternating short segments: dark A band and light I bands.
22
Q
What is the cross-section of the skeletal muscle characterized by?
A
Polygonal-shaped muscle fibers. The cross-banded pattern of striated muscle is due to the orderly arrangement of actin and myosin filaments. I and A band form a sarcomere that extends between 2 adjacent Z disks.
23
Q
What is the component of a myofibril?
A
Myofilament
24
Q
What are the 2 major classes of myofilament?
A
Thin actin filament and thick myosin filament.
25
What is the predominant component of I band?
Actin
26
What is the predominant component of A band?
Myosin
27
What forms a sarcomere?
I and A bands
28
How does the skeletal muscle develop?
Myoblasts( mesenchymal calls) align and fuse to make longer multinucleated tubes called myotubes.
Myotubes then synthesize the proteins that make myofilaments and cross striations start to be seen by LM. Nuclei are displaced against the sarcolemma.
Some of the myoblasts don't fuse and differentiate, remain as a group of mesenchymal cells called satellite cells (on the external surface of muscle fibers inside the external lamina).
29
What are satellite cells?
A group of mesenchymal cells due to the myoblasts don't fuse and differentiate
30
What are reserve cells?
Satellite cells that proliferate and produce new muscle fibers following muscle injury.
31
What are the MASTER Transcription Factors?
PAX7 (Paired box 7)
MYOD (Myogenic differentiation factor)
32
What is the active MASTER Transcription Factor?
PAX7 (Paired box 7)
33
What is the silent MASTER Transcription Factor?
MYOD (Myogenic differentiation factor)
34
Satellite cell and muscle repair
35
What is the function of the connective tissue and what does it surround?
A rich supply of blood vessels and nerves.
Surrounds: Individual muscle fibers and bundles of muscle fibers.
36
What does the connective tissue form at the end?
Tendon
37
What does a tendon do?
Attaches muscle to bone.
38
What are the 3 connective tissues in the skeletal muscle?
Endomysium
Perimysium (thicker)
Epimysium (sheath of dense connective tissue)
39
Location of Endomysium?
Around individual muscle fibers
have very small blood vessels and fine nerves.
40
Location of Perimysium?
Thicker connective tissue.
Around a group of fibers to form a bundle or a fascicle.
*Fascicles are functional units of muscle fibers working together.
Perimysium has larger blood vessels and nerves.
41
Location of Epimysium?
Surrounds a collection of fascicles.
Major vascular and nerve supplies penetrate the epimysium.
42
What are the functional units of muscle fibers working together?
Fascicles
43
Where is a rich network of capillaries surrounding muscle fibers found?
Endomysium
44
Skeletal muscle consists of (A) held together by (B).
A- striated muscle fibers
B-connective tissue
45
The dense collagen fibers of a tendon (T) are continuous with those in the three connective tissue layers around muscle fibers (M), forming a strong unit that allows muscle contraction to move other structures.
46
Tendons join (A) to (B)
A- muscles
B- periosteum of bones
47
MF: muscle fiber, MF’: terminating muscle fiber,
T: tendon, Tc: tendinocytes, Arrows: collagen fibrils
Muscle-tendon (myotendinal) junction
48
Skeletal muscles such as those that move the eyes and eyelids need to...
contract rapidly
49
Skeletal muscles for bodily posture must...
maintain tension for longer periods while resisting fatigue
50
On what basis are skeletal muscle fibers identified?
1. rate of contraction (fast or slow fibers)
2. pathway for ATP synthesis (oxidative phosphorylation or glycolysis).
51
Skeletal muscle fibers are identified by what in vivo?
Color: Red, White, Intermediate.
Based on oxidative enzyme activity by succinic dehydrogenase (SDH) or NADH-TR (nicotinamide adenine dinucleotide tetrazolium)
52
Skeletal muscle fibers are characterized by?
Speed of contraction, enzymatic velocity, and metabolic activity
53
Classification of skeletal muscle fibers.
54
What are the 3 types of skeletal muscle fibers?
Type I fibers (slow oxidative)
Type IIa fibers (fast oxidative glycolytic)
Type IIb (fast glycolytic)
55
The metabolic type of each fiber is determined by?
Rate of impulse conduction along its motor nerve supply.
56
Most skeletal muscles receive motor input from (A) contain a (B)
A- multiple nerves
B- a mixture of fiber types
57
How are skeletal fiber types determined clinically? What do we look for?
Needle biopsies: diagnosis of specific myopathies (muscle pathologies), motor neuron diseases, and other causes of muscle atrophy (thinning of muscle mass).
58
Cross section of a skeletal muscle stained histochemically for myosin ATPase at acidic pH.
What are the 3 main fiber types?
Slow oxidative (SO) or type I fibers have high levels of acidic ATPase activity and stain the darkest.
Fast glycolytic (FG) or type IIb fibers stain the lightest.
Fast oxidative-glycolytic (FOG) or type IIa fibers are intermediate between the other two types
59
What is glycolysis?
cytoplasmic pathway which breaks down glucose into two three-carbon compounds and generates energy.
60
What is the structural and functional subunit of the muscle fiber?
Myofibril
61
A muscle fiber is filled with longitudinally arrayed (A) extend the entire length of the muscle cell.
Myofibrils
62
(A) are found between the myofibrils, which typically have diameters of 1-2 μm.
Mitochondria and sarcoplasmic reticulum
63
Myofibrils consist of an end-to-end repetitive arrangement of...
Sarcomeres
63
Myofibrils consist of an end-to-end repetitive arrangement of...
Sarcomeres
64
Myofibrils are composed of ...
Myofilaments
65
What are myofilaments?
Individual filamentous polymers of myosin II (thick filaments) and actin and its associated proteins (thin filaments)
66
What are actual contractile element of striated muscle?
Myofilaments
67
Skeletal muscle fibers show cross striations of alternating...
Light and dark bands
68
Dark-staining A bands alternate with lighter I bands
69
What are myofibrils
cylindrical bundles of thick and thin myofilaments which fill most of each muscle fiber and run parallel to the long axis of the fiber
70
The dark bands on the myofibrils are called
A band (anisotropic or birefringent in polarized light microscopy);
71
The light bands are called
I bands (isotropic, do not alter polarized light).
72
What is the functional unit of the myofibril
Sarcomere
73
Make repeats that correspond to the specific and orderly arrangement of myofibrils in the sarcoplasm of skeletal and cardiac muscle cells.
74
What is Myofiber?
Muscle cell
75
What is Myofibril?
actin and myosin combination that forms the sarcomere
76
What is Myofilament?
Actin or myosin
77
TEM of a Sarcomere
In its middle is an electron-dense A band bisected by a narrow, less dense region called the H zone. On each side of the A band are the lighter-stained I bands, each bisected by a dense Z disc which marks one end of the sarcomere.
Mitochondria (M), glycogen granules, and small cisternae of SER occur around the Z disc.
78
TEM of a Sarcomere
In its middle is an electron-dense A band bisected by a narrow, less dense region called the H zone. On each side of the A band are the lighter-stained I bands, each bisected by a dense Z disc which marks one end of the sarcomere.
Mitochondria (M), glycogen granules, and small cisternae of SER occur around the Z disc.
79
The repetitive functional subunit of the contractile apparatus, the sarcomere extends from
Z-disc to Z-disc
80
How long is the sarcomere in resting muscle
2.5-μm
81
What does myofilament consist of?
Contractile protein arrays bundled within myofibrils.
82
What does a thick myofilament (15nm) contain?
200-500 molecules of myosin
83
What does a thin myofilament (8nm) contain?
F-actin, tropomyosin, and troponin.
84
What does Myosin II use to generate motile force?
ATP
85
What is the component of Myosin II?
two identical heavy chains and two pairs of light chains (four chains).
86
What are myosin heavy chains?
thin, twisted together as myosin tails.
87
How is the head (globular projection) of the myosin formed?
Globular projections containing the four myosin light chains form a head at one end of each heavy chain
88
What are the 2 types of light chains of the myosin?
essential and regulatory light chains
89
What does the myosin head bind?
Actin and ATP (actomyosin ATPase and motor activity). Catalyze energy release.
90
How does the myosin molecules in striated muscle align?
tail to tail to form thick myosin filaments
91
What is the H band in the sarcomere?
The bare zone without globular heads and contains no actin filaments.
92
What is the M-line (Ger, Mittel) in the sarcomere?
Attachment site for the thick filaments.
93
The projecting globular heads cross-bridge between...
Thick and thin filaments
94
What do thin filaments contain?
F-actin, tropomyosin and troponin
95
What is the F-actin?
G-actin polymerizes to form double stranded F-actin
The plus end is bound to Z-line by α-actinin
The minus end extends toward the M-line and
protected by an actin capping protein-tropomodulin
96
What is tropomyosin and where is it located?
64 kD double helix of two polypeptides
Runs in groove between two F-actin molecules
97
What are the 3 globular units of troponin?
Troponin C (TnC), Troponin I (TnI) and Troponin T (TnT)
98
What's the function of Troponin C (TnC)?
binds Ca2+ (essential for initiation of contraction)
99
What's the function of Troponin T (TnT)?
binds tropomyosin
100
What's the function of Troponin I (TnI)?
binds to actin and inhibits actin-myosin interaction
101
In a resting muscle.......mask myosin-binding site on actin molecule.
Tropomyosin, its regulatory protein and troponin complex
102
Sarcomere
103
Sarcomere
104
Explain myosin containing thick filament. (length and location)
1.5μm long
Restricted to central portion of sarcomere
105
Where are thin filaments located?
attach to Z-line and extend into A band to the edge of H-band
106
What constitutes the I band and what does it contain?
Portions of two sarcomeres on either site of Z-line and it only contains thin filaments
107
What is the appearance of the Z-line and function?
appears as a zigzag. Z-line and its matrix anchor thin filaments by actin binding protein α-actinin
108
Other components of the sarcomere DESMIN, PLECTIN, αB-crystallin
109
What does a mutation in DESMIN, PLECTIN, αB-crystallin determine?
determines the destruction of myofibrils after repetitive mechanical stress.
110
What is the function of accessory proteins?
Maintain precise spacing, attachment, and alignment of thin and thick filaments
111
What are the accessory proteins?
Titin, α-ACTININ, NEBULIN, TROPOMODULIN, , DESMIN, MYOMESIN, C PROTEIN, DYSTROPHIN
112
What's the function of TITIN?
large, anchors thick filaments to Z-lines. Extends from Z disc to M line. Prevents excess stretching of sarcomere
113
What's the function of α-ACTININ?
Bundles thin filaments to parallel arrays and binds actin to Z-line
114
WHat's the function of Nebulin?
a giant protein (600–900-kD) associated with thin (F-actin) filaments; it inserts into the Z disk and acts as a stabilizer required for maintaining the length of F-actin
115
What's the function of TROPOMODULIN?
Actin capping protein, maintains the length of actin
116
What's the function of DESMIN?
Surrounds sarcomere at Z-line level. Maintenance of mechanical integrity. Determines the distribution and function of mitochondria in skeletal and cardiac muscle.
117
What's the function of MYOMESIN?
Binds myosin, holds thick filaments at M-line
118
What's the function of Protein C?
Similar to myomesin
119
What's the function of DYSTROPHIN?
Links laminin to actin
120
What does an absence of Dystrophin cause?
Duschenne’s Muscular Atrophy
121
What is dystrophin, its location and function?
a large actin-binding protein located inside the sarcolemma and involved in the organization of myofibrils.
122
What is Duchenne muscular dystrophy?
mutations of the dystrophin gene leads to defective linkages between the cytoskeleton and the extracellular matrix (ECM).
123
What can muscle contractions do in the case of Duchenne muscular dystrophy?
can disrupt these weak linkages, causing the atrophy of muscle fibers typical of this disease
124
What are the 1 and 2 steps of muscle contraction?
125
What are 3,4 and 5 steps of muscle contraction?
Attach-Pivot-Detach-Return
126
What is the contraction (cross-bridge) cycle?
(5 steps)
Attachment: Myosin head is tightly bound to actin molecule (no ATP-rigor configuration).
Release: Myosin head is uncoupled from thin filament by binding of ATP.
Bending: Myosin head advances a short distance by ATP hydrolysis.
Force generation: Myosin head releases inorganic phosphate. This release causes an increase in binding affinity to new site and myosin head generates a force while going back to unbent position: power stroke.
Reattachment: Myosin head binds tightly to new actin molecule.
127
During muscle contraction how much of the muscle shortens?
the muscle shortens about one-third of its original length.
128
What are the aspects of muscle shortening?
129
What is the organization of a skeletal muscle fiber?
Each myofibril extends the length of the muscle fiber and is surrounded by parts of the sarcoplasmic reticulum.
The sarcolemma has deep invaginations called T-tubules, each of which becomes associated with two terminal cisternae of the sarcoplasmic reticulum.
A T-tubule and its two associated terminal cisternae comprise a “triad” which are small spaces along the surface of the myofibrils.
130
What is needed for contraction?
Ca2+
Sarcoplasmic Reticulum
Transverse Tubular System (T-tubule)
131
Why is Ca2+ essential for contraction?
essential for the reaction between actin and myosin
132
After contraction what must be removed rapidly?
Ca2+
133
Which structures rapidly remove Ca2+?
sarcoplasmic reticulum and transverse tubular system
134
What surrounds the bundles of myofilaments and what are they.
Sarcoplasmic reticulum, is arranged as repeating networks around myofibrils.
135
hat 2 networks does the SR surround
from one A-I band junction to the next A-I band junction
THUS; one network surrounds A, the other surrounds I band
136
Terminal cisternae and what does it serve as?
Where two networks meet SR forms a more regular ring that serves as a Ca2+ reservoir
137
Granules in association with SR
Mitochondria and glycogen granules
138
T-tubule
Numerous tubular invaginations of plasma membrane
139
T-tubule location and penetration
at A-I band junction, between terminal cisternae.
Penetrate all levels of muscle fiber
140
Innervation
Myelinated motor nerves branch out within the perimysium, where each nerve gives rise to several unmyelinated terminal twigs that pass through endomysium and form synapses with individual muscle fibers.
141
NEUROMUSCULAR JUNCTION (MOTOR END PLATE-MEP):
Contact made by terminal branches of axon with muscle fiber.
142
Silver staining can reveal the nerve bundle (NB), the terminal axonal twigs, and the motor end plates (MEPs, also called neuromuscular junctions or NMJ) on striated muscle fibers (S).
143
At the end of axon
shallow depressions on surface of muscle fiber
144
Synaptic cleft
20-30 nm space (formed by deep infoldings of sarcolemma) separating presynaptic neuron from postsynaptic structure.
145
Axon end
presynaptic structure and has many mitochondria and synaptic vesicles carrying acetylcholine (Ach) neurotransmitter.
146
Plasma membrane of muscle fiber under synaptic clefts
many deep junctional folds (subneural folds) and they have specific cholinergic receptors.
147
S: Schwann cell cytoplasm, JF: junctional folds, SV: synaptic vesicles, MF: myofibrils, M: mitochondria, SnC: subneural clefts, N: nucleus
Schwann cells enclose the small axon branches and cover their points of contact with the muscle cells; the external lamina of the Schwann cell fuses with that of the sarcolemma.
148
Clinical importance of neuromuscular junction
149
Myasthenia gravis
an autoimmune disorder that involves circulating antibodies against proteins of acetylcholine receptors.
150
Antibody binding to the antigenic sites interferes with acetylcholine activation of their receptors, leading to intermittent periods of skeletal muscle weakness.
As the body attempts to correct the condition, junctional folds of sarcolemma with affected receptors are internalized, digested by lysosomes, and replaced by newly formed receptors.
These receptors are again made unresponsive to acetylcholine by similar antibodies, and the disease follows a progressive course.
The extraocular muscles of the eyes are commonly the first affected.
151
1..from a single motor neuron can form motor end plates (MEPs) with..2
1. Axon
2. one or many muscle fibers
152
Innervation of single muscle fiber by single motor neuron
provides precise control of muscle activity and occurs, for example, in the extraocular muscles for eye movements.
153
Larger muscles with coarser movements have
motor axons that typically branch and innervate 100 or more muscle fibers. In this case, the single axon and all the muscle fibers in contact with its branches make up a motor unit.
154
neuromuscular spindle
Muscles have a specialized encapsulated sensor that contains sensory and motor components.
155
muscle spindle
specialized stretch receptor in the skeletal muscle
156
Muscle spindle function
transmits information about the degree of stretching
157
muscle spindle has two types of modified muscle fibers
(intrafusal fibers) that possess capsules around them & (extrafusal fibers)
158
Golgi tendon organs
Plays a similar role , much smaller encapsulated structures that enclose sensory axons penetrating among the collagen bundles at the myotendinous junction .
159
Tendon organs function
detect changes in tension within tendons produced by muscle contraction and act to inhibit motor nerve activity if tension becomes excessive.
160
161
How do Intrafusal muscle fibers differ from ordinary skeletal muscle fibers?
very few myofibrils
162
Intrafusal spindle cells have two types:
Nuclear bag fiber: Nuclei aggregated
Nuclear chain fiber: Nuclei in a chain
163
A TEM cross section near the end of a muscle spindle shows the capsule (C), lightly myelinated axons (MA) of a sensory nerve, and the intrafusal muscle fibers (MF).
Muscle satellite cells (SC) are also present within the external lamina of the intrafusal fibers.
164
Sensory (afferent, a ) nerve fibers function and what are similar receptors found in tendons called
carry the information from the spindle.
Golgi tendon organs (only sensory afferent lb)
165
How do spindle cells receive information from the brain and spinal cord?
Gamma Motor (efferent) nerve fibers
166
What do the muscle spindles detect
Any changes in length (i.e by stretching) of surrounding muscle fibers (extrafusal fibers).
167
Which are thicker intrafusal or extrafusal fibers?
Extrafusal fibers
168
How are arrangments of Cardiac muscles different than skeletal muscle?
-Nucleus lies in the center.
-Unlike striated muscle- end-end arrangment rather than multinucleated syncytium.
-branched fibers
-Intercalated discs between adjacent cells (transverse and longitudinal components)
169
TEM Cardiac Muscle
Two components (stairway)-both have cell-cell junctions
170
LM Cardiac Muscle
densely staining linear structure transverse to fibers (Intercalated discs)
171
Junctions of Intercalated discs
Fascia adherens
Macula adherentes (Desmosome)
Gap junctions
172
Junctions of Intercalated discs
Fascia adherens
Macula adherentes (Desmosome)
Gap junctions
173
Fascia adherens
Major in transverse component
Thin filaments on terminal sarcomere adhere here
174
Macula adherentes (Desmosome)
Found in transverse (and sometimes longitudinal) components
Binds individual muscle cells together
Prevents pulling apart
175
Gap junctions
Major in longitudinal component,
Provide ionic continuity,
Allow passage of macromolecules
Cardiac muscle fibers
behave in a syncytium
176
TEM image of cardiac muscle
SR: sarcoplasmic reticulum, D: diad, M: mitochondria
shows abundant mitochondria (M) and sparse sarcoplasmic reticulum (SR) in the areas between myofibrils.
T-tubules are less well-organized and are usually associated with one expanded terminal cistern of SR, forming dyads (D) rather than the triads of skeletal muscle
177
Are Diad and Triad structures functionally similar?
Yes
178
What is stored near each Myofibril in Cardiac muscle
Numerous large mitochondria and glycogen
179
In atria of the heart what have 2 types of polypeptide hormones?
Atrial granules
180
2 types of polypeptide hormones of Atrial granules
Atrial natriuretic factor (ANF)
Brain natriuretic factor (BNF)
181
What does Atrial natriuretic factor (ANF) do to the cells of the kidneys
Targets the cells and brings sodium and water loss
182
Sarcoplasmic reticulum of Cardiac muscle
183
Describe Sarcoplasmic reticulum of Cardiac muscle
- not as well organized as skeletal muscle
- organized along sarcomere from Z to Z
- only 1 T-tubule per sarcomere
-DIAD at Z-line: small terminal cisternae+T-tubules.
-T-tubules larger and more in ventricles and less in atria of heart
184
Explain Cardiac Muscle contraction
1.Depolarization of T-tubule activates voltage sensor proteins (act as Ca2+ channels).
2. Ca2+ is transported from lumen of T-tubule through channels in voltage sensor proteins into sarcoplasm
3. Ca2+ activates gated Ca2+ release channels in adjacent terminal sacs: Ca2+ TRIGGERED CA2+ RELEASE, causes massive and rapid release of additional Ca2+
185
What do Cardiac muscle cells exhibit?
spontaneous rhytmic contraction
186
In which cardiac muscle cells are Intrinsic contractions (heartbeats) present
Culture and embryonic stem cells
187
Heartbeat initiated by cardiac conducting cells forming
Nodes (Sinoatrial and atrioventricular nodes)
Highly specialized fibers (Purkinje fibers)
188
LM image of cardiac muscle-Purkinje fibers
CM: cardiac muscle, PF: Purkinje fibers, NF: nerve fibers, GC: ganglion cell, BV: blood vessel
Purkinje fibers: These are pale-staining fibers, larger than the adjacent contractile fibers.
189
Purkinje fibers
At the apex of the heart, these bundles (two nodes) subdivide further into a subendocardial conducting network of cardiac muscle fibers
190
Myocardial infarction
loss of blood supply to the myocardium caused by an obstruction of an artery.
191
Myocardial ischemia: clinical outcome depends on
the anatomic region affected and the extent and duration of disrupted blood flow.
192
Irreversible damage of cardiocytes occurs when
the loss of blood supply lasts more than 20 minutes.
193
reperfusion
If blood flow is restored in less than 20 minutes and cardiocyte cell viability is maintained.
194
Smooth muscle shape
Bundles or sheets of fusiform elongated cells with finely tapered ends
195
Smooth muscle location
Found in walls of tubular organs, walls of most blood vessels, iris and ciliary body of eye and arrector pili muscle of hair follicle
196
Smooth muscle cells are also called
fibers
197
Smooth muscle interconnection
Gap junctions
198
Why is smooth muscle stained with eosin?
actin and myosin
199
Cross section of smooth muscle
round nucleus
200
Longitudinal section of smooth muscle
Nuclei located in the center, corkscrew appearance
201
Fibroblast vs Smooth Muscle
202
To contractile activity, smooth muscle cells
supplement fibroblast activity, synthesizing collagen, elastin, and proteoglycans (contractile cells are abundant)
203
Smooth muscle cells can secrete
Collagen type IV (basal lamina)-they have external lamina
Collagen type III (reticular fibers)
Elastin (in blood vessels)
204
Arrows: dense bodies, PV: pinocytotic vesicles, BL: basal (external lamina)
TEM image of smooth muscle
205
Isolated, small, irregular electron dense bodies. Longitudinal section
205
Isolated, small, irregular electron dense bodies. Longitudinal section
206
Typical secretory cell of Smooth muscle
cytoplasmic organelles concentrated at each end of nucleus; numerous mitochondria, well developed RER, free ribosomes, glycogen, Golgi apparatus.
207
The contractile filaments of smooth muscle are oriented
oblique angles to the long axis of the cell, resulting in a twisting of the smooth muscle cells during contraction.
208
Thin filaments are attached to
cytoplasmic dense bodies
209
Dense bodies location
scattered in the cytoplasm in a network of desmin and vimentin filaments
210
Dense bodies function and location
Provide attachment site for thin and intermediate filaments
Contain alpha-actinin
Important role in transmitting contractile forces.
Analogs of Z-line in striated muscle
Three-dimensional anastomosing network
Extends from sarcolemma into the interior of cell
211
Smooth muscle thin filaments
Actin
Tropomyosin (smooth muscle isoform)
Caldesmon and calponin (smooth muscle specific actin binding proteins)
212
Smooth muscle thick filaments
Myosin II: 2 heavy, 4 light chains but
Side polar arrangement (rather than bipolar in striated muscle)
213
The arrangement of the contractile proteins and the mechanism of contraction of smooth muscle differ
1. NO sarcomeres
2. NO troponin
3. Ca2+ ions derive from outside the cell rather than from the SR.
4. Myosin light-chain kinase (instead of troponin, which is not present in smooth muscle cells) is responsible for the Ca2+ sensitivity
214
Smooth muscle contraction can be initiated by
Mechanical impulses (passive stretching)
Electrical depolarization (release of neurotransmitters)
Chemical stimulus (some hormones causing release of second messengers as IP3 and NO-cGMP)
215
Smooth muscle is specialized for and regulated by what?
slow, prolonged contraction regulated by post synaptic neurons of ANS (autonomic nervous system)
216
Essential proteins for regulation of contraction in Smooth muscle
1. Myosin light chain kinase (MLCK): Phosphorylates myosin regulatory light chains to form a cross bridge with actin.
2. Calmodulin: Ca2+-calmodulin complex binds to MLCK to activate it.
217
What does a Smooth muscle contraction lack?
Lacks a T-system
218
Explain Smooth muscle contraction
Invaginations of plasma membrane (caveola) together with adjacent SR act like a T-tubule system
Ca2+ is elevated (by depolarization by voltage gated channels or direct activation of gated Ca2+ release channels in SR by second messengers).
Ca2+-calmodulin complex forms
MLCK is activated
Contraction begins
Ca2+ is removed by ATP-dependent Ca2+ pumps after contraction
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Smooth muscle contraction
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Smooth muscle medical application
Leiomyoma
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leiomyomas
Benign tumors that develop in smooth muscle fibers
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Where do leiomyomas most commonly occur?
Wall of uterus (called fibroids), become sufficiently large and produce painful pressure and unexpected bleeding
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Different potentials for regeneration after injury of 3 muscles?
Skeletal muscle: limited regeneration by satellite cells.
Cardiac muscle: lacks satellite cells and shows very little regenerative capacity. Damage to heart muscles replaced by proliferating fibroblasts and growth of connective tissue forming myocardial scars.
Smooth muscle: simple mononucleated cells capable of active regenerative response. After injury smooth muscles undergo mitosis and replace damaged tissue.
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Comparison of 3 muscle types
