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BLOCK 2 - Histology (Grace) > Muscle Tissue > Flashcards

Muscle Tissue Flashcards

1
Q

What are the 2 types of muslce tissue?

A
  • striated muscle
  • smooth muscle
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2
Q

What are the 2 subdivisions of striated muscle?

A
  • skeletal muscle
  • cardiac muscle
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3
Q

Comparison between Skeletal, Cardiac & Smooth muscle

A
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4
Q

What are the 2 major contractile fibers components in muscle cells?

A
  • actin
  • myosin
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5
Q

Which muscles control voluntary contraction?

A

skeletal muscles

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6
Q

Which muscles control involuntary contraction?

A

cardiac + smooth muscles

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7
Q

Why are connective tissues investments important in skeletal muscles?

A

they provide vascular + neural elements to muscle cells

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8
Q

Epimysium

A

surrounds an entire muscle

  • forms aponeuroses (skeletal muscle <–> muscle)
  • forms tendons (skeletal muscle <–> bone)
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9
Q

Perimysium

A

**surrounds fascicles of muscle cells **(small bundles)

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10
Q

Endomysium

A

surrounds individual muscle cells

  • composed of reticular fibers + external lamina
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11
Q

a muscle cell (*muscle fiber) *is also called…

A

a multinucleated syncytium

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12
Q

muscle fibers develop from…?

A

… the fusion of small, individual muscle cells called

myoblasts

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13
Q

Describe a muscle cell as seen through a light microscope.

A
  • multinucleated
  • polygonal shape (transvers view)
  • long, cylindrical (longitudinal view)
  • enveloped by external lamina + reticular fibers
  • diameter of 10-100 um (micrometers)
  • nuclei lie just beneath plasma membrane
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14
Q

What is a good way to differentiat between connective tissue and muscle fibers?

A

muscle cells = cellular elements

connective tissue = extracellular products of CT cells

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15
Q

what is a muscle cell plasmalemma also know as?

A

Sarcolemma

(plasma membrane + external lamina + surrounding reticular lamina)

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16
Q

What are the 3 types of muscle fibers?

A
  • Red fibers
  • White fibers
  • Intermediate fibers
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17
Q

Red Muscle Fibers

(Type 1)

A
  • Slow contraction
  • do NOT fatigue easily
  • High myoglobin content
  • High # of mitochondria
  • High in oxidative enzymes
  • Low in ATPase
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18
Q

White Muscle Fiber

(Type 2B)

A
  • Fast contraction
  • fatigue easily
  • Low myoglobin content
  • Low # of mitochondria
  • Low in oxidative enzymes
  • High in ATPase + phosphorylation
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19
Q

Intermediate Muscle Fiber

(Type 2A)

A
  • **Intermediate **myoglobin content
  • ** Intermediate **# of mitochondria
  • ** Intermediate **# of oxidative enzymes
  • ** Intermediate** amount of ATPase
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20
Q

Red Fibers:

What type of contraction?

Do they fatigue easily?

Method of ATPase production?

A

Red Fibers:

  • slow + repetitive contraction
  • do not fatigue easily
  • oxidative phosphorylation (ATPase)
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21
Q

White Fibers:

What type of contraction?

Do they fatigue easily?

Method of ATPase production?

A

White Fibers:

  • fast contraction
  • fatigue easily
  • anerobic glycolysis (ATPase)
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22
Q

Intermediate Fibers:

What type of contraction?

Do they fatigue easily?

Method of ATPase production?

A

Intermediate Fibers:

  • fast contraction
  • NOT easily fatigued
  • oxidative phosphorylation + anerobic glycolysis (ATPase)
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23
Q

What is Myoglobin ?

A
  • a protein similar to hemoglobin
  • binds O2
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24
Q

What can change the type of muscle fibers?

Which type of fiber can change (and why would it)?

A

change in innervation can change a fiber type

  • if a RED fiber becomes denervated, its innervation can be replaced by WHITE fiber innervation, changing it into a WHITE fiber.
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25
Q

Which fibers are slow-twitch motor units** ** and are integral to back posture?

A

red fibers

(less MUSCLE TENSION than white)

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26
Q

Which fibers are fast-twitch motor units and are inteegral for fine, precise movements in the digits?

A

white fibers

(more NEUROMUSCULAR JUNCTIONS than red)

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27
Q

Skeletal Muscle Structure

A
  • “banding pattern” (alignment of myofibrils)

–> dark “A bands”

–> light “I bands” (bisected by Z discs)

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28
Q

What does the intermediate filament **desmin **assist with?

A
  • holding myofibrils in alignment

(during embryonic development = Desmin + vimentin)

  • connects cytoskeleton, nucleus, motor end plates, and mitochondria to myofibrils
  • (distributes force of contraction –> protects structural integrity)*
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29
Q

What does the** plectin** assist with?

A
  • helps hold myfibrils in alignment
  • tethers adjacent Z discs to each other
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30
Q

what is a sarcomere?

A
  • regular repeating region between successive Z disks

functional unit of contraction

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31
Q

What is the sarcomeric reticulum (SR)?

A

modified SER that surrounds myofilaments + forms a meshwork around each myofibril

  • forms a pair of dilated terminal cisternae (encircle myofibrils at junction of each A and I band)

- regulates muscle contraction:

–> sequestering calcium ions (relaxation)

–> releasing calcium ions (contraction)

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32
Q

What is a triad?

A

specialized complexes consisting of a narrow central T tubule flanked on each side by terminal cisternae of the SR

- located at the A–I junction

- help provide uniform contraction

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33
Q

What are myofilaments?

A

thick filaments (15 nm in diameter and 1.5 um long)

+

thin filaments (7 nm in diameter and 1.0 um long)

  • lie parallel to the long axis of the myofibril
  • responsible for the sarcomere banding pattern
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34
Q

What are satellite cells?

A

(myoblast-like)

regenerative cells

- differentiate

- fuse with one another

- form skeletal muscle cells as needed

  • probably left over from embryonic development
  • lie within basal lamina of skeletal muscle cells
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35
Q

What is myostatin?

A
  • protein manufactured + released by muscle cells

- restricts the size of individual skeletal muscle cells

  • (so that muscle cells do not get too long or broad)*
  • member of the tumor growth factor B(beta) superfamily
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36
Q

A bands

A

- anisotropic with polarized light

(different properties when observed in different directions)

- usually stain dark

  • contain both thin and thick filaments, which overlap and interdigitate
  • (Six thin filaments surround each thick filament)*
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37
Q

I bands

A

- isotropic with polarized light

(same properties when observed in different directions)

- appear lightly stained

- They contain only thin filaments

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38
Q

H bands

A
  • light regions transecting A bands
  • consist of thick filaments only.
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39
Q

M lines

A
  • narrow, dark regions at the center of H bands
  • formed by several cross-connections (M-bridges) at the centers of adjacent thick filaments
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40
Q

Z disks (lines)

A
  • dense regions bisecting each I band
  • contain a(alha)-actinin and Cap Z proteins
  • (bind to thin filaments + anchor them to Z disks with help of nebulin)*
  • -* peripherally located Z disks anchored to regions of sarcolemma (“costameres”) by vinculin and dystrophin
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41
Q

Thin filaments are composed of…?

A
  • F-actin
  • tropomyosin
  • troponin
  • associated proteins
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42
Q

F-actin

(thin filament)

A

polymer of G-actin monomers arranged in a double helix

- each monomer possesses an active site that can interact with myosin

  • diameter of 5–7 nm
  • exhibit polarity, having a (+) and a (-) end
  • (plus end tethered to cap Z of the Z disk; minus end, capped by tropomodulin, is located at the H band)*

(-) end = growing end of the F-actin

  • loses and gains back G-actin molecules at both its plus and minus ends (turn over rate is very slow = a few days)
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43
Q

Tropomyosin

(thin filament molecule)

A
  • 40 nm in length
  • bind head to tail, forming filaments that are located in the grooves of the F-actin helix
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44
Q

Troponin

(thin filament proteins - 3)

A
  • associated with each tropomyosin molecule
  • composed of:

–> Troponin T (TnT) forms the tail

(binding the troponin complex to tropomyosin)

–> Troponin C (TnC) 4 binding sites for calcium

(may be related to calmodulin)

–> Troponin I (TnI) binds to actin

(inhibits interaction of myosin and actin)

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45
Q

Identify the following structures from the image:

  • M
  • S
  • Sr
A
  • M = myofibrils
  • S = sarcomeres
  • Sr = sarcoplasm (cytoplasm of muscle cell)
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46
Q

Nebulin

(thin filament protein)

A
  • long, inelastic protein
  • 2 nebulin molecules wrap around each thin filament

(assist in anchoring it to the Z disk)

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47
Q

Tropomodulin

A
  • caps the (-) end of each thin filament
  • prevents addition of more G-actin molecules to growing end
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48
Q

Thick Filaments contain…?

A
  • approximately 250 myosin II molecules
  • (arranged in an antiparallel fashion)*
  • three associated proteins:

–> myomesin

–> titin

–> C protein

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49
Q

Myosin II

A
  • composed of 2 identical heavy chains + 2 pairs of light chains
  • resembles a double-headed golf club

* at least 18 different subtypes of myosin*

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50
Q

Myocine II - Heavy Chains

A
  • long rod like “tail” and a globular “head”

tails:

  • wind around each other in an (alpha)-helical configuration
  • function in self-assembly of myosin molecules into bipolar thick filaments

heads:

  • actin-binding sites of the heads function in contraction
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51
Q

Myosin II - light chains

A
  • two types; one molecule of each type is associated with the globular head of each heavy chain
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52
Q

Digestion of myosin

A
  1. enzyme trypsin cleaves myosin into:
    - light meromyosin (part of the tail portion)
    - heavy meromyosin (the two heads and the remainder of the tail)
  2. enzyme papain cleaves the heavy meromyosin releasing the

short tail (S2 fragment)

+ two globular heads (S1 fragments)

These S1 fragments have ATPase activity but require interaction with actin to release the noncovalently bound adenosine diphosphate (ADP) and Pi

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53
Q

Myomesin

A
  • protein at the M line that cross-links adjacent thick filaments
  • maintains their spatial relations
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54
Q

C protein

A
  • binds to thick filaments in the vicinity of M lines along much of their lengths

(between M line and end of thin filament in vicinity of the A–I junction)

*This region of the A band is referred to as the C zone*

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55
Q

Titin

A
  • large linear protein that displays axial periodicity (reoccuring)
  • forms an elastic lattice that parallels the thick and thin filaments,
  • two titin filaments anchor each thick filament to the Z disk
  • (maintains their architectural relationships to each other)*

>> amino terminal of the titin molecule spans entire thickness of the Z disk and binds to a-actinin and Z proteins.

>> within the Z disk, titin overlaps with other titin molecules from the neighboring sarcomere and probably forms bonds with them or with unidentified linker proteins

>> The carboxyl terminal of the titin molecule spans the entire M line and overlaps with titin molecules from the other half of the same sarcomere, and binds to the protein myomesin

>> Within the I band, in the vicinity of the Z disk, titin interacts with thin filaments

>> Within the A band, titin interacts with C protein

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56
Q

General features of cardiac muscle cells:

A
  • contract spontaneously; display a rhythmic beat (modified by hormonal + neural stimuli -> sympathetic + parasympathetic)
  • may branch at ends = connect w. adjacent cells
  • contain one central nucleus (occasionally two)
  • contain glycogen granules (esp. at poles of nucleus)
  • sarcoplasm is rich in myoglobin
  • have thick + thin filaments arranged in poorly defined myofibrils
  • cross-banding pattern
  • do NOT regenerate; injuries repaired by formation of fibrous CT

(scar tissue fr. fibroblasts)

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57
Q

Structural components of cardiac muscle cells:

A
  • T tubules larger than skeletal m. + linked by external lamina

(invaginate fr. the sarcolemma at Z discs)

  • SR is poorly defined + contributes to dyad formation

(dyad = T tubule + one SR profile)

- **Calcium ions: **

–> relaxation = Ca2 leaks into sarcoplasm @slow rate = automatic rhythm

–> Ca2 enters cardiac muscle cells fr. extracellular environment

(voltage-gated Ca2 channels of T tubules and sarcolemma)

–> Ca2 released fr. SR + corbular sarcoplasmic reticulum via ryanodine receptors (response to Ca2 entering channels) = cause contraction of cardiac muscle.

–> force of contraction directly dependent on availability of

Ca2 in sarcoplasm

(basal cardiac contraction, only 50% of available calcium-binding sites of TnC are occupied)

58
Q

How does SR presnt in the vacinity of Z discs in cardiac muscle?

A
  • as small, basketlike saccules known as corbular sarcoplasmic reticulum

(region rich in Ca2-release channels (junctional feet) –> analogous to the SR terminal cisternae)

59
Q

Functional anatomy of cardiac muscle:

A

–Striated
–Short branched cells
–Uninucleate
–Intercalated discs
–T-tubules larger + over z-discs

60
Q

How is injured cardiac tissue repaired?

A
  • formation of fibrous connective cissue produced by fibroblasts

= scar tissue

61
Q

good to know

A

good to know

62
Q

Function of cardiac valves is…?

A

to prevent backflow

63
Q

Atrioventricular Valves

A
  • Prevent backflow to the atria
  • Prolapse is prevented by the chordae tendinae
    (Tensioned by the papillary muscles)
64
Q

the function of semilunar valves is…?

A
  • Prevent backflow into ventricles
65
Q

These structures are more abundant in cardiac muscle, and lie parallel to the I bands and often are adjacent to lipids.

A

mitochondria

66
Q

Where are atrial granules found and what is their function?

A
  • present in the atrial cardiac muscle cells
  • contain precursor of atrial natriuretic peptide

(acts to decrease resorption of sodium and water in the kidneys)

= reducing body fluid volume and blood pressure

67
Q

Identify the muscle tissues:

A

A- Skeletal

B- Smooth

C- Cardiac

68
Q

Intercalated disks

A
  • complex steplike junctions
  • form end-to end attachments b/t adjacent cardiac muscle cells
  • _ transverse portion of disks runs across muscle fibers @right angles + possesses three specializations:_
    1. fasciae adherentes (analogous to zonula adherentes) actin filaments attach to these
    2. desmosomes (macula adherentes)
    3. gap junctions
69
Q

Skeletal Muscle (comparison)

A
  • long, cylindrical shape
  • many, peripheral nuclei
  • striated
  • has triads (T tubules & 2 SE) at A-I junctions
  • no gap junctions
  • sarcomeres
  • restricted regeneration
  • voluntary contraction
70
Q

Cardiac Muscle (comparison)

A
  • blunt-ended, branched shape
  • 1 or 2 central nuclei
  • striated
  • has **dyads **( T tubule + 1 SE) at Z discs
  • gap junctions at intercalated discs
  • has sarcomeres
  • no regeneration
  • no voluntary constriction
71
Q

Smooth Muscle (comparison)

A
  • short, spindle shaped
  • one central nucleus
  • not striated
  • has caveolae (but no T tubules) + some SER
  • gap junctions in sarcolemme = “nexus”
  • no sarcomeres
  • extensive regeneration
  • no voluntary contraction
72
Q

Huxley’s sliding-filament model

(muscle contraction)

A
  • contraction = thick + thin filaments do not shorten but increase their overlap
  • thin filaments slide past thick filaments + penetrate more deeply into the A band (remains constant in length)
  • I bands + H bands shorten as Z disks are drawn closer together
73
Q

Initiation of muscle contraction: Step 1

A

Depolarization + release of Ca2+ triggers binding of actin and myosin

= contraction

  1. sarcolemma depolarizes at myoneural junction
  2. T tubules convey wave of depolarization to myofibrils.
  3. Voltage-sensitive dihydropyridine (DHP) receptors alter their conformation (membrane depolarization)
  4. Ca2+ released into cytosol at A–I junctions via Ca2+-release channels (junctional feet, ryanodine receptors) of the SR terminal cisternae
    * (opened by activated DHP receptors)*

As long as the Ca2+ level is sufficiently high, the contraction cycle will continue

74
Q

Initiation of muscle contraction: Step 2

A

Activation of Actin by Ca2+

- resting state: myosin-binding sites on thin (actin) filaments are partially covered by tropomyosin

  • TnI is bound to actin and hinders myosin–actin interaction

- active state: Ca2+ binding by TnC = conformational change

(breaks the TnI–actin bond)

  • tropomyosin shifts slightly + uncovers the myosin-binding sites
75
Q

Relaxation of muscle contraction (step 3)

A

Ca2+concentration in the cytosol is reduced enough that TnC loses its bound Ca2+

  • tropomyosin returns to its resting position, covering actin’s binding sites + restoring the resting state
  • relaxation depends on Relaxation depends on a Ca2
76
Q

What is a Motor Unit?

A

a neuron and every muscle cell it innervates

  • muscle cells of a single motor unit contract in unison
  • follow the “all or none law”
77
Q

myoneural junction

(neuromuscular junction)

A

a synapse between a branch of a motor nerve axon + a skeletal muscle cell

B. synaptic cleft

  • narrow space between presynaptic membrane of axon terminal & the postsynaptic membrane (“motor end plate”)
  • contains an amorphous external lamina (basal laminalike material) derived from the muscle cell
78
Q

axon terminal

A
  • mitochondria + synaptic vesicles (acetylcholine) + SER elements
  • axon terminal lacks myelin; has a Schwann cell on nonsynaptic surface
  • membrane on axon terminal synaptic surface = presynaptic membrane
79
Q

synaptic cleft

A
  • narrow space between presynaptic membrane of axon terminal & the postsynaptic membrane (“motor end plate”)
  • contains an amorphous external lamina (basal laminalike material) derived from the muscle cell
80
Q

Muscle cell components near the myoneural junction

A
  • junctional folds
  • Acetylcholine receptors
  • sarcoplasm is rich in mitochondria, ribosomes, and rough endoplasmic reticulum (RER)
81
Q

junctional folds

A
  • sarcolemmal invaginations (of the postsynaptic membrane)
  • lined by an external lamina + extend inward from synaptic cleft
82
Q

Acetylcholine receptors

A
  • located in the postsynaptic membrane
  • binding sites for ACh
83
Q

What occurs as the presynaptic membrane is depolarized at a myoneural junction?

A
  • voltage-gated Ca2+ channels open
  • extracellular Ca2+ enters into the axon terminal
  • Ca2+ triggers synaptic vesicles to release acetylcholine (ACh) in quanta into the synaptic cleft
  • quantum* = approx. 20,000 acetylcholine molecules
84
Q

What occurs when acetylcholine is released into the synaptic cleft?

A
  • released from synaptic vesicles
  • ACh binds to receptors of postsynaptic membrane

= depolarization of sarcolemma + generation of action potential

  • acetylcholinesterase (enzyme) located in external lamina lining junctional folds of motor end plate degrades acetylcholine = ending the depolarizing signal
85
Q

What happens to “left over” acetylcholine in the synaptic cleft?

A
  • recycled as **choline **(by acetylcholinesterase) –> returned to the axon terminal
  • recombined with acetyl coenzyme A (CoA) (from mitochondria) under the influence of choline acetyl transferase enzyme
  • forms acetylcholine –> stored in synaptic vesicles
  • Membranes of emptied synaptic vesicles = recycled via clathrin-coated endocytic vesicles
86
Q

What does the** “all or none” law** refer to?

A

an individual muscle cell either contracts or does not contract.

*there’s no half-assing it*

(all muscle cells of a single motor unit contract in unison)

87
Q

concentric contraction

A

as a muscle contracts the sarcomeres shorten

= the entire muscle becomes shorter

88
Q

isometric contraction

A

sarcomeres do not shorten

= entire muscle remains the same length

(e.g. squeezing a hard object)

89
Q

Muscle innervation consists of what types of nerve endings?

A
  • motor nerve endings (myoneural junctions)
  • two types of sensory nerve endings (muscle spindles and Golgi tendon organs)
90
Q

Muscle spindles & _golgi tendon organs _function in what sensation?

A

proprioception

“ability to sense stimuli arising within the body regarding position, motion, and equilibrium”

91
Q

What happens to the membranes of emptied synaptic vesicles once they’ve been used?

A

recycled via clathrin-coated endocytic vesicles

92
Q

muscle spindle (neuromuscular spindle)

A
  • elongated, fusiform sensory organ in skeletal muscle
  • functions primarily as a stretch receptor
93
Q

Structure of a muscle spindle:

A
  • bounded by a connective tissue capsule enclosing the fluid-filled periaxial space + 8 to 10 modified skeletal muscle fibers (intrafusal fibers).
  • surrounded by normal skeletal muscle fibers (extrafusal fibers)
  • anchored via capsule to perimysium + endomysium of extrafusal fibers
94
Q

Muscle cells depend on energy from ATP + phosphocreatine.The metabolism of what 2 substances creates this energy?

A

fatty acids + glucose

95
Q

What is the primary metabolic substrate in actively contracting muscles?

A

glucose

96
Q

What are the five stages of the skeletal muscle contraction cycle?

A
  1. attachment
  2. release
  3. bending
  4. force generation
  5. reattachment
97
Q

Muscle Spindle function

A
  • muscle stretch = spindle stretch = stimulates afferent nerve endings; send impulses to the CNS.

(response to both rate - phasic response + duration - tonic response)

  • depolarization of y(gamma)-efferent neurons = stimulates intrafusal nerve endings; rate + duration of stimulation monitored same way as stretching
  • muscle overstimulation; initiates contraction to counteract stretching
98
Q

What happens during **overstimulation **of the muscles?

A

results from stretching at too great a frequency or too long a time

  • causes stimulation of a(alpha)-efferent neurons to the muscle = initiating contraction + counteracting the stretching
99
Q

Golgi tendon organ

A
  • located in tendons; counteracts effects of muscle spindles
  • composed of encapsulated collagen fibers surrounded by terminal branches of type Ib sensory nerves
  • stimulated when muscle contracts too strenuously, increasing tension on the tendon
  • impulses from type Ib neurons inhibit a(alpha)-efferent neurons = preventing further contraction
100
Q

the lateral portion of intercalated disks has desmosomes + numerour gap junctions.

These facilitate what?

A

ionic coupling between cells

+ aid in coordinating contraction

101
Q

Cardiac muscle behaves as a ……?

A

functional syncytium

  • *uninucleated cells acting in syncronisation as a multinucleated cell = performing same function* *
  • (WARNING: this is Grace’s definition, not from a dictionary - but at least I know what it means…*ahem* unlike some people)*
102
Q

The thin filiments of cardiac muscle are secured to the Z disk by …?

A

a(alpha)-actinin + nebulette

*nebulette = nebulin-like molecule; extends proximal 25% of thin filament*

103
Q

What type of tissue is this?

Identify the structures indicated by the N and the arrows

A

CARDIAC TISSUE

N = nuclei

arrows = intercalated disks

104
Q

Cardiac cell connective tissue supports a rich capillary bed that supplies…?

What does this maintain?

A
  • sufficient nutrients + oxygen
  • maintains the high metabolic rate
105
Q

What percentage of the energy production of cardiac muscle cells is generated by aerobic respiration?

A

At least 90%

106
Q

What type of fibers are purkinji fibers?

Where are they located?

A
  • modified cardiac muscle cells
  • located in bundle of His
107
Q

Structure & function of purkinji fibers?

A
  • specialized for conduction
  • contain a few peripheral myofibrils
  • large, pale cells; rich in glycogen + mitochondria
  • form gap junctions, fasciae adherents, desmosomes w. cardiac muscle cells

(but not through typical intercalated disks)

108
Q

Ischemia

A

“Inadequate blood supply to a local area due to blockage of blood vessels leading to that area. Treatment is directed toward increasing the circulation to the affected body area.”

109
Q

Functional anatomy of the heart

(intrinsic conduction system)

A
  • consists of “pacemaker” cells + conduction pathways
  • coordinates contraction of ventricles + atria
110
Q

Autorhythmic Cells (Pacemaker Cells)

A
  • smaller than contractile cells
  • do NOT contain myofibrils
  • no organized sacromere structure

do not contribute to contractile force of heart

  • unstable membrane potential*
  • myogenic
111
Q

Pacemaker Cells have an unstable membrane potential.

At what electrical charges do these cells “bottom out” and “drift upward” to ?

A

“bottom out” at** -60mV**

“drifts upward” to **-40mV **= “pacemaker potential”

112
Q

The upward “drift” in pacemaker cells allows the membrane to reach threshold potential (-40mV) by itself.

This “drift” is due to what?

A

1. Slow leakage of K+ out & faster leakage Na+ in

= slow depolarization
= through If channels (f=funny); open at negative membrane potentials + start closing as membrane approaches threshold potential

2. Ca2+ channels opening as membrane approaches threshold

= @threshold additional Ca2+ ion channels open

= more rapid depolarization
(deactivate shortly after)

  1. Slow K+ channels open as membrane depolarizes causing an
    efflux of K+ and a repolarization of membrane
113
Q

Smooth Muscle Cells

A
  • non-striated, fusiform
  • 20um (sm. blood vessels) - 500um (uterus)
  • single nucleus
  • actively regenerate
  • surrounded by external lamina + reticular fiber network
  • arranged in layers, sm. bundles, or helices (in arteries)
114
Q

Smooth Muscle: Nucleus

A
  • centrally located
  • may not be visible in each cell (in cross-section)
  • has corkscrew shape + deeply indented (in longitudinal sections)
115
Q

Smooth Muscle: Mitochondria, RER + Golgi complex

A
  • concentrated near the nucleus
  • involved in synthesis of_ _Type III collegen, elastin, GAGs, external lamina, growth factors
116
Q

Smooth Muscle: ** Sarcolemmal Vesicles (Caveolae)**

A
  • along periphery of smooth muscle cells
  • may function in uptake/release of Ca2+
  • SER is sparce; may be associated w. caveolae
117
Q

Smooth Muscle: contractile filaments

A

actin + myocin; not organized into myofibrils

  • attached to peripheral + cytoplasmic densities; alignes obliquely to longitudinal axis of smooth muscle cells

Thick filaments

Thin filaments

118
Q

Thick filaments of smooth muscle are composed of what?

A

composed of myosin II

(each surrounded by ~ 15 thin filaments)

119
Q

In contrast to striated muscle, the heads of the myosin molecules_________________?

A

all point in the same direction

120
Q

Thin filaments of smooth muscle are composed of what?

A

actin

caldesmon

tropomyosin

calponin (functions similar to TnT + TnI)

121
Q

Intermediate filaments of smooth muscle are attached to cytoplasmic densities.

What types are included in vascular smooth muscle cells?

What types are included in nonvasculaar smooth muscle cells?

A

vascular = **vimentin + desmin **

nonvascular **= desmin **

122
Q

Ctyoplasmic densities in smooth muscle cells are believed to be …?What do they contain and what is their main function?

A
  • analogous to Z disks
    contain: a(alpha)-actinin
    function: as a filament attachment site
123
Q

Smooth Muscle Gap Junctions

A
  • between smooth muscles
  • facilitate spread of excitment
  • collectively called a “nexus”
124
Q

Contraction of smooth muscle

A
  • occurs more slowly + lasts longer (than skeletal)

…because ATP hydrolysis = slower

  • regulated by different mechanism (than skeletal)
125
Q

The contraction cycle in smooth muscle is stimulated by…?

What happens next?

A

stimulated by: transient increase in cytosolic Ca2+

  • Ca2+binds to calmodulin = alters conformation
  • Ca2+–calmodulin complex activates enzyme myosin light-chain kinase = catalyzes phosphorylation of one light chain of myosin
  • presence of Ca2+: inhibitory effect of **caldesmon–tropomyosin complex **are eliminated
  • globular head of phosphorylated myosin interacts w. actin; stimulates myosin ATPase = contraction
  • (myosin in phosphorylated form = contraction cycle continues)*
  • (Dephosphorylation of myosin disturbs myosin–actin interaction*
  • = relaxation)*
126
Q

In vascular smooth muscle, contraction is usually triggered by…?

A

a nerve impulse

(little spread of impulse from cell to cell)

127
Q

In visceral smooth muscle, contraction is triggered by…?

A

stretching of the muscle itself (myogenic)

(signal spreads from cell to cell)

128
Q

In the uterus during labor, what triggers smooth muscle contraction?

A

oxytocin

129
Q

In smooth muscle throughout in the body (other than uterus), what triggers muscle contraction?

A

epinepherine

130
Q

What types of nerve fibers stimulate smooth muscle?

A

Sympathetic + Parasympathetic

  • act in antagonistic fashion to stimulate or depress activity
131
Q

Nerve terminales with empty vesicles are considered…?

A

“cholinergic”

  • parasympathetic

(secreting acetylcholine)

132
Q

Nerve terminales with vesicles filled with dense granular material are considered to be…?

A

“adrenergic”

  • sympathetic

(secreting norepinepherine)

133
Q

Nerve terminals with vesicles containing an opaque content are considered to be…?

A

“purinergic”

(secreting other neurotransmitters in general)

134
Q

nerve endings in smooth muscles that are considered sensory have what two characterstics?

A
  • contain primarily mitochondria
  • have no vesicles
135
Q

In certain glands, this type of cell shares the basal laminae of secretory and duct cells

A

Myoepithelial cells

(attached to basal lamina via hemidesmosomes)

136
Q

What type of tissue do myoepithelial cells arise form?

What happens when they contract?

A

arise from ectoderm

**- **contract to express secretory material from glandular

epithelium into ducts and out of the gland

137
Q

What type of contractile, nonmuscle cell has a basketlike shape and several radiating processes?

A

myoepithelial cells

138
Q

What do myoepithelial cells contain?

A

actin

myocine

intermediate filaments

cytoplasmic peripheral densities (attach to filaments)

139
Q

Myoepithelial cells:

  1. contraction generally occurs via what process?
  2. In lactating mammary glands, contraction occurs in response to…?
  3. In lacrimal glands, contraction occurs in response to…?
A
  1. generally = calmodulim-mediated perocess
  2. mammary glands = oyxtocin
  3. lacrimal glands = acetylcholine
140
Q

What cells resemble fibroblasts, but possess higher amounts of actin and myosin and are capable of contraction?

A

Myofibroblasts

141
Q

What do myofibroblasts do during wound healing?

A

may contract to decrease the size of the defect

(wound contraction)

BLOCK 2 - Histology (Grace) (10 decks)

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