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Contractile cells Flashcards

1
Q

4 groups of contractile cells

A

muscle cells
myoepithelial cells
myofibroblasts
pericytes

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2
Q

muscle cells

A

striated (voluntary)

cardiac and smooth (involuntary)

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3
Q

myofibroblasts

A

contractile role and collagen secretion

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4
Q

pericytes

A

smooth, muscle-like cells surrounding blood vessels

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5
Q

myoepithelial cells

A

component of certain secretory glands

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6
Q

skeletal muscle

A

voluntary movement
influenced by nervous system
maintenance of posture

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7
Q

development of skeletal muscle

A

embryogenesis
fusion of precursor cells (myoblasts)
syncytium with hundreds of nuclei beneath cell membrane

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8
Q

structure of skeletal muscle

A 
long thin cylindrical structure
50-60 um diameter
up to 10cm long
hexagonal profile (cross section)
fibrocollagenous septa
numerous nuclei at side
mitochondria and glycogen
external lamina
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9
Q

satellite cells

A

adult muscle

muscle precursor cells dividing to form new muscle cells

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10
Q

sarcolemma

A

cell membrane

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11
Q

sarcoplasm

A

cell cytoplasm

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12
Q

sarcoplasmic reticulum

A

ER

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13
Q

contractile elements of skeletal muscle cells

A

myofibrils
thin cylindrical structures 1-2 um in diameter
overlapping, repeating assemblies of thick (myosin) and thin (actin) filaments

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14
Q

sarcomere

A

functional unit of myofibrils

plates of accessory proteins hold filaments in place and divide myofibrils

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15
Q

arrangement of contractile proteins in sarcomeres

A

thick filament surrounded by 6 thin filaments

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16
Q

bands in contraction

A

thick and thin filaments slide past eachother
decrease in width of light bands
width of dark bands is unchanged

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17
Q

A band

A

dark band
thick filament band
includes zone where thin filaments overlap with thick filaments

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18
Q

H zone

A

pale staining area in centre of A band

no thin filaments overlap with thick filaments

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19
Q

I band

A

zone of thin filaments not overlapping with thick filaments

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20
Q

Z line

A

dark band in centre of I band

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21
Q

M line

A

runs down centre of H band

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22
Q

myosin molecules

A

2 tadpole shaped heavy chains
tails coil around eachother
4 small light chains attached to head portions
tail portions aggregate to form filament
head portions project out in regular helical pattern

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23
Q

thin filaments

A

8nm diameter
thin filament (F actin) formed by polymerisation of single molecules of globular actin (G actin)
polar
G-actin molecules point in same direction

2 actin filaments attach by tail ends to alpha actinin in Z line, opposite direction

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24
Q

thick filaments

A 
myosin
polar
2 myosin filaments attach by tail ends
face opposite direction, away from M line
isoforms present
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25
accessory proteins of molecules
``` actinin nebulin myomesin titin desmin C protein ```
26
actinin
holds actinin filaments in lattice arrangement in Z disk
27
Z disk proteins
actinin filamin amorphin Z protein
28
nebulin
associated with actin containing thin filaents
29
myomesin
holds myosin filaments in lattice arrangement region of M line associated with creatine kinase and M protein
30
titin
long elastic protein runs parallel to filament array links ends of thick filaments to Z disk
31
desmin
link adjacent myofibrils to eachother | link myofibrils to membrane
32
C protein
myosin binding protein | localised in 7 stripes running parallel to M band in first half of A band
33
use of ATP by myosin binding to actin
ATP bound to myosin head hydrolysed to ADP and phosphate myosin binds loosely to actin phosphate released and myosin binds tightly to actin
34
binding of myosin to actin
folding of myosin to cause movement of it relative to actin filament ADP released, fresh ATP binds and myosin returns to non attached state
35
tropomyosin
long rod like protein winding around actin to stabilise and stiffen it
36
troponin complex
regulates actin and myosin binding | attached to tropomyosin and contains 3 polypeptides: troponins T, I and C
37
troponin T
binds complex to tropomyosin | positions complex at site where actin binds to myosin
38
troponin I
physically prevents myosin binding to actin
39
troponin C
binds Ca2+ ions, causing a conformational change in troponin complex allowing myosin access to actin
40
how are nerve signals conveyed?
excitation of muscle cell membrane conveyed to interior of cell via membranous channels (transverse tubular system of T tubules) extending from muscle surface to surround each myofibril
41
terminal cisternae
2 portions of sarcoplasmic reticulum running alongside T tubule high conc of Ca2+ ion channels in wall membrane excitation of tubule system causes channels to open
42
membrane triad
association of T tubules and sarcoplasmic reticulum forms 3 tubules in cross section surrounds every myofibril in AI junction - 2 triads to each sarcomere
43
T tubular system
internal membrane system extends from the surface membrane as thin tubules deep through muscle fibre along region of AI junction 2 extensions of sarcoplasmic reticulum with high Ca2+ conc
44
differences between cardiac and skeletal muscle
cardiac muscle cells mononuclear and shorter (nuclei) long cardiac muscle fibres produced by lining cells via anchoring cell type junctions population of stem cells, analogous to satellite cells of skeletal muscle, not present in cardiac cells - no regeneration
45
structure of cardiac muscle cells
15 um diameter 100 um long central nucleus intercalated disks
46
3 types of cell junction in intercalated disks
desmosomal junctions - intermediate filaments adherent-type junctions anchor actin fibres of sarcomeres to end of cell communicating gap junctions facilitate passage of membrane excitation and synchronisation of contraction
47
molecular basis of contraction of cardiac muscle
transverse T tubule have wider invaginations of cell surface sarcoplasmic reticulum not as regular or as organised as in skeletal muscle association of cardiac sarcoplasmic reticulum is form of dyads, not triads, and is in region of Z lines rather than AI junction
48
smooth muscle cells structure
less organised system of contractile proteins than skeletal and cardiac muscle cells anchored together into functional units by BM material spindle shaped 20um - 500 um single, centrally located nucleus elongated in shape external lamina bundles by fine collagenous tissue containing blood vessels and nerves
49
where are smooth muscle cells located?
gut, urinary bladder and uterus blood vessel walls and secretory gland ducts sustained slow or rhythmic contractions not under voluntary control
50
cross sectional/longitudinal smooth muscle cells
polygonal profiles | linear bundles
51
contractile proteins in smooth muscle cells
bundles of contractile proteins crisscrossing the cell inserted into anchoring points (focal densities)
52
how does a mass of smooth muscle cells function as one unit?
tension generated by contraction transmitted through focal densities surrounding network of external lamina
53
how is energy supplied in smooth muscle cells?
numerous mitochondria | located with ER around nucleus, in area devoid of contractile filaments
54
nexus junctions
gap junctions in smooth muscle
55
invaginations in smooth muscle cells
similar to T tubules
56
contraction of smooth muscle cells
contraction of cell membrane results in shortening of the cell, which assumes a globular shape elongated shape in relaxed state
57
filaments in smooth muscle
thin filaments of actin (isoform specific to smooth muscle) associated with tropomyosin - no troponin thick filaments composed of myosin (different type than skeletal muscle) - only binds to actin if its light chain is phosphorylated
58
control of Ca2+ ion movements
relaxed - Ca2+ ions sequestered in sarcoplasmic reticulum excitation - released into cytoplasm and bind to calmodulin (calcium binding protein) calcium-calmodulin complex activates enzyme myosin light-chain kinase - phosphorylates myosin light chain and allows it to bind to actin
59
functional types of smooth muscle
unitary and multiunit | sheets with cells arranged circumfrentially or longitudinally
60
unitary smooth muscle
generate own low level of rhythmic contraction, stimulated by stretch, transmitted cell to cell via gap junctions innervated by ANS increases or decreases levels of spontaneous contraction, not initiate it slow contraction, no action potentials, low fast myosin
61
phasic smooth muscle
iris of eye ANS controls contraction vas deferens and large arteries rapid contractions, distinct action potentials, high fast myosin
62
myofibroblasts
spindle shaped cells secrete collagen well defined contractile properties
63
myofibroblasts structure
actin and desmin lack external lamina spindle shaped cells
64
myofibroblasts after damage
become active and proliferate repair defects from tissue death secrete collagen for firm scaffold to consolidate a damaged area myofibrils contract and pulls extracellular matrix together to reduce physical size of damaged area
65
pericytes
``` spindle-shaped cells circumfrentially arranged around capillaries and venules external lamina little cytoplasmic differentiation actin and myosin ```
66
pericytes after tissue damage
proliferate assume role of primitive mesenchymal cells differentiate into myofibroblasts and mesenchymal tissue
67
myoepithelial cells structure
``` layer of flat cells around acini and ducts dark staining rounded nuclei clear cytoplasm contractile proteins desmosomes desmin ```
68
myoepithelial cells around acini
stellate, multi processes morphology in 3D | contractile meshwork enclosing secretory units of glands
69
myoepithelial cells around ducts
fusiform | surround periphery of ducts
70
myoepithelial cells function
controlled by ANS and contract and expel glandular secretions

Histology (10 decks)

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