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physiology and anatomy > week 3: skeletal muscle organisation, activation and deactivation-10.1, 10.2, 10.3 > Flashcards

week 3: skeletal muscle organisation, activation and deactivation-10.1, 10.2, 10.3 Flashcards

1
Q

whole muscle is sheathed within

A

layer of connective tissue

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2
Q

muscle fibre diameter

A

10-100 micrometre

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3
Q

muscle fibre surrounded by

A

sacrolemma

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4
Q

how does skeletal muscle move the body

A

by pulling on our bones

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5
Q

four common properties of muscle tissue

A

excitability
contractility
extensibility
elasticity

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6
Q

excitability

A

ability to recieve and respond to stimulus

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7
Q

what do muscle tissue respond to

A

chemical stimulus from a nerve cell with a change in membrane potential

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8
Q

contractility

A

ability of a muscle cell to shorten when stimulated

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9
Q

extensibility

A

stretching movement of a muscle

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10
Q

elasticity

A

ability of a muscle to recoil to resting length

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11
Q

6 main functions of skeletal muscle

A

producing movement
maintaining posture and body position
supporting soft tissue
guarding body entrances and exits
maintaining body temperature
storing nutrients

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12
Q

what does skeletal muscle organs contain

A

skeletal muscle tissue
connective tissue
blood vessels
nerves

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13
Q

what is the muscle tissue of skeletal muscle surround by

A

three layers of connective tissue
- epimysium
-perimysium
-endomysium

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14
Q

epimysium

A

dense layer of collagen fibres that surrounds the entire muscle
separates muscle from nearby tissues and organs
connected to deep fascia- dense layer of connective tissue

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15
Q

perimysium

A

divides skeletal muscle into series of compartments-fascicles
contains collagen and elastic fibres as well as blood vessels and nerves

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16
Q

endomysium

A

delicate connective tissue surrounds individual skeletal mucle cells within a fascicle
loosley interconnects adjacent muscle fibres
(seperates muscle fibres from another)
flexible, elastc tissue layer contains capillary networks, myosatellite cells, stem cells

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17
Q

how are the collagen fibers of the perimysium and endomysium arranged

A

interwoven and blend into one another

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18
Q

at each end of the muscle, collagen fibers of the epimysium, perimysium and endomysium

A

come togehter to form either a bundle-tendon
or a broad sheet- aponeurosis

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19
Q

function of tendons and aponeuroses

A

usually attach skeletal muscles to bones

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20
Q

what happens where collagen fibre contact the bone

A

collagen fibers extend into bone matrix, providing a firm attachment
as a result, contraction of muscle pulls on attached bone

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21
Q

what does the connective tissue of the endomysium and perimysium contain

A

blood vessels and nerves that suply the muscle fibres

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22
Q

why is an extensive vascular network needed

A

delivers necessary oxygen and nutrients
carries away metabolic waste generated by active skeletal muscles

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23
Q

blood vessels and nerves in muscle

A

blood vessels and nerves normally enter muscles together and follow the same branching course through the perimysium
each fascicle recieves branches of these blood vessles and nerves

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24
Q

arterioles within endomysium

A

supply blood to capillary network that services the individual muscle fiber

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25
axons
nerve fibers extending from neurons penetrate the epimysium branch through perimysium enter endomysium to innervate individual muscle fibers
26
multinucleate
each skeletal muscle fibre contains hundreds of nucleui just internal to the plasma membrane
27
genes of nuclei of multinucleate muscle fibres
control production of enzymes and structural proteins required for normal muscle contraction
28
the more copies of the genes,
the faster these proteins can be produced
29
development of skeletal muscle fibers
groups of myoblasts fuse, forming individual multinucleate skeletal muscle fibers each nucleus in skeletal muscle fiber reflects the contribution of a single myoblast
30
unfused myoblasts
remain in adult skeletal muscle tissues as myosatellite cells
31
myosatellite cells after an injury
enlarge and divde fuse with damaged muscle fibers assisting in repir of tissue
32
skeletal muscle tissue is known as
striated muscle striations visible with a light microscope
33
striations are due to
precise arrangement of actin and mysosin filaments in myofibrils each muscle fibre contains hundreds to thousands of cyclindrical myofibrils
34
arrangement of actin and myosin filaments forms
functional repeating unit: sarcomere
35
sacrolemma
plasma membrane of a muscle fiber surrounds sarcoplasm has a characteristic membrane potential in skeletal muscle fiber, a sudden change in the membrane potential is the first step that leads to contraction
36
transverse tubules
narrow tubes whose surface are continous with the sarcolemma (extensions of sacrolemma) and extend deep into sacroplasm filled with extracellular fluid and form passafeways through the muscle fiber
37
function of T tubules
propagate action potentials generated by sarcolemma electrical impulses travel along t tubules into cell interior
38
importance of T tubules
all regions of large skeletal muscle fiber must contract at the same time signal to contract must be distributed quickly throughout interior of cell
39
sarcoplasmic reticulum
membrane complex forms a tubular network around each myofibril
40
wherever a T tubule encircles a myofibril
the tubule is tightly bound to the membranes of the SR
41
terminal cisternae
on either side of a T tubule, tubules of SR enlarge, fuse and form expanded chambers: terminal cisternae
42
triad
combination of a pair of terminal cisternae plus a T tubule
43
fluid contents of triad
separate and distinct despite membranes being tightly bound
44
what is the SR specialised for
storage and release of calcium ions
45
myofibril dimensions
1-2 micrometres in diameter and as long as the muscle fibre
46
what is responsible for skeletal muscle fiber contraction
active shortening of myofibrils
47
myofibrils consist of
myofilaments: bundles of protein filaments
48
types of myofilaments
actin myosin titin
49
why does the entire cell shorten and pull on a tendon when myofibrils contract
myofibrils are anchored to the inner surface of the sarcolemma at each end of a skeletal muscle fiber outer surface of the sarcolemma is attached to collagen fibers of the tendon of the skeletal muscle
50
what provides energy in the form of ATP for short- duration, maximum-intensity muscular contractions
mitochondria and granules of glycogen scattered among the myofibrils mitochondrial activity and glucose breakdown by glycolysis
51
sacromere
repeating functional units made up of thin and thick myofilaments smallest functional unit of muscle fiber
52
how many sarcomeres does a myofibril consists of
approx 10,000 end to end
53
what does a sacromere contain
thin filaments thich filamets proteins that stabilise the positions of thick and thin filaments proteins that regulate the interactions between thick and thin filaments
54
what are sacromeres seperated by
z discs
55
I band
thin filaments
56
A band
thick filaments overlap region
57
thick filaments held in place by
titin
58
myosin molecules are
polar
59
because myosin molecules are polar
region in middle of thick filament with no myosin heads
60
titin
large protein spans half of sacromere spring like properties- resists overstretching of muscle preventing damage
61
thin filmants
composed largely of actin G-actin z discs contain a-actinin which anchors thin filaments nebulin holds thin filaments together also contain tropomyosin and troponin proteins structure strongly conserved
62
G actin
globular protein polymerises into double stranded helix filamentous form, F actin
63
tropomysoin and troponin involved in
regulation of muscle contraction control whether myosin heads can form cross-bridge links with thin filaments
64
[Ca2+] < 0.1 μM
tropomyosin covers binding site on actin- prevents cross bridge attachement
65
[Ca2+] > 1μM
Ca2+ binds to Tn-c troponin undergoes conformational change tropomyosin pulled out of the groove cross-bridges can now form
66
isoforms of Tn-C
fast and slow isoforms specific to fast and slow muscles
67
excitation contraction coupling
the sequence of events whereby the nerve impulse results in Ca2+ release in the fibre link between the generation of action potnetial in sacrolemma and the start of a muscle contraction
68
where does the excitation-contraction coupling occur
at the triads
69
what happens when action potential reaches a triad
triggers the release of Ca2+ from the terminal cisternae of the sarcoplasmic reticulum
70
how long does the change in permeability of the SR to Ca2+ last
0.03 seconds
71
[Ca2+] in and around sarcomere after AP reaches triad
100 times resting level
72
why is the effect of calcium ion release almost instantaneous
because terminal cisternae are loacted at zones of overlpa where thick and thin filaments ineract
73
calcium ion binding to troponin
changes the shape of the troponin molecule weakens the bond between troponin and actin troponin molecule changes position rolling the attached tropomyosin strand away from the active sites contraction cycle begins
74
contraction cycle
series of molecular events that enable muscle contraction
75
after active sights are exposed
myosin heads bind to them forming cross bridges
76
connection between head and tail
functions as a hinge that leads the head pivot pivots using energy released from hydrolysis of ATP head swings towards the M line-power stroke pivoting is the key step in muscle contraction
77
calcium regulation in the muscle occurs via the
SR
78
SR relaxed muscle
in relaxed muscle, Ca2+ bound to calsequestrin in terminal cisternae (stored) low Ca2+ conc in sacrolasm (app 1μM)
79
SR
free [Ca2+] in sarcoplasm rises (app 10μM) diffuses to the myofibrils and binds with Tn-C Tn-C undergoes conformational change allowing cross-bridges to form
80
at end of contraction,
Ca2+ pumps in SR actively transport it back to lumen of SR
81
why must calcium be removed from myofibrils at end of contraction
prevent further formation of actin-myosin cross bridges
82
steps that result in muscle activation
1. AP arrives at motor end plate 2. synaptic trasnmission: ACh release, diffusion and binding to voltage-gated channels, triggers AP in sarcolemma 3. AP conducted into the cell via T tubule 4. voltage-gated conformational change occurs in the dihydropyridine receptor (DHPR) 5. conformational chnage in DHPR is transmitted to the Ryanodine receptor ( the calcium release channel) opening the channel and releasing Ca2+ into the myofibrillar space 6. Ca2+ diffuses into myofibrils and binds to troponin C on the thin filament 7. conformational change in troponin C alters the binding of troponin I to actin and releases the troponin-tropomyosin complex 8. tropomyosin is able to move, allows mysoin head to bind 9. cross-bridge cycling can occur as long as system stays activated
83
steps in muscle deactivation
1. Ca2+ is pumped back into SR by the Ca2+-ATPase lowering myoplasmic [Ca2+] 2. Ca2+ is released from troponin-C because of the lower conc 3. cross-bridges released from actin, binding sites for myosin on actin get covered up by tropomyosin 4. number of strongly bound cross-bridges decline, force declines

physiology and anatomy (31 decks)

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