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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
Q

axons

A

nerve fibers extending from neurons
penetrate the epimysium
branch through perimysium
enter endomysium
to innervate individual muscle fibers

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26
Q

multinucleate

A

each skeletal muscle fibre contains hundreds of nucleui just internal to the plasma membrane

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27
Q

genes of nuclei of multinucleate muscle fibres

A

control production of enzymes and structural proteins required for normal muscle contraction

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28
Q

the more copies of the genes,

A

the faster these proteins can be produced

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29
Q

development of skeletal muscle fibers

A

groups of myoblasts fuse, forming individual multinucleate skeletal muscle fibers
each nucleus in skeletal muscle fiber reflects the contribution of a single myoblast

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30
Q

unfused myoblasts

A

remain in adult skeletal muscle tissues as myosatellite cells

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31
Q

myosatellite cells after an injury

A

enlarge and divde
fuse with damaged muscle fibers
assisting in repir of tissue

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32
Q

skeletal muscle tissue is known as

A

striated muscle
striations visible with a light microscope

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33
Q

striations are due to

A

precise arrangement of actin and mysosin filaments in myofibrils
each muscle fibre contains hundreds to thousands of cyclindrical myofibrils

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34
Q

arrangement of actin and myosin filaments forms

A

functional repeating unit: sarcomere

35
Q

sacrolemma

A

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
Q

transverse tubules

A

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
Q

function of T tubules

A

propagate action potentials generated by sarcolemma
electrical impulses travel along t tubules into cell interior

38
Q

importance of T tubules

A

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
Q

sarcoplasmic reticulum

A

membrane complex
forms a tubular network around each myofibril

40
Q

wherever a T tubule encircles a myofibril

A

the tubule is tightly bound to the membranes of the SR

41
Q

terminal cisternae

A

on either side of a T tubule, tubules of SR enlarge, fuse and form expanded chambers: terminal cisternae

42
Q

triad

A

combination of a pair of terminal cisternae plus a T tubule

43
Q

fluid contents of triad

A

separate and distinct despite membranes being tightly bound

44
Q

what is the SR specialised for

A

storage and release of calcium ions

45
Q

myofibril dimensions

A

1-2 micrometres in diameter and as long as the muscle fibre

46
Q

what is responsible for skeletal muscle fiber contraction

A

active shortening of myofibrils

47
Q

myofibrils consist of

A

myofilaments: bundles of protein filaments

48
Q

types of myofilaments

A

actin
myosin
titin

49
Q

why does the entire cell shorten and pull on a tendon when myofibrils contract

A

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
Q

what provides energy in the form of ATP for short- duration, maximum-intensity muscular contractions

A

mitochondria and granules of glycogen scattered among the myofibrils
mitochondrial activity and glucose breakdown by glycolysis

51
Q

sacromere

A

repeating functional units
made up of thin and thick myofilaments
smallest functional unit of muscle fiber

52
Q

how many sarcomeres does a myofibril consists of

A

approx 10,000 end to end

53
Q

what does a sacromere contain

A

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
Q

what are sacromeres seperated by

A

z discs

55
Q

I band

A

thin filaments

56
Q

A band

A

thick filaments
overlap region

57
Q

thick filaments held in place by

A

titin

58
Q

myosin molecules are

A

polar

59
Q

because myosin molecules are polar

A

region in middle of thick filament with no myosin heads

60
Q

titin

A

large protein
spans half of sacromere
spring like properties- resists overstretching of muscle preventing damage

61
Q

thin filmants

A

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
Q

G actin

A

globular protein
polymerises into double stranded helix filamentous form, F actin

63
Q

tropomysoin and troponin involved in

A

regulation of muscle contraction
control whether myosin heads can form cross-bridge links with thin filaments

64
Q

[Ca2+] < 0.1 μM

A

tropomyosin covers binding site on actin- prevents cross bridge attachement

65
Q

[Ca2+] > 1μM

A

Ca2+ binds to Tn-c
troponin undergoes conformational change
tropomyosin pulled out of the groove
cross-bridges can now form

66
Q

isoforms of Tn-C

A

fast and slow isoforms specific to fast and slow muscles

67
Q

excitation contraction coupling

A

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
Q

where does the excitation-contraction coupling occur

A

at the triads

69
Q

what happens when action potential reaches a triad

A

triggers the release of Ca2+ from the terminal cisternae of the sarcoplasmic reticulum

70
Q

how long does the change in permeability of the SR to Ca2+ last

A

0.03 seconds

71
Q

[Ca2+] in and around sarcomere after AP reaches triad

A

100 times resting level

72
Q

why is the effect of calcium ion release almost instantaneous

A

because terminal cisternae are loacted at zones of overlpa where thick and thin filaments ineract

73
Q

calcium ion binding to troponin

A

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
Q

contraction cycle

A

series of molecular events that enable muscle contraction

75
Q

after active sights are exposed

A

myosin heads bind to them forming cross bridges

76
Q

connection between head and tail

A

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
Q

calcium regulation in the muscle occurs via the

A

SR

78
Q

SR relaxed muscle

A

in relaxed muscle, Ca2+ bound to calsequestrin in terminal cisternae (stored)
low Ca2+ conc in sacrolasm (app 1μM)

79
Q

SR

A

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
Q

at end of contraction,

A

Ca2+ pumps in SR actively transport it back to lumen of SR

81
Q

why must calcium be removed from myofibrils at end of contraction

A

prevent further formation of actin-myosin cross bridges

82
Q

steps that result in muscle activation

A
  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
Q

steps in muscle deactivation

A
  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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