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year 2 sem 2 motor systems > muscles > Flashcards

muscles Flashcards

1
Q

smooth muscle length, nucleus, appearance, location and control

A

-30- 200um
-mono-nucleated, central
-spindle shaped, tapered ends, non-striated
-lining tracts: respiratory, cardiovascular, digestive, reproductive
-involuntary (autonomic)

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2
Q

cardiac smooth muscle length, nucleus, appearance, location and control

A

-50-100um
-mono-nucleated mainly (<5)
-branched, striated
-lining of the heart
-self contractable, involuntary (autonomic NS)

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3
Q

skeletal muscle length, nucleus, appearance, location and control

A

-up to 0.3m
-multi nucleated (>100s)
-elongated, striated
-muscles, attached to skeleton
-voluntary (somatic NS)

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4
Q

flexors

A

close angle between limb and body

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5
Q

extensors

A

increase angle between limb and body

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6
Q

abductor

A

movement of limb away from body

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7
Q

adductor

A

movement of limb towards body

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8
Q

prime mover

A

main muscle

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9
Q

antagonists

A

muscles working in opposite directions

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10
Q

fixators/ fixator muscles

A

stabilise

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11
Q

components of skeletal muscle (basic organisation)

A

muscle–> fascicles –>fibres

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12
Q

what makes up a muscle fibre

A

a bundle of filaments

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13
Q

myofibril

A

a muscle fibre (single cell)
elongated rod like shapes

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14
Q

sarcomere

A

smallest contractile unit in a muscle fibre
interdigitated thick and thin filaments, bounded by z discs

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15
Q

how many sarcomeres does each myofibril contain?

A

20,000 sarcomeres in a series

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16
Q

thin filament projection

A

project from z line towards the middle

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17
Q

thick filament projection

A

connected in the middle of the sarcomere, project towards the z lines

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18
Q

M line

A

The line at the centre of a sarcomere to which myosin bind

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19
Q

what is each thin filament composed of?

A

a F actin arranges as a helix plus tropomyosin and troponin

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20
Q

composition of thick filament

A

is made up of about 250 myosin molecules: myosin molecules have globular head

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21
Q

connectins

A

protein

fine, thin, elastic filaments connecting ends of tick filaments and Z-dicks

give muscle its springlike property (this springlike property is important for contraction)

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22
Q

myosin

A

thick filament

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23
Q

actin

A

thin filaments

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24
Q

contractile proteins

A

actin and myosin

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25
Q

what is contractile force caused by

A

produced by molecular cross bridges between thick and thin filaments

26
Q

what block the binding sites on actin

A

troponin-tropomyosin complexes on thin filaments block the binding sites on the actin

27
Q

what are myosin heads bound by at rest? what does this mean?

A

ADP-bound

ready to move, but dont have the energy yet

28
Q

what position are myosin heads in at rest?

A

cocked position

29
Q

calcium in sarcoplasm at rest

A

low (~ 10^-7 - 10^-8 M)
because there is no action potential

30
Q

cross bridges at rest

A

no cross-brides between thick and thin filaments

31
Q

activation in sarcomere

A

muscle fibre is activated (action potential travels down T-tubules)

Calcium is released from the cisternae of the sarcoplasmic reticulum (SPR)

calcium binds to troponin

conformational changes in tin filament exposes actin binding sites

attachment of cocked myosin heads = cross-bridge formation

32
Q

sarcomere sliding of filaments

A

Upon formation of cross-bridges, mechanical energy (from ATP dephosphorylation) stored in “cocked” myosin heads is released - POWER STROKE - moves the filament

Myosin heads have shed bound ADP: resume relaxed / native state while remaining cross-linked to thin strand

Longitudinal force pulls the thin and thick filaments into greater overlap (~0.06 µm) -shortens the muscle fibre (sarcomere) .

33
Q

myosin detachment

A

ATP binds to Myosin heads which then detaches from its actin binding site

Actin-binding site is released and can form another cross-bridge to sustain muscle contraction

34
Q

reactivation of myosin (sarcomere)

A

Thick filament: Energy released by dephosphorylation of ATP to bound ADP is stored in myosin heads - myosin heads are “re-cocked”

Thin filament: High [Ca2+]: system remains activated (step 2), muscle contraction persists. Low [Ca2+ ]: return to resting state (step 1): myosin heads are cocked but unable to form cross-bridge.

35
Q

what do muscle fibres contain

A

a network of longitudinal tubules and chamber (sarcoplasmic reticulum, SPR)

36
Q

role of sarcoplasmic reticulum

A

sequester, store and release calcium

at rest intracellular calcium is low in the muscle fibre, actively pumped into SPR

37
Q

Where is action potential for muscle contraction initiated

A

neuro muscular junction

38
Q

speed of release of calcium

A

very rapid
20-50ms to activate the thin filaments fully

39
Q

speed of reuptake of calcium

A

rapid, decrease in cross brides 80-200ms

40
Q

twitches

A

Low frequency of APs → twitches
Limited Ca2+ release
Enough time for Ca2+ reuptake/ relaxation before next contraction

41
Q

tetani

A

High frequency of APs → tetani

More Ca2+ is released

Less time for Ca2+ reuptake
Summation/ fusion

Tetani sometimes used for heavy lifting

Fused or sustained tetanus associated with disease

42
Q

length-tension relationship

A

In addition to frequency of AP, the amount of force developed depends on the overlap between thick and thin filaments (= muscle length) prior to stimulation.

43
Q

overlap during contraction

A

no overlap

44
Q

overlap during contraction

A

complete overlap

45
Q

what is length-tension relationship determined by

A

the number of actin:myosin cross-bride connections avaliable

46
Q

cross bridges when the muscle is too stretched (relaxed)

A

less cross-bridges available = less force cant generate force directly from this position

47
Q

cross bridges when the muscles is too contracted

A

all available cross-bridges occupied = no additional force possible

48
Q

optimal length of sarcomere

A

overlap between myosin and actin, cross brides still available for further contraction

49
Q

red muscles

A

mainly slow-twitch muscle fibres (type I fibres)

can sustain small amounts of tension for long periods (resistant to fatigue)

aerobic metabolism, many mitochondria and capillaries, myoglobin rich (allows us to metabolise oxygen more efficiently)

50
Q

function red muscles

A

(anti-gravity/postural) – standing, walking

51
Q

pale muscles

A

Pale muscles - shorter bursts of activity, less mitochondria, less myoglobin

Mix of:
fast-twitch (type II) : (not resistant to fatigue)
-fast fatigue-resistant (type IIA) fibres
-fast fatigable (type IIB) fibres
slow-twitch (type I) fibres

52
Q

fast fatigue-resistant (type IIA) fibres

A

enough aerobic capacity to resist fatigue for a few minutes

53
Q

fast fatigable (type IIB) fibres

A

anaerobic catabolism, use glycogen, forms lactic acid

54
Q

why are red muscles more red when it is used for more persistent exercise

A

more myoglobin and therefore more red

55
Q

muscles stained light (negative) by ATPase stain

A

type I muscle fibres

56
Q

muscles stained dark (positive) by ATPase stain

A

type II muscle fibres

57
Q

distribution of type I and type II muscle fibres in an average person

A

Approximately 50:50 type I:type II muscle fibres, random distribution, similar diameter

58
Q

type I muscle fibres

A

Slow contraction (50-110ms twitch time) – `slow’ myosin isoform

Small force (<20g tetanic tension) - `few’ muscle fibres/MU

Resistant to fatigue (oxidative metabolism, many mitochondria, good blood supply)

Recruited first during contraction

59
Q

Type IIA muscle fibres

A

Fast Contraction time (25-45ms) “fast” myosin isoform

Intermediate force (20-60g tetanic tension) – intermediate number of muscle fibres/MU

Resistant to fatigue (oxidative metabolism)

Intermediate recruitment order

60
Q

type IIB muscle fibres

A

Very fast contraction (<10ms)  “Fast” myosin isoform

High force(50-150g)  many, large muscle fibres / MU

Fatigue easily (anaerobic metabolism, glycogen store, few mitochondria)

Recruited last during contraction

year 2 sem 2 motor systems (1 decks)

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