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Biology > structure and physiology of muscle > Flashcards

structure and physiology of muscle Flashcards

1
Q

what is the target of many nerve fibres?

A

the target of many nerve fibres is muscle

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2
Q

what do motor nerves innervate?

A

motor nerves innervate muscle cells

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3
Q

what properties do muscle cells share with nerve cells?

A

conduction of action potential

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4
Q

what are skeletal muscle?

A

. they are attached to a skeleton
. they are voluntary ( somatic )
. they are striated

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5
Q

what are cardiac muscles?

A

. muscles of the heart
. striated
. involuntary ( autonomic )

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6
Q

what are smooth muscles?

A

. found in hollow organs e.g. blood vessel , digestive tract
. non -striated
. involuntary ( autonomic )

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7
Q

what are muscle cells know as?

A

muscle cells are known as fibres as they are elongated in one direction

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8
Q

what is the size of muscle cells?

A

3-4 cm long

10-150 um diameter

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9
Q

what are fibres grouped into?

A

fibres are grouped into fascicles

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10
Q

what surrounds fibres?

A

fibres are surrounded by a connective tissue perimysium

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11
Q

what makes up a whole muscle cell?

A

fascicles make up the whole muscle cell, which is surrounded by the epimysium

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12
Q

how do skeletal muscle attach to the bone?

A

skeletal muscle is attached to bone by tendons

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13
Q

what is the outer membrane of a muscle cell called?

A

the outer membrane of a muscle cell is called sarcolemma

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14
Q

what does each skeletal muscle fibre contain?

A

each skeletal muscle fibre contains several nuclei

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15
Q

where is the nuclei of skeletal muscle fibre located?

A

the nuclei lie at the periphery of the cell

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16
Q

what is the cell filled with?

A

the cell is filled with sarcoplasm which contains all the usual organelles ,. especially mitochondria

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17
Q

how does skeletal muscle appear in longitudinal section?

A

long ,thin cells

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18
Q

how does skeletal muscle appear in transverse section?

A

round

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19
Q

what do skeletal muscle contain ?

A

nerve tissue

blood vessels

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20
Q

why do skeletal muscles contain blood vessels?

A

skeletal muscles are very metabolically active therefore it needs to be supplied with oxygen and nutrients

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21
Q

what is the most prominent feature of skeletal muscle fibre?

A

striations

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22
Q

describe the organisation of a skeletal muscle?

A

. muscle is made up of several fascicles
. each fasicle is made up of several muscle fibres
. every fibre contains several myofibrils - which have a rod like structure

23
Q

what is each myofibril made of ?

A

. each myofibril is made up of series of sarcomeres which contain two proteins actin and myosin

24
Q

what is a sarcomere?

A

sarcomere is the distance between two z lines ( connective tissue )

25
Q

what is actin attached to?

A

. actin filaments are attached to the z lines forming light stripes

26
Q

what is interdigitating between actin filaments?

A

. thicker myosin filaments

27
Q

what is the light area of sarcomere?

A

. I band

this region contains thin actin filaments

28
Q

what is the dark area of sarcomere ?

A

. A band

. the area of overlapping actin and thicker myosin

29
Q

what is the band between A band in the sarcomere?

A

.lighter band which only contains myosin

. H zone

30
Q

what is each myofibril made of?

A

. each myofibril is made up of series of end to end sarcomeres

31
Q

what is each muscle fibre surrounded by?

A

. each muscle fibre is surrounded by a plasma membrane housing several myofibrils

32
Q

what is small bundle of myofibrils surrounded by?

A

. small bundle of myofibrils is surrounded by sacroplasmic reticulum

33
Q

what is sacroplasmic reticulum?

A

. modified ER - network of tubes enclosed in a membrane

34
Q

what is another system running at right angle to the surface of fibre?

A

transverse tubular system

35
Q

what is transverse tubular system?

A

is a continuation of the sarcolemma.

36
Q

where does the transverse tubular system end ?

A

the system ends along the terminal cisternae of the SR , on each sarcomere forming a triad

37
Q

summary of skeletal muscle?

A

. muscles are made of fascicles
.fascicles are made of fibres
. fibres contain myofibril
. myofibril are made of actin and myosin
myofibrils are surrounded by sacroplasmic reticulum
.transverse tubular system is a continuation of the sarcolemma

38
Q

what do the lumps on myosin represent?

A

. lumps on myosin represent cross-bridges

39
Q

what do cross bridges enable?

A

. cross-bridges enable attachement of myosin to actin

40
Q

what is the structure of myosin molecule?

A

. elongated molecules composed of a heavy tail ( dense protein) (2 heavy myosin molecules)
. 2 lighter heads ( light protein)- globular head
.the junction of the heads and tail is known as a hinge
.the heads form part of cross-bridge that attach to actin

41
Q

what is a thick myosin filament made of?

A

. thick myosin filaments is made up of many individual myosin molecules

42
Q

how are cross bridges of individual myosin molecules arranged?

A

. cross bridges point in opposite directions at the 2 ends of a thick myosin filament

43
Q

what is the structure of thin actin filaments?

A

. two strands of globular actin with active sites
.thin rod like tropomyosin molecule in a helix
. troponin at regular intervals along tropomyosin

44
Q

what is troponin?

A

complex of three proteins one which has high affinity for calcium ions

45
Q

why cant cross bridge attach to active site on each actin monomer?

A

. on each actin monomer you have active site
. active site is where myosin croos bridge willwant to attach
. they cant attach because active site is covered by tropomyosin

46
Q

what happens when muscles contract ?

A

EM showed
. width of A band( actin + myosin ) is unchanged
. width of I band ( actin only ) decreased

47
Q

why does width of I band decrease?

A

. the shortening is due to sliding the actin and myosin over each other

48
Q

what is sliding filament theory?

A

I band shortening due to actin and myosin sliding over each other

49
Q

explain the early stages of excitation-contraction coupling?

A
  1. action potential in motor neuron
  2. synaptic events lead to ACH release
  3. binding of ACH to post synaptic receptors
  4. depolarisation of muscle fibre (epp)
  5. surface propagation of action potential
50
Q

explain the early middle stages of excitation-contraction coupling?

A
  1. action potential goes down t-tubule system to reach myofibril
  2. depolarises terminal cisternae of SR
  3. SR releases calcium
51
Q

explain the late middle stages of excitation-contraction coupling?

A
  1. calcium released from the sr binds onto troponin
  2. conformational change in troponin
  3. pulls tropomyosin from actin
  4. uncovers active site on actin
  5. myosin cross cross bridges attach
52
Q

what is the effect of calcium binding to troponin?

A

calcium binding to troponin uncovers active site on actin , allowing myosin to form cross bridges

53
Q

explain the later stage of excitation-contraction coupling?

A
  1. mysoin cross bridges attaches to actin
  2. myosin head tilts
  3. myosin cross bridge detached
  4. cross bridge attaches to next active site
  5. actin is pulled toward centre of sarcomere and sarcomere shortens
54
Q

what happens at the end of muscle contraction?

A

. calcium is pumped back into the sr

Biology (30 decks)

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