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Biological Sciences > Structure and Physiology of muscle > Flashcards

Structure and Physiology of muscle Flashcards

1
Q

What is similarity between nerve cells and muscle cells

A

Share many properties

e.g. muscle cells also conduct action potentials

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2
Q

What is the target of many nerve fibres

A

Muscles

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3
Q

what are skeletal muscle?

A 
. Attached to a skeleton
. Voluntary ( somatic )
. Striated
. Movement 
. Most common
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4
Q

what are cardiac muscles?

A

. Muscles of the heart
. Striated
. Voluntary ( somatic )
. Forceful and quick

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5
Q

what are smooth muscles?

A

. Found in hollow organs e.g. blood vessel , digestive tract, inside eye, respiratory system
. Non -striated
. Involuntary

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6
Q

What are muscle cells known as and why

A

Fibres - individual cells

They are elongated in one direction

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7
Q

Measurements of muscle cells

A

Up to 3-4cm long

Diameter of 10-150 micrometres

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8
Q

What are fibres

A

Individual cells - muscle cells - long and thin cell

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9
Q

What is a muscle made up of

A

1000s of such muscle fibres ( several fascicles )

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10
Q

What are fibres grouped into

A

Fascicles

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11
Q

What are fascicles surrounded by

A

Perimysium connective tissue

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12
Q

What make up the whole muscle cell

A

Several fascicles

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13
Q

What surrounds the whole muscle

A

Epimysium connective tissue

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14
Q

What is each fascicle made up of

A

Several cells

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15
Q

What separates muscle fibres

A

Endomysium

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16
Q

How do skeletal muscle attach to the bone?

A

Skeletal muscle is attached to bone by tendons

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17
Q

What is the outer membrane of a muscle cell called

A

Sarcolemma

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18
Q

What does each skeletal muscle fibre contain and why

A

Several nuclei

Because muscle fibres are long and thin so many more

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19
Q

Where is nuclei of skeletal muscle located and why

A

Periphery ( edge ) of cell

Because most of cell is made of striations

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20
Q

What is cell filled with and what is it like

A

Sarcoplasm

Like cytoplasm - contains usual organelles especially mitochondria

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21
Q

What does skeletal muscle appearance depend on

A

Plane of section - how you’re looking at it - look different when on different sides

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22
Q

How does skeletal muscle appear in longitudinal section?

A

Long and thin

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23
Q

How does skeletal muscle appear in transverse section?

A

Round - circles

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24
Q

What do skeletal muscle contain ?

A

Nerve tissue

Blood vessels

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25
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 and take away waste products( needs blood supply )

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26
Q

What is the most prominent feature of skeletal muscle fibre?

A

Striations - light and dark stripes

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27
Q

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

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28
Q

What are myofibrils

A

2 rod like structures inside muscle cell - made of 2 proteins ( myofilaments ) - actin and myosin

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29
Q

What is each myofibril made up of

A

Series of sarcomeres composed of the myofilaments actin and myosin

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30
Q

What is a sarcomere

A

Distance between two z lines ( connective tissue )

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31
Q

What are actin filaments attached to

A

Z lines

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32
Q

What are between the actin filaments

A

Myosin filaments

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33
Q

Actin

A

Thin
Light
I band
Attached to z line

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34
Q

Myosin

A

Thick
Dark
A band

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35
Q

What is the A band

A

Area of overlapping actin and myosin

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36
Q

What is the region of only myosin - no overlap

A

H zone

middle of A band

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37
Q

What makes the sarcromere

A

Actin and myosin overlap - arranged in a regular way

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38
Q

What are Z lines

A

Disks of connective tissue

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39
Q

What is each myofibril made up of

A

Series of end to end sarcomeres

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40
Q

What is muscle fibre surrounded by and what is inside

A

Plasma membrane

Several myofibrils

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41
Q

What is small bundle of myofibrils surrounded by?

A

Sarcoplasmic reticulum

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42
Q

What is the system of tubes running right angles to surface of fibre

A

Transverse tubular system - continuation of sarcolemma ( membrane )

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43
Q

Where does the transverse tubular system end ?

A

Along the terminal cisternae of the SR , on each sarcomere forming a triad

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44
Q

What is Sarcoplasmic reticulum

A

Modified ER - network/series of hollow tubes enclosed in a membrane - act as calcium store

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45
Q

What are the 2 series of tubes surrounding myofibrils

A

Transverse tubules

Sarcoplasmic reticulum

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46
Q

What happens to membrane of sarcolemma

A

Continues down into muscle cell forming transverse tubular system

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47
Q

Summary of skeletal muscle

A

. Muscles are made of bundles 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

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48
Q

What do the lumps on myosin represent?

A

Cross bridges

Myosin sticks out - attaches to actin

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49
Q

What do cross bridges enable?

A

Attachment of myosin to actin

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50
Q

Structure of myosin molecule

A

. Elongated molecules composed of….
- a heavy tail ( dense protein)
- 2 heads ( light protein) ( less dense )
.The junction of the heads and tail is known as a hinge
.The heads form part of cross bridge that attach to actin

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51
Q

What is the hinge region of myosin

A

Where head and tail join

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52
Q

What is a thick myosin filament made of?

A

Many individual myosin molecules

Many mysoin molecules get together to from one of dark myosin filaments

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53
Q

How are cross bridges of individual myosin molecules arranged?

A

Point in opposite directions at the 2 ends of a thick myosin filament

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54
Q

Myosin heads

A

Point in different directions in the 2 halves of the myosin filaments
Stick out - forming crossbridges which attach to actin

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55
Q

What is structure of actin filaments

A

3 components…..
. Helix of two strands of globular actin with active sites
.Thin rod like tropomyosin molecule in a helix
. troponin at regular intervals along tropomyosin

56
Q

What is tropomyosin

A

Lie in the groove formed by twisted actin ( cover active sites in resting state )
Rod like, thin

57
Q

What is troponin

A

Complex of three proteins one which has high affinity for calcium ions
Attach to tropomyosin

58
Q

What attaches to active site of actin monomer

A

Myosin crossbridge

59
Q

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

A

Active site is covered by tropomyosin

60
Q

What happened in 1954

A
  • Worked out how muscle contracted

- Invented electron microscope - looked at skeletal muscle under microscope

61
Q

What assumption was made prior to the EM and why

A

Filaments folded in some undefined way
Arrangement of skeletal muscle into sarcomeres was not known or contraction mechanism
Assumed that actin and myosin is randomly distributed in muscle fibre

62
Q

What happens during resting muscle

A

Cross bridge can’t attach to actin because tropomyosin is blocking active site ( attached itself ) so myosin can’t attach to myosin
Troponin is bound to tropomyosin

63
Q

What happens during muscle contraction

A

EM showed
. width of A band( actin + myosin overlapping ) is unchanged
. width of I band ( actin only ) decreased
Actin and myosin slide over each other

64
Q

Why does width of I band decrease

A

Due to sliding the actin and myosin over each other

65
Q

What eventually happens to I band

A

Eventually disappears - only happens if actin and myosin slid over each other

66
Q

What is sliding filament theory

A

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

67
Q

What are the early stages of excitation-contraction coupling?

A
  1. action potential in motor neuron - gets to synapse
  2. synaptic events lead to ACH release
  3. binding of ACH to post synaptic receptors = opens Na+ channels
  4. Small depolarisation of muscle fibre (epp)
  5. surface propagation of action potential
68
Q

Where does action potential travel

A

Along surface of muscle cell on sarcolemma

69
Q

What are the first 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
70
Q

What is inside of muscle cell bathed with

A

Calcium

71
Q

Structure of t- tubule system

A
  • Ends close to SR

- Straight down it to individual myofibrils - indentation of surface of muscle cell

72
Q

What happens when action potential goes right down into centre of muscle cell

A

Opens Ca ion channels in SR = Ca out of SR into muscle

73
Q

What are the second middle stages of excitation-contraction coupling?

A
  1. calcium released from the sr binds onto troponin - part of troponin has high affinity for Ca
  2. conformational change in troponin = changes shape
  3. pulls tropomyosin from actin
  4. uncovers active site on actin
  5. myosin cross cross bridges attach
74
Q

What is the effect of calcium binding to troponin?

A

Uncovers active site on actin , allowing myosin to form cross bridges as it attaches
Troponin changes shape and pulls tropomyosin away from active site = actin and myosin join to each other

75
Q

What are the later stages of excitation-contraction coupling?

A
  1. Myosin cross bridges attaches to actin
  2. myosin head tilts - hinge bends
  3. myosin cross bridge detached
  4. cross bridge attaches to next active site
  5. actin is pulled toward centre of sarcomere and sarcomere shortens
76
Q

What happens at the end of muscle contraction?

A

Calcium is pumped back into the SR and muscle relaxes

77
Q

What happens when muscle contracts - sliding filament theory of muscle contraction

A

Actin and myosin slide over each other
Sacromere shortens when it tilts
Myosin crossbridge attaches to actin - tilts - hinge bends - cross bridge attaches to next active site

78
Q

What is each tilt

A

Power stroke

79
Q

Where does energy come from in muscle contraction

A

ATP

80
Q

Summary of excitation - contraction coupling

A
  • Action potential along surface of muscle cell in motor neuron
  • Causes vesicles containing AcH to go to pre - synaptic neuron and bind
  • Releases AcH and diffuses to post - synaptic neuron
  • Opens Na+ channels - small depolarisation - EPP
  • Action potential down transverse tubules in tubular system- reaches SR
  • Opens Ca channels - Ca moves out - binds to tropomyosin - changes shape - pulls tropomyosin away from active site.
81
Q

What is slow muscle?

A
  • Active for long time(e.g maintain posture)
  • Uses lots of energy therefore have mitochondria
  • Myoglobin ( bind to O2) for oxygen storage
  • Red colour
  • Big muscles
82
Q

What is fast muscle?

A
  • Breifly active - shorts amount of time
  • Large sarcoplasmic reticulum for rapid release and uptake of calcium
  • Little myoglobin - white colour
  • Often small muscles
83
Q

Example of fast muscle

A

Extraocular muscles ( inferior rectus ) - fast for rapid eye movements called SACCADE

84
Q

Examples of slow muscle

A

Gastrocnemius

Soleus

85
Q

What is Gastrocnemius

A

Muscle at back of lower leg = lift leg up and walking

86
Q

Example of fish for slow and fast muscles

A

Different fish have different colours
Tuna - slow muscles - spends all its time cruising through ocean - can of tuna is red because lots of myoglobin
- Dover sole fish - live on ocean floor and ocassionally go up and back on ocean floor, don’t swim for long times = quick = white - fast muscle = lighter in colour

87
Q

Why do cows have red meat

A

Cows came from animals that lived in planes and had to always be on the move,running away = need energy

88
Q

What are the 2 ways you can control the size of muscle contraction ( when and how much we contract it)

A

Spatial

temporal

89
Q

Define spatial summation

A

Motor unit recruitment

Varying the number of active motor units/fibres = vary muscle contraction size

90
Q

What is a motor unit

A

A single neuron and all the muscle fibres it innervates

91
Q

What is muscle made up of

A

Hundreds of different motor units

92
Q

When do we get a big contraction ( more cells shortening )

A

When LOTS of motor units active

93
Q

When do we get a small contraction

A

ONE/FEW motor units active - only few muscle cells shorten and soft contraction

94
Q

What is motor unit recruitment

A

Each motor neuron supplies a few muscle fibres

95
Q

Why do different muscles contract at different rates

A

It’s to do with their….

  • Size
  • Whether they have myoglobin or not
  • How deep their SR is
96
Q

What does the degree of fine control of a muscle depend on

A

Size of motor units
Fine control of muscles - dictate whether small or big contraction
Muscles that require a fine degree of control have numerous small motor units

97
Q

What would the smallest motor unit be

A

ONE motor neuron contacting a SINGLE muscle fibre

98
Q

Link between number of motor units and degrees of contraction

A

The number of motor units is the same as the number of different degrees of contract e.g. 10 motor units = 10 different degrees of contraction

99
Q

What does muscle of larynx in sounds produce

A

Small motor units - 2/3 muscle fibres

100
Q

How many muscle units do eye muscles have

A

3 - 10

101
Q

What do small delicate muscles with fine degree of control contain

A

Motor units containing only a few muscle fibres

102
Q

How many muscle fibres in larger muscles

A

Units of about 150 - 500 muscle fibres

E.g. those in movement - gastoral

103
Q

What is temporal summation

A

Varying the frequency of stimuli - how frequently you stimulate muscle

104
Q

What is the response of a muscle to a single stimulus?

A

A muscle twitch

105
Q

What are the 3 phases?

A
  • Latent period: interval between stimulus and beginning of contraction - before muscle contracts
  • Contraction period- when the muscle is shortening
  • Relaxation Period- during which tension declines
106
Q

How long is average muscle twitch

A

100ms

107
Q

What does length of contraction period depend on

A

Whether its fast or slow muscle

108
Q

Explain the steps of stimulating muscle cell twice with different intervals between stimulation

A
  • When the time between stimuli is far apart, so observe seperate twitches
  • When the time between stimuli is decreased, the 2nd contraction starts before the previous one is over- the amplitude of contraction is bigger
  • the largest contraction- when the 2nd contraction begins before the muscle has relaxed from previous stimulus
109
Q

When is the electrical event leading to muscle contraction over and what can this allow

A

Before muscle twitch begins
Stimulate muscle again before contraction caused by first stimulus is over because action potential that triggered contraction is so brief (1ms or 2)

110
Q

How does stimuli closeness affect contraction size

A

The closer the stimuli are together, the bigger the contraction

111
Q

What happens if you stimulate muscle cell twice but LONG interval between stimuli

A

individual small contractions

contracts then relaxes

112
Q

What happens if you stimulate muscle cell twice but stimuli CLOSER together

A

Before 1st contraction fully relaxes, there’s another contraction
2nd contraction starts before 1st one is finished so final contraction is bigger

113
Q

What is a tetanus?

A

A large smooth contraction in response to a series of stimuli - stimulate muscle so frequently

114
Q

What are the 2 types of contraction?

A

Isometric- muscle doesnt shorten when contracts- same length

Isotonic- muscle shorten

115
Q

What are most contraction and example

A

Mixture of both muscle contractions

e.g. walking - lift leg isotonically but hit ground - tens muscle isometrically

116
Q

What is the structure of cardiac muscle?

A
  • Striated - therefore actin and myosin are arraned into sarcomeres
  • Fibres branched
  • Single central nucleus per fibre
  • Intercalated discs act as gap junction ( electrical synapses between adjacent muscle cells )
117
Q

Role of intercalated discs and branching

A

Rapid conduction of action potentials throughout heart and in many directions

118
Q

What is the structure of smooth muscle?

A
  • Composed of small spindle shaped cells (20-500 x 5 um)
  • No striations
  • One nucleus in centre
119
Q

What are ocular structures which have smooth muscle?

A

Iris ( sphincter and dilator )

Ciliary body

120
Q

What does no striations in smooth muscle mean

A

Actin and myosin cannot be arranged in sarcomeres; as there is little of them they are irregularly arranged
Can’t see light and dark bands

121
Q

What is the structure of smooth muscle fibre?

A
  • Not arranged in sarcomere
  • Less actin and myosin than skeletal
    ratio is 16:1 actin:myosin in smooth muscle however in skeletal it is (2:1)
    -No z- lines ( actin not attached to z lines ) - actin and myosin are then connected to dense bodies or to the cell membrane
    -Poorly developed SR- slow calcium released and pump very slow compared in the SR of skeletal muscle
    -therefore contraction is slower and less powerful
122
Q

Why is it good that smooth muscle contraction is slow and feeble?

A
  • It uses less energy (which is good as smooth muscle is continuously active) - energy efficient
  • Ones does not want to generate a lot of force
123
Q

Why smooth muscle in gut

A
  • In the gut there are contractions every 20s to mix food
    so you need a lot of energy
  • Weaker and slower - don’t want powerful contractions of gut
124
Q

What is skeletal muscle not good for

A

Digesting food in gut and altering blood vessel diameter

don’t want forceful

125
Q

What happens if the muscle is too stretched in skeletal muscle and why

A

The sarcomere will not contract
If you stretch muscle sooner or later actin and myosin not going to overlap anymore - not form crossbridge - muscle cant contract

126
Q

What does sarcomere arrangement of skeletal muscle ensure

A

Powerful and rapid contractions - due to actin and myosin sliding over each other

127
Q

What happens if the muscle is too stretched in smooth muscle?

A

Actin and myosin irregularly arranged = there is always enough overlap of actin and myosin to generate tension
Actin and myosin always overlapping = still contract een when smooth muscle very stretched i.e. bladder FULL

128
Q

Examples of smooth muscle stretching

A

Walls of bladder - grown by about 2/3 times normal size when its full after drinking and need to pee
Womb - Give birth - stretched by 8 times its normal size

129
Q

What is the similarity between smooth muscle and skeletal muscle contraction?

A

actin and myosin both slide over each other
calcium is involved
ATP is required

130
Q

What are the 2 ways smooth muscle can be made to contract?

A
  1. Depolarisation of the cell membrane

2. Chemically ( main way ) - release things by body that cause smooth muscle contraction

131
Q

How does depolarisation of cell membrane cause smooth muscle contraction

A
  • Smooth muscle innervated from ANS ( sympathetic and parasympathetic ) - innervation can be excitatory/stimulate or inhibitory
  • Smooth muscle/nerve junctions - transmitter releases from varicosities
132
Q

What are the two ways chemically contract smooth muscle

A
  • Local tissue factors

- Hormones

133
Q

How does local tissue factor contract smooth muscle

A
  • Local build up of CO2 acts directly on smooth muscle - blood vessels dilate
  • Low O2 or High CO2 levels act on vascular smooth muscle to cause vasodilation ( more O2 when dilation of blood vessel = contracts )
134
Q

How do hormones contract smooth muscle

A

E.g. oxytocin stimulating uterine contraction during childbirth

135
Q

What are two types of smooth muscle

A
  • Single unit ( visceral ) - individual fibres joined by gap junctions - large sheet acts as a unit - often spontaneously active
  • Multi unit - muscle fibres independent of one another - rich nerve supply - contraction graded e.g. large arteries

Biological Sciences (27 decks)

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