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Muscles Flashcards

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1
Q

how many skeletal muscles’ do humans have

A

~660 skeletal muscles

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2
Q

muscle mass in adults, for female and male

A

females 13-30 kg;
males 18-40 kg

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3
Q

what is the average amount and length and diameter of muscle fibres

A

~100,000 fibres

D: 10 -100 micrometre
L: 1-500 mm (Harris et al 2005)

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4
Q

how does muscle determine identity

A

through voice

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5
Q

what is the skeletal muscle a source of and what process does it help

A

source of amino acids, homeostasis…

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6
Q

different muscle fibres shape: pectoralis major

A

convergent

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7
Q

different muscle fibres shape: orbicularis oris

A

circular

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8
Q

different muscle fibres shape: deltoid

A

multipennate

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9
Q

different muscle fibres shape: sartorius

A

parallel

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10
Q

different muscle fibres shape: biceps brachii

A

fusiform

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11
Q

different muscle fibres shape: extensor digitorum longus

A

unipennate

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12
Q

different muscle fibres shape: rectus femoris

A

bipennate

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13
Q

role on connective tissue

A

maintains integrity of
the muscle and is important in
transmission of force

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14
Q

roles of tendons

A

Muscles connect to bones by tendons

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15
Q

role of epimysium

A

Muscles are enclosed by epimysium
(connective tissue)

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16
Q

what is a muscle fascicles and perimysium

A

Groups of fibres form muscle fascicles
surrounded by perimysium

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17
Q

what is a endomysium

A

Each muscle fibre is enclosed by
endomysium which consists of extracellular matrix (made of collagen)

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18
Q

how do Structural intracellular proteins of muscle
fibre link to endomysium and why are they important

A

Structural intracellular proteins of muscle
fibre link to the endomysium via focal
adhesions (important for force
transmission)

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19
Q

what are sarcolemma

A

Muscle fibres (10-100
μm) are covered by
sarcolemma (≈7.5 nm
thick

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20
Q

what are t tubules

A

T-tubules are invaginations
of sarcolemma

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21
Q

what is Sarcoplasmic reticulum

A

is a network of tubes
surrounding myofibrils

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22
Q

what is Sarcoplasm

A

is fluid
enclosed within the fibre

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23
Q

what are myofibrils

A

( ~1 μm) are
packed bundles of
myofilaments running along
the fibre

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24
Q

name 2 types of myofilaments

A

thick (darker) and thin (lighter) filaments

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25
Q

what do thick filaments consist of

A

C protein, H
protein, M protein, myomesin

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26
Q

what do thin filaments consist of

A

actin, tropomyosin and
troponin complex (TN-T,
TN-I, TN-C

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27
Q

how are myofilaments arranged within myofibrils

A

a series of
repeating units, the
sarcomere, which is basic
contractile unit of muscle

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28
Q

what happens in the sarcomere unit

A

One end of thin filaments projects into the sarcomere while another connects the Z line
* Thin filaments contain troponin and tropomyosin proteins that participate in blocking
and unblocking of thin filaments. Because of this function troponin and tropomyosin are
referred to as regulatory proteins.
* Thick filaments (myosin) are in the centre of sarcomere and overlap thin filaments from
both sides

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29
Q

what 6 proteins is the myosin molecule compose of

A
  • two myosin heavy chains (MyHC)
  • one essential myosin light chain (MLC) on each MyHC
  • one regulatory myosin light chain (MLC) on each MyHC
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30
Q

what is MyHC role

A

MyHC contains ATP- and actin-binding sites (essential for muscle contraction)

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31
Q

what is the tole of titin

A

acts as a molecular spring permitting return of
stretched sarcomeres to “optimal” length

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32
Q

3 different contraction types

A

concentric, isometric, eccentric

33
Q

what happens during concentric contractions
(also on a force-velocity relationship )

A

muscle
shortens and
generates force
(least amount of force generated, longest velocity)

34
Q

what happens during isometric contractions
(also on a force-velocity relationship )

A

muscle
generates force,
length remains
constant (middle for both velocity and force)

35
Q

what happens during eccentric contractions
(also on a force-velocity relationship )

A

muscle
generates force while
lengthening (most amount of force generated, shorter velocity)

36
Q

how long is the delay between action potential and initiation of contraction

A

~20 ms delay

37
Q

how long does it take until the peak force to develop

A

30ms

38
Q

example of sarcomeres in
series add up

A

-10-cm fibre contains ~4,000,000
sarcomeres
– Each sarcomere shortening by 1 μm
shortens the fibre to 6 cm

39
Q

describe the steps of the cross bridge cycle step 1

A
  1. ATP hydrolysis
    increases affinity of
    myosin for actin
40
Q

describe the steps of the cross bridge cycle step 2

A
  1. Following Ca++ release from SR myosin binds actin
    Dissociation of Pi results in
    5-10 nm displacement
    (power stroke) followed
    by ~2pN force (strong
    binding)
    ADP dissociation ends the strong binding phase yet cross-bridge remains
    attached
41
Q

describe the steps of the cross bridge cycle step 3

A
  1. ATP binds to myosin
    decreasing its affinity
    for actin
42
Q

describe the steps of the cross bridge cycle step 4

A
  1. Myosin dissociates
    from actin, ATP is
    hydrolysed
43
Q

what part of the cycle contributes to concentric contractions

A

“power stroke”
cross-bridges, smaller pool of contribution

44
Q

what part of the cycle contributes to eccentric contractions

A

all associated cross- bridges contribute
- larger pool of contributions

45
Q

what is a hallmark of msucle fatigue

A

Slowing relaxation is one of the
hallmarks of muscle fatigue
following repeated contractions

46
Q

what is the cause of slowing relaxation of muscles

A

a decrease in concentration ATP
leading to impaired dissociation of
these metabolites from the myosin

47
Q

describe Force-velocity relationship

A

speed of contraction decreases
with increasing resistance

48
Q

state all the connective tissue

A

endomysium, perimysium, epimysium, tendons

49
Q

what is the role of connective tissue

A

Muscle contractile force is transmitted through connective
tissue

50
Q

role of one alpha motor neuron

A

innervates a group of
muscle fibres
- divides into terminals that form neuromuscular junctions on muscle fibres

51
Q

what do nerve fibres do

A

(axons) conduct
action potentials (APs) at a fast
rate (~40-80 m/s)

52
Q

where do terminals of motor nerves form from

A

neuromuscular junctions
(also called motor end plates)

53
Q

what is the key functions of neuromuscular junctions

A

is transmission of activation
from nerve to muscle fibres

54
Q

what does the arrival of AP do at a nerve terminal : step 1

A

triggers release of acetylcholine (Ach)
into the synaptic cleft

55
Q

what does the arrival of AP do at a nerve terminal : step 2

A
  1. Ach is made from acetyl-CoA released
    from mitochondria and choline in nerve
    terminals
56
Q

what does the arrival of AP do at a nerve terminal : step 3

A
  1. Released Ach binds to receptors on the
    muscle fibre and triggers influx of Na+
    followed by generation of action potential
    (AP) in muscle fibres
57
Q

what does the arrival of AP do at a nerve terminal : step 4

A
  1. Ach acts for a short time since it is
    degraded by Ach esterase enzyme
    * Choline is taken up by nerve terminals
    for re-synthesis of Ach
58
Q

what happens when there is low levels of Ach

A

Myasthenia gravis

Eyelids are dropped due to muscle
weakness
* Injection of a drug which blocks Ach
esterase helps to regain muscle
strength: eyelids open

59
Q

what causes Myasthenia gravis and what is used in operations to help

A

autoimmune disease due to low levels of Ach or Ach receptors
Drugs blocking neuromuscular transmission are muscle relaxants used during
operations

60
Q

what is Neuromuscular electrical stimulation (NMES) used for

A

functional and therapeutic applications in subjects
with spinal cord injury or stroke

61
Q

what does contraction force depend on and what happens to the force-freq relationship

A

frequency of action
potentials

change in
frequency of AP results in
proportional change of
force

62
Q

what freq does the muscle fibres activate

A

at 5-100 Hz
frequencies in voluntary
contractions

63
Q

what is a tetanic contraction and how is it generated

A

Continuous stimulation at
100 Hz causes a sustained
increase in intracellular
Ca2+ - [Ca2+]I and generates
tetanic contractions
(smooth contractions)

64
Q

what does a decrease in [Ca2+] mean

A

results in lower contractile force – one of the mechanisms of muscle fatigue

65
Q

how are muscle fibres divided into

A

subdivided in
two main types: type
I and type II
–

66
Q

how is type II muscle fibres divided

A

the type II is further
divided into IIA & IIX
– rodent muscle also
contain large numbers of type IIB fibres

67
Q

what is not a homogenous tissue

A

skeletal muscles

68
Q

what are the 2 main factors separating the fibre types

A

1 – isoform of expressed myosin
2 – metabolic profile (mitochondrial content, capacity of glycolytic enzymes)

69
Q

how does being encoded by different genes affect myosin isoforms

A

Different functional properties:
ATPase activity: Type I < Type IIA < Type IIX
Function: fibre shortening velocity Type I < Type IIA < Type IIX

70
Q

what the difference between type I and II muscles fibres

A

type 1 has more mitochondria
less glycolytic enzymes
…

71
Q

what the difference between type I and IIA/IIX muscles fibres

A

mitochondria
type I >IIA >IIX
glycolytic enzymes
type I < IIA < IIX

72
Q

functional role of fibre types

A

Muscle composed of different fibre types differ in contractile properties

Slower contraction and relaxation in type I fibre dominated muscle

73
Q

what determines the speed of AP

A

how quickly the calcium can go from sarcoplasmic reticulum out of sarcoplasm

74
Q

how are MyHcs encoded in mammals and in humans

A

MyHCs are encoded by the same set of homologous genes
* However, not all MyHCs are expressed in human
muscles
No type 2B MyHC is expressed in human locomotory muscles

75
Q

what are the Factors affecting proportion of fibre types

A

genetic factors, adaptation to physical activity or lack of it

76
Q

on average how much muscle fibres does vastus lateralis consists of

A

~50% of type I fibres
(but there is a broad range of variation ~20% to >80% of type I fibres)

77
Q

what are the consequences of variation of fibre type composition

A

Prevalence of certain fibre type favours some athletic activities
increasing proportion of type II fibres is associated with prevalence to weight gain and cardiovascular risk

78
Q

which muscle fibres favours endurance events and which for speed/power events

A

type I – endurance events,
type II – speed and power events

79
Q
A

sports sciencee (8 decks)

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