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Y2 MSK > Muscle physiology > Flashcards

Muscle physiology Flashcards

1
Q

what are physiological functions of skeletal muscles

A
  • maintain posture
  • purposeful movement
  • respiratory movement
  • heat production
  • whole body metabolism
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2
Q

what type of muscle is skeletal

A

striated - alternating dark bands (caused by myosin thick filaments) and light bands ( caused by actin thin filaments)

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3
Q

what innervates skeletal muscle

A

somatic nervous system and are subject to voluntary control

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4
Q

what initiates and propagates contraction in skeletal muscle

A

Neurogenic initiation of contraction
Motor units
Neuromuscular junction present
No gap junctions

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5
Q

what is the gradation of contraction by skeletal muscle

A
  1. motor unit recruitment

2. summation of contractions

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6
Q

what is the neurotransmitter between the nerve and skeletal muscle

A

acetylcholine

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7
Q

what is a motor unit

A

single alpha motor neurone and all the skeletal muscle fibres it innervates

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8
Q

what structures does a muscle fibre contain

A

myofibril and sarcomere that contain myosin and actin

myosin (thick filament) and actin (thin filament)

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9
Q

what causes the light appliance in myofibrils and fibers and what causes the dark appearance

A

light - actin

dark - myosin

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10
Q

what are sarcomeres

A

actin and myosin are arranged into sarcomeres - these are the functional units of muscle

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11
Q

what is the functional unit of any organ

A

smallest component capable of performing all the functions of that organ

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12
Q

what is the functional unit of the skeletal muscle

A

sarcomere

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13
Q

what is the function of the Z line

A

connect the thin filaments of 2 adding sarcomeres

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14
Q

what is A band

A

made up of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments

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15
Q

what is the H zone

A

lighter area within middle of A band where the thin filaments dont reach

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16
Q

what is the M line

A

extends vertically down the middle of A band with the centre of H zone

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17
Q

what is the I band

A

consists of remaining portion of thin filaments that do not project in A band

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18
Q

how is muscle tension produced

A

by sliding actin filament of myosin filament = sliding filament theory

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19
Q

when is Ca2+ released from the lateral sacs in the SR

A

when the surface action potential spreads down the transverse (T)-tubules

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20
Q

what is the process of muscle contraction

A
  1. ACh released by axon of motor neurone crosses clear and bind to receptors on motor end plate
  2. Action potential generated in response to binding of ACh and subsequent end-plate potential is propagated across surface membrane and down T tubules of muscle cell
  3. Action potential in T tubules triggers Ca2+ release from the sarcoplasmic reticulum
  4. Ca2+ released from lateral sacs, bind to troponin on actin filaments and leads to tropomyosin being physically moved alongside to uncover cross bridge binding sites on actin
  5. myosin cross bridges attach to actin and bend, pulling actin filaments towards centre of sarcomere; powered bu energy provided by ATP
  6. Ca2+ actively taken up by SR when there is no longer an action potential
  7. with Ca2+ no longer bound to troponin, tropomyosin slips back to its blocking position over binding sites on actin, contraction ends, actin passively slide snack to its original resting position
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21
Q

what is Ca2+ needed for in regards to skeletal muscle

A
  • switch on cross bridge formation
  • Ca2+ is the link between excitation and contraction
  • Ca2+ is entirely derived from SR in skeletal muscle
22
Q

what is ATP needed for when it comes to skeletal muscle

A

During muscle contraction
- to power cross bridges

During relaxation

  • to release cross bridges
  • to pump Ca2+ back into the SR
23
Q

what does the graduation of skeletal muscle tension depend on

A
  1. number of muscle fibres contracting within the muscle

2. tension developed by each contracting muscle fibre

24
Q

what is produced when skeletal muscle is stimulated once

A

twitch

25
Q

how does the tension of skeletal muscle increase

A

increase frequency of stimulation

26
Q

when can maximal sustained contraction be achieved

A

when the muscle is at its optimal length (lo) before the onset of contraction

27
Q

what are the 2 types of skeletal muscle contraction

A
  1. Isotonic contraction: used for body movements and moving object. Muscle tension remains constant as the muscle length changes
  2. Isometric contraction: used for supporting objects in fixed positions and for maintaining body posture. Muscle tension develops at constant muscle length
28
Q

how is muscle tension transmitted to the bone

A

via elastic components of the muscle

29
Q

does the velocity of muscle shortening increase or decrease as the load increases

A

decreases

30
Q

what are the main differences between different types of skeletal muscle fibres

A
  • the enzymatic pathway for ATP synthesis
  • the resistance to fatigue - muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue
  • the activity of myosin ATPase - this determines the speed at which energy is made available for cross bridge cycling ie the speed of contraction
31
Q

what are the 3 metabolic pathways that supply ATP in muscle fibres

A
  • transfer of high energy phosphate from creatine phosphate to ADP - immediate source of ATP
  • oxidative phosporylation: main source when O2 is present
  • glycolysis: main source when O2 is not present
32
Q

what are slow oxidative type 1 fibres

A
  • slow twitch fibres

- prolonged relatively low work aerobic activities ie maintain posture

33
Q

what are fast oxidative type IIa fibres

A
  • immediate twitch fibres

- use both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities eg jogging

34
Q

what are fast glycolytic type IIx fibres

A
  • fast twitch fibers
  • use anaerobic metabolism
  • mainly used for short term high intensity activities eg jumping
35
Q

what is the stretch reflex

A

serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle

36
Q

what does activation of the stretch reflex cause

A

contraction of stretched muscle

37
Q

what coordinates the stretch reflex

A

simultaneous relaxation of antagonist muscle

38
Q

when can the stretch reflex be elicited

A

by tapping the muscle tendon with a rubber hammer which rapidly stretches the muscle resulting in contraction

39
Q

what spinal segment and peripheral nerve are in relation to the knee jerk

A

L3,L4

femoral nerve

40
Q

what spinal segment and peripheral nerve are in relation to the ankle jerk

A

S1,S2

tibial nerve

41
Q

what spinal segment and peripheral nerve are in relation to the biceps jerk

A

C5,C6

musculocutaneous nerve

42
Q

what spinal segment and peripheral nerve are in relation to the brachioradialis

A

C5,C6

radial nerve

43
Q

what spinal segment and peripheral nerve are in relation to the triceps jerk

A

C6,C7

radial nerve

44
Q

what are muscle spindles

A
  • sensory receptors for stretch reflex
  • collection of specialised muscle fibres
  • intramural fibres
  • found within the belly of muscles and run parallel to ordinary muscle fibres (extramural fibres)
  • muscle spindles have sensory nerve endings known as annulospiral fibres
45
Q

what are the efferent neurones that supply to muscle spindles are called

A

gamma (g) motor neurones

46
Q

what may impair skeletal muscle function

A
  • intrinsic disease of muscle
  • disease of NMJ
  • disease of lower motor neurones which supply the muscle
  • disruption of input to motor nerves (eg upper motor neurone disease)
47
Q

what are features of congenital myopathies

A

characteristic microscopic changes leading to reduced contractile ability of muscles

chronic degeneration of contractile elements - muscular dystrophy

abnormalities in muscle membrane ion channels eg myotonia

48
Q

what are types of acquired myopathies

A
  • inflammatory myopathies eg polymyositis
  • non inflammatory myopathies eg fibromyalgia
  • endocrine myopathies eg cushings syndrome
  • toxic myopathies ef alhohol
49
Q

what are symptoms of muscle disease

A
  • muscle weakness/tiredness
  • delayed relaxation after voluntary contraction (myotonia)
  • muscle pain (myalgia)
  • muscle stiffness
50
Q

what are useful investigations in neuromuscular disease

A
  • electromyography
  • nerve conduction studies
  • muscle enzymes
  • inflammatory markers
  • muscle biopsy

Y2 MSK (13 decks)

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