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Science for Medicine > Autonomic physiology, Muscles, Reflexes and Sensory Receptors > Flashcards

Autonomic physiology, Muscles, Reflexes and Sensory Receptors Flashcards

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1
Q

Describe the anatomy of the sympathetic branches of the ANS.

A
  1. Short pre-ganglionc fibres (myelinated)

2. Long post-ganglionic fibres (unmyelinated)

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2
Q

At what levels of the spinal cord do the sympathetic nerves originate?

A

T1-12 and L1-5

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3
Q

Where do the sympathetic ganglia lie?

A

From ventral root, close to spinal cord in sympathetic trunk.

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4
Q

Describe the postganglionic cells of the adrenal medulla.

A

No axons, but release A/NA into blood.

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5
Q

In the sympathetic nervous system, what neurotransmitter is released at the synapse between the pre-ganglionic and post-ganglionic fibres?

A

Acetylcholine

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6
Q

In the sympathetic system, what receptors do acetylcholine act on at the synapse between pre and post-ganglionic fibres?

A

Nicotinic receptors

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7
Q

At what spinal level do the parasympathetic nerves arise from?

A

Cranial (I - XII) and sacral (S2-4)

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8
Q

Describe the anatomy of the parasympathetic fibres.

A 
Pre-ganglionic = long (myelinated)
Post-ganglionic = short (non-myelinated)
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9
Q

What neurotransmitter is released at the junction of the pre and post parasympathetic fibres?

A

Acetylcholine

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10
Q

In the parasympathetic nervous system, what neurotransmitter is released at the synapse between the pre-ganglionic and post-ganglionic fibres?

A

Nicotinic receptors

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11
Q

What neurotransmitter is released from the sympathetic postganglionic fibres to the effector organ and what receptor(s) does it bind to?

A

Noradrenaline to alpha or beta adrenergic receptors

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12
Q

What neurotransmitter is released from the parasympathetic postganglionic fibres to the effector organ and what receptor(s) does it bind to?

A

Acetylcholine to muscarinic receptors.

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13
Q

Describe the role of the neurotransmitter at the NMJ.

A

Specialised, bind to inotropic receptors and always excite target.

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14
Q

Describe the role of acetylcholine and noradrenaline at the autonomic synapse.

A

Less-specialised, metabotropic receptors which can excite OR inhibit target.

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15
Q

What are the three branches of the autonomic nervous system?

A
  1. Sympathetic
  2. Parasympathetic
  3. Enteric
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16
Q

Describe the effect of sympathetic innervation on the heart.

A

Increase heart rate and increase strength of contraction (B1 receptors)

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17
Q

Describe the effect of parsympathetic innervation on the heart.

A

Decrease hear rate (muscarinic receptors on pacemaker cells) and little effect on myocytes.

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18
Q

Describe the action of atenolol.

A

B1 antagonist therefore decreases heart rate.

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19
Q

Describe the effect of sympathetic innervation on the lungs.

A

Dilate airways as smooth muscle relaxes (B2 receptors)

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20
Q

Describe the action of salbutamol.

A

B2 agonist therefore dilates airways (NOTE: “Can b2 relaxed”)

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21
Q

Describe the effect of parasympathetic innervation on the lungs.

A

Constrict airways as smooth muscle contracts (muscarinic receptors)

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22
Q

Describe the effect of sympathetic innervation on the blood vessels.

A
  1. Activate a1 on smooth muscle to contract and decrease flow to gut.
  2. Activate b2 on smooth muscle and relax to increase flow to organs.
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23
Q

Describe the effect of parasympathetic innervation on the blood vessels.

A

Usually no effect (apart from salivary glands and genitalia)

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24
Q

Describe the effect of sympathetic innervation on the gut.

A
  1. Decrease gut motility by acting on a and B receptors

2. Decreasing enzyme secretion by acting on a receptors in pancreas.

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25
Q

Describe the effect of parasympathetic innervation on the gut.

A
  1. Act on muscarinic receptors in the gut muscle to increase gut motility
  2. Act on muscarinic receptors in pancreas to increase enzyme secretion.
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26
Q

Describe the effect of sympathetic innervation on the eyes.

A
  1. Beta relaxes smooth ciliary muscles round lens.
  2. alpha contacts radial muscles
    * pupils dilate and focus far away*
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27
Q

Describe the effect of parasympathetic innervation on the eyes.

A

Muscarinic on ciliary and sphincter muscles

constrict and focus close up

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28
Q

What controls simple autonomic reflexes and what is their action on the target?

A

Central control from hypothalamus and can excite or inhibit target.

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29
Q

Give an example of an autonomic reflex.

A

Baroreceptor reflex (detect BP)

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30
Q

Give an example of where antagonistic muscles can be found.

A

Eyes and bladder

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31
Q

What is the general rule for a1, B2 and muscarinic receptors?

A 
a1 = contract
B2 = relax
muscarinic = parasympathetic
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32
Q

Describe the structure of skeletal muscle.

A
  • Striated
  • Lots of nuclei
  • Multiple cells fused together to form to produce a large filament.
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33
Q

What replaces striated muscle cells after injury?

A

Satellite cells

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34
Q

Describe striations.

A

regular repeated units (sarcomere) in myofibrils.

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35
Q

What units are muscle fibres made of?

A

Myofibrils

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36
Q

What units are myofibrils made of?

A

Sarcomeres

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37
Q

Describe the A band in the sarcomere.

A

Actin and Myosin with M line in H zone.

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38
Q

In the sarcomere, what is the name of the thick filaments?

A

Myosin

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39
Q

In the sarcomere, what is the name of the thin filaments?

A

Actin

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40
Q

Describe the structure of Myosin.

A

Contains cross-bridge heads.

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41
Q

Describe the structure of actin.

A

Contains tropomyosin and troponin.

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42
Q

Explain the process of excitation-contraction coupling.

A

Converting electrical energy to chemical energy to create a mechanical event.

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43
Q

Describe the 5 steps in muscle contraction.

A
  1. Muscle AP propagated
  2. Depolarisation takes place in transfers tubules deep in muscles
  3. Calcium channels (linked to ryanodine receptor and DHP) open and release calcium from lateral sac of sarcoplasmic reticulum.
  4. Calcium binds to troponin and removes blocking action of tropomyosin to expose more binding sites.
  5. Cross-bridge moves ATP.
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44
Q

Describe the 2 main steps in muscle relaxation.

A
  1. Calcium taken up by sarcoplasmic reticulum by ATP pump.

2. Calcium removal from troponin restores tropomyosin blocking action.

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45
Q

Does contraction and/or relaxation require energy?

A

Both.

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46
Q

Define tension.

A

Force exerted by muscle.

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47
Q

Define load.

A

Force exerted on muscle.

48
Q

Define isometric.

A

Contraction with constant length.

49
Q

Define isotonic.

A

Contraction with shortening length.

50
Q

Define lengthening contraction.

A

Contraction with increase in length.

51
Q

Define the sliding-filament theory.

A

Contraction - cross-bridge cycle.

52
Q

Describe the 4 steps of the cross-bridge cycle.

A
  1. Myosin cross-bridge binds to actin as calcium concentration increases.
  2. Cross-bridge moves and releases ADP +Pi waste products.
  3. ATP binds to myosin causing cross-bridge to detach.
  4. Hydrolysis of ATP energises cross-bridge to enable relaxation.
53
Q

Define twitches.

A

Single AP to a single muscle fibre.

54
Q

Compare isometric and isotonic twitches.

A

Isometric = constant length (shorter latent period but longer contraction period)

Isotonic = shortening length (longer time to shorten)

55
Q

Describe the relationship between the sliding filament theory and the length of muscle tension.

A

Less overlap of filaments = less tension.
More overlap of filaments = more tension.
Too much overlap = filaments interfere with each other and less bind sites interact with cross-bridge heads.

56
Q

What is the optimal length (lo)?

A

Length of greatest isometric tension.

57
Q

Describe the lever system.

A

Amplifies muscle shortening velocity to increase manoeuvreability.

58
Q

Describe the link between load and motor unit recruitment.

A

Increase load = increased activation of motor units (recruitment).

59
Q

What order are muscle fibres activated?

A
  1. Slow oxidative fibres
  2. Fast oxidative fibres
  3. Glycolytic fibres
60
Q

What is tetanus?

A

Calcium never gets low enough to allow troponin/tropomyosin to re-block myosin binding sites, therefore summation of APs and twitches create titanic tension and patients can’t relax.

61
Q

What is fatigue?

A
  • Repeated muscle stimulation due to high calcium levels.

- Prevents muscle using up vast amounts of ATP and therefore not activate new cross-bridge cycles.

62
Q

What factors cause muscle fatigue?

A
  1. High intensity, short duration exercise.
  2. Conduction failure due to increased potassium (depolarisation not able to propagate AP)
  3. Increase in lactic acid acidifies proteins
63
Q

What results in long term, low-intensity exercise?

A

Dehydration, decrease in muscle glycogen and blood glucose.

64
Q

Define central command fatigue.

A

Cerebral cortex cannot excite motor neurons.

65
Q

Describe aerobic properties of muscle.

A
  • Oxidative fibres using O2
  • mitochondria (more oxidative phosphorylation)
  • increased vascularisation
  • Myoglobulin
  • thin red fibres
66
Q

Describe anaerobic properties of muscle.

A
  • Don’t rely on O2
  • Few mitochondria
  • Lower blood supply
  • Increased glycolytic enzymes and glycogen
  • No myoglobin
  • Large and white fibres
67
Q

What are the three types of muscle fibres and describe their resistance to fatigue.

A
  1. Slow oxidative (I) - resist fatigue
  2. Fast oxidative (IIa) - intermediate resistance to fatigue
  3. Fast glycolytic (IIb) - fatigue quickly
68
Q

What is the function of smooth muscle?

A

Hollow organs innervated by ANS (i.e not voluntary contractions)

69
Q

Describe the structure of smooth muscle.

A

No striations, spindle shaped, mononucleate, actin & myosin filaments arranged diagonally across cell and anchored by dense bodies, has X-bridge cycle and and calcium usage.

70
Q

Describe the steps of contraction and relaxation in smooth muscle.

A
  1. Calcium increases
  2. Binds calmodulin
  3. Ca2+ - calmodulin binds to myosin light chain kinase
  4. Kinase phosphorylates myosin x-bridges with ATP
  5. Phosphorylated x-bridges bind to actin
  6. Contraction and tension
71
Q

Describe how smooth muscle relaxes.

A

Via action of myosin light chain phosphatase to dephosphorylate X-bridges.

72
Q

What are the sources of calcium in smooth muscle?

A
  1. Less in SR, no t-tubules

2. Extracellular calcium from voltage activated channels (VACC)

73
Q

How is calcium pumped out of smooth muscle?

A

By calciumATPase pumping into SR (slower than skeletal)

74
Q

What type of muscle contracts the fastest?

A

Skeletal muscle.

75
Q

Describe tone in smooth muscle.

A

Basal level of calcium causes constant level of tension in smooth muscle.

76
Q

Does smooth muscle respond to stretch?

A

No.

77
Q

Name two types of cutaneous receptors.

A
  1. Mechanoreceptors

2. Proprioreceptors

78
Q

Describe mechanoreceptors.

A

Mechanical stimulation (pressure stretch or deformation)

79
Q

Provide an example of a mechanoreceptor.

A

Pacinian corpuscle.

80
Q

What is the function of proprioreceptors?

A

Signal info about limb position.

81
Q

Explain the mechanisms of sensory transduction in the skin.

A

Ion channels open/close and adequate stimulus causes graded membrane potential.

82
Q

What is an adequate stimulus for mechano- and proprioreceptors?

A

Membrane deformation

83
Q

Describe how membrane deformation generates an AP.

A

Activates stretch-sensitive ion channels causing ion flow across the membrane.

84
Q

Explain concept of frequency coding.

A

Larger stimulus = larger receptor potential = higher frequency of APs in sensory nerve.

85
Q

What is the function of the muscle spindle?

A

Monitor length and rate of change of muscle, therefore control reflexes and voluntary movements.

86
Q

Describe intrafusal muscle fibres.

A

Contained within a capsule, specialised sensory and motor innervation, lie in parallel with muscle fibres.

87
Q

What are the two types of intrafusal fibres?

A
  1. Nuclear bag fibres

2. Nuclear chain fibres

88
Q

What innervates intrafusal fibres?

A

Gamma motor neurons

89
Q

What innervates extrafusal fibres?

A

Alpha motorneurons

90
Q

What is the function of gamma motor neurons?

A

Contracts poles of muscle spindles shortens to match shortening of muscle.

91
Q

What will happen if alpha motorneurons fire without gamma motorneurons?

A

Extrafusal fibres contract and shorten.

Intrafusal fibres same length so spindle slackens and sensory afferent Ia decrease during shortening.

92
Q

What will happen if alpha and gamma motorneurons fire together?

A

Muscle and spindle shorten, spindle stretch reset to match spindle stretch, no drop in Ia firing during contraction.

93
Q

Where do the Ia afferents synapse?

A

Around nuclei in chain and bag fibres.

94
Q

Where do II afferents synapse?

A

Before the nuclei on the muscle spindle.

95
Q

Describe the role of the Golgi tendon organ?

A

Monitor tension on tendons.

96
Q

Describe the mechanism of action of the Golgi tendon organ.

A

Nerve endings of GTO mingle with tendon bundles at ends of muscles with stretch receptors to monitor stretch.
Provide sensory info to drive spinal cord reflexes.

97
Q

What is the simplest reflex?

A

The stretch reflex.

98
Q

Give an example of the stretch reflex.

A

Knee-jerk reflex.

99
Q

Describe the reflex arc in the stretch reflex.

A

Monosynaptic.

100
Q

Describe the steps in the stretch reflex.

A
  1. Sharp tap to an elastic tendon.
  2. Force transmitted to muscle fibre
  3. Activates sensory nerve in muscle spindle.
  4. Increase APs in afferent neurons in spinal cord through dorsal horn.
101
Q

How does the muscle relax after contraction?

A

Negative feedback loop in the reflex arc to shorten muscle back to previous length.

102
Q

What is the inverse stretch reflex?

A
  • Muscle contracts, pulls Ib sensory nerve from GTO which increases firing of APs.
  • Activation of inhibitory interneurons to agonist muscle
  • Activation of excitatory neurons to antagonist muscles.
103
Q

What is described as the post-synaptic and protective mechanism?

A

Inverse stretch reflex.

104
Q

What reflex prevents muscle contracting too hard and tendon coming away from the bone?

A

Inverse stretch reflex.

105
Q

How does info about muscle tension get transmitted to somatosensory cortex?

A

Ascends through dorsal column.

106
Q

What is the role of interneurons?

A

Create neural circuits to allow communication between sensory, motor neurons and the CNS.

107
Q

What is an ipsilateral reflex?

A

Interneurons on same side of spinal cord therefore produces reflex action on same side where stimulus was perceived.
This is the case for ALL monosynaptic reflexes.

108
Q

What is a contralateral reflex?

A

Motorneuron leaves spinal cord on different side to sensory neurone. The impulses cross the centre of the grey matter in a reflex arc and therefore, produce action on opposite side of body (PROTECTIVE MECHANISM).

109
Q

What reflex acts as a protective mechanism?

A

Contralateral reflex.

110
Q

What is the flexor-withdrawal reflex?

A
  1. Nociceptor fibres trigger pain and enter cord.
  2. Activates alpha motorneurons in several spinal segments.
    AT SAME TIME BELOW OCCURS:
    Excitatory neurons cross cord and excite contralateral extensors and inhibit contralateral flexors.
111
Q

What is the main function of the flexor-withdrawal reflex?

A

Prevent falls etc by extending contralateral limb.

112
Q

In the flexor-withdrawal reflex, how does the sensory info ascend to the brain?

A

Via contralateral spinothalamic tract.

113
Q

What is the role of higher centres in reflexes?

A

Stretch reflex can be consciously overridden.

114
Q

How can stretch receptors be overridden?

A

Descending voluntary excitation of alpha motorneurons which override inhibition from GTOs and maintain contraction (reflex can’t be evoked)

115
Q

Contraction of skeletal muscle requires what?

A

The release of calcium from the sarcoplasmic reticulum

116
Q

in the sympathetic nervous system, where is the spinal out-flow from?

A

Thoraco-lumbar.

117
Q

What drugs block transmission at the NMJ?

A

Botulinum, Curare, Hemicholinium, Tetrodotoxin

Science for Medicine (8 decks)

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