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My Neurology > Physiology > Flashcards

Physiology Flashcards

1
Q

What are the two directions that impulses can move along an axon?

A
  • anterograde is away from the soma

- retrograde is towards soma (used by viruses)

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2
Q

What are the different types of neurons?

A
  • unipolar
  • pseudounipolar: bifurcating axons
  • bipolar: dendrites and axon
  • multipolar: 1+ dendrites
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3
Q

Do passive signals or actions potentials decay?

A
  • APs never decay

- passive signals decay due to leaky nerve cell membrane

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4
Q

How do you increase the passive current spread?

A
  • increase radius to decrease resistance

- add myelin

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5
Q

What can axons synapse onto?

A
  • dendrites
  • soma
  • another axon
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6
Q

What is the most frequent neurotransmitter for excitatory and inhibitory responses?

A
  • excitatory: (cause depolarisation)

- inhibitory: GABA or glycine (cause hyperpolarization eg with Cl- influx)

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7
Q

What are the types of summation?

A
  • spatial: many inputs at different places on the one soma

- temporal: many action potentials at the same time on the axon

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8
Q

What is an inotropic receptor?

A
  • direct gating to the ACh channel

- FAST

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9
Q

What is a metabotropic receptor?

A
  • ACh binding causes activation of a G protein which then causes K+ efflux
  • SLOW
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10
Q

What are the three different channels that glutamate can bind to?

A

AMPA, kainate and NMDA

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11
Q

What things does the somatosensory system mediate?

A
  • fine touch
  • proprioception
  • temperature
  • pain
  • itch
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12
Q

What are the three subdivisions of the somatosensory system?

A
  • exteroceptive (information from surface of the body)
  • proprioceptive (posture and movement)
  • enteroceptive (internal state of the body)
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13
Q

What is the chain of neurons in a somatosensory impulse?

A

primary sensory afferent (in dorsal root ganglia or cranial ganglia) –> projection neuron (in brainstem or dorsal horn of spinal cord) –> projection neuron (in thalamic nuclei) –> somatosensory cortex

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14
Q

What do slow adapting sensory units do?

A

give continuous information to CNS about degree of stretch, force and position

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15
Q

What do fast adapting sensory units do?

A

detect a change in stimulus strength so the no. of impulses is proportional to the rate of change of the stimulus

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16
Q

What do very fast adapting sensory units do?

A

only response and make an AP for very fast movement

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17
Q

What is the receptive field or RF?

A

the area where the sensory unit can be excited for a particular neuron

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18
Q

What determines a high acuity in terms of RF and innervation?

A

small RF and high density of innervation

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19
Q

What determines a low acuity in terms of RF and innervation?

A

large RF and low density of innervation

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20
Q

What is the difference in the RF’s of Meissener’s and Pacinian corpuscles?

A

Meissener’s for touch = smaller RF

Pacinian for pressure = larger RF

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21
Q

What are the main two somatic sensory pathways?

A
  • spinothalamic tract

- dorsal column medial lemniscal pathway

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22
Q

What are the functions of the spinothalamic tract?

A

pain, temperature, itch

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23
Q

What are the functions of the DCML?

A

discriminatory touch, pressure, vibration, weight discrimination, conscious proprioception

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24
Q

What are the two main tracts in the sensory dorsal columns?

A
  • medial gracile tract (T6 and below)

- cuneate tract (T6 and above)

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25
Q

What is the arrangement of the sensory dorsal column?

A

lateral to medial is cervical, thoracic, lumbar and sacral

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26
Q

What is the main route for touch and conscious proprioception to the cerebral cortex?

A

dorsal column medial lemniscal pathway

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27
Q

What is the DCML sensory pathway?

A

1st neuron enters dorsal horn and branches to a synapse in horn (for spinal reflex) and long ascending axon –> via gracile or cuneate tract to either gracile nucleus or cuneate nucleus in the medulla –> next neuron crosses sides and ascends in medial lemniscus to the ventral posterior lateral nucleus of the thalamus
–> last neuron projects to the primary somatosensory cortex

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28
Q

What is lateral inhibition of neurons?

A

one active neuron inhibiting the neurons next to it to sharpen the stimulus perception

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29
Q

What is the pathway of the trigeminal sensory system?

A

three branches of CNV –> trigeminal ganglion –> synapse in the chief sensory nucleus or spinal nucleus –> fibres cross and go up to the VPM nucleus of the thalamus –> another neuron goes on to the cortex

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30
Q

What is the function of the posterior parietal cortex?

A

receives and integrates information from the somatosensory cortex and from other cortical areas eg visual, auditory etc

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31
Q

What do upper motor neurons do?

A

supply input to lower motor neurons to modulate their activity

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32
Q

What do LMNs do?

A
  • receive information from UMNs
  • receive information from proprioceptors and interneurons
  • cause muscle contraction
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33
Q

What are the two types of LMNs?

A
  • alpha motor neurons: innervate fibres that make force

- gamma motor neurons: innervate the muscle spindle (sensory)

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34
Q

What do the different motor neurons at different levels innervate?

A
  • distal and proximal muscles = cervical and lumbar-sacral segments (enlargements)
  • axial muscles = all levels
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35
Q

What is a motor neuron pool?

A

collection of alpha motor neurons that innervate a single muscle

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36
Q

What is the arrangement of LMNs in the ventral horn?

A
  • LMNs for the axial muscles are medial to the LMNs for the distal muscles
    • LMNs for the flexors are dorsal to the LMNs for the extensors
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37
Q

What are the three things that regulate an alpha MN’s activity?

A
  • central terminals of dorsal root ganglion cells
  • UMNs in the brainstem and motor cortex
  • spinal interneurons
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38
Q

What does muscle strength depend on?

A
  • Activation of muscle fibres: firing rates of LMNs, no of active LMNs and coordination of the movement
  • Force made by innervated fibres: fibre size and fibre phenotype
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39
Q

What causes sustained contraction of a muscle?

A

summation of muscle twitches (many Eps) in an alpha MN

40
Q

What is the size of the motor unit relative to the size of the alpha motor neuron?

A

small motor units are innervated by small alpha motor neurons and vice versa

41
Q

What is the scientific difference between slow and fast twitch fibres?

A

how quickly myosin ATPase splits ATP for cross bridge cycling

42
Q

What are the features of slow (type 1) muscle fibres?

A
  • ATP from oxidative phosphorylation
  • slow
  • fatigue resistant
  • red due to myoglobin
  • small alpha MN
43
Q

What are the features of fast (types 2a and 2b) fibres?

A
  • 2a: ATP from oxidative phosphorylation, red and fatigue resistant
  • 2b: is ATP from glycolysis, fast and can fatigue, pale, large alpha MN
44
Q

What is the difference in excitation of LMNs in relation to their size?

A

small LMNs are more easily excited than large LMNs so fine control of muscle force

45
Q

What is the myotatic reflex?

A

when a skeletal muscle is pulled it pulls back because the change in length is registered by the muscle spindle eg knee jerk reflex

46
Q

What is the reflex for muscle spindle fibres?

A
  • monosynaptic reflex arc
  • rapid
  • extensor muscles
47
Q

What is the Jendrassik manoeuvre and what does it prove?

A
  • interlocking fingers and pulling accentuates the myotatic reflex
  • proves that simple reflexes can be modulated by descending control
48
Q

What are the intrafusal fibres in muscle spindle innervated by?

A

gamma motor neurons and stimulation causes contraction

49
Q

What are the two types of intrafusal fibres?

A
  • nuclear bag fibres

- chain fibres

50
Q

Which intrafusal fibres are dynamic and which are static?

A
  • nuclear bag fibres can be either dynamic (very sensitive to the rate of change) or static (more sensitive to the absolute length of the muscle)
  • chain fibres are sensitive to the absolute length of the muscle (static gamma MNs)
51
Q

What are the two types of fibres that innervate the intrafusal fibres?

A
  • 1a = forms a primary annulospiral nerve around the centre of all of the fibres and are sensitive to the rate of change of stretch
  • 2 = form flower spray endings and are sensitive to the absolute length
52
Q

What does stimulation of the different types of gamma MN cause?

A
  • static gamma MN fibres causes steady state to increase

- dynamic gamma MN enhances the dynamic response to stretch fibres

53
Q

What are the uses for static and dynamic gamma MNs?

A
  • static = slow and predictable movements

- dynamic = rapid and unpredictable muscle length changes

54
Q

What do Golgi tendon organs do?

A
  • at the junction of the muscle and tendon
  • monitor changes in muscle tension and keep it in optimal range
  • protect muscle from overload
55
Q

What are Golgi tendon organs innervated by?

A

group 1b sensory afferents

56
Q

What does the inverse myotatic reflex involve?

A

excitation of 1b from the golgi tendon organ –> excitatory synapse with an inhibitory neuron in the spinal cord –> inhibition of the alpha MN going to the muscle –> relaxation

57
Q

What are proprioceptive axons?

A
  • present in connective tissue of joints

eg free nerve endings, golgi-type endings, Paciniform endings and Ruffini endings

58
Q

What are the three ways that proprioceptive information can arise?

A
  • muscle spindles
  • golgi tendon organs
  • joint receptors
59
Q

What do inhibitory interneurons do?

A
  • mediate the inverse myotatic response (relaxation of the antagonist muscle)
  • reciprocal inhibition between extensor and flexor muscles
60
Q

What do excitatory interneurons do?

A
  • flexor reflex (noxious stimulus causes limb to flex so excitatory interneurons cause the flexion)
  • crossed extensor reflex (the same noxious stimulus causes opposite side to support body during reflex on other side)
61
Q

What is the most important ion in the auditory system?

A

K+ which moves in through the hair cells and the channels open and close based on direction of the stereo cilia in relation to the kinocilium

62
Q

Where do the auditory nerve axons synapse?

A

at the base of the hair cells in the inner ear

63
Q

What does tectorial membrane vibration cause?

A
  • hair cells bend
  • neurotransmitter release (depending on direction of bend)
  • K+ will enter the hair cells and this is caught in the nerve fibres
64
Q

What do the different directions of the stereocilia mean?

A
  • away from kinocilium = closed

- towards kinocilium = open channels

65
Q

How are the K+ ions recycled in hearing?

A

through connective tissue and back into the scala media and damage to this pathway can cause deafness

66
Q

How does different parts of the basilar membrane pick up different frequency sounds?

A
  • width and the stiffness of the basilar membrane change
  • hair cells are affected differently by different frequencies
  • near oval window = higher frequency sounds
67
Q

What are the roles of the inner and outer hair cells?

A
  • inner hair cells = afferent signals

- outer hair cells = efferent inputs as they amplify membrane vibration

68
Q

What do cochlear amplifiers do?

A

contract and expand to change the length of the outer hair cell

69
Q

What does the frequency of sound directly correspond to?

A

how many APs are created

70
Q

How do the impulses travel to the brain after the cochlear nucleus?

A
  • mixing of stimuli from the two ears

- tonotopy is maintained all the way to the auditory cortex

71
Q

What is linear and rotational movement detected by?

A
  • Linear movement = otolith organs

- Rotational movement = semicircular canals

72
Q

How are impulses created from the cupula?

A
  • fluid displaces the cupula
  • causes crista movement
  • determines glutamate release
73
Q

What happens to the contralateral ear when there is an increased in firing in one ear?

A

decrease in contralateral ear

74
Q

What are the three main vestibular reflexes?

A
  • vestibulo-ocular (eyes move to keep gaze fixed when head moves)
  • vestibulo-colic (keeps head still when walking)
  • vestibular-spinal (adjusts posture in rapid movements)
75
Q

What is the dark current in relation to vision?

A

photoreceptors generate a current in the absence of light with a sodium influx so there is depolarisation in the dark

76
Q

What do the different types of bipolar cells do in response to glutamate in vision?

A

some depolarise and some hyperpolarise

77
Q

What does lateral inhibition in the retina cause?

A

center-surround organisation

78
Q

How do visual impulses get from the retina to the brain?

A

retina –> lateral geniculate nucleus –> primary visual cortex

79
Q

What is the simplified motor control pathway?

A

neocortical association areas and basal ganglia –> motor cortex and cerebellum –> brain stem and spinal cord

80
Q

What are the two important divisions of the motor pathways?

A
  • lateral eg corticospinal and rubrospinal

- ventromedial eg vestibulospinal, tectospinal and pontine/medullary reticulospinal

81
Q

What is the difference between lateral and ventromedial pathways?

A
  • Lateral pathways: under cerebral cortex control, voluntary control of distal muscles esp fine movements
  • Ventromedial pathways: under brain stem control, posture and locomotion
82
Q

What does the rubrospinal tract do?

A
  • cell bodies in red nucleus
  • decussation at ventral tegmental decussation
  • control over LMNs of limb flexor muscles
83
Q

What compensates when there is damage to the corticospinal tract?

A

rubrospinal tract can compensate (otherwise used less)

84
Q

What does the tectospinal tract do?

A
  • cell bodies in the superior colliculus
  • gets visual/sensory and auditory information
  • axons decussate in the dorsal tegmental decussation
85
Q

What do the pontine/medullary reticulospinal tracts do?

A
  • come from reticular formation
  • pontine = medial and descends ipsilaterally to do standing posture
  • medullary = lateral and descends bilaterally to oppose medial tract
86
Q

What are the three forms of pain?

A
  • nociceptive (adaptive, immediate protective response)
  • inflammatory (adaptive, assists in healing)
  • pathological (maladaptive, no purpose)
87
Q

What are the differences between Adelta and C fibres?

A
  • Adelta- fibres are mechanical/thermal nociceptors which respond quickly to stimuli to mediate fast pain
  • C- fibres respond to all stimuli and mediate slow pain
88
Q

What is the pathway from stimulus to pain perception?

A

stimulus onto free nerve ending → axon of nociceptor → via dorsal root ganglion → dorsal horn → second order projection neuron → spinothalamic and spinoreticulothalamic tract

89
Q

What is special about peptidergic polymodal nociceptors?

A

subset of C-fibres and they have both

  • afferent (transmit nociceptive info to CNS in dorsal horn)
  • efferent (release pro-inflammatory mediators to contribute to neurogenic inflammation) functions
90
Q

What is the process of neurogenic inflammation?

A

peptides released from free nerve ending due to tissue damage or inflammatory mediators → vasodilation, release of histamines and sensitisation of nociceptors → hyperalgesia and allodynia

91
Q

How do visceral afferents get to the dorsal horn?

A

from nociceptors they then follow sympathetic pathways

92
Q

How does referred pain work?

A
  • brain can interpret the nociceptive information from the viscera as coming from the skin
  • some visceral and skin afferents converge on the same spinothalamic neurons
93
Q

What is the gate control theory?

A
  • Abeta fibre activity > C/Adeltaf fibre = spinal gate is closed and the pain is not perceived
  • if the reverse is true then the pain is perceived
94
Q

What are the two major nociceptive tracts?

A

spinothalamic tract and the spinoreticular tract

95
Q

What are the features of REM sleep?

A
  • fast EEG activity which is similar to wakefulness
  • muscle atonia
  • narrative dreams
  • happens at the end of the night
96
Q

What are the features of non-REM sleep?

A
  • slow EEG waves
  • body is relaxed with reduced HR and BP
  • non-narrative images dreams
  • start of night

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