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Neurology > Physiology > Flashcards

Physiology Flashcards

1
Q

What does the somatosensory system mediate?

A 
Fine discriminatory touch
Joint & muscle position sense (proprioception)
Temperature
Pain
Itch
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2
Q

Name the 3 divisions of the somatosensory system.

A

exteroceptive
proprioceptive
enteroceptive

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3
Q

Which division of the somatosensory system registers information from the surface of the body?

A

exteroceptive division

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4
Q

Which somatosensory division monitors postures and movement? Where are its receptors found?

A

proprioceptive

sensors in muscle, tendons and joints

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5
Q

Which division of the somatosensory system reports upon the internal state of the body?

A

enteroceptive division

- closely related to autonomic function

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6
Q

The primary sensory afferent neurone in the somatosensory pathway is normally found in the CNS.
T/F?

A

false - in PNS

cell body in either dorsal root ganglia or cranial ganglia

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7
Q

Where are the cell bodies of 2nd order somatosensory neurones found?

A

dorsal (post) horn of spinal cord or brainstem nuclei

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8
Q

Where are the cell bodies of 3rd order somatosensory neurones found?

A

thalamic nuclei

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9
Q

How is the receptor potential elicited?

A

stimulus (mechanical, thermal. chemical) opens cation-selective channels in peripheral terminal of primary sensory afferent neurone -> depolarising receptor potential

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10
Q

How is the amplitude of the receptor potential related to stimulus intensity?

A

graded and proportional to stimulus intensity

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11
Q

What triggers ‘all or none’ action potentials?

A

a supra-threshold receptor potential

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12
Q

The frequency of ‘all or none’ action potentials produced is proportional to the receptor potential amplitude.
T/F?

A

true

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13
Q

What happens when action potentials arrive at the central terminal?

A

the graded release of neurotransmitter on to the 2nd order neurones

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14
Q

What is the term used to describe how primary afferent neurones are especially tuned to respond to a specific type of energy?

A

the adequate stimulus

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15
Q

Name the 2 different threshold units in sensory receptors.

A

low threshold units

high threshold units

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16
Q

What types of threshold unit responds to fine discriminatory touch?

A

low threshold mechanoreceptors (LTMs)

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17
Q

What kind of threshold unit responds to cold-hot?

A

low threshold thermoreceptors

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18
Q

What is the response by low threshold units to increasing stimuli strength?

A

increased rate of firing of Low threshold mechanoreceptors (LTMs) + perception of increasing intensity

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19
Q

If the stimuli to low threshold mechanoreceptors (LTMs) is of extreme intensity, the qualitative character of the stimulus changes to emphasise the signal.
T/F?

A

False - the qualitative character (e.g. pressure) does not change (e.g. to pain), provided only LTMs are activated.

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20
Q

What type of threshold units are nociceptors?

A

high threshold (HT) units - respond to high (noxious, potentially damaging), nut not (normally) low intensity stimuli

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21
Q

What do thermal nociceptors respond to ?

A

high intensity to extreme degrees of heat (>45 or <10-15 degrees)

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22
Q

What do polymodal nociceptors receptors respond to ?

A

AT LEAST 2 of the HT unit category:
High intensity mechanical stimuli
Extremes of heat
Substances in tissue e.g. inflammatory-like response

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23
Q

What is adaptation?

A

determines whether sensory units change their firing rate in response to a stimulus of changing intensity, or fire continuously throughout a constant stimulus.

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24
Q

Slow adaptation (SA) or tonic/static response is used by which sort of receptors and why?

A

e.g. stretch receptors - continuous information to CNS - provides information about position, degree of stretch or force.

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25
Q

What are the characteristics of a slowly adapting response?

A

sensory units fire APs continuously throughout a constant stimulus and increase firing rate with increasing stimulus

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26
Q

Describe fast adapting responses.

A

the stimulus strength is detected and the number of impulses is proportional to rate of change of stimulus

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27
Q

What is an example of a very fast adapting sensory unit response?

A

vibration of different intensities e.g. Pacinian corpuscle

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28
Q

Which sensory receptors have the fasted conduction velocity?

A

proprioceptors of skeletal muscle (group A-alpha)

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29
Q

Which sensory receptors have the slowest conduction velocity?

A

group C - temperature, pain, itch

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30
Q

What is the receptive field (RF)?

A

the target territory from which a sensory unit can be excited

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31
Q

RF size varies greatly over the body and is inversely related to ….?

A

innervation density and sensory acuity

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32
Q

Areas with high density of innervation will have what size of RF and what type fo acuity?

A

small RF and high acuity

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33
Q

Areas with low density of innervation will have what size of RF and what type fo acuity?

A

large RF and low acuity

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34
Q

Which skin mechanoreceptors respond to touch and are abundant in areas of high 2-point discrimination?

A

meissner’s corpuscles

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35
Q

Which skin mechanoreceptors are deep in dermis and joint capsules and respond to deep pressure?

A

ruffini endings

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36
Q

What is an Iggo dome?

A

multiple Merkel cells grouped together and innervated by a single myelinated fibre

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37
Q

Describe Pacinian corpuscles.

A

unmyelinated ending of sensory nerve cell surrounded by a capsule - response to pressure.
Found in dermis and sometimes in fascia

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38
Q

What is found at the border of dry skin and mucous membranes?

A

Krause end bulbs

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39
Q

What do two-point thresholds match the diameter of?

A

the corresponding receptive field

40
Q

Describe the laminae found in grey matter.

A

10 distinct laminae of Rexed found from dorsal to ventral (I-X) horns

41
Q

In which grey matter laminae are nociceptors found and which fibre class are they?

A 
laminae I and II
fibre class A-delta/C
42
Q

In which grey matter laminae are LTMs found and which fibre class are they?

A 
laminae III to VI
fibre class A-beta
43
Q

in which grey matter laminae are Proprioceptors found and which fibre type are they?

A

laminae VII to IX

A-alpha fibres

44
Q

Sensory input to which dermatomes travels in the gracile tract (fasciculus gracilis)?

A

T6 and below (legs and lower trunk)

45
Q

Sensory input to which dermatomes travels in the cuneate tract (fasciculus cuneatus)

A

input above T6 (arms and upper trunk)

46
Q

describe contrast enhancement.

A

as information is conveyed from one neurone to the next in a sensory pathway, differences in the activity of adjacent neurones are amplified –> contrast enhancement

47
Q

Describe lateral inhibition.

A

When one neurone is active, it inhibits activity of its neighbours via inhibitory interneurones & contrast enhancement = lateral inhibition

48
Q

What effect does lateral inhibition have on stimulus perception?

A

it sharpens stimulus perception

49
Q

What are Brodmann areas? Where does it get input from?

A

These areas are found and make up the S1 area immediately posterior to the central sulcus
BA 1, 2, 3a and 3b
input from VP thalamus

50
Q

Which type of input does area Ba 3a receive?

A

proprioceptors (muscle spindles)

51
Q

Which type of input does area BA 3b receive?

A

cutaneous - touch (texture, shape, stimulus size)

52
Q

Which type of input does area BA 2 receive?

A

joint afferents, golgi tendon organs, deep tissues –> pressure & joint position; object perception

53
Q

Which type of input does area BA 1 receive?

A

cutaneous - texture discrimination

54
Q

A deficit in texture and shape discrimination would indicate a small lesion in which BA region?

A

3b

55
Q

A loss of texture discrimination would indicate a small lesion in which BA region?

A

1

56
Q

Impaired grasping and size and shape discrimination would indicate a small lesion in which BA lesion?

A

2

57
Q

what does astereognosis mean?

A

impaired size and shape discrimination

58
Q

How many cell layers does the somatosensory cortex have?

A 
6 cell layers (I-VI)
1 - molecular
2 - external granular 
3 - external pyramidal 
4 - internal granular 
5 - internal pyramidal
6 - multiform 
white matter
59
Q

Thalamic inputs to SI terminate mainly on neurones within which layer of the somatosensory cortex?

A

layer 4 - internal granular

60
Q

neglect syndrome is usually the result of damage to the …. cortex?

A

right parietal cortex - patients believe the left side of the world does not exist and may even disclaim the existence of the left side of their body.

61
Q

Describe the hierarchy of motor control.

A

involves at least 3 levels, e.g. high, middle and low.
hierarchy from top (forebrain) to bottom (spinal cord).
Motor control is initiated by multiple sensory inputs and a need to move using internal mechanisms.

62
Q

What is the function of high level in motor control hierarchy? Which structures are involved?

A

Function = strategy;

neocortical association areas; Basal ganglia

63
Q

What is the function of the middle level in motor control hierarchy? Which structures are involved?

A

Function = tactics

Motor cortex, cerebellum

64
Q

What is the function of low level in motor control hierarchy? Which structures are involved?

A

Function = execution

Brain stem, spinal cord

65
Q

LMNs supply input to UMNs to modulate their activity.

T/F?

A

False - UMNs supply input to LMNs to modulate their activity.

66
Q

Where do LMNs get input from and what is their role?

A

input: UMNs, proprioceptors, interneurones

They command muscle contraction and form the ‘final common pathway’.

67
Q

What is the role of alpha-motor neurones (a-MNs)?

A

innervate bulks of fibres within muscle that generate force.

68
Q

What do gamma-MNs do?

A

innervate sensory organ with muscle aka. muscle spindle

69
Q

Do axons of LMNs exit the spinal cord via dorsal or ventral roots?

A

ventral roots (or via cranial nerves)

70
Q

Where in the spinal cord would you find a greater number of motor neurones?

A

cervical enlargement (C3-T1) and lumbar enlargement (L1-3)

71
Q

Describe the distinct distribution of LMN soma in the ventral horn.

A

LMNs to axial muscles are MEDIAL to those innervating distal muscles.
LMNs to flexors are DORSAL to those supplying extensors.

72
Q

Name the 3 sources of input regulating the activity of an alpha-MN.

A

Central terminals of DRG cells whose axons innervate muscle spindles.
UMNs in the motor cortex & brainstem.
Spinal interneurones.

73
Q

alpha-MN + all the skeletal muscle fibres it innervates –> ?

A

motor unit

74
Q

Muscle contraction results from…?

A

Individual and combined action of motor units which must be co-ordinated.

75
Q

The collection of alpha-MNs that innervate a single muscle = ?

A

motor neurone pool

76
Q

What are the 2 principle mechanisms which grade the force of muscle contraction by alpha-MN?

A

Frequency of AP discharge of the a-MN

The recruitment of additional, synergistic, motor units.

77
Q

Activation of muscle fibres depends on ?

A

The firing rates of the LMNs involved; The number of LMNs that are simultaneously active; The co-ordination of the movement.

78
Q

Fibre size and phenotype are important factors in determining ?

A

force production by innervated muscle fibres

79
Q

What is the result of a single AP in an alpha-MN?

A

causes muscle fibre to twitch

80
Q

How do slow twitch and fast twitch skeletal muscle fibres differ?

A

In how quickly myosin ATPase splits ATP to provide energy for cross bridge cycling.
They also express different myosin heavy chains (MHC)

81
Q

Time to develop peak tension is a reflection of…

A

myosin ATPase activity

82
Q

Describe slow-oxidative (type 1 ) fibres.

A

ATP from oxidative phosphorylation
Slow contraction and relaxation
Fatigue resistant

83
Q

Describe type IIa (fast oxidative) fibres.

A

ATP from oxidative phosphorylation
Fast contraction and relaxation
Fatigue resistant

84
Q

Describe type IIb (fast glycolytic) fibres.

A

ATP from glycolysis (anaerobic)

Fast contraction - not fatigue resistant (not much ATP produced)

85
Q

What colour are each type of skeletal muscle fibres?

A

type 1 and type IIa = red

type IIb = pale

86
Q

Fast fatiguing motor units are connected with which type of muscle fibres?

A

IIb/IIx

= burst power

87
Q

Fatigue resistant motor units are connected with which type of muscle fibre?

A

type IIa

= sustained locomotion

88
Q

Slow motor units are connected with which muscle fibre type?

A

type 1 fibres

= antigravity, sustained movement

89
Q

Describe the Henneman Size Principle.

A

The susceptibility of an a-MN to discharge action potentials is a function of its size.
i.e. slow (& small) motor units are more easily activated - have a lower threshold than larger ones.

90
Q

What does recruitment of alpha motor neurones by size allow for?

A

the fine and graded development of muscle force - motor units are recruited in order of their size.
This type of activation allows for fine control of muscle force across a wide range of tensions developed.

91
Q

What is the myotonic reflex?

A

when a skeletal muscle is pulled, it pulls back.

92
Q

What does the muscle spindle register?

A

change in length (& rate of change)

93
Q

What does a muscle spindle consist of?

A

A fibrous capsule
Intrafusal muscle fibres
Sensory afferents - innervate the intra-fusal fibres (Ia class)
Gamma motor neurone efferents - innervate infra-fugal fibres

94
Q

How can the myotonic reflex be reinforced?

A

the Jendrassik manoeuvre - ask patient to interlock fingers and try pull hands apart when instructed. tap tendon immediately - the reflex is usually exaggerated.

95
Q

During voluntary movement, alpha and gamma MNs are normally co-activated.
T/F?

A

True -
so that the intra-fusal muscle fibres contract in parallel with the extrafusal fibres.
Maintains the sensitivity of the spindle to stop it from ‘going slack’ when the extrafusal fibres contract

Neurology (11 decks)

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