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MBBS II HNNS > L14 - Somatic sensation > Flashcards

L14 - Somatic sensation Flashcards

1
Q

Define the 4 modalities of somatic senses.

A
  1. Touch (Mechanoception)
  2. Body position & movement (Proprioception)
  3. Temperature (Thermoception)
  4. Pain (Nociception)
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2
Q

3 types of sensations?

A

special sense, visceral sense and somatic sense

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3
Q

Location of soma and 5 types of mechanoreceptors?

A

Located in dorsal root ganglion or trigeminal ganglia

a) Encapsulated:
 Meissner’s corpuscles
 Pacinian corpuscles
 Ruffini corpuscles

b) Unencapsulated:
 Merkel disc
( Hair follicle receptor)

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4
Q

List the submodalities of mechanoreception?

A

1.Touch 2.Pressure 3.Vibration and flutter

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5
Q

Define receptive field of mechanoreceptors?

A

area of the skin in which a stimulus activates a particular mechanoreceptor

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6
Q

Submodality, location, receptive field size and rate of adaptation of Meissner’s corpuscles?

A
  • Touch, flutter, movement
  • Superficial
  • Small, discrete hot spots of receptive field (more sensitive)
  • Moderately rapid adapting
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7
Q

Submodality, location, receptive field size and rate of adaptation of Pacinian corpuscles?

A
  • Vibration/ acceleration + rapid repetitive displacement of skin
  • Deeper layer
  • No hotspots of receptive field, big area
  • Rapidly adapting
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8
Q

Submodality, location, receptive field size and rate of adaptation of Ruffini corpuscles ?

A
  • Skin stretch, depth of skin indentation, intensity and texture
  • Deep layer
  • No hotspot of receptive field, big area
  • Slowly adapting
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9
Q

Submodality, location, receptive field size and rate of adaptation of Merkel disc?

A
  • Touch, pressure, form, depth of skin indentation
  • Superficial layer
  • Small hotspots (more sensitive)
  • Slowly adapting
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10
Q

Define rate of adaptation in mechanoreceptors?

A

decline in firing rate of afferent fibers with prolonged stimulus

Slow = continue to respond through duration of applied stimulus

Rapid = Respond to constantly applied stimulus only at the first instance

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11
Q

Define the 3 rates of adaptation and give examples of mechanoreceptors.

A
  1. Slowly adapting: Merkel disk, Ruffini’s corpuscle
  2. Moderately Rapid adapting: Meissner’s corpuscle, hair follicle receptor
  3. Rapidly adapting: Pacinian corpuscle (in glabrous and hairy skin)
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12
Q

Compare what submodalities of stimuli are measured in mechanoreceptors of different rate of adaptation?

A

Slowly: Measures depth of skin indentation + Intensity detector + perceives form & texture

Moderately rapid = Velocity detector + Perceives flutter & motion

Rapidly = Acceleration, vibration +rapid repetitive displacement of skin

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13
Q

3 qualities of proprioception? Definition?

A

Sense of body position and sense of movement (kinesthesia)

  1. Position(static limb position & trunk orientation)
  2. Movement(dynamic movement; velocity & direction of joint movement)
  3. Forces generated by muscle contractions
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14
Q

Perception of head / body position in space is derived from integrative inputs of?

A

 Proprioceptors
 Labyrinth receptors of the inner ear
 Visual input

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15
Q

Test for proprioception?

A

Romberg test:

 Requires patient to maintain balance while standing with feet together, eyes closed

 Tests whether the isolated proprioceptive components are working properly when visual cues are missing

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16
Q

3 types of proprioceptors? Respective function?

A
  1. Muscle spindle = Sense muscle length or stretch (static) & velocity of stretch during body movement (dynamic)
  2. Golgi tendon organ = muscle tension
  3. Joint receptor = dynamic response, finger position
    (4. cutaneous mechanoreceptors)
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17
Q

Compare the nerve endings between muscle spindle and joint receptors?

A

Muscle spindle = intrafusal muscle fibers = Annulospiral and flower-spray endings (sensitivity controlled by activity of γ motor neuron)

Joint receptor = Free nerve ending & corpuscular receptors @ connective tissues, capsule and ligaments of joints

18
Q

Muscle spindle sensitivity is controlled by which type of neuron?

A

Activity of γ motor neuron

19
Q

Types of thermoreceptors and mechanism?

A

 Cold, warm receptors

 Express temperature-gated ion channels (identified by mints, capsaicin)

20
Q

Different mechanisms of mechanoreceptors? (3)

A

Activated by mechanical stimulus (force changes conformation of ion channel) = action potential:

1) Direct activation through lipid tension
2) Direct activation through structural proteins
3) Indirect action through membrane structural proteins

21
Q

Describe how temeprature detection changes in: constant temp, changing temp, extreme temp?

A

 Static temperature detection: detect constant skin temperature

 Dynamic temperature detection / sensation: detect transient changes in skin temperature

 Below 10oC / above 45oC (extreme temperatures) = stimulate nociceptors

22
Q

Different modalities of somatosensation are transmitted by the same type of fibers. True or false?

A

False

Different modalities of somatosensation have different:

 Thickness of afferent axons
 Myelination
 Speed of conduction of action potential

23
Q

Describe the segregation of sensory afferent fibers with different modalities when they enter the spinal cord?

A

Segregate into different laminae of the grey matter in dorsal horn of spinal cord

Pain, temperature (Aδ, C fibers) = I, II, V laminae (enters laterally into dorsal horn)

Mechanoreceptors of skin(Aβ fibers) + Proprioceptor (Aα fibers) = IV (enters medially into dorsal horn)

24
Q

Compare the ascending pathways taken by different sensory afferents?

A

Proprioception, Mechanoception = DCML

Thermo, Nociception = spinothalamic

25
Q

List the sensations relayed by DCML?

A

Mechanoception, proprioception

For discriminative touch (recognition of shape, size & texture), pressure, vibration, proprioception

26
Q

List the sensations relayed by Spinothalamic tract?

A

Thermoception, Nociception

Crude touch, temperature and pain, tickle, itch

27
Q

List the sensations relayed by Spinocerebellar tract?

A

mechanoception and proprioception

28
Q

Divide the somatosensory cortex into 3 groups.

A
  • Primary somatosensory cortex (S-I; areas 3, 2, 1)
  • Secondary somatosensory cortex (S-II; area 43)
  • Posterior parietal cortex (areas 5, 7, 39, 40)
29
Q

Function of the somatosensory cortex?

A

1) DECODE the localization and types/qualities of the sensory information from contralteral side of body
2) INTEGRATE multiple input sensory information from different locations and of different types/qualities&raquo_space; Higher order processing

30
Q

Explain how the somatosensory cortex can decode sensory info.

A

Highly organized according to the location of the sensory receptors

Unique group/patterns of neurons activated by stimuli of specific modality/submodality from a particular location

31
Q

Relate the areas of thalamus corresponding to Brodmann areas of primary somatosensory cortex after sensory activation.

A

1) Proprioceptive stimuli:
•VPS (ventral posterior superior nucleus)&raquo_space; 3a, 2

2) Tactile (mechanoceptive) stimuli:
•VPL (ventral posterior lateral nucleus)&raquo_space; 3b, 1, 2
•VPM (ventral posterior medial nucleus)&raquo_space; 3b, 1, 2

3) Pain and temp:
•VPI&raquo_space; S2 (secondary somatosensory cortex)

Most inputs from the thalamus go to areas 3a and 3b, which then project to areas 1 and 2

32
Q

What sensory info can Brodman area 2 of Primary somatosensory cortex process?

A

Area 2 process both tactile and proprioceptive information

33
Q

Describe the organization of primary somatosensory cortex (S-1)

A
  • 6 layers of neurons (molecular, external granular, external pyramidal…etc); arranged into functional columns (1,2,3a,3b,4,5)
  • Each column is very narrow and all neurons within the column receive inputs from the same body area with a specific sensory submodality
34
Q

Receptive field of neuron in SI is much larger than that of the mechanoreceptor on the skin. True or False?

A

True

SI neuron receives inputs from multiple receptor neurons

35
Q

Define what brodmann area 1, 2, 3a and 3b in primary somatosensory cortex process?

A

 1: texture of objects (rapidly adapting receptors on skin)

 2: size, shape of objects (pressure, joint position in deep tissue)

 3a: muscle stretch receptors in deep tissue

 3b: slowly, rapidly adapting receptors in skin

36
Q

Describe preliminary higher order processing of the somatosensory cortex?

A

neurons in S1 stimulated by specific combination of stimuli, e.g. respond to specific motion

> > Processing to deduce Direction and Orientation

37
Q

Location of Primary somatosensory cortex S-I?

A

Postcentral gyrus & in depth of central sulcus

Brodmann area 1, 2, 3a, 3b

38
Q

Function of secondary somatosensory cortex?

A
  • Receives inputs from S-I
  • Recognize objects
  • Input to amygdala and hippocampus (for emotion and memory)
39
Q

Function of posterior somatosensory cortex?

A
  • Receives inputs from S-I and S-II
  • Integrates different sensory modalities (e.g. tactile and visual stimuli for eye-hand coordination)
  • Output to motor areas; for guidance of movement
40
Q

Clinical presentation of lesion of S-I?

A

Impaired mechanoreceptive, proprioceptive senses:

  • Difficulty with simple tactile tests
  • contralateral loss of discriminative touch (difficulty to discriminate size and form of objects)
  • Impaired positional sense
41
Q

Clinical presentation of lesion of Posterior parietal cortex?

A
  • Only mild difficulty with simple tactile tests
  • Tactile apraxia (disturbed hand movement with an object)
  • Deficit in the ability to relate to extrapersonal space; e.g. constructional apraxia, neglect syndrome

MBBS II HNNS (57 decks)

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