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Neuroscience Y2 > Somatasensation > Flashcards

Somatasensation Flashcards

1
Q

What are the three functions of Primary afferent neurones

A
  1. Exteroception
    - from external environment
  2. Proprioception
    - posture and movement
  3. Inter/enteriception
    - internal environment
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2
Q

What information about stimuli can PANs encode

A 
Modality= type of stimuli 
Intensity= total stimuli energy 
Timing= when starts/ stops 
Location= where receptors are active
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3
Q

What property of PANs allows for detection of modality

A
  1. Respond to one form of energy more than any other

2. Respond to a narrow range of stimuli

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4
Q

Describe ‘adequate stimulus’

A
  1. Type of stimulus receptors respond to under normal conditions
  2. Type of stimulus that has lowest threshold for receptor activation
  3. Primary afferent fibres carry information from a single type of receptor
  4. Verity of specialised receptor structures = submodalites
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5
Q

Describe ‘labelled line code’

A

Perceived MODALITY depends on SPECIFICITY of receptor and fibre type activated and pathway to area of cortex

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6
Q

Describe the specificity principle

A

Whatever the stimulus the perception is the same (rub eyes but see stars)

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7
Q

Describe free nerve endings

A
  1. Most body tissue
  2. ## Pain, temp and pressureCan be modified (Merkles Discs)
  3. Basal layer of epidermis
  4. Light pressure
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8
Q

Define sensory threshold

A

Minimum intensity of a stimulus to produce response from sensory system

  1. Receptor threshold
  2. AP threshold
  3. Perception threshold
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9
Q

Define saturation

A

Maximum Intensity of stimuli to produce a response from sensory system

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10
Q

Define the ‘dynamic range’

A
  1. The rage of intensities that will produce a response from receptor/ sensory system
  2. The range between threshold and saturation
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11
Q

Describe how receptor threshold can be modified

A

ADAPTATION

Receptor process when response to constant stimulus declines over time

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12
Q

What are the two types of adaptation

A

Slow
- better for coding intensity of stimulus for entire duration

Fast
- better for coding changes in stimulus intensity but not duration

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13
Q

What defines speed of conduction

A
  1. Diameter= faster AP conduction

2. Myelination

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14
Q

What are the three pathways in the ascending sensory system

A
  1. Anterolateral system
  2. Dorsal column-medial lemniscal pathway
  3. Somatosensory cerebellum pathway
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15
Q

Describe the anterolateral system

A

Includes:

  • Spinothalamic
  • spinohypothalamic
  • spinoreticular
  • spinomesencephalic
  • spinotectal

Relay of

  • pain and temperature
  • non-discriminative touch (crude non localised)
  • touch
  • pressure
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16
Q

Describe the Dorsal-column medial lemniscus pathway

A 
Includes:
- fasciculus garcilis
- fasciculus cuneatus
- medial lemmiscus
Relays
- fine touch 
- vibration 
- position sense
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17
Q

Describe the somatosensory pathways to the cerebellum

A
  • anterior
  • posterior
  • rostral
    Spinocerebelluar tracts
    + cuneocetebllar tract

Relays proprioceptive information

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18
Q

What tracts relay conscious perception

A
  1. Spinothalamic
  2. DCML
    To the ventral posterior lateral nucleus of thalamus
19
Q

Describe the transmission of discriminative touch

A
  • low threshold non-noxious
  • mechanoreceptors and proprioceptors
    DCML pathways
20
Q

Describe the transmission of pain and temperature

A
  • high threshold noxious
  • temp, itch, crude and visceral sensation
    Anterolateral pathways
21
Q

Describe the transmission of proprioception

A
  • low threshold non-noxious
  • muscle stretch, joint position, tendon tension
    Cerebellar pathways
22
Q

Describe the general organisation of sensory pathway to cortex

A
  1. Receptor
  2. PAN synapses on the dorsal root ganglion
  3. Projects to nucleus (medulla or other)
  4. Nucleus to Thalamus via lemniscus
  5. From thalamus to cerebral cortex via thalamus radiations
23
Q

What are the 3 fundamental steps in informational processing

A
  1. Receptor - transduction
  2. Neural pathways - transmission (& modulation)
  3. Cerebral cortex- perception
24
Q

Describe stage one of DCML pathways

A
  1. PANs detect sensation at receptor
  2. Enters through dorsal root
    Cell bodies in DRGA
25
Q

Describe the second stage of DCML

A
  1. Second order neurone in medulla
  2. Multiple PANs synapse
  3. Respond to mine than one class of PAN = convergence
  4. Inhibitory receptive fields (mediated though interneurones
26
Q

Describe the 3rd stage of DCML pathway

A
  1. Synapse on third order neurones in thalamus
  2. Cell bodies in VPL nucleus of thalamus
  3. Radiations via posterior limb of internal capsule
  4. Somatotopy maintained
27
Q

Where does spinoreticular tract terminate

A

Reticular formation -> cortex

28
Q

Where does the Spinomesencephalic tract terminate

A

Midbrain nuclei (including PAG)

29
Q

What is the primary nociceptive NT

A

Glutamate (excitatory)

30
Q

What do the Lateral/anterior spinothalamic tracts carry

A

These are the direct tracts
Lateral (neospinalthalmic tract)
- pain and temperature

Anterior (paleo)
Crude touch and pressure

31
Q

Describe some characteristics of the spinothalamic pathway

A
  1. Intensity: sharp dull pain
  2. Location- poor localisation
  3. Timing- ongoing, can be chronic
32
Q

What does the dorsal horn contain

A

Afferent nuclei

33
Q

What does the lateral horn contain

A

Afferent and efferent nuclear columns

34
Q

What does the ventral horn contain

A

Motor nuclei (skeletal muscle innervation)

35
Q

Describe lamina 1

A
  1. Low neuronal density

2. Variable size and distribution

36
Q

Lamina 2

A
  1. High neuronal density
  2. Small fusiform neurones
  3. Islet cells, GABA and Stalked cells
37
Q

Lamina 4

A
  1. Dendrites spread towards lamina 2 and 3

2. Transverse cells

38
Q

Lamina 5 & 6

A
  1. Fusiform and triangular neurones (medial part)

2. Medium sized multipolar neurones (lateral part)

39
Q

Where do pain and temp receptors (free nerve ending) synapse

A

The substantia gelatinosa

40
Q

What are the two ways of coding stimulus intensity

A

Frequency coding

  • increasing size of receptor potential
  • increasing stimulus intensity
  • stimulating receptive field

Population coding

  • increase no. Of neurones responding
  • recruitment of neurones with high threshold
  • stimulating more of receptive field
41
Q

Role of Acetylcholine

A
  • Primary afferent terminals innervate dorsal horn laminae I, III, IV
  • activate interneurones to modulator motor and nociceotive pathways
42
Q

Role of monoamines (Na, 5-HT, DA)

A
  • Dorsal horn, intermediate gray, ventral horn

- alagesia

43
Q

What are the 3 types of unencaplusated receptors

A
  1. Free nerve endings
  2. Modified free nerve endings like Merkles discs AND
    Hair follicle receptors
44
Q

What are the 3 types of encapsulated receptors

A
  1. Mesisners corpuscles (tactile)
    - dermal papillae of hairless skin
    - light pressure and vibration
  2. Pacini corpuscles (lamellar)
    - subcutaneous tissue, joints, fingers
    - deep pressure, stretch, vibration
  3. Ruffini endings (bulbous)
    - deep in dermis, joint capsules
    - deep pressure, stretch

Neuroscience Y2 (12 decks)

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