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Neuroscience, Behavior and Social Sciences > Somatosensory Systems > Flashcards

Somatosensory Systems Flashcards

1
Q

Definition of proprioception

A

Limb position and movement of the body

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2
Q

Definition of transduciton

A

Conversion of energy from the stimulus to electrical

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3
Q

Definition of modality

A

Specificity of receptors to specific stimuli

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4
Q

Definition of receptive field

A

Spatial domain where stimulation excites/inhibits neurone

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5
Q

Definition of polymodal

A

Nerve endings that respond to many stimuli (mechanical, thermal, chemical)

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6
Q

What are the 5 modalities in somatosensation and what are they stimulated by

A 
Touch, 
-skin deformation and motion
Proprioception, 
-muscle length, force and joint angle
Pain
-noxious stimuli
Itch
-histamine
Visceral
-thermal, chemical, mechanical
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7
Q

What are the 4 steps involved in sensation

When do these steps not happen

A

Transduction
-Energy from stimulus converted to electrical

Transmission
-AP sent up spinal cord => thalamus => somatosensory cortex

Perception
-The sensation is felt

Modulation
-The intensity of the sensation can be increased/decreased

Perception doesnt happen when under general anaesthesia

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8
Q

What are the 2 types of sensory neurone
Where are they found
What is their function

A

Dorsal root ganglion neurones
-found in the body

Trigeminal sensory neurones
-found in the head and neck

Transduce stimuli energy
Transmit signals to CNS dorsally

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9
Q 
What are the 3 types of primary sensory neurone
Describe the
-axon diameter
-myelination
-function
-relative speed
A

Ab

  • wide axon
  • highly myelinated
  • touch, proprioception
  • v fast

Ad

  • medium axon
  • highly myelinated
  • cold, nociceptors
  • fast

C

  • tiny axon in a bundle
  • no myelination, bundles surrounded by non myelinating Schwann cells
  • warm, itch
  • vv slow
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10
Q

What primary sensory neurone is affected in diabetic neuropathy and what are the consequences

A

C fibres as they are the smallest

Lose pain sensation

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11
Q

What are the 4 main properties of stimuli

What are the effects of these properties on receptors

A

Modality

  • Receptors only respond to specific stimuli
  • Depends on presence of specific transduction molecules

Intensity

  • Encoded by firing frequency and no of activated receptors
  • Different receptors have different thresholds

Duration
-Encoded by duration of firing

Location (sensory field)
-Related to receptive fields

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12
Q

What are the 2 types of receptor

What are the properties of each receptor

A

Slowly adapting

  • APs fire when stimulus applied
  • increase stimulus intensity => increased rate of AP firing

Rapidly adapting

  • APs fire when intensity of stimulus changes
  • Increased change in intensity => increased rate of AP firing
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13
Q

What is the receptive field

How does it relate to the 2 point threshold

A

Spatial domain where stimulation excites/inhibits neurone

Different concentrations of sensory neurones =>different 2 point perceptual thresholds of different body parts
-the increased [sensory receptors] => lower 2 point threshold

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14
Q

What are the 4 types of mechanoreceptor

  • location
  • receptive field size
  • type of receptor
A

Meissner corpuscle

  • superficial
  • small
  • rapidly adapting

Merkel cells

  • superficial
  • small
  • slowly adapting

Pacinian corpuscle

  • deep
  • large
  • rapidly adapting

Ruffini endings

  • deep
  • large
  • slowly adapting
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15
Q

What are joint capsule receptors

What do they aim to do and how do they do this

A

Sensory receptors in joints transduce tension in joint capsule

Perception of angle achieved from afferent signals from muscle spindles and efferent motor commands

Aims to prevent hyperextension

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16
Q

What are the 2 types of proprioceptor in the muscles

A

Muscle spindles

Golgi tendon organs

17
Q

Describe the properties of the muscle spindles

What are they sensitive to

A

Parallel with myofibres
Sensitive to small length changes with range set by special motor input
Regulate motor control of muscle length
Contributes to the sense of limb position

Wraps around intrafusal fibres between extrafusal fibres

18
Q

Describe the properties of the golgi tendon organs

What are they sensitive to

A

Series with myofibres. embedded between collagen fibres in tendinomuscular junction
Sensitive to changes in tension

19
Q

What are the 2 types of thermoreceptors

  • what fibres are they
  • when do they start and stop responding
A

Cold

  • Ad myelinated
  • sensitive to the non damaging cold
  • paradoxical response in 45C and above

Hot

  • C unmyelinated
  • stop responding when temp in damaging range
  • some are ad
20
Q

How are nociceptors involved in temperature detection

How does intensity relate to the APs fired

A

Fire in damaging temperature range
As you increase temp, thermoreceptors stop firing and nociceptors start firing

Increased intensity of stimuli => increased APs fired

21
Q

What are the 4 modalities of nociceptor

  • types of receptor end
  • fibre type
  • stimuli
A

Thermal

  • no specialised nerve ending, bare fibres
  • Ad
  • thermal

Mechanical

  • no specialised nerve ending, bare fibres
  • Ad
  • mechanical

Polymodal

  • no specialised nerve ending, bare fibres
  • C
  • thermal, mechanical, chemical

Silent

  • no specialised nerve ending, bare fibres
  • C
  • mechanical when activated by inflammation
22
Q

If the nociceptors have no specialised nerve ending, how can they function differently?

A

Transduction molecules expressed determines nociceptor diversity

23
Q

How do dorsal root ganglia relate to dermatomes

A

Each dermatome is innervated by a single dorsal root ganglion
If sensation lost in 1 region of the skin, can pinpoint the location of the spinal lesion

24
Q

Describe the sensory pathway taken by sensory afferents via the dorsal column/medial leminiscal system

What fibre is associated with medial leminscal system

What happens when the spinal cord is damaged

A

Sensory afferent from Ab
DRG => Cuneate/gracile fascicle in SC
Cuneate/gracile nucleus in medulla

Decussation to ventral contralateral in medulla oblongata

Medial leminiscal tract => VPL nucleus in thalamus
Somatosensory cortex

Loss of sensory in ipsilateral side

25
Q

Describe the nociceptor pathway taken via the spinoreticular, spinomesencephalic, spinothalamic system

What happens when the spinal cord is damaged

A

Nociceptor afferents
DRG => dorsal horn in SC

Decussation to ventral colateral in spinal cord

Spinothalamic tract => VPL nucleus in thalamus
Somatosensory cortex

Loss of pain, temp, visceral sensation in contralateral side

26
Q

Describe the divisions of the somatosensory cortex

A

Posterior to the central sulcus
Mainly SI (primary somatosensory cortex)
SII is more lateral (secondary somatosensory cortex

Post central gyrus is between the central sulcus and post central sulcus

27
Q

Describe the 4 Brodmann areas on the post central gyrus

Where do they receive innervation from

A

4 cytoarchitectonic areas
From anterior => posterior
-3a deep tissue (muscle stretch receptor)
-3b (skin RA, SA)
-1 (largest area) (skin RA)
-2 (largest on the posterior side) (deep tissue, pressure and joint position)

28
Q

Describe the somatotopic map of the body surface on the primary cortex

A

Discontinuous and disturbed

  • Face is the most lateral
  • lower limbs are the most medial

Areas that need to receive more sensory input get a larger area of the cortex

29
Q

Describe the 2 methods of organisation on the somatosensory cortex

A

Different types of modality/sensory info is segregated and processed parallel to each other in columns according to the area innervated and the types of receptor (slow and rapidly adapting fibres)

Projections from the thalamus => info sent to Brodmann’s areas are processed serially
3a => 3b => 1 => 2

30
Q

Why is it important to process sensory info in parallel and in series

A

Info segregated in parallel so it can be integrated further in series to get a broader understanding of the sensory info

31
Q

Describe the relationship between the receptive fields and neurons of SI (primary somatosensory cortex)

A

As the inputs are processed serially, the receptive fields will converge as you get more modalities

Neurones in Brodmann’s area 1 and 2 have larger receptive fields than 3b

32
Q

Where is the location of pain processing in the brain

A

A mystery

33
Q

Describe the plastic nature of the somatosensory map (learning)

A

The more you use a body part in sensory innervation, the sensory area on the brain related to that body part increases

Somatosensory evoked potential mapping

34
Q

Describe the plastic nature of the somatosensory map (phantom pain)

A

Somatosensory map will change to accommodate for the lack of a limb
Body parts that remain => increased cortical area

35
Q

Describe the plastic nature of the somatosensory map (chronic neuropathic pain)

A

Nerve damage can cause areas affected by pain to increase but at the expense of other body parts
Areas of sensory innervation can shift

Neuroscience, Behavior and Social Sciences (50 decks)

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