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Somatic sensory Flashcards

1
Q

Defn stimulus

A

A change detectable by the body

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2
Q

What is stimulus perceived by?

A

Receptors

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3
Q

What are the divisions of the somatosensory system?

A
  • Cutaneous (Skin) sensations
  • Visceral (internal organs and deep tissues)
  • Proprioception (awareness of position of limbs and body in space)
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4
Q

Give 4 different types of receptors.

A

Mechanoreceptors
Thermoreceptors
Chemoreceptors
Nociceptors

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5
Q

What do mechanoreceptors detect?

A

Mechanical energy e.g. stretching muscles- touch and position of the body

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6
Q

What do thermoreceptors detect?

A

Heat and cold

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7
Q

What do chemoreceptors detect?

A

Specific chemicals eg O2

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8
Q

What do nociceptors detect?

A

Pain receptors e.g. pinching, burning (free nerve endings)

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9
Q

What are the four stimulus properties?

A
  1. Stimulus modality
  2. Stimulus location
  3. Stimulus intensity
  4. Stimulus duration
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10
Q

Most common receptor on skin

A

Mechanoreceptors

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11
Q

What are mechanoreceptors sensitive to?

A

Physical distortion i.e. bending or stretching

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12
Q

5 types of mechanoreceptors

A 
Meissner’s corpuscle 
Merkel disc receptors 
Ruffini ending 
Pacinian corpuscle 
Bare nerve endings
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13
Q

Meissner’s corpuscle response and function

A

Respond to touch; are thought to be responsible for fine & discriminative touch in glabrous skin.

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14
Q

What are the Merkel disc receptors ?

A

Slowly adapting touch receptor

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15
Q

What is a Ruffini ending?

A

A slowly adapting touch receptor

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16
Q

What is a Pacinian corpuscle?

A

A rapidly adapting: vibration sensor

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17
Q

What are bare nerve endings stimulated by?

A

Pain and heat

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18
Q

Describe Meissner corpuscle

A

Connective tissue capsule, glabrous, beneath epidermis of fingers, palms, soles; low frequencies; textures; 40%

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19
Q

Describe Pacinian corpuscle

A

Encapsulated endings with fluid-filled spaces (onion-like), subcutaneous, vibration; higher frequencies than MC; 15%

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20
Q

Describe Ruffini’s capsule

A

Elongated spindle-shaped capsular; deep in skin; oriented with stretch-lines of skin; cutaneous stretching by digit/limb; proprioception? 20%

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21
Q

Describe Merkel’s disc

A

Saucer-shaped, Epidermis, dense in fingertips, lips & genitalia; shapes, edges & rough texture; 25%

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22
Q

Function of sensory transduction

A

Convert stimulus energy into a graded electrical signal (graded by strength of stimulus) - receptor potential or generator potential

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23
Q

What happens if receptor potential exceeds threhold?

A
  • Action potentials (nerve impulses)

* Stimulus strength coded by firing rate (impulses per second) and number of receptors activated

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24
Q

What are the types of receptors (persistence)?

A
  • Tonic (Slowly-Adapting; SA) receptors

- Phasic (Rapidly or Fast-adapting) receptors:

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25
Describe tonic receptors
Do not adapt or adapt slowly to a sustained stimulus : Provide continuous information about the stimulus (proportional receptors)
26
Describe phasic receptors
Adapt rapidly to a sustained stimulus and frequently exhibits an off response when the stimulus is removed: The receptor signals changes in stimulus intensity (differential receptors).
27
Defn receptive fields
Region of space in which the presence of a stimulus will alter the firing of a neuron.
28
Defn dermatome
Area of skin innervated left and right by the nerves belonging to a specific spinal segment
29
Somatosensory ascendent pathways
1st order afferent neuron 2nd order afferent 3rd order afferent
30
1st order afferent neuron
Cell body located in peripheral sensory ganglion, peripheral axon branch forms or innervates receptors, central axon synapses with a 2nd order afferent neuron
31
2nd order afferent
In spinal cord, synapses with 3rd order in thalamus
32
3rd order afferent
In thalamus, project to primary somatosensory cortex
33
What does the Dorsal Column-Medial Lemniscal Pathway carry information about?
* fine touch * vibration (e.g. from hand moving over surface) * stimuli moving on skin
34
Where does the information of the Dorsal Column-Medial Lemniscal Pathway crossover?
At the level of medulla • Left side of body to right cortex • Right side of body to left cortex
35
What does lateral inhibition involve?
Fibres from neighbouring receptive fields inhibit one another.
36
Where does most of the somatosensory information get processed?
In the parietal lobe: Primary Somatosensory Cortex (S1, Area 3b)
37
Defn somatotopic representation
Representation of body mapped on cortical surface.
38
What happens when somatosensory cortex is electrically stimulated?
It evokes somatosensory experiences
39
What does the primary somatosensory cortex receive input from?
VP thalamic area
40
What do lesions in S1 impair?
Impair somatic sensations
41
Agnosia
Inability to recognize an object even though simple sensory skills are normal
42
What is the cause of spatial neglect?
Posterior parietal lesions
43
Spatial neglect symptoms / characteristics.
* Ignore contralateral extrapersonal space * Deny body parts (incomplete dressing etc) * Incomplete copying of drawings * Body centred (recall from memory depends on view point)
44
Pain defn
An unpleasant sensory or emotional experience associated with actual or potential tissue damage.
45
Nociception defn
The processing of information about damaging stimuli by the nervous system up to the point of where perception occurs.
46
What are nociceptors?
Free nerve endings found in every tissue in the body except for the brain.
47
What are nociceptors activated by?
By intense thermal, mechanical or chemical stimuli
48
What does tissue irritation or injury cause (nociceptors)?
The release of chemicals such as prostaglandins, bradykinin, H+, K+ etc that stimulate nociceptors.
49
Threshold and frequency of nociceptors
Nociceptors have higher threshold and increase frequency of AP with increased stimulus intensity
50
3 type of gated channels
* Temperature-gated channels (thermal nociceptors) * Mechanically-gated channels (mechanical nociceptor) * Ligand-gated ion channels and receptors (chemical nociceptor)
51
What is vanilloid receptor responsive to?
Capsaicin and heat
52
Where are vanilloid receptors (VR-1 or TRPV1) found?
Found in C and Aδ fibres
53
Capsaicin and heat activation of TRPV1 in nociceptors
Activation of cation current, mediated by transient receptor potential TRPV1 channels, depolarizes nociceptors in the tongue: spicy food feels hot
54
Ad and C fibres functions
Transfer pain information with different characteristics
55
Where are cell bodies of pain fibres?
In root ganglia
56
Where do pain fibres enter the spinal cord?
Through dorsal horn
57
Spinothalamic pathway
First synapse 1. Spinal cord 2. Medulla (brainstem) 3. Thalamus
58
In the spine - touch vs pain pathway
Touch ascends ipsilaterally and pain ascends contralaterally
59
Spinothalamic vs Dorsal column fibres
Ab vs Ad and C
60
Spinal cord injury
1. Sensory ascends ipsilaterally to medulla and Pain ascends contralaterally 2. Depending on level of injury we may have opposite effects on sensory and pain perception 3. Unilateral spinal lesion may result in loss of mechanosensory perception on one side but decreased perception of pain on the other side
61
Propioception defn
Information of mechanoreceptors in our joints to determine the position of the body.
62
What is propioception coupled to?
Aalpha fibers
63
Mechanisms of pain control
1. Afferent Regulation 2. Descending Regulation 3. Endogenous Opioids
64
What occurs in afferent regulation?
Mechanosensory stimulation can reduce the activity of nociceptors → rubbing the skin when it hurts
65
What occurs in descending regulastion?
• Activation of neurons of the PAG can inhibit nociceptive neurons in the spinal cord: Stimulating PAG induces analgesia • Pathways involve release of serotonin from the nucleus raphe and noradrenaline from the locus coeruleus •Projections from PAG into the dorsal horn stimulate opioid release from inhibitory interneurons and inhibit nociceptive signalling • Opioids act centrally and peripherally
66
3 endogenous opioids
- Enkephalins - Endorphins - Dynorphins
67
Where do endogenous opioids act?
They act at brain regions involved in modulation of pain and at nociceptive fibres
68
What activates 2nd order projection neuron?
Glutamate + neuropeptides released from nociceptor
69
What blocks transmission in 2nd order neuron
Release of enkephalin from interneuron acts pre- and postsynaptically to block transmission
70
What are hot receptors coupled to?
C fibres
71
What are cold receptors coupled to?
Adelta and C fibers
72
What is the temperature pathway paralled to?
To pain pathway (spinothalamic)

Physiology (28 decks)

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