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SMP - Neurophysio Exam 1 > Lecture 13 & 14 - Somatosensory System > Flashcards

Lecture 13 & 14 - Somatosensory System Flashcards

1
Q

What are the 2 types of sensory systems? Do both of them have CNS and PSN components?

A
  1. General 2. Special YUP
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2
Q

What is another name for our general sensory systems?

A

Somato sensory systems

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3
Q

What are the 2 general sensory systems?

A
  1. Touch/proprioception 2. Temperature/pain
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4
Q

What is proprioception?

A

Sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement

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5
Q

What are the 5 special sensory systems and each of the stimulus they transduce?

A
  1. Gustatory: water soluble molecules 2. Olfactory: odorant molecules 3. Visual: electromagnetic radiation 4. Auditory: mechanoreceptive stimulus 5. Vestibular: mechanoreceptive stimulus
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6
Q

What is the main role of sensory systems?

A

Transduces stimuli into electrical signals

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7
Q

By what is pain and temperature sensed?

A

Free nerve endings

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8
Q

By what is touch/vibration sensed on the skin?

A

4 main types of mechanoreceptors:

  1. Meissner corpuscle
  2. Pacinian corpuscle
  3. Merkel’s corpuscle
  4. Ruffini endings
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9
Q

How are the special senses distributed throughout the body?

A

Discretely distributed receptors

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10
Q

How are the general senses distributed throughout the body?

A

Broadly distributed receptors

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11
Q

Do the special senses have unimodal or polymodal receptors? What does this mean?

A

Unimodal receptors: one type of receptor for each sense

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12
Q

Do the general senses have unimodal or polymodal receptors? What does this mean?

A

Polymodal receptors mostly: each receptor has multiple functions

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13
Q

What 5 stimuli can somatosensory receptors perceive?

A
  1. Pressure 2. Vibration 3. Temperature 4. Cellular distress 5. Other chemical signals
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14
Q

Where are afferent somatosensory neurons found in the PNS? 2 places

A
  1. Spinal nerves 2. Cranial nerves
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15
Q

What are the 2 specialized terminal ends of afferent somatosensory neurons?

A
  1. Mechanoreceptors 2. Nocireceptors
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16
Q

What type of receptors are mechanoreceptors? What senses do they perceive?

A

Mechanically gated ion channels Touch/vibration and proprioception

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17
Q

Are mechanoreceptor terminated afferent axons myelinated?

A

YUP

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18
Q

What type of receptors are nociceptors? What senses do they perceive?

A

Polymodal receptors Temperature and pain

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19
Q

Are nociceptor terminated afferent axons myelinated?

A

NOPE or very thinly

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20
Q

What are the 4 CNS structures that play a role in the somatosensory systems?

A
  1. Dorsal horns 2. Brainstem 3. Thalamus 4. Cortex
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21
Q

What is this?

A

Pacinian corpuscle

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22
Q

What is this?

A

Free nerve ending

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23
Q

Where are nerve endings located in the skin?

A

Superficial dermis

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24
Q

What is this? Numbers?

A

Nerve ending

  1. Dermis
  2. Epidermis
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25
Q

Which is close to skin surface: dermis or epidermis?

A

Epidermis

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26
Q

What is a receptive field test?

A

Stimulus probe is placed on the hand and electrical signals along the median nerve in the arm are recorded

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27
Q

How do the stimuli recorded in the receptive field tests evolve overtime? What does this demonstrate?

A

Bursts of APs that slow over time ⇒ touch adaptation

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28
Q

Meissner’s corpuscles:

  1. Location?
  2. Encapsulated or not?
  3. Structure?
  4. Size of receptive field?
  5. What type of sense does it perceive?
  6. Touch adaptation speed?
  7. Receptive field test result?
A
  1. Superficial dermis
  2. Encapsulated
  3. Single branched axon women into a connective tissue sheath
  4. Small receptive field
  5. Light superficial touch
  6. Rapid touch adaptation
  7. Small AP burst that decreases quickly
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29
Q

What’s this?

A

Meissner’s corpuscle

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30
Q

Merkel’s disks

  1. Location?
  2. Encapsulated or not?
  3. Structure?
  4. Size of receptive field?
  5. What type of sense does it perceive?
  6. Touch adaptation speed?
  7. Receptive field test result?
A
  1. Extreme superficial dermis
  2. Unencapsulated
  3. Contain several mitochondria and branch outward away from the epithelial tissue
  4. Small receptive field
  5. Sustained light pressure
  6. Slow touch adaptation
  7. Large AP burst that slowly decreases
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31
Q

Pacinian corpuscles:

  1. Location?
  2. Encapsulated or not?
  3. Structure?
  4. Size of receptive field?
  5. What type of sense does it perceive?
  6. Touch adaptation speed?
  7. Receptive field test result?
A
  1. Deeper in dermis than Meissner’s corpuscles and Merkel’s disks
  2. Encapsulated
  3. Branched axon in the center of the multi layer encapsulation = red onion appearance
  4. Large receptive field
  5. Deep touch
  6. Rapid touch adaptation
  7. Large AP burst with rapid decrease
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32
Q

Ruffini’s endings

  1. Location?
  2. Encapsulated or not?
  3. Structure?
  4. Size of receptive field?
  5. What type of sense does it perceive?
  6. Touch adaptation speed?
  7. Receptive field test result?
A
  1. Deeper in dermis than Meissner’s corpuscles and Merkel’s disks
  2. Encapsulated
  3. Inner bundle of branched axons with one large capsule around it
  4. Large receptive field
  5. Sustained deep touch
  6. Slow touch adaptation
  7. Large burst of APs that decrease slowly
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33
Q

What is this (yellow part)?

A

Merkel’s disks

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34
Q

What is this on the right?

A

Pacinian corpuscle

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35
Q

What’s this?

A

Ruffini’s endings

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36
Q

What’s this?

A

Ruffini’s endings

37
Q

What is the 2 point discrimination? What 2 factors is it dependent upon?

A

At various parts of the body we can distinguish 2 points very close together (eg: digits), whereas at other parts of the body (eg: back and calves) sensations must be further from one another to be distinguishable

Dependent on:

  1. Receptive field size: the smaller, the greater acuity
  2. Receptor density: the higher the density the greater the acuity
38
Q

What is lateral inhibition? How does this affect two point discrimination? What does it explain?

A

Individual cell sends APs via afferent neurons and inhibits this in neighboring lateral axons

This is what allows 2 point discrimination and explains why there is a more robust signal in the center of the receptive field

39
Q

What are the 3 proposed theories to explain how mechanoreceptors work?

A
  1. The membrane bound channels open because they are spread apart when tissue is stretched
  2. The membrane bound channels open because they are anchored to proteins which pull them apart
  3. The membrane bound channels open because there is a second messenger system that facilites this in response to mechanical stimuli
40
Q

Are free nerve endings encapsulated?

A

NOPE

41
Q

What are the smallest somatosensory fibers?

A

Nocireceptor terminated fibers

42
Q

What are the 3 types of unimodal nociceptors?

A
  1. Mechanoreceptive
  2. Chemoreceptive
  3. Thermoreceptive
43
Q

Are most nociceptors unimodal or polymodal?

A

Polymodal

44
Q

What receptors are sensitive to temperature? Aka thermoreceptive nociceptors?

A

Transient receptor potential ion channels (TRP channels)

45
Q

How many human TRP channels are there?

A

28

46
Q

How many families of TRP channels are there? What are the 3 most important ones? What are they classified by?

A

6 families

3 most important:

  1. Akyrin TRP channels (TRPA)
  2. Melastatin TRP channels (TRPM)
  3. Vanilloid TRP channels (TRPV)

Classified by temperature range

47
Q

What chemicals do TRP channels also respond to?

A

Chemicals such as allicin, menthol, camphor, and capsaicin

48
Q

How many transmembrane domains do TRP channels have?

A

7

49
Q

What are chemoreceptive nociceptive receptors sensitive to?

A
  1. NTs
  2. Chemicals released during cellular damage
50
Q

What is an example of 5 chemicals released during cellular damage?

A
  • Histamine
  • Prostaglandins
  • Substance P
  • Bradykinin
  • K+
51
Q

What does substance P on chemoreceptive nociceptors cause?

A

Hyperalgesia = abnormally heightened sensitivity to pain

52
Q

How do NSAID’s work?

A

They prevent the stimulation of chemoreceptive nociceptors by prostaglandins by preventing their production:

they inhibit cyclooxygenase 2 which converts arachidonic acid into prostaglandins and thromboxanes

53
Q

Describe the pathway of somatosensory information from somatosensory receptors to the CNS.

A

Sensory receptor → Dorsal root ganglion → Dorsal root → Dorsal horn of the spinal cord → CNS

54
Q

What are afferent fibers classified according to?

A
  • Size
  • Level of myelination
55
Q

What are the 4 types of afferent fibers?

A
  1. A alpha
  2. A beta
  3. A delta
  4. C
56
Q

A alpha afferent fibers:

  • Speed (in m/s)
  • Level of myelination
  • Function
A
  • 80-120 m/s
  • Highly myelinated
  • Proprioreceptors of skeletal muscle
57
Q

A beta afferent fibers:

  • Speed (in m/s)
  • Level of myelination
  • Function
A
  • 35-75 m/s
  • Moderate myelination
  • Mechanoreceptors of skin
58
Q

A delta afferent fibers:

  • Speed (in m/s)
  • Level of myelination
  • Function
A
  • 5-30 m/s
  • Low myelination
  • Pain and temperature perception
59
Q

C afferent fibers:

  • Speed (in m/s)
  • Level of myelination
  • Function
A
  • 0.5-2 m/s
  • No myelination
  • Temperature, pain, and itch perception
60
Q

What are the 2 types of pain? What type of afferent fiber is each felt by?

A
  1. First pain: A delta fibers
  2. Second pain: C fibers (persisting pain)
61
Q

Does the somatosensory system display dermatomes?

A

YUP

62
Q

What are the 3 ascending somatosensory pathways? Where is each located? What sensation(s) does each PRIMARILY perceive?

A
  1. Dorsal column-medial lemniscus pathway: body → touch and proprioception
  2. Spinothalamic pathway: body → pain and temperature
  3. Trigerminal pathway: face → all types
63
Q

Describe the dorsal column-medial lemniscus pathway.

A

Afferent fibers in dorsal root ganglion → dorsal root axons in dorsal column: cuneate fasciculus (upper limbs) + gracile fasciculus (lower limbs) → synapse in dorsal column nuclei in medulla (cuneate and gracile) → internal arcuate fibers with decussation → medial lemniscus (through pons) → synapse in ventral posterior nucleus of thalamus (VPN) → synapse in primary somatosensory cortex (S1)

64
Q

What does nociception refer to?

A

Pain + temperature

65
Q

Describe the spinothalamic pathway.

A

Afferent fibers in dorsal root ganglion → dorsal root axons synapse in dorsal horn of spinal cord → decussation at spinal cord level → lateral spinothalamic tract (through medulla) → synapse in ventral posterior nucleus of thalamus (VPN) → synapse in primary somatosensory cortex (S1)

66
Q

Describe the trigeminal pathway.

A

3 branches of trigeminal nerve → trigeminal ganglion → synapse trigeminal nucleus in pons → decussation at the pons → trigeminothalamic tract → synapse in ventral posterior nucleus of thalamus (VPN) → synapse in primary somatosensory cortex (S1)

67
Q

From what side of the body or face does S1 receive input form?

A

Contralateral side

68
Q

At which point of the 3 ascending somatosensory pathways do we become conscious of the somatosensory input?

A

S1

69
Q

Where is S1 located?

A

Parietal lobe, caudal to the postcentral gyrus

70
Q

What Brodman areas does S1 contain?

A
  • 1
  • 2
  • 3a
  • 3b
71
Q

Where is the secondary somatosensory cortex? What is another name for it? What Brodman areas does it contain?

A

Posterior parietal cortex (PPC)

Caudal to S1

  • 5
  • 7
72
Q

What is a homunculus? 2 types? 3 main categories?

A

Neurological “map” of the anatomical divisions of the body. Sensory and motor types

  1. Trunk/extremities
  2. Face
  3. Interior of mouth/abdominal organs
73
Q

What is the main somatosensory receptors on rodents’ noses? How are these innervated?

A

Whiskers = vibrissae

Each has 1 somatosensory barrel leading up to S1

74
Q

What are the 4 defining characteristics of the primary sensory system?

A
  1. Receives dense direct input from thalamus
  2. Neurons are unisensory
  3. Lesions produce unisensory impairment
  4. Electric stimulation evokes unisensory perception
75
Q

What is phantom limb syndrome? What is it due to?

A

This occurs when a patient has an amputated extremity but still feels a vivid/painful impression that the limb is still present.

Due to a reorganization of the cortical map (homunculus) where neighboring regions of S1 expand to cover the area that corresponded to that limb

76
Q

Where is the olfactory complex?

A

Base of forebrain

77
Q

Where is the auditory cortex?

A

Temporal love

78
Q

Where is the visual cortex located?

A

Occipital lobe

79
Q

What is agnosia? What is it due to?

What can it cause?

A

Inability to attend to/recognize contralateral stimuli despite sensory and motor systems being intact (no memory loss) due to damage to the PPC

Can cause ADD

80
Q

What are the 2 types of agnosias? 2 names for each

A
  1. Tactile = astereognosis: inability to identify an object by touch only
  2. Visual agnosia = neglect syndome: inability to identify an object by vision only
81
Q

On what 5 parts of the NS do opoids act?

A
  1. Forebrain
  2. Midbrain
  3. Brainstem
  4. Spinal cord dorsal horns
  5. Peripheral nerves
82
Q

Can our thoughts control pain? Explain.

A

YUP

Perception of pain is subject to central modulation: top down influence and is context dependent (eg: emotions and activities can influence pain levels)

83
Q

What is the gate theory of pain? How does this work?

A

Non-painful input (like rubbing) closes the “gates” to painful input, which prevents and suppresses the pain sensation from traveling to the CNS

A beta fiber from skin mechanoreceptors stimulates an inhibitory interneuron that connects to a second-order C afferent neuron

84
Q

What is congenital analgesia? What is it due to?

A

Mutation in the SCN9A gene which is responsible for the nociceptive VG-Na+ channels → inability to feel pain and a person can end up not realizing they have caused tissue damage. This is very dangerous!!

85
Q

How do the gracile fasciculus and the cuneate fasciculus differ?

A

Cuneate mediates both vibratory and position sense

Gracile only mediates position

86
Q

Does the spinothalamic tract have tactile function?

A

Yes but way less fine resolution

87
Q

By what mechanoreceptor is vibration sensed?

A

Pacinian corpuscles

88
Q

What sensory receptors

A
89
Q

What mechanoreceptors senses proprioception in distal joints?

A

Ruffini receptors

SMP - Neurophysio Exam 1 (13 decks)

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