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Neuroanatomy (OCCU 6140) > Midterm 3 > Flashcards

Midterm 3 Flashcards

Touch & Pain

1
Q

What is the function of acute pain?

A

To detect tissue damage or impending damage and/or to initiate avoidance reaction

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2
Q

Acute pain is a clearly defined stimulus and the stimulus determines the ___________ and ___________ of pain.

A

intensity and duration of pain

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3
Q

Persistence of pain, often in absence of obvious stimulus is referred to as…

A

chronic pain

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4
Q

A type of pain that may be felt in the absence of any physiological disruption

A

Chronic pain

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5
Q

The cause and mechanisms of chronic pain are largely unknown, but it often involves changes in…

A

pain pathways (neural plasticity)

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6
Q

What are some pathological examples of chronic pain?

A

De-afferentation pain (phantom limb pain)
Neuropathic pain
Thalamic pain
Trigeminal neuralgia

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7
Q

What are the 3 common properties of mechanoreceptors?

A
  1. Force produces opening of Na+ channels (transduction)
  2. If there is an adequate stimulus, depolarization occurs
  3. There is NO spontaneous activity (action potentials are only produced when adequate stimulus is present)
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8
Q

Somatic sensation originates from the activity of _____________________ whose peripheral processes ramify within the skin

A

Afferent nerve fibers

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9
Q

Different sensory modalities take different anatomical pathways within the CNS…

Discriminative touch and proprioception take which pathway?

A

Posterior column/ medial lemniscus

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10
Q

Different sensory modalities take different anatomical pathways within the CNS…

Pain, temperature and crude touch take which pathway?

A

Spinothalamic pathway

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11
Q

The process of converting the energy of a stimulus into an electrical signal so that our brain can understand it

A

Sensory transduction

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12
Q

For touch, a stimulus alters the permeability of cation channels in the afferent nerve endings, this generates a de-polarizing current called the _____________________

A

Receptor potential

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13
Q

For touch, a stimulus alters the permeability of cation channels in the afferent nerve endings, this generates a de-polarizing current called the receptor potential.

If sufficient in magnitude, the receptor potential reaches threshold for the generation of action potentials in the afferent fiber.

The action potentials fire at a rate that is proportional to the magnitude of…

A

Depolarization

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14
Q

When thinking of touch and the generation of action potentials, the threshold potential is better known or thought of as the __________________.

A

Receptor potential

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15
Q

There are two types of afferent nerves, distinguished by their ‘endings’, what are they?

A

Free nerve endings (pain)
Encapsulated endings (non-painful sensation, surrounded by specialized receptor cells, mechanoreceptors)

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16
Q

What are the 4 types of mechanoreceptors for this course?

A
  1. Meissner corpuscle
  2. Merkel cell neurite complex
  3. Ruffini ending
  4. Pacinian corpuscle
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17
Q

What are the 3 common properties of mechanoreceptors?

A
  1. Force produces opening of Na+ channels
  2. If there is adequate stimulus depolarization occurs
  3. There is no spontaneous activity, action potentials are produced when adequate stimulus is present
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18
Q

Describe the route of the PCML pathway (posterior column/medial lemniscus)

A

Sensory pathway, it conveys sensation of touch, vibration, pressure, two-point discrimination and proprioception.

Consists of two parts (posterior column which runs from the spinal cord to the medulla, and the medial lemniscus which runs as a continuation from the medulla to the primary somatosensory cortex of the postcentral gyrus).

The posterior column is formed by two large fasciculi (fasciculus Gracilis and cuneatus) which gather sensory information from the body’s periphery and send the information to superior cerebral structures.

When an AP is generated by a mechanoreceptor in the tissue, the impulse travels along the peripheral axons of the first-order neuron, through the dorsal root and into the posterior horn.

The fasciculi ascend the spinal cord to reach the lower (closed) part of the medulla oblongata. In the medulla, axons in the fasciculus Gracilis synapse with the Gracilis nucleus and same for the cuneatus. The neurons of these two medullary nuclei are second-order neurons.

Their axons cross over to the other side of the medulla and are named internal arcuate fibers (the crossing is known as sensory decussation)

The internal arcuate fibers eventually form the medial lemniscus.

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19
Q

Name the first-order neurons and second-order neurons in the posterior column/medial lemniscus pathway

A

First-order neurons: Fasciculus gracilis and fasciculus cuneatus

Second-order neurons: Nucleus gracilis and nucleus cuneatus

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20
Q

In the posterior column/ medial lemniscus pathway, after decussation, the internal arcuate fibers form the medial lemniscus which ascends towards the _______________________ nucleus of the thalamus and then projects onwards to the primary somatosensory cortex.

A

ventral posterolateral nucleus

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21
Q

Name the four steps of sensory transduction

A
  1. A stimulus alters the permeability of cation channels in the afferent nerve endings (mechanoreceptors)
  2. This generates a de-polarizing current called the receptor potential
  3. If sufficient in magnitude, the receptor potential reaches threshold for the generation of action potentials in the afferent fiber
  4. The action potentials fire in a rate that is proportional to the magnitude of depolarization
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22
Q

Name four differences between different types of mechanoreceptors

A
  1. Axon diameter
  2. Receptive field size
  3. Temporal dynamics of response
  4. Quality of somatic stimulation
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23
Q

Axon diameter determines ___________________

A

Conduction speed

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24
Q

The area of skin surface over which stimulation results in a significant rate of action potentials, this distinct functional property is referred to as the __________________ of a mechanoreceptor.

A

Receptive field size

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25
Q

Some afferents fire rapidly, whereas others generate sustained discharge, this functional property is referred to as…

A

Temporal dynamics of response

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26
Q

A functional property of mechanoreceptors which allows the brain to determine the location of the stimulus

A

Receptive field

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27
Q

Every sensory neuron has a ____________________: the region of skin that influences that neuron

A

receptive field

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28
Q

Receptive fields of first-order afferents vary in ‘size’, the ‘size’ of the receptive field depends on…

A

How widespread the branching (ramifying) of its terminal are

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29
Q

In terms of receptive fields of afferents, what size field is more accurate/precise in detecting the information on location of the stimulus?

A

Small receptive fields are more precise in detecting the information on location of the stimulus on the skin.

Large receptive fields can’t give accurate information about where the stimulus is within this field.

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30
Q

What is spatial acuity?

A

Ability to distinguish different points on the skin

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31
Q

What is spatial acuity dependent on?

A
  1. Innervation density (how many receptors there are in an area)
  2. Receptive field size of the receptor
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32
Q

Two-point discrimination is a test of…

A

Spatial acuity

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33
Q

Receptors differ in their ability to sustain discharge, this allows for information to be obtained about _______________ and ________________ aspects of a stimulus

A

Static and dynamic aspects of a stimulus

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34
Q

Receptors differ in their ability to sustain discharge, what is the functional reason behind this property?

A

Allows for information to be obtained about static (slowly adapting) and dynamic (rapidly adapting) aspects of a stimulus

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35
Q

Merkel and Ruffini mechanoreceptors have the ability to sustain discharge statically or dynamically?

A

Statically

36
Q

Meissner and Pacinian mechanoreceptors have the ability to sustain discharge statically or dynamically?

A

Dynamically

37
Q

Explain the characteristics of the Meissner, Merkel, Pacinian and Ruffini receptors/corpuscles receptive field sizes

A

Meissner: Small
Merkel: Small
Pacinian: Large
Ruffini: Large

38
Q

Explain the characteristics of the Meissner’s corpuscle

A
  • Dense innervation
  • 40% of mechano-sensory innervation of the hand
  • Lie in the tips of dermal papillae closer to skins surface
  • Small receptive field (high quality of stimulus)
39
Q

Explain the characteristics of the Merkel receptors

A
  • 25% of mechano-sensory innervation of the hand
  • Increased number in the fingertips
  • Lie in the fingerprint ridges on the fingers’ surface
  • Small receptive field (highest spatial resolution)
  • Sensitive to points, curves and edges (form and texture)
40
Q

Explain the characteristics of the Pacinian corpuscles

A
  • 10-15% of mechano-sensory innervation of the hand
  • Located in the dermis or subcutaneous layer
  • Large receptive field (boundaries are difficult to define)
  • Well suited to detect vibration through objects
41
Q

Explain the characteristics of the Ruffini corpuscles

A
  • 20% of mechano-sensory innervation of the hand
  • Located deep in the skin and in ligaments and tendons
  • Sensitive to stretching of the skin produced by digit/limb movement
  • Aids in localization of finger position (and conformation of the hand)
42
Q

How does the CNS figure out if a stimulus is moving (direction, speed, etc.) across the skin?
Hint: what do Merkel, Meissner, Pacinian and Ruffini receptors/corpuscles contribute?

A

Meissner: Coarseness
Merkel: Details
Pacinian and Ruffini: No detail but rather tracking of finger movement and position (proprioception)

43
Q

The amount of brain devoted to a body part is related to ______________.

A

Tactile acuity

44
Q

The primary cortex contains the Brodmann areas 1, 2, 3a and 3b, explain the functions and characteristics of these areas

A

All of the Brodmann areas are concerned with sensation and each area has a medial to lateral representation of the body.

Functional properties of neurons in each area are distinct (cytoarchitecture is also distinct).

Areas 1 and 3b: respond to cutaneous stimuli
Area 2: responds to proprioception
Area 3a: responds to tactile and proprioception

45
Q

If someone has damage/lesion to the Brodmann area 3b, they will have deficits in…

A

in all forms of tactile sensation (info from cutaneous receptors is not passed to areas 1 and 2)

46
Q

If someone has damage/lesion to the Brodmann area 1, they will have deficits in…

A

perceiving the texture of objects (info from 3b intact, so can perceive touch)

47
Q

If someone has damage/lesion to the Brodmann area 2, they will have deficits in…

A

perceiving size and shape of objects (info from 3b and 1 intact, so can perceive touch and texture)

48
Q

In the secondary somatic sensory cortex: projections to limbic structures (amygdala and hippocampus) are integral in what functions?

A

Tactile learning and memory

49
Q

In the primary sensory cortex, projections to pre-motor and motor areas are integral for the integration of ___________ and ____________ information.

A

sensory and motor information

50
Q

Nociceptors, similar to mechanoreceptors… (3 factors)

A

Arise from cell bodies in the dorsal root ganglion, transduce a variety of stimuli into receptor potentials to trigger action potentials, and follow frequency (rate) coding (increased stimulus intensity results in increased depolarization of receptors, increased firing rate of pain afferents)

51
Q

There is a wide variety of nociceptors, name 4 types

A
  1. Mechano-nociceptors
  2. Thermo-nociceptors
  3. Chemo-nociceptors
  4. Polymodal nociceptors
52
Q

Name an example of a nociceptor that is specific to one type of stimulus and a nociceptor that is non-specific

A

Specific to one-type of stimulus: mechano-nociceptors, thermo-nociceptors, chemo-nociceptors

Non-specific: polymodal nociceptors

53
Q

Nociceptors are slow at relaying signals in comparison to other neurons/afferents, true or false?

A

True

54
Q

The two types of pain experienced are due to two different sized afferents, the first is ________________ and the second is __________________

A
  1. Fast (sharp) - 5-30 m/s
  2. Slow (dull/burning) - <2 m/s
55
Q

Nociceptors are different from other afferents in which ways? (4 factors)

A
  1. Specialized for damaging (nociceptive) stimulation
  2. Information travels much more slowly (fast pain vs slow pain)
  3. Localization is relatively poor (due to widespread branching of afferents in the skin, receptive field)
  4. Repeated of prolonged stimulation often leads to a stronger response (sensitization), rather than adaptation
56
Q

The perception of pain (nociception) depends on specifically dedicated receptors and pathways, NOT excessive stimulation of the same receptors that generate other somatic sensations, true or false?

A

True

57
Q

What are the similarities between nociceptors and other afferents? (2)

A
  1. Transduce a variety of stimuli into receptor potentials (trigger action potentials)
  2. Frequency coding (the stimulus intensity is proportional to the depolarization of receptors and the firing rate of receptors)
58
Q

Which pathway relays pain, temperature and crude touch sensations?

A

Spinothalamic pathway

59
Q

Nociceptors are the first-order sensory neurons that make synaptic contact with second-order neurons in the dorsal horn of the spinal cord, as an alternative to spinal cord nuclei there are identified layers (laminae) within the spinal cord where cells are grouped according to their structure and function, describe lamina I, II, and V

A

Lamina I: corresponds to the marginal zone, tip of the dorsal horn, cells respond to noxious and thermal stimuli, sends info to the brain by the contralateral spinothalamic tract

Lamina II: corresponds to the substantia gelatinosa, sensation of noxious and non-noxious stimuli and modulating sensory input (painful or not), sends info to lamina III and IV

Lamina V: base of dorsal horn, relays sensory, including nociceptive information to the brain via the contralateral spinothalamic tracts

60
Q

What is the difference and similarity between A-delta and C-nerve fibers?

A

A-delta fibers are myelinated whereas C-fibers are not.

Both A-delta and C-nerve fibers are involved in the sensation of pain (nociception).

61
Q

Name which type of nerve fiber input (A-delta or C-nerve) is related to lamina I, lamina II and lamina V

A

Lamina I: A-delta fiber
Lamina II: C-nerve fiber
Lamina V: A-delta fiber

62
Q

Many neurons in the dorsal horn of the spinal cord are specialized for transmission of visceral (internal) pain, true or false?

A

False, very few neurons in the dorsal horn of the spinal cord are specialized for transmission of visceral pain

63
Q

Spinal visceral afferents can travel with somatic afferents and are represented (at higher levels) as somatic pain, this is called…

A

Referred pain

64
Q

We recognize visceral pain, but it is conveyed centrally via ______________________ that are also concerned with cutaneous pain.

A

dorsal horn neurons

65
Q

Sometimes the disorder of an internal organ is perceived as cutaneous pain, true or false?

A

True

66
Q

What are the two aspects of pain?

A

Sensory-discriminative
Affective-motivational

67
Q

What is the difference in the pathways of sensory-discriminative (first pain) and affective-motivational (second pain)?

A

Both involve the spinothalamic tract and are parallel pathways.

Sensory-discriminative pain follows the spinothalamic tract, the neurons then synapse onto second-order neurons in the ventral posterior lateral nucleus (VPL) of the thalamus , these neurons communicate with the primary sensory cortex.

Affective-motivational pain follows the spinothalamic tract, the neurons involved in this pain synapse onto the anterior nucleus of the thalamus, these neurons communicate with the anterior cingulate cortex and the insular cortex.

68
Q

Explain two ways in which relief of pain is achieved via utilization of descending pathways to modulate the ascending transmission of pain information

A
  1. Gate control theory
  2. Central mechanisms theory (endogenous opioids)
69
Q

Explain the gate theory relating to pain control

A

According to this theory the body has a gate that can either allow or block pain signals from reaching the brain.

Transcutaneous electrical nerve stimulation (TENS) is a method that uses electrical impulses to activate the pain gate mechanism and inhibit pain signals going up to the brain, thus reducing the sensation of pain.

70
Q

Name the three endogenous opioids

A
  1. Enkephalins
  2. Endorphins
  3. Dynorphins
71
Q

Endogenous opioids are present in the ______________________

A

Periaqueductal gray midbrain

72
Q

Opioid-sensitive neurons reside in the ___________________ of the spinal cord

A

dorsal horn

73
Q

If an endogenous opioid is released in the dorsal horn the descending input excites local circuit neuron resulting in the release of the endogenous opioid onto the receptive terminal, how does this system achieve relief from pain?

A

This system inhibits the release of neurotransmitter, thus decreasing the signal of pain sent to higher centers in the CNS

74
Q

Explain peripheral sensitization

A

Peripheral sensitization involves the interaction of nociceptors with ‘inflammatory soup’ of substances released due to tissue damage

75
Q

Explain the ‘inflammatory soup’ associated with peripheral sensitization

A

Nociceptors release peptides and neurotransmitters, this causes vasodilation, swelling, and histamine release.

Non-neuronal cells augment the inflammatory process.

76
Q

Explain allodynia

A

Allodynia (painful sensation to non-painful stimuli) outside zone of terminal branching (of nociceptors) - not due to peripheral mechanisms - must be centrally mediated

77
Q

What is allodynia?

A

Stimuli that, under normal conditions, would be innocuous, activate second-order neurons in the dorsal horn that would typically only respond to nociceptive information.

78
Q

Explain the process of central sensitization

A

Immediate-onset activity-dependent increases in the excitability of neurons in the dorsal horn of the spinal cord following high levels of activity in the nociceptive afferents.

Activity levels in the nociceptive afferents that were subthreshold prior to the sensitizing event become sufficient to generate action potentials in dorsal horn neurons, contributing to an increase in pain sensitivity.

Although central sensitization is triggered in dorsal horn neurons by the activity of nociceptors, the effects generalize to other inputs that arise from low-threshold mechanoreceptors.

78
Q

With tissue healing, sensitization (peripheral and central) increases, true or false?

A

False, with tissue healing, sensitization (peripheral and central) decreases

79
Q

Damage to nerve structures themselves (afferent fibers/central pathways) result in ___________________ pain.

A

Neuropathic pain

80
Q

Hyperalgesia is related to _______________ sensitization.

A

Peripheral sensitization

81
Q

Allodynia is related to ____________ sensitization.

A

Central sensitization

82
Q

Increased pain sensation in the area surrounding an injury refers to ______________.

A

Hyperalgesia (peripheral sensitization)

83
Q

Endogenous opioids alter descending or ascending control to relieve sensations of pain?

A

Descending control, descending pathways can modulate the transmission of pain information

84
Q

Sustained, abnormal input leads to long-lasting changes in synapses in the pathway, this process is referred to as…

A

Sensitization

Neuroanatomy (OCCU 6140) (20 decks)

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