Somatosensation and Pain Flashcards by Yan Lin

When does Nociception occurs?

Occurs with pain
Also with heat and cold
Often depends on the magnitude of the sensation

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Where is nociception found?

throughout the body, including the skin,
muscles, joints, bone, and viscera (internal organs).

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What is the adaptation reason of nocieception?

Alert the body to potentially damaging stimuli, such as extremes in
temperature and pressure, and injury-related chemicals

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What are the two fibres involved in nocieception?

A-delta (some of the A type fibers): These are small, myelinated nerve
fibers that transmit sharp, fast pain sensations.
C fibers: Unmyelinated nerve fibers that transmit dull, burning pain
sensations.

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What is the definition of noxious?

perceived as
harmful i.e.
poison pain etc

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What is the definition of exogenous?

having an
external cause
or origin

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What is the definition of ganglion?

body of nerve
cells

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What is the pathway of exogenous pain producing stimuli?

1)Mechanical 2)Chemical 3)Thermal 4)Electrical
1.Primary afferent nociception
2. dorsal roots ganglion
3. Neuron
4. Spinal cord
5. Spinthalamic tract
6. Thalamus
7. Brain cortex

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What consists of The somatosensory system?

thermoception & nociception

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Where does Thermoreceptors located?

on the tips
of free nerve endings(pain, hot and cold)

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What are the characteristics of Thermoreceptors ?

Different thermoreceptors have
different activation thresholds
Encode subtle differences in temp
from cold → hot

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What did David Julius win the Nobel Prize?

they were able to identify the single gene that made cells
sensitive to capsaicin (as well as hot temperatures)

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Suppose an experimenter decides to test the effects of a new drug on pain
perception. To do this, participants are administered capsaicin
subcutaneously while sensory nerve activation is also measured.
Increasing concentrations of capsaicin are administered and participants
are asked to rate pain intensity from 1-10 (1 being very weak and 10
being the worst pain imaginable). The psychophysical method being used
in this experiment is:

Magnitude estimation (also referred to as magnitude scaling)(rating)

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What are some brief details of The somatosensory system?

Transient Receptor Potential (TRP) channels
BRIEF: Family of ion channels that pass Na+ and Ca2+
ions
Many different kinds
Some are activated by cold, some by cool, some by
warm, some by hot temperature(different
channels have different temperature sensitivities)
NB there are many different receptors/channels that
contribute to thermoception
Channel opens at particular temperature; ions flow causing depolarisation; triggers an
action potential in the sensory nerve

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What is definition of chemaesthesis?

– involves receptor activation on free nerve
endings. (i.e., Cranial Nerve V with chemical substance on
the facial skin)

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Can you find free nerve ending in all corpuscles?

Free nerve endings found on
Merkel’s disks (on fingers) are
very common.
Ruffini and Meissner’s corpuscles
are mechanoreceptors that
contain encapsulated nerve
endings (not free nerve endings)

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Is chemaesthesis only associated with the face?

No, it occurs on all skin
* Cranial Nerve V (Trigeminal Nerve) innervates the
skin of the face, the nasal cavity, mouth, cornea
and conjunctiva of the eye
* Innervation around eye is very sensitive to
chemical stimuli (low threshold)

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What does nociception serve?

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Serves as a safety surveillance system
- initiates protective mechanisms: tearing, mucus,
salivation, coughing,
sneezing, vasodilation/flushing

How does the chemaesthetic stimuli convert to the pain (nociception)?

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Pain is always subjective and thus is modulated by past experiences and
setting, affect, cognitive influences, gender and even cultural
expectations

What are the properties of the dorsal leminiscal system?

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Touch sensation: high sensations:high degree of localisation of stimulus.
-fine graduation in intensity of stimulus(vibrations)
-Sensation of movement aganist skin
-Fine positional and pressure sensation

What are the properties of anterolateral spinothalamic system?

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Thermal sensations:cold and warm
-Pain sensations.
-Crude pressure and touch sensations
-Tickle and itch sensation
-Sexual sensations

What is the route of dorsal leminiscal system?

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1.Different spinal levels such as Lower limbs ie
ankle, foot
2.Posterior horn aka dorsal horn
3.Sensory input goes
through dorsal column nuclei
crosses in the medulla
then to VPN (thalamus)
then cortex
4.Thalamus: ventral posterior
thalamic nucleus (VPN)
5. Cortex(S1and S2 on parietal lobe)

What is Rolandic
fissure?

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Central sulcus separates the frontal lobe
from the parietal lobe.

What is route of spinothalamic tract?

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Thermoreceptors on sensory nerve free endings
1
st order (afferent) neuron projects to spinal
cord
Decussate (cross over) in the spinal cord
Synapses with second order neuron, which
travels to thalamus
Synapses with 3rd order neuron which travels to
primary somatosensory cortex (SI)

What is pain?

An unpleasant sensory or emotional experience associated with actual or potential tissue damage, or described in terms of such damage

What are the three types of pain?

- abrupt/strong cutaneous sensation, tissue damage - damage to neural structures, neural supersensitivity - physical pain of psychological origin

What experiment is used to test nociceptive fibres?

microneurography experiment

Which two direction does thalamus go?

Medial thalamus projects to frontal cortex, and lateral thalamus projects to SI and SII somatosensory cortex

What is pain matrix?

a set of brain areas including SI & SII, prefrontal cortex, anterior cingulate cortex, thalamus, insula (primary) that consistently respond to painful stimuli. Some would add limbic system (ie., amygdala: emotion) also (hippocampus).

What happens in Singer and coworkers using fMRI?

(1)Receive painful stimulation vs (2)Watch a person receiving painful stimulation

What is the result of this experiment?

When you see someone in pain, the non-sensory parts of the matrix are activated. Because of empathic response, does not involve the somatosensory cortex; does activate the insula and ACC

What happens in study about the pain and empathetic comments and its result?

Activation of pain matrix(including insula) with the pain stimuli, they are not correlate S1 and S2

What is the key finding of nociception and pain matrix?

-‘pain matrix’ brain regions respond to nociceptive somatosensory, non-nociceptive somatosensory, auditory and visual stimuli.

What happens in the study by Salomons et al.?

Noxious mechanical stimuli given to healthy individuals and individuals with a genetic mutation that makes them unable to sense pain.

What's result of Salomons' study?

Similar activity in ‘pain matrix’ brain regions (thalamus, insula, S2, and anterior cingulate cortex) of both groups Not primary areas though (S1, specially for pain fibres)

What is the definition of perception?

when you become aware or conscious of pain, which is the perception of pain

What does the experience of the pain requires?

Interactions between somatosensory, affective and cognitive systems Different cortical circuits involving the anterior cingulate: some for pain and others for attention

What is afferent system?

Involved in processing of pleasant and unpleasant information and also emotional processing.

What are diffuse areas with chronic pain?

Pain matrix

What is referred sensation?

sensations (such as pain) coming from a different body part than the injured or stimulated one

What happens in the study about Consciousness and the perception of pain?

Those with minimally conscious state MCS still feel pain Areas showing greater activity in MCS(minimally conscious state) compared to persistent vegetative state (PVS) (persistent vegetative state, no no awareness of self or environment)in response to noxious stimulus: the pain neuromatrix was more activated with MCS

A 42-year-old man is brought to the emergency department after falling from a ladder. An MRI scan finds a bilateral lesion in the dorsal portion of the spinal cord at T12. What impact would this lesion have on his sensory and motor systems?

* Bilateral loss of pain and temperature sensations from the lower limbs * Bilateral loss of fine touch, vibrations, and proprioception sensations at the level of the lesion and below

A 37-year-old woman was involved in a motorcycle accident and sustained a penetrating injury to the right side of her neck. Imaging reveals a unilateral lesion of the spinal cord on the right side at the C5–C6 level, affecting both the dorsal and ventral portions of the spinal cord. What impact would this lesion have on her sensory and motor systems?

* Loss of pain and temperature sensation on the left side of the body for regions BELOW the lesion * Loss of pain and temperature sensation on the right side of the body at the level of the lesion * Loss of motor output for the right upper and lower limbs * Ipsilateral loss of fine touch and proprioception on the right side of the body (including regions below the lesion)

Somatosensation and Pain Flashcards

(43 cards)