C7 Chapitre Flashcards
Which sense is usually ranked as the least preferred to lose?
Vision, followed by hearing, somatosensation, then taste and smell.
Why might we underestimate the importance of somatosensation?
Because body sensations are often not in our conscious awareness unless there’s something wrong.
Why is somatosensation essential for interacting with the world?
It enables us to manipulate objects, walk, talk, and take care of injuries.
Who was Ian Waterman and what happened to him in 1971?
Ian Waterman was a 19-year-old who lost the ability to sense touch and limb position due to an autoimmune response triggered by a virus.
What challenge did Ian Waterman face after losing somatosensation?
He became virtually paralyzed as he couldn’t control his movements without sensory feedback.
How did Ian Waterman learn to walk again?
He used vision and residual temperature sensations to relearn walking.
What metaphor is used to describe Ian Waterman’s experience of controlling his movements?
It was like being a pilot directing a ship, as paraphrased from Descartes.
What is meant by overlapping receptive fields?
It means that several somatosensory receptors can be activated simultaneously even by a very small stimulus.
What technique is used to assess tactile acuity?
The two-point touch threshold technique, initially developed by Weber.
How is the two-point threshold assessed?
By applying the two points of a drawing compass on the skin and asking if one or two points are perceived.
What body regions have the greatest tactile acuity?
The face and hands.
What does greater tactile acuity indicate?
A smaller distance is required to discriminate two points, indicating better tactile sensitivity.
What are fast-adapting (FA) receptors?
Receptors that respond strongly to the onset of a stimulus but decrease firing rate even if the stimulus is maintained.
What are slow-adapting (SA) receptors?
Receptors with sustained responses throughout the application of a mechanical stimulus.
What structures are FAII receptors attached to?
Pacinian corpuscles.
What do Pacinian corpuscles do?
They confer fast-adapting properties to FAII receptors and absorb mechanical energy.
What are FAII receptors sensitive to?
High-frequency vibration, useful for perceiving textures and manipulating tools.
Where are FAI receptors found and what are they attached to?
Mostly in the fingertips, attached to Meissner corpuscles.
What are FAI receptors sensitive to?
Movement and low-frequency vibration, useful for perceiving slip and maintaining grip.
What structures are SAII receptors thought to be attached to?
Ruffini endings.
What are SAII receptors responsive to?
Skin stretching, useful for perceiving hand conformation.
What are SAI receptors attached to?
Merkel cells.
What do SAI receptors help perceive?
Pattern, texture, and shape, useful for tasks like reading Braille.
What are proprioceptors and where are they located?
Receptors conveying mechanical force information, located in muscle spindles, Golgi tendon organs, and ligaments.
What are nociceptors?
Receptors that encode noxious (potentially injurious) stimuli.
What kind of stimuli can trigger pain?
Mechanical, thermal, or chemical stimuli.
What does the term nociception mean?
Processing of stimuli that have the potential to cause injury.
What are high-threshold polymodal nociceptors?
Receptors that respond to various noxious stimuli and require high-intensity activation.
What natural compound binds to VR1 transducers?
Capsaicin, found in hot peppers.
What sensation does capsaicin produce and why?
A burning sensation, because it activates VR1 receptors that respond to heat.
What compound and receptor are involved in sensing cold?
Menthol and CMR1 transducers.
What defines the receptive field of cutaneous or sub-cutaneous receptors?
The area of the skin where a stimulation can elicit a response in the receptor.
What happens to receptive field size as receptor concentration increases?
The receptive fields become smaller, increasing spatial resolution.
What does high spatial resolution in a skin area indicate?
A greater capacity to identify the precise location of an object touching the skin.
How does the depth of a receptor in the skin affect its receptive field size?
Receptors located deeper in the skin tend to have larger receptive fields than those on the surface.
What is meant by overlapping receptive fields?
It means that several somatosensory receptors can be activated simultaneously even by a very small stimulus.
What technique is used to assess tactile acuity?
The two-point touch threshold technique, initially developed by Weber.
How is the two-point threshold assessed?
By applying the two points of a drawing compass on the skin and asking if one or two points are perceived.
What body regions have the greatest tactile acuity?
The face and hands.
What does greater tactile acuity indicate?
A smaller distance is required to discriminate two points, indicating better tactile sensitivity.
What are fast-adapting (FA) receptors?
Receptors that respond strongly to the onset of a stimulus but decrease firing rate even if the stimulus is maintained.
What are slow-adapting (SA) receptors?
Receptors with sustained responses throughout the application of a mechanical stimulus.
What structures are FAII receptors attached to?
Pacinian corpuscles.
What do Pacinian corpuscles do?
They confer fast-adapting properties to FAII receptors and absorb mechanical energy.
What are FAII receptors sensitive to?
High-frequency vibration, useful for perceiving textures and manipulating tools.
Where are FAI receptors found and what are they attached to?
Mostly in the fingertips, attached to Meissner corpuscles.
What are FAI receptors sensitive to?
Movement and low-frequency vibration, useful for perceiving slip and maintaining grip.
What structures are SAII receptors thought to be attached to?
Ruffini endings.
What are SAII receptors responsive to?
Skin stretching, useful for perceiving hand conformation.
What are SAI receptors attached to?
Merkel cells.
What do SAI receptors help perceive?
Pattern, texture, and shape, useful for tasks like reading Braille.
What are proprioceptors and where are they located?
Receptors conveying mechanical force information, located in muscle spindles, Golgi tendon organs, and ligaments.
What are nociceptors?
Receptors that encode noxious (potentially injurious) stimuli.
What kind of stimuli can trigger pain?
Mechanical, thermal, or chemical stimuli.
What does the term nociception mean?
Processing of stimuli that have the potential to cause injury.
What are high-threshold polymodal nociceptors?
Receptors that respond to various noxious stimuli and require high-intensity activation.
What natural compound binds to VR1 transducers?
Capsaicin, found in hot peppers.
What sensation does capsaicin produce and why?
A burning sensation, because it activates VR1 receptors that respond to heat.
What compound and receptor are involved in sensing cold?
Menthol and CMR1 transducers.
What determines the conduction velocity of somatosensory receptors?
The thickness of the myelin sheath surrounding their axon.
Which somatosensory fibers have the highest conduction velocity?
Tactile (A-beta) and proprioceptive (A-alpha) fibers (70-120 m/s).
What are the conduction velocities of A-delta and C fibers?
A-delta: ~36 m/s; C fibers: 0.4-2 m/s.
What fibers were affected in Ian Waterman’s condition?
Thickly myelinated fibers responsible for proprioception and touch.
What fibers were spared in Ian Waterman’s condition?
Lightly myelinated pain and temperature fibers.
What causes congenital insensitivity to pain?
A genetic mutation impairing the development of A-delta and C fibers.
Why is pain perception essential for survival?
It serves as a warning signal to attend to injuries or illnesses.
What is the founder effect?
The loss of genetic variation in a population founded by a small number of individuals.
Where was congenital insensitivity to pain historically observed?
Brittany, France and Lanaudière, Quebec.
What is the difference between first and second pain?
First pain is sharp and fast (A-delta), second pain is slow and burning (C fibers).
Why does a numb limb lose sharp pain but not temperature perception?
Because A-delta fibers are impaired due to lack of blood, but C-fibers remain functional.
Through which part of the spinal cord do peripheral somatosensory axons enter the CNS?
Through the dorsal part of the spinal cord.
Where do pain and temperature fibers synapse after entering the spinal cord?
In the dorsal horn of the spinal cord.
What is the name of the pathway that carries pain and temperature information to the brain?
The spinothalamic pathway.
How does the spinothalamic pathway ascend in the spinal cord?
It crosses over to the contralateral side and ascends in the anterolateral quadrant.
What pathway do tactile and proprioceptive fibers follow in the CNS?
The dorsal column-medial lemniscal (DCML) pathway.
Where do tactile and proprioceptive fibers decussate (cross sides)?
At the level of the medulla, specifically at the pyramids.
What is the result of a unilateral spinal cord lesion on tactile vs. thermoalgesic sensitivity?
Loss of tactile sensitivity on the same side as the lesion and loss of pain/temperature sensitivity on the opposite side.
What is this dissociation of sensory loss called?
Brown-Séquard syndrome.
Where do tactile and nociceptive pathways interact in the spinal cord?
In the dorsal horn of the spinal cord.
What theory explains why rubbing a sore area can reduce pain?
The Gate Control Theory of Pain.
Who proposed the Gate Control Theory of Pain?
Dr. Ronald Melzack and Patrick Wall.
According to the Gate Control Theory, how is pain inhibited?
Large-diameter tactile afferents excite inhibitory interneurons, which inhibit nociceptive spinal projection neurons.
What debate did the Gate Control Theory help resolve?
The debate between intensity theories (pain from high activation of any fiber) and specificity theories (pain as a distinct sense).
What are phantom sensations and when do they commonly occur?
Phantom sensations are perceptions in a missing limb and occur commonly after amputation.
Why do phantom sensations occur even after a limb is lost?
Because the S1 region representing the limb remains intact and begins interpreting sensory ‘noise’ as ‘signal.’
What proportion of amputees report painful phantom sensations?
About 5–10%.
What factor is phantom limb pain correlated with in the brain?
The degree of reorganization in the primary somatosensory cortex (S1).
What happens in S1 after a limb is amputated?
Adjacent areas (e.g. face or shoulder) may invade the denervated area of the cortex.
What therapy methods aim to reduce phantom limb pain by ‘tricking’ the brain?
Use of prosthetics or mirror therapy.
What thalamic nuclei receive nociceptive input from the spinothalamic tract?
The ventral posterior (VP) nucleus, posterior-suprageniculate (Po-SG) complex, and medio-dorsal (MD) nucleus.
What is the function of the VP nucleus in pain perception?
It projects to S1 and contributes to the sensory-discriminative dimension of pain (location and intensity).
What is the role of the insula in pain processing?
It represents the interoceptive aspect of pain—monitoring the internal state of the body.
What is the function of the anterior cingulate cortex (ACC) in pain perception?
It serves the affective dimension of pain—i.e., how unpleasant the pain feels.
What is pain asymbolia?
A rare condition where pain is perceived but not experienced as unpleasant.
How does pain asymbolia differ from congenital insensitivity to pain?
In pain asymbolia, pain is felt but ignored; in congenital insensitivity, pain is not felt at all.
What happens if the primary somatosensory cortex (S1) is lesioned?
Patients lose tactile and nociceptive sensations, but retain the affective aspect of pain.
How would a patient with S1 damage describe painful stimuli?
As a vague unpleasant feeling in a broad area rather than localized pain.
