Cours 7 - Perception du corps - Chapitre 11 Flashcards
What are the main goals of Chapter 11?
1) Understand somatosensory system architecture (peripheral & central).
2) Know the different somatosensory receptors (touch, proprioception, pain/temp).
3) Describe the pathways for each sensory modality.
4) Identify brain areas for touch/pain and effects of lesions.
Why is somatosensation crucial despite being often overlooked?
It’s essential for interacting with the world (movement, speech, injury care).
What happened to Ian Waterman?
He lost tactile and proprioceptive feedback due to a virus, became virtually paralyzed, and learned to walk using vision and residual thermal sensation.
What are the 3 types of somatosensory sensations?
1) Touch.
2) Proprioception.
3) Pain & temperature.
What are the 3 components of a somatosensory receptor?
1) Nerve endings (may be specialized).
2) Axon (more or less myelinated).
3) Cell body in the dorsal root ganglion (DRG).
What is a dermatome?
A skin region innervated by a single nerve from a specific spinal segment.
What determines tactile acuity?
Receptive field size and receptor density—higher density = smaller fields = better acuity.
What is the two-point discrimination technique?
A test to assess tactile acuity by measuring how close two stimuli can be perceived as separate.
Which body parts have the best tactile acuity?
The hands and the face.
What are FA and SA receptors?
FA (fast-adapting): respond at onset, then reduce firing.
SA (slow-adapting): maintain response during stimulus.
Describe FAII receptors.
Attached to Pacinian corpuscles, deep in skin, large receptive fields, sensitive to high-frequency vibrations (e.g. fine texture).
Describe FAI receptors.
Attached to Meissner corpuscles, small receptive fields, sensitive to low-frequency vibration, good for grip control.
Describe SAII receptors.
Likely attached to Ruffini endings, detect skin stretch, large receptive fields.
Describe SAI receptors.
Attached to Merkel cells, small receptive fields, encode pattern, texture, shape (important for Braille).
Where are proprioceptors located?
In muscle spindles, Golgi tendon organs, and ligaments.
What are nociceptors?
Receptors for noxious stimuli (mechanical, thermal, chemical), often polymodal, with high response thresholds.
What fibers carry pain and temperature info?
A-delta (thinly myelinated) and C fibers (unmyelinated).
What causes the burning sensation of chili peppers?
Capsaicin binds to VR1 receptors on C fibers (normally detect heat).
What happened to Ian Waterman’s nerve fibers?
His A-alpha and A-beta fibers (touch/proprioception) were attacked, but his A-delta and C fibers (pain/temp) were spared.
What is congenital insensitivity to pain?
A condition caused by defective A-delta & C fibers; patients don’t feel pain and are more prone to injuries.
What is ‘first’ vs ‘second’ pain?
‘First’: sharp, fast (A-delta);
‘Second’: slow, burning (C fibers).
What is the dorsal column-medial lemniscal (DCML) pathway?
Conveys touch & proprioception. Ascends ipsilaterally, crosses in the medulla.
What is the spinothalamic pathway?
Conveys pain & temperature. Crosses in the spinal cord, ascends contralaterally.
What is Brown-Séquard syndrome?
A lesion on one side of the spinal cord causes loss of touch/proprioception on the same side and pain/temp on the opposite side.
What is the gate control theory of pain?
Large tactile fibers activate inhibitory interneurons in the spinal cord to reduce pain signals from small nociceptive fibers.
Where do most somatosensory signals go first in the brain?
The thalamus (VP nucleus). Proprioception also projects to the cerebellum.
What is S1?
The primary somatosensory cortex, located in the postcentral gyrus. It has a somatotopic map with cortical magnification for the hands and face.
What is cortical magnification?
Disproportionately large cortical areas dedicated to body parts with fine sensory resolution (e.g. fingers, face).
What causes phantom limb pain?
Maladaptive reorganization of S1—adjacent body part representations invade the denervated area, creating painful ‘phantom’ sensations.
How can phantom limb pain be reduced?
By tricking the brain into thinking the limb is still there (e.g. mirror therapy, prosthetics).
What are the three thalamic destinations for nociceptive input?
1) VP nucleus – sensory-discriminative.
2) Po-SG complex – internal state (insula).
3) MD nucleus – emotional response (ACC).
What is the role of the insula in pain?
It monitors the internal state of the body, contributing to interoception.
What does the anterior cingulate cortex (ACC) do in pain processing?
It mediates the affective (emotional) component of pain.
What is pain asymbolia?
A condition where pain is felt but not perceived as unpleasant—due to ACC lesions.
How is pain asymbolia different from congenital insensitivity to pain?
In asymbolia, pain is felt but not bothersome; in congenital insensitivity, pain is not felt at all.
What are the main takeaways from Chapter 11?
The chapter covers the architecture of the somatosensory system, types of receptors, pathways for sensory modalities, and brain areas involved in touch and pain.
