PURVES NEUROSCIENCE CHAPTER 9: THE SOMATOSENSORY SYSTEM
Glabrous (hairless) regions of the skin surface are specialized to generate a high-definition neural
image of manipulated objects.
Haptics = active touching. Involves the interpretation of complex spatiotemporal patterns of stimuli
that are likely to activate many classes of mechanoreceptors.
Stereognosis = identifying an object by manipulating it with the hand.
There are four mechanoreceptive afferents:
1. MERKEL
2. MEISSNER
3. PACINIAN
4. RUFFINI
Merkel cell afferents:
- Slowly adapting fibers
- Small receptive field
- 25% of mechanosensory afferents in the hand
- Only afferents to sample information from receptor cells in the epidermis
- Lie at the tip op epidermal sweat ridges
- Express Piezo2 as a result Merkel cells and their afferent axons can sense mechanical
stimuli
- Release neuropeptides on the neurites
- Have the highest spatial resolution of the sensory afferents
- Highly sensitive to points, edges, and curvature processing information about shape and
texture.
Meissner afferents:
- Express Piezo2
- Rapidly adapting fibers
- Small receptive field
- 40% of the mechanosensory innervation of the hand
- Lie in the tips of the dermal papillae adjacent to the primary ridges and closest to the skin
surface
- More than four times as sensitive to skin deformation as Merkel afferents.
- Less special resolution than Merkel cells
- Motion detection grip control.
Pacinian afferents:
- Rapidly adapting fibers
- Large receptive field
- 10-15% of mechanosensory innervation in the hand
- Located deep in the dermis or subcutaneous tissue
- Perceptions of distant events through transmitted vibrations tool use.
Ruffini afferents:
- Slowly adapting fibers
- Large receptive field
- 20% of mechanoreceptors in the hand
- Sensitive to skin stretch.
The cell bodies of afferent fibers reside in a series of ganglia that lie alongside the spinal cord and the
brainstem and are considered part of the PNS.
Glabrous (hairless) regions of the skin surface are specialized to generate a high-definition neural
image of manipulated objects.
Haptics = active touching. Involves the interpretation of complex spatiotemporal patterns of stimuli
that are likely to activate many classes of mechanoreceptors.
Stereognosis = identifying an object by manipulating it with the hand.
There are four mechanoreceptive afferents:
1. MERKEL
2. MEISSNER
3. PACINIAN
4. RUFFINI
Merkel cell afferents:
- Slowly adapting fibers
- Small receptive field
- 25% of mechanosensory afferents in the hand
- Only afferents to sample information from receptor cells in the epidermis
- Lie at the tip op epidermal sweat ridges
- Express Piezo2 as a result Merkel cells and their afferent axons can sense mechanical
stimuli
- Release neuropeptides on the neurites
- Have the highest spatial resolution of the sensory afferents
- Highly sensitive to points, edges, and curvature processing information about shape and
texture.
Meissner afferents:
- Express Piezo2
- Rapidly adapting fibers
- Small receptive field
- 40% of the mechanosensory innervation of the hand
- Lie in the tips of the dermal papillae adjacent to the primary ridges and closest to the skin
surface
- More than four times as sensitive to skin deformation as Merkel afferents.
- Less special resolution than Merkel cells
- Motion detection grip control.
Pacinian afferents:
- Rapidly adapting fibers
- Large receptive field
- 10-15% of mechanosensory innervation in the hand
- Located deep in the dermis or subcutaneous tissue
- Perceptions of distant events through transmitted vibrations tool use.
Ruffini afferents:
- Slowly adapting fibers
- Large receptive field
- 20% of mechanoreceptors in the hand
- Sensitive to skin stretch.
The cell bodies of afferent fibers reside in a series of ganglia that lie alongside the spinal cord and the
brainstem and are considered part of the PNS.
