Anatomical Substrates
of
Somatic Sensation
| The 2 principal somatic sensory systems: |
||
| Dorsal column-medial lemniscal system | ||
| Anterolateral system | ||
Dorsal Column-Medial Lemniscal System
| •Mediates mechanical sensations | |
| -touch, limb position sense, vibration sense | |
| •Well established; clinical & experimental |
| •Mediates protective sensations | |
| -Pain | |
| -Temperature (cold & warmth) | |
| -Itch | |
| •Not as definitively established as is the DC-ML system for touch |
| Peripheral somatic sensory receptors are sensitive to different stimulus qualities | ||
| Mechanical | ||
| Thermal (warm, cold) | ||
| Noxious (mechanical, thermal, polymodal) | ||
| Different receptor classes provide
input to different somatic sensory pathways |
||
| Differential thalamic and cortical localization | ||
Dorsal column-medial lemniscal system: Mechanical sensations
Anterolateral system:
Pain,
Thermal, Itch
Mechanoreceptors
are encapsulated
Nociceptors,
thermoreceptors, & itch receptors are
bare nerve endings
Key Characteristics of DRG Neurons
| Peripheral receptive field | ||
| Spatial area within which
stimulation activates the sensory neuron |
||
CNS Neurons have Receptive Fields
Key Characteristics of DRG Neurons
| Peripheral receptive field | ||
| Spatial area within which
stimulation activates the sensory neuron |
||
Mechano-
receptor
receptive
fields
Mechano-
receptor
receptive
fields
Nociceptors,
thermoreceptors, & itch receptors are
bare nerve endings
Nociceptors
respond to
noxious
stimuli
Peripheral
nerve
cross
section
Fiber Histogram: Sensory axon innervating the skin
Fiber Histogram: Sensory axon innervating a muscle
Receptor projections to systems
Brodmann’s
cytoarchitectonic
areas
Somatic Sensory Cortical
Areas
for Mechanosensations
1° Somatic Sensory Cortex Output Systems
| Early morphological specialization of DRG neurons sets stage for separate mechanosensory and pain/temp/itch systems | |