Meissner Corpuscle
- RA
- Tap/flutter
- Small RF
Hair follicle receptor
- SA or RA
- Motion and direction
Pacinian Corpuscle
- RA
- Vibration
- Large RF
Merkel Disc
- SA
- Touch and pressure
- Small RF
Ruffini Corpuscle
- SA
- Skin Stretch
- Large RF
Pathway of Pre-Synaptic Inhibition
- GABAergic influx of Cl- into axon
- Hyperpolarization occurs
- Less Ca2+ enters cytosol
- Less NT released
Why do we have pre-synaptic inhibition?
To improve brain’s ability to localize the signal
Neurons stacked above and below?
Fundamentally similar
Neuronal columns side-by-side
Significantly different (same body region, different modality)
What layers of cortex are important for sensory input?
III and IV are enlarged in primary sensory cortex/ main site of termination of axons from thalamus
- Main output neurons are pyramindal cells
- *IV is first area to receive input
Primary Somatosensory Cortex
- @ post-central gyrus
- Brodmann Areas 3, 1, 2
- First area for most cutaneous sensations
- Integration of information for position sense as well as size and shape discrimination
Secondary Somatosensory Cortex
- @ wall of Sylvian fissure
- receives input from S1
- Comparisons b/w objects, different tactile sensations/determining whether something becomes a memory
Characteristics of parieto-temporal-occipital association cortex (PTO)
- High levels of interpretation of sensory inputs
- Receives input from multiple sensory areas
- Analyzes spatial coordinates of self in environment
- Names objects
What typically characterizes corticofugal signals?
- Travels from cortex to lower relay stations in thalamus, medulla or SC
- Controls intensity of sensory sensitivity
- Typically inhibitory and suppresses sensory input
Doctrine of specific nerve energies
No matter where stimulated, sensation that occurs is determined by nature of sensory receptor in periphery connected to that pathway
Law of projections
No matter where stimulated, perceived sensation arises from origin of the sensation
Pain vs. nociception
Pain is just an experience, while nociception is an actual or potential injury that leads to a neural signal
Peptidergic free nerve endings
- Substance P and CGRP
- Responsive to NGF
- Most of visceral afferents
- 1/2 of cutaneous afferents (chronic inflammation/visceral pain)
Non-peptidergic free nerve endings
- No neuropeptides expressed
- Responsive to GDNF
- Few visceral afferents
- 1/2 of cutaneous afferents (diabetic neuropathy)
TRPV1
Capsaicin
50*C
TRPA1
Allyl isothiocyanate
10*C
TRPM8
Methyl
20*C
Other signaling modalities for noxious stimuli
- Nav 1.7
- P2X
- ASIC
- SP and CGRP
- Histamine
- Bradykinin
Na v 1.7
Mechanosensitive sodium channel
- Mutations responsible for both pain-insensitivity and paroxysmal extreme pain disorder
