Peripheral Sensory Mechanisms Flashcards
What does the somatosensory system do?
Mediates sensations from the whole body surface, including the skin and deeper tissues.
What are the 4 types of mechanoreceptors in glabrous skin?
Where are their cell bodies?
German sounding ones are closer to the surface (Meissner’s and Merkel’s)
Italian sounding ones are deeper down
(Pacinian and Ruffini)
They are innervated by large myelinated axons and their cell bodies are located in the dorsal root ganglion.
Which skin layer is each mechanoreceptor localized to?
Epidermis contains:
Free nerve ending (pain, nociceptors)
Meissner’s corpuscle
Merkel cell-neurite complex
Dermis:
- Rufini corpuscle
- Pacinian
Subcutaneous layer:
Pacinian corpuscle
How does transduction occur in a mechanosensory afferent neuron?
Mechanical distortion applied to receptor, the membrane is stretched, sodium gated channels open, depolarization occurs down the axon.
Stimulus must be sufficiently large to reach the depolarization threshold.
How do slowly adapting mechanoreceptors adapt to a constant stimulus vs rapidly adapting mechanoreceptors? Which type of receptors are they specifically?
Slowly adapting will fire fast initiatially, then slower over time.
- Merkel complexes at tips of epidermal ridges and respond to indentation
- Ruffini ending are in upper dermis, with sustained response to skin movement
Rapidly adapting will fire fast initially and then cease (ie so you dont keep feeling your clothes after you put them on).
- Meissner receptors near skin surface
- Pacinian located deep in dermis and hypodermis
Pain receptors (nociceptors) however will fire faster as the pain stimulus persists.
Tactile receptors will fire as long as the stimulus is applied.
Which mechanoreceptors are most superficial in the skin?
German sounding ones: Merkel’s and Meissner’s.
Which mechanoreptors are highest density in the skin?
Meissner (40%)
Which mechanoreptor in the skin has the smallest receptive field?
Merkel
Which mechanoreptors is specialized for proprioception??
Ruffini (deep receptor)
Which mechanoreptors are most sensitive and detect vibrations in the skin?
Pacinian (least dense)
what is the two point discrimination test meant to show?
Tests spatial resolution of a nerve ending. Smaller the spatial resolution, the more discriminating and localized the nerve afferent information can be. Hairy forearm skin has reduced spatial resolution compared to fingers and hand.
What is a dermatome?
the area of skin supplied with afferent nerve fibers by a single posterior spinal root.
Where is the C1 dermatome?
It doesn’t exist. C1 is a motor nerve only.
What are the divisions of the trigeminal nerve (V)?
Ophthalmic, maxillary, and mandibular.
