somatosensory Flashcards
Meissner (or Tactile) Corpuscles
Location: dermal papillae of skin, esp. palms, eyelids, lips, tongue etc.)
Modality: Light touch, texture (movement)
- Sensitive to 30-50Hz
- Rapidly adapting
encapsulated
Pacinian (or Lamellated) Corpuscles
Location: dermis, joint capsules, viscera
Modality: Deep pressure, stretch, tickle, vibration
- Sensitive to 250-350Hz
- Rapidly adapting
encapulated
Ruffini Corpuscles
Ruffini Corpuscles
Location: dermis, subcutaneous tissue, joint capsules
Modality: Heavy touch, pressure, skin stretch, joint movements. A kind of proprioceptor?
- Slowly adapting
encapsulated
Merkel (or Tactile) Discs
Location: superficial skin (epidermis)
Modality: Light touch, texture, edges, shapes
- Slowly adapting
unecapsulated
Free nerve endings
Location: widespread in epithelia and connective tissues
Modality: Pain, heat, cold
unencapsulated
Hair follicles
Location: widespread in epithelia
Modality: Varied according to type
- Both rapid and slowly adapting subtypes
unencapsulated
molecular receptors -
a molecule, usually located on the surface of a cell with a transmembrane linkage to the cytoplasm, that detects changes in molecular environment (e.g growth factors, hormones etc.)
cellular receptors-
device’ made of cells that detects changes in the body or the environmemt
phasic vs tonic
Rapidly adapting, or phasic receptors give information about changes in the stimulus e.g pacinian
Slowly adapting or tonic receptors, continue to respond as long as stimulus is present (gives info about persistence of stimulus) e.g. ruffini
how are axons from the skin named
designated by letters (A, B, C; A = fastest/largest; C = slowest/smallest).
The ‘A’ group further broken down by Greek character alpha beta delta; alpha = fastes t;delta = slowest)
how are axons from the muscle named
Axons coming from the muscles designated by Roman numerals:
I, II, III, IV; (I = largest; IV = smallest)
1st 2nd 3rd order neurones
First-order neurons detect the stimulus and transmit to spinal cord
Second-order neurons relay the signal to the thalamus, the “gateway” to the cortex
Third-order carry the signal from the thalamus to the cortex
2nd order axons cross the midline; ie are commissural
dermatome
Each sensory ganglion innervates a specific region of skin called a dermatome
derive from somites during development
In the embryo, each sensory ganglion (DRG) is associated with a specific somite and subsequently innervates the tissues arising from that somite
receptive field
The size of a receptive field can be measured by assessing the ability to discriminate two sharp points set apart at different distances
large field in arms/legs
small in fingers as discrimination high
