Central Nervous System
The distance by which two touch stimuli must be separated to be perceived as two separate stimuli is greatest:
|B||The palm of the hand|
|C||The back of scapula|
|D||The dorsum of the hand.|
a. Meissner corpuscles and Paccian corpusclesare rapidly adapting touch receptors Q
b. Merkel disks (Iggo dome Receptor) and Ruffini endings are slowly adapting touch receptors Q
A. Touch receptors are most numerous in the skin of the fingers and lips and relatively scarce in the skin of the trunk. Q
a. "The A β-sensory (large diameter myelinated) fibers that transmit impulse from touch receptors to CNS"
b. Some touch impulses are also conducted via C-fibers (unmyelinated).
c. Tracts - involved in transmission
i. Dorsal column - mediallemniscal system
1) Requiring a high degree of localization of the stimulus and transmission of fine gradation of intensity
ii. Antero-lateral spine-thalamic tract :
1) Crude touch and crude localization.
- Two-point discrimination
a. The minimal distance by which two touch stimuli must be separated to be perceived as separate is called the two-point threshold. It depends upon touch plus the cortical component of identifying one or two stimuli.
i. a. Smallest where the touch receptors are most abundant as on finger tips Q→where two stimuli be resolved if they are separated as little as 3 mm. Q
ii. Largest where the touch receptors are scarse as on the back Qwhere two stimuli must be separated by 65 mm or more before they can be distinguished as separate points.