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Physiology

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Central Nervous System

Question
17 out of 20
 

The distance by which two touch stimuli must be separated to be perceived as two separate stimuli is greatest:



A The lips

B The palm of the hand

C The back of scapula

D The dorsum of the hand.

Ans. C The back of scapula

Touch:

  1. Receptors

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

  1. Transmission

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.

  1. 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 Qwhere 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.

Central Nervous System Flashcard List

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