What is sensation?
A feeling caused by a stimulus.
From which body parts do somatic sensations arise?
Skin, muscles, and joints.
What type of sensations come from painful viscera, micturition, and defecation?
Visceral sensations.
Which sensations include hunger, thirst, and sex?
Organic sensations.
What are special sensations?
Hearing, smell, taste, vision, and equilibrium.
From which structures are somatic sensations felt?
Somatic sensations are felt from somatic structures.
Which types of sensations are included in somatic sensations?
Somatic sensations include mechanoreceptive, thermoreceptive, and pain sensations.
What sensations do exteroreceptive sensations include?
Exteroreceptive sensations include pain, touch, and temperature.
From which receptors do proprioceptive sensations arise?
Proprioceptive sensations arise from deep receptors.
What detects mechanoreceptive sensations?
Mechanoreceptors detect mechanoreceptive sensations.
Into which two categories are mechanoreceptive sensations divided?
Cutaneous and deep mechanoreceptive sensations.
Name two types of cutaneous mechanoreceptors.
Free nerve endings and basket endings around hair follicles.
Which cutaneous mechanoreceptors are expanded endings?
Merkel discs and Ruffini corpuscles.
Which cutaneous mechanoreceptors are encapsulated endings?
Pacinian and Meissner corpuscles.
What type of receptor is the muscle spindle?
A stretch receptor in the fleshy part of skeletal muscle.
What type of receptor is the Golgi tendon organ?
A tension receptor in skeletal muscle tendons.
How is crude touch different from fine touch in localization?
Crude touch is poorly localized, fine touch is highly localized.
What kind of stimuli does crude touch require?
Crude touch requires strong stimuli.
How is crude touch examined clinically?
By touching the skin with a piece of cotton while eyes are closed.
What is tactile discrimination?
The ability to perceive two simultaneous stimuli as separate points with eyes closed.
What is the threshold distance at the tip of the tongue?
1 mm
What is the threshold distance at the fingertips?
3 mm
What is the threshold distance on the back, shoulders, and thighs?
70 mm
What is stereognosis?
The ability to identify an object without vision requiring prior learning.
What produces pressure sensation in subcutaneous tissues?
Several mechanoreceptors produce pressure sensation.
Which mechanoreceptor rapidly adapts to pressure?
Pacinian corpuscles rapidly adapt to pressure.
Which mechanoreceptor slowly adapts to pressure?
Ruffini spray-type endings slowly adapt to pressure.
What causes vibration sensation?
Repetitive stimulation of mechanoreceptors causes vibration sensation.
What frequency range do Meissner corpuscles respond to?
Meissner corpuscles respond up to 80 cycles per second.
What frequency range do Pacinian corpuscles respond to?
Pacinian corpuscles respond up to 500–800 cycles per second.
What two senses are included in kinesthetic sensations?
Sense of position and sense of joint movement are kinesthetic sensations.
Which receptors are used for position sense and which for joint movement sense?
Position sense uses Ruffini endings, muscle spindles, and Golgi tendon organs; joint movement sense uses Pacinian corpuscles and Golgi tendon organs.
What sensation produces a desire to scratch due to skin irritation?
Itch.
What can cause itch besides skin irritation?
Moving tactile stimulation or substances like histamine.
Which nerve endings transmit itch sensations?
Specialized, highly sensitive, rapidly adapting free nerve endings.
Through which fibers is itch transmitted?
Slowly conducting type C fibers.
Which spinal tract may carry itch signals?
The ventral spinothalamic tract.
What reflex does itch initiate to remove irritants?
The scratch reflex.
What is thermoreceptive sensation?
The perception of different temperatures from freezing to burning.
Where are thermal receptors located in the skin?
In the epidermis at cold spots, warm spots, and insensitive areas.
Which type of thermal spots are more numerous, cold or warm?
Cold spots are 3–10 times more numerous than warm spots.
What types of nerve endings do cold receptors include?
Krause end bulbs and some free nerve endings.
At what temperature do cold receptors stop discharging?
Cold receptors stop discharging at 35°C.
Through which fibers do warm receptors conduct impulses?
Warm receptors conduct impulses through C fibers.
What causes paradoxical cold sensation?
Stimulating cold receptors when temperature exceeds 45°C causes it.
Why does a cold metal object feel heavier than wood in Weber's illusion?
Because metal conducts heat away from skin faster, stimulating pressure-sensitive Ruffini endings.
How many orders of neurons do sensory pathways generally contain?
Three orders of neurons.
Where are sensations perceived relative to the stimulated body side?
In the cerebral cortex on the opposite side.
Which body part sensations does the gracile tract carry?
Sensations from the lower body.
Which body part sensations does the cuneate tract carry?
Sensations from the upper body.
Name one type of sensation carried by the gracile and cuneate tracts.
Tactile localization.
What sensation type do the lateral and ventral spinothalamic tracts carry?
Crude touch and pressure.
What sensations are carried by the spinal lemniscus?
Pain, temperature, tickle, itch, and sexual sensations.
Test your knowledge with 25 questions on Sensory Physiology.
1. What is a sensation?
2. Which classification correctly matches each sensory group with its sources?
Review the complete course in the study sheet for Sensory Physiology.
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