Somatosensation

Question 1

what are sensory receptors?

Answer 1

modified epithelial cells or modified dendrites of sensory neurons

Question 2

what are the two somatosensory pathways and what receptors do they use?

Answer 2

• touch and position pathway : mechanoreceptors
• pain and temperature pathway : thermoreceptors, chemoreceptors etc

Question 3

what sensations do mechanoreceptors pick up?

Answer 3

• light touch, pressure and vibration

Question 4

what are the five types of mechanoreceptors?

Answer 4

• pacinian corpuscle
• ruffini organ
• merkel disks
• meissner corpuscle
• free nerve endings

Question 5

what are the skin stimuli for the 5 mechanoreceptors?

Answer 5

• RC: stretch
• Merkel C: indentation depth; texture and fine tactical discrimination
• PC: vibration
• Meissner C: dynamic deformation light touch and low frequencies

Question 6

what can sensory receptors receive detailed information about?

Answer 6

1. intensity
2. duration
3. location
4. modulation

Question 7

how do mechanoreceptors encode stimulus intensity?

Answer 7

1. frequency coding : how many action potentials
2. population coding: how many receptors are stimulated

Question 8

what are the two types of sensory receptors that are for encoding stimulus duration?

Answer 8

slow adapting
rapidly adapting

Question 9

how is location stimulus encoded?

Answer 9

encoded by the receptive fields of the primary sensory afferent endings and then the route by which they project through the CNS

Question 10

where is the greatest 2-point discrimination and point localization accuracy located?

Answer 10

in skin areas with the smallest receptive fields and afferent nerve highest density

Question 11

what does encoding of modality mean?

Answer 11

Mechanoreceptors are specialized to detect different types of mechanical stimuli

Question 12

what is paresthesia?

Answer 12

usually painless and described as tingling or numbness, skin crawling or itching

Question 13

what is hypoesthesia ?

Answer 13

reduced sense of touch or sensation

Question 14

what is anesthesia?

Answer 14

total loss of sensation

Question 15

what does the information travel along in the touch somatosensory pathway?

Answer 15

dorsal column of the spinal cord and medial lemniscus in the brain

Question 16

what does the information travel along in the pain and temperature somatosensory pathway?

Answer 16

anteriolateral pathway in the spinal cord and spinothalamic tract of the brain

Question 17

List the steps of the dorsal column pathway

Answer 17

dorsal root ganglion —–> dorsal spinal cord —> fasciculus gracilis/cuneatis ——> nucleus gracilis/cuneatis ——> decussation in medulla ——> medial lemniscus —–> thalamus —–> ventral posterior lateral nucleus —–> primary somatosensory cortex in parietal lobe

Question 18

what are trigeminothalamic tracts ?

Answer 18

• sensations for the face have their own separate tracts for fine touch, vibration, pain and temperature

Question 19

list the steps of the trigeminothalamic tract

Answer 19

trigeminal ganglion —-> main sensory nucleus of the pons —-> decussates —–> ventral posterior medial nucleus of the thalamus —–> somatosensory cortex