The somatosensory system

Question 1

What is the purpose of the somatosensory system?

Answer 1

• provides information about touch, pressure, temperature and pain
• concerns sensations on the surface of the skin and inside the body

Question 2

What are the three interacting somatosensory systems?

Answer 2

• Exteroceptive system
• Interoceptive system
• Proprioceptive system

Question 3

What is the purpose of the extereoceptive system?

Answer 3

• cutaneous senses
• responds to stimuli applied to the skin

Question 4

What sensations are associated with the extereoceptive system?

Answer 4

• touch
• temperature

Question 5

What is the purpose of the interoceptive system?

Answer 5

• provides information about conditions within the body
• responsible for the efficient regulation of the internal milieu of the body

Question 6

What senses are associated with each division of the somatosensory system?

Answer 6

• extereoceptive: cutaneous senses
• interoceptive: organic senses
• Proprioceptive: kinesthesia

Question 7

What sensations are associated with the interoceptive system?

Answer 7

• heart rate
• breathing
• hunger
• bladder

Question 8

What is the purpose of the proprioceptive system?

Answer 8

• monitors information about the position of the body, its posture and its movements

Question 9

How does the proprioceptive system obtain its information?

Answer 9

• through the tension of muscles in the body

Question 10

How are the cutaneous sensations sensed?

Answer 10

• through sensory neurons that will be dedicated specifically to one sensation

Question 11

What are the stimuli that can be encoded by the cutaneous senses?

Answer 11

• pressure
• vibration
• temperature
• pain

Question 12

What causes the sensation of pressure/touch?

Answer 12

mechanical deformation fo the skin

Question 13

What causes the sensation of vibration?

Answer 13

moving fingers across a rough surface

Question 14

What causes the sensation of temperature?

Answer 14

objects that heat or cool the skin

Question 15

What causes the sensation of pain?

Answer 15

Many elements, but mostly tissue damage

Question 16

What are the three layers of the skin? Go from outside to inside.

Answer 16

1) epidermis
2) dermis
3) hypodermis

Question 17

What are the different types of sensory neurons that are found in the skin?

Answer 17

• Merkel’s disks
• Ruffini corpuscules
• Free nerve endings
• Pacinian corpuscules
• Meissner’s corpuscules

Question 18

What is the particularity of meissner’s corpuscules?

Answer 18

They are only found in glabrous skin

Question 19

How is the epidermis sustained in oxygen?

Answer 19

• through direct contact with the air

Question 20

Is the perception of temperature localized?

Answer 20

No

Question 21

What are the different types of thermal receptors?

Answer 21

• respond to warmth
• respond to coolness

Question 22

What can activate the thermal receptors?

Answer 22

temperature OR liguands

Question 23

What type of cutaneous sensory neurons are thermal receptors?

Answer 23

free nerve endings

Question 24

Where are situated Merkel’s disks?

Answer 24

on the epidermis

Question 25

What is the neuronal structure of Merkel's disks?

Answer 25

Ion receptors Activated by strong touch and pressure

Question 26

What do merkel's disks sense?

Answer 26

Local skin intendation (that is strong)

Question 27

What senses are Ruffini corpuscules associated to?

Answer 27

Kinesthetic senses (kinesthesia, proprioceptive system)

Question 28

What are Ruffini corpuscules sensitive to?

Answer 28

Stretch

Question 29

What information do ruffini corpuscules provide?

Answer 29

- finger position - movement

Question 30

What are pacinian corpuscules sensitive to?

Answer 30

Skin vibrations

Question 31

Where are pacinian corpuscules situated?

Answer 31

hypodermis

Question 32

What are meissner's corpuscules sensitive to?

Answer 32

very light touch/pressure

Question 33

What do Meissner's corpuscules detect?

Answer 33

- very light touch - Localized edge contour

Question 34

What are free nerve endings sensitive to?

Answer 34

- temperature - pain

Question 35

What type of information do free nerve endings provide?

Answer 35

- diffuse/non localized sensation - slow transfer information

Question 36

What type of sensory neurons allow to read Braille?

Answer 36

Meissners corpuscules

Question 37

What is the thermal grid illusion?

Answer 37

- alternance of two slightly warm and slightly cold rods - brain is unable to process such close opposing signals - sensation of burning heat

Question 38

What are high-threshold mechanoreceptors?

Answer 38

- pressure receptor cells - free nerve endings that respond to intense pressure - touch-sensitive ion channels

Question 39

What are the different stimuli that pain receptors may respond to?

Answer 39

- intense pressure - extreme heat - the presence of molecules that should not be there

Question 40

How do the axons from skin, muscle and internal organs enter the CNS?

Answer 40

- via spinal nerves

Question 41

What are the two main pathways that that the spinal nerves follow to reach the CNS?

Answer 41

1) Spinothalamic tract 2) dorsal column

Question 42

What is the general name of the pain-specialized receptors?

Answer 42

Nocireceptors

Question 43

Where do the dorsal and spinothalamic tract meet?

Answer 43

in the midbrain

Question 44

Where do the conjoined dorsal and spinathalamic tract synapse?

Answer 44

in the thalamus

Question 45

From the thalamus, where does the somatosensory information go?

Answer 45

Primary somatosensory cortex in the parietal lobe

Question 46

What follows from damage in an area of the somatosensory cortex?

Answer 46

loss of sensitivity in the associated part of the body

Question 47

What type of information travels through the spinothalamic tract?

Answer 47

- low spatial resolution - crude touch, pain, temperature

Question 48

What is the path of the information that travels through the spinothalamic tract?

Answer 48

- first synapse in the spinal chord - information crosses over the midline in the spinal chord - information asciends controlaterally to the thalamus

Question 49

How does information from the skin, muscles and internal organs enter the CNS?

Answer 49

- through spinal nerves

Question 50

What type of information travels through the dorsal column?

Answer 50

- highly localized information - relates to fine touch - relates to kinesthesia

Question 51

How does the informaiton ascend through the spinothalamic tract?

Answer 51

- controlterally

Question 52

How does the information ascend through the dorsal tract?

Answer 52

- ipsilaterally

Question 53

What is the path of the information that travels through the dorsal tract?

Answer 53

- ascends ipsilaterally - synapses first in the medulla - information crosses over to the contralateral side in the medulla - ascends to the thalamus

Question 54

What is chronic pain most frequently associated with?

Answer 54

- a lesion in the somatosensory cortex

Question 55

What is phantom limb pain?

Answer 55

- Pain sensation that occurs after a limb has been amputated - the missing limb is reported to still exist and to hurt

Question 56

What could explain phatom limb pain?

Answer 56

- confusion in the somatosensory cortices (primary and association) - the neurons that have been cut try to be useful to the system in any way possible, so they send nonsense signals that they infer from getting other sensory axons to synapse on them - The brain therefore gets nonsense signals, that it has difficulty interpreting, and interprets it as pain

Question 57

What is tactile agnosia?

Answer 57

- incapacity to verbally identify an object by touch alone - often: they can draw the object that they touch

Question 58

What causes tactile agnosia?

Answer 58

Lesion in the somatosensory association cortex

Question 59

how is the somatosensory cortex organized?

Answer 59

It is a somatotopic map: every area is associated with a part of the body

Question 60

What is the difference between the dorsal and spinothalamic tract

Answer 60

- Spinathalamic synapses directly in the spinal chord and ascends to the brain controlaterally - dorsal ascends ipsilaterally and crosses over in the medulla

Question 61

Where do the spinothalamic and dorsal tracts bundle?

Answer 61

in the midbrain