Touch

Question 1

What is the somatosensory system?

Answer 1

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

Question 2

What are the 3 interacting somatosensory systems?

Answer 2

• the exteroceptive system
• the interoceptive system
• the proprioceptive (kinesthesia) system

Question 3

What is the exteroceptive system?

Answer 3

• cutaneous/skin senses
• responds to external stimuli applied to the skin

Question 4

What is the interoceptive system?

Answer 4

• organic senses
• provides information about conditions within the body and is responsible for efficient regulation of its internal milieu

Question 5

What is the proprioceptive system?

Answer 5

• monitors information about the position of the body in space, posture, and movement

Question 6

What are the cutaneous senses?

Answer 6

• skin
• encode different types of external stimuli

Question 7

What are the different types of external stimuli the cutaneous senses encode?

Answer 7

• pressure
• vibrations
• temperature
• pain

Question 8

What is pressure caused by?

Answer 8

• touch
• mechanical deformation of the skin

Question 9

When do vibrations occur?

Answer 9

• we move our fingers across a rough surface

Question 10

What is temperature produced by?

Answer 10

• objects that heat or cool the skin

Question 11

What is pain caused by?

Answer 11

• many different types of stimuli, but primarily tissue damage

Question 12

What is the anatomy of the skin?

Answer 12

• epidermis
• dermis
• hypodermis
• Merkel’s disk
• Ruffini corpuscles
• Pacinian corpuscles
• Glbrous skin
• free nerve endings
• Meissner’s corpuscles

Question 13

How many layers of the skin are there?

Answer 13

• 3 (outermost, middle, deepest)

Question 14

What is the dermis?

Answer 14

• the outermost layer of skin
• cells here get oxygen from the air (not the blood)
• collection of dead skin cells, no blood vessels

Question 15

What is the dermis?

Answer 15

• middle layer of the skin

Question 16

What is the hypodermis?

Answer 16

• subcutaneous
• below the skin
• deepest layer of the skin

Question 17

What are Merkel’s disks?

Answer 17

• respond to local skin indentations (simple touch)

Question 18

What are Ruffini corpuscles?

Answer 18

• sensitive to stretch and the kinesthetic sense of finger position and movement

Question 19

What are Pacinian corpuscles?

Answer 19

• respond to skin vibrations

Question 20

What are Meissner’s corpuscles?

Answer 20

• only found in glabrous skin
• detect very light touch and localized edge contours (brail-like stimuli)

Question 21

What are free nerve endings?

Answer 21

• primarily respond to temperature and pain

Question 22

What is Glabrous skin?

Answer 22

• hairless skin

Question 23

What are the 2 categories of thermal receptors?

Answer 23

• those that respond to warmth
• those that respond to coolness
• pain information is also conveyed by some of these cells

Question 24

What are thermal receptors?

Answer 24

• carry temperature information
• pain information is also conveyed by some of these cells
• information is poorly localized
• the axons that carry it to the CNS are unmyelinated or thinly myelinated (slow action potential)
• some of the receptor proteins that are sensitive to temperature can also be activated by certain ligands

Question 25

What are the ligands that can activate receptor proteins sensitive to temperature?

Answer 25

- capsaicin molecules activate heat receptors - menthol molecules activate cold receptors

Question 26

What is the thermal grill illusion?

Answer 26

- 4 pins; 2 warm, 2 cold - when pins move together, can't tell that it's two temperatures - sensory system gets confused when sharp change in temp, think it's painful

Question 27

What are sensation of pain and temperature transduced by?

Answer 27

- free nerve endings in the skin

Question 28

What are nociceptors?

Answer 28

- detectors of noxious stimuli - pain receptor cells

Question 29

What are the high-threshold mechanoreceptors?

Answer 29

- one type of pain receptor cell - pressure receptor cell - free nerve endings that respond to intense pressure, like striking, stretching, or pinching

Question 30

How does touch information travel from the body to the brain?

Answer 30

- axons from skin, muscles, and internal organs enter the CNS via spinal nerves - 2 main pathways

Question 31

What are the 2 main pathways of touch?

Answer 31

- spinothalamic tract - dorsal columns

Question 32

What is the spinothalamic tract pathway?

Answer 32

- poorly localized information (crude touch, temp, pain) crosses over the midline in the spinal cord (ascends contralaterally), just after the first synaptic connection - this information ascends to the thalamus through the spinothalamic tract

Question 33

What is the dorsal columns pathway?

Answer 33

- highly localized information (fine touch) ascends ipsilaterally through the dorsal column of the spinal cord - first synapse in this pathway is in the medulla - the information crosses over to the contralateral side as it ascends to the thalamus

Question 34

Where do the 2 pathways meet?

Answer 34

- get bundled together in the midbrain - synapse in the thalamus - information goes to primary somatosensory cortex in the parietal lobe

Question 35

Where is the somatosensory homunculus?

Answer 35

- in parietal lobe, in somatosensory cortex - right next to primary motor cortex

Question 36

What is the somatosensory homunculus?

Answer 36

- somatotopic map - when different sites of primary somatosensory cortex are electrically stimulated, patients report somatosensory sensations in specific parts of their bodies - the relationship between cortical stimulations and body sensations is reflected in a somatotopic map of the body surface

Question 37

What is tactile agnosia?

Answer 37

- damage to somatosensory association cortex - have trouble identifying objects by touch alone - can often draw objects that they are touching, without looking, and they can sometimes identify objects from their drawings

Question 38

What is phantom limb?

Answer 38

- a form of pain sensation that occurs after a limb has been amputated - amputees report that the missing limb still exists and that it often hurts - due to confusion in the somatosensory cortices (primary and association) - brain gets nonsense signals and has difficulty interpreting them

Question 39

What is the treatment for phantom limb?

Answer 39

- pharmacological, electrical, or behavioural have not proven to be very effective - mirror box is cheap and easy but effectiveness is unclear