Touch and pain part 1

Question 1

Descartes

Answer 1

• In addition to thinking our bodies were like machines, he thought humans have immaterial souls, and that the only thing we can be certain of is this immaterial soul (”I think therefore I am”)
• Our senses are not accurate : we can doubt them, perhaps they are only a dream or illusion

Question 2

Passions of the soul (Descartes)

Answer 2

Sensations impose themselves on our soul
- Passion comes from pathos, meaning suffering (sensations that force themselves on you)
- We do not perceive injuries through our reason : we directly feel it : this is important otherwise we would die

Question 3

How touch perception works according to Descartes

Answer 3

Particles interact with “animal spirits” in our nerves that pull the string that constitutes the nerve. A bell will ring in the brain or pineal gland : how our immaterial will get informed of the material.

Question 4

Man that lost tactile sensation and proprioception

Answer 4

• After a viral infection, his immune system attacked the peripheral nerve fibers that are responsible for tactile sensation, and proprioception (feeling body in space) below the neck
• Except : temperature and pain

Question 5

Impact of tactile sensation and proprioception loss

Answer 5

Touch and proprioception is unconscious, but lacking it requires you to consciously bring movement you want to do to mind; touch and proprioception are important for coordinating movement

Question 6

Motor cortex location

Answer 6

in front of central sulcus

Question 7

somatosensory cortex location

Answer 7

Behind central sulcus

Question 8

Cortex responsible for perceiving the body

Answer 8

Somatosensory cortex

Question 9

The ____ and _________ cortex communicate together

Answer 9

Motor and somatosensory

Question 10

Proprioception

Answer 10

Sense of body position
- is based on the ability to perceive the position of the joints.
- also includes vestibular sensations (sense of balance).

Question 11

Kinesthesia

Answer 11

• Perception of movement
• does not include balance
• substantially the same receptors as proprioception.
• Closely related to proprioception

Question 12

Muscle spindle

Answer 12

nerve fibers, attached to muscular fibers.
- perceive stretch of a muscle fiber from within

Question 13

Golgi tendon organ

Answer 13

• in tendons (part of muscle that is attached to the articulation)
• can perceive how much pull there is on a tendon

Question 14

Tactile perception

Answer 14

Perception of objects that come into contact with the skin

Question 15

exteroceptive sense

Answer 15

perception of the external world, outside of the body (such as vision, hearing or touch)

Question 16

True or false : temperature and pain are part of the same system

Answer 16

True (thermoalgesia)

Question 17

Interoception

Answer 17

perception of the internal state of the body (such as hunger, thirst, the urge to urinate).
- Temperature is an interoceptive sense (measures skin temperature)

Question 18

Corpuscles : differences between temperature and touch

Answer 18

• Touch is associated with peripheral nerve fibers that are linked to corpuscles at their dendritic ends that allow perception of different dimensions of touch
  For thermoalgesia/temperature : terminal endings of their nerves have no corpuscles

Question 19

Size of the fibers for touch and thermoalgesia

Answer 19

• The nerve fibers of touch and proprioception are quite large and heavily myelinated, thus faster
• Pain fibers are smaller

Question 20

Slow adaptation rate

Answer 20

Fibers with a slow adaptation rate will start firing upon contact, and will continue for as long as touch continues

Question 21

fast adaptation rate

Answer 21

Tactile receptors that have a fast adaptation rate will fire on contact, but if the contact is maintained with no change, they will adapt and stop firing : more interested by movement or change in intensity of the tactile stimulus

Question 22

SA1 cells

Answer 22

associated with the Merkel receptors
- Small receptive field : more accurate
- Slow adaptting, will continue to fire with constant touch
- Good for perception of fine grained patterns of tactile stimulation (e.g. reading braille)

Question 23

SA2 cells

Answer 23

• Only on hands
• Larger receptive field
• slow adapting
• Good for perceiving skin deformations : preparing to grab object
• Associated with Ruffini corpuscles

Question 24

FA1 fibers

Answer 24

• Associated with meissner corpuscles
• good for holding grip onto object
• Fast adaptation rate, able to perceive vibrations at the surface of the skin, particularly low frequency vibration

Question 25

FA2 fibers

Answer 25

- Associated with Pacinian receptors - More sensitive to high frequency vibrations - Useful for interacting with tools - E.g. writing with pencil

Question 26

All the touch fibers eventually group together into a nerve that enters the ...

Answer 26

spinal cord between each spinal disc.

Question 27

Each area of the skin innervated by a specific nerve is called a ________

Answer 27

Dermatoma

Question 28

Most of the tactile information as it enters the spinal cord will directly ascend towards the brain, following the _____ _______ pathway

Answer 28

dorsal column

Question 29

The dorsal columns

Answer 29

Back side of spinal cord filled with bumps or columns (bundles of axons coming from tactile receptors in the body) sending info. to the brain

Question 30

Pathway of touch information

Answer 30

1. When tactile information enters the spinal cord, it stays on the same side 2. Tactile information makes the first relay in the brain stem in the gracile and cuneate nuclei. 3. The axons cross over to the other side, and make a second synapse in the ventral posterior nucleus of the thalamus 4.The information will then each the somatosensory cortex (posterior to the central sulcus).

Question 31

somatotopic map

Answer 31

The somatosensory cortex has a somatototopic organization : for every body part, there is a corresponding area in the somatosensory cortex that will specifically receive information from this body part

Question 32

Measuring tactile sensitivity : 2-points discrimination threshold (Weber)

Answer 32

2 pins on skin will be separated by distance that varies : participant has to say if they perceive one pin or clearly perceive both pins

Question 33

2 pins discrimination in most body parts

Answer 33

In most body parts, we have large receptive fields and cannot perceive the 2 pins (only one nerve fiber is activated)

Question 34

2 pins discrimination in the hands or face

Answer 34

More nerve fibers with smaller receptive field will tend to activate different receptive fields, allowing us to distinguish the 2 pins when they are closer

Question 35

Pain

Answer 35

An unpleasant sensory and emotional experience (qualia, subjective feeling) associated with, or resembling that associated with, actual or potential tissue damage.

Question 36

Nociception

Answer 36

The neural process of **encoding** nociceptive stimuli. - Stimulus that trigger nociception are the most proximal cause of pain

Question 37

Nociceptive stimulus

Answer 37

An actual or potentially tissue-damaging event transduced and encoded by nociceptors. - Pain is somehow the perception of injury or potential injury - Stimulus needs to have a high intensity

Question 38

Intensity theory

Answer 38

- Pain is nothing more than excessive sensory stimulation - Whatever sensation is perceived as high intensity will cause pain : e.g. burning fire, bright flash of light, loud noises

Question 39

Pain perceiving system according to intensity theory

Answer 39

No specific neural system for perceiving pain - Same system as for audition, somatosensation, etc. : if that system is activated by a very high intensity stimulus, we will perceive pain - The same neuron will be activated by innocuous (non painful) and noxious (painful stimulation), but will be more activated for noxious stimulation

Question 40

Specificity theory

Answer 40

Certain neurons will selectively respond to stimulation in the noxious range (not to non-painful stimulation) - Pain forms a distinct system

Question 41

Peripheral Nociceptors

Answer 41

Sensory receptors that transmit information about **harmful** stimulation that may cause damage to the skin or lead to a risk of damage (supports specificity theory) - Are only activated by nociceptive stimulation - Free nerve endings (no corpuscles)

Question 42

A-delta (Aδ) fibers (nociceptors)

Answer 42

Intermediate-sized, myelinated sensory nerve fibers that transmit pain and temperature signals.

Question 43

C fibers (nociceptors)

Answer 43

Small-diameter, non-myelinated sensory nerve fibers that transmit pain and temperature signals.

Question 44

2 stages of pain perception

Answer 44

1. sharp, rapid pain (A-delta fibers) 2. throbbing sensation (C fibers).

Question 45

Nodes of Ranvier

Answer 45

- distance between sheets of myelin - Action potential jumps from node of ranvier to node of ranvier : saltatory conduction that speeds up action potential - Why more myelinated = faster

Question 46

Impairing the functioning of _____ fibers is easier because neurons with myelin are larger, more complex : need more oxygen to function properly

Answer 46

C-fibers

Question 47

Feeling pins and needles is due to...

Answer 47

A-delta myelinated fibers not working anymore when sitting on hands for a certain time

Question 48

Pain-specific transducers

Answer 48

We have different transducers (proteins) at the surface (membrane) of the nociceptors that perceive different kind of stimuli that can potentially cause harm (nociceptive stimuli) - The same nerve fiber can perceive all these things but only at a certain threshold that can cause pain (specificity theory)

Question 49

Local anasthesia

Answer 49

- Enter the nerve and prevent sodium from entering the sodium channel, blocking the propagation of the action potential

Question 50

Size of fibers from largest to smallest

Answer 50

1. tactile fibers (including proprioceptive fibers) 2. A-delta fibers 3. C-fibers

Question 51

Injecting a large quantity of local anasthesia will block ...

Answer 51

everything : cannot feel pain, touch or move (paralyzed nerve with 3 nodes of Ranvier blocked)

Question 52

Reducing the quantity of the local anasthesic will conserve _______

Answer 52

Motricity (only blocking 2 nodes of Ranvier = only touch and pain are blocked)

Question 53

Infusing even less local anasthesic will create ...

Answer 53

more selective block of pain, leaving touch and motricity intact

Question 54

Difference in quantity of anasthesia needed for myelinated A-delta fibers vs unmyelinated C fibers

Answer 54

A-delta fibers : the action potential can jump over a single blocked node of Ranvier : need to block a couple of nodes to prevent the signal from being conducted through the nerve fibers (3 to block signal) C fibers : only a bit of anasthesia blocks the signal

Question 55

What can happen when anasthesia is not inserted right ?

Answer 55

Can kill nerve if not inserted right (but effective way to block pain )