NA and NP (4) - processing sensory info.

Question 1

What are the 3 levels of processing sensory info?

Answer 1

1. Generating a signal at the receptor level via sensory receptors

• Stimulus energy must match the receptor specifity
• Stimulus must be applied in the receptive field
• Transduction needs to occur (conversion of stimulus to graded potential to EPSP or IPSP

2. Processing at the circuit level via ascending pathways

• Getting info to the correct area of cortex for awareness (perception) and so source of stimulus can be localized
• chains of 3 neurons (1st/2nd/3rd)
  1st order brings info to the CNS, of which some may synapse with 2nd order neurons ascending towards the brain where the 3rd order neurons will take the info to the correct sensory area of the cerebral cortex

3. Processing at the perceptual level

• info must get to the right place to be understood and localized by using the correct neural pathway

Question 2

What are phasic receptors vs tonic receptors

Answer 2

Phasic = fast adapting (lamellar, tacile corpuscles, some special senses)

• provides info about rate of change of a stimulus such as going from darkness to bright light, our eyes may be blurry at first but adjust rather quickly

Tonic = sustained responses with little to no adaptation (nociceptors for pain)

• info is important and informs about the presence and strength of a stimulus

Question 3

What are the 3 main pathways of the circuit level

Answer 3

1) Dorsal column-medial lemniscal pathway

• target is thalamus
• decussation at level of medulla
• single type of receptor that can be precisely localized on body surface (discrimative touch, vibrations..)

2) Spinothalamic pathways

• target is thalamus
• takes input from several types of receptors with info about pain, temperature, coarse touch, pressure
• not as precise localization
• decussation at level of spinal cord

3) Spinocerebellal pathways

• target is the cerebellum
• info about muscle/tendon stretch so that cerebellum can coodinate skeletal muscle activity
• ipsilateral meaning there is no decussation (or we are not consciously aware of no crossing over)

Question 4

Difference between sensation and perception

Answer 4

Sensation = awareness of changes in internal/external environment

Perception = conscious interpretation of those changes - perception determines the manner of response i.e. understanding the changes allows for a response

Question 5

What is adaptation?
Central vs peripheral adaptation?

Answer 5

Adaptation = reduction in sensitivity in the presenc of a constant stimulus, occurs quickly in stimuli that arent painful

Central adaptation = at level of neural pathways to the braina nd involve brain nuclei

Peripheral adaptation = at levelk of receptor and reduces how much info is sent to the CNS (how much a receptor continues to be activated)

Question 6

List some properties of sensory perception (6)

Answer 6

1. Perceptual detection - being aware, inputs are summed from several receptors that allow for detection (intensity of light/surroundings…)
2. Magnitude estimation - intensity of the stimulus encoded by AP frequency (strong stimulus = higher frequency - vice versa)
3. Spatial discrimination - localizing the stimulus
4. Feature abstraction - each neuron is only tuned to 1 feature or property of a stimulus, several features can then come together for sensory experiences
5. Quality discrimination - distinguish submodalities of a particular sensation (eating something might taste BOTH sweet and salty)
6. Pattern recognition - recognition of words, a familiar face, letters, music…

Question 7

Difference between sharp pain and burning pain

Answer 7

Sharp pain usually comes first, followed by burning pain

Sharp pain = smallest myelinated fibers; A delta fibers

Burning pain = slowly by small NONmyelinated C fibers

Question 8

What is the process of pain suppresion?

Answer 8

Signals are sent through endogenous opioids to endorphins and enkephalins via the periaqueductal gray matter of the midbrain

Question 9

List the 4 types of pain

Answer 9

1) Somatic pain (musculoskeletal); easy to localize because bones and muscles are well innervated

2) Visceral pain; associated with organs of the thorax and abdominal cavity, is a result of extreme tissue stretching, irritating chemicals, muscle spasms…

• uses same pathways as somatic which is what may cause referred pain

3) Referred pain; pain arising from one part of the body appears to come from somewhere else

4) Phantom pain; type of hypealgesia (pain amplification) involing NMDA receptors (AKA learned pain)

• might not necessarily be conscious of pain felt (if your leg is paralyzed or amputated but you still feel pain there) - pain signals reach the spinal cord but not the cortex