8.2. The somatovisceral Sensory System: properties of the receptors, afferent pathways, role of the thalamus and the cerebral cortex. Tactile sensations.

Question 1

I. Basics
1. What are the features of Somato-visceral sensory system?

Answer 1

• Analyzes sensory events relating to the mechanical, thermal or chemical
  stimulations of the body and face
• Part of the sensory system concerned with the conscious perception of touch,
  pressure, pain, temperature, position, movement and vibration, which arise from the muscles, joints, skin and fascia

Question 2

II. PROPERTIES AND CODING OF SENSORY INFORMATION
1. What are the 4 major properties of the incoming sensory information?

Answer 2

• Whatever our sensory receptors can code, those are the properties of information which can be forwarded to our sensory system
• There are 4 major properties of the incoming sensory information, which can be coded for our CNS: modality, intensity, duration and location

Question 3

II. PROPERTIES AND CODING OF SENSORY INFORMATION
2A. What is modality?

Answer 3

quality of incoming sensory information

Question 4

II. PROPERTIES AND CODING OF SENSORY INFORMATION
2B. List 5 “classical” modalities

Answer 4

vision, hearing, taste, smell, touch-pressure

Question 5

II. PROPERTIES AND CODING OF SENSORY INFORMATION
2C. List other modalities except “Classical” modalities

Answer 5

flutter-vibration, cold, warmth, proprioception, linear
acceleration, rotational acceleration, pain

Question 6

II. PROPERTIES AND CODING OF SENSORY INFORMATION
2D. What are the characteristics of Labelled line code?

Answer 6

• the sensory modality is encoded starting at the receptor, then including all the nerves that carry sensory information, all the way to the cortex where the information is received
• e.g.: visual pathway from retina to the visual cortex is the ‘’labelled line’’ -> by electrically stimulating a part of that line, you may perceive a particular sense
• we have a line from receptor to cortex dedicated to each sensory modality, so there is a different labelled line for hearing, smell, etc.

Question 7

II. PROPERTIES AND CODING OF SENSORY INFORMATION
2E. What is the feature of coding by APs?

Answer 7

APs will be created in the corresponding nerves
-> e.g.: visual information is coded as APs for the optic nerve

Question 8

II. PROPERTIES AND CODING OF SENSORY INFORMATION
3A. What is intensity?

Answer 8

incoming stimuli usually have threshold
=> A stimuli must reach past the threshold in order to be sensed

Question 9

II. PROPERTIES AND CODING OF SENSORY INFORMATION
3B. What is threshold?

Answer 9

Threshold is defined as the stimulus intensity detected 50% of the time
=> Threshold: detectability (min.load we can detect – 1AP) + criterion (conditions – from CNS)

Question 10

II. PROPERTIES AND CODING OF SENSORY INFORMATION
3C. What are the features of Just noticeable difference (JND)?

Answer 10

• The difference (change) in stimulus intensity depends on the original stimulus intensity
• The change in stimulus intensity (ΔS) detected and compared to the original stimulus (S), is a constant
  => ∆S/S = constant (linear relationship)

Question 11

II. PROPERTIES AND CODING OF SENSORY INFORMATION
3D1. What is sensation intensity? (psychophysics)

Answer 11

• Relationship between magnitude of a physical stimulus and the intensity/strength
  that people feel (sensation)
  => Sensation intensity ~ (S – S threshold)^n

Question 12

II. PROPERTIES AND CODING OF SENSORY INFORMATION
3D2. The Sensation intensity ~ (S – S threshold)^n
=> What happen if n < 1?

Answer 12

Usually, n<1 (logarithmic relationship)
=> able to detect a large (sensory) physical stimulus intensity, because relatively large changes cause a relatively small change in our perception
=> that helps to increase the range we can detect

Question 13

II. PROPERTIES AND CODING OF SENSORY INFORMATION
3D3. The Sensation intensity ~ (S – S threshold)^n
=> What happen if n > 1?

Answer 13

When n>1 => pain sensation (exception)
- In pain sensation, threshold is very high
- A relatively small increase in stimulus intensity causes a relatively large
increase in pain sensation
= We can detect intensity (low / high)

Question 14

II. PROPERTIES AND CODING OF SENSORY INFORMATION
3D4. The Sensation intensity ~ (S – S threshold)^n
=> What happen if n = 1?

Answer 14

There will be a linear relationship between magnitude of a physical stimulus and the intensity/strength that people feel (sensation)

Question 15

II. PROPERTIES AND CODING OF SENSORY INFORMATION
3D5. Features of coding in intensity

Answer 15

1. AP frequency: the higher the intensity, the higher the AP frequency
2. Population coding: with a higher intensity stimulus, more sensory nerves are activated (larger population of sensory nerves will detect a larger incoming stimulus)
3. Related, but different type of receptors are activated: as in the case of light touch
   versus putting enough pressure on the skin that it becomes painful, both mechanoreceptors and nociceptors are activated

Question 16

II. PROPERTIES AND CODING OF SENSORY INFORMATION
4A. What are the feature of duration?

Answer 16

• When there is a stimulus = AP firing, if no stimulus = no AP firing
• The duration of the perceived sense can be altered by adaptation

Question 17

II. PROPERTIES AND CODING OF SENSORY INFORMATION
4B1. How does the adaptation to the stimulus occur in general?

Answer 17

• The receptor potential is an electrotonic potential evoked by the stimulus
• The receptor initially produce an electrotonic potential, and if this potential reaches the threshold of VG Na+-channels in the nerves => there will be AP firing

Question 18

II. PROPERTIES AND CODING OF SENSORY INFORMATION
4B1. How does the adaptation to the stimulus occur in general?

Answer 18

• The receptor potential is an electrotonic potential evoked by the stimulus
• The receptor initially produce an electrotonic potential, and if this potential reaches the threshold of VG Na+-channels in the nerves => there will be AP firing

Question 19

II. PROPERTIES AND CODING OF SENSORY INFORMATION
4B. How does the adaptation to the stimulus occur in general?

Answer 19

• The receptor potential is an electrotonic potential evoked by the stimulus
• The receptor initially produce an electrotonic potential, and if this potential reaches the threshold of VG Na+-channels in the nerves => there will be AP firing

Question 20

II. PROPERTIES AND CODING OF SENSORY INFORMATION
4C1. What are the 3 types of adaptation to stimulus?

Answer 20

1. Rapidly adapting (phasic)
2. Slowly adapting (tonic)
3. Rapid/slowly adapting (phasic/tonic)

Question 21

II. PROPERTIES AND CODING OF SENSORY INFORMATION - Adaptation to the stimulus
4C2. What happen if there is rapidly adapting to stimulus (phasic)?

Answer 21

1. The stimulus causes a response (AP firing), but after that, despite of the continuous presence of the stimulus, there will be no more AP firing -> adaptation occurs
2. Both the receptor (electrotonic potential) and the sensory nerve (AP firing) show adaptation

Question 22

II. PROPERTIES AND CODING OF SENSORY INFORMATION - Adaptation to the stimulus
4C3. What happen to firing pattern if there is slowly adapting to stimulus (tonic)?

Answer 22

1. The electrotonic potential will be present
   during the entire stimulus, with just a little
   decrease
2. The AP firing will also be present till the
   stimulus is over, but with a decreasing
   frequency

Question 23

II. PROPERTIES AND CODING OF SENSORY INFORMATION - Adaptation to the stimulus
4C4. What happen if there is rapidly/slowly adapting to stimulus (phasic/tonic)?

Answer 23

Mixture of both the rapid and slowly adaptations

Question 24

II. PROPERTIES AND CODING OF SENSORY INFORMATION
4D2. What are the features of firing pattern in slowly adapting receptors in firing pattern?

Answer 24

• There will be a continuous firing during the presence of the stimulus
• If we increase the amplitude of the stimulus, the AP firing will get increased as well
• Whenever the stimulus is present, then the AP firing will be present, that is the coding of the duration of the outside stimulus

Question 25

II. PROPERTIES AND CODING OF SENSORY INFORMATION
4D2. What are the features of stimulus in slowly adapting receptors in firing pattern?

Answer 25

• When there is a continuous stimulation, they respond to the initial stimulus and to the end -> will signal the start and the end of the stimulus
• They will also signal if there is a change in the intensity of the stimulus -> there will be a continuous increase, followed by a continuous firing. But when it reaches the maximum = no firing, when stimulus is stopped = another firing

Question 26

II. PROPERTIES AND CODING OF SENSORY INFORMATION
4E. What are the 3 main mechanisms of adaptation?

Answer 26

1. Mechanical (Pacinian corpuscle)
2. Inactivation of channels
3. Opening of Ca2+-sensitive K+-channels

Question 27

II. PROPERTIES AND CODING OF SENSORY INFORMATION - Mechanisms of adaptation
4F1. What are the characteristics of Mechanical (Pacinian corpuscle)?

Answer 27

• Pacinian corpuscle (in the skin) is a sensory nerve ending, which is responsible for vibration, high frequency changes in the stimulus intensity -> a rapidly adapting sensor
• The corpuscle is made up of an ending of a sensory nerve of an axon, which is surrounded by a CT structure with ‘’onion-like’’ laminae

Question 28

II. PROPERTIES AND CODING OF SENSORY INFORMATION - Mechanisms of adaptation
4F2. What is the adaptation mechanism of Pacinian corpuscle?

Answer 28

• A mechanical stimulus will push away the CT structure, so everything moves away and since there is a link in the inner layer -> stretch on the nerve ending, which will cause potential generation + firing in the nerve ending
• But if the stimulus is present after the first instance, since the laminae are flexible -> they will move back to the original place step-by-step
• Stretch on the axon will be minimal and that is why
  (mechanically) the stimulus will stop, because of the flexibility of the CT structure
  => The Pacinian corpuscle, based on the mechanical
  properties, can show adaptation

Question 29

II. PROPERTIES AND CODING OF SENSORY INFORMATION - Mechanisms of adaptation
4G. How does Inactivation of channels help in adaptation to stimulus?

Answer 29

When the initial stimulus causes a potential change in nerve ending
-> VG Na+-channels open
-> AP formation
-> VG channels stand to inactivation if the stimulus is constantly present
-> inactivation
-> adaptation

Question 30

II. PROPERTIES AND CODING OF SENSORY INFORMATION - Mechanisms of adaptation
4H. How does Opening of Ca2+-sensitive K+-channels help in adaptation to stimulus?

Answer 30

Stimulus
-> depolarization
-> opening of Ca2+-channels
-> Ca2+-influx in nerve terminal
-> Ca2+-sensitive K+-channel open
-> hyperpolarization (counteract the depol.)
=> adaptation

Question 31

II. PROPERTIES AND CODING OF SENSORY INFORMATION
5A. What is the role of LOCATION in SENSORY INFORMATION?

Answer 31

determination of the location of a stimulus id done via somatotopic organization

Question 32

II. PROPERTIES AND CODING OF SENSORY INFORMATION
5B. What are the features of coding in relation to location?

Answer 32

• Depends on the localization of the sensory nerve
• The same kind of mechanoreceptors are present throughout the body, and depending on which receptors get activated – we can localize the stimulus

Question 33

II. PROPERTIES AND CODING OF SENSORY INFORMATION
5C. What are the features of 2-point discrimination (2PD)?

Answer 33

The ability to recognize that 2 nearby objects touching the skin are truly 2 distinct points. The receptor density determines the sensitivity of the 2-point discrimination:
- If receptor density is high = the 2PD is more accurate (e.g. lip, tongue, fingers)
- If receptor density is low = the 2PD is inaccurate (e.g. back, arm, calf)
=> In order to detect the 2PD, 2 different populations of nerve cells must get activated
=> If the populations are different enough, that our CNS can detect the difference, then the 2PD can work

Question 34

III. SENSORY SYSTEMS HAVE A COMMON PLAN
1. Physical energy is converted to ____

Answer 34

electrochemical energy

Question 35

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Physical energy is converted to electrochemical energy
2. What happen if we evoke mechanical stimuli of small intensity?

Answer 35

If we evoke mechanical stimuli of small intensity, initially a small AP is generated (local phenomenon)
- Small AP = receptor (generator) potential = electrotonic potential (local)
- If we have a high enough stimulus intensity
-> depolarization
-> reach threshold of VG Na+-ch.
-> AP generation (propagating phenomenon – it will travel through the nerve toward CNS)
-> this is how physical (mechanical) stimulus is converted to electrochemical potential

Question 36

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Physical energy is converted to electrochemical energy
3. If we evoke mechanical stimuli of small intensity, initially a small AP is generated (local phenomenon)
=> The above mentioned mechanism occurs in receptors located in _____ (2)

Answer 36

1. Sensory nerve endings (Pacinian C) + mechano-/nocireceptors
2. Associated CT structures (e.g. taste buds)

Question 37

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Physical energy is converted to electrochemical energy
4. If we evoke mechanical stimuli of small intensity, initially a small AP is generated (local phenomenon)
=> What happen if we use lidocaine?

Answer 37

If we use lidocaine, which blocks VG Na+-ch.
-> receptor (generator) potential still there, but AP will not be there

Question 38

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Physical energy is converted to electrochemical energy
5. What happen In Merkel receptor cells?

Answer 38

In Merkel receptor cells, opening of mechanosensitive Piezo-2 cation channels cause depolarization and mediator release:
- touch the skin
-> channel open (depol.)
-> Ca2+-signal
-> transmitter release
-> cause activation of sensory nerve -> CNS

Question 39

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Physical energy is converted to electrochemical energy
6A. Channels can get activated by different mechanisms
-> What are the 3 main mechanisms?

Answer 39

1. Channels can get activate by tension of plasma membrane
2. Mechanical coupling between outside stimulus and the channel
3. Channels can be indirectly activated by separate proteins

Question 40

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Physical energy is converted to electrochemical energy
6B. How can channels get activated by tension of plasma membrane?

Answer 40

Channels can get activate by tension of PM
-> channels open (depol.)
-> receptor potential. E.g.: osmotic swelling

Question 41

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Physical energy is converted to electrochemical energy
6C. How can channels get activated by Mechanical coupling between outside stimulus and the
channel?

Answer 41

• Mechanical coupling between outside stimulus and the channel.
• Due to the flexibility of the structural proteins: if there is a tension, they will pull the receptor in a way that the channels open -> receptor potential

Question 42

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Physical energy is converted to electrochemical energy
6D. How can channels indirectly get activated by separate proteins?

Answer 42

Channels can be indirectly activated by separate proteins.
-> An 2nd messenger carries the sensory signal from the mechanosensitive protein to the channel
-> receptor potential

Question 43

III. SENSORY SYSTEMS HAVE A COMMON PLAN - anatomical structures
7A. What are the characteristics of anatomical structures of sensory systems?

Answer 43

• Sensory neurons are pseudounipolar (1st order neuron) located in the DRG or other ganglion cells
• The ending of the pseudounipolar neuron (peripheral axon) is the receptor itself
• If the receptor gets activated, the AP will form and travel toward the pseudounipolar cell body, and with the other axon (central axon) it will go into the CNS
• The central axon will also go the relay nucleus, which is a nerve cell that receives incoming information and axon of the relay nucleus (2nd order neuron) will forward the information toward the thalamus
• The thalamic neuron (3rd order neuron) will project to the cortex

Question 44

III. SENSORY SYSTEMS HAVE A COMMON PLAN - anatomical structures
7B. What are the shape and location of sensory neurons?

Answer 44

Sensory neurons are pseudounipolar (1st order neuron) located in the DRG or other ganglion cells

Question 45

III. SENSORY SYSTEMS HAVE A COMMON PLAN - anatomical structures
7C. ____ is the receptor itself

Answer 45

The ending of the pseudounipolar neuron (peripheral axon)

Question 46

III. SENSORY SYSTEMS HAVE A COMMON PLAN - anatomical structures
7D. If the receptor gets activated, what will happen?

Answer 46

The AP will form and travel toward the pseudounipolar cell body, and with the other axon (central axon) it will go into the CNS

Question 47

III. SENSORY SYSTEMS HAVE A COMMON PLAN - anatomical structures
7E. The central axon will also go to ____

Answer 47

the relay nucleus

Question 48

III. SENSORY SYSTEMS HAVE A COMMON PLAN - anatomical structures
7F. What are the feature and role of relay nucleus?

Answer 48

the relay nucleus, which is a nerve
cell that receives incoming information
-> axon of the relay nucleus (2nd order neuron) will forward the information toward the thalamus

Question 49

III. SENSORY SYSTEMS HAVE A COMMON PLAN - anatomical structures
7G. Where will the thalamic neuron (3rd order neuron) project to? What are the characteristics of this region?

Answer 49

The thalamic neuron (3rd order neuron) will project to the cortex
- Characteristic of the somatosensory system, which area of the cortex will get stimulated (auditory, visual, etc.)
- The primary information always arrives first from the thalamus to the primary corresponding sensory cortical regions

Question 50

III. SENSORY SYSTEMS HAVE A COMMON PLAN - anatomical structures
8. How is the olfactory system different from general sensory system?

Answer 50

The olfactory system is different, because:
(1) it does not have a pseudounipolar cell, but bipolar cell – function is same
(2) the pathway which goes through the thalamus does exist, but is not the main one

Question 51

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Vertical and horizontal organization
9A. What are the features of vertical organization?

Answer 51

what was mentioned above (1, 2,3-order neuron, relay nucleus, etc.)

Question 52

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Vertical and horizontal organization
9B. What are the features of horizontal pathways?

Answer 52

There are parallel pathways, which are very well organized (somatotopy, retinotopy, tonotopy, etc.)
=> causes characteristic localization of the incoming information

Question 53

III. SENSORY SYSTEMS HAVE A COMMON PLAN
10A. What are the 4 types of topology?

Answer 53

1. Somatotopy
2. Retinotopy
3. Tonotopy
4. Dermatome

Question 54

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Topology
10B. What are the features of somatotopy?

Answer 54

point-for-point correspondence of an area of the body to a specific point on the CNS

Question 55

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Topology
10C. What are the features of Retinotopy?

Answer 55

mapping of visual input from the retina to neurons

Question 56

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Topology
10D. What are the features of Tonotopy?

Answer 56

spatial arrangement of where sounds of different frequency are processed in the brain

Question 57

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Topology
10E. What are the features of Dermatome?

Answer 57

• Different vertebral segment where the sensory nerves enter
• An area of the skin that is supplied by afferent nerve fibers
• The face is innervated by the trigeminal nerve (1 = ophthalmic, 2 = maxillary, 3 = mandibular)

Question 58

III. SENSORY SYSTEMS HAVE A COMMON PLAN
11. What are the characteristics of receptive fields?

Answer 58

• The area where 1st, 2nd and 3rd order neurons can receive information from
• The 2nd order neuron receives information from several 1st order neurons = 2nd order neurons have a wider receptive field
• As we go higher (3rd, 4th etc.), there will be more receptive fields

Question 59

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Dorsal column – medial lemniscus pathway
12A. What type of receptors used in medial lemniscus pathway?

Answer 59

Uses mechanoreceptors (Pacinian, Ruffini, Merkel,
Meissner) and proprioceptors

Question 60

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Dorsal column – medial lemniscus pathway
12B. What is the role of medial lemniscus pathway?

Answer 60

Responsible for detection of fine touch, vibration,
proprioception (body in space) and 2-point-
discrimination

Question 61

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Dorsal column – medial lemniscus pathway
12C. Describe the medial lemniscus pathway

Answer 61

1st order neurons have their cell bodies in the DRG,
then they ascend ipsilaterally to the gracile/cuneate
nucleus in the medulla
- There, they synapse with 2nd order neurons which
then cross and ascend via the medial lemniscus to the contralateral thalamus
=> information goes to VPL (body) or VPM (head)
- In the thalamus, they synapse again and 3rd order neurons extend to the somatosensory cortex
=> The initial part of the pathway, the peripheral
axon of the pseudounipolar neuron, is responsible for the receptor function

Question 62

III. SENSORY SYSTEMS HAVE A COMMON PLAN
13A. What are the types of nerve fibers in peripheral nerves?

Answer 62

Aα, Aβ, Aδ and C-fibers

Question 63

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Dorsal column – medial lemniscus pathway
13B. What types of nerve fibers contained in muscle nerves?

Answer 63

Muscle nerve contains Aα, Aβ, Aδ and C-fibers

Question 64

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Dorsal column – medial lemniscus pathway
13C. What types of nerve fibers contained in cutaneous nerves?

Answer 64

Aβ, Aδ and C-fibers

Question 65

III. SENSORY SYSTEMS HAVE A COMMON PLAN - Dorsal column – medial lemniscus pathway
13D. What are the features of C- and A-fibers?

Answer 65

C-fibers has no myelin sheath, while all A-fibers have
=> C-fibers have the lowest conduction velocity

Question 66

III. SENSORY SYSTEMS HAVE A COMMON PLAN
13E. Which nerve fiber(s) have the lowest conduction velocity?

Answer 66

C-fibers has no myelin sheath
=> C-fibers have the lowest conduction velocity

Question 67

III. SENSORY SYSTEMS HAVE A COMMON PLAN
13F. What is the relationship between the axon diameter and the conduction velocity?

Answer 67

Axon diameter strongly correlates with the conduction velocity
-> also with the presence/absence of myelin sheath

Question 68

III. SENSORY SYSTEMS HAVE A COMMON PLAN
13G. The axon diameter and conduction velocity of C-fibers?

Answer 68

Axon diameter (μm): 1
Conduction velocity (m/s): 0.3 - 1

Question 69

III. SENSORY SYSTEMS HAVE A COMMON PLAN
13H. The axon diameter and conduction velocity of Aδ-fibers?

Answer 69

Axon diameter (μm): 5
Conduction velocity (m/s): 30

Question 70

III. SENSORY SYSTEMS HAVE A COMMON PLAN
13I. The axon diameter and conduction velocity of Aβ-fibers?

Answer 70

Axon diameter (μm): 12
Conduction velocity (m/s): 35 - 75

Question 71

III. SENSORY SYSTEMS HAVE A COMMON PLAN
13J. The axon diameter and conduction velocity of Aα-fibers?

Answer 71

Axon diameter (μm): 20
Conduction velocity (m/s): 80 - 120

Question 72

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Touch-pressure, flutter-vibration
1. What is in the hairy skin?

Answer 72

Hairy skin: receptor of hair follicle, surrounded by nerve endings

Question 73

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Touch-pressure, flutter-vibration
2. What is in the Glabrous (hairless) skin?

Answer 73

• The receptors close to the skin surface have small receptive fields = ↑ resolution
• Rapidly adapting receptors respond when stimulus changes, while slowly adapting receptors respond throughout the stimulus

Question 74

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Touch-pressure, flutter-vibration
3A. What are the 4 types of receptors responsible for Touch-pressure, flutter-vibration?

Answer 74

1. Meissner’s corpuscle
2. Merkel’s disk
3. Pacinian corpuscle
4. Ruffini endings

Question 75

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Touch-pressure, flutter-vibration
3B. Meissner’s corpuscle
- Location: ???
- Adaptation: ???
- Receptive field: ???
- Function: ???

Answer 75

Meissner’s corpuscle
- Location: SUPERFICIAL
- Adaptation: RAPIDLY
- Receptive field: SMALL (=↑resolution)
- Function: Motion (lateral)

Question 76

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Touch-pressure, flutter-vibration
3C. Merkel’s disk
- Location: ???
- Adaptation: ???
- Receptive field: ???
- Function: ???

Answer 76

Merkel’s disk
- Location: SUPERFICIAL
- Adaptation: SLOWLY
- Receptive field: SMALL
- Function: Edges, points

Question 77

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Touch-pressure, flutter-vibration
3D. Pacinian corpuscle
- Location: ???
- Adaptation: ???
- Receptive field: ???
- Function: ???

Answer 77

Pacinian corpuscle
- Location: DEEP
- Adaptation: RAPIDLY
- Receptive field: WIDE (=↓resolution)
- Function: Vibration

Question 78

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Touch-pressure, flutter-vibration
3E. Ruffini endings
- Location: ???
- Adaptation: ???
- Receptive field: ???
- Function: ???

Answer 78

Ruffini endings
- Location: DEEP
- Adaptation: SLOWLY
- Receptive field: WIDE
- Function: Skin stretch

Question 79

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
4. What are the characteristics of Proprioception?

Answer 79

• The somatosensory system which is connected to muscle movement
• The proprioceptors are localized in the muscles: in muscle spindles / joints
• The axons which come out of the proprioceptors belong to the Aα and Aβ-fibers = thickest + fastest fibers of the sensory system

Question 80

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
5A. What is relay nuclei?

Answer 80

Neural networks in relay nuclei integrate sensory information
1. Divergence
2. Convergence
3. Lateral inhibition

Question 81

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
5B. In relay nuclei, what does divergence mean?

Answer 81

the relay nuclei will receive information from more than 1 ganglionic neuron

Question 82

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
5D3. How can lateral inhibition occur as feedback inhibition?

Answer 82

Feedback inhibition: produced by recurrent collateral axon of neurons. Interneurons inhibit surrounding neurons

Question 83

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
5D In relay nuclei, what does Lateral inhibition mean?

Answer 83

Although the information will be processed and diverted to other neurons, due to the presence of lateral inhibition, the contrast will be maintained
=> the stimulus only has a high amplitude response in the center of the PW, while there is an inhibition in the surrounding parts

Question 84

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
5D1. What are the 3 ways that lateral inhibition can occur?

Answer 84

1. feed-forward inhibition
2. feedback inhibition
3. descending inhibition

Question 85

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
5D2. How can lateral inhibition occur as feed-forward inhibition?

Answer 85

presynaptic neuron activates an inhibitory interneuron, which in turn inhibits the neuron of the next order

Question 86

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
5C. In relay nuclei, what does Convergence mean?

Answer 86

On 1 relay nucleus, information from more than 1 neuron will change

Question 87

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
5D4. How can lateral inhibition occur as descending inhibition?

Answer 87

Descending inhibition: pathways initiated from the cortex descend to the spinal cord and give collaterals, by which they connect to interneurons and inhibit the activity of relay nuclei
=> important in pain sensation

Question 88

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
6A. What are the features of receptive field of the 2nd order neurons?

Answer 88

The receptive fields of the 2nd, 3rd order neurons and so on will be different from the 1st order neurons:
- 2nd order neurons have wider receptive fields than 1st order neurons, because many 1st order neurons converge on one 2nd order neuron
-> summation of the fields
- 2nd order neurons will have inhibitory receptive fields (which 1st order neurons do not have)
- Adaptations are similar in the 1st and 2nd order neurons: if the 1st order neuron was rapidly adapting, it will connect to the rapidly adapting 2nd order neurons
-> rapidly adapting neuron in the cortex
=> Important, because in this way the information from the periphery will be faithfully represented in the cortex

Question 89

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Proprioception
6B. Why do 2nd order neurons have wider receptive fields than 1st order neurons?

Answer 89

2nd order neurons have wider receptive fields than 1st order neurons, because many 1st order neurons converge on one 2nd order neuron

Question 90

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Somatosensory cortex
7A. Where is the area where the sensory information first arrives?

Answer 90

Primary somatosensory cortex

Question 91

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Somatosensory cortex
7B. What is the fate of all the incoming sensory information from the receptors?

Answer 91

All the incoming information form the receptors will activate the population of the cells in the primary somatosensory cortex

Question 92

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Somatosensory cortex
7C. Where is the Primary somatosensory cortex located?

Answer 92

Located in the postcentral gyrus

Question 93

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Somatosensory cortex
8. What are the features of sensory homunculus?

Answer 93

Somatosensory map = homunculus (overview of how different parts of the body are represented in the primary somatosensory cortex)
1. Different sensory areas are not proportional to their actual body size
-> lips + mouth are over-represented in the map, while the legs + abdomen are under-represented
-> reason is the receptor density
2. Higher density area = higher area of cortical localization

Question 94

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Somatosensory cortex organization
9A. Describe Somatosensory cortex organization

Answer 94

• In each region of the somatosensory cortex, inputs are organized in columns -> 1 column deals with 1 sensory modality
• Receptive fields of neurons in the somatosensory cortex are arranged in distinct regions -> Brodmann areas (3, 1, 2)

Question 95

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Somatosensory cortex organization
9B. How are receptive fields of neurons in the somatosensory cortex?

Answer 95

Receptive fields of neurons in the somatosensory cortex are arranged in distinct regions -> Brodmann areas (3, 1, 2)

Question 96

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Somatosensory cortex organization
10A. Describe parts of Somatosensory cortex (S1)

Answer 96

1/ 3a: muscle spindles (proprioceptors)
2/ 3b: Merkel, Meissner (SA1, RA1 receptors)
3/ 1: Ruffini, Pacini (RA1, RA2 receptors)
4/ 2: complex touch, proprioception
=> In the primary somatosensory cortex, each sensory information + location coming from the periphery will have its own neuron group which responds to it -> primary representation of the somatosensory information in the cortex

Question 97

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Somatosensory cortex
11. How does processing of the primary information occur?

Answer 97

• The incoming primary information will converge into neurons which are responsible for the processing.
• (S2) somatosensory cortex is the one which primarily deals with processing of incoming somatosensory input:
  +) Posterior parietal cortex will receive incoming information from all sensory areas (visual, auditory etc.)
  +) In the posterior parietal cortex, the processing of all sensory information occurs

Question 98

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Anterolateral pathway – spinothalamic tract
12A. What are the types of receptors used in Anterolateral pathway – spinothalamic tract?

Answer 98

Uses warm and cold thermoreceptors and nociceptors for pain

Question 99

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Anterolateral pathway – spinothalamic tract
12B. Describe Anterolateral pathway – spinothalamic tract

Answer 99

• Anterior spinothalamic tract carries information about crude touch
• Lateral spinothalamic tract carries information about pain and temperature
• 1st order neurons (pseudounipolar neurons) have their cell bodies in DRG, then synapse with 2nd order neurons in the spinal cord
• 2nd order neurons cross in the spinal cord and ascend to the contralateral thalamus, where they synapse with 3rd order neurons that go to the primary somatosensory cortex

Question 100

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Anterolateral pathway – spinothalamic tract
12B. Describe Anterolateral pathway – spinothalamic tract

Answer 100

• Anterior spinothalamic tract carries information about
  crude touch
• Lateral spinothalamic tract carries information about pain
  and temperature
• 1st order neurons (pseudounipolar neurons) have their cell bodies in DRG, then synapse with 2nd order neurons in the spinal cord
• 2nd order neurons cross in the spinal cord and ascend to the contralateral thalamus, where they synapse with 3rd order neurons that go to the primary somatosensory cortex

Question 101

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Anterolateral pathway – spinothalamic tract
12C. What is the role of The anterolateral (spinothalamic) system?

Answer 101

The anterolateral (spinothalamic) system is responsible for the mediation of thermal and pain sensation

Question 102

IV. CODING OF MODALITY IN THE SOMATOSENSORY SYSTEM - Anterolateral pathway – spinothalamic tract
12D. What is the role of Peripheral receptors?

Answer 102

Peripheral receptors of thermal and pain sensation are free nerve endings