Session 6: Ascending Somatosensory Systems Flashcards
(112 cards)
1
Q
What is the purpose of pathways ?
A
Carry somatosensation for the body
2
Q
What types of sensations are carried through ascending pathways?
A
- Pain
- Temperature
- Vibration
- Body position in space
- Discriminative touch
3
Q
Where/how do somatosensations enter the spinal cord?
A
Enter the spinal cord in a segmental fashion over the dorsal root of each spinal nerve.
4
Q
A dermatomal map is a reflection of what? What is its origin?
A
The segmental arrangement of the spinal cord, which is from embryological origin.
5
Q
How are pathways of somatosensation viewed in their simplest form?
A
- As a three neuron pathway, using just 3 neurons to carry the somatosensation from the peripheral receptors to the brain for perception of that somatosensory modality.
6
Q
How is the segmental arrangement maintained as information is transferred from the periphery to the brain? What is this arrangement referred to?
A
Maintained as a topographic map within the pathways and nuclei carrying each sensation.
Referred to as a somatotropic organization.
7
Q
How is somatorophic organization represented in the brain?
A
In the homunculus positioned over both the primary somatosensory cortex and primary motor cortex.
8
Q
What modalities are carried via the dorsal column/medial meniscus system? (4)
A
- conscious proprioception
- discriminative touch (two point discrimination, light touch)
- position sense (proprioseption)
- vibratory sensations.
9
Q
What carries sensations of conscious proprioception, discriminative touch, position sense and vibrations for the face?
A
The trigeminal nerve and related pathways
10
Q
What is proprioception?
A
The modality that provides information concerning movement and position of body parts (in part, joint position in space)
11
Q
What are the two modalities of proprioception?
A
- conscious
2. unconscious
12
Q
Conscious proprioception is involved in what?
A
Kinesthesia (the sense of perception of movement of joints).
13
Q
What sensations are necessary for steriognosis (the ability to identify an object by feel)? What system carries these sensations?
A
Sensations of proprioception and discriminative touch.
Carried by the dorsal column/medial lemniscus system.
14
Q
What tract carries unconscious proprioception?
A
The Spinoceerebellar tract.
15
Q
Where is the cell body of the primary/first order neuron located?
A
Dorsal root ganglia from S5-C1
16
Q
First order neurons are pseudounipolar neurons. What does this mean?
A
The neuron contains an axon that has split into two branches; one branch runs to the periphery and the other to the spinal cord.
17
Q
Where do the peripheral processes of first order neurons travel?
A
Axons travel up to the level of the dorsal root ganglion.
18
Q
Are the peripheral processes of first order neurons lightly, heavily, or unmyelinated?
A
Heavily myelinated (Ia, Ib, II)
19
Q
What type of receptors do the peripheral processes of first order neurons synapse with? Give specific examples (4)
A
Synapse with encapsulated receptors:
- muscle spindles
- golgi tendon organs
- pacinian corpuscles
- joint receptors
20
Q
Are the central processes of first order neurons lightly, heavily, or unmyelinated (Ia, Ib, II)?
A
Heavily myelinated (Ia, Ib, II)
21
Q
The central processes enter the spinal cord segmentally and ascend without synapsing to one of two places. what are they? (2)
A
- Fasciculus gracilis
2. Fasciculus cuneatus
22
Q
What is fasciculus gracilis?
A
A bundle of axon fibers, originating from S5-T7, in the posterior column-medial lemniscus pathway of the spinal cord and carries information from the lower trunk and lower limbs
23
Q
What is fasciculus cuneatus?
A
A tract of nerves originating from T6-C1, that primarily transmit information from the upper trunk and upper limb.
It is part of the posterior column-medial lemniscus pathway.
24
Q
Fasciculus gracilis and fasciculus cuneatus make up what columns?
A
Dorsal/posterior columns
25
The fasciculus gracilis and fasciculus cuneatus are added sequentially within the dorsal columns. How are they arranged?
In a topographic fashion from medial (lower extremities) to lateral (upper extremities
26
What are secondary or second order neurons?
Cell bodies located in the nucleus gracilis and nucleus cuneatus, respectively.
27
What is the nucleus gracilis?
One of the dorsal column nuclei and part of posterior column-medial lemniscus pathway, that participates in the sensation of fine touch and proprioception of the lower body (legs and trunk).
28
What is the nucleus cuneatus?
one of the dorsal column nuclei and part of posterior column-medial lemniscus pathway, carrying fine touch and proprioceptive information from the upper body
29
Where are the nucleus gracilis and nucleus cuneatus located?
at the level of the closed or caudal medulla.
30
What synapses on the nucleus gracilis and nucleus cuneatus?
Ascending fibers in the dorsal columns
31
What is formed by the axons of secondary neurons?
Internal arcuate fibers, which cross the midline and form the contralateral medial lemniscus
32
What are internal arcuate fibers?
axons of second-order neurons that are contained within the gracile and cuneate nuclei of the medulla oblongata.
33
What is the contralateral medial lemniscus?
A large ascending bundle of heavily myelinated axons that cross in the brain stem, specifically in the medulla.
Formed from the internal arcuate fibers that cross the midline
34
How is the medial lemniscus organized?
Somatotopically
35
Where does the medial lemniscus project to?
The ventral posterolateral nucleus of the thalamus (VPL)
36
What are tertiary or third order neurons?
Cell bodies located in the VPL
37
The axons of third order neurons project where?
Through the posterior limb of the internal capsule to the primary somatosensory cortex.
38
Where is the primary somatosensory cortex? What Areas are located within?
postcentral gyrus in the parietal lobe
Areas 3,1,2
39
True or false. The distribution of the third order neuron projections to the postcentral gyrus is no longer a somatotopic organization.
False.
Still organized as a somatotopic organization (the somatosensory homunculus)
40
What ares of the body have the greatest representation within the cortex? Give examples.
Areas that are the most sensitive.
Examples: index finger, tongue
41
Proprioception of the lower extremity includes what two nuclei?
```
Nucleus Z (part of Nucleus Gracilis)
Clarke's Nucleus
```
42
Where is Clarke's Nucleus found?
Spinal cord levels T1-L2
43
The alternative pathway that includes Nucleus Z and Clarke's nucleus carries what?
Some of the modality of conscious proprioception for the lower extremities.
44
What is added between the dorsal root ganglion and the nucleus gracilis?
An extra neuron.
45
In the alternative pathway involving Nucleus Z and Clarke's Nucleus,some of the large diameter first order fibers end where?
ipsilateral dorsal nucleus of Clarke
46
What is the dorsal nucleus of Clarke?
A group of interneurons found in the medial part of Lamina VII. It is an important structure for proprioception.
47
What is nucleus Z?
Located at the rostral end of nucleus gracilis.
48
In the alternative pathway a second neuron travels (IPSILATERLLY/CONTRALATERALLY) to ascend where?
Ipsilaterally
Dorsolateral fasciculus.
49
What is the dorsolateral fasciculus adjacent to?
The dorsal spinocerebellar tract
50
After ascending in the dorsolateral fasciculus, where does a scond neuron from the alternative pathway synapse?
In Nucleus Z
51
What do axons of nucleus Z join and where do go?
Join the internal arcuate fibers.
Cross to ascend as part of the contralateral medial lemniscus.
52
Once axons in the alternative pathway join the contralateral medial lemniscus, is the pathway the same or different?
The pathway is the same.
53
What is the proposed reason for the presence of the alternative pathway? What is the clinical significance?
Proposed as a possible neural pathway by which some conscious perception of proprioception for the lower extremities is maintained when the dorsal column system is damaged due to trauma or degenerative illness.
54
What sensory modalities are carried over the anterolateral/spinothalamic system? (3)
1. pain
2. temperature
3. non-discriminative touch
55
What are the two primary pathways in the anterolateral/spinothalamic system?
1. Lateral spinothalamic pathway
| 2. Anterior spinothalamic pathway.
56
What nerves/tracts transmit pain, temperature and non-discriminative touch for the anterior 2/3 of the head/face, oral and nasal cavities?
Trigeminal nerve and its central nuclei and tracts.
57
What tract carries the sensation for pain and temperature?
Lateral spinothalamic tract
58
What is the lateral spinothalamic tract named for?
The position of the fiber bundle of axons from the second neuron of the 3-neuron chain.
59
The first/primary neuron in the lateral spinothalamic tract is what type neuron? Where is the cell body located?
pseudounipolar
cell body in dorsal root ganglia
60
The peripheral receptors in the lateral spinothalamic tract are what type of ending?
Free nerve endings (non-encapsulated)
61
What type of fibers are a part of the lateral spinothalamic tract? (include type, size and myelination level)
A-delta
small
lightly myelinated
62
The A-delta fibers in the lateral spinothalamic tract transmit information at what speed?
Quickly (6-36 M/sec)
63
What sensation is carried by the A-delta fibers in the lateral spinothalamic tract? Is it localizable?
pricking pain
Fairly localizble.
64
Where do the central processes enter the spinal cord in the lateral spinothalamic tract?
Laterally
65
Once the central processes have entered the spinal cord, what happens?
They bifurcate in the Lissauer's tract
66
Once inLissauer's tract ,axons can travel in what directions? (3)
1. Ascend several segments
2. Descend several segments
3. Enter the dorsal horn at the current level
67
Once in the appropriate segment, axons from the central process will synapse where?
on neurons in the substantia gelatinos/nucleus proprius (Lamina of Rexed II, III)
68
What neurotransmitter is most likely used between all neurons in the lateral spinothalamic tract?
glutamate
69
Where is the cell body for the second order neuron most likely located?
substantia gelatinosa
70
Where to axons travel once they leave the substantia gelatinous?
In what direction and over how many segments?
across the midline, through the anterior white commissure.
Travels in an ascending/oblique direction (1-2 segments)
71
What is the anterior white commissure?
a bundle of nerve fibers which cross the midline of the spinal cord just anterior to the gray commissure
72
What do the axons of the second order neurons form they cross the midline? On what side of the cord?
The lateral spiothalamic tract on the contralateral side of the cord.
73
What type of organization does the lateral spinothalamic pathway have?
somatropic
74
Within the lateral spinothalamic pathway, the more lateral fibers carry pain and temperature sensations from where?
Lower body segments
75
Within the lateral spinothalamic pathway, the more medial fibers carry pain and temperature sensations from where?
Higher levels of the spinal cord
76
The spinothalamic tract ascends through the spinal cord and brainstem to reach what?
Ventral posterolateral thalamic nucleus (VPL) and intralaminar thalamic nuclei
77
Where is the third neuron cell body located?
VPL
78
True or False. The somatotropic distribution is maintained from the lateral spinothalamic tract to the VPL.
True.
The neurons situated most laterally are used to transfer information concerning pain from the lower extremity (lumbar scaral dermatomes).
79
Once axons leave VPL, they travel to where?
ascend to the primary somatosensory cortex?
80
How to axons travel from the VPL to the primary somatosensory cortex?
Via the superior thalamic radiations (the medial part of the posterior limb of the internal capsule)
81
Where is the primary somatosensory cortex located? What cortical areas?
In the postcentral gyrus
Cortical areas 3,1, 2
82
True or false. The primary somatosensory organizaion is represented along the cortex.
True
83
What does the homunculus represent?
The contralateral body somatotopic organization
84
Describe the position of the "little man"
upside down, as it if is hanging by the lower limb with the leg representation in the midline cortex and the rest of hte body on the lateral surface with the neck and head towards the lateral sulcus.
85
What does the homunculus representation allow for?
Allows for the precise localization of pricking pain (burning is less localized)
86
What are the clinical implications of the loss of 3rd order neurons?
Will result in the loss of localization of pain, but not the affective emotional response to pain
87
The precision of the lateral spinothalamic tract makes it useful to dermine what? Give an example
Lesion sites. By using the fact that the sensations cross in a relatively segmental manner, it is possible to identify the level of a spinal cord lesion by the loss of painful stimulation (anasthesia).
Example: loss of pain over half the body would be a hemi-anesthesia.
88
What three tracts run in parallel with the lateral spinothalamic tract?
1. Spinocervicothalamic
2. Spinoreticulothalamic
3. Spinomesencephalic
89
The spinocervicothalamic pathway contains an extra what?
Extra neuron.
90
Where does the extra neuron in the spinocervicothalamic pathway originate and travel?
Originates in the dorsal horn and ascends ipsilaterally to a group of cells located at the level of the cervical dorsal horn.
91
Once the fibers in the spinocervicothalamic pathway reach the cervical dorsal horn, where do they go?
They joint hte medial lemniscal system.
92
What is the medial lemniscal system?
An alternative pathway carrying modalities of conscious proprioception, discriminative touch and pain and termperature.
93
True or False. The information in the medial lemniscal system is localizable.
False.
Information in this pathway is non-localizable.
94
The spinoreticulothalamic pathway has a synapse where in the brainstem?
In the reticular formation
95
The spinoreticulothalamic pathway eventually reaches where?
Medial and intralaminar thalamic nuclei
96
Where do the medial and intralaminar thalamic nuclei project?
To widespread cortical areas including the limbic system
97
The limbic system connection involves what? What does it do?
The hypothalamus.
The hypothalamus activates or influences the ANS.
98
What does the spinoreticulothalamic pathway help analyze?
The stimulus within the emotional domain.
Also functions to activate the SNS response
99
The spinomessencephalic pathway projects where?
To the superior colliculus and periaqueductal gray in the midbrain
100
What can be activated by the spinomesencephalic pathway?
Descending pathways that are critical for modulating incoming painful stimuli
101
What can be activated by the spinoreticulothalamic and spinomesencephalic pathways?
Descending pathways originating from Raphe' nuclei (serotonin) and locus ceruleus (noepinephrine) of the reticular formation.
102
What is the function of the descending projections to the spinal cord from Raphe nuclei and locus ceruleus?
Function in the proposed circuitry used in the modification of the transmission of painful sensations
103
The anterior spinothalamic pathway carries what modalities? (2)
1. Light/Nondiscriminative touch
| 2. Pain sensation.
104
The majority of 1st order fibers of this pathway are (SMALL/LARGE), MYELINATED/UNMYELINATED)
small
| unmyelinated (C-fibers)
105
The Cfibers carry the sensation of what? (2)
1. burning pain
| 2. Thermal nociceptive impusles
106
What neurotransmitter is used in the anterior spinothalamic pathway?
Substance P
107
The neuron cell body locations in the anterior spinothalamic tract are the same as what other tract?
The Lateral spinothalamic tract
108
Give an example of a stimulus going through the anterior spinothalamic pathway
brushing a piece of cotton across the skin.
Aware of being touched by unable to identify texture or precise limits of the stimulation.
109
How is the trajectory of the 2nd order neuron in the anterior spinothalamic pathway different than the lateral spinothalamic pathway?
It is random.
It may travel up or down 10-12 segments before it crosses through crosses through the anterior white commissure.
110
Where do 2nd order axons form the anterior spinothalamic pathway?
Once they have crossed through the anterior white commissure.
111
Where does the anterior spinothalamic pathway end?
VPL
112
What else is carried in the anterior spinothalamic pathway besides nondiscriminative touch and pain?
non-specific temperature information.
