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Anatomy 6512 > Ascending Sensory System > Flashcards

Ascending Sensory System Flashcards

1
Q

What do somatosensory receptors detect?

A

Mechanical, Chemical, and Thermal changes

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2
Q

What type of neurons are somatosensory receptors and what are a few characteristics?

A

They are all pseudounipolar neurons with:

  1. Cell body in DRG or CN ganglion
  2. A central CNS process (spinal cord or brainstem)
  3. Peripheral process with an ending in skin, muscle, or a joint
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3
Q

Pacinian Corpuscles:

  1. encapsulated (layered/thin)/nonencapsulated (accessory structures or none)
  2. Adaptation
  3. Modality
A
  1. Encapsulated/ Layered
  2. Adapt rapidly
  3. Vibration
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4
Q

Meissner Corpuscles:

  1. encapsulated (layered/thin)/nonencapsulated (accessory structures or none)
  2. Adaptation
  3. Modality
A
  1. Encapsulated/ Layered
  2. Adapt rapidly
  3. Touch
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5
Q

Ruffini ending:

  1. encapsulated (layered/thin)/nonencapsulated (accessory structures or none)
  2. Adaptation
  3. Modality
A
  1. Encapsulated/ Thin
  2. Adapt slow
  3. Pressure
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6
Q

Endings around hair cells:

  1. encapsulated (layered/thin)/nonencapsulated (accessory structures or none)
  2. Adaptation
  3. Modality
A
  1. Accessory structures
  2. Adapt rapidly
  3. Touch
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7
Q

Merkel endings:

  1. encapsulated (layered/thin)/nonencapsulated (accessory structures or none)
  2. Adaptation
  3. Modality
A
  1. Accessory structures
  2. Adapt slow
  3. Touch
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8
Q

Free nerve endings:

  1. encapsulated (layered/thin)/nonencapsulated (accessory structures or none)
  2. Adaptation
  3. Modality
A
  1. None
  2. Adapt slow
  3. Pain, temp, itch, touch
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9
Q

What receptor types are in hairy skin?

A
  • Receptor endings wrap around hair cells

- Nerve ending at a Merkel cell in the basal layer of skin

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10
Q

What receptor types are in Glabrous (hairless) skin?

A

Meissner corpuscle
Merkel cell
Pacinian corpuscle
Ruffini ending

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11
Q

Meissner corpuscle:

  1. function
  2. location
  3. fiber type
A
  1. Discriminative touch (2 pt. discrimination)
  2. Concentrated in finger tips
  3. A-beta fiber (fast conducting)
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12
Q

Merkel nerve ending:

  1. function
  2. location
  3. fiber type
A
  1. Discriminative touch (2 pt. discrimination)
    • fine touch detail (edges of objects; texture)
  2. Concentrated in fingertips
  3. A-beta fiber (fast conducting)
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13
Q

What is the function of the posterior column-medial lemniscal pathway?

A

-2pt. discrimination
-Conscious proprioception
-Vibratory sense
(A-beta fiber/collateral to lamina II)

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14
Q

Where does the posterior column-medial lemniscus pathway decussate? Relay? Terminate?

A

-Decussates in medulla
-Relays in lateral thalamus
(Ventral posterolateral nucleus)
-Terminates in postcentral gyrus

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15
Q

What is spatial resolution?

A

Spatial resolution correlate w/ number of cutaneous receptors. For example, 2 pt. discrimination is more sensitive in the fingertips b/c there are more Meissner corpuscles and Merkel nerve endings.

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16
Q

Pacinian corpuscle:

  1. function
  2. location
  3. fiber type
A
  1. Detection of vibration
  2. Concentrated in fingers and in palm
  3. A-beta fiber (fast conducting)
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17
Q

What do free nerve endings sense?

A

Sensation of:

  • pain
  • crude touch
  • temperature
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18
Q

Temperature sensitivity is due to what?

A

Channels that open with a specific range of temperatures

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19
Q

What are the 2 phases of pain? What type of fibers are they carried by?

A
  1. Fast or Delta pain
    - Sharp prick, well-localized, short duration
    * Carried by rapidly conducting myelinated fibers
  2. Slow pain
    - Slow, poorly localized, aching pain that may follow
    * Carried by unmyelinated fibers
20
Q

What are propriospinal fibers?

A

-Short fibers that interconnect different spinal cord levels. These fibers help coordinate flexor reflexes.

21
Q

Where are descending tracts primarily located?

A

-Anterior and Lateral Funiculi

22
Q

Where are Ascending tracts primarily located?

A

-In all 3 funiculi (anterior,posterior, and lateral)

23
Q

Where are propriospinal fibers primarily located?

A

-They surround the spinal cord gray matter (propriospinal tract)

24
Q

Describe the function of the posterior column-medial lemniscus system.

A

-It conveys touch, pressure, vibration and limb position/movement information (location and nature of these stimulus). It is the main way info from cutaneous, joint and muscle receptors reach the cortex.

Posterior columns-mostly ascending large myelinated primary afferents from various mechanoreceptors.

25
Q

Where do spinal afferents have their cell bodies?

A

-Ipsilateral Dorsal root ganglia

26
Q

In the posterior column- medial lemniscus system, as DRG rootlets enter, cord fibers divide into what 2 divisions?

A
  1. Medial: heavily myelinated, large diameter fibers; enter posterior column and ascend to brainstem
  2. Lateral: finely myelinated and unmyelinated, small diameter fibers
27
Q

In the posterior column- medial lemniscus system, what beings to happen rostral to T6?

A

-Fibers are added to fasiculus gracilis and fasiculus cuneatus starts to form. Fibers entering posterior columns are added laterally to those present, so a pattern of lamination develops (sacral levels most medial, cervical levels most lateral)

28
Q

What happens if there is an injury to the posterior column-medial lemniscus system?

A
  • Leads to impaired proprioception and discriminative tactile functions, especially complex tactile discrimination.
  • Proprioception could be lost completely, resulting in ataxia, uncoordinated movements bc brain cannot direct motor activity without feedback from the body
29
Q

How is an injury to the posterior column-medial lemniscus system tested clinically?

A

-By placing a vibrating tuning fork on body surface or have patient identify a pattern drawn on their skin

30
Q

Although injuries to the posterior column are possible to recover from over time, what is likely to remain repaired?

A

-The ability to discriminate complex shape of an object (sterognosis) or the direction or speed of the stimulus moving across the skin

31
Q

Describe the pathway of the posterior column-medial lemniscus system.

A

-Fibers reach the brainstem and synapse in nucleus gracilis and cuneatus (posterior column nuclei). Then second order fibers cross the midline (decussate) in caudal medulla to form the medial lemniscus. Lastly, third order fibers originate in the thalamus (ventral posterolateral nucleus) ascend thru internal capsule and synapse primarily in primary somatosensory cortex in post central gyrus.

32
Q

What is the function of the spinothalamic tract?

A
  • One of the many pathways (anterolateral) that convey pain and temperature info. Involved in awareness, nature, and localization of painful stimuli.
  • Ultimately ends in VPL of thalamus and some nearby thalamic nuclei
33
Q

Describe the pathway of the spinothalamic tract/anterolateral pathway.

A

-Pain, temp, and some mechanoreceptor fibers enter cord via lateral division of dorsal root, project branches to posterior horn, many synapse in substanstia gelatinosa (lamina 2). Neurons in other laminae form second order neurons cross midline with rostral inclination, collect and form anterolateral pathway.

34
Q

Describe the somatotopic organization of the anterolatelr pathway.

A

-New fibers join at the anteromedial edge. Caudal body parts (leg) are in posteriolateral portion, rostral body parts (arm) in anteromedial portion.

35
Q

What spinomesencephalic fibers important for?

A

–From laminae I and V, important in pain control mechanisms

36
Q

What do spinohypothalamic fibers mediate?

A

-Autonomic response to pain

37
Q

Damage to the anterolateral pathway causes loss of what?

A
  • Pain and temperature sensations

- Itch and tickle sensations

38
Q

What are the effects of a unilateral injury to the anterolateral pathway on bowel and bladder pressure, and sexual sensation?

A

-It does not leave a deficit because these fibers ascend bilaterally.

39
Q

What is a cordotomy?

A

-Destroy spinothalamic tract to produce contralateral analgesia in patients with intractable pain. Cut lateral funiculus from dentate ligament to ventral root rostral to highest dermatomal pain level.
(Analgesia lasts several months)

40
Q

What does the cerebellum use information from the spinal cord for? Direct? Indirect?

A

-to coordinate movement
Direct: Spinothalamic tracts, 3 well characterized
Indirect: via brainstem relay nuclei

41
Q

What does the posterior spinocerebellar tract (PSCT) convey?

A

-Proprioceptive information

42
Q

Posterior Spinocerebellar tract:

  1. Origin
  2. Body part represented
  3. Major inputs
  4. Midline crossing
  5. Peduncle used to enter cerebellum
A
  1. Clarke’s nucleus (T1-L2/3)
  2. Trunk/leg
  3. Mechanoreceptors in muscles, joints, skin
  4. None
  5. Inferior
43
Q

Anterior Spinocerebellar tract:

  1. Origin
  2. Body part represented
  3. Major inputs
  4. Midline crossing
  5. Peduncle used to enter cerebellum
A
  1. Spinal border cells (lateral surface of anterior horn at lumbar levels)
  2. Trunk, leg (but differs from PSCT)
    * Inputs more complex (cutaneous receptors, interneurons and from fibers in descending tracts) so more related to attempted movements than simple sensory signals
  3. Mechanoreceptors, movement-related interneurons
  4. Twice: First in spinal cord then in cerebellum (ultimately fibers end ipsilateral to source)
  5. Superior
44
Q

Cuneocerebellar tract:

  1. Origin
  2. Body part represented
  3. Major inputs
  4. Midline crossing
  5. Peduncle used to enter cerebellum
A
  1. Arm afferents ascend in funiculus cuneatus to lateral cuneate nucleus in medulla
  2. Trunk, arm
  3. Mechanoreceptors in muscles, joints, skin
  4. None
  5. Inferior to synapse in vermis and nearby cerebellar hemisphere
45
Q

In the posterior Spinocerebellar tract, what do afferents caudal to T2 do?

A

-Ascend to L2 via fasciculus gracilis and synapse on clarke’s nucleus

Anatomy 6512 (9 decks)

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