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Neuroscience > Somatosensory Pathway 1 > Flashcards

Somatosensory Pathway 1 Flashcards

1
Q

Transmits and analyzes touch or tactile information from external & internal locations on the body & head

A

The Somatosensory System

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2
Q

The Somatosensory System is transmitted via which pathways?

A
  • Posterior column-medial lemniscal pathway
  • Trigeminothalamic pathway
  • Spinocerebellar pathway
  • Anterolateral system
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3
Q

Involved with the perception and appreciation of mechanical stimuli

A

Posterior Column–Medial Lemniscal System (PCMLS)

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4
Q

ability to discriminate between two

stimuli simultaneously

A

Two-point discrimination

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5
Q

Characteristic features of. which pathway?
relays

  • Afferent fibers with fast conduction velocities & limited number of synaptic
  • Precise SOMATOTOPIC organization
A

Posterior Column–Medial Lemniscal System (PCMLS)

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6
Q

Peripheral Receptors
• Digits and perioral region have ? density of
tactile receptors

• Other regions, like the back, have ? density

A
  • increased

- decreased

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7
Q

area of skin innervated by a somatic afferent fibers

A

Receptive field

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8
Q
  • Small receptive fields have ? receptor density

- Large receptive fields have ? receptor density

A
  • high

- low

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9
Q

Primary Afferent Fibers

  • Consist of what 3 things?
A
  1. Peripheral process
  2. Central Process
  3. Pseudounipolar cell body
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10
Q

Primary Afferent Fibers:
1. ? extending from the DRG
(mechanoreceptor or free nerve ending)

  1. ? extending from DRG into
    CNS
  2. ? in the DRG
A
  • Peripheral process
  • Central process
  • Pseudounipolar cell body
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11
Q

Peripheral distribution of the afferent nerves arising from each spinal level delineates the segmental pattern of ?

A

dermatomes

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12
Q

fasciculus

gracilis or fasciculus cuneatus are collectively called?

A

posterior columns

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13
Q

Posterior Column

  • Sacral level fibers are positioned ? and fibers from progressively more rostral levels (up to thoracic level T6) are added ? → form the ?
A
  • medially
  • laterally
  • fasciculus gracile
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14
Q

Posterior Column

  • Thoracic fibers above T6 & cervical fibers are lateral → form the ?
A

fasciculus cuneatus

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15
Q

Spinal cord lesions result in ?

A

ipsilateral reduction or loss of discriminative, positional, & vibratory tactile sensations at & below the segmental level of injury

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16
Q

loss of muscle stretch (tendon) reflexes, and

proprioceptive losses from the extremities due to lack of sensory input

A

Sensory ataxia

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17
Q

Posterior Column Nuclei
• Segregation of tactile inputs occurs w/in the nuclei:
- Core “clusters” receive inputs from ?

A

rapidly- & slowly adapting afferents

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18
Q

Posterior Column Nuclei:
• Segregation of tactile inputs occurs w/in the nuclei:
- Outer “shells” receive inputs from ?

A

muscle spindles, joints,

& Pacinian corpuscles

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19
Q

Thalamic Relays:

  • ? of PC nuclei send axons to contralateral thalamus
A

Second-order neurons

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20
Q

Thalamic Relays:

• Second-order neurons of PC nuclei send axons to
contralateral thalamus

  • ? loop anteromedially in
    medulla
  • Cross the midline as the ?
  • Ascend as the ? on the
    opposite side
  • As ML extends rostrally, it rotates laterally in the ?
  • Upper extremity fibers lie ? and lower extremity fibers ?
  • Somatotopic organization is
    maintained as ML terminates in ? of the
    thalamus
A
  • Internal arcuate fibers
  • sensory decussation
  • medial
    lemniscus (ML)
  • pons
  • medially
  • laterally
  • ventral posterolateral
    nucleus (VPL)
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21
Q

Thalamic Rays (PC)

  • At medulla, it is fed by ? artery
A

Anterior spinal A.

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22
Q

Midbrain PC Lesions:

Damage at brainstem levels leads to deficits in discriminative touch, vibratory, & positional sensibilities over the ? side of the body

A

contralateral

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23
Q

Wedge-shaped cell group located in caudal

thalamus

A

Ventral Posterior Nuclei

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24
Q

Ventral Posterior Nuclei:
- Comprised of the ? & the ?

  • Separated by fibers of the ?
  • VPM receives ? sensory information
A
  • ventral posterolateral nucleus (VPL)
  • ventral posteromedial nucleus (VPM)
  • arcuate lamina
  • trigeminal
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25
Q

Ventral Posterior Nuclei:

  • Somatotopic arrangement of the body is
    maintained in the ?
A

VPL

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26
Q

Ventral Posterior Nuclei:

  • VPL & VPM are supplied by thalamogeniculate
    branches of ?
  • Compromise can result in loss of all tactile
    sensation over the ? body & head
A
  • posterior cerebral artery

- contralateral

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27
Q

PC

  • Receives ascending input from medial lemniscus
A

VPL (ventral posterolateral nucleus)

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28
Q

PC:

The VPL for the trunk & extremities contains two populations of
identified neurons:

A
  1. Third-order neurons

2. Local circuit interneurons

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29
Q

Third-order neurons:
- large-diameter axons that traverse posterior
limb of the internal capsule & terminate in the ? & ?

A
  • primary (SI)

- secondary (SII) somatosensory cortices

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30
Q

receive excitatory
corticothalamic inputs & influence the firing rates of third-order
neurons

A

Local circuit interneurons (inhibitory)

31
Q

Axons from third-order neurons (thalamus) terminate in?

A

primary somatosensory (SI) cortex

32
Q

• Comprises postcentral gyrus and posterior paracentral gyrus

• Bordered by central sulcus (anteriorly) & postcentral sulcus
(posteriorly)

A

primary somatosensory (SI) cortex

33
Q

“Foot to tongue” pattern along

medial → lateral axis

A

homunculus

34
Q

Homunculus

  • Regions with ↑↑↑ receptor density, have large amount of
    dedicated cortical tissue
A

hand/lips

35
Q

Homunculus

  • Regions with ↓↓ receptor density have small cortical
    representations
A

back

36
Q

Blood supply to the SI cortical areas is provided by?

A

anterior & middle cerebral arteries

(MCA lesions produce tactile loss over the CONTRALATERAL UPPER body & face; ACA lesions affect the contralateral LOWER limb)

37
Q

Subdivisions of SI:

  • ? is located in the depths of the central sulcus, abuts area 4 (primary motor cortex)
A

Area 3a

38
Q

Subdivisions of SI:

  • extend up the bank of the sulcus onto the shoulder of the postcentral gyrus
A

Areas 3b & 1

39
Q

Subdivisions of SI:

  • lies on the gyral surface and abuts area 5 (somatosensory association cortex)
A

Area 2

40
Q
  • Lies deep in the inner face of the upper bank of lateral sulcus
  • Contains somatotopically representation of body surface
• Inputs arise from ipsilateral SI cortex & ventral posterior
inferior nucleus (VPI) of the thalamus
A

Secondary somatosensory (SII) cortex:

41
Q
  • receive tactile inputs
  • Posterior to area 2, includes area 5 and area 7 (7b)
  • Receive some medial lemniscal input & inputs from SI
A

Parietal cortical regions

42
Q

Lesions in parietal association area can produce?

A

agnosia

43
Q

• Contralateral body parts are lost from the personal body map

• Sensation is not radically altered, but the limb is not
recognized as part of the patient’s own body

A

Agnosia

44
Q

? input plays an
integral role in guiding control
of body muscle tone,
movement, and posture

A

Cerebellar

45
Q

transmit proprioceptive & limited cutaneous information to the
cerebellum

  • Includes information about limb
    position, joint angles, and muscle
    tension/length
A

Spinocerebellar pathways

46
Q

• Mixed nerve with sensory and motor components

  • Main sensory nerve for the head
  • Innervates the muscles of mastication
A

Trigeminal Nerve

47
Q

Attaches to the brainstem as two adjacent roots (? and ?) on ventrolateral aspect
of the pons

A
  • large sensory

- smaller motor

48
Q

Form a continuous cell column that extends
from spinomedullary junction to rostral levels of
mesencephalon/midbrain

A

Trigeminal Nuclei

49
Q

4 nucleus of Trigeminal Nuclei?

A
  1. Main sensory nucleus (msT)
  2. Trigeminal motor nucleus (mT)
  3. Spinal nucleus
  4. Mesencephalic nucleus (mes)
50
Q

Functions of the 4 trigeminal nuclei?
1. Main sensory nucleus (msT)

  1. Trigeminal motor nucleus (mT)
  2. Spinal nucleus
  3. Mesencephalic nucleus (mes)
A
  1. Main sensory nucleus (msT): touch &
    pressure
  2. Trigeminal motor nucleus (mT): muscles of
    mastication
  3. Spinal nucleus: pain & temperature
  4. Mesencephalic nucleus (mes): proprioceptive
    afferents from the TMJ & masticatory m
51
Q

Locations of the 4 trigeminal nuclei?

  1. Main sensory nucleus (msT)
  2. Trigeminal motor nucleus (mT)
  3. Spinal nucleus
  4. Mesencephalic nucleus (mes)
A
  1. Main sensory nucleus (msT)
    - midpons, slightly lateral to motor
    nucleus
  2. Trigeminal motor nucleus (mT)
  3. Spinal nucleus
    - extends caudally
    from this level
  4. Mesencephalic nucleus (mes)
    - extends rostrally (all the way into the midbrain), as name implies
52
Q

Sensory Nerve for the Head

A

CN V

53
Q

Main Sensory Nucleus

  • afferent input from oral cavity
A

Dorsomedial division

54
Q

Main Sensory Nucleus

  • afferents from V1, V2, V3
A

Ventrolateral division

55
Q
  • Two-point localization
  • Vibratory sense
  • Position sense
A

Trigeminal System

56
Q

Main Sensory Nucleus:

  • 2nd order fibers of dorsomedial division project ipsilaterally via ?
A

posterior trigeminothalamic tract

57
Q

Main Sensory Nucleus:

  • 2nd order fibers of ventrolateral division project contralaterally via ?
A

anterior trigeminothalamic tract

58
Q

Main Sensory Nucleus:

• Both tracts target ? of the thalamus

  • Somatotopic arrangement
  • Oral cavity = medial, external face = lateral
A

ventral posteromedial (VPM) nucleus

59
Q

Main Sensory Nucleus:

  • 3rd order axons from VPM project via ? → ?
A
  • posterior limb of internal capsule

- primary somatosensory cortex

60
Q

Tactile & proprioceptive information from upper & lower extremities, & head/neck is relayed via ?

A

PCMLS & Main sensory of V

61
Q
  • Comprised of pseudounipolar neurons
  • Conveys unconscious proprioceptive &
    pressure information from muscles of the
    oral region
A

Mesencephalic Nucleus

62
Q

Mesencephalic Nucleus
- Projects to the ?

  • Permits the conscious awareness of facial & oral proprioception via the ?
  • Some axons terminate in ? → forms circuit for the jaw-jerk reflex
A
  • main sensory nucleus (and spinal nucleus)
  • anterior/posterior
    trigeminothalamic tract
  • trigeminal motor nucleus
63
Q

Stretching the masseter (downward
tap on chin), causes it to contract
bilaterally

A

Jaw-jerk Reflex

64
Q

What are the Trigeminocerebellar Pathways?

A
  • Mesencephalic nucleus via Spinal nucleus (Pars interpolaris)
  • Main sensory nucleus
65
Q

Which Trigeminocerebellar Pathway?

• Proprioceptive input from the jaw related to
chewing/jaw placement

• Via the superior cerebellar peduncle
(restiform body)

A

Mesencephalic nucleus via Spinal nucleus (Pars interpolaris)

66
Q

Which Trigeminocerebellar Pathway?

  • Moderate amount of secondary neurons project to the anterior vermis of the cerebellum
  • Via the superior cerebellar peduncle
A

Main sensory nucleus

67
Q

• Brainstem or SC lesions that result in deficits on
that differ between each half of the body -
dependent upon where fibers cross

A

Cross Sensory Syndrome

68
Q

Cross Sensory Syndrome:

• Brainstem lesions can result in:
- Sensory deficits of trunk/extremities ? to
the lesion, but sensory deficits of face/CN ? to
the lesion

  • The right face and the left arm/leg lack proprioceptive
    information
A
  • contralateral

- ipsilateral

69
Q

Cross Sensory Syndrome

• SC lesions can result in:

-? deficits on the right, but ? on the left (or vice versa)

A
  • Proprioceptive

- anesthesia

70
Q

Typically, SI lesions usually include larger areas & frequently result in more global deficits:

  • Loss of proprioception, position sense, vibratory sense, and pain & thermal
    sensations on the ? side of the body
A

contralateral

71
Q

SI Lesions and Sensory Dissociation:

  • Lesions involving area ? produce a deficit in texture discrimination, whereas damage to area ? results in loss of size and shape discrimination (astereognosis)
A
  • 1

- 2

72
Q

SI Lesions and Sensory Dissociation:

  • Injury to area ? has a more profound effect than does damage to either area 1 or 2 alone → have deficits in both texture and size/shape discrimination
A

3b

73
Q

SI Lesions & Sensory Dissociation:

  • Area ? performs initial processing and distributes information to areas 1 & 2
A

3b

74
Q

Thalamic Rays (PC) :

• In spinal cord, these columns when they are coming in as afferents and first order neurons are fed by the?

A

Posterior spinal artery

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