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Sensory Pathways Flashcards

1
Q

What is proprioception?

A

Proprioception consists of both a sense of a limbs position in space and a limbs movement.

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2
Q

Where are proprioception sensory receptors located?

A

Proprioception sensory receptors are predominantly located within muscle spindles (intrafusal muscle fibres), tendons (golgi tendon organs) and joint capsual and ligaments.

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3
Q

What sensations are tested in physical examination?

A
  1. Mechano receptors detect mechanical sensation (touch, pressure, vibration, proprioception).
  2. Pain (nociceptors) and temperature (thermoreceptors) sensation.
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4
Q

What are the two main pathways named that carry conscious somatic sensation?

A

DCML and the Antero-lateral System (ALS)

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5
Q

What does the DCML pathway carry?

A
  1. Conscious proprioception
  2. Discriminative touch
  3. Vibration
  4. Pressure and
  5. Back up for crude touch
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6
Q

What information does the Anterio-lateral system (ALS) carry?

A
  1. Pain
  2. Temperature
  3. Crude touch
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7
Q

What is the role of the spinocerebella tracts?

A

Sensory input - Unconscious proprioception (mostly for coordination and supervision of ongoing movements). Does not reach cortex - therefore not conscious.

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8
Q

What is graphestheisa?

A

Being able to dicern letters / shapes being drawn on the skin.

DCML pathway

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9
Q

What is stereognosis?

A

Identifying of objects by touch.

DCML pathway

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10
Q

What information is carried in the fasciculus cuneate?

A

Sensory information from above T6

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11
Q

What information is carried in the fasciculus gracile?

A

Sensory information collected below T6.

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12
Q

Where are first order neurons located in the sensory pathways (DCML / Anterolateral System)?

A

FIrst order sensory neurons are located outside of the CNS. Their receptor processes are at the site of input ie the skin for mechanoreceptors (vibration, pressure, discriminative touch & back up crude touch); their cell bodies lie in the dorsal route ganglion (near the spinal cord) and their proximal processes enter the spinal cord via the dorsal horn and synapse onto the second order neuron here.
With cranial nerves the ganglion of the first order neurons is located with in the relevant cranial nerve ganglion (mostly within the trigeminal ganglion).

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13
Q

Where is the body of the cranial nerve first order neurons located?

A

Within the cranial nerve ganglion (mostly the trigeminal n ganglion).

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14
Q

Which neuron (1st, 2nd, 3rd) order decussates in the DCML & Anteriolateral system (ALS) pathway?

A

The second order neuron decussates and this occurs close to its origin.

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15
Q

Does the 2nd order neurons in the DCML & ALS pathway exist within the CNS, PNS or both?

A

2nd order neurons located within the DCML & ALS sensory pathways are located within the CNS (spinal cord or medulla).

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16
Q

Where is the body of the third order neurons located in the DCML and ALS sensory pathways?

A

The third order neuron is located within the thalamus (VPL). and extends up to the primary somatosensory cortex.

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17
Q

What are the main receptors for proprioception for the DCML pathway?

A
  1. (stretch of intrafusal muscle fibres containing muscle spindles detects stretch = proprioception) & 2. golgi tendon organs (located in the tendon and activated by tension of the tendon).
  2. Joint kinesthetic receptors (types I-IV)
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18
Q

What are the primary receptors for crude touch?

A

Free nerve endings
Hair follicles

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19
Q

What are the primary receptors for fine touch?

A

Merkel receptors

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20
Q

What are the primary receptors for Flutter / stroking touch?

A

Meissner corpuscle

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21
Q

What are the primary receptors for Vibration / pressure?

A

Pacinian corpuscle

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22
Q

What are the primary receptors for skin stretch?

A

Ruffini endings

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23
Q

What are the primary receptors for skin stretch?

A

Ruffini endings

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24
Q

Where in the medulla does the DCML pathways decussate?

A

Within the medulla ABOVE the motor decussation.

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25
Q

While travelling through the brain stem the DCML fibres travel through the medial lemniscus. Where within the midbrain (at each segment) does the medial lemniscus ascend? Think in terms of anterior / medial / lateral etc

A

In the medulla and pons the DCML pathway ascending within the medial lemniscus is located in the anterior tegmentum (not far from the pyramidal tracts and fascicles).
In the midbrain the medial lemniscus moves more posteriorly and is positioned more centrally (medially between the anterior and posterior tegmentum).

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26
Q

Considering the sensory homunculus distribution where would sensory input from the lower limb terminate in the primary somatosensory cortex?

A

Medial aspect of the primary somatosensory cortex (adjacent to the longitudinal fissure).

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27
Q

What types of nerve fibres comprise the DCML pathway?

A

The DCML Pathway consists of A-a and A-B type neurons (fast conduction).

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28
Q

Where does the gracile fasiculus terminate?

A

Gracile tubercle

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29
Q

What neuronal cell bodies are located within the gracile tubercle?

A

Second order neurons?

29
Q

What neuronal cell bodies are located within the gracile tubercle?

A

Second order neurons?

30
Q

Where are the second order neurons located for the DCML pathway from the upper limb found?

A

Upper limb sensory information (proprioception, discriminative touch, vibration and back up crude touch) is travels within the DCML pathway until it reaches the second order neurons located within the cuneate nucleus in the medulla.

31
Q

Does sensory information detected by first order neurons of the DCML pathway ascend the spinal cord ipsilaterally or controlaterally?

A

Ipsilaterally, as decussation occurs via the second order neuron within the medulla (above the motor decussation).

32
Q

How do you test the DCML pathways

A
  1. Proprioception
    - Big toe for LL; thumb / finger for UL.
    Hold the joint lightly perpendicular to the axis of movement.
  2. Vibration
    - Use 128hz tuning fork and test on bony prominence) starting distally.
  3. Two point discrimination (2mm in finger tips & 5mm in palm are normal).
33
Q

What is Romberg sign

A

Eyes open & feet together.
Close eyes
Look for unsteadiness and swaying to one side.

34
Q

What does a positive Romberg’s sign indicate?

A

Positive Romberg’s sign indicates either a vestibular or proprioceptive disturbance.

35
Q

If a patient is unsteady at the first stage of a Romberg’s test (eyes open feet together) do they likely have a DCML - proprioception problem?

A

No they have a cerebella problem.
Visual feedback, conscious proprioception and vestibular input is required to perform a Romberg’s test. The test occurs when one of these three systems is removed (vision) and the other two are required to keep the patient upright and steady.

36
Q

Why do patients with proprioceptive deficits have more trouble at night?

A

Visual input pathway is reduced at night and thus patients with proprioceptive deficits lose one of the two systems they rely upon (vision, vestibular and proprioceptive inputs) to maintain truncal stability.

37
Q

What is the likely issue with this patients truncal instability?

A

This patient is showing signs of cerebellar ataxia.

A cerebellar problem is the likely cause as truncal stability relies on the cerebellum PLUS at least 2 of the following:
1. Vestibular input,
2. Visual input,
3. Proprioceptive input.
A positive Romber’s sign without any of these three removed inputs removed indicates a cerebella dysfunction.

38
Q

What is the likely issue with this patients truncal instabililty.

A

This patient is showing signs of a positive Romberg’s sign and thus sensory ataxia.
The patient is able to maintain stability when all three sensory inputs are present (eyes open) before the test however loses truncal stability when the visual input is removed.
Truncal stability requires at least two of the following inputs:
1. Vestibular input,
2. Visual input,
3. Proprioceptive input.

By removing vision the other two can be tested for intactness.

39
Q

Sensory ataxia / DCML lesions gait presents as?

A

Tampling / stomping gate caused by loss of proprioception - relying on other sensory inputs to detect their position in space.

40
Q

What does cerebella ataxia present as?

A

Wide based - tottering gait.

41
Q

Lesions of the right Spinal cord or cerebellum will present with a patient leaning / swaying to which side and why?

A

A patient with a right spinal cord lesion or a right cerebellar lesion will lean / sway to the right because DCML sensation (proprioception) ascends the spinal cord on the ipsilateral side (until decussating in the medulla). The cerebellum also provides motor adjustment signals via the ### pathway which descends ipsilaterally (no decussation for the cerebellum).

42
Q

How does a patient with sensory ataxia present? (4)

A

Sensory ataxia presents with:
1. Truncal stability deficits
2. which is worse at night (reduced visual input to compensate).
3. Associated DCML sensory deficits such as vibration, discriminative touch).
4. NO associated muscle weakness.

43
Q

Acute pain travels via fast sensory fibres. Receptors are mostly?

A

Free nerve endings detect pain. The are located superficially within the dermis of the skin.

44
Q

Where are the fast pain fibres located?

A

The Lateral spinothalamic tract.
This is the tract tested with the pinprick test and the temperature tract.

45
Q

Crude touch sensory information is carried in which sensory pathway?

A

The Anterior spinothalamic tract relays sensory information from the periphery to the thalamus.

46
Q

What do the pink segments in the attached diagram represent?

A

The pink segments represent the ALS anterolateral spinothalamic tracts for transmission of sensory (pain and temperature) from the periphery to the thalamus.

  1. The lateral spinothalamic tract.
  2. The anterior spinothalamic tract.
47
Q

Where are the first order neurons of the ALS (anteriolateral system) located?

A

LL are located in the dorsal root ganglia housed within the lumbosacral plexuses.
UL are located in the dorsal root ganglia housed within the brachial plexuses.

48
Q

Where are second order neurons located in the ALS sensory pathway?

A

The dorsal horn of the spinal cord.
Therefore decussation occurs immediately, running obliquely up approximately two spinal segments to the contralateral lateral spinothalamic tract > lateral spinal lemniscus in the brain stem to the thalamus.

49
Q

Fill in the gaps in this pathway:

Mechano receptor in lower limb > dorsal root ganglion > dorsal horn > __________ (ipsilateral / contralateral side) > __________ nucleus (medulla) > ___________lemniscus > thalamus (VPL) > internal capsule (posterior limb) > primary somatosensory cortex.

A

Mechano receptor in lower limb > dorsal root ganglion > dorsal horn > gracile fasciculus (ipsilateral side) > gracile nucleus (medulla) > decussation then ascend medial lemniscus > thalamus (VPL) > internal capsule (posterior limb) > primary somatosensory cortex.

50
Q

Fill in the gaps in this pathway:

Nociceptor activated in hand > Brachial _________ ganglion > ___________ & ____________ > ____________ tract > __________ lemniscus > thalamus (____) > internal capsule (posterior limb) > primary somatosensory cortex

A

Nociceptor activated in hand > *Brachial dorsal root ganglion > decussation & assention oblique via 2 spinal segments > lateral spinothalamic tract > lateral lemniscus > thalamus (VPL) > internal capsule (posterior limb) > primary somatosensory cortex

51
Q

How do we test ALS pathway?

A

Pin prick - toothpick / safety pin: do you feel dull / sharp following dermatome pattern.
Warm / cold test tubes: do you feel warm or cold?
Crude: use cotton wool ball to stroke - tell me when you can feel me touch you?

52
Q

Which pathway decussates and ascends obliquely within the spinal cord?

A

Anteriolateral spinothalamic (ALS) sensory pathway decussates and ascends in an oblique fashion up approximately 2 segments.
Thus a lesion at a specific level will effect input from the ALS (pain & temperature) from 2 spinal cord segments below.

53
Q

What information does the ventral trigeminal thalamic tract?

A

Sensory for the face head and neck.

54
Q

Where are the first order neurons located for the Opthalmic, maxillary and mandibular branches of the trigeminal nerve?

A

The trigeminal ganglion.

55
Q

The Ventral Trigeminothalamic tract (VTT) caries:
* unconcious proprioception,
* touch and
* conscious proprioception as well as
* pain sensory information
via all three branches of the trigeminal nerve.

First order neurons for each of these are located within the trigeminal ganglion. The second order neurons are housed within three different sensory nuclei in the brain stem. Match the imput with the second order neruon nuclei.

A
  1. Midbrain (Mesencehpalic nucleus): unconscious proprioception.
  2. Pons (Chief sensory nuclei): conscious proprioception and crude touch.
  3. Medulla (spinal nucleus of trigeminal): temperature and pain.
    4*Spinal nucleus of trigeminal descends down into medulla and top of the spinal cord.
56
Q

Is cerebella control ispilateral or controlateral?

A
57
Q

What is the role of spinocerebella pathways? (3)

A
  1. Transmit unconscious proprioceptive inputs.
  2. Imputs always go to the ipsilateral cerebellar hemisphere.
  3. Provide important imputs for cerebellum about executed movments to supervise coordinated movement.
58
Q

What are the roles of the cerebella peduncles?

A

Transmits information from the spinocerebella tracts > brainstem > the cerbellum via the inferior and superior cerebellar peduncles.

59
Q

What degree of sensation is felt at the thalamic level?

A

Pain and touch but no discrimination or localisation possible.

60
Q

Sensations percieved by the primary somatosensory cortext inlcude?

A

Being able to localise imputs, determine their quality and intensity.

61
Q

Cortical sensations requiring association cortices include:

A

Graphestesia and steriognosis (the integration of fine touch combined with pressure etc).

62
Q

What will the sensory deficits observed in a patient with sensory association area (parietal lobe)?

A

Sensory tests will show sensation can be detected (somatosensory cortex) however more complex sensation ssuch as graphestheisa and steriognosis will be effected.

63
Q

Visual spatial awareness is controlled in the Occipital cortices.
The Right occipital lobe controls BOTH right an left visual spatial awareness howerver
The Left occipital love only controls the left visual spatial awareness.
What is seen with right and left lesions in the occipital lobe regions controlling visual spatial awareness?

A

A lesion in the right parietal lobe is likely to result in a Left visuospatial deficit HOWEVER a
Left parietal lobe lesion is unlikely to result in a right visual spatial deficit due to reduncancy on the right.

64
Q

What tests can be done to observe cortical sensation?

A

Eyes closed for Stereognosis and Graphaesthesia.

Visual and tactile present input similtaneously.

65
Q

What is the somatotopic organisation of the sensory pathways in the spinal cord?

A

The more medial the section of the sensory pathway the more superior the region represented:
Cervical inflow - most medial
Thoracic inflow - medial
Lumbar inflow - more lateral
Sacral inflow - most lateral

Therefore medial expanding lesions / tumour in the cervial region are called sacral sparing (damage is medially placed and therefore the laterally placed sections of the DCML and ALS are spared (sacral inflow).

66
Q

Can you identify each of these sensory pathways?

A

Bright Green: VTT from head and neck (proprioception and touch) mesencephalic nucleus)
Brown: Ventral Trigeminothalamic tract (spinal nucleus of trigeminal) VTT (pain and temperature)
Dark green: DCML
Pink: Lateral spinothalamic tract

67
Q

Sensory dissociation defines a presentation where an individual has loss of pain and temperature sensation on one side of the body and loss of proprioception and vibration on the opposite side. There is only one location in the CNS where lesions cause this presentation.
Where is that?

A

Within the spinal cord.
* DCML sensory pathway ascends in the ipsilateral side of the spinal cord until the medulla deccusation.
* The spinothalamic pathways carrying pain and temperature information cross immediately (obliquely up 2 segments) upon entry into the spinal cord.
Thus sensation is disassociated with spinal cord lesions only.

68
Q

Lesions above the level of the pons will result in contralateral hemi-sensory loss (R - L) side of body. Why?

A

At the level of the pons or above all sensory pathways (VTT, spinothalamic and DCML) have decussated by this point and thus sensory loss will be contralateral to the lesion.

69
Q

Dermatomal sensory loss occurs as a result of?

A
  1. Lesions of the dorsal horn of the spinal cord will cause sensory deficits in the dermatomal areas supplied by that spinal segment.
  2. Spinal nerve root damage can cause sensory loss in a dermatomal arrangement also.
70
Q

What is the deccussation points for the:
Corticospinal pathway (lateral),
Spinocerebella pathways,
Spinothalamic pathways, &
Posterior columns (DCML)?

A

Neuro (23 decks)

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