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Neurology > The Somatosensory System 2 > Flashcards

The Somatosensory System 2 Flashcards

1
Q

What are the 2 main parts of the somatosensory pathways?

A

Dorsal column leminscal (DCML) pathway

SpinothalamicTract (STT)

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2
Q

What do both DCML and STT consist of?

A

3 neurons in series: 1st, 2nd and 3rd order neurones

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3
Q

Where is the cell body of the 3rd order neurone?

A

THALAMUS

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4
Q

Where does the 3rd order neurone project to?

A

SOMATOSENSORY CORTEX

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5
Q

What is the DCML pathway responsible for?

A

Discriminative touch
Pressure
Vibration
Conscious proprioception

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6
Q

What is the STT pathway responsible for?

A 
Pain
Thermosensation
Crude touch
Itch
Tickle
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7
Q

Where does the decussation of DCML fibres take place?

A

At the great sensory decussation of the MEDULLA

2nd order neurones all cross together here

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8
Q

Where does the decussation of STT fibres take place?

A

At all levels of the spinal cord, close to the point of entry, via Lissauer’s tract.
 ie. synapse in the dorsal horn of the spinal cord, meaning that information ascends contralaterally.

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9
Q

Brown - Sequard Syndrome explains?

A

The differences in the level of decussation of the DCML and STT

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10
Q

What do the dorsal columns consist of?

A

The medial fasiculus gracilis (gracile tract)
+
The more lateral fasiculus cuneatus (cuneate tract)

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11
Q

Where does sensory input to T6 and below (inc. legs and lower trunk) travel?

A

In the fasiculus gracilis (which runs the length of the cord)

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12
Q

Where does sensory input to T6 and above (inc. arms and upper trunk) travel?

A

In the fasiculus cuneatus

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13
Q

DCML is the major route by which?

A

Touch and proprioceptive information ascends to the cerebral cortex (apart from anterior head)

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14
Q

DCML primary afferent (1st order neurone) enters the dorsal horn and branches to 1 of 2 things. What are these?

A

1) Synapses deep in the dorsal horn upon second order neurones
2) An immediately ascending component (via the dorsal column fasiculus gracilis and fasiculus cuneatus)

Then to the GN or CN

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15
Q

Where do axons of 2nd order neurones of the dorsal column nuclei cross?

A

COLLECTIVELY, in the greater sensory decussation

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16
Q

What happens after the axons of the 2nd order neurones of the dorsal column nuclei cross?

A

They ascend in the medial lemniscus, to the ventral posteriolateral (VPL) nucleus of the thalamus

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17
Q

Where do 3rd order neurons of the dorsal column project to?

A

Project to the primary somatosensory cortex (S1), via the posterior internal capsule

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18
Q

What conveys sensory information to the head?

A

The Trigeminal System

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19
Q

Outline the 5 capabilities of the DCML pathway.

A
  • Stereognosis  the ability to recognise an object by feeling it.
  • Vibration detection.
  • Weight discrimination.
  • Fine touch  ability to recognise exact location of light touch – 2 point discrimination.
  • Conscious Proprioception  awareness of body position and awareness of body movements (kinaesthesia).
20
Q

How do you test stereognosis?

A

Ask subject to identify familiar object by touch alone

21
Q

What does testing stereognosis evaluate?

A

Cortical function

22
Q

How is vibration detection tested?

A

Clinician places 128Hz tuning fork against a finger tip, top of toe or a bony prominence

23
Q

How is conscious proprioception tested?

A

Clinician moves a finger, toe, hand or foot – subject asked (with eyes closed) to report if the structure is being moved up, or down

24
Q

What produces contrast enhancement?

A

When information is conveyed from one neurone to the next in a sensory pathway, the differences in the activity of adjacent neurones are amplified

25
Q

What does the trigeminothalamic pathway provide sensory innveration to?

A 
ANTERIOR HEAD
Oral cavity
Nasal cavity
Paranasal sinuses
Teeth
Dura
Cerebral arteries
26
Q

What nerve innervates the trigeminal system?

A

CN V

27
Q

Where are the soma of sensory neurones of the trigeminal system located?

A

In trigeminal sensory ganglion

28
Q

What do 3rd order neurones relay information to the cortex via?

A

Thalamocortical neurones

29
Q

Central terminals of the trigeminal nerve synapse upon second order neurones in the chief sensory nucleus (general tactile stimuli), or spinal nucleus (pain, temperature information) which in turn decussate and project (via the trigeminal lemniscus) to the ventroposteriomedial (VPM) nucleus of the thalamus

A

NOTE

30
Q

Where is the somatosensory cortex located?

A

In the POST-CENTRAL GYRUS of the PARIETAL CORTEX, immediately posterior to the CENTRAL SULCUS and adjacent to the POSTERIOR PARIETAL CORTEX

31
Q

What does the somatosensory cortex consist of?

A

Brodmann areas (BA) 1, 2, 3a and 3b (the latter being denoted ‘primary somatosensory cortex’ in some texts, S1)

32
Q

Where does the somatosensory cortex receive input from?

A

THALAMUS

33
Q

What do receptive fields of SI neurones form?

A

An orderly somatotopic map of the body surface on the primary somatosensory cortex.
(revealed by electrical stimulation and neuronal recording techniques)

34
Q

Scaling the body surface to the volume of SI cortex devoted to the representation of a body part gives rise to the ………?

A

Homunculus

35
Q

Reveals the relative volume of cortex devoted to each body part is correlated with the density of sensory input from that part (not its size) and hence sensory acuity and importance of sensory input

A

TRUE

36
Q

How many cell layers are there in the somatosensory cortex?

A

Six - I to VI

37
Q

Where do thalamic inputs to SI terminate?

A

On neurones in layer VI

38
Q

What do neurones in layer IV project to?

A

Cells towards the surface of the cortex, and also deeper layers

39
Q

What extends across each of the 6 layers?

A

Vertical columns (0.3 to 0.5mm diameter) of neurones (about 10,000)

40
Q

What does each vertical column consist of?

A

Neurones with similar inputs and responses

41
Q

Adjacent strips of the cortex map…..

A

The same parts of the body in parallel to each other

42
Q

The maps are not identical or mirror images of each other?

A

FALSE - they are mirror images of each other

43
Q

What does the posterior parietal cortex do?

A

Receives and integrates information from SI and other cortical areas (visual, auditory) and sub-cortical areas (thalamus)

44
Q

What is the posterior parietal cortex important for?

A

Deciphering the deeper meaning of the information in S 1

45
Q

What can damage to the posterior parietal cortex result in?

A

Bizarre neurological disorders (ie. agnosia, astereognosia, hemispatial neglect syndrome) with simple sensory skills remaining intact

46
Q

What condition occurs as a result of damage to the RIGHT posterior parietal cortex?

A

Neglect syndrome

47
Q

What happens to patients with Neglect Syndrome?

A

Believe that the left side of the world does not exist, and may even disclaim the existence of the left side of their body

Neurology (42 decks)

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