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SA Clinical Neuroscience > S3) Somatic Sensation and Ascending Pathways > Flashcards

S3) Somatic Sensation and Ascending Pathways Flashcards

1
Q

What are the two types of sensation?

A
  • General sensation
  • Special sensation
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2
Q

What are the two types of general sensation?

A
  • Somatic sensation (conscious)
  • Visceral sensation (unconscious)
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3
Q

What are sensory modalities?

A

Sensory modalities are different forms of sensory experience e.g. pain, temperature which exists due to various types of receptors

these types of modalities are crucial to survive

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4
Q

Besides pain and temperature, identify five other sensory modalities

A
  • Pressure (crude touch)
  • Vibration
  • Distension
  • Proprioception (being aware of limb placement even if you can’t see them)
  • Fine touch

→ all these allow humans/ animals to be more complex that others

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5
Q

Where are primary sensory neurones found?

A

The cell body of primary sensory neurones lies in the dorsal root ganglion and the axon transmits information to the dorsal horn of the spinal cord where the neurone synapses

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6
Q

Describe the relationship between the cell body and axon for primary sensory neurones

A

For primary sensory neurones, the axon runs ipsilaterally to the cell body

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7
Q

The modality of the stimulus is dependent on the type of receptor activated.

What are the different types of receptors?

A
  • Nociceptor
  • Mechanoreceptors
  • Thermoreceptors
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8
Q

Different types of receptors adapt in different ways.

What is a tonic receptor?

A

Tonic receptors are slow adapting receptors, respond to the stimulus as long as it persists, and produce a continuous high frequency of action potentials e.g. all nociceptors (pain)

→ without it you wouldn’t go and fix the problem

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9
Q

Different types of receptors adapt in different ways.

What is a phasic receptor?

A

- Phasic receptors are rapidly adapting receptors and respond quickly to stimuli but stop responding upon continual stimulation

  • Action potential frequency decreases during prolonged stimulation and the receptor remains sensitive to a change/removal of stimulus
  • eg putting clothes on → you get used to the feeling
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10
Q

What is a nociceptor?

A

Nociceptors are tonic receptors, which respond to noxious stimuli (stimuli that would cause tissue injury if they were to persist) and result in the sensation of pain

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11
Q

What is a mechanoreceptor?

A

A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion by the means of pressure, touch, vibration or stretch

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12
Q

What is a thermoreceptor?

A

Thermoreceptors are tonic receptors that respond to warmth and cold

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13
Q

What is a dermatome?

A

A dermatome is an area of skin supplied by a single spinal nerve

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14
Q

Where are second order sensory neurones found?

A

The cell body of second order sensory neurones lies in the dorsal horn of the spinal cord

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15
Q

Where are third order sensory neurones found?

A

The cell body of third order sensory neurones is located in the thalamus and the axon extends into the somatosensory cortex

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16
Q

Where are the majority of the ascending tracts found?

A

The destination of the majority of the ascending tracts is the somatosensory cortex in the postcentral gyrus of the parietal lobe

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17
Q

What is the sensory homunculus?

A

The somatosensory cortex corresponds to the sensory homunculus, which is a map of brain areas dedicated to sensory processing for different anatomical divisions of the body

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18
Q

Explain how CNS lesions can show varied patterns

A
  • Dermatomal pattern of sensory loss suggests a lesion at the level of the spinal nerve
  • Homuncular pattern of sensory loss suggests a lesion at the level of the cortex
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19
Q

Describe the somatotropic organisation of the spinal cord tracts

A
  • In the dorsal column pathway, the lower body maps to the medial portion of the tract
  • In the spinothalamic tract, the lower body maps to the lateral portion of the tract
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20
Q

What is the significance of the varying somatotropic organisation of the spinal cord tracts?

A

A central cord lesion can affect dorsal column and spinothalamic tracts differentially

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21
Q

Different ascending tracts are found in specific locations in the spinal cord, and each of the ascending pathways carry information about specific sensory modalities.

Identify two ascending tracts of interest and their location

A
  • Dorsal column-medial lemniscus (DCML)
  • Spinothalamic tract
22
Q

Information for which sensory modalities is relayed by the DCML?

A

The dorsal column-medial lemniscus relays information relating to conscious proprioception of the limbs, fine touch and vibration

23
Q

How do isolated lesions of the DC pathway present?

A

Isolated lesions of DC pathway in the cord lead to ipsilateral signs below the lesion

24
Q

Describe the significance of the following in the dorsal column pathway:

  • Gracile/cuneate nucleus
  • Medial leminiscus
A
  • The cell bodies lie in the gracile/cuneate nucleus
  • The fibres decussate to the contralateral side at the great sensory decussation in the medulla oblongata, and then ascend via the medial leminiscus and terminate at the thalamus
25
Q

Describe and illustrate the organisation of the homunculus in the dorsal column pathway

A

In the sensory and motor homunculus, the lower limb is represented medially and the upper limb and face are represented laterally

26
Q

Information for which sensory modalities is relayed by the spinothalamic tracts?

A

The spinothalamic tract relays information relating to pain, temperature, and pressure

27
Q

How do isolated lesions of spinothalamic tract present?

A

Isolated lesions of spinothalamic tract in cord lead to contralateral signs below the lesion

28
Q

What is the ventral white commissure and what is its significance in the spinothalamic pathway?

A

The axons of the tract cells decussate to the other side of the spinal cord via the anterior/ventral white commissure and to the anterolateral corner of the spinal cord

29
Q

Illustrate the ascension of axons in the spinothalamic pathway

A
30
Q

Describe and illustrate the organisation of the homunculus in the spinothalamic pathway

A

In the sensory and motor homunculus, the lower limb is represented laterally and the upper limb and face are represented medially

31
Q

What is Brown-Sequard syndrome?

A
  • Brown-Sequard syndrome is the clinical syndrome that emerges when one destroys one half of the spinal cord
  • It demonstrates the rare occurrence of a hemisection (only right or left is severed) of the spinal cord
32
Q

In Brown-Sequard syndrome, consider a complete cord hemisection causing destruction of a single cord segment resulting from trauma or ischaemia and identify the five structures that will be completely destroyed unilaterally

A
  • The dorsal horn
  • The ventral horn
  • All other cord grey matter
  • All white matter pathways
  • Dorsal and ventral roots
33
Q

How does Brown-Sequard syndrome present?

A
  • Ipsilateral complete segmental anaesthesia affecting a single dermatome (due to destruction of dorsal root and dorsal horn)
  • Ipsilateral loss of dorsal column modalities below the lesion
  • Contralateral loss of spinothalamic modalities below the lesion
34
Q

Describe the respective functions of A fibres and C fibres in analgesia

A
  • A fibres carry impulses from mechanoreceptors in the skin
  • C fibres carry pain
35
Q

Explain how the activation of mechanoreceptors alleviates pain

A

Activation of mechanoreceptors alleviates pain (i.e. rubbing a painful area helps) by exciting inhibitory enkephalinergic interneurones in the cord

36
Q

what are some examples of spinothalamic modalities

A

-temp, pain, pressure

37
Q

what are some examples of dorsal column modalities?

A
  • sophisticated modalities
38
Q

what is a receptive field

A

→ territory of skin that a set of receptors relate to

39
Q

state where the first order, second order and third order nerves are located

A
  1. Dorsal root ganglion
  2. medulla/dorsal horn
  3. thalamus
40
Q

homunculus

A
41
Q

what is lissaures tract

A
  • to do with the spinothalamic tract
  • the first order neurones as ascend up 2 levels and synapse with second order higher up rather than at level of entering
  • if you were to have a lesion in the C5 vertebra you might only feel symptoms from the C7 vertebra as its neurones travel up to C5 level
42
Q

diabetic neuropathy?

A

→ lose touch in peripheries in palms and soles of foot

→ peripheral nerve problem not up in the brain

43
Q

what can a deficiency in B12 cause in the spinal tract

A

→ subacute combined degeneration of the spinal cord

(white streak → area of demyelination)

44
Q

what is sensory ataxia?

A
  • sensory deficit in the dorsal column
  • lose proprioception and so can’t walk properly => sensory ataxia gait
45
Q

how is sensory ataxia distinguished from cerebellar ataxia

A
  • presence of near normal coordination when eyes are open but then when eyes are closed lose coordination
46
Q

what Can a midline lesion in the central canal cause in a spinothalamic tract problem

A
  • bilateral nature
  • wont see any abnormalities below the level that is effected as the nerve crosses at the level it enters
  • can be due to a cyst in the spinal cord
47
Q

what are some reasons for insensitivity for pain aside from the activation of mechanoreceptors

A

→ TB drug: isoniazid

→ alcohol and chemo

48
Q

what half of the body does the cunate nucleus supply?

A

upper half of body C7 up

49
Q

what half of the body does the gracile nucleus supply?

A
  • supplies the lower half of the body C7 down
50
Q

if you had a tumour growing on the cerebral peduncle which system would be effected

A

lose MOTOR function

51
Q

dorsal column pathway / medial meniscus

A
52
Q

spinothalamic tract pathway

A

SA Clinical Neuroscience (23 decks)

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