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MD4001 > Ascending Pathways > Flashcards

Ascending Pathways Flashcards

1
Q

What is the modality and rate of adaption of Hair Follicle Receptors?

A
  • Touch

* Rapidly adapting

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2
Q

What is the modality and rate of adaption of Merkel Endings?

A
  • Pressure, low frequency vibration

* Slowly adapting

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3
Q

What is the modality and rate of adaption of Meissner Corpuscles?

A
  • Light Touch

* Rapidly adapting

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4
Q

What is the modality and rate of adaption of Pacinian Corpuscles?

A
  • Vibration, joint position sense

* Rapidly adapting

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5
Q

What is the modality and rate of adaption of Ruffini Endings?

A
  • Skin stretch, joint position sense, pressure

* Slowly adapting

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6
Q

What is the modality and rate of adaption of Nociceptors?

A
  • Pain

* Free nerve endings

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7
Q

What is the modality of muscle spindles?

A
  • Muscle length

* Proprioception

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8
Q

What is the modality and rate of adaption of Golgi Tendon Organs?

A
  • Joint position sense (JPS)

* Slowly adapting

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9
Q

Describe the sensor response

A
  • Increased permeability to all ions
  • Sodium predominates because of the max difference between intra/extracellular concentrations, therefore similar in ion movements to APs
  • Generator potential in the sensor region causes a spike in the adjacent membrane then propagated as an action potential
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10
Q

Describe Aα axons

A
  • Fastest - 270mph
  • Proprioceptors of skeletal muscle
  • Largest diameter - 13-20µm
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11
Q

Describe Aβ axons

A
  • 167mph (second fastest)
  • 6-12µm diameter
  • Mechanoreceptors of the skin
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12
Q

Describe Aδ axons

A
  • 1-5µm diameter
  • 67mph
  • Pain, temperature, localised pain
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13
Q

Describe C axons

A
  • 0.2-1.5µm diameter (smallest)
  • 5mph (slowest)
  • Temperature, pain, itch
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14
Q

Describe lateral inhibition

A
  • A way of improving localisation
  • Each sensory neurone has a receptive field, dendrites are dense at the centre of this field, closer to the cell body and more diffuse at the periphery
  • Stimuli firing at the centre of the receptive field will activate more dendrites than at the periphery resulting in faster firing
  • The receptive fields of neurones overlap, the stimulation will be more intense for the neurone experiencing the stimulus closer to the cell body
  • The neurones will have branches that will inhibit the neighbouring neurone, the one experiencing a stronger stimulus will inhibit the neighbouring neurone to a greater extent
  • The result is a bigger difference in the firing rate of the neurones, helping the brain to discriminate between 2 points
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15
Q

What is a dermatome?

A
  • Area of skin with a sensory supply from a single spinal nerve
  • The 1st neuron in the ascending pathway sense and exits from their cognate dermatome then feeds into a chunk of spinal cord that belongs to that body segment
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16
Q

Where do motor neurones exit the spinal cord?

A

Ventral root

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17
Q

Where do the sensory neurones enter the spinal cord?

A

Dorsal root

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18
Q

What are the 2 pathways for conscious sensation?

A
  • Anterolateral tract (spinothalamic)

* Dorsal column (medial lemniscal pathway)

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19
Q

What sensation is carried by the anterolateral tract?

A
  • Pain
  • Temperature
  • Itch
  • Crude touch
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20
Q

What sensation is carried by the dorsal column (medial lemniscal tract)?

A
  • Proprioception (conscious)
  • Vibration
  • Light touch/ fine touch - 2 point discrimination
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21
Q

Where does the anterolateral (spinothalamic) tract cross the midline?

A

Close to the entry level, in the white commissure

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22
Q

Where does the dorsal column (medial lemniscal) tract cross the midline?

A

In the medulla

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23
Q

Describe the route of the dorsal column pathway

A
  • The first neuron (DRG) enters the spinal cord and ascends on the same side to the medulla
  • The second neurone crosses over in the medulla and ascends to the thalamus
  • The third neurone in the thalamus ascends to the cerebral cortex (the post central gyrus)
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24
Q

What are the differences in the dorsal column pathway for the arm vs the leg?

A
  • For the leg, the first neuron fibres travel in the gracile tract, whereas the arm travel in the cuneate tract
  • The leg fibres cross in the gracile nucleus, the arm in the cuneate nucleus
  • In the spinal cord the arm fibres are more lateral than the leg
  • In the brainstem, the arm fibres are more medial than the leg fibres
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25
Q

Where is the motor cortex

A

• Precentral gyrus

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26
Q

Where is the primary somatic sensory cortex?

A

• Postcentral gyrus

27
Q

What is the information from the dorsal column (medial lemniscal) pathway used to do?

A

• Determine the shape of an object without sight - Stereognosis
- proprioception from the finger joints and fine discriminating touch provides an accurate model of an object that is handled
• Determine the texture of an object without sight - Astereognosis
- texture is determined by vibration and slip (Meissner) receptors as well as fine discriminating touch
- pleasure can also be associated with this pathway

28
Q

What area of the brain must be functioning in order for the dorsal column pathway to function?

A

The somatosensory association area in the parietal lobe

29
Q

Describe the route of the anterolateral (spinothalamic) pathway

A
  • 1st neurone (DRG) enters the spinal cord
  • 2nd neurone in the posterior horn crosses to the opposite side close to the entry level in the white commissure and ascends to the thalamus
  • 3rd neurone in the thalamus projects to the cerebral cortex
30
Q

What are the two types of pain?

A
  • Discriminative - localising pain, well localised and brief
  • Affective -‘suffering pain’ less localised and longer lasting
31
Q

What type of fibres carry discriminative pain?

A

• A delta fibres

32
Q

Where is discriminative pain location perception

A

Post central gyrus

33
Q

What type of fibres carry affective pain?

A

Unmyelinated C fibres

34
Q

Describe the path of the fibres carrying affective fibres in the Brain

A
  • Arrives at the reticular formation in the brainstem (parabrachial nucleus)
  • Then goes either to the thalamus (intralaminar nucleus) or the hypothalamus (physiological response)
  • From the thalamus, fibres travel to the amygdala deep in the temporal lobe then to either the cingulate gyrus (emotion) or the insula (avoidance)
35
Q

Why can pain prevent sleep?

A
  • Affective pain

* Synapse with brainstem nuclei to increase arousal, preventing sleep

36
Q

Why can pain make you sweat/feel sick?

A
  • Indirectly stimulates the autonomic circuitry

* Hypothalamus

37
Q

What provides us with the pain basis for avoidance behaviours?

A
  • The insula

* it integrates discriminative and affective pain, co-ordinating pain avoidance

38
Q

What are the cortical areas of pain perception?

A
  • Discriminative pain = post central gyrus

* Affective pain = cingulate gyrus

39
Q

Opioids

A
  • Treat pain
  • Reduce the fMRI signals in the insula and the thalamus
  • Work at spinal, brainstem and cortical levels
40
Q

What is the spinal cord gate theory?

A
  • Interneurones downstream of the touch pathways inhibit pain pathways
  • e.g. rubbing helps with the pain
  • TENS trans-electrical nerve stimulators (applied near to the damaged area)
41
Q

What is the brain stem to spinal cord pathways - descending control of pain?

A
  • The periaqueductal matter is a continuation of the periventricular grey matter, located around the cerebral aqueduct in the midbrain
  • It sends descending projections to the spinal cord and ascending projections to the thalamus and frontal lobes
  • Terminate on inhibitory interneurones in the dorsal horn of the spinal cord
42
Q

What is the thalamus?

A

A collection of nuclei on diverse pathways to the cerebral cortex

43
Q

What are the functions of the thalamus?

A
  • Conscious sensation relay and processing
  • Motor circuits - basal ganglia to motor cortex
  • Emotions/memory
  • Special sense haring and vision
44
Q

What are the connections of the cortex and the thalamus?

A
  • White matter bundles
  • Thalamic connections forming peduncles (anterior, inferior, posterior, inferior)
  • Thalamic connections form part of the internal capsule (anterior thalamic radiation, superior thalamic radiation, auditory thalamic radiation, optic radiation)
45
Q

What are the main pathways of the thalamus?

A
  • Sensory relay
  • Motor circuits
  • Limbic systems
  • Special sense
46
Q

Sensory relay pathway of the thalamus

A
  • Sensory info from the head through the VPM- ventral posteromedial nucleus
  • Sensory info from the body via the VPL - ventral posterolateral nucleus
47
Q

Motor circuit pathway of the thalamus

A
  • To motor cortices from the basal ganglia and cerebellum

* Ventral lateral nucleus and ventral anterior nucleus

48
Q

Limbic system pathway of the thalamus

A

• Nuclei on emotion, pain and memory pathways

49
Q

Special sense pathway of the thalamus

A
  • Vision through the lateral geniculate body (LGB)

* Auditory through the medial geniculate body (MGB)

50
Q

What occurs in a anterolateral tract lesion?

A

• Decreased perception of pain and temperature on the contralateral side of the body, one or two dermatomes below the lesion

51
Q

How can anterolateral tract pathway lesions be utilised?

A
  • In surgery to offer pain relief of a terminal disease and pain
  • Pain returns approx 1 year after procedure
52
Q

What are anterolateral fibres susceptible to?

A
  • Central cord pathology e.g. swelling can obliterate fibres
  • They are susceptible because they cross early
53
Q

What is the result of a hemi-section of the spinal cord?

A

Results in loss of pain perception on the contralateral side and a loss of proprioception on the ipsilateral side

54
Q

What conditions affect the dorsal spinal cord?

A
  • Vitamin B12 deficiency
  • HIV myelopathy
  • Tabes Dorsalis (syphilis)
  • Multiple Sclerosis
55
Q

Describe the spinocerebellar pathway

A
  • Unconscious proprioception

* Does not cross the midline - always ends up on the same side of the Brain

56
Q

What part of the brain issues correction information to achieve smooth accurate movements?

A

The cerebellum

57
Q

Fasciculus gracilis

A

Carries information from the lower body extremities (touch, vibration, conscious proprioception)

58
Q

Fasciulus cuneatus

A

Carries information from he upper body extremities (touch, vibration, conscious proprioception)

59
Q

Dorsal and ventral spinocerebellar tracts

A

Proprioceptive information from the muscle spindle (dorsal) and the Golgi tendon organs (ventral)

60
Q

Anterolateral tract

A

Tocu, pain, itch, temperature

61
Q

what does testing the joint position sense do?

A

Exclusively dorsal columns

62
Q

What does testing pain and temperature sensation do?

A

Exclusively lateral spinothalamic tracts

63
Q

What does testing light touch do?

A

Localises lesion

64
Q

What does testing vibration sense do?

A

Good for screening several pathologies

MD4001 (28 decks)

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