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B3 CAI > Spinal Cord, Ascending Tracts and Sensation > Flashcards

Spinal Cord, Ascending Tracts and Sensation Flashcards

1
Q

what layer of tissue has the most densely packed sensory receptors?

A

the epidermis and dermis layer

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2
Q

5 examples of sensory receptor

A

meissner corpuscle, pacinian corpuscle, ruffini ending, merkel disc, free nerve ending

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3
Q

what does meissner corpuscle allow us to detect?

A

discriminative touch (rapid adapting)

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4
Q

what does pacinian corpuscle allow us to detect?

A

deep pressure and vibration (rapid adapting)

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5
Q

what does ruffini ending allow us to detect?

A

touch, sheer stress/forces (slow adapting)

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6
Q

what does merkel disc allow us to detect?

A

light, sustained touch (slow adapting)

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7
Q

what do free nerve endings allow us to detect?

A

pain (slow adapting) and temperature (rapid adapting)

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8
Q

what is an adaptation of temperature receptors?

A

they are rapidly adapting and allow us to quickly detect relative changes

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9
Q

where do sensory cortexes sit?

A

within the left and right parietal lobes

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10
Q

where does the primary somatosensory cortex sit?

A

immediately behind the deep central sulcus

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11
Q

what does the primary somatosensory cortex receive?

A

contralateral sensory input from the body (including taste)

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12
Q

what helps the primary somatosensory cortex integrate incoming sensory signals?

A

the parietal lobes

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13
Q

what does the superior parietal lobe do?

A

integrates sensory input, sensory memory, and perception of contralateral self/world

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14
Q

what does each cerebral hemisphere do in general?

A

perceives sensations from, and controls the movements of, the opposite (contralateral) side of the body

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15
Q

what is the amount of cortical surface area that a region gets proportional to?

A

the body part and the amount of sensation that that body part has and likely needs in order to function (e.g. the hands are more sensitive than the kneecaps and thus get more cortical surface area)

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16
Q

what is the internal capsule?

A

a dense collection of white matter (myelinated axons) that carry sensory and motor tracts to and from the cortex

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17
Q

what happens to the internal capsule as we move superiorly towards the cerebral cortex?

A

the internal capsule fans upwards and outwards into a structure called the corona radiata

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18
Q

what tracts do the internal capsule contain?

A

ascending and descending tracts

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19
Q

what are the 4 parts of the internal capsule?

A

anterior limb, genu, posterior limb and retrolenticular part

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20
Q

where is the retrolenticular part located?

A

behind the lentiform nucleus

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21
Q

what two nuclei come together to form the lentiform nucleus?

A

the putamen and globus pallidus

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22
Q

what does the anterior limb contain?

A

connections between parts of the thalamus and prefrontal cortex, and different nuclei in the pons of the brainstem

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23
Q

what do the genu and posterior limb contain?

A

motor fibres travelling from the cortex

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24
Q

what does the retrolenticular part contain?

A

fibres that deal with visual and auditory information

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25
Q

what will small focal lesions limited to a specific area of the internal capsule result in?

A

contralateral spastic paralysis in specific parts of the body, as both sensory and motor neurons have a somatotopic arrangement

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26
Q

what will damage to large parts of the internal capsule (e.g. stroke/tumour) lead to?

A

widespread contralateral motor and/or sensory symptoms

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27
Q

what is the general structure of the ascending sensory pathway?

A

it consists of a 3 neuron chain from the periphery to the primary cortex

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28
Q

how do 1st order neurons ascend in the dorsal column pathway?

A

ipsilaterally

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29
Q

what determines how far 1st order neurons ascend before decussating?

A

the sensory path and the sense it is conveying

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30
Q

what does the thalamus represent?

A

an organised collection of subcortical relay nuclei

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31
Q

what are the two main nuclei within the thalamus, important for somatosensory input?

A

the ventral posterior lateral nucleus (VPL) and the ventral posterior medial nucleus (VPM)

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32
Q

what is the ventral posterior lateral nucleus?

A

receives 2nd order neurone input from the limbs and trunk and is where 2nd order neurons will synapse onto 3rd order neurons. these ascend to sensory cortex

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33
Q

what is the ventral posterior medial nucleus?

A

receives 2nd order neurone input from the face and most of the head and is where 2nd order neurons will synapse onto 3rd order neurons. sends 3rd order neurons via internal capsule through corona radiata to terminate at primary somatosensory cortex

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34
Q

what happens to 3rd order neurons once they have left the thalamus?

A

they travel through the internal capsule, through the corona radiata and terminate upon the appropriate part of the primary somatosensory cortex

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35
Q

what is the anterior white commissure?

A

a bundle of white matter that connects the left and right spinal cord

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36
Q

how is grey matter organised in the spinal cord?

A

the sensory dorsal horn and the motor ventral horn are organised into zones with different functions (rexed lamina), and these areas are where the ascending (sensory) and descending (motor) fibres synapse onto other neurons

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37
Q

what will the size of the dorsal and ventral horn vary according to?

A

the spinal cord level

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38
Q

where do afferent fibres enter and terminate in the spinal cord?

A

enter via the dorsal root and terminate in the dorsal horn

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39
Q

what will the ventral horn contain?

A

cell bodies of motor neurons that exit through the ventral nerve roots and eventually innervate skeletal muscle

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40
Q

how can white matter within the spinal cord be grouped?

A

into 3 funiculi (bundles of more than one tract)

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41
Q

what are the 3 ascending tracts of the spinal cord?

A

dorsal column pathway, spinocerebellar tract, spinothalamic tract

42
Q

what are located on either side of the dorsal columns?

A

fasciculus cuneatus (located laterally and from above T6) and fasciculus gracilis (located medially and from below T6)

43
Q

What type of sensation does dorsal column pathway carry?

A

discriminative touch, vibration and conscious proprioception

44
Q

where does information from the upper limb and trunk enter the dorsal column pathway?

A

they are above T6 and thus they enter the more lateral fasciculus cuneatus

45
Q

where does information from the lower limb and trunk enter the dorsal column pathway?

A

they are below T6 and thus they enter the more medial fasciculus gracilis

46
Q

why does innervation from the face have a different path?

A

because it comes from above the spinal cord

47
Q

what determines which area of the CN V sensory nucleus the 1st order trigeminal neurons head towards?

A

the sensory (proprioception, touch/pressure, pain/temperature) information that they are carrynig

48
Q

give 3 examples of nuclei within the CN V sensory nucleus

A

mesencephalic nucleus, chief sensory nucleus, spinal nucleus

49
Q

what nuclei of the CN V sensory nucleus do proprioception sensations go to?

A

the mesencephalic nucleus

50
Q

what nuclei of the CN V sensory nucleus do touch/pressure sensations go to?

A

chief sensory nucleus

51
Q

what nuclei of the CN V sensory nucleus do pain/temperature sensations go to?

A

spinal nucleus

52
Q

what are the 2nd order trigeminal neurons collectively known as?

A

the trigeminothalamic tract (trigeminal lemniscus)

53
Q

what does dorsal column damage in the spinal cord cause?

A

ipsilateral loss of discriminative touch, vibration and conscious proprioception below the level of the lesion (i.e. a lesion on the right side at T10 will lead to all fibres below T10 on the right side being lost as they are trying to ascend through a damaged area)

54
Q

what can affect the dorsal column, causing damage?

A

compression, infarction, infection, vitamin B12 deficiency, tertiary syphilis

55
Q

how does tertiary syphilis damage the dorsal column?

A

it causes demyelination and destruction of dorsal columns

56
Q

what are 2 symptoms of dorsal column damage?

A

pseudoathetosis and sensory ataxia

57
Q

what is pseudoathetosis?

A

writhing of digits, hands and feet

58
Q

what does sensory ataxia lead to?

A

Positive Romberg sign and stamping gait. The Romberg sign is present when a patient is able to stand with feet together and eyes open, but sways or falls with eyes closed.

59
Q

where does the spinothalamic tract lie?

A

lateral and ventral to the ventral horn

60
Q

What type of sensation does spinothalamic tract carry?

A

information related to pain, temperature and simple touch

61
Q

what is syringomyelia?

A

a condition where the spinothalamic tract is damaged, due to enlargement of the central canal within the spinal cord, forming a cavity that compresses adjacent nerve fibres

62
Q

what part of the spinothalamic tract is damaged during syringomyelia?

A

2nd order neurons as they get damaged when they decussate across the anterior white commissure if the central canal expands

63
Q

why is there a cape-like distribution loss of pain and temperature during syringomyelia?

A

the lesion only affects the anterior white commissure and not the entire spionthalamic tract

it is sacral sparing

64
Q

what can cause syringomyelia?

A

idiopathic, trauma, or development disorders of the CNS (e.g. chiari malformation)

65
Q

what is the clinical relevance of the spinothalamic tract being somatotopically organised?

A

expansion of a ventral gray matter tumour will knock out contralateral pain and temperature but may not affect the sacral region due to the way this type of tumour expands (more anterior than lateral, leading to sacral sparing (pain and temperature preserved in the sacral region of the body)

66
Q

what will happen if we squash the spinothalamic tract on one side?

A

the patient will feel a loss of pain/temperature on the contralateral side

67
Q

why is the spinocerebellar tract a unique tract?

A

it starts in the spinal cord and ends in the cerebellum meaning it only has 2 neurons in its chain

68
Q

what are the two types of spinocerebellar tract?

A

dorsal spinocerebellar tract and ventral spinocerebellar tract

69
Q

what does the dorsal spinocerebellar tract receive input from?

A

muscle spindles

70
Q

what does the ventral spinocerebellar tract receive input from?

A

golgi tendon organs

71
Q

What type of sensation does spinocerebellar tract carry?

A

unconscious proprioception to the ipsilateral cerebellum

72
Q

what do the fibres in the spinocerebellar tract monitor?

A

muscle length, speed of contraction and tension

73
Q

which side of the cerebellum will fibres in the spinocerebellar tract end up in?

A

the same side (ipsilateral) e.g. if fibres are coming from the left lower limb they will end up in the left cerebellum

74
Q

what will a cerebellar lesion result in?

A

ipsilateral body symptoms as fibres from the spinocerebellar tract end up on the ipsilateral side of the cerebellum

75
Q

why is damage to the spinocerebellar tract rarely seen in isolation?

A

if damage occurs in the spinal cord, symptoms are normally masked by other major motor tracts being lost

76
Q

what do pure lesions to the spinocerebellar tract result in?

A

Freidreich’s ataxia, resulting in malcoordination of motor action and a wide-based gait

77
Q

What do association fibres do?

A

Allow one area of cortex to communicate with another area of cortex on the same side of hemisphere

78
Q

What do commissural fibres do?

A

Allow communication between different hemispheres eg. corpus callosum

79
Q

What do projection fibres do?

A

Allow communication between brainstem and spinal cord

80
Q

Where does decussation occur?

A

second order neurons

81
Q

What input does ventral posterior medial nucleus (VPM) receive?

A

Sensory input from face CN V

82
Q

What input does ventral posterior lateral nucleus (VPL) receive?

A

Sensory input from body

83
Q

What sensation and from where does fasciculus gracilis carry?

A

Discriminative touch & vibration; conscious proprioception from legs (below T6)

84
Q

What sensation and from where does fasciculus cuneatus carry?

A

Discriminative touch & vibration; conscious proprioception from arms (above T6)

85
Q

What is the sensory homunculus? Draw it out

A

The sensory homunculus is a map along the cerebral cortex of where sensory processing for different parts of the body is processed.

86
Q

What makes up the white matter and grey matter of the spinal cord?

A

White = ascending and descending tracts.

Grey = ventral and dorsal horn.

87
Q

What does the ascending tract do?

A

A nerve pathway that goes upward from the spinal cord toward the brain carrying sensory information from the body to the brain. There are 3 types of ascending tracts.

88
Q

What makes up the ascending tracts?

A
89
Q

How do ascending sensory paths reach the cortex?

A

1st order neurons synapse to 2nd order neurons in medulla. The bundle of fibres that ascends to thalamus is called lemniscus. Frpm thalamus, 3rd order neurons leave and ascend to cortax via internal capsules.

90
Q

How do you view an axial CT/MRI of the spinal cord?

A

From above.

Normal standard for biewing axial CT/MRI is from below.

91
Q

Where do afferent and efferent fibres enter/leave the spinal cord?

A

Afferent (sensory) enters via dorsal horn.

Efferent (motor) leaves via ventral horn.

92
Q

What are the 3 funiculi?

A

Dorsal funiculus

Lateral funiculus

Ventral funiculus

93
Q

Where are the 3 ascending tracts located on the spinal cord?

A
94
Q

What sensory receptors are in each of the ascending tracts? What are each of the ascending tracts responsible for?

A
95
Q

Where are the 1st, 2nd, 3rd and 4th order neurons located/where do they synapse in the ascending tracts?

A
96
Q

Describe and draw out the dorsal column medial lemniscus pathway

A
97
Q

Describe and draw out the dorsal column trigeminal lemniscus pathway

A
98
Q

What will happen here?

A

Damage to dorsal column pathway - sensory loss of discriminative touch, vibration and conscious proprioception on the left side, below the level of the lesion.

99
Q

Describe and draw out the spinothalmic tract

A
100
Q

Describe and draw out the spinocerebellar tract

A

B3 CAI (13 decks)

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