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Neuroscience - spring 2024 > lec 8 - sensory tracts of the spinal cord > Flashcards

lec 8 - sensory tracts of the spinal cord Flashcards

1
Q

White matter tracts of the spinal cord:

A

Ascending tracts
Descending tracts

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2
Q

Ascending tracts =

A

Typically, sensory input pathways

Mainly located in dorsal and lateral columns/funiculi of white matter

Ascending tracts ascend through the white matter of the spinal cord carrying sensory input to the cerebral cortex

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3
Q

Descending tracts =

A

Typically, motor output pathways

Mainly located in ventral and lateral columns/funiculi of white matter

Descending tracts descend through the white matter of the spinal cord carrying motor output from the cerebral cortex

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4
Q

Notice that ___ is synonymous with tract

A

fasciculus
(e.g., fasciculus cuneatus = cuneate tract)

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5
Q

Also notice that ___ is synonymous with column

A

funiculus
(e.g., dorsal column = dorsal funiculus)

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6
Q

The dorsal/posterior column is composed of:

A

> ascending tracts carrying sensory information up the spinal cord to the brain

> specifically ascending tracts for somatosensation and proprioception

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7
Q

The lateral column is composed of:

A

> ascending and descending tracts carrying both sensory and motor information up and down the spinal cord

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8
Q

The ventral/anterior column is composed of:

A

> ascending and descending tracts carrying both sensory and motor information up and down the spinal cord

> primarily has descending motor tracts

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9
Q

tract =

A

> a bundle of axons that travel in the white matter of the CNS with a common origin, termination, and function

> commonly named according to their origin and destination

> Some tracts are named for their location within the white matter

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10
Q

the spinocerebellar tract has its cell body in the ____, synapses in the ____ and is an ____ tract

A

spinal cord

cerebellum

ascending sensory

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11
Q

the corticospinal tract has its cell body in the ____, synapses in the ____, and is a ______ tract

A

cerebral cortex

spinal cord

descending motor

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12
Q

pathway =

A

> linkage of functionally similar tracts that convey information through one or more intervening neuronal populations

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13
Q

dorsal column-medial lemniscus pathway =

A

> composed of two tracts located in the dorsal column of the spinal cord and some of the sensory neurons pass through the medial lemniscus before reaching the thalamus

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14
Q

Types of ascending tracts -

A

> Dorsal column medial lemniscus (DCML) pathway

> Spinocerebellar tracts

> Anterolateral system (ALS)/spinothalamic tracts

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15
Q

Dorsal column medial lemniscus (DCML) pathway =

A

splits into:
> Cuneate tract/fasciculus cuneatus
> Gracile tract/fasciculus gracilis

> also called the posterior column-medial lemniscus (PCML) pathway

> conveys proprioception, vibration sense, and fine, discriminative touch information

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16
Q

gracile tract =

A

> conveys proprioception, vibration sense, and discriminative touch information

> for the lower limb and lower half of the body

> At medial aspect of dorsal column

> Present at all spinal levels

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17
Q

cuneate tract =

A

> conveys proprioception, vibration sense, and discriminative touch information

> for the upper limb and upper half of the body

> At lateral aspect of dorsal column

> Present at cervical and upper thoracic spinal levels (C1-T6)

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18
Q

Spinocerebellar tracts =

A

splits into:
> Dorsal spinocerebellar tract
> Ventral spinocerebellar tract
> Cuneocerebellar tract

> convey proprioceptive information from proprioceptors in muscles and joints to the cerebellum (unconscious proprioception)

> information from the body to the cerebellum about joint position, muscle length, and muscle tension

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19
Q

Both the dorsal and ventral spinocerebellar tracts are in the ____

A

lateral column/funiculus

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20
Q

The dorsal spinocerebellar tract =

A

carries proprioceptive information for the lower limb

present in cervical, thoracic, and upper lumbar spinal levels (down to L2/L3)

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21
Q

Ventral spinocerebellar tract =

A

Conveys information about activity of interneurons in spinal cord (thought to reflect amount of activity in descending pathways) for lower trunk and lower limb

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22
Q

Cuneocerebellar tract:

A

equivalent to dorsal spinocerebellar tract for upper body

Conveys unconscious proprioception from upper trunk and upper limb to the cerebellum

Primary afferent fibers hitchhike in cuneate tract until they reach the medulla, then they synapse and enter the cuneocerebellar tract

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23
Q

___ fibers conveying unconscious proprioception synapse in the ____ before entering and ascending in the ____

A

Primary afferent

column of Clarke/Clarke’s nucleus/nucleus dorsalis

dorsal spinocerebellar tract

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24
Q

Recall that Clarke’s nucleus is present from ____

A

C8-L2/L3 spinal levels

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25
Q

The cuneocerebellar tract =

A

carries proprioceptive information for the upper limb

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26
Q

Anterolateral system (ALS)/spinothalamic tracts =

A

> Lateral spinothalamic tract
Ventral spinothalamic tract

> conveys pain, temperature, and crude touch information

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27
Q

numerous associated tracts that the anterolateral system encompasses:

A

primary tracts:
> lateral and ventral spinothalamic tracts

other tracts include:
> spinoreticular
> spinomesenencephalic tracts

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28
Q

_____ and “anterolateral system” interchangeably

A

”spinothalamic tract”

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29
Q

Modality:

A

a single sensory quality

example:
> pain
> temperature
> crude touch
> vibration
> fine touch
> proprioception

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30
Q

Sensory system:

A

a group of modalities that are carried together in the same pathway

example:
> pain, temperature, and crude touch
> proprioception, vibration, and fine touch

Sensory systems follow specific tracts to the 1° somatosensory cortex

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31
Q

Dorsal column medial lemniscus (DCML) pathway:

A

> Sensory Systems and Ascending Tracts

> gracile and cuneate tracts

> Convey somatosensation (vibration, discriminative/fine touch, and proprioception) to contralateral 1° somatosensory cortex

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32
Q

Spinocerebellar tracts:

A

> Sensory Systems and Ascending Tracts

> Convey proprioception to ipsilateral cerebellum (unconscious)

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33
Q

Anterolateral system (ALS)/spinothalamic tracts:

A

> Sensory Systems and Ascending Tracts

> Convey pain, temperature, and crude touch to contralateral 1° somatosensory cortex

34
Q

Ascending tracts are typically 3-neuron systems:

A

1st order neurons: receives initial stimulus from receptor
> Cell body in dorsal root ganglia (DRG)

2nd order neuron: typically decussates and relays to contralateral thalamus
> Decussation can occur at/around level of entry in spinal cord or in brainstem

3rd order neuron: typically relays from thalamus to 1° somatosensory cortex

35
Q

1st order afferent sensory neuron =

A

> receptor in the skin, muscle, joints, etc. detects a stimulus

> activates a 1st order afferent sensory neuron in the PNS that is matched to the receptor activated

> cell bodies of these 1st order afferent sensory neurons are in dorsal root ganglia

> central process of these 1st order neurons enters the spinal cord and can synapse with a 2nd order neuron in the dorsal horn or enter and ascend in an ascending tract

36
Q

2nd order neurons usually decussate/cross in ____

A

the brainstem or the anterior/ventral white commissure of the spinal cord

37
Q

Primary Somatosensory Cortex

A

> in the postcentral gyrus of the parietal lobe

> allows for conscious detection of somatosensory stimuli

> site of sensory stimulus detection

38
Q

There is a large area posterior to the postcentral gyrus that is called the ____, where ____ are interpreted

A

somatosensory association cortex

sensations

39
Q

The _____ is the map of the body on the primary somatosensory cortex

A

somatosensory homunculus

40
Q

The _____ detects the fuzziness of an object, but the _____ is responsible for determining whether the fuzzy object is a peach or a tennis ball

A

primary somatosensory cortex

somatosensory association cortex

41
Q

The dorsal column medial lemniscus (DCML) pathway conveys proprioception, vibration, and fine/discriminative touch information from:

A

the trunk and limbs to the thalamus, and up to the 1° somatosensory cortex

42
Q

The dorsal column medial lemniscus (DCML) receptors =

A

mechanoreceptors (cutaneous and joint), muscle spindles, and Golgi tendon organs (GTOs)

43
Q

DCML: Gracile and Cuneate Tracts

1st order neuron=

A

Conveys: proprioception, vibration, and fine touch from trunk and limbs

enters spinal cord = ascends in gracile or cuneate tract to gracile or cuneate nucleus in medulla

> Cell body in DRG

> Synapse in gracile or cuneate nucleus

44
Q

DCML: Gracile and Cuneate Tracts

2nd order neuron =

A

decussates in internal arcuate fibers of medulla = ascends in medial lemniscus to contralateral thalamus

> Cell body in gracile or cuneate nucleus

> Synapse in thalamus

45
Q

DCML: Gracile and Cuneate Tracts

3rd order neuron =

A

relays to 1° somatosensory cortex

> Cell body in thalamus

> Synapse in 1° somatosensory cortex

46
Q

DCML Pathway Lesion Signs

A

Tactile: 2-point discrimination test, stereognosis test, and vibration test with a tuning fork of various frequencies

Proprioception: Romberg test
> Patients stand with feet together
> If patient loses balance with eyes closed = positive Romberg sign = DCML pathway damage

47
Q

Clinically testing the integrity of the DCML pathway requires testing ___ and ____.

A

somatosensation

proprioception

48
Q

To test the somatosensory part, start by ____

A

> touching the patient on the right and left limbs to ensure they sense the touch on both sides

> do a two-point discrimination test to test the patient’s discriminative touch and ability to differentiate two distinct stimuli = examines the integrity of pressure receptors in the skin

49
Q

To test vibratory sensation ____

A

> use a tuning fork

> see if and how long the patient is able to feel the vibration

50
Q

To test stereognosis (ability to perceive and recognize a recognizable object in the absence of visual aid) ____

A

> place an easily identifiable object in the patient’s hand

> ask them to identify it by touch

51
Q

If the patient begins to lose their balance with their eyes open, then there is an issue with ____

A

the cerebellum or the vestibular apparatus of the inner ear

52
Q

If the person can balance with their eyes open, then _____

A

the patient is using visual information to sense their body position

53
Q

If the patient loses their balance with their eyes closed, then the patient has a problem with _____

A

their conscious proprioception (DCML pathway)

54
Q

If a patient loses their balance with their eyes closed, the patient has a ____ Romberg sign, which is indicative of ____

A

positive

DCML damage

55
Q

Conscious proprioceptive information is sent to the ___ then to the ____ via the ____

A

thalamus

1° somatosensory cortex

DCML pathway

56
Q

Unconscious proprioceptive information is sent to the ___ via ____ and does not reach the level of the ___, thus, it is unconscious

A

cerebellum

spinocerebellar tracts

cortex

57
Q

This unconscious proprioceptive information allows the cerebellum to:

A

compare motor behaviors and actions with motor plans

then make adjustments to motor plans based on that information

58
Q

Dorsal Spinocerebellar Tract

1st order neuron =

A

enters gracile tract to ascend to L2/L3 spinal level, then enters Clarke’s nucleus

> Cell body in DRG
Synapse in Clarke’s nucleus

59
Q

Dorsal Spinocerebellar Tract

2nd order neuron =

A

ascends in ipsilateral dorsal spinocerebellar tract to reach cerebellum

> Cell body in Clarke’s nucleus
Synapse in cerebellum

60
Q

The dorsal spinocerebellar tract transmits ____ information that is used in the fine coordination of ____

A

modality-specific and space-specific

individual limb muscles.

61
Q

The dorsal spinocerebellar tract is lateral to the ____ tract and begins at spinal level _____. It passes through the _____ to reach the ____. This tract terminates in the ____.

A

lateral corticospinal

L3 and enlarges as it ascends

inferior cerebellar peduncle

cerebellum

ipsilateral cerebellum

62
Q

Recall that Clarke’s column is only present at ___ spinal levels, yet the dorsal spinocerebellar tract carries proprioceptive information from the lower limb, which is innervated by spinal levels ____. Thus, afferent sensory neurons carrying proprioceptive information from sacral and lower lumbar spinal levels ascend in the gracile tract until they reach the ___ spinal level, where they synapse on _____, which then ascend in the ____.

A

C8-L3

L1/L2-S4/S5

L3

L3 Clarke’s column neurons

ipsilateral dorsal spinocerebellar tract

63
Q

Unconscious proprioceptive information remains ____. Therefore, damage to the ____ will result in ____.

A

ipsilateral

cerebellum

ipsilateral deficits

64
Q

Damage to the ____ will also result in ipsilateral deficits, specifically ____

A

dorsal spinocerebellar tract

dyscoordination of the ipsilateral lower limb (i.e., ataxic gait)

65
Q

___ refers to walking with a wide stance, lack of arm swing, and walking with extended arms to provide balance

A

Ataxic gait

66
Q

Cerebellar Lesion Signs

A

Patients with cerebellar injuries will display discoordination/dysmetria of the lower and upper extremity

67
Q

If the dorsal spinocerebellar tract is injured, then the patient would display _____

A

lower extremity dysmetria

68
Q

If the cuneocerebellar tract is injured, then the patient would display ____

A

upper extremity dysmetria

69
Q

Dysmetria:

A

dyscoordination

70
Q

Ataxic gait:

A

atypical gait characterized by a wide stance with extended arms

Involuntary movements, overshoots, clumsiness, and poor balance

poor balance and dyscoordination

Patients often overshoot movements and have involuntary movements when they are trying to perform slow, controlled movements

Patients often walk with a wide stance and their arms are commonly extended in order to help stabilize them

71
Q

Intention tremor:

A

tremor begins upon initiation of movement/motor activity and worsens with movement

cerebellum is unable to coordinate the movement

72
Q

resting tremor

A

(characteristic of Parkinson’s disease)

present at rest and subsides with movement

73
Q

Balance is impacted with cerebellar damage because:

A

the vestibular apparatus of the inner ear relays to the cerebellum

74
Q

Patients with cerebellar injury will lose balance when they are asked to stand:

A

with their feet together while their eyes are still open

75
Q

Anterolateral System (ALS)

conveys:
receptors:

A

conveys: pain, temperature, and crude touch from the trunk and limbs

Receptors: nociceptors, thermoreceptors, and mechanoreceptors

76
Q

The anterolateral system primarily consists of the spinothalamic tracts:

A

The lateral spinothalamic tract conveys pain and temperature from the trunk and limbs

The ventral spinothalamic tract conveys crude touch information from the trunk and limbs

77
Q

lateral spinothalamic tract

splits into 2 tracts:

A

Neospinothalamic tract: may be specific for acute pain and extreme temperatures

Paleospinothalamic tract: may be specific for chronic pain and mild-to-moderate temperatures

78
Q

Anterolateral System (ALS)

1st order neurons:

A

enters dorsal horn = synapses at level of entry in marginal zone or substantia gelatinosa

> Cell body in DRG
Synapse in marginal zone or substantia gelatinosa

79
Q

Anterolateral System (ALS)

2nd order neurons:

A

decussates in ventral commissure = ascends in contralateral ALS

> decussation takes about 1-3 spinal cord segments/levels

> Cell body in marginal zone or nucleus proprius
Synapse in thalamus

80
Q

Anterolateral System (ALS)

3rd order neurons:

A

relays to 1° somatosensory cortex

> Cell body in thalamus
Synapse in 1° somatosensory cortex

Neuroscience - spring 2024 (10 decks)

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