Ascending and Descending Pathways Flashcards

1
Q

What is the term for when a neuron which crosses over the midline of the spinal cord?

A

Axonal decussation

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2
Q

How many neurons are involved in the spine-thalamic pathway?

A

X3

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3
Q

What type of sensory information does the spinal-thalamic pathway carry?

A

Pain, temperature, light touch

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4
Q

Where does the first order neuron of the spino-thalamic pathway enter the spinal cord?

A

Via the dorsal root into the dorsal horn

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6
Q

Where does the first order neuron synapse with the second order neuron in the spino-thalamic pathway?

A

In the dorsal horn of the spinal cord

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7
Q

What happens to the second order neuron in the spino-thalamic pathway?

A

It undergoes axonal decussation and also travels centrally into the spine-thalami tract, which from here ascends to the thalamus

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8
Q

Where do the second and third order neurons in the spinal-thalami tract synapse?

A

In the thalamus

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9
Q

Where is the soma for the third order neuron of the spino-thalamic pathway?

A

In the VPL, ventro-posterior lateral nucleus of the thalamus

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10
Q

Which tract does the 3rd order neuron in the spino-thalami pathway use to reach the somatosensory cortex?

A

The thalamo-cortical tract

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11
Q

Where is the 3rd synapse in the cortico-spinal pathway?

A

It is the 3rd order neuron synapsing in the somatosensory cortex.

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12
Q

What sensory information does the dorsal column - medial lemniscus pathway carry?

A

Touch, proprioception and vibrations

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13
Q

What is the name of the X2 tracts which relay sensory information from different levels of the the body in the dorsal column - medial lemniscus pathway?

A

The gracile and cuneate tracts

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14
Q

Where does the gracile tract relay information from?

Where does this sit in relation to the cuneate fascicles in the dorsal horn?

A

It relays information from below T6

It sits in the dorsal horn, medially to the cuneate fascicles

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15
Q

Where does the cuneate tract relay information from?

Where does this sit in relation to the gracile fascicles in the dorsal horn?

A

It relays information from above T6

It sits in the dorsal horn, laterally to the cuneate fascicles

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16
Q

Where is the soma of the first order neuron of the dorsal column - medial lemniscus pathway?

A

In the dorsal root ganglia

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17
Q

What is the journey of the first order neuron in the dorsal column - medial lemniscus pathway?

A

It travels into the dorsal horn and into either the gracile or cuneate fascicles (depending on level of entry) and ascends in these dorsal columns until it reaches the gracile/cuneate nucleus in the medulla

18
Q

Where do the first and second order neurons in the dorsal column - medial lemniscus pathway synapse?

A

In the gracile/cuneate nucleus of the medulla

19
Q

Where is the soma of the second order neuron in the dorsal column - medial lemniscus pathway?

A

In the medulla

20
Q

What happens to the second order neuron in the dorsal column - medial lemniscus pathway?

A

It undergoes axonal decussation and also travels ventrally into a tract called the medial lemniscus. It ascends via this tract into the thalamus where it synapses with the third order neuron of the pathway.

21
Q

Where is the soma of the third order neuron of the dorsal column - medial lemniscus pathway?

A

In the VPL of the thalamus

22
Q

What tract does the third order neuron of the dorsal column - medial lemniscus pathway use to ascend to the somatosensory cortex?

A

The thalamo-cortical tract

23
Q

Where is the third synapse in the dorsal column - medial lemniscus pathway?

A

At the somatosensory cortex involving the third order neuron

24
Q

What type of pathway is the cortical-spinal pathway?

A

A descending pathway

25
Q

How many neurons are involved in the cortical-spinal pathway?

26
What information does the cortical-spinal pathway carry?
Somatic motor command
27
Where is the soma of the first order neuron in the cortical-spinal pathway?
In the primary motor cortex, located in the frontal lobe just in front of the central sulcus.
28
Where does the first order neuron in the cortical-spinal pathway terminate?
At a level close to that of its target motor neuron
29
85% of axons in the cortical-spinal pathway undergo axonal decussation at which level? What is this type of decussation called? What type of cortical-spinal tract do these axons form?
In the pyramids of the ventral medulla This is called pyramidal decussation They form the LATERAL cortical-spinal tract
30
15% of axons in the cortical-spinal pathway undergo axonal decussation at which level? What type of cortical-spinal tract do these axons form?
They decussate at a level close to where they terminate They form the ANTERIOR/VENTRAL cortico-spinal tract
31
Where is the soma of the second order neuron in the cortico-spinal pathway?
It is in the ventral horn of the CNS at the level at which it is exiting the CNS, as it is a motor neuron.
32
Which ascending pathway is fast and which is slow conducting?
Spino-thalamic = slow conducting Dorsal column - medial lemniscus = fast conducting
33
How many neurons are involved in the dorsal column - medial lemniscus pathway?
X3