Neuroanatomy: Tracts

Front 1

the dorsal root ganglion neurons that synapse in the dorsal horn are part of a circuit for protective senses like

Back 1

pain, temp, itch

Front 2

the dorsal root ganglion neurons that branch in the white matter enter the _______.these transmit to the brainstem sensory info about touch and proprioception

what is this system called?

Back 2

dorsal column

dorsal column-medial lemniscal system

Front 3

The posterior column is involved in the dorsal column-medial lemniscus (DC -ML) tract. This tract carries ascending sensory fibers mediating ____________



an important landmark for DC-ML is ____

This is because below this, we only are gathering sensation fibers for the lower limbs (after all, the arms don't exist at and below the lower thoracic level). So, the posterior column BELOW T6 consists ONLY of the fasciculus gracilis. Once we hit T6, we start to get sensory fibers for the upper limbs, so we can now add in the fasciculus cuneatus. But, of course, we don't LOSE the gracilis fibers, since everything is heading for the cerebral cortex. So, the posterior (or dorsal) column keeps getting bigger, and, rostral to T6, we now divide it (on the left and right sides each) into two sections -- gracilis and cuneatus.

Back 3

fine touch and proprioception

T6

Front 4

what's the anterior corticospinal tract?

Back 4

its the corticospinal fibers that don't decussate

Front 5

corticospinal fibers are involved in motor control, and therefore, are a ______ tract. The signal originates in the primary motor cortex and is transmitted to the spinal cord; the tract decussates at the pyramids of the medulla and the signal continues to the cord through the __________


The UMN then synapses in the ventral horn of the cord (at a given level, depending on what muscle group you are telling your brain to move) and now the signal is picked up by the ______

Back 5

descending

upper motor neuron

lower motor neuron (LMN; a post-synaptic neuron, a peripheral nerve).

Front 6

the corticospinal tract is actually two tracts:

1. the lateral corticospinal tract, located in the lateral funiculus of the cord. This makes up 85% of the corticospinal tract fibers, and decussates in the medulla at the _________



2. the anterior corticospinal tract, located anteriorly in the anterior funiculus.
does not decussate until in the cord itself, or does not cross at all (some fibers supply motor control to ipsilateral muscle groups).

Back 6

pyramids

Front 7

Substantia gelatinosa (a nucleus of neurons)
- lightly myelinated and unmyelinated neurons
- relays mainly __________

Back 7

pain +temp info

Front 8

Clarke’s nucleus
- distinctive region between _____
- relays information from lower limbs to _____

Back 8

T1-L2

cerebellum

Front 9

for the Spinothalamic Tract (STT) where do the fibers decussate?


and then where do they go?

what info does it carry?

Back 9

at spinal level of entry...they decussate IMMEDIATELY...

to thalamus (ventral posterolateral nucleus VPL)
(there's also branches that go to the periaqueductal gray in the midbrain)

pain + temp


The Trigeminal's involvement in the anterolateral/spinothalamic system:

central processes of trigeminal ganglion cells go down the spinal trigeminal tract to caudal parts of the trigeminal nucleus)
(the trigeminal pain + temp fibers got to VPM)

axons of these 2nd order neurons cross the midline and join the somatotopically appropiate region of the spinothalamic tract, and ascend to VPM of the thalamus!!
(note that trigeminal pain + temp goes to VPM, and that the rest of the anterolateral system (mostly spinothalamic) goes to VPL)

Front 10

How many neurons in the system?

Corticospinal Tract (CST):
Spinothalamic Tract (STT):
Dorsal Column - Medial Lemniscus Tract (DC-ML):

Back 10

Corticospinal Tract (CST): 2
Spinothalamic Tract (STT): 3
Dorsal Column - Medial Lemniscus Tract (DC-ML): 3

Front 11

descending or ascending?
Corticospinal Tract (CST):
Spinothalamic Tract (STT):
Dorsal Column - Medial Lemniscus Tract (DC-ML):

Back 11

Corticospinal Tract (CST):desc
Spinothalamic Tract (STT): asc
Dorsal Column - Medial Lemniscus Tract (DC-ML): asc

Front 12

what are the 1st and 2nd order neurons called of the CST tract?

Back 12

UMN, LMN

Front 13

Most UMNs (of CST) decussate at spinomedullary jxn/caudal medulla as _____

Back 13

pyramidal decussation

Front 14

in STT, 2nd order neuron decussates at spinal cord level at

Back 14

anterior white commissure
(the little strip posterior to the gray matter in the middle of the spinal cord)

Front 15

in DC-ML, 2 order neuron decussates in caudal medulla as

Back 15

internal arcuate fibers

Front 16

primary afferent axons from dorsal root ganglia

stay on the same side where they came(are ipsilateral)

project to 1 of 2 places:

Back 16

- synapse with relay neurons in gray matter of spinal cord and/or
- ascend and synapse with medullary relay neurons

Front 17

DC-ML system

Mediates fine touch, proprioception and vibration

Ascends in dorsal columns (Fasciculus ____ and Fascicululs ____)


Synapses in Nucleus Gracilis and Nucleus Cuneatus

2nd-order neuron decussates (CROSSES OVER) in the _________

Courses through the medial lemniscus to the ______of the thalamus

Synapse in the thalamus, then project through internal capsule to primary somatosensory cortex (S1)

Synapses in S1

Back 17

Fasciculus Gracilis and Fascicululs Cuneatus)

internal arcuate fibers

VPM/VPL nuclei

Front 18

STT:
Mediates temperature, pain, and gross touch

Synapses within dorsal gray matter of spinal cord (substantia gelatinosa) near entry level

2nd order neurons (IMMEDIATELY) decussate in the _______

Fibers run rostrally (toward the head) in the spinothalamic tract

Synapse in VPM/VPL nuclei of the thalamus

3rd-order neurons project through the internal capsule to S1

Back 18

anterior white commissure

Front 19

CS tract

Descending motor control

1st order neuron is from layer ____ of Primary Motor Cortex (M1)

Fibers course caudally (towards the tail) through the internal capsule, into the cerebral peduncles, the corticospinal tract in the basal pons, and the pyramids.

Most 1st order fibers decussate in the pyramidal decussation.

Run caudally in the lateral corticospinal tract

Back 19

5

Front 20

proprioception-stereognosis has a conscious and an unconcious component.

the conscious pathway, connects with the thalamus and cerebral cortex

the unconscious pathway connects with the cerebellum (an "unconscious organ") as the ___________

Back 20

spinocerebellar pathway

Front 21

unlike the other sensory pathways which cross contralaterally, the_______ stays on the same side

(it's the one that controlls unconscious proprioception)

Back 21

spinocerebellar

Front 22

t/f

upper motor neurons (of the corticospinal tract) are 2nd order neurons

Back 22

false!

they're first order

Front 23

a hemisection of the spinal cord at the level of T1 actually produces contralateral loss of pain-temp sensation of T3 and below, rather than at T1 and below. Why?

Back 23

pain-temp fibers do not ALL cross over immediately ...many ascend 1, 2 segments before crossing over

if this doesn't make sense to you, draw out fibers coming in at T1, T2, T3 levels

Front 24

the pain-temp fibers in the spinothalamic tract are arranged so that Leg fibers are lateral to Arm fibers. ...a tumor pressing in from outside the cord may affect the ______ extremitis fibers first

Back 24

low

Front 25

at what level--peripheral nerve, spinal cord, or above---would you expect a lesion to lie, with the following sign:

sensory loss along a give dermatome, unilaterally

Back 25

peripheral nerve or its entry point into the spinal cord

(unlikely that a SINGLE dermotome is affected with lesions elsewhere)

Front 26

at what level--peripheral nerve, spinal cord, or above---would you expect a lesion to lie, with the following sign:

bilateral sensory loss in the hands or feet

Back 26

peripheral neuropathy
(commonly of metabolic etiology...diabetes or alcoholism...resulting in selective involvement these regions)

Front 27

at what level--peripheral nerve, spinal cord, or above---would you expect a lesion to lie, with the following sign:

loss of pain-temp sense on the left side of the body below the neck, and paralysis and loss of proprioception-stereognosis below the neck on the right

Back 27

hemisection of the right cervical cord

Front 28

a patient with a tumor experiences loss of pain-temp in the left lower extremity followed by spastic paralysis on the right? where's the tumor?

Back 28

in the right anterolateral aspect of the cord, compressing first the right spinothalamic tract and then enlargin to involve the coricospinal tract

Front 29

_____________ are the axons of second-order neurons contained within the gracile and cuneate nuclei of the medulla oblongata.

These fibers cross (decussate) from one side of the medulla to the other to form the medial lemniscus.

Back 29

internal arcuate fibers

Front 30

For the motor pathway, which neuron decussates? Where?
Where does the 2nd order neuron synapse with the 3rd order neuron in the spinalthalamic tract?
Where does the cell body of the 1st order neuron for the DC-ML tract sit?
What is the most likely deficit in an individual who suffers damage to their posterior spinal artery?

Back 30

For the motor pathway, which neuron decussates? Where?
UMN at the Pyramidal decussation (level of the Caudal Medulla)


Where does the 2nd order neuron synapse with the 3rd order neuron in the spinalthalamic tract?
VPL (Thalamus)

Where does the cell body of the 1st order neuron for the DC-ML tract sit?
DORSAL ROOT GANGLION

What is the most likely deficit in an individual who suffers damage to their posterior spinal artery?
Damage to the DC-ML resulting in loss of fine touch and proprioception (that is ipsilateral to the side of posterior spinal artery lesion)