Tactile Pathway

What are the 3 neurons of the DCML pathway

1st order → DRG → Spinal cord

2nd order → Medulla → Crosses

3rd order → Thalamus → Cortex

1st order goes with what

DRG & Spinal Cord

2nd order goes with what

Medulla & Crosses

3rd order goes with what

Thalamus & Cortex

Where is the signal Ipsilateral

Spinal Cord → Medulla (before crossing)

Where is the signal Contralateral

After Medulla

Where does Decussation occur in DCML

Caudal Medulla via internal arcuate fibers

What structure carries the signal after crossing

Medial Lemniscus

Where are dorsal columns located in cross section

Posterior (back) of spinal cord

Where is fascicles gracilis located

Medial Dorsal Column

Where is fascicles cuneatus located

Lateral Dorsal Column (only above T6)

What does a lumbar cross section show

Only gracilis (lower body input)

What does a cervical cross section show

Gracilis (medial) + Cuneatus (lateral)

How are fibers arranged in dorsal columns

Medial = Lower body

Lateral + Upper body

What happens as you go up the spinal cord

New fibers are added laterally

What happens in caudal medulla

Synapse in nucleus gracilis/cuneatus

Crossing occurs

What are nucleus gracilis and cuneatus located

Posterior Medulla

What are internal arcuate fibers

Crossing fibers in medulla

After crossing, what structure forms

Medial Lemniscus

What is the shape/orientation of medial lemniscus in medulla

Vertical

In the pons the medial lemniscus becomes

More horizontal

In the midbrain, medial lemniscus is

Rotated/shifted laterally

The rotation in the midbrain (medial lemniscus) is

Shown across levels

What is the order of the brainstem levels (caudal → rostral)

Medulla → Pons → Midbrain

What stays consistent through all levels

Medial Lemniscus carries contralateral information

Where do 2nd order neurons synapse

VPL nucleus of thalamus

Where do 3rd order neurons go

Postcentral Gyrus

What is the path from the thalamus to cortex

Internal Capsule → Corona Radiata

What determines side of sensory loss

Whether lesion is before or after crossing

Damage to dorsal columns in spinal cord causes

Ipsilateral loss below lesion

Lesion before crossing in medulla causes

Ipsilateral loss

Lesion after crossing in medulla causes

Contralateral loss

Lesion above medulla cause

Contralateral sensory loss

What happens if DCML pathway is interrupted anywhere

Loss of tactile sensation

Why are cross sections important clinically

Help localize lesion based on structure + side + symptom

Pt has right-sided vibration loss from leg, lesion is in spinal cord. Where is the lesion

Right side (Ipsilateral, before crossing)

Pt has left sided loss, lesion is in brainstem. Where is the lesion

Right side (Contralateral after crossing)

Why does medial lemniscus orientation matter

Helps identify brain stem level on cross section

Key feature of spinal cord

Dorsal Columns

What is a key feature of the Brainstem cross section

Medial Lemniscus

Spinal cord is

Butterfly gray matter + dorsal columns

Brainstem is

No butterfly, distinct nuclei + tracts

What is the fastest way to identify dorsal columns on a cross section

Look for posterior midline white matter columns

If you see two separate posterior tracts (medial + lateral), what level are you at

Above T6 (gracilis + cuneatus present)

If the dorsal column is one continuous region what does that mean

Below T6 (only gracilis)

Which fibers are most vulnerable in medial dorsal column lesion

Lower body (gracilis)

Which fibers are most vulnerable in lateral dorsal column lesion

Upper body (cuneatus)

Why does somatotopy matter clinically

Lesion location predicts which body region loses sensation

If a lesion selectively affects medial lemniscus orientation, what else does it reveal

The brainstem level (bc orientation changes with level)

Why does medial lemniscus rotate as it ascends

Due to reorganization of somatotopic mapping in brainstem

What happens to body representation during medial lemniscus rotation

Lower vs Upper body positions shift relative to each other

Why is medial lemniscus harder to identify than dorsal columns

It changes shape + orientation across levels

Dorsal columns visually have

Stable location

Medial Lemniscus visually have

Shifting structure

What makes caudal medulla unique compared to rostral medulla

Presence of crossing (internal arcuate fibers)

What disappears as you go from caudal to rostral medulla

Distinct dorsal column tracts

What replaces dorsal columns in rostral medulla

Distince dorsal column tracts

What replaces dorsal column in rostral medulla

Medial lemniscus

What is the functional significance of internal arcuate fibers

They create contralateral representation

Why is crossing in medulla (not spinal cord) clinically important

Determines Ipsilateral vs Contralateral deficits

Why is VPL specifically used for body sensation

It receives input from medial lemniscus (body, not face)

What would damage to internal capsule cause

Loss of sensory signals reaching cortex

Why is corona radiate important clinically

Final distribution of sensory signals to cortex

Why must lesion side always be interpreted relative to stimulus origin

Crossing changes side representation

If a lesion affects both gracilis and cuneatus, what does that suggest

Lesion is above T6

If only lower body sensation is lost, where is the lesion likely

Gracilis ( Medial Dorsal Column)

What feature tells you that you are looking at the brainstem cross section

Large presence of large nuclei and complex tract organization

What is the easiest landmark for identifying medulla vs pons

Shape + position of medial lemniscus

What changes most as you move rostrally in the brainstem

Orientation of medial lemniscus

Why is it not enough to memorize structures without location

Function depends on position in pathway