MRCP-1 Spinal Cord Tracts Neuroanatomy Quiz

Описание: Spinal Cord Tracts Neuroanatomy: The Body's Information Superhighway
Think of your spinal cord as the body's central data cable. It contains specific, organized bundles of nerve fibers called tracts or pathways. These are the dedicated "lanes" for sending information up to the brain (ascending tracts = sensory) and down from the brain (descending tracts = motor). Their precise organization allows neurologists to pinpoint the location of damage based on which functions are lost.
The Core Concept: Somatotopic Organization
Tracts are somatotopically arranged. This means fibers are laid out in a specific map corresponding to body parts. For example, in key pathways, information from the legs travels in the outer parts of the tract, while information from the arms travels more centrally. This is crucial for localizing injuries.
Major Ascending (Sensory) Tracts: Feeling the World
These carry sensory information to the brain. Two critical pathways are:
Dorsal Columns (Medial Lemniscal Pathway):
Function: Carries fine touch, vibration, and proprioception (the sense of your body's position in space).
Pathway: Sensory input enters the spinal cord and travels ipsilaterally (same side) up the back (dorsal part) to the brainstem. There, it crosses over to the opposite side before reaching the brain's sensory cortex.
Test: Check vibration sense with a tuning fork; check proprioception by moving the patient's big toe up/down with their eyes closed.

Spinothalamic Tract (Anterolateral Pathway):

Function: Carries pain, temperature, and crude touch.

Pathway: Sensory input enters the spinal cord, then immediately crosses over to the opposite side within one or two spinal levels. It then travels up the front-side (anterolateral part) of the cord to the brain.

Test: Use a safe pinprick for pain; test tubes with warm/cold water for temperature.

Major Descending (Motor) Tracts: Command and Control
These carry motor commands from the brain to the body. The most important is:

Corticospinal Tract (Pyramidal Tract):

Function: Provides voluntary, skilled motor control (especially of hands and fingers).

Pathway: Originates in the brain's motor cortex. Most fibers (85%) cross over in the medulla (forming the "pyramidal decussation") and then travel down the opposite side of the spinal cord in the Lateral Corticospinal Tract. The uncrossed fibers travel in the Anterior Corticospinal Tract.

Test: Assess fine motor skills (finger taps, rapid alternating movements) and strength.

The Clinical Clue: Patterns of Deficit
Knowing the pathway anatomy lets you locate a spinal cord lesion:

Hemisection (Brown-Séquard Syndrome): Damage to one side of the cord causes a classic pattern:

Ipsilateral (same side) loss: Dorsal column function (fine touch, vibration, proprioception) below the injury.

Contralateral (opposite side) loss: Spinothalamic function (pain & temperature) 1-2 levels below the injury.

Ipsilateral weakness: Corticospinal tract damage (voluntary motor control) below the injury.

Complete Cord Transection: Loss of all motor and sensory function below the level of injury.

In summary: Spinal cord tracts are the meticulously organized one-way streets for sensation and movement. The dorsal columns carry fine touch/vibration/proprioception and cross high in the brainstem. The spinothalamic tract carries pain/temperature and crosses immediately in the spinal cord. The corticospinal tract carries voluntary motor commands and crosses in the medulla. Understanding which "lane" is blocked reveals exactly where the spinal "accident" occurred.