A 54-year-old man is brought to the emergency department 30 minutes after being hit by a car while crossing the street. He had a left-sided tonic-clonic seizure and one episode of vomiting while being transported to the hospital. On arrival, he is not oriented to person, place, or time. Physical examination shows flaccid paralysis of all extremities. A CT scan of the head is shown. This patient's symptoms are most likely the result of a hemorrhage in which of the following structures?

Between the arachnoid mater and the pia mater

Between the dura mater and the arachnoid mater

Between the skull and the dura mater

A 22-year-old man is rushed to the emergency department after a motor vehicle accident. The patient states that he feels weakness and numbness in both of his legs. He also reports pain in his lower back. His airway, breathing, and circulation is intact, and he is conversational. Neurologic exam is significant for bilateral lower extremity flaccid paralysis and impaired pain and temperature sensation up to T10-T11 with normal vibration sense. A computerized tomography scan of the spine is performed which shows a vertebral burst fracture of the vertebral body at the level of T11. Which of the following findings is most likely present in this patient?

Flaccid paralysis at the level of the lesion

A 55-year-old construction worker falls off a 2-story scaffolding and injures his back. His coworkers bring him to the urgent care clinic within 30 minutes of the fall. He complains of left lower-limb weakness and loss of sensation in the right lower limb. He does not have any past medical history. His vital signs are stable. A neurologic examination reveals a total loss of motor function when testing left knee extension, along with the left-sided loss of light touch sensation from the mid-thigh and below. There is a right-sided loss of pin-prick sensation of the lateral leg and entire foot. At this time of acute injury, what other finding is most likely to be found in this patient?

Left-sided loss of proprioception and vibration sensation

Left-sided extensor plantar response

Intact voluntary anal contraction

Left-sided spastic paralysis below the lesion

Left-sided numbness at the level of the lesion

Spinal cord organization for USMLE Step 2 CK: High-Yield Anatomy Lessons

Gross Anatomy - The Cord's Protective Layers

Vertebral Column: Bony housing for the spinal cord.
Epidural Space: Contains fat, veins. Site for epidural anesthesia.
Meninges (Superficial to Deep): 📌 Mnemonic: DAP
- Dura Mater: "Tough mother." Outermost, durable layer.
- Arachnoid Mater: Web-like layer. Creates the subarachnoid space filled with Cerebrospinal Fluid (CSF).
- Pia Mater: "Tender mother." Adheres directly to the spinal cord. Forms denticulate ligaments (anchoring cord laterally) and the filum terminale (anchoring inferiorly).

Meningeal layers and spaces of the brain and spinal cord

⭐ Clinical Pearl: During a lumbar puncture (spinal tap), the needle must pierce the dura and arachnoid mater to enter the subarachnoid space to sample CSF. The spinal cord ends at L1-L2, but the dural sac extends to S2.

Gray Matter - The Central Butterfly

Spinal Cord Gray Matter: Rexed Laminae and Nuclei

Dorsal (Posterior) Horn: Sensory input (afferent).
- Substantia Gelatinosa: Pain & temperature modulation.
- Nucleus Proprius: Light touch & proprioception.
Ventral (Anterior) Horn: Motor output (efferent) to skeletal muscle.
- Contains α- and γ-motor neurons.
- Somatotopically organized.
Intermediate Zone & Lateral Horn: Autonomic nervous system.
- Lateral Horn (T1-L2): Sympathetic preganglionic neurons.
- Sacral Parasympathetic Nucleus (S2-S4): Parasympathetic preganglionic neurons.

⭐ Exam Favorite: Ventral horn organization is key: axial/proximal muscles are represented medially, while distal limb muscles are lateral. Flexor motor neurons are located dorsally to extensor neurons.

White Matter Tracts - Information Superhighways

Spinal Cord Cross-Section: Ascending & Descending Pathways

Ascending (Sensory) Tracts: Sensory data travels up to the brain.
- Dorsal Column-Medial Lemniscus:
  - Function: Fine touch, vibration, proprioception.
  - Decussation: Medulla.
- Spinothalamic Tract (Anterolateral):
  - Function: Pain, temperature, crude touch.
  - Decussation: Spinal cord (anterior commissure).
- Spinocerebellar Tracts:
  - Function: Unconscious proprioception to cerebellum.
Descending (Motor) Tracts: Motor commands travel down from the brain.
- Lateral Corticospinal Tract:
  - Function: Voluntary motor control of limbs.
  - Decussation: Pyramids (caudal medulla).

⭐ Brown-Séquard Syndrome (Hemi-section): Ipsilateral UMN weakness, loss of vibration/proprioception below lesion. Contralateral loss of pain/temperature starting 2-3 segments below lesion.

High‑Yield Points - ⚡ Biggest Takeaways

The spinal cord terminates at the L1-L2 vertebral level; lumbar punctures target the cauda equina.

Dorsal columns (gracilis, cuneatus) sense proprioception, vibration, and fine touch, decussating in the medulla.

Spinothalamic tract senses pain, temperature, and crude touch, decussating in the spinal cord.

Lateral corticospinal tract is the primary motor pathway for voluntary movement, decussating in the pyramids.

Central gray matter contains cell bodies; surrounding white matter contains myelinated axons (tracts).

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