Makindo Medical Notes

Anatomy of the Spinal Cord

The spinal cord is a long, cylindrical structure extending continuous with the brainstem (foramen magnum) to L1/L2 lumbar region of the vertebral column. It is part of the central nervous system (CNS) and acts as a conduit for signals between the brain and the rest of the body. The spinal cord is protected by the vertebrae, meninges, and cerebrospinal fluid (CSF).

Regions of the Spinal Cord

• Cervical Region: The uppermost part of the spinal cord, extending from the foramen magnum to the first thoracic vertebra (C1 to C7). It controls motor and sensory signals to the neck, arms, hands, and diaphragm.
• Thoracic Region: The mid-portion of the spinal cord (T1 to T12), associated with the chest, upper abdominal muscles, and parts of the upper back.
• Lumbar Region: The lower portion of the spinal cord (L1 to L5), which controls movements of the lower back, hips, and legs.
• Sacral Region: The lowest region of the spinal cord (S1 to S5), which controls pelvic organs, the bladder, and lower limbs.

Structure of the Spinal Cord

• Gray Matter: Located centrally, the gray matter forms an "H" or butterfly shape, containing neuron cell bodies, dendrites, and synapses. It is divided into:
  • Ventral Horn: Contains motor neurons responsible for voluntary movement.
  • Dorsal Horn: Contains sensory neurons that process input from peripheral sensory receptors.
  • Lateral Horn: Present in the thoracic and upper lumbar regions, housing autonomic neurons (primarily sympathetic).
• White Matter: Surrounds the gray matter and contains myelinated axons that transmit signals. White matter is divided into:
  • Ascending Tracts: Carry sensory information (e.g., pain, touch, proprioception) from the body to the brain.
  • Descending Tracts: Transmit motor commands from the brain to the body.
• Meninges: Three protective layers that surround the spinal cord:
  • Dura Mater: The tough, outer layer.
  • Arachnoid Mater: The middle layer, which contains cerebrospinal fluid (CSF).
  • Pia Mater: The delicate inner layer closely adhering to the spinal cord.

Blood Supply of the Spinal Cord

• Anterior Spinal Artery: Supplies the anterior two-thirds of the spinal cord, including motor tracts.
• Posterior Spinal Arteries: Supply the posterior one-third, affecting sensory tracts.
• Radicular Arteries: Branch from segmental arteries to provide additional blood flow.

Physiology of the Spinal Cord

The spinal cord functions as a communication highway between the brain and body, enabling sensory input, motor output, and reflexes.

Functions of the Spinal Cord

• Sensory Conduction: Sensory signals (e.g., pain, temperature, touch) travel from sensory neurons in the dorsal roots to the brain through ascending tracts for processing.
• Motor Conduction: Motor signals from the brain descend through the spinal cord's descending tracts, reaching motor neurons in the ventral horn, which stimulate skeletal muscle contraction.
• Reflex Arcs: The spinal cord enables quick, involuntary responses to stimuli (e.g., the withdrawal reflex). Reflex arcs allow the spinal cord to process sensory input and generate motor output without involving the brain.

Anatomy of the Cauda Equina

The cauda equina ("horse’s tail") consists of a bundle of spinal nerve roots located below the level where the spinal cord terminates (L1-L2 in adults). These nerves extend downward and exit through the lower lumbar, sacral, and coccygeal regions, controlling the lower limbs and pelvic organs.

Structure of the Cauda Equina

• The cauda equina includes the lumbar, sacral, and coccygeal nerve roots.
• These nerve roots exit the vertebral column via intervertebral foramina, traveling to their target areas in the lower extremities and pelvis.

Physiology of the Cauda Equina

• Sensory Function: The cauda equina contains sensory fibers that transmit signals such as touch, temperature, and pain from the lower body (legs, buttocks, pelvic organs).
• Motor Function: Motor fibers in the cauda equina control the muscles of the hips, knees, ankles, and toes, as well as muscles controlling bladder, bowel, and sexual function.
• Autonomic Function: Autonomic fibers in the cauda equina manage involuntary functions, including bladder and bowel control, as well as aspects of sexual function.

Clinical Relevance

• Spinal Cord Injury (SCI): Trauma to the spinal cord can lead to paralysis (quadriplegia or paraplegia), sensory deficits, and impaired autonomic function. The severity depends on the level and extent of the injury.
• Cauda Equina Syndrome: Compression of the cauda equina results in lower back pain, bowel/bladder dysfunction, saddle anesthesia, and lower limb weakness. It is a surgical emergency that requires immediate decompression.
• Spinal Stenosis: Narrowing of the spinal canal can compress the spinal cord or cauda equina, causing pain, weakness, and sensory loss, particularly in the lower extremities.
• Herniated Disc: A herniated intervertebral disc can press on nearby spinal nerves or the spinal cord itself, leading to pain, weakness, and sensory disturbances, often in a dermatomal distribution.

Comparison of Spinal Cord Lesions vs. Cauda Equina Lesions

Clinical Feature	Spinal Cord Lesion	Cauda Equina Lesion
Location of Injury	Upper spinal cord (cervical, thoracic, or upper lumbar region)	Injury to the nerve roots in the lower lumbar and sacral regions (L2 and below)
Type of Neurons Affected	Upper motor neurons (UMNs)	Lower motor neurons (LMNs)
Motor Symptoms	Spastic paralysis, hypertonia, hyperreflexia (due to UMN damage)	Flaccid paralysis, hypotonia, hyporeflexia or areflexia (due to LMN damage)
Reflexes	Exaggerated reflexes (e.g., hyperreflexia, clonus, positive Babinski sign)	Absent or diminished reflexes (e.g., loss of knee/ankle reflexes)
Sensory Symptoms	May involve a **sensory level** (a distinct level of sensory loss below the lesion), with dermatomal distribution	Dermatomal sensory loss in the lower extremities, saddle anesthesia (loss of sensation in the perineal area)
Bladder and Bowel Dysfunction	Urinary retention with possible spastic bladder (hyperreflexic), constipation	Urinary retention, incontinence, loss of anal sphincter tone (flaccid bladder, bowel dysfunction)
Sexual Function	May have Priapism initially due to loss of inhibition but eventually involve erectile dysfunction and loss of sensation	Impaired sexual function due to damage to sacral nerve roots (e.g., erectile dysfunction, loss of sensation)
Muscle Atrophy	Minimal atrophy, primarily due to disuse (UMN lesions preserve muscle bulk)	Marked atrophy (LMN lesions lead to rapid muscle wasting)
Pain	May present with bilateral or unilateral pain; commonly described as burning or aching	Severe radicular pain, often bilateral in lower limbs (sciatica-like symptoms)
Common Causes	Trauma, multiple sclerosis, spinal cord tumours, transverse myelitis	Herniated disc, spinal stenosis, trauma, tumours, infections, cauda equina syndrome
Prognosis	Often depends on the level and extent of the lesion. Partial recovery possible with treatment.	Requires urgent treatment to prevent permanent damage. Early intervention improves prognosis.
Imaging	MRI of the spinal cord to evaluate the lesion level	MRI of the lumbar spine to assess nerve root compression
Emergency	Not always urgent, unless causing rapid deterioration or spinal cord compression	Cauda Equina Syndrome is a surgical emergency requiring immediate decompression