Spinal Cord

Spinal Cord Structures

• Central nervous system is protected by bone (skull and vertebral column) and meninges. The bony structures provide a rigid shield, while the meninges offer a layered protective covering.

• Meninges:

  • Dura mater: The outermost, toughest layer.

  • Arachnoid: The middle layer, characterized by its web-like structure.

  • Pia mater: The innermost, delicate layer that adheres directly to the surface of the spinal cord and brain.

• Blood supply: The spinal cord receives blood supply from vertebral arteries and segmental arteries, which are crucial for its function and survival.

• Brainstem: Connects the spinal cord to the brain, integrating vital functions.

• Dorsal roots of spinal nerve: Carry sensory information into the spinal cord.

• Spinal cord: A long, tubular structure extending from the brainstem, carrying neural signals between the brain and the rest of the body.

• Conus medullaris: The tapered, lower end of the spinal cord, typically around the L1-L2 vertebral level in adults.

• Cauda equina: A bundle of nerve roots that originate from the conus medullaris and extend downward through the vertebral canal, resembling a horse's tail.

• Filum terminale: A slender strand of fibrous tissue that extends from the conus medullaris to the coccyx, providing longitudinal support to the spinal cord.

• Dorsal (posterior) horn: Site of termination of many afferent neurons via root, processing sensory information.

• Ventral (anterior) horn: Contains lower motor neurons (efferent) via root, responsible for transmitting motor commands to muscles.

• Lateral horn: Processes autonomic information (only at T1–L2 spinal segments), involved in sympathetic nervous system functions.

• Dorsal (posterior) root: Afferent fibers with cell bodies located in dorsal root ganglia, carrying sensory input.

• Ventral (anterior) root: Efferent fibers with cell bodies lying within the spinal grey matter, carrying motor output.

• Bilateral (mirror) white matter: Contains ascending and descending tracts, facilitating communication between different levels of the spinal cord and the brain.

• Ascending tracts: Afferent pathways that transmit sensory information from the spinal cord to the brain.

• Descending tracts: Efferent pathways that transmit motor commands from the brain to the spinal cord.

• 31 Spinal nerves: Exit vertebral canal through intervertebral foramina.

  • Part of the peripheral nervous system, connecting the central nervous system to the body.

  • Contain both motor and sensory axons, enabling both sensory perception and motor control.

  • Divided into segments:

    • 8 Cervical nerves (C1-C8): Innervate the neck, shoulders, arms, and hands.

    • 12 Thoracic nerves (T1-T12): Innervate the trunk and abdomen.

    • 5 Lumbar nerves (L1-L5): Innervate the lower back, hips, and legs.

    • 5 Sacral nerves (S1-S5): Innervate the pelvis, buttocks, and feet.

    • 1-2 Coccyx nerves: Supply the skin around the coccyx.

• Spinal nerves: Mixture of sensory and motor axons from one spinal cord segment.

• Dorsal ramus: Supplies muscles of back and overlying skin.

• Ventral ramus: Supplies muscles of trunk & limbs and overlying skin.

• Dermatomes: Area of skin (“Dermis”) innervated by a single spinal nerve; afferent. Clinical significance: Dermatomes are clinically important for assessing the level of spinal cord injuries or nerve compression.

• Myotomes: Group of muscles innervated by a single spinal nerve; efferent. Myotomes help in identifying the affected spinal nerve level in cases of motor deficits.

  • C5: Elbow flexion (Biceps)

  • C6: Wrist extension (Wrist extensors)

  • C7: Elbow extension (Triceps)

  • C8: Flexion of tip of middle finger (Finger flexors)

  • T1: Finger abduction (Interossei)

  • L2: Hip flexion (Iliopsoas)

  • L3: Knee extension (Quadriceps)

  • L4: Ankle dorsiflexion (Tibialis anterior)

  • L5: Great toe extension (Extensor hallucis longus)

  • S1: Ankle plantarflexion (Gastrocnemius, Soleus)

Spinal Cord Injuries Overview

• Spinal cord injury is damage to the spinal cord that may cause temporary or permanent change to function of the cord. The extent of functional loss depends on the severity and level of the injury.

• Spinal Cord Injury is often used to describe damage following a traumatic injury to the spinal cord, such as car accidents, falls, or sports injuries.

• Spinal cord syndromes describe location of the lesion (not the cause). These syndromes provide specific patterns of motor and sensory loss based on the area of the spinal cord affected.

• Examples of spinal cord syndromes are cord hemisection (Brown-Sequard syndrome), central cord syndrome, anterior cord syndrome, cauda equina syndrome. Understanding these syndromes aids in accurate diagnosis and prognosis.

• Loss of all forms of sensation: Indicates damage to sensory pathways in the spinal cord.

• Reduced or Inability to feel pain (Analgesia): Suggests disruption of nociceptive pathways.

• Loss of ability to move – inability to voluntarily contract muscle(s) (Paralysis): Signifies damage to motor pathways.

• Partial loss of voluntary movement (Paresis): Indicates incomplete damage to motor pathways.

• Altered or lost sensation in a dermatome at and below the level of the lesion. This sensory loss follows dermatomal patterns, helping to localize the injury.

• Decreased or lost muscle power in a myotome at and below the level of the lesion. Motor weakness or paralysis corresponds to specific myotomes, assisting in determining the level of injury.

• Decreased or lost stretch reflex: Indicates damage to the reflex arcs involving the spinal cord.

• Altered or lost control of BP, bladder and bowel control, and thermoregulation. These autonomic dysfunctions arise from damage to the autonomic pathways in the spinal cord.

Spinal Cord Injuries Classification

• Complete injury: Lack of sensory and motor function in the lowest sacral segments (S4-S5).

• Incomplete injury: Preservation of sensory and/or motor function in the lowest sacral segments.

Quadriplegia or Tetraplegia:

• Damage to the cervical with impairment of arm, trunk, lower limb, and pelvic organ function. The higher the level of cervical injury, the more extensive the functional loss.

• Injury of the cervical cord results in quadriplegia i.e. paralysis of the upper and lower limbs (C1 – T1). Injuries at different cervical levels result in varying degrees of functional impairment.

• C1-C3 – paralysis of the diaphragm and respiratory muscles, often requiring mechanical ventilation.

• Most common level of injury C4-5: Often results in significant functional impairment but may spare some shoulder and elbow movements.

Paraplegia

• Damage to the cord below the cervical level, sparing arm function. Paraplegia typically involves paralysis or weakness of the lower limbs and trunk.

• Injury of the thoracic and lumbar cord i.e. paralysis of the lower limbs (Below T1). The higher the thoracic level, the greater the impact on trunk stability and respiratory function.

• Patients with thoracic paraplegia will have full upper limb movement and varying degrees of trunk paralysis and complete lower limb paralysis. Trunk control is essential for maintaining balance and functional activities.

• Patients with Lumbar or Sacral paraplegia will have varying degrees of lower limb paralysis. Sacral injuries may also affect bowel, bladder, and sexual function.

• Most common level of injury T12/L1: Often results in loss of motor and sensory function in the lower extremities and impaired bowel and bladder control.

Spinal Cord Injuries Examples

Segmental nerve lesions:

• Altered or lost sensation in a dermatome at that level: Sensory deficits are localized to the specific dermatome affected by the nerve lesion.

• Decreased or lost muscle power in a myotome at that level: Motor weakness or paralysis is limited to the muscles innervated by the affected nerve root.

• Decreased or lost stretch reflex: Reflexes mediated by the affected nerve root are diminished or absent.

Vertical tract lesion is in the spinal cord vertical tracts, and result in:

• Altered or lost sensation below the level of the lesion: Sensory loss affects all dermatomes below the level of the spinal cord damage.

• Motor tract signs: Upper motor neuron signs such as spasticity, hyperreflexia, and Babinski sign are present below the lesion.

• Altered or lost control of BP, bladder, bowel control, and thermoregulation: Autonomic dysfunction occurs due to disruption of descending autonomic pathways.

Peripheral nerve injury

• Peripheral nerve lesions cause:

  • Altered or lost sensation in a peripheral nerve distribution: Sensory deficits follow the distribution of the affected peripheral nerve.

  • Decreased or lost muscle power in a peripheral nerve distribution: Motor weakness or paralysis is limited to the muscles innervated by the affected peripheral nerve.

  • Decreased or lost stretch reflex: Reflexes mediated by the affected peripheral nerve are diminished or absent.

Spinal Cord Injuries Syndromes

Brown-Sequard syndrome

• Segmental: Ipsilateral loss of lower motor neurons and sensations.

• Below: Ipsilateral loss of voluntary motor control, conscious proprioception and light touch. Contralateral loss of nociceptive and temperature sensation. This pattern arises from damage to one side of the spinal cord.

Central cord syndrome

• Usually occurs at the cervical level as a result of trauma. The central part of the spinal cord is preferentially affected.

• Small lesion: Loss of nociceptive and temperature at the level of the lesion. This is due to the crossing of spinothalamic fibers in the central cord.

• Larger lesion: Impair upper limb motor: Upper extremities are more affected than lower extremities due to the somatotopic organization of the corticospinal tract.

Anterior cord syndrome

• Damage to anterior spinal cord: Typically results from infarction of the anterior spinal artery.

• Loss pain and temperature sensation: Due to damage to the spinothalamic tract.

• Loss of motor control: Due to damage to the corticospinal tract.

• Preserved conscious proprioception and light touch: As the dorsal columns are spared.

Spinal Cord Injuries Shock

• A temporary loss of all functions below the lesion due: To the sudden disruption of neural pathways.

• Resulting in flaccid paralysis and sensory loss.

• Last about a day but can persist for up to a month: The duration of spinal shock varies among individuals.

• Reflexes gradually return, progressing from flaccid paralysis to spastic paresis.

• Muscle tone and tendon reflexes may take months to recover. The recovery process can be slow and variable.

Spinal Cord Injuries Assessment (AISA)

• Standardized assessment for evaluating neurologic level in spinal cord injury. The ASIA scale is widely used to classify the severity of spinal cord injuries.

• Sensory Examination: Examines 28 specific dermatomes bilaterally for light touch and pin prick. Sensory testing helps determine the extent of sensory loss.

• Motor Examination: Grade muscle strength of 5 specific muscles in upper limb & 5 specific muscles in the lower limb. Muscles are graded 0-5 on the right and the left. Motor testing assesses the strength of key muscles to determine the motor level.

• Anorectal examination: Examination for voluntary contraction and ability to sense deep pressure. Essential for determining completeness of injury and presence of spinal shock. This examination is crucial for classifying the injury as complete or incomplete.

  • ASIA A = Complete injury. No sensory or motor function preserved in the sacral segments S4-5: Indicates a complete disruption of neural pathways.

  • ASIA B = Sensory incomplete. Preservation of sensory function in S4-S5: But no motor function is preserved below the neurological level.

  • ASIA C = Motor incomplete. Motor function preserved at the most caudal segments for voluntary anal contraction. OR the patient meets the criteria for sensory incomplete status (sensory function preserved at the most caudal sacral segments (S4-S5) by LT, PP or DAP), and has some sparing of motor function more than three levels below the ipsilateral motor level on either side of the body.: Most of the key muscles below the neurological level have a muscle grade less than 3.

  • ASIA D = Motor incomplete. Motor Incomplete. Motor incomplete status as defined above, with at least half (half or more) of key muscle functions below the single NLI having a muscle grade ≥ 3.

  • ASIA E = Normal. Normal motor and sensory function. This indicates complete recovery.

Spinal Cord Injuries Key Takeaways

• Understanding spinal cord anatomy is crucial for predicting clinical outcomes. Knowledge of anatomical structures helps correlate injury levels with functional deficits.

• Level of injury determines severity & presentation (e.g., cervical = quadriplegia, lumbar = paraplegia).

• Distinguishing between complete vs. incomplete SCI is essential for prognosis. Incomplete injuries have a greater potential for recovery.

• SCI differs from peripheral nerve injuries in terms of affected function. Spinal cord injuries typically result in more widespread deficits compared to peripheral nerve injuries.

• Clinical assessment tools (e.g., ASIA scale) aid in diagnosing & managing SCI patients. Standardized assessments like the ASIA scale provide objective measures for tracking progress and planning rehabilitation strategies.