Spine

Expectations for Video Content

  • The video is related both to Lab One assignment and Test One.

  • Contents from pre-recorded lectures will be included in the test, consistent with all materials on Blackboard.

Class Materials Access

  • Students experiencing access issues with clinical batches should wait for breaks or after class to resolve this.

  • The lecturer does not manage video passwords; students should find it embedded in the video screen.

  • Pre-recorded lectures will only be available on Blackboard for one week, then reposted in the week leading up to the test.

Today's Lecture Overview

  • Focus on spinal cord anatomy; next week will address the peripheral nervous system.

  • Understanding the anatomy of the spinal cord and the arrangement of white matter is essential for discussing spinal cord injuries in upcoming sessions.

  • Key objectives:

    • General anatomy and function of the spinal cord.

    • White matter arrangement: ascending and descending tracts.

    • Review muscle tone, dermatomes, and reflexes related to spinal cord injuries.

Anatomy of the Spinal Cord

  • Spinal cord surrounded by 3 layers of meninges: dura mater, arachnoid mater, and pia mater.

  • Spinal nerves connect to the spinal cord via dorsal and ventral roots.

  • Cross-sectional view shows:

    • Dorsal and ventral horns; sensory neurons in the dorsal horns and motor neurons in the ventral horns.

    • Lateral horns contain sympathetic motor neurons, present only in T1-L2 and S2-S4.

White Matter in the Spinal Cord

  • White matter is composed of myelinated fibers organized into columns:

    • Posterior (dorsal) column.

    • Anterior (ventral) column.

    • Lateral column.

  • Ascending and descending tracts are organized and crucial for diagnosis and treatment of spinal injuries.

Tracts of the Spinal Cord

Sensory (Ascending) Tracts

  1. Spinothalamic Tract

    • Carries pain (nociception) and temperature sensations.

    • Split into lateral (pain, temperature) and anterior (light touch, pressure) spinothalamic tracts.

    • Pathway: Dorsal root ganglion → spinal cord (synapse) → cross to opposite side → thalamus → sensory cortex.

  2. Dorsal Column Medial Lemniscus

    • Carries information on fine touch, proprioception, and vibration.

    • Pathway: Dorsal root ganglion → ascends to medulla (without synapse) → synapse in dorsal column nuclei → crosses over → thalamus → sensory cortex.

  3. Spinocerebellar Tracts

    • Carries unconscious proprioceptive information to the cerebellum.

    • Posterior and anterior spinocerebellar tracts both serve lower limb proprioception.

Motor (Descending) Tracts

  1. Corticospinal Tract

    • Major pathway for voluntary motor control.

    • Lateral corticospinal tract crosses at medulla, innervating limb muscles; anterior remains on the same side, innervating trunk.

  2. Vestibulospinal Tract

    • Involuntary tract involved in balance and postural control.

    • Receives input from inner ear and cerebellum.

  3. Reticulospinal Tract

    • Involved in maintaining posture and facilitating voluntary movement.

    • Medial vs. lateral functions towards extensors and flexors, respectively.

Spinal Cord Injury Overview

  • Spinal cord injury (SCI) assessment is crucial for treatment planning.

  • Key concepts include:

    • Definition: Any trauma to spinal cord below foramen magnum affecting motor and sensory abilities.

    • Types: Complete SCI (total transaction) vs. incomplete SCI (partial intact pathways).

    • Symptoms of spinal shock: Areflexia, hypotonia, followed by hyperreflexia as regeneration begins.

Syndromes Associated with Incomplete SCI

  • Anterior Cord Syndrome: Loss of pain and temperature sensations below lesion, but proprioception and touch preserved.

  • Central Cord Syndrome: Impaired motor function more in upper limbs than lower limbs, often due to hyperextension injuries.

  • Brown-Séquard Syndrome: Loss of proprioception and touch sensation on one side and pain/temperature sensation on the opposite side due to lateral injury.

Reflexes

  1. Stretch Reflex (e.g., Patellar Reflex): Monosynaptic; includes reciprocal inhibition to also inhibit antagonistic muscle.

  2. Withdrawal Reflex: Polysynaptic; protects body from damaging stimuli via interneurons and multiple synapses.

  3. Crossed Extension Reflex: Involves activation and inhibition across the contralateral side of the body to maintain balance.

Conclusion & Next Steps

  • Review lecture notes and pre-recorded videos.

  • Prepare for practical discussions and applications in the next class regarding peripheral nerves and injuries.