Lecture 3 - Spinal Cord (42)

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Title

Anatomy & Physiology of the Spinal Cord – Lecture 1

• Copyright © John Wiley & Sons, Inc. All rights reserved.

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Introduction to the Spinal Cord

• The spinal cord consists of approximately 100 million neurons and a greater number of neuroglia.

• Serves as part of the central nervous system (CNS) extending from the brain.

• Contains reflex circuits to regulate rapid reactions to environmental changes.

• Gray matter is responsible for the integration of postsynaptic potentials.

• White matter comprises sensory and motor tracts facilitating communication between the cord and the brain.

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Protection of Nervous Tissue

1. First Layer: Hard bony skull and vertebral column protect the CNS.

2. Second Layer: Meninges (3 membranes) provide additional protection.

3. Subarachnoid Space: Contains cerebrospinal fluid (CSF) for cushioning and nutrient transport.

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External Cord Anatomy

• Detailed illustrations depict vertebral anatomy and structure surrounding the spinal cord.

• Key terms to remember:

  • Facet of superior articular process

  • Vertebral foramen

  • Spinous process

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External Cord Anatomy

• Spinal cord begins at the medulla oblongata, extending from the foramen magnum of the occipital bone.

• Terminates at the conus medullaris located between lumbar vertebrae L1 and L2.

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External Cord Anatomy

• Spinal cord is oval with slight anterior and posterior flattening.

• Two connective tissue layers offer protection:

  • Bony vertebral column for hard protection.

  • Spinal meninges, continuous with cranial meninges, surround the cord.

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External Cord Anatomy

• Meninges as Protective Layers:

  • Dura Mater: Outermost, forming an enclosing sac for the cord.

  • Arachnoid Mater: Delicate avascular layer attached to the inside of dura, forming the roof of the subarachnoid space (SAS).

  • Pia Mater: Thin, transparent layer pressed against the cord with blood vessels.

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Spinal Cord Structure Overview

• Components:

  • Gray matter (dorsal and ventral horns) and white matter.

  • Posterior median sulcus and Anterior median fissure delineate segmentation.

  • Spinal Nerve connections.

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External Cord Anatomy

• Denticulate Ligaments:

  • 21 pairs anchoring pia mater to arachnoid and dura layers.

  • Provide stability against shocks and displacements within the vertebral column.

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External Cord Anatomy

• Epidural Space: Located between the dura mater and ligamentum flavum, important for anesthetic procedures.

• Space between the dura and arachnoid is noted as significant for various functions.

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External Cord Anatomy

• Cord Enlargements:

  • Cervical Enlargement: From C4–T1, handles sensory and motor output to the upper appendages.

  • Lumbar Enlargement: Between T9–T12, connecting to the lower limbs.

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Spinal Nerve Structures

• Breakdown of spinal and plexus organization:

  • Cervical Plexus (C1-C5): Contains critical nerves such as phrenic, musculocutaneous, and more.

  • Brachial Plexus (C5-T1): Connects various important nerves for the upper limb.

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External Cord Anatomy

• Filum Terminale:

  • Extension of the pia mater anchoring the spinal cord to the coccyx.

  • Cauda Equina: “Horse's tail,” consisting of lower spinal nerves below the conus medullaris.

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Spinal Curvature

• Normal spinal curves are essential for structural support:

  • Cervical, Thoracic, Lumbar, and Sacral Curves identified from right lateral view.

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External Cord Anatomy

• The size of the spinal cord diminishes from superior to inferior.

• Reduced white matter as levels descend, affecting sensory and motor tracts dynamically.

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External Cord Anatomy

• Spinal Nerve Roots:

  • Roots connect spinal nerves with the spinal cord through rootlets.

  • Posterior root: Contains sensory axons transmitting impulses to the CNS.

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External Cord Anatomy

• The Posterior Root Ganglion: Cell bodies of sensory neurons.

• Anterior Root: Contains motor neuron axons transmitting impulses to muscles and glands.

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Internal Cord Anatomy

• Layout: White matter surrounds the central gray matter, opposite of the brain.

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Internal Cord Anatomy

• White Matter: Contains nerve fibers transmitting signals across body regions.

• Gray Matter: Butterfly-shaped center containing nerve cell bodies.

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Internal Cord Anatomy

• Key anatomical features:

  • Anterior median fissure, posterior median sulcus, gray and white commissures, and central canal.

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Internal Cord Anatomy

• Transverse Section Mechanics:

  • Features of the anatomy, including both sensory and motor neuron pathways.

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Internal Cord Anatomy

• Anterior Gray Horns: Contain somatic motor neurons.

• Posterior Gray Horns: Involves somatic and autonomic sensory nuclei.

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Internal Cord Anatomy

• Critical nerve impulse mechanics for sensation and motor function through spinal nerve architecture.

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Internal Cord Anatomy

• Tracts: Bundles of neuronal axons organized by function and destination within the cord.

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Internal Cord Anatomy

• Lateral Gray Horns: Present in selective spinal segments—their autonomic roles.

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Internal Cord Anatomy

• Relationship between interconnected spinal components and their functions within sensory and motor tracts.

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Internal Cord Anatomy

• Classification of spinal cord columns into anterior, posterior, and lateral based on ascending and descending tracts.

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Internal Cord Anatomy

• Tract Naming: Based on origin and destination, e.g., spinothalamic and corticospinal tracts.

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Internal Cord Anatomy

• Posterior Columns: Responsible for fine touch, pressure, and proprioception.

• Spinothalamic Tract: Delivers sensations including pain and temperature.

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Internal Cord Anatomy

• Motor Pathways: Direct and indirect pathways influencing skeletal muscle movements through cortical control.

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Internal Cord Anatomy

• Categorization of tracts into ascending sensory and descending motor pathways within the spinal cord.

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Lumbar Puncture

• A procedure performed to access subarachnoid space for CSF withdrawal or drug administration.

• Utilized for diagnostic purposes or pressure management.

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Lumbar Puncture

• Commonly performed between the 3rd and 4th lumbar vertebrae, sampling CSF safely.

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Epidural Anesthesia

• Administered to provide local anesthesia during labor, using a needle inserted between spinal bones.

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Damage to the Cord

• Transection: Describes severing of spinal cord tracts, leading to paralysis dependent on injury level.

• Outcomes vary from death (upper cervical) to different forms of paralysis.

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Upcoming Assessments

• Quiz on lectures 1 & 2 covering spinal cord functionality and structure.

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Chapter 13 Review Q’s

• True/False questions addressing spinal gray matter functions and spatial relationship of sensory paths.

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Chapter 13 Review Q’s

• True/False questions concerning spinothalamic tract functions, commissures, and lumbar horn positions.

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Chapter 13 Review Q’s

• Sequence activity related to a reflex action from a finger prick based on functional neural pathways.

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Chapter 13 Review Q’s

• Identification of motor versus sensory tracts and their specific functional involvements.

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Chapter 13 Review Q’s

• Effects of cutting nutritional pathways in spinal nerves impacting sensory signal integrity.