VIDEO
HIGHLIGHT
Log InSign up
Spinal cord /part-2/
SummaryTranscriptChat

Spinal cord /part-2/

Spinal Cord Anatomy and Structure

Overview of the Spinal Cord

  • The spinal cord is a cylindrical structure located in the upper two-thirds of the vertebral canal, with the inferior one-third containing the cauda equina and filum terminale.
  • The connection between the spinal cord and medulla oblongata occurs at the foramen magnum, with the adult spinal cord ending at the intervertebral disc between L1 and L2.

Structural Features

  • The conical structure known as conus medullaris is found at the inferior end of the spinal cord, from which filum terminale descends.
  • Two notable enlargements occur in specific regions: cervical enlargement (C4 to T1) and lumbar enlargement (L1 to S3).

Surface Anatomy

  • Anterior median fissure runs along the midline of the anterior surface; motor roots emerge from anterolateral sulcus.
  • Posterior median sulcus is present on the posterior surface, where sensory roots enter through posterolateral sulcus. Dorsal root ganglion contains pseudo-unipolar neurons.

Internal Structure of Spinal Cord

Gray Matter Composition

  • The internal structure consists of gray matter centrally located and white matter peripherally arranged, divided into three parts: anterior gray column, posterior gray column, and intermediate gray column.
  • Central canal lined by ependymal cells is situated within this central region. Four distinct regions are identified in posterior gray column: apex, head, neck, base.

Lamina Organization

  • Each side of gray matter features ten laminae; lamina 1 (posteromarginal) begins at apex of posterior gray column while other laminae include substantia gelatinosa (lamina 2), among others up to lamina 10 surrounding central canal.
  • Notable nuclei include medial cell group extending throughout spinal length for axial muscle innervation; lateral cell group found in cervical/lumbar enlargements for limb innervation.

Functional Groups Within Gray Matter

Nuclei Distribution

  • In T1 to L2 segments' intermediate gray column lies an elevation called lateral horn housing intermediolateral nuclei involved in autonomic functions.
  • Medial cell groups relate to axial muscles while lateral groups correspond to upper/lower limb innervations; central group contributes to phrenic nucleus formation affecting diaphragm control.

Understanding the Structure and Function of Spinal Nerves

Anatomy of Spinal Nerves

  • Motor nerves emerge from the anterior root (also known as ventral root), while sensory nerves originate from the posterior root, which contains the dorsal root ganglion (DRG).
  • The DRG consists of pseudo-unipolar neurons located in the peripheral part of the ganglion, with each nerve having one peripheral and one central branch.

Formation and Branching of Spinal Nerves

  • The spinal nerve is formed by the merging of motor (anterior) and sensory (posterior) roots, resulting in a mixed nerve that carries both types of signals.
  • Upon emerging from the intervertebral foramen, spinal nerves divide into anterior (larger) and posterior branches; anterior branches serve the front body while posterior branches serve the back.

Sympathetic Nervous System Connections

  • Neurons from the intermediolateral nucleus are associated with sympathetic functions; their fibers enter through the anterior root to reach sympathetic ganglia.
  • Preganglionic fibers are myelinated B-type fibers that synapse at sympathetic ganglia or ascend/descend within sympathetic chains without synapsing.

Splanchnic Nerves and Peripheral Ganglia

  • Greater splanchnic nerve is formed by multiple sympathetic ganglia; some preganglionic fibers travel to peripheral ganglia like celiac or renal without synapsing.
  • Fibers can either synapse at their respective ganglion or ascend/descend to connect with other parts of the sympathetic chain.

Neurotransmitter Differences in Autonomic Systems

  • Postganglionic fibers in sympathetic systems lack myelin, contrasting with preganglionic fibers which are myelinated.
  • Acetylcholine serves as a neurotransmitter for both preganglionic fibers in sympathetic and parasympathetic systems; however, postganglionic sympathetic fibers utilize norepinephrine.

Pathways Within Spinal Cord

  • Central DRG fibers enter via postrolateral sulcus into three pathways: some remain at their level, others ascend/descend before entering gray matter.
  • A specific tract called Lisser's tract allows certain fibers to ascend or descend without entering gray matter before reaching medulla oblongata.

Role of Astrocytes in Neural Regeneration

  • Astrocytes inhibit axon regeneration through gliosis; they have vascular feet that contribute to forming blood-brain barrier, regulating material exchange between blood and brain.

Understanding the Blood-Brain Barrier and CNS Cell Types

Overview of CNS Cells

  • The blood-brain barrier presents limitations for transporting materials in the central nervous system (CNS).
  • Four types of glial cells in the CNS are identified: astrocytes, oligodendrocytes, microglia, and ependymal cells.

Microglia Functionality

  • Microglia exist in two states: inactive with many processes and active resembling macrophages.
  • There are two types of microglia: M1 (protective, inhibits neuroinflammation) and M2 (damaging, promotes neuroinflammation).

Intermediate Filaments in Different Cell Types

Structure of Intermediate Filaments

  • Three structures in the cytoskeleton include microfilaments (6 nm), microtubules (24 nm), and intermediate filaments (10-12 nm).

Specific Intermediate Filament Proteins

  • Various cell types have specific intermediate filament proteins:
  • Muscular cells: desmin
  • Connective tissue cells: vimentin
  • Epithelial cells: tonofilament and cytokeratin
  • Neurons: neurofilament
  • Astrocytes: GFAP (Glial Fibrillary Acidic Protein)

Spinal Cord Anatomy and Ascending Pathways

Spinal Cord White Matter Organization

  • The spinal cord's white matter is divided into three funiculi: posterior/dorsal, lateral, and anterior.

Posterior Funiculus Details

  • The posterior funiculus contains a sulcus called the posterior intermediate sulcus leading to a septum known as the posterior intermediate septum.

Ascending Fasciculi Functions

  • Two main ascending fasciculi are identified:
  • Fasciculus gracilis conveys fine touch/vibration from lower limbs/trunk.
  • Fasciculus cuneatus conveys similar sensations from upper limbs/trunk.

Proprioception Pathways

Sensory Impulses Conveyed by Fasciculi

  • Fasciculus gracilis transmits impulses related to discriminative touch/vibration from lower limbs.
  • Fasciculus cuneatus begins at T6 level for upper limb proprioception; it does not exist below this level.

Ascending Fiber Pathway

  • These fibers ascend through dorsal funiculus without entering gray matter before reaching medulla oblongata.

Descending Fibers in Dorsal Funiculus

Location of Descending Fibers

  • Descending fibers located near the posterior median septum form a structure called fasciculus interfacicularis below T6.

Lateral Funiculus Composition

  • The lateral funiculus contains both ascending and descending tracts named based on their origin/destination.

Cerebellar Tracts Overview

Spinal Cerebellar Tracts Description

  • Two key tracts include:
  • Posterior spinal cerebellar tract originating from Clarke's nucleus ascends to cerebellum without crossing.
  • Anterior spinal cerebellar tract involves two decussations—one within the spinal cord and another at the cerebellum.

Understanding Spinal Tracts and Their Functions

Overview of Spinal Cerebellar Tracts

  • The posterior spinal cerebellar tract does not cross over, while the anterior spinal cerebellar tract has two crossings (decussations).
  • In the lateral funiculus, besides the posterior and anterior spinal cerebellar tracts, there is the lateral spinothalamic tract, which is associated with pain and temperature sensations.

Sensory Pathways

  • The dorsal columns (fasciculus gracilis and cuneatus) are responsible for discriminative touch, vibration, and proprioception.
  • The posterior and anterior spinal cerebellar tracts relate to lower limb proprioception; the lateral spinothalamic tract relates to pain and temperature.

Ascending Pathways

  • After crossing over in the gray column, fibers ascend into the lateral spinothalamic tract.
  • These fibers reach the ventral posterolateral (VPL) nucleus of the thalamus for processing pain and temperature information.

Light Touch vs. Discriminative Touch

  • A distinction is made between light touch (general sensation without detail about object identity) and discriminative touch (ability to identify texture or specific characteristics).
  • Discriminative touch ascends through fasciculus gracilis/cuneatus while light touch ascends via the anterior spinothalamic tract.

Descending Tracts in Lateral Funiculus

  • In addition to various ascending tracts, descending pathways include the lateral corticospinal tract and rubrospinal tract.
  • The corticospinal tract originates from motor cortex; 75%-80% of its fibers cross at medulla oblongata affecting contralateral muscle control.

Functionality of Cortical Tracts

  • Both corticospinal and rubrospinal tracts facilitate flexor muscle contraction while inhibiting extensor muscles.

Additional Descending Tracts in Anterior Funiculus

  • The tectospinal tract begins at superior colliculus in midbrain; it descends into anterior funiculus after decussation.
  • The vestibulospinal tract originates from lateral vestibular nucleus without crossing; it functions oppositely to cortical tracts by contracting extensor muscles during falls.

Cross-sectional Anatomy Insights

  • Discussion on cross-sections reveals variations in gray matter size across different regions of the spinal cord.
  • Notable differences exist between cervical enlargement (larger gray matter), thoracic region (smaller gray matter), and lumbar enlargement with distinct lateral horns.

Neuroanatomy Overview

Spinal Cord Tracts and Functions

  • Discussion of Clark's noclose or no close dorsalis, highlighting three main cell groups in the anterior gray column: medial, lateral, and central.
  • Introduction of various spinal tracts including the dorsal spinal cerebellar tract and ventral spinal cerebellar tract, along with their respective functions.
  • Identification of key tracts such as the lateral cortical spinal tract and rubrospinal tract, emphasizing their roles in motor control.
  • Explanation of the anterior spinal thalamic and vestibular spinal tracts within the context of motor pathways; mention of Lisser's tract as a significant structure.
  • Clarification on posterior vs. anterior spinal cerebellar tracts regarding crossing over (decussation), with specific focus on pain and temperature sensation pathways.

Upper Motor Neuron Syndromes

  • Description of Brown-Séquard syndrome effects: ipsilateral upper motor neuron syndrome below lesion level, loss of discriminative touch, and contralateral loss of pain/temperature sensation due to posterior white column lesions.
  • Further elaboration on symptoms associated with syringomyelia (Seringo Melia), detailing bilateral loss of pain at initial stages leading to broader dysfunction as the condition progresses.

Review Questions

  • Interactive review session where participants identify various fasciculi:
  • Number one identified as Faciculus Gracilis
  • Number two identified as Faciculus Conatus
  • Additional identification includes posterior/anterior spinal cerebellar tracts among others.