Spinal Cord

Spinal Cord Overview

  • White Matter vs. Gray Matter

    • Gray matter is predominantly found in the spinal cord.

    • White matter consists of tracks crucial for spinal cord function.

    • Tracks in the spinal cord are critical pathways for communication.

Roles of the Spinal Cord

  • The spinal cord serves two main roles:

    1. Relay Station

    • Functions as a communication link between the brain and the body.

    • Receives outgoing and incoming stimuli crucial for bodily functions.

    1. Processing Station

    • Integrates and processes incoming stimuli.

    • Controls spinal reflexes that can occur without brain involvement.

Spinal Meninges

  • Important structures surrounding the spinal cord:

    1. Dura Mater

    • Lacks a peristeal layer; consists only of a meningeal layer in the spinal region.

    1. Arachnoid Mater

    • Positioned in the middle layer, covering the spinal cord.

    • Contains the subarachnoid space (SAS), which houses cerebrospinal fluid (CSF).

    1. Pia Mater

    • Attaches directly to the spinal cord surface, providing support.

    • Contains denticulate ligaments that anchor the spinal cord to the vertebral cavity.

Spinal Cord Spaces

  • Epidural Space

    • Located between the meningeal dura; filled with veins and adipose tissue, providing cushioning.

  • Subdural Space

    • Adheres dura and arachnoid; generally exists as a potential space.

  • Subarachnoid Space

    • Found between arachnoid and pia mater.

    • Contains a thin layer of cerebrospinal fluid (CSF).

Clinical Applications of CSF

  • CSF Sampling

    • Important for diagnosing conditions; performed via lumbar puncture (spinal tap).

    • Conditions such as meningitis, encephalitis, and multiple sclerosis can be detected from CSF analysis.

External Anatomy of the Spinal Cord

  • Starting Point

    • Commences at the foramen magnum (the base of the skull) and extends down.

    • Terminates between the first and second lumbar vertebrae.

    • Spinal Nerves are responsible for sensory and motor impulses to and from the spinal cord.

  • Cauda Equina

    • A bundle of spinal nerves that extend below the termination point of the spinal cord.

Internal Anatomy of the Spinal Cord

  • Gray Matter Structure

    • Shaped like a butterfly, forming three distinct horns:

    1. Anterior Horn

      • Involved in somatic motor functions.

    2. Posterior Horn

      • Contains visceral sensory neurons.

    3. Lateral Horn

      • Associated with autonomic functions.

  • White Matter Organization

    • Comprised of funiculi (columns) which contain ascending and descending tracts:

    1. Ascending Tracts (sensory):

      • Posterior Columns:

        • Include gracilis and cuneatus tracts for touch and joint position sense.

      • Spinocerebellar Tracts (anterior & posterior):

        • Relay joint position and muscle stretch information to the cerebellum.

      • Anterolateral System (spinothalamic tracts):

        • Transmits pain and temperature signals to the brain.

    2. Descending Tracts (motor):

      • Corticospinal Tract:

        • Controls voluntary skeletal muscles below the neck.

Sensory Pathways

  • Sensation Process

    • Detected by peripheral nervous system neurons and relayed to the CNS.

    • First Order Neurons: Pseudo unipolar sensory neurons detect stimuli in nerves.

    • Second Order Neurons: Located in gray matter, transmit to the thalamus.

    • Third Order Neurons: Found in the thalamus, project to the cerebral cortex.

  • Perception

    • Conscious awareness of sensation, requires intact sensory pathways and integration in the CNS.

Voluntary Movement

  • Control of Movement

    • Involves several structures: cerebral cortex, basal nuclei, cerebellum, and spinal cord.

    • Motor neurons necessary for muscle contraction include:

    1. Upper Motor Neurons (UMN): Located in motor cortex, plan and initiate movements.

    2. Interneurons: Relay signals within the CNS.

    3. Lower Motor Neurons (LMN): Located in the anterior horn of the spinal cord, responsible for muscle contraction.

  • Corticospinal and Corticonuclear Tracts:

    • Corticospinal Tracts: Control skeletal muscles below head and neck.

    • Corticonuclear Tracts (previously corticobulbar): Control muscles of the head and neck.

Nervous System Functionality

  • The nervous system directs perception, voluntary movement, consciousness, and learning.

  • Works closely with the endocrine system to maintain homeostasis.

Summary of Nervous System Components

  • Central Nervous System (CNS): Comprises brain and spinal cord.

  • Peripheral Nervous System (PNS): Includes cranial and spinal nerves.

    • Somatic sensory and motor divisions are conscious.

    • Visceral sensory and motor divisions are generally subconscious.

Key Terms**

  • Action Potentials (AP): Electrical signals traveling along neurons.

  • Myelination: Process of forming a myelin sheath around nerves to facilitate faster signal conduction.

  • Voltage-Gated Ion Channels: Channels that open or close in response to changes in membrane voltage, crucial in the generation of action potentials.

  • Cerebrospinal Fluid (CSF): A fluid that cushions the spinal cord and provides necessary nutrients.