Spinal Cord Anatomy

• What is the Nervous System?

  A) brain

  B) spinal cord

  C) cranial

  D) spinal

  
• Spinal Cord

  Function:

  1.Pathway of communication between the brain & the rest of the body

  2.Reflex integration

  Location: The spinal cord is located within and protected by the vertebral column.

  Boundaries:

  •Rostral: Foramen Magnum

  Caudal: L1/L2 in adults

  
• Cervical Enlargement:

  •Levels: C4-T1

  •Brachial Plexus to Upper Limb Innervation

  
• Lumbar (Lumbosacral) Enlargement:

  •Levels: T11-S1

  •Lumbosacral Plexus to Lower Limb Innervation

  
• Conus Medullaris:

  The caudal end of the spinal cord about L1/L2 level.
• Cauda Equina:

  Bundle of spinal nerve roots resembling a horse’s tail below the L1/L2 level.
• Filum Terminale:

  A thin strand of pia mater anchoring the spinal cord to the coccyx.
• Caudal Structures

  A) Conus Medullaris

  B) Cauda Equina

  C) Filum Terminale

  
• Spinal Meninges

  Dura Mater:

  •Tough Superficial Layer

  •Forms Dural Sac

  •Anchored by Filum Terminale

  •Termination of dural sac at S2

  
• Spinal Meninges

  Arachnoid Mater:

  •Delicate Middle Layer

  •Forms Subarachnoid Space Containing CSF

  
• Spinal Meninges

  Pia Mater:

  •Transparent Deep Layer

  •Forms Filum Terminale

  •Forms Denticulate Ligaments - help anchor the spinal cord to the dural SAC.

  
• Epidural Space(most superficial):

  •Separates Vertebral Column & Dura

  •Contains: Vertebral Venous Plexus & Fat

  Clinical Connection: Epidurals for childbirth are given in the epidural space around L4/L5.

  
• Subdural Space:

  •Separates Dura & Arachnoid

  •POTENTIAL SPACE ( CSF in here)

  
• Subarachnoid Space:

  •Separates Arachnoid & Pia - contain CSF and arachnoid trabeculae.

  •Lumbar Cistern: Enlargement Caudal to Conus Medullaris

  Clinical Connection: CSF samples are taken from the lumbar cistern around the L4 level during spinal taps.

  
• Spinal Nerves - Structures of Peripheral Nervous System

  •Bilateral Pairs - 31

  •8 Cervical

  •12 Thoracic

  •5 Lumbar

  •5 Sacral

  •1 Coccygeal

  •C1-C7 exit vertebral column ABOVE respective vertebra

  •C8 exits vertebral column BETWEEN C7 & T1 Vertebrae

  •T1 and caudal exit vertebral column BELOW respective vertebra.

  All these leave from the intervertebral foramen created by corresponding  vertebrae.

  
• Dermatome:

  An area of skin innervated by sensory fibres from a single spinal nerve.

  
• Myotome:

  A group of muscles innervated by motor fibres from a single spinal nerve.

  
• Cross-Sectional Anatomy - Overview

  A) posterior medium sulcus

  B) anterior median fissure

  C) central canal

  D) grey matter

  E) white matter

  
• Central Canal:A small CSF-filled channel in the centre of the spinal cord, continuous with the ventricular system of the brain.
• Grey Matter:Centrally located H-shaped region of the spinal cord containing cell bodies
• White Matter:Peripherally located region of the spinal cord containing axons/tracts transmitting information between the brain & body
• grey matter-Dorsal Horn:Dorsal (Posterior) region of grey matter receiving & processing sensory (afferent) input from the body.

  
• grey matter -Ventral Horn:Ventral (Anterior) region of grey matter containing motor (efferent) neurons sending signals to the muscles.

  
• Cross-Sectional Anatomy – Grey Matter

  A) white matter

  B) grey matter

  C) dorsal root

  D) ventral root

  E) spinal nerve

  F) dorsal root ganglion

  G) sensory neurone soma

  H) motor neuron soma

  
• Cross-Sectional Anatomy – White Matter

  Anterior Funiculus(yellow):

  •Spinothalamic Tract

  •Anterior Corticospinal Tract

  •More descending (motor)

  Lateral Funiculus(green):

  •Spinothalamic Tract

  •Lateral Corticospinal Tract

  •About 50/50 of ascending/descending

  Posterior Funiculus(purple):

  •DCML Tract

  •More ascending than descending pathways

  Ascending Pathways: Afferent, Sensory

  Descending Pathways: Efferent, Motor

  
• Cross-Sectional Anatomy – White Matter

  A) Anterior Corticospinal Tract

  B) Lateral Corticospinal Tract

  C) Posterior Funiculus

  D) Spinothalamic Tract

  
• Cross-Sectional Anatomy – Spinal Nerves

  1.Rootlets (Dorsal/Ventral)(1)

  2.Roots

  a)Dorsal Roots(2a): Sensory Fibres

  •Dorsal Root Ganglion(cell bodies)

  b)Ventral Roots(3b): Motor Fibres

  3.Mixed Spinal Nerve(3): Sensory & Motor Fibres

  4.Primary Rami: Sensory & Motor Fibres

  a)Anterior Primary Rami(4a): Anterior/Lateral Skin, Limbs – Brachial & Lumbosacral Plexi

  b)Posterior Primary Rami(4b): Deep Back Muscles and back skin

  
• Cross-Sectional Anatomy – Putting It All Together

  A) grey matter

  B) white matter

  C) sensory neurone soma

  D) dorsal root ganglion

  E) dorsal root

  F) spinal nerve

  G) ventral root

  H) motor neurone soma

  
• Cross-Sectional Anatomy - Comparison

  1.Overall Size:

  •Decreases from upper to lower segments

  2.Grey Matter:

  •Expanded in cervical & lumbosacral regions as you have Plexus

  •Smaller in thoracic region no Plexus

  3.White Matter:

  •Decreases from upper to lower segments as more ascending fibres as you go further up. same with descending fibres. Don’t want upper limb info in lower limb plexus

  4.Thoracic Region:

  •Lateral horn of grey matter with autonomic neurons for sympathetic innervation(T1 – L2)

  
• Vertebral Arteries give rise to:

  Anterior Spinal Artery (1):

  •Supplies Anterior 2/3 of Spinal Cord

  Posterior Spinal Arteries (2):

  •Supply Posterior 1/3 of Spinal Cord

  Supported by Segmental Medullary(spinal cord enlargements) & Radicular Arteries(supply nerve roots ), run along spinal nerve roots

  
• Venous Drainage

  •Anterior Spinal Veins (3) & Posterior Spinal Veins (3) drain into Internal Vertebral Venous Plexus in the Epidural Space.

  •Blood is then drained into the Dural Sinuses & Vertebral Veins.

  •Supported by Segmental Medullary & Radicular veins

  
• White Matter

  Ascending Pathways: Afferent, Sensory

  Descending Pathways: Efferent, Motor
• Spinothalamic Tract

  Ascending Tract

  Function: Pain, Temperature, Crude Touch

  Neuron Pathway:

  1.Receptors to Dorsal Horn (Synapse)

  2.Spinothalamic Tract(goes through brain stems lateral lemniscus) to Thalamus – VPL/VPM nuclei  (Synapse)

  3.Primary Somatosensory Cortex (Synapse)

  Decussation Level: Spinal Cord Entry

  Destination: Primary Somatosensory Cortex

  
• Dorsal Column Medial Lemniscus (DCML)

  Ascending Tract

  Neuron Pathway:

  1.Receptors(which it goes to the dorsal column on the  ipsilateral side. There are two types of dorsal columns gracile fasciculus which is for lower limb or caudal to T6 and cuneate fasciculus is for upper limb or anything above T6) to Medulla Oblongata (Synapse)

  2.Medial Lemniscus(in brainstem) to Thalamus – VPL/VPM (Synapse)

  3.Primary Somatosensory Cortex (Synapse)

  
• Dorsal Column Medial Lemniscus (DCML)

  Ascending Tract

  Function: Fine Touch, 2-Point Discrimination, Proprioception, & Vibration

  Decussation Level: Caudal Medulla Oblongata

  Destination: Primary Somatosensory Cortex

  
• Corticospinal Tract

  Descending Tract

  Function: Voluntary Movement

  Neuron Pathway:

  1.Primary Motor Cortex à Ventral Horn (Synapse)

  2.Skeletal Muscle (Synapse)

  Decussation Level:

  •Anterior Tract(mostly for posture so ends around mid thoracic region): Spinal Cord Exit Level

  •Lateral Tract(majority so for all limbs): Medulla

  Destination: Skeletal Muscle