Spinal Cord & Brain Stem Overview

• Lecture 021325 covers the Spinal Cord, Brain Stem Overview, Chapters 9 & 10 and RQ 3

Spinal Cord Topics

• Gross anatomy and vasculature is one topic
• Spinal column and disc herniation are considered
• Spinal cord and spinal segment divisions are examined
• Reed’s laminae are another area of focus
• Fiber tracts are discussed
• Spinal Reflexes are covered

Brain Stem

• Brain Stem Overview covers regions and regional anatomy

Spinal Column Development

• Primary neurulation occurs in the cervical, thoracic, and lumbar regions
• Secondary neurulation occurs in the sacral and coccygeal regions
• The anterior basal plate forms the anterior (Ventral) horn and motor column
• The posterior alar plate forms the posterior (Dorsal) horn and sensory column
• The neural crest forms the posterior (dorsal) root ganglion

Spinal Cord Segments

• Cervical segments are C1-C8, are enlarged
• Thoracic segments are T1-T12
• Lumbar segments are L1-L5, are enlarged
• Sacral segments are S1-S5
• The coccygeal segment is Co1

Spinal Cord Segment Details

• The dorsal sensory root is also known as the dorsal horn
• Intermediate gray matter exists
• Ventral motor horn is the ventral root
• The dorsal, lateral, and ventral columns are discussed

Spinal Cord Traits

• Segments trail behind the vertebral column from T1 to Coc1
• Meningeal dura, arachnoid denticulate ligaments span the sub arachnoid
• Cauda equina is made of spinal nerves in the lumbar cistern, specifically L2 to Coc1
• Conus medullaris is the end of the spinal cord

Spinal Cord Outer Layers

• Pia mater extends as the filum terminale internum
• Meningeal dura extends as filum terminale externum

Spinal Column and Cord Details

• Vertebrae have articulating processes that create nerve foramina
• The spinal canal contains epidural fat
• Batson’s venous plexus and the dural sac are there
• Inter-vertebral discs consist of the nucleus pulposus and annulus fibrosus
• Ligaments include the ligamentum flavum, interspinous ligament, and posterior longitudinal ligament

Radiculopathy Types

• Cervical radiculopathy involves nerve roots exiting above the vertebrae with lateral herniation
• Lumbo-sacral radiculopathy involves nerve roots exiting below vertebrae with central, lateral, and posterolateral herniation

Radiculopathy Cases

• Cervical disk herniation (C5-C6): unilateral neck pain, left arm pain, decreased arm strength, numbness in thumb and index finger
• Lumbosacral disk herniation (L5-S1): unilateral back pain, left lower leg paresthesias and numbness, decreased sensation, Achilles tendon reflex

Spinal Cord Divisions

• White matter consists of the posterior, lateral, and anterior funiculus
• Gray matter Reed’s laminae encompasses I-X
• Sensory areas are in the Dorsal Horn
• Motor areas are in the Ventral Horn

Fiber Tracts

• White matter (sensory) includes dorsal columns gracile, cuneate fasiculi (dorsal column medial lemniscus), Lissauer’s tract, anterolateral spinothalamic tracts (anterolateral system), spino-cerebellar tracts
• White matter (motor) includes the lateral corticospinal tract (LCS), anterior corticospinal tract (ACS), rubrospinal tract
• Other motor tracts: recticulo-, vestibulo- & tecto-(spinal) tracts

Gray Matter

• Dorsal horn: substantia gelatinosa, Reed’s laminae
• Ventral (anterior) horn: Reed’s laminae
• Lateral (intermediate) horn: Clarke’s nucleus

Sensory Fibers

• Heavily myelinated proprioceptive fibers; lateral division of posterior root, terminate in laminae III-V, VII, MNs (touch, proprioception); GSA = somatic, GVA = visceral
• Less myelinated exteroceptive fibers; middle division of posterior root, terminate in Lissaeur's tract or laminae I-V (pain, temperature)
• Interoceptive fibers; medial division of posterior root, terminate in laminae I, V-VII (visceral sensory from autonomic ganglia)
• Motor efferent fibers: somatic efferents (heavily myelinated), supply skeletal muscles and spindles; MNs of laminae VIII, IX
• Visceral efferents supply visceromotor ganglia; MNs of intermediate zone, lamina VII; GSE = somatic, GVE = visceral

Spinal Cord Supply

• Vertebral artery branches supply anterior, posterior spinal arteries
• Provides arterial vasocorona and central, sulcal arteries
• Segmental arteries consist of medullary and radicular arteries and the great radicular artery of Adamkiewicz

Spinal Cord Drainage

• Spinal Venous Drainage happens through Anterior, posterior, and lateral spinal veins, anterior and posterior radicular spinal veins, and the anterior and posterior internal and external plexus

Spinal Cord Cross Sections

• S2 segment: Gracile fasciulus lower extremities, Lateral corticospinal tract, Reticulospinal tract, General propriospinal fibers, Anterolateral system
• L4 segment: Gracile fasciulus lower extremities, LCS and rubrospinal tracts, Anterolateral system Medial longitudinal fasiculus Anterior corticospinal tract
• T4 segment: Gracile and cuneate fasciuli, Anterior, posterior spinocerebellar tracts, Anterolateral system, Medial longitudinal fasiculus, Anterior corticospinal tract
• C7 segment: Gracile and cuneate fasciuli Anterior, posterior spinocerebellar tracts, Anterolateral system, Medial longitudinal fasiculus, tectospinal, reticulospinal & vestibulospinal tract, Anterior corticospinal tract
• C1 segment: Gracile and cuneate fasciuli, Anterior, posterior spinocerebellar tracts Medial longitudinal fasiculus, tectospinal tract, Reticulospinal tract, vestibulospinal tract, Anterior corticospinal tract

Spinal Reflex Circuit - Two Types

• Myotatic Stretch Reflex
• Nociceptive Reflex
• Crossed Extension Reflex

Inhibition in Neural Circuit

• What is being inhibited in reflex actions can be both Muscles & Neurons

Types of Spinal Reflexes

• Muscle stretch (myotatic, deep tendon) reflex and reciprocal inhibition of competing behavior
• Autogenic inhibition (inverse myotatic, Golgi tendon reflex)
• Withdrawal (flexor, nociceptive) reflex
• Crossed extension reflex

Spinal Reflex Questions

• What is the stimulus for each reflex?
• How is appropriate behavior elicited?
• How are inappropriate behaviors denied?

Brainstem Regions

• The brainstem consists of midbrain, pons, medulla
• Basilar region are the long fiber tracts, CNs
• Tegmentum contains reticular nuclei and fibers
• Midbrain tectum houses corpora quadrigemina

Brainstem Key Features

• Each has cranial nuclei and nerve components in midbrain, pons, medulla
• Midbrain tectum houses the superior and inferior colliculi
• Pontine, medullary and midbrain tegmentum contains the nuclei, reticular system, fiber tracts
• Basis is the medullary pyramids the (LCS decussation), brachium pontis, crus cerebri (cerebral peduncle)
• Fourth ventricle is the roof and floor structures, last slide

Landmarks for specific regions

• Medulla / pons junction has cranial nerves VI, VII, VIII, brachium pontis / pyramids
• Pons / midbrain junction has cranial nerve IV, brachium pontis / cerebral peduncles
• Midbrain / thalamus junction has cranial nerve III, mammillary bodies (+ posterior commissure)

Medulla Details

• Pyramids
• Olive
• Tubercles and Trigones

Midbrain Details

• Colliculi
• Mammilary Bodies

Region Similarities

• Pons: Cerebellar peduncles
• All: Cranial nerves

Brainstem: Cerebellum Removed

• The cerebral aqueduct connects the 3rd/4th ventricles
• The 4th ventricle roof anterior medullary velum and caudal tela choroidea
• The 4th ventricle floor (rhomboid fossa) has hypoglossal and vagal trigones, sulcus limitans, striae medullaris, superior and inferior fovea, vestibular area also present
• Foramina of Luschka and Foramen of Magendie are discussed
• Gracile tubercle, cuneate tubercle, and facial colliculus