Neuroanatomy: White Matter and Neurons

Here are the study notes:

White Matter and Neurons

• White matter: consists of myelinated axons, which gives a whitish appearance
• Myelin sheath: a lipid protein sheet surrounding the axon, allowing for action potentials to be carried quickly
• Neuron structure: has dendrites (receptive region), cell body (nucleus), axon terminal (axon bulb), and myelin sheath

Tracts

• Tract: a bundle of axons in the central nervous system
• Ascending tracts: carry sensory information up the spinal cord
• Descending tracts: carry motor information down the spinal cord

Anatomy of White Matter in the Spinal Cord

• Columns: white columns or funiculi (dorsal, lateral, ventral)
• Dorsal white column: posterior to gray matter
• Lateral white column: on the side of gray matter
• Ventral white column: anterior to gray matter
• Anterior white commissure: a structure where fibers cross over in the ventral white column

Function of White Matter

• Ascending tracks: carry sensory information (e.g., pain, temperature) up the spinal cord
• Descending tracks: carry motor information (e.g., voluntary control of skeletal muscles) down the spinal cord

Specific Tracts

• Lateral corticospinal tract: a descending motor tract in the lateral white column; stimulates lower motor neurons for voluntary control of skeletal muscles
• Rubrospinal tract: a descending motor tract in the lateral white column
• Dorsal column tracts: ascending sensory tracts in the dorsal white column, carrying fine touch, vibration, and proprioception (position and movement) information
• Lateral spinothalamic tract: an ascending sensory tract in the lateral white column, carrying pain and temperature information
• Anterior spinothalamic tract: an ascending sensory tract in the anterior white column, carrying pain and temperature information
• Tractus de Lasauer: an ascending tract that allows pain and temperature fibers to ascend one to two segments before synapsing on posterior gray horn neurons

Somatotopic Arrangement

• Lateral corticospinal tract: legs are laterally, with sacral supply most laterally, then lumbar, thoracic, and cervical

• Dorsal column: sacral supply is most medially, then lumbar, thoracic, and cervical

• Lateral spinothalamic tract: legs are laterally, with sacral supply most laterally, then lumbar, thoracic, and cervical### Descending Tracts in Lateral White Column

• Lateral reticulospinal tract (also known as medullary reticulospinal tract) primarily stimulates flexors

• Medial reticulospinal tract (also known as pontine reticulospinal tract) primarily supplies extensors

• Vestibulospinal tract primarily stimulates extensors, specifically anti-gravity muscles

• Tectospinal tract sends information for movement of the head, neck, and eye movements

• Ventral or anterior corticospinal tract stimulates lower motor neurons for voluntary skeletal muscle control

Ascending Tracts in Lateral White Column

• Dorsal spinocerebellar tract picks up proprioceptive sensations from C8 to L2 via Clark's column
• Ventral spinocerebellar tract picks up proprioceptive sensations from L2 to the coccygeal region
• Spino-olivary tract picks up proprioception and sends information to the inferior olives, which then sends it to the cerebellum via climbing fibers
• Lateral spinothalamic tract carries pain and temperature sensations
• Anterior spinothalamic tract carries crude touch and pressure sensations

White Matter and Neurons

• White matter composition: myelinated axons, giving a whitish appearance
• Myelin sheath function: allows for rapid action potential transmission
• Neuron structure components: dendrites, cell body, axon terminal, and myelin sheath

Tracts

• Tract definition: a bundle of axons in the central nervous system
• Ascending tracts function: carry sensory information up the spinal cord
• Descending tracts function: carry motor information down the spinal cord

Spinal Cord Anatomy

• White columns: dorsal, lateral, and ventral columns (funiculi)
• Dorsal white column location: posterior to gray matter
• Lateral white column location: on the side of gray matter
• Ventral white column location: anterior to gray matter
• Anterior white commissure function: fibers cross over in the ventral white column

White Matter Functions

• Ascending tracts sensory information: pain, temperature, etc.
• Descending tracts motor information: voluntary control of skeletal muscles

Specific Tracts

• Lateral corticospinal tract function: stimulates lower motor neurons for voluntary control of skeletal muscles
• Rubrospinal tract function: descending motor tract
• Dorsal column tracts sensory information: fine touch, vibration, and proprioception
• Lateral spinothalamic tract sensory information: pain and temperature
• Anterior spinothalamic tract sensory information: pain and temperature
• Tractus de Lasauer function: allows pain and temperature fibers to ascend before synapsing

Somatotopic Arrangement

• Lateral corticospinal tract organization: legs are laterally, with sacral supply most laterally
• Dorsal column organization: sacral supply is most medially
• Lateral spinothalamic tract organization: legs are laterally, with sacral supply most laterally

Descending Tracts in Lateral White Column

• Lateral reticulospinal tract function: stimulates flexors
• Medial reticulospinal tract function: supplies extensors
• Vestibulospinal tract function: stimulates extensors, specifically anti-gravity muscles
• Tectospinal tract function: sends information for head, neck, and eye movements
• Ventral or anterior corticospinal tract function: stimulates lower motor neurons for voluntary skeletal muscle control

Ascending Tracts in Lateral White Column

• Dorsal spinocerebellar tract function: picks up proprioceptive sensations from C8 to L2
• Ventral spinocerebellar tract function: picks up proprioceptive sensations from L2 to the coccygeal region
• Spino-olivary tract function: picks up proprioception and sends it to the cerebellum
• Lateral spinothalamic tract function: carries pain and temperature sensations
• Anterior spinothalamic tract function: carries crude touch and pressure sensations