Central Nervous System

Pyramidal Cells and Motor Pathways

  • Pyramidal Cells (Upper Motor Neurons)

    • Location: Primary motor cortex
    • Function: Involved in voluntary motor control

  • Internal Capsule

    • Structure: Contains descending motor pathways

  • Cerebral Peduncle

    • Structure: Pathway for descending fibers located in the midbrain

  • Pyramids

    • Location: Medulla oblongata
    • Function: Contains corticospinal tracts

  • Decussation of Pyramids

    • Meaning: Crossing over of motor fibers to the opposite side

  • Lateral Corticospinal Tract

    • Function: Controls skilled voluntary movements of contralateral side

  • Ventral Corticospinal Tract

    • Function: Also involved in motor control, fibers cross at spinal cord level

  • Rubrospinal Tract

    • Location: Originates in red nucleus of midbrain
    • Function: Modulates muscle tone, especially in distal limbs
Major Ascending (Sensory) Pathways and Spinal Cord Tracts

  • Dorsal Column-Medial Lemniscal Pathways

    • Function: Transmits proprioception and fine touch
    • Includes fasciculus cuneatus (upper limbs) and fasciculus gracilis (lower limbs)

  • Spinothalamic Pathways

    • Function: Transmits pain and temperature sensations
    • Includes lateral spinothalamic (pain) and ventral spinothalamic (crude touch) tracts

  • Spinocerebellar Pathways

    • Function: Carries proprioceptive information from limbs to cerebellum
    • Dorsal: Uncrossed fibers, informs cerebellum of same side's position
    • Ventral: Crossed fibers that re-cross at the level of the pons
Major Descending (Motor) Pathways and Spinal Cord Tracts

  • Direct (Pyramidal) Pathways

    • Lateral Corticospinal

    • Origin: Motor cortex of the cerebrum

    • Function: Voluntary motor control, fibers cross at medulla

    • Ventral Corticospinal

    • Same as lateral, but fibers cross at spinal level

  • Indirect Pathways

    • Tectospinal

    • Origin: Superior colliculus, mediates head and eye movements

    • Vestibulospinal

    • Origin: Vestibular nuclei, helps maintain balance

    • Rubrospinal

    • Modulates tone and limb movement, primarily for distal muscles

Developmental Aspects of the Central Nervous System

  • Neural Tube Formation

    • Origin: Ectoderm thickens to form neural plate, which then invaginates
    • Development of CNS structures occurs from neural tube by week four of gestation

  • Neuroblast Development

    • Development of dorsal alar plate (interneurons) and ventral basal plate (motor neurons) by week six

  • Neural Crest

    • Gives rise to sensory neurons in the dorsal root ganglia
Congenital Malformations and Their Effects

  • Cerebral Palsy

    • Neuromuscular disability resulting from brain damage, often due to oxygen deprivation during birth

  • Anencephaly

    • Condition where brain structures do not develop, resulting in death shortly after birth

  • Spina Bifida

    • Incomplete formation of the vertebral arches leading to potential neurological deficits

  • Preventative Measures

    • Importance of maternal folic acid to reduce risks of neural tube defects
Aging and the Central Nervous System
  • Cognitive Declines with Age
    • Losses occur after the seventh decade, primarily in spatial ability and processing speed
    • Brain continues to maintain learning capacity despite neuron loss