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