Cerebral Cortex

Question 1

Major divisions of the cerebral cortex

Answer 1

• neocortex (“isocortex”) vs. allocortex (“other” cortex)
  
  • neocortex = 6-layered cortex
    
    • most extensive
    • variations of cell size/density btwn layers ==> broadmann’s subdivisions
• granular vs. agranular cortex
  
  • agranular cortex = motor + premotor cortex (BA 4 and 6)
    
    • granule cells = poorly developed
    • pyramidal layers = prominent
    • fxn = output
  • granular cortex
    
    • cell layers receive inputs
    • fxn = sensory/afferent

Question 2

Characteristics of layers of neocortex

Answer 2

• Ascending pathway
  
  • target of the ascending pathway = layer 4
  • layer 4 relay signals to layers 3 and 2
• Descending pathway
  
  • layer 1 = target of descending
    
    • almost devoid of cell bodies
    • incoming axonal ramifications + branching apical dendrites + glial
  • inputs to layer 5 from layer 2/3

Question 3

EEG measurements

Answer 3

• electrical potential fluctuations at scalp surface
• temporal and spatial summation of
  electrical currents caused by the relatively slow postsynaptic potentials induced in neruons of cerebral cortex
• Frequencies and patterns relate roughly to different states of being (Relaxed/Alert/Drowsy/REM/Dreamless)
  
  • higher frequecies = more activity
  • lower frequencies = less activity

Question 4

Classification of EEG rhythms

Answer 4

• Αlpha rhythms are in sensory cortices when you aren’t doing very much
• Beta rhythms = alert, REM sleep
• δ: below 3.5Hz
• Θ : 4-7.5 Hz
• α 8-13 Hz
• β: 14-30 Hz
• ɣ: 30-100 Hz

Question 5

Rhythmic vs. Random discharge of thalamic neurons

Answer 5

• Rhythmic
  
  • e.g. reticular nucleus
  • T-type channels ==> rhythmic firing during:
    
    • slow-wave sleep
    • deep anesthesia
    • absence seizures
  • represents temporary detachment of thalamic relay cells from sensory inputs
• Random
  
  • ACh depolarizes relay neurons & inhibits reticular nucleus
  • ACh “opens” thalamocortical gate to sensory info ==> attention and arousal