Intro to Brain Anatomy - Cortical Cytoarchitecture

Question 1

Cytoarchitecture

Answer 1

• Cyto = cell
• Architecture = structure
• Study of how the layers change in thickness and density provides us insight into function

Question 2

Early Studies

Answer 2

• End 19th century
• Alcohol harden the brain
  
  • Could inspect thin sections of tissue and stain
• Many pertinent studies in early 20th century

Question 3

Staining Techniques

Answer 3

• Golgi stain
• Nissl stain
• Weigert stain

Question 4

Golgi Stain

Answer 4

• Stains about 10% of neurons
• Can see the morphology of the neuron

Question 5

Nissl Stain

Answer 5

• Stains the cell bodies of all neurons
• Great for cytoarchitecture since determines the cell densities

Question 6

Weigert Stain

Answer 6

• Stains the axons

Question 7

Cortical Cytoarchitecture

Answer 7

• Two main types of neurons in the cortex:
  
  • Pyramidal neurons
  • Granule/stellate neurons

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Question 8

Pyramidal Neurons

Answer 8

• Soma shaped like a pyramid
• Basal dendrites
• Apical dendrite
• long axon that exits the cortex
• The typical cortical neuron

Question 9

Granulate (stellate) neurons

Answer 9

• Smaller and rounder
• Axons usually do not leave the cortex
  
  • Mainly distribute information to neighbouring layers
• Does not always appear in old cortex

Question 10

Cortical Layers

Answer 10

1. Layer I:
   Few cells
   Info from apical dendrites of neurons in lower levels
2. Layer II:
   External granular layer although now understood to consists of mainly pyramidal layers.
3. Layer III:
   External pyramidal layer
   Pyramidal cells increase in size from outer to inner boundary
   Project axons to cortical areas
   cortico-cortical connections
4. Layer IV:
   Internal Granular layer
   Granular neurons
   Receive input from cortical and subcortical areas
5. Layer V:
   Internal Pyramidal layer
   Pyramidal neurons
   Axons extend to subcortical structures
   cortical-subcortical connections
6. Layer VI:
   Spindle-shaped neurons (modified pyramidal form neuron)
   Axons mainly project to subcortical structures

Question 11

Function Example 1 :

Primary Motor Cortex is _______

Answer 11

1. Agranular
2. Large pyramidal neurons occupy layer V and project to the spinal cord to control movement

Motor cortex cares more about sendin**g information than receiving.

Question 12

Function Example 2:

Primary sensory areas are ________

Answer 12

1. Hypergranular
   
   1. referred as korniocortex (dust cortex)
2. Receive a lot of input from the thalamus

Question 13

Agranular

Answer 13

Separation between pyramidal cells of layers III and V is not clear.

Question 14

Dysgranular

Answer 14

Separation between layers III and V is interrupted

Question 15

Granular

Answer 15

Separation between layers III and V is very clear

Question 16

Old Cortex

Answer 16

• Fewer than 6 layers
• Hippocampus
  
  • Part of it just 1 layer

Question 17

Parahippocampal Gyrus

Answer 17

• Contains (From up to down):
  
  • Thalamus
  • Hippocampal Sulcus
  • Pyriform Cortex
  • Entorhinal Cortex
  • Parahippocampal Cortex
  • Rhinal Sulcus
  • Collateral Sulcus
  • Fusiform Gyrus
  • Occipito-Temporal Sulcus
  • Inferior Temporal Gyrus (ITG)
• L4 p.22:
  
  • Used to be referred as Rhinencephalon (nose brain)
  • Patient H.M.
    
    • Important for Memory consolidation
  • Pyriform cortex
  • Entorhinal cortex
  • Parahippocampal cortex

Question 18

Pyriform cortex

Answer 18

• Primary olfactory cortex
• Also known as: Paleocortex (old cortex)

Question 19

Entorhinal cortex

Answer 19

• Above amygdala and anterior hippocampus

Question 20

Parahippocampal cortex

Answer 20

• Above the posterior hippocampus

Question 21

From where did all the cortex evolved?

Answer 21

From the archicortex and paleocortex

Question 22

Which is the most famous cytoarchitectonic map?

Answer 22

• Brodmann’s
• Brodmann areas

Question 23

Precentral Gyrus

Answer 23

• At least two cytoarchitectonic areas:
  
  • Area 4
    
    • Real M1
    • Fast direct projections to spinal cord
    • Layer V: Beltz cells
  • Area 6
    
    • ​Premotor cortex
• Both agranular

Question 24

Beltz Cells

Answer 24

• Extremely large pyramidal neurons
• In layer V of Area 4
• Axons are big and very myelinated

Question 25

Why are the Beltz cells the largest on the dorsal motor cortex?

Answer 25

• Given Penfield’s schema, the dorsal part of the motor cortex is the one in charge of controlling the legs.
• The information needs to get further down the spinal cord
  
  • Longer axon = larger cell body

Question 26

Postcentral Gyrus

Answer 26

• 3 cytoarchitectural areas:
  
  • Area 3:
    
    • Real S1 (primary somatosensory cortex)
    • posterior bank of central sulcus
    • Input from thalamus
  • Area 1:
    
    • ​Postcentral gyrus
  • Area 2:
    
    • ​Anterior bank of postcentral sulcus

Question 27

What are those!

Answer 27

• Green: Pars Triangularis
• Pink: Pars Opercularis
• Blue: Pars Orbitalis

Question 28

Area 44

Answer 28

• Approximately Pars Opercularis
• Dysgranular

Question 29

Area 45

Answer 29

• Approximately Pars Triangularis
• Granular frontal cortex
• Unusually large pyramidal neurons

Question 30

Area 47/12

Answer 30

• Approximately Pars Orbitalis
• (Not a Brodmann Area)
• Granular frontal cortex
• lacks usually large pyramidal neurons

Question 31

True or False

Brodmann’s Areas only exists in the language dominant hemisphere.

Answer 31

False

They exist in both hemispheres and their functionality is pretty much the same.

We say that the left hemisphere is dominant for language.

Question 32

True or False

The left hemisphere is the language dominant hemisphere.

Answer 32

True

Question 33

Traditional Broca’s Area

Answer 33

• Areas 44 and 45
  
  • Some people don’t include the pars triangularis
  • Some people don’t include the pars opercularis

Question 34

Primary Auditory Cortex A1

Answer 34

• Area 41
• Occupies the transverse temporal gyrus within the Sylvian fissure
  
  • Heschl’s gyrus

Question 35

Heschl’s Gyrus

Answer 35

• Area 41
• A1
• Can be one or two:
  
  • Is two the Area 41 is in the most anterior

Question 36

Areas to know

Answer 36

• 4: M1
• 6: Premotor cortex
• 3: S1
• 1, 2: Somatosensory cortex
• 17: V1 (superior to calcarine sulcus)
• 18: “V2”
• 41: A1
• 44: pars opercularis
• 45: pars triangularis
• 47/12: pars orbitalis
• 22: STG
• 40: Supramarginal gyrus
• 39: Angular Gyrus

L5 p. 17