Cytoarchitecture of the cortex

Question 1

Cortical Layer I

Answer 1

• consists of few cells

- Probably pools information from apical dendrites of neurons in lower layers.

Question 2

Cortical Layer II

Answer 2

external granular layer, although now understood to consist mainly of small pyramidal neurons

Question 3

Cortical Layer III

Answer 3

• external pyramidal layer
• Pyramidal neurons that increase in size from outer to inner boundary
• Mainly project axons to other cortical areas –> cortico-cortical connections.

Question 4

Cortical Layer IV

Answer 4

• internal granular layer

- Consists of granular neurons that receive input from cortical and sub-cortical areas

Question 5

Cortical Layer V

Answer 5

• internal pyramidal layer

- Pyramidal neurons whose axons mainly extend to subcortical structures à cortico-subcortical connections.

Question 6

Cortical Layer VI

Answer 6

• primarily spindle-shaped neurons, a modified form of the pyramidal neuron, whose axons mainly project to subcortical structures

Question 7

study of the cytoarchitecture of the cortex

Answer 7

study of how cortical layers change in thickness and density, including changes in cell sizes, etc.

Question 8

agranular

Answer 8

lacks cells in layer IV

ex: primary motor cortex
- -> Instead, large pyramidal neurons occupy layer V and project to the spinal cord to control movement

Question 9

hypergranular

Answer 9

have a very wide and dense layer IV

ex: primary sensory areas
- -> because of all input from thalamus
- -> referred to as koniocortex “dust cortex”

Question 10

parahippocampal gyrus

Answer 10

• used to think that the entire PHG was for
processing smell…
• Was referred to as the “Rhinencephalon” –> “nose
brain”
• Until patient H.M. in the 1950’s…bilateral resection
and could no longer form new memories
• The hippocampus is one of many structures
important for memory consolidation

Question 11

Pyriform cortex

Answer 11

primary olfactory cortex (extends from orbitofrontal cortex). Also known as Paleocortex (“old cortex”)

Question 12

Random things about cortex

Answer 12

• All cortex evolved from archicortex and paleocortex
• Reptiles have subcortical structures, questionable whether birds have cortex
• Rats, for instance, have large amounts of olfactory cortex, hippocampus, and very little prefrontal cortex

Question 13

Limbic Cortex

Answer 13

• Phylogenetically old cortex
• Used to be called the “limbic lobe”
• Not the usual 6 layers of neocortex (“new
cortex”)

Question 14

most famous cytoarchitectonic map

Answer 14

• Korbinian Brodmann, 1909
• German neurologist
• In neuroimaging studies, functional activation peaks are
still often expressed as occurring in “Brodmann areas”

Question 15

precentral gyrus

Answer 15

Consists of at least two cytoarchitectonic areas:
• area 4 = the the real “M1” –> primary motor cortex –> fast, direct projections to spinal cord
• area 6 = premotor cortex
both areas agranular

Question 16

Betz cells

Answer 16

extremely large pyramidal neurons interspersed in
layer V of area 4 whose axons are very large and heavily myelinated for fast transmission.
• These cells are a defining feature of the primary motor cortex.
• Largest at the dorsal motor cortex

Question 17

Why are Betz cells the largest in dorsal motor cortex?

Answer 17

need to project further down spinal cord to control lower

extremities. Longer axon = larger cell body!

Question 18

postcentral gyrus

Answer 18

• Penfield called this “S1” based on his macrostimulations
• Cytoarchitectonically, there are three distinct areas:
- area 3 (posterior bank of central sulcus) the real “S1” –> primary somatosensory cortex –> receives most of the input from the thalamus
- area 1 (postcentral gyrus)
- area 2 (anterior bank of postcentral sulcus)
all 3 areas are hypergranular

Question 19

Pars opercularis

Answer 19

approximately cytoarchitectonic area 44

Question 20

Pars triangularis

Answer 20

approximately cytoarchitectonic area 45

Question 21

Pars orbitalis

Answer 21

approximately area cytoarchitectonic 47/12

Question 22

Area 44

Answer 22

dysgranular cortex: a poorly developed layer IV with interruptions from pyramidal neurons in neighbouring layers III and V.

Question 23

Area 45

Answer 23

Typical granular frontal cortex.

Also has unusually large pyramidal neurons in layer III.

Question 24

Area 47/12

Answer 24

Typical granular frontal cortex that lacks the usually large pyramidal neurons found in area 45

Question 25

Area 41

Answer 25

• primary auditory cortex

* Occupies the transverse temporal gyrus within the Sylvian fissure: Heschl’s gyrus