SNELL'S NEUROANATOMY CH. 8

Cerebral cortex

What is the complete covering of the cerebral hemisphere composed of?

Gray matter

What type of matter primarily composes the cerebral cortex?

Approximately 10 billion neurons

Roughly how many neurons are estimated to be in the cerebral cortex?

Gyri

What are the convolutions or folds on the surface of the cortex called?

Sulci or fissures

What separates the gyri on the surface of the cortex?

1.5 to 4.5 mm

What is the approximate thickness range of the cerebral cortex?

Thickest over the crest of a gyrus

Where is the cerebral cortex typically the thickest?

Thinnest in the depth of a sulcus

Where is the cerebral cortex typically the thinnest?

Nerve cells, nerve fibers, neuroglia, and blood vessels

What are the main components of the cerebral cortex tissue?

Pyramidal cells

Name one type of nerve cell present in the cerebral cortex.

Stellate cells

Name another type of nerve cell found in the cerebral cortex.

Fusiform cells

Give a third example of a nerve cell in the cerebral cortex.

Horizontal cells of Cajal

Mention a fourth type of neuron present in the cerebral cortex.

Cells of Martinotti

What is the fifth type of nerve cell found in the cerebral cortex?

Shape of their cell bodies

What is the basis for naming pyramidal cells?

10 to 50 um

What is the typical length measurement of most pyramidal cell bodies?

Giant pyramidal cells or Betz cells

What are the very large pyramidal cells found in the motor precentral gyrus called?

Up to 120 um

What is the maximum length that the cell bodies of Betz cells can measure?

Motor precentral gyrus of the frontal lobe

Where are Betz cells primarily located?

Pial surface of the cortex

Toward what surface of the cortex are the apices of pyramidal cells oriented?

Apical dendrite

What thick dendrite extends upward from the apex of a pyramidal cell?

Basal dendrites

What dendrites pass laterally from the basal angles of a pyramidal cell?

Dendritic spines

What numerous structures are found on dendrites for synaptic junctions?

Base of the cell body

Where does the axon of a pyramidal cell arise from?

Deeper cortical layers or white matter

Where can the axon of a pyramidal cell terminate?

Projection, association, or commissural fiber

As what type of fiber does a pyramidal cell axon enter the white matter?

Granule cells

What is another name sometimes used for stellate cells?

Polygonal

What is the general shape of stellate cells?

About 8 pm in diameter

What is the approximate diameter of a stellate cell body?

Multiple branching dendrites

Describe the dendritic arborization of stellate cells.

Short axon

What is a characteristic feature of the axon of a stellate cell?

Nearby neuron

Where does the axon of a stellate cell typically terminate?

Vertical to the surface

What is the orientation of the long axis of fusiform cells?

Deepest cortical layers

Where are fusiform cells mainly concentrated?

Each pole of the cell body

Where do dendrites arise from in fusiform cells?

Same cellular layer

Where does the inferior dendrite of a fusiform cell branch?

Superficial layers

Where does the superficial dendrite of a fusiform cell branch?

Inferior part of the cell body

Where does the axon of a fusiform cell arise from?

White matter

Where does the axon of a fusiform cell enter?

Small, fusiform, horizontally oriented

Describe the morphology of horizontal cells of Cajal.

Most superficial layers

Where are horizontal cells of Cajal found?

Each end of the cell

Where does a dendrite emerge from in a horizontal cell of Cajal?

Parallel to the surface of the cortex

In what direction does the axon of a horizontal cell of Cajal run?

Dendrites of pyramidal cells

With what structures do the axons of horizontal cells of Cajal make contact?

Small, multipolar

Describe the morphology of cells of Martinotti.

Throughout the levels of the cortex

Where are cells of Martinotti present?

Short

What is a characteristic of the dendrites of cells of Martinotti?

Pial surface of the cortex

Toward what surface of the cortex is the axon of a cell of Martinotti directed?

More superficial layer, commonly the most superficial layer

Where does the axon of a cell of Martinotti end?

Few short collateral branches

What is a feature of the axon of a cell of Martinotti en route?

Radially and tangentially

How are the nerve fibers of the cerebral cortex arranged?

Right angles to the cortical surface

What is the orientation of radial nerve fibers relative to the cortical surface?

Afferent entering projection, association, and commissural fibers

Name one type of fiber included in radial fibers entering the cortex.

Axons of pyramidal, stellate, and fusiform cells

Name one type of fiber included in radial fibers leaving the cortex.

Projection, association, and commissural fibers of the white matter

What do the axons leaving the cortex become?

Parallel to the cortical surface

What is the orientation of tangential nerve fibers relative to the cortical surface?

Collateral and terminal branches of afferent fibers

What is a major component of tangential fibers?

Axons of horizontal and stellate cells

Name another component of tangential fibers.

Collateral branches of pyramidal and fusiform cells

Give a further example of tangential fibers.

Layers 4 and 5

In which layers are tangential fibers most concentrated?

Outer and inner bands of Baillarger

What are the tangential fibers in layers 4 and 5 referred to as, respectively?

Sensory areas

In which areas are the bands of Baillarger particularly well developed?

High concentration of the terminal parts of the thalamo-cortical fibers

What accounts for the well-developed bands of Baillarger in sensory areas?

Visual cortex

In which specific cortical area is the outer band of Baillarger so thick it's visible to the naked eye?

Stria of Gennari

What is the outer band of Baillarger called in the visual cortex?

Walls of the calcarine sulcus

Where is the visual cortex located?

Striate cortex

What is another name sometimes used for the visual cortex due to the stria of Gennari?

Type, density, and arrangement of their cells

What are the distinguishing features used to divide the cerebral cortex into layers?

Molecular layer (plexiform layer)

What is the most superficial layer of the cerebral cortex called?

Dense network of tangentially oriented nerve fibers

What is the main composition of the molecular layer?

Apical dendrites of pyramidal and fusiform cells

Name one source of nerve fibers in the molecular layer.

Axons of stellate cells

Give another source of nerve fibers in the molecular layer.

Cells of Martinotti

Mention a third source of nerve fibers in the molecular layer.

Afferent fibers from the thalamus

What is one type of afferent fiber present in the molecular layer?

Association and commissural fibers

What are other types of fibers present in the molecular layer?

Occasional horizontal cells of Cajal

What type of nerve cell is scattered among the nerve fibers in the molecular layer?

Large numbers of synapses

What is a key feature occurring in the molecular layer?

External granular layer

What is the second layer of the cerebral cortex from the surface?

Small pyramidal cells and stellate cells

What are the main cell types found in the external granular layer?

Molecular layer

Where do the dendrites of cells in the external granular layer terminate?

Deeper layers or white matter

Where do the axons of cells in the external granular layer terminate or pass on to?

External pyramidal layer

What is the third cortical layer?

Pyramidal cells

What is the primary cell type in the external pyramidal layer?

Superficial to deeper borders

How does the cell body size of pyramidal cells change within the external pyramidal layer?

Projection, association, or commissural fibers

As what type of fibers do the axons from the external pyramidal layer enter the white matter?

Internal granular layer

What is the fourth layer of the cerebral cortex?

Closely packed stellate cells

What is the main cell type in the internal granular layer?

Horizontally arranged fibers known as the external band of Baillarger

What is a characteristic feature of the internal granular layer in terms of nerve fibers?

Ganglionic layer (internal pyramidal layer)

What is the fifth layer of the cerebral cortex called?

Very large and medium-size pyramidal cells

What is the primary cell type in the ganglionic layer?

Stellate cells and cells of Martinotti

What other cell types are scattered among the pyramidal cells in the ganglionic layer?

Inner band of Baillarger

What band of horizontally arranged fibers is found in the ganglionic layer?

Motor cortex of the precentral gyrus

Where are the pyramidal cells of the ganglionic layer very large and known as Betz cells?

About 3%

What percentage of the projection fibers of the corticospinal tract do Betz cells account for?

Multiform layer (layer of polymorphic cells)

What is the deepest layer of the cerebral cortex?

Fusiform cells

What is the majority cell type in the multiform layer?

Modified pyramidal cells (triangular or ovoid)

What other types of cells are found in the multiform layer besides fusiform cells?

Cells of Martinotti

What other conspicuous cell type is present in the multiform layer?

Entering or leaving the underlying white matter

What is the direction of many nerve fibers present in the multiform layer?

Brodmann (1909)

Whose system of numbering and nomenclature of cortical layers is commonly used?