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Introduction
The neurons of the cerebral cortex
Study methodology
Laminae (layers)

Hemisphere surface (cerebral cortex) is called pallium
having variable depth/thickness (15–45mm) from one
area to another.
- thicker in the summit of the gyli, and thinner on the
depth of the sulci.

The pallium has laminar (layers) arrangement which
associate with blood vessels – angioarchtecture.

Neurons are forming a microarchtecture by presenting
different types of cell morphologies

These morphologies are
 i. Pyramidal cells
 ii. Non-pyramidal cells called stellate or granule cells
- They are spiny or non-spiny.

Cells are also subdivided basing on their sizes,
shapes and neuritic arrays.

This section is showing cells in different orientation as they
are seen in the neuropil.

1. Pyramidal cell: This is a flask-shaped or triangular cell
body with single apical or multiple basal dendrities.
- Form most of the majority of projection neurons.


2. Spiny stellate cells: most of these are multipolar cells.
- Numerous in the lamina IV.
- They have relatively small sized cell bodies and spiny
dendrites.
- Their axons ramify within the gray matter in a vertical
plane.
3. Non spiny stellate cells: These are numerous
group of interneurons (association neurons).
- They have different shapes like basket, chandelier,
double bouquet, neuroglial forms bipolar or
fusiform and horizontal cells.

.
.
This is a histological slide
of the cerebrum.
Numerous pyramidal
shaped neurons are
present within
perineuronal spaces. These
cells have large vesicular
nuclei. The small cells seen
only as nuclei are glial
cells. The stringy pink
background is the
neuropil. At high power, a
small blood vessel
surrounded by a clear
Virchow-Robin space is
seen.
Chandelier design
Bouquet design

4. Glial cells: This is a group of supporting
cells in the NS which are associating with the
neurons.
- They include
i. astrocytes
ii. oligodendrocytes
iii. ependymal cells
iv. microgliae .
- They are occupying the neuropil part of the
cerebral cortex.
Normal astrocytes
Cortical astrocytes – fluorecence
technique

Study of neurons in the cerebral cortex involving
staining techniques is known as artechitectonics.
- study by staining the cell bodies
arrangements is termed cytoarchtechtonics.
- the use of myelin stained material is termed
myeloarchtectonics.
- the use of stained pigment distribution is
termed as pigmentoarchtectonics.




The pallium has six distinctive layers which may occasionally
be appreciated by the naked eyes. The layers are lying parallel
to the surface.
LAYER I: This is the molecular or plexiform layer.
- it contains scattered horizontal cells and the apical
dendrites of all pyramidal neurons of the cerebral cortex.
LAYER II: External granular lamina.
- it contains small neuronal cell bodies (pyramidal and non
pyramidal neurons).
LAYER III: External pyramidal lamina.
- it contains pyramidal cells of different sizes.



LAYER IV: Internal granular layer.
- this is the narrowest of the cellular laminae
- it contains densely parked small round pyramidal cells
LAYER V: Internal pyramidal lamina.
- it contains the larger pyramidal cells and scattered nonpyramidal cells.
LAYER VI: The multiform layer.
- it contains variety of shapes eg. Pyramidal, spindle, ovoid
and many other shaped somata.
- the cells are small to medium sized.
- this layer blends with the white matter.
Introduction
The neurons (cells) of the cerebellar cortex
Important fibres
The cerebellum is a smaller region in the lower
part of the brain. For the large region of the
brain.
 it plays an important role in motor control.

it may also be involved in some cognitive
function such as attention and language.

it regulates fear and pleasure responses,

it has movement-related functions which does
not initiate movement, but it contributes to coodination, precision, and accurate timing.


It receives input from sensory system of the
spinal cord and from other parts of the brain and
integrates these inputs to fine-tune motor
activity.
Cerebellar damage produces disorders in fine
movement, equilibrium, posture, and motor
learning.
• [It is extremely important to remember that cerebellum is
able to perform everyday voluntary (done with purpose and
intent) tasks such as walking and writing.
• It is also essential to being able to stay balanced and
upright. Patients who have suffered from damaged
cerebellums often struggle with keeping their balance and
maintaining proper muscle coordination]

Cerebellar substance is divided into outer
cerebellar cortex (gray matter) and inner
cerebellar medullar (white matter).
 The gray matter is composed of three layers
i. Molecular cell layer
ii. Purkinje cell layer
iii. Granular cell layer
 The white matter comprises of neuronal fibres
mostly myelinated.
MOLECULAR LAYER
 the outer lamina of the cortex lying directly
below the pia mater, containing the cell
bodies (unless the Purkinje cell layer is
designated as a separate layer) and dendrites
of Purkinje cells; non-myelinated axons of
the granular layer cells; the cell bodies,
dendrites, and axons of basket cells and
superficially located stellate cells; and the
dendrites of Golgi cells plus cerebellar glial
cells.
◦ Basket cells are multipolar interneurons found in
molecular layer that function to make inhibitory
synapses and control the overall potentials of target
cells.
◦ stellate cells are neurons. The three most common
stellate cells are the inhibitory interneurons found within
the molecular layer of the cerebellum, excitatory spiny
stellate cells and inhibitory aspiny stellate interneurons.

PURKINJE CELL LAYER
◦ The large, spherical cell bodies of Purkinje cells
are packed into a narrow layer (one cell thick)
of the cerebellar cortex, called the Purkinje
layer.
◦ Purkinje cells are among the most distinctive neurons in
the brain and only cerebellar cortex neurons which send
information (always inhibitory) to the outside.
◦ are distinguished by the shape of their dendritic tree and
their myelinated axons project to the white matter.
◦ The dendrites branch very profusely, but are severely
flattened in a plane perpendicular to the cerebellar folds.
◦ The dendrites are covered with dendritic spines, each of
which receives synaptic input from a parallel fiber.
◦ Purkinje cells receive more synaptic inputs than any
other type of cell in the brain.



Purkinje cells use GABA as their
neurotransmitter, and therefore exert
inhibitory effects on their targets.
Purkinje cells normally emit action potentials
at a high rate even in the absence of the
synaptic input.
Other cells found in Purkinje layer include
Bergmann cells a type of glia also known as
radial epithelial cells or Golgi epithelial cells


Bergmann cells are astrocytes in the
cerebellum that have their cell bodies in the
Purkinje cell layer and processes that extend
into the molecular layer, terminating with
bulbous end feet at the pial (vascular)
surface.
Bergmann glia are also required for the
pruning or addition of synapses.

GRANULAR CELL LAYER:
◦ Cerebellar granule cells, in contrast to Purkinje
cells, are among the smallest neurons in the brain.
They are also easily the most numerous neurons in
the brain: In humans, estimates of their total
number average around 50 billion, which means
that about 3/4 of the brain's neurons are cerebellar
granule cells.
◦ Their cell bodies are packed into a thick layer at the
bottom of the cerebellar cortex.
◦ A granule cell emits only four to five dendrites,
each of which ends in an enlargement called a
dendritic claw . These enlargements are sites of
excitatory input from mossy fibers and inhibitory
input from Golgi cells.


The thin, unmyelinated axons of granule cells
rise vertically to the upper (molecular) layer of
the cortex, where they split in two, with each
branch traveling horizontally to form a
parallel fiber; the splitting of the vertical
branch into two horizontal branches gives
rise to a distinctive "T" shape.
Granule cells use glutamate as their
neurotransmitter, and therefore exert
excitatory effects on their targets.

Cerebellar fibres:
Mossy fiber (cerebellum)
 are one of the major inputs to cerebellum. There are many
sources of this pathway, the largest of which is the cerebral
cortex, which sends input to the cerebellum via the
pontocerebellar pathway. Other contributors include the
vestibular nerve and nuclei, the spinal cord, the reticular
formation, and feedback from deep cerebellar nuclei. Axons
enter the cerebellum via the middle and inferior cerebellar
peduncles
Climbing fiber
are the name given to a series of neuronal projections from
the inferior olivary nucleus located in the medulla oblongata.
These axons pass through the pons and enter the cerebellum
via the inferior cerebellar peduncle where they form
synapses with the deep cerebellar nuclei and Purkinje cells

The climbing fibers carry information from
various sources such as the spinal cord,
vestibular system, red nucleus, superior
colliculus, reticular formation and sensory and
motor cortices. Climbing fiber activation is
thought to serve as a motor error signal sent to
the cerebellum, and is an important signal for
motor timing.
Parallel fiber:
arise from granule cells in the cerebellar cortex.
They form excitatory synapses onto the dendrites
of Purkinje cells (the output neurons of the
cerebellum) and the dendrites of the inhibitory
interneurons basket cells and stellate cells of the
molecular layer.

Figure: Microcircuitry of the cerebellum. Excitatory synapses are denoted by (+)
and inhibitory synapses by (-). MF: Mossy fiber. DCN: Deep cerebellar nuclei. IO:
Inferior olive. CF: Climbing fiber. GC: Granule cell. PF: Parallel fiber. PC: Purkinje
cell. GgC: Golgi cell. SC: Stellate cell. BC: Basket cell.