Cerebellum在线视频

Hi, everyone. I am Dr.Ma,

from 1st affiliated hospital

of Shantou University Medical College.

Welcome to this session of Clinical Histology.

Today we will talk about the cerebellum.

Here are the learning objectives for you.

At the end of this session,

you should be able to

outline the function of cerebellum.

describe the layers of cerebellar cortex

summarize the function of Purkinje cells

explain the symptoms of cerebellar ataxia

Let's start off with a case.

Mr.Simmons,

a 30-year-old man

presented to the clinic

with complaints of difficulty walking

in a straight line and swaying

while walking in a narrow passages for 5 years.

He had a slow progression of symptoms

On examination,

his muscle tone was normal

but coordination was impaired by severe ataxia.

His mother and maternal uncle

also had problems with gait,

which were progressive

and began during adulthood.

MRI of the brain revealed cerebellar folia atrophy

and the patient was diagnosed

as having cerebellar ataxia.

The cerebellum sits in the back of the brain

posterior to the brainstem.

If you take the section of cerebellum,

we can see white matter and gray matter,

and some gray areas

that are basically the nuclei in the cerebellum

Neurons send their axons

carrying input from the spinal cord,

the brain and the internal ear

through the brainstem into the cerebellum.

Once there,

the cerebellum uses this information to coordinate

and plan movement as well as maintain balance.

Here is a microscopic section of cerebellum

under low magnification.

We can see the surface depressions of fissures

shown by arrows separating the folia.

The cerebellum consists of

an outer convoluted cortex containing neurons

and a central core of white matter

containing ascending and descending fibers.

One of the characteristic features of the cerebellum

is the uniform thickness of the cortex

irrespective of where we take the section.

Let's have a closer look

into the cortex of the cerebellum.

There are 3 layers in the cerebellar cortex.

From outside inwards,

we have the molecular layer,

the Purkinje cell layer

and the granule cell layer.

These 3 layers are named

according to the type of neurons.

Let's begin with the molecular layer

which is the outermost layer of the cerebellum,

we can see it is the pale staining superficial layer

which mainly consists of neural processes

with very few cells.

The neural processes found in this level

include dendrites of the Purkinje cells,

parallel fibers

which arise from the axons of the granule cells

and the climbing fibers.

It also has cell bodies

and processes of 2 types of interneurons.

The stellate cells

are found close to the surface of the cerebellum

and basket cells

are located in the deeper part of the molecular layer.

These cells are involved in the feed

forward inhibition of Purkinje cells.

The middle layer is the Purkinje cells layer.

It has a single layer of large

pear shaped Purkinje cells

Purkinje cell is one of the most beautiful neurons

that you will ever want to see under the microscope.

It has a very large cell body

that gives rise to these incredibly remarkable

branching patterns of dendrites.

While most neurons in the brain grow

dendrites in all different directions,

the Purkinje cells develop theirs in a flat plane.

Purkinje cell is the principle integrator of inputs

that are coming into the cerebellar cortex.

Dendrites of Purkinje cells

are present in the molecular layer

as we said before

The proximal dendrite branches of Purkinje cells

are smooth and they synapse with climbing fibers,

while the distal smaller dendrite branches

have numerous spines on their surface

which synapse with parallel fibers.

Dendrites of Purkinje cell receive massive

inputs from these fibers,

then send information out through axons.

Purkinje cells are the only cells

transmitting output signals from the cerebellar cortex

to its deep nuclei.

The innermost layer of cerebellar cortex

is the granular cell layer.

As we can see here,

there are numerous densely packed

basophilic nuclei in this layer.

These are the soma of granule cells

that account for the majority cells of the cerebellum.

The un-myelinated axon of granular cell

ascends to the molecular layer.

Then it bifurcates into 2 branches

and runs parallel to the surface of cerebellar cortex

as so are known as parallel fibers.

Purkinje cell receives lots of inputs

from the axons of these tiny cells.

In summary,

the cerebellum coordinates our body movements.

The cerebellar cortex receives information

from most parts of the body

and from many other regions of the brain.

It has 3 layers,

the molecular, Purkinje cell,

and the granule cell layers.

Purkinje cells integrates information

and send signal out to the deep cerebellar nuclei,

enabling accurate and well-coordinated movements.

In our case of Mr. Simmons,

the atrophy of his cerebellar cortex

lead to clumsy,

poorly coordinated movements.

Although his muscle tone was normal,

the ataxia caused him the loss of

skillful movements.

Thank you.

See you next time.