Sheet: Histology of CNS Done by: Yousef Qandeel

Histology of the CNS

Lecture Objectives

• Describe the histology of the cerebral cortex layers.

• Describe the histological features of the cerebellum; layers and cells of cerebellar cortex.

• Describe the elements of the blood‐brain barrier and the blood‐CSF barrier.

• Describe the structure of the choroid plexus and the meninges.

The central nervous system

• Major parts – Cerebrum

• Cerebral cortex • Basal ganglia

– Diencephalon • Thalamus • Hypothalamus • Epithalamus

– Brainstem • Medulla • Pons • Midbrain

– Cerebellum – Spinal cord

The central nervous system

• Cerebrum, Cerebellum & Spinal cord

• Almost no connective tissue therefore a relatively soft, gel‐like organs

Cerebral Cortex

• Cerebral cortex is gray matter overlying white matter – 2‐4 mm thick

containing billions of cells

• Has six layers of cells with different forms and sizes

Cerebral Cortex • Neuronal cells in cortex

– Pyramidal cells • Efferent fibers • Small – more superficial • Large – Betz cells (motor cells) And sometimes there is intermediate Sizes vary from 10-120 μ (small – large)

– Stellate (granule) cells • Star shape • Connect to near neurons (within same layer) Mainly exist in the upper half an d most of the afferent fibers connected to it

– Cells of Martinotti • Axons to superficial layers Same as stellate cells but larger and connect to neurons in the superficial layers so it’s axons traverses the layers where analysis happens

– Fusiform cells • Spindle shape • Vertical orientation • In deep layers

– Horizontal cells of Cajal • Spindle shape • Horizontal orientation • In superficial layers • Connect pyramidal cells

Pyramidal cells are the largest cells in the cerebral cortex and it’s axons make the major efferent fibers which will form the association, commissural, and projection fibers depending on the area function. Most of the fibers from the precentral gyrus are projection because it’s the primary motor area ,but in the sensory area most of them are association and commissural

Cerebral Cortex • Layers of cerebral cortex

– Molecular layer • Area of connection between

different cells where analysis and connections happen

– Outer granular layer • Small pyramidal & stellate cells some reflexes and analysis of information

– Pyramidal cell layer • Medium size pyramidal cells &

Martinotti cells association and commissural fibers

تبط Martinotti cellمقل ما حكينا مع الخاليا بترالثانية بالطبقة االوىل و بتنقل المعلومات اىل

pyramidal cells ي الجسم باالخت عشانتوصل لباقر

projection fibersعن طريق – Inner granular layer

• Stellate cells (modulations of other layers)

– Ganglionic layer • Large pyramidal cells projection fibers (so mostly in motor area)

– Multiform cell layer • Mix of different cells highway for axons (efferent & afferent)

Maximum is 6 layers but not everywhere in the brain like in the hippocampus and dentate gyrus there is 3 layers

Granular layer because it has the granular cells (stellate) that receive afferent fibers

granularبكون على حساب ال 6غالبا لما ٌكون عدد الطبقات اقل من layer ً1بصٌر بس 2بدل ما ٌكون ف

Cerebral Cortex

– I – Molecular layer

– II – Outer granular layer

– III – Pyramidal cell layer

– IV – Inner granular layer

– V – Ganglionic layer

– VI – Multiform cell layer

Cerebral Cortex: Pyramidal cells

النها pyramidal cellاكثر اشً سهل نمٌزه هو

االكبر الباقً حسب مكانه او شوي من خصائصه

اكثر من طبقة بخترق axonمثل انه ال

Medial Temporal Lobe Hippocampal Formation

Collateral sulcus

• Parahippocampal gyrus • Perirhinal cortex

• Entorhinal cortex

• Parahippocampal cortex

• Subiculum

Hippocampal sulcus

• Hippocampus (cornu ammonis)

• CA1, CA2, CA3

• Dentate gyrus

بشكل hippocampusمن مكان لمكان و ال بختلفواطبقات و 3

efferent fibers of hippocampal formation عشان هٌك

بتجمع dentate gyrusام ال pyramidal cellsبنشوف فٌه

بدل granule cellsو بكون فٌها afferent fibersفٌها ال

pyramidal cells

Hippocampus • The hippocampal cortex has 3 layers

• Molecular layer at the center

• Consists of interacting axons & dendrites

Represent the superficial layer but it’s central according to the anatomy of the hippocampal formation

• Prominent pyramidal cell layer of large neurons

• Polymorphic layer containing axons, dendrites & interneurons

Considered the most external to the

hippocampus

• The dentate gyrus has 3 layers like hippocampus but the pyramidal cell layer is replaced by granule cell layer

Receive afferent fibers and connected to near

pyramidal layer CA3 then CA3 connects to CA2

and CA1 then CA1 connects to Subiculum

And don’t forget that CA3 forms the efferent fibers as

we said before

Cerebellum

• Content – Cerebellar cortex (folia) & central (cerebellar) nuclei are grey matter

– Arbor vitae = tree of life = white matter

Cerebellum

• Cerebellar cortex

• White mater (medulla)

Cerebellar cortex

• Three layers – Outer molecular layer – Central layer of large Purkinje

cells Very thin layer (only 1 layer of purkinje cells) – Inner granule layer Also here the Purkinje cells forms the efferent fibers like pyramidal cells in the cerebrum and the granule cells receive the afferent fibers

Cerebellar cortex • Has three layers

– Outer molecular layer • Few neurons • Mostly unmyelinated fibers

– Central layer of large Purkinje cells • One layer of large cells

– Inner granule layer • Very small neurons (smallest in the

body) that is compactly disposed – Connect with the afferent fibers

Purkinje Cells

• Purkinje cells has highly developed dendrites – Dendrites occupy most of

the molecular layer – Axons traverse the granular

layer to the central nuclei of the cerebellum

Spinal Cord

• Anterior median fissure

• Posterior median sulcus

• Gray and white commissures

• Central canal

• Anterior, posterior & lateral gray horns – Anterior horns contain motor neurons

– Posterior horns receive sensory fibers from neurons in the spinal ganglia

• Anterior, posterior & lateral white columns

Internal Anatomy of Spinal Cord

Spinal Cord

Remember that white matter decrease in size as we go down the spinal cord because efferent fibers have left the spinal cord and afferent fibers still not received

And for the grey matter it’s larger in cervical and lumbar regions due to the enlargements

Here we have grey matter enlargement and the white matter is big so we are in the cervical region

Here there is no enlargement and white matter is less and we can see lateral horn so it’s the thoracic region

Spinal Cord

Here also we see grey matter enlargement but the white matter is small so it’s lumbar region

Here 1st thing we can see the caudae equinae and grey & white matter are small so it’s most caudal part in sacral region

Gray matter of spinal cord Neurons in grey matter are interneurons / multipolar

Central Canal

Spinal Cord • Gray mater

– Substantia gelatinosa (entire SC)

– Nucleus proprius (entire SC) – Nucleus dorsalis (C8‐L2) – Intermediolateral cell column

(T1‐L2, S2‐S4) – Medial motor nucleus (entire

SC) – Lateral motor nucleus

(enlargements)

• White mater – Fasciculus gracilis (entire SC) – Fasciculus cuneatus (C1‐T6)

خلوها هاي

بنحكًلبعدٌن

عنها

Spinal Cord

Spinal Cord نفس الكالم سابقا

بس انه هون مبٌن

lateral horn

بشكل اوضح

Spinal Cord

Spinal Cord

Meninges

• Meninges

– Dura mater

– Arachnoid mater

– Pia mater

• Spaces

– Subdural space

– Subarachnoid space

Meninges

• Dura mater – Dense fibroelastic tissue

– Lined with a layer of flat cells (squamous cells)

• Arachnoid mater – Fibrous layer

– Lined and covered by flat cells

– Fibrous strands connect it to pia mater

• Pia mater – Delicate layer

– Covered by mesothelial layer

Meninges • Suparachnoid space

– Contains blood vessels

• When the arteries penetrate the brain tissue it takes with it

– Arachnoid mesothelium

– Pia mater

– Perivascular space

» Continuous with subarachnoid space

And it’s covered by subarachnoid space until certain area then disappears and only pia matter continues as tela choroidea

until choroid plexus

Arachnoid matter forms fibers that attach to pia matter because they have the same embryonic origin and at the beginning they are one layer Leptomeninges (arachnoid and pia matter)

Blood Brain Barrier

• protects cells from some toxins and pathogens – proteins & antibiotics can

not pass but alcohol & anesthetics do

• Structure – tight junctions seal

together epithelial cells

– continuous basement membrane

– astrocyte processes covering capillaries

Blood Brain Barrier

• Areas without BBB

– Area postrema in the floor of the fourth ventricle

– Areas in the hypothalamus

• Structure

– Endothelial fenestrations

Blood Cerebrospinal Fluid Barrier

• Structure

– Endothelial cells

– BM of endothelial cells

– Pale cells

– BM of choroidal epithelial cells

– Tight junctions seal the choroidal epithelial cells