Modul IB

Nerve tissueNerve tissuehistology and histology and embryologyembryology

Martin ŠpačekMartin Špaček(m.(m.spacekspacek@centrum.@centrum.czcz))

• Pictures from:• Junqueira et al.: Basic histology• Rarey, Romrell: Clinical human embryology• Young, Heath: Wheather’s functional histology• http://www.med.unc.edu/embryo_images• http://www.meddean.luc.edu/lumen/meded/Histo/frames/

histo_frames.html

http://www.lf3.cuni.cz/histologie

Development

• Formation of the notochord (notochordal or head process)• inductive influence on the

overlying ectoderm

Development• Nerve tissue develops from

the ectoderm• At the beginning of the 3rd

week the ectoderm overlying the notochord forms the neural plate

Development• Neural plate

• neural groove• neural folds – approach each other in

the midline, where they fuse ⇒

• Neural tube is formed• This process is known as

neurulation

Development• Neural crest

• during neurulation a specialized portion of the neural plate separates from the neural tube

• give rise to heterogeneous array of tissues

Development• Neural crest

• during neurulation a specialized portion of the neural plate separates from the neural tube

• give rise to heterogeneous array of tissues

• spinal and autonomic ganglia • Schwann cells• odontoblasts• chromaffin cells of the adrenal medulla • pigment cells (melanocytes)• meninges• Merkel cells

• spinal and autonomic ganglia • Schwann cells• odontoblasts• chromaffin cells of the adrenal medulla • pigment cells (melanocytes)• meninges• Merkel cells

Development

• Histogenesis of the neural tube

• the wall of the tube consists of the pseudostratified columnar epithelium – neuroepithelium– formed by 3 zones:

• 1) ventricular zone• progenitor cells

• 2) intermediate zone• neurons migrate toward →

• 3) cortical plate• the future gray matter

lumen

Development

• Histological differentiation

1. nerve cells (neurons)2. glia cells

„connective tissue of the CNS“

3. neural crest cells

Types of neurons

• According to the number ofprocesses:

• Multipolar• the most abundant• pyramidal cells, Purkinje cells

• Bipolar• visual, auditory system

• Pseudounipolar• sensory ganglia

Types of neurons

Types of neurons

• Based on the length of the axon:

• Golgi type I• the axon extends beyond the

dendritic tree• pyramidal cells, Purkynje cells

• Golgi type II• axon terminates in the

immediate area of the cell body• stellate cells

Components of a neuron

Perikaryon (soma)• nucleus

• large, spherical, euchromatic• prominent nucleolus• ↑ synthetic activity

• endoplasmic ret.• Nissl bodies in light microscope• highly developed

• Golgi complex• only in the perikaryon• transfer and secretory vesicles

• mitochondria• abundant in the axon terminals

• cytoskeleton• neurofilaments, microtubules

• inclusions• lipofuscin, melanin

Dendrites• Are the „receiving“ surface

of the neuron• Neurons have numerous

dendrites • Composition of the

cytoplasm is similar to that of the perikaryon

Axons

• Most neurons have only one axon

• Originate from axon hillock • Dependent on the

perikaryon for its maintenance – axonal transport

Axonal Transport

• Microtubules form tracks within the axon to carry organelles and vesicles

Motor Proteins Transport Cargo

• Proteins related to axon flow include• dynein & kinesin• they both have two ATP-

biding heads & a tail

Synapses• Enlarged endings of

terminal branches • Axodendritic• Axosomatic• Axoaxonic

Synapses

• Presynaptic ending• contains synaptic vesicles with

neurotransmitters (chemicals that cross the synapse between two neurons)

• Synaptic cleft• a region of extracellular space

(20-30 nm)• Postsynaptic ending

• contains receptor sites for neurotransmitters

Synaptic transmission

N1 – cerebrum (HE)

N2 – cerebrum (Nissl)

Cerebellum• Cerebellar layers:• Molecular layer

• mostly neuronal fibers• Purkynje layer

• large multipolar neurons• Granule cell layer

• small integrator neurons

N4 – cerebellum (HE)

N4 – cerebellum (HE)

Neuroglia• 10 glial cells for each neuron• About half of the volume of

nerve tissue• Function: provide neurons

with structural support and maintain local conditions for neuronal function

• Staining: silver or gold impregnation, histochemicaltechnique

• 4 morphologic types

I. astrocytes

• The largest • Vascular feet – surround and

ensheathe all vessels• Structural support for nerve

tissue• Form glial scar

I. astrocytes

• A. protoplasmic • granular cytoplasm• envelop the surface of nerve

cells and blood vessels• B. fibrous

• long processes• predominantly in white matter

I. astrocytes

N8 – cerebrum(astrocytes), Antibody

Anti-S-100 protein, ABC

II. oligodendrocytes

• Smaller, ↓processes• Processes envelop axons

and form myelin sheath• Are found in both gray and

white matter• The formation of the myelin

sheath is similar to that of Schwann cells in peripheral nerves

II. oligodendrocytes

III. microglia

• Phagocytic cells• Derived from mesoderm• Small cell bodies• Their nuclei have elongated

shape • other neuroglia have spherical

• Short processes with small expansions – thorny appearance

III. microglia

IV. ependymal cells

• Epithelial arrangement• Line the cavities of the

brain and spinal cord• Motile cilia (movement of the

cerebrospinal fluid)

N5 – spinal cord (HE)

• Central canal of spinal cord lined with ependymal cells

Nerve fibres

• Consist of axons enveloped by special sheaths of ectodermal origin

• Groups of nerve fibresconstitute:• the tracts of the brain

(oligodendrocytes) • peripheral nerves (Schwann

cells)• Fibres:

• unmyelinated• myelinated

Unmyelinated fibres• CNS – axons run free

among the other neuronal and glial processes

• PNS – axons are enveloped within simple clefts of Schwann cells

Unmyelinated fibres

Myelinated fibres• myelin formation:

• in the PNS a single axon is embedded in a Schwann cell

• the plasma membrane of a Schwann cell wraps in a spiral around the axon

Myelinated fibres

• S – Schwann cell nucleolus• A – axonal cytoplasm• M – myelin sheath

13 – Myelinated axon

Myelinated fibres

Myelinated fibres• nodes of Ranvier – gaps

between Schwann cells

N3 – cerebrum (Myelin)

Peripheral nervous system

• nerves• nerve fibres grouped in bundles• connective tissue coverings:

• endoneurium• perineurium• epineurium

Nerves

Nerves

Nerves

N7 – peripheral nerve (HE)

N7 – peripheral nerve (HE)

Peripheral nervoussystem

• Ganglia• aggregations of nerve cell

bodies outside the CNS• a connective tissue capsule• each neuronal cell body is

surrounded by Schwann cell-like satellite cell

• Two main classes• craniospinal (sensory)• autonomic (motor)

N6 – autonomic ganglia (HE)

Meninges

Meninges• Dura mater

• external meninx• dense connective tissue• subdural space

• Arachnoid• connective tissue devoid of

blood vessels• a layer in contact with dura

mater• system of trabeculae –

cavities form subarachnoidspace (filled with CSF)

• Pia mater• loose connective tissue

containing many blood vessels

Meninges