Histology                                                                                                                     Stanley Shostak
BioSc 1450                                                                                                                  Spring 03

Lecture 20: Central Nervous System (CNS)

Definitions

commissure: coming together
folia: leaves
falx: sickle; falx cerebri: vertical extensions of dura mater
fasciculi: bundles (nerve bundles = tracts through brain)
funiculi: cords (lg. fiber columns through spinal cord)
gyri: circles; convolutions of brain (cerebellum, cerebral hemispheres)
sulci: furrows
vermis: worm
Anatomical division of Central nervous system (CNS):

CNS: brain and spinal cord

Devoid of collagen except in vicinity of blood vessels and meninges; contains no lymphocytes
blood-brain barrier: CNS capillaries impermeable to certain plasma constituents especially larger molecules; absent in choroid plexus, pituitary and pineal glands and vomiting center of hypothalamus capillary endothelium: junctions btwn endothelial cells are sealed; little or no pinocytosis in endothelium; luminal surface membranes contain enzymes which destroy neurotoxic metabolites (neuroactive humoral substances)
astrocyte foot processes: maintain barrier


Gray (grey) matter: almost all neuron cell bodies and axons

neuropil: feltwork of axons and dendrites surrounding neurons and neuroglia; esosinophilic; largely devoid of myelin
non-myelinated nerve fibers: when neurolemmocyte only investment: small diameter axons (autonomic nervous system and small pain fibres)
neuroglia: all neuroepithelial-derived non-neural cells of CNS
astrocytes: star-shaped with heavy metal impregnation; most numerous glial cells in gray matter; highly branched packing cells; form mass surrounding nerve cells processes and oligodendrocytes; rounded, nuclei closely enmeshed in neuropil; mediate metabolic exchange btwn neurons and blood; regulate composition of intercellular environment in CNS Glial fibrillary acidic protein (GFAP): unique intermediate filament; demonstrated by immunoperoxidase method
fibrous astrocytes: astrocytes of white matter with relatively straight cytoplasmic processes
protoplasmic astrocytes: astrocytes of gray matter with numerous short highly branched cytoplasmic processes
glial limitans: relatively impermeable; foot processes invest basement membrane CNS and innermost layer of meninges (pia mater)
perivascular feet: terminate upon basement membranes of capillaries; cover most of surface of capillary
oligodendrocytes invest axons in myelin; form multiple myelin internodes; contribute to ensheathment of as many as 50 individual axons; small rounded condensed uclei; cytoplasm unstained by H&E; tend to be aggregated around neuron cell bodies; most numerous glial cell in white matter; analogous to satellite cells in ganglia; analogous to neurolemmocytes in nerves light oligodendrocytes: capable of cell division; highly active in myelin sheath formation (predominant in fetus and neonate)
dark oligodendrocytes: main form in mature CNS
medium oligodendrocytes: immature form involved in myelination and maturation; capacity for remyelination after demyelinating disease such as multiple sclerosis
microglia (misnoma): monocyte-macrophage cells; invade CNS during fetal period; small irregular nuclei; relatively little cytoplasm forms fine, highly-branched processes; transform into large amoeboid phagocytic cells
White matter (myelin): tracts of nerve fibers; substantial numbers myelinated myelinated nerve fibers: increased velocity of action potential; ÎMyelin sheath formation begins in the CNS of the human embryo at about 4 months gestational age with the formation of most sheaths at least commenced by about the age of one year. From this time, successive layers continue to be laid down with final myelin sheath thickness being achieved by the time of physical maturity.â ependymal cells: cuboidal or low columnar; luminal junctional complexes; no basement membrane; bases taper and break up into fine branches that ramify into underlying layer with astrocytes; luminal: variable number of cilia; microvilli also present; lining epithelium of ventricles and spinal canal   Choroid plexus: arises from wall of four ventricles of brain; produces cerebrospinal fluid (CSF); consists of mass of capillaries projecting into ventricle; invested by modified ependymal cells separated from underlying capillaries and suporting tissue by basement membrane; long bulbous microvilli project from luminal surface ; continuous tight junctions (zonula occludens) form blood-CSF barrier

Meninges

dura mater: thick; fibrous

arachnoid: nonvascular; spaces filled with cerebrospinal fluid (CSF)

pia mater: invests CNS
Parts of Brain

Medulla oblongata
brain stem; divided upper (open) and lower (closed) parts
upper medullary level: 4th ventricle closes to become narrow, central canal;

[Note: olivary complex on ventral-lateral {not upper half} aspect of medulla oblongata] inferior olivary nucleus: convoluted apearance in transverse section; adjacent to dorsal and medial accessory olivary nuclei completing the inferior olivary complex (neurons relay central and spinal afferent stimuli to cerebellar cortex).

gracile & cuneate fasciculi and nuclei (fibers pass upwards to thalamus via medial lemniscus; cell bodies of second order neurons)

medial lemniscus: medial to inferior olivary complex; conveys fibers to thalamus

pyramids: on each side of medulla; axons from motor cortex break up into small bundles in pons and converge; 85% fibers cross in decussation (to make in the form of an X; Roman ten) of the pyramids

spinal nucleus of trigeminal tract: dorsolateral throughout medulla; white matter superficial

hypoglossal nucleus:

tracts and nuclei of eigth to twelfth cranial nerves 

Pons: middle portion brain stem; btwn midbrain and medulla; two parts in transverse section [basal pons & tegmental region]

basal pons (criss-crossed bundles of longitudinal and transverse fibers btwn neuron cell bodies = pontine nuclei)
middle peduncles: of fibers from pontine nuclei that have passed in transverse bundles across mid-line to enter cerebellum

tegmental region: (covering)

ascending spinothalamic (sensory) tracts and nuclei of 5th, 6th & 7th cranial nerves

medial lemniscus (ribbon): upward continuation of proprioceptive, vibration and fine touch pathways from gracile and cuneate nuclei of medulla

cerebellar peduncles: middle peduncle in mid pontine level; superior peduncles priminent; made up of fibers from central nuclei of cerebellum passing upward to thalamus and projecting to the motor cortex

inferior cerebellar peduncle linking afferent & efferent fibers to medulla
middle cerebellar peduncle linking afferent & efferent fibers to pons
superior cerebellar peduncle linking afferent & efferent fibers to midbrain

Cerebellum: cortex of gray matter with central core of white matter containing four pairs of nuclei; cortex in series deep convoluted folds = folia; supported by branching medulla of white matter = arbor vitae Cortex: three layers (= gray); white matter = medulla
molecular layer contains few neurons and lg number unmyelinated fibers; stellate cells and basket cells

piriform (pear shaped) cells = Purkinge cells; fine axon extends downward throug granular cell layer; extensively branching dendritic system arborizes into outer molecular layer (demonstrated with heavy metal methods)

granular cell layer extremely cellular; non-myelinated axons pass outward to molecular layer; bifurcate to run parallel to surface; synapse with dendrites of piriform cells; plus  great stellate neurons = Golgi cell type II in superficial part granular cell layer (more like deep part molecular layer)

 Substantia nigra: lg mass gray matter extending throuout midbrain; divides cerebral peduncles into dorsal and ventral parts; easily recognized by black pigment (melanin in cytoplasm); extensive cnnections with cortex, spinal cord, corpus striatum and reticular formation; functions in fine control of motor function; multipolar neurons; contain dopamine (DOPA: dihydroxyphenylalanine; precursor of dopamine and melanin) neurotransmitter causing inhibitory effects on neurons of corpus striatum; L-dopa, a dopamine precursor crosses blood-brain barrier.

Thalamus: thalami (pl): lg masses gray matter on each side of third ventricle; diencephalon; core of cerebrum; subdivided into lg number nuclei including reticular and motor as well as specific sensory nuclei;

Cerebral cortex: convoluted cortex of gray matter overlying central medullary mass of white matter conveying fibers btwn pts of cortex and pts of CNS; five different morphological types of neurons arranged in layers (I toVI or VII); neocortex consisting of six layers of neurons followed by white matter (VII), including sensory and motor areas of cortex & association cortex; 3 layers in olfactory cortex and cortical pt limbic system in temporal lobe.
neurone types in cerebral cortex: (plus neuroglial cells: astrocytes, olidgodendroglia and microglia)

pryamidal cells: apex toward surface; slender axon from base passes into underlying whte matter (or deep layers of cortex); thick, branching apical dendrite passes toward surface; short dendrites from edges of base ramify laterally; smaller cells found more superficially; Betz cells: huge upper motor neurons of motor cortex; largest pyramidal cells

stellate (or granule) cells: small neurons with short verticl axon and several short branching dendrites; basket & neurogliaform subtypes

small neurons = cells of Martinotti: axons directed upward; bifurcate to run horizontally, usually in most superficiallayer; few short dendrites

fusiform cells: long axis perpendicular to surface; lateral axon passes superficially; dendrites from each end, branching into deeper and more superficial layers

horizontal cells (of Cajal): small and spindle-shaped; oriented parallel to surface; least common cell types; found in most superficial layer; axons pass laterally to synapse with denderites of pyramidal cells

 layers of neocortex: Note: stellate = granular; I: plexiform (molecular): dendrites and axons of cortical neurons making synapses; neuroglia and rare horizontal cells

II: outer granular: dense population small pyramidal cells and stellate cells [small neurons]; various axons and dendritec connections

III: (outer) pyramidal cell: moderate size; increasing size deeper

IV: inner granular: densely packed stellate cells

V: ganglionic or inner pyramidal: lg pyramidal cells (including Betz cells) and smaller numbers of stellate cells and small neurons

VI: multiform (fusiform) cell: numerous small neurons, small pyramidal cells, stellate cells, especially superficially and fusiform cells in deeper part.

 Nomenclature (Latinates) for the Central Nervous System approved by Nomina Histologica
Pars centralis (Central nervous system)

Encephalon

Cortex cerebralis

stratum moleuclare (plexiforme)

neuron horizontal

stratum granulare externum

neuron pyramidale parvum

stratum neurium pyramidalium externum

neuron pyramidale magnum

stratum granulare interium

neuron stellatum parvum

neuron pyramidale medium

neuron pyramidale magnum

stratum neurium fusiformium

neuron fusiforme parvum

neuron fusiforme medium

Cerebellum

Corpus medullare

Lamina alba

Cortex cerebellaris

Stratum moleculare (plexiforme)

neuron stellatum

neuron corbifer (basket)

Stratum neurium piriformium

corbis neurofibrarum

neuron piriforme (purkingiense)

Stratum granulosum

neuron stellatum magnum = Golgi cell

neuron granuliforme

glomerulus

Neurofibria muscoidea

Neurofibria ascendens

Neurofibria parallela

Medulla spinalis

Canalis centralis

Ependymocytus

Substantia alba

Astrocytus fibrosus

Oligodendrocytus

Neurofibria myelinata

Funiculus dorsalis

Funiculus lateralis

Funiculus ventralis

substantia grisea

Neuron, neuria

neurofibria nonmyelinata

astrocytus protoplasmaticus

neuropilus

Columna prisea

columna dorsalis (cornu dorsale)

columna lateralis (cornu laterale)

columna ventralis (cornu ventrale)

Neuria motoria

neuron somaticum

neuron autonomicum

neuron fusi neuromuscularis

Neuria internuncialia

neuron commissurale

neuron noncommissurale

Formatio reticulare

Neurolgia (of CNS)

Gliocytus

corpus gliocytum

processus gliocyticus

gliofil amentum

Gliocytus centralis

ependymocytus

" columnaris

" ciliatus

" choroideus

" taeniatus

Astrocytus

astorcytus protoplasmicus (or mossy)

" fibrosus (spiderlike)

processus vascularis

" pialis

membrana limitans glialis superficialus

" " " perivascularis

" " " periventricularis

Oligodentrocytus

processus myelinopoieticus

Microglia
 

last revised: 04-04-03