basic neuroanatomy - univerzita...

Basic

neuroanatomy

© David Kachlík 30.9.2015

Characteristic of nervous tissue

• Nervous tissue is specialized for intake, workabout

and transfer of infos and that way coordinates most of the functions in the body

• cells:

– proper excitability neurons

– Support cells (astrocytes, oligodendrocytes, microglia and

ependymal cells)

• Anatomically we divide nervous system into central

(CNS – brain and medulla spinalis) and peripheral (PNS – nerves and ganglias)

• In the CNS we distinguish gray and white matter

• White matter visage is due to myelin – lipoprotein complex covering individual axons


Classification of nervous tissue cells

• Nervous tissue contains two types of cells:

– neurons – major cells carrying informations

– Glial cells (neuroglia, glia) (neuroglia) – provide

support for neurons, protect them and

participate in nutrition and function

• astrocytes (astrocytus)

• oligodendrocytes (oligodendrocytus)

• mikroglia (microgliocytus)

• Ependymal cells (ependymocytus)


Neurons I

• Are principal units of nervous tissue

• Responsible for intake, workabout and transfer of signal

• Composed of cell body (soma, perikaryon), dendrites(dendritum) and axon (axon)

• Size of neurons vary in interval 5 µm (granular cells of cerebellum) to 150 µm (Purkynje cells of cerebellum)

• After delivery no mitoses (not valid for hippocampal cells and bulbus olfactorius)

• Wallerian neurodegeneration and neuroregeneration rules(axon and dendrite regenerate regularly, neuronal body only in several localities – dentate gyrus of hippocampus)


Neurons II


Neurons classification I• According to shape we divide neurons into:

– multipolar (neuron multipolare)• More then 2 outlets (axon + dendrites)

• Vast majority of neurons

– bipolar (neuron bipolare)• Only 2 extensions (axon + dendrite)

• retina, olfactory epithelium, ganglion n. vestibulocochlearis (VIII) etc.

– pseudounipolar (neuron pseudounipolare)• Only 1 extension, subs. Splitting into dendrite and axon „T“

shaped

• Sensory ganglia of spinal and cranial nerves

– unipolar (neuron unipolare)• only 1 extension

• Amacrine and horizontal cells of retina© David Kachlík 30.9.2015

Neurons classification II


Neurons classification III

• From functional point we divide them into:

– motor neurons (neuron motorium)

• Controll effector organs (skeletal and smooth

muscles; endocrine and exocrine glands)

– sensory neurons (neuron sensorium)

• Maintain infos intake from body and environment

– interneurons (interneuron, neuron internuntiale)

• Create complicated net between sensory and morot neurons


Perikaryon (soma) I

• Nucleus is big, ovoid and euchromatic with prominent nucleolus – great transcriptory activity

• GER is rich and on surface it has numerous

polyribosomes – together it forms so called Nissl substance

• GA is located only in perikaryon and it gives rise to

transport and secretory vesicules

• mitochondrias are concentrated mostly in axonal hillocks

and in pericaryon


Perikaryon (soma) II

• From cytoskeletal structures are important:

– microtubules – maintain axonal transport (Hemeroff

theory of quantuum states mediating quantuum information share in the matter)

– neurofilaments – 10 nm thick intermediary filaments

specific for nervous tissue – stained by silver or gold.

• In the cytoplasm we may find also lipofuscin inclusions

(„pigment from wearing out“) or melanin


Perikaryon (soma) III


Dendrites

• Are short extensions amplifying neuron surface enabling 1 neuron to receive infos from many neurons

• In contrast to axon their width decreases with branching

• At the synapsis there are dendritic spikes (its decrease is effect of chronic stress –Sapolsky et al.)

• Cytoplasm of dendrites is almost equivalent to perikaryon, but no GA


Dendritic

spikes


Dendritic spikes


Axon I

• Provides signal transduction from perikaryon and

its further elaboration to other neuron or effector cell

• neuron contains mostly 1 axon

• At the origin is axonal hillock with no ribosomes or GER from perikaryon

• In myelinized axons is between axonal hillock

and origin of myelin sheet inicial segment (dense layer under axolemma in EM) – here originates

action potencial


Hillock and initial segment


Axon II

• axon is not branching for most of its course with

exception of collateral branches returning into perikaryon

• Branching happens at the terminal part of axon and each branch has synaptic ending – so called

bouton terminaux

• synaptic endings may be present during axonal

course as boutons en passage


Bouton

terminauxVisual cortex, Macaque, Nature

2006


Axonal transport I• Due to missing GER is axon dependent of protein

supply from perikaryon

• Nutrition maintains axonal transport

• Function of axonal transport is granted by specific

microtubular organization – these function oas „railroad “

• „machine“ of carried particles (secretory vesicles

with neuromediators, mitochondrias etc.) is

molecular engine dynein and kinesin

• There is axonal transport anterograde (from

perikaryon) and retrograde (to perikaryon)© David Kachlík 30.9.2015

Axonal transport II

http://www.bio.unipd.it/~bubacco/html/body_lrrk2.html


Synapse I

• synapse (synapsis) is specialized structure for

excitation transfer from on neuron to the other on (or on effector cell)

• According to transfer variant we divide synapses into:

– chemical (synapsis chemica): happens molecular

secretion diffusing to target cell

– electrical (synapsis electrica): cells are directly

connected by nexus – depolarization

propagates directly to target cell - rare


Synapse II

• According to location are synapses:

– axodendritic (synapsis axodendritica) – most

common

– axosomatic (synapsis axosomatica)

– axoaxonal – for example in presynaptic

inhibition when carrying painful stimuli

– dendritodendritic (synapsis dendritodendritica) –rare


Synapse III


Chemical synapse I

• Three major subparts:

– presynaptic membrane (membrana presynaptica) –cytoplasmatic membrane of axonal terminal –

cytoplasm rich in secretory (synaptic) vesicules with neurotransmitter

– synaptic cleft (fissura synaptica) – 20-30 nm wide (wider

then between neuron and glia)

– postsynaptic membrane (membrana postsynaptica) –cytoplasmatic membrane of target cell containing

receptores for neurotransmitter


Chemical synapse II

• synaptic transfer has several phases:

– Action potential after „arriving“ into synpase opens voltage

gated Ca2+ channels – influx of Ca2+ into axonal teminal

– Increased concentration of Ca2+ starts exocytosis of

synaptic vesicles

– Ca2+ is fast inactivated – pumped into ECT

– Mediators from synaptic vesicles diffuse to target cell and

react with its receptors

– By reaction with receptors is indirectly changed

permeability of post synaptic membrane for Na+, K+, Cl- or

other ions – creation of excitatory post synaptic potential

(EPSP) or inhibitory post synaptic potential (IPSP)

• Synaptic delay is 0,3-0,5 s© David Kachlík 30.9.2015

Chemical synapse III


Neuromediators• Chemical substances at

the connection between neurons or neurons-muscles or other cells

• acetylcholin

• monoamines(noradrenalin, dopamin)

• serotonin

• GABA

• glycin

• Motor plate – presynaptic membrane of axon, synaptic cleft, postsynaptic membrane of muscle

• substance P, neuropeptid Y© David Kachlík 30.9.2015

Glial cells (neuroglia)

• More numerous then neurons 10-50x, but due to

smaller size form approx. 50 % of the CNS

• „cooperate“ with neurons – offer support,

nutrition, form myelin sheath of axons, phagocyte etc.

• Staining by silver or gold impregnation and histochemical methods

• Morphologically 4 types – astrocytes, oligodendrocytes, microglia and ependymal cells

• After delivery may do mitosis


Astrocytes I

• Bigest neuroglial cells

• Emanates numerous extensions (so colled vascular pedicles) covering blood vessels

– Participate in hematoencephalic barrier

• Contain numerous 10 nm thick intermediary

filaments formed by glial fibrilal acidic protein

(GFAP)

• Offer neurons mechanical protection and help with metabolism

• In case of injury astrocytes proliferate and form glial scar


Blood-brain barrier

(hematoencephalic barrier)


Astrocytes II

• Morphologically we recognize 2 types:

– protoplasmic astrocytes

• Numerous granulas in cytoplasm

• Extensions are shorter and richly branching

• Occur mostly in grey matter

– Fibrilary astrocytes

• Longer externsions w/o branching

• Occur mostly in white matter


Astrocytes III


Astrocytes IV


Oligodendrocytes I

• Smaller compared to astrocytes and have less intermediary filaments

• Form myelin sheath in the CNS

– Perform same function as Schwann cells in PNS

• Oligodendrocytes contain more axons at

once (in contrast to Schwann cells)

• Their number phylogenetically increases


Oligodendrocytes II


Microglia I• Smallest neuroglia

• Part of monocyto-macrophage system

– Mesodermic origin

• Movable and phagocytic

• Nuclei elongated

– As opposed to other glial cells that have round nuclei

• have „spiky“ shape

– During activation acquire shape of macrophages


Microglia II


Microglia III


Ependymal cells I (ependymocyti)

• Originate from inner (germinal) zone of neuroepithelium

• Maintain epiteloid arrangement

• ependyme covers CNS cavities – brain ventricles, Sylvius

aqueduct, central canal of medulla spinalis

• Cells have nexus and zonulae occludentes

• Cillia at the apical pole facilitate flow of CSF

• tanycytes

– Special group o ependymal cells at the bottom of the 3rd

ventricle

– Have long extensions into nervous tissue

– May play role in chemical singal transduction from CSF


Ependymal cells II


Nerve fibers (neurofibra)

• Axons or dendrites covered by special sheaths of ectodermal origin

• Nerve fiber bundles form:

– In CNS tracts (cover is formed by

oligodendrocytes)

– In PNS nerves (cover formed by Schwann

cells)

• We recognize fibers:

– Non-myelinated

– myelinated © David Kachlík 30.9.2015

Non myelinated nerve fibers I

• In the CNS located freely between neurons and glial cells

• In the PNS „invaginates“ into simple rifts in

Schwann cells

• Schwann cells (Schwannocytus) located

along nerve fiber mutually interconnected

– missing Ranvier fissures


Non myelinated nerve fibers II


Myelinated nerve fibers I

• Myelination occurs in several steps:

– Invagination of axon into sulcus of sheat cell

(oligodendrocyte or Schwann cell) originate so

called mesaxon (mesaxon)

– mesaxon „rotates“ around axon by 150x

– By modification of cytoplasmic membrane of

covering cell originate lipoprotein complex

myelin


Myelinated nerve fibers II


Myelinated nerve fibers III

• Between individual Schwann cells is myelin sheath interrupted by Ranvier fissure (nodi interruptionis myelini)

• Interval between Ranvier fissures is named internodium and has length 1-2 mm

• In the CNS are Ranvier fissures not readily visible

• Schmidt-Lanterman incisure (incisurae myelini)

– cytoplasm of Schwann cell „imprisoned“ during

myelination inside myelin sheath

– Form lighter stripes in myelin sheath

http://en.wikipedia.org/wiki/Myelin_sheath_gap


Myelinated nerve fibers IV


Myelin sheath – electrone microscope


Schmidt – Lanterman incisures

J Neurosci 2013 © David Kachlík 30.9.2015

Nerves I• Formed by bundles of nerve fibers

• Nerve fibers have coverings similar to muscle

fibers:

– endoneurium

• Layer of reticular fibers around individual nerve fibers

– perineurium

• „sleeve“ covering bundles of nerve fibers formed by

layers of epitheloid cells

• Numerous zonulae occludentes – non passable barrier

protecting nerve fibers

– epineurium

• Tissue cover of whole nerve© David Kachlík 30.9.2015

Nerves II


Ganglia I• Nerve ganglia is accumulation of perikarya in

the PNS

• Have ovoid shape and their surface is covered by pouch from thick non arranged tissue

• Typical are so called satellite cells (gliocyti ganglionici) – snall cuboideal cells surrounding

neuronal perikarya

http://en.wikipedia.org/wiki/Dorsal_root_ganglion http://www.pharmainfo.net/introduction-autonomic-nervous-system/classification


Ganglia II

• spinal ganglia

– sensory (ganglion sensorium)

– In posterior radices of spinal nerves and in the course of

cranial nerves (V, IX, X)

– Contain typical pseudounipolar neurons

– Bring in sensory inputs from periphery to CNS

• autonomous (vegetative) ganglia (ganglion autonomicum)

– In the course of autonomic nerves

– Contain multipolar neurons

– Layer of satellite cells is not complete

– intramural ganglia

• parasympatic ganglia in the wall of the hollow organs© David Kachlík 30.9.2015

Ganglia III


Development of neural tube I

Nervous tissue originates from

neuroectoderm

• NE originates from ectoderm by induction of notochored

neural plate durgin neurulation process

creates neural tub = foundation of CNS

• Remnant of neuroectoderm separates

neural crest (crista neuralis) = foundation of

PNS and other structures (ectomesenchyme of the head ) © David Kachlík 30.9.2015

Development of neural tube II

• Primary neurulation

– Separates ectoderm into three cell types

(inside positioned nerve tube, epidermis externally and cells of the neural crest)

• Secondary neurulation

– Cells of the nerve plate form chorda dorsalis

• In the time of 35th somite formation


Development of neural tube III

Epitelium of nerve tube soon changes into multilayer neuroepithelium where are 3 layers:

• inner (germinal) zone (zona ventricularis; matrix germinalis)– Up to half of gravidity richly proliferates (origin of

neuroblasts)– Then reduced into ependyme

• Middle (shell) zone (zona intermedia; zona pallii)– Formed primarilly by migrating neuroblasts

– Gives rise to grey matter

• outer (marginal) zone (zona marginalis)– Formed by extensions of neuroblasts

– Gives rise to white matter


Development of neural tube IV


Somite (somitus)

• somitomeres around 3rd week

• At the end of 5th week 42-44 somites

http://www.aps.uoguelph.ca/~swatland/HTML10234/LEC5/LEC5.html

http://www.uprightape.net/Image_Pages/UA_Fig7-4_SomiteDevel.html


Myotome

• Central part of initial

segment

• During differentiation

from 4th week it retain

longest epitheloid organization

• Gives rise to skeletal muscle


Sclerotome

• Dorsomedial part of initial segment

• During differentiation from 4th week transforms into mesenchyme

• Thickens around chorda dorsalis

• Gives rise to axial skeleton (vertebras, costas, sternum) and basis of the skull


• Ventrolateral part of initial segment

• During differentiation from 4th week transforms into mesenchyme

• Migrates into somatopleura

• Gives rise to connective tissue basis of skin (dermis and tela subcutanea)

• Parts arising from the same dermatome have same innervation via spinal root

Dermatome


Composition of brain tissue

• Grey matter (substantia grisea)– perikarya of neurons, mostly non myelinated

nerve fibers

– Protoplasmic astrocytes, oligodendrocytes andmicroglia

• White matter (substantia alba)– Mostly myelinated fibers

– Fibrilar astrocytes, oligodendrocytes and microglia

http://library.med.utah.edu/WebPath/HISTHTML/NEURANAT/CNS230A.htmlhttp://fuckyeahnervoussystem.tumblr.com/post/1276369326/spinal-cord-light-micrograph-of-a-cross-section


CNS description - parts

• Spinal cord (Medulla spinalis)• Brain stem (Truncus encephali)

– Oblongate (Medulla oblongata)– Pons (Pons) – formerly pons Varoli– Midbrain (Mesencephalon)– Hindbrain (Rhombencephalon)

• Cerebellum (Cerebellum)• Diencephalon (Diencephalon)• Terminal brain (Telencephalon)

– Bazal ganglia (nuclei basales)– Brain cortex (cortex cerebri)– Forebrain (ventral brain)


Mesencephalon

Pons

Medulla oblongata

Medulla spinalis

Brain stem


CNS description

• Inside CNS cavities

– 4th ventricle, 3rd ventricle and two lateral ventricles

• CNS covered by meninx:– Hard meninx (pachymeninx

= dura mater)

– Soft meninx (leptomeninx)

• arachnoidea (arachnoidea mater)

• pia (pia mater)

• Inside cavities cerebospinal fluid (liquor cerebrospinalis = CSF)

http://faculty.irsc.edu/FACULTY/TFischer/AP1/AP%201%20resources.htm

http://mortdev.blogspot.cz/2008/09/brain-autopsy.html


Brain stem

• Transfer of all ascending and descending nerve pathways(tractus)

• Reticular formation (RF; formatio reticularis)– Vitaly important reflexory centers

• Cardiac activity, respiration, vasomotorics, consciousness

• Nuclei of cranial nerves– n. III - XII


CNS function

• Spine – reflexes, ascending and descending tracts

• Brain stem – vitally importatn reflexes (respiratory,

cardiovascular, vomitus, eye ball synchro)

• Midbrain – hormonal production, circadian rhythm,

termoregulation, food intake, autonomic regulation

• Terminal brain

– Brain cortex: functional cortical areas

– Basal ganglias: motion patterns

• limbic system – behavior, emotions, memory


Peripheral nervous system

(Systema nervosum periphericum)

• spinal nerves (nervi spinales) – 31 pairs

• cranial nerves (nervi craniales) – 12 pairs

• autonomic nerves (systema autonomicum)

– sympathetic (pars sympathica)

– parasympathetic (pars parasympathica)

– enteric system


Macroscopy of spinal nerve branching


Pyramidal tract

(Tractus pyramidalis)

• 2-neuron pathway

• cerebral cortex → skeletal muscle

• 1st neuron = pyramidal cell of cortex

• 2nd neuron = alfa-motoneuron of anterior horn of spinal cord

• decussated (C1 level)

• disorder: central contralateral palsy


Rami anteriores

nervorum spinalium

• plexus cervicalis (C1-4)

• plexus brachialis (C4-T1)

• nn. intercostales (T1-T12)

• plexus lumbalis (T12-L4)

• plexus sacralis (L4-S4)

• plexus coccygeus (S5-Co) © David Kachlík 30.9.2015

Plexus brachialis (C4-T1)

• truncus (trunk)superior (C4+C5+C6)medius (C7)inferior (C8+T1)

fissura scalenorum• fasciculus (cord)

lateralis medialisposterior

axilla - relation to a. axillaris• pars supraclavicularis• pars infraclavicularis


Plexus brachialis - axilla


Plexus brachialis

Nerves and their roots

n. musculocutaneus C5-7

n. medianus C5-T1

n. ulnaris

n. cutaneus antebrachii med.

n. cutaneus brachii med.

C8-T1

n. axillaris C5-6

n. radialis C5-C8 (T1)


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