Transcript Obecná neuroanatomie

Basic
neuroanatomy
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
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
terminaux
Visual 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)
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
Chemical synapse III
Neuromediators
• Chemical substances at
the connection between
neurons or neuronsmuscles 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
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
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
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
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
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 )
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
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
Dermatome
• 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
Composition of brain tissue
• Grey matter (substantia grisea)
– perikarya of neurons, mostly non myelinated
nerve fibers
– Protoplasmic astrocytes, oligodendrocytes and
microglia
• White matter (substantia alba)
– Mostly myelinated fibers
– Fibrilar astrocytes, oligodendrocytes and
microglia
http://fuckyeahnervoussystem.tumblr.com/post/1276369326/spinal-cord-light-micrograph-of-a-cross-section
http://library.med.utah.edu/WebPath/HISTHTML/NEURANAT/CNS230A.html
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)
Brain stem
Mesencephalon
Pons
Medulla oblongata
Medulla spinalis
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)
http://faculty.irsc.edu/FACULTY/TFischer/AP1/AP%201%20resources.htm
• Inside cavities cerebospinal fluid (liquor
cerebrospinalis = CSF)
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)
Plexus brachialis (C4-T1)
• truncus (trunk)
superior (C4+C5+C6)
medius (C7)
inferior (C8+T1)
fissura scalenorum
• fasciculus (cord)
lateralis
medialis
posterior
axilla - relation to a. axillaris
• pars supraclavicularis
Plexus brachialis - axilla
Plexus brachialis
Nerves and their roots
n. musculocutaneus
n. medianus
n. ulnaris
n. cutaneus antebrachii med.
n. cutaneus brachii med.
n. axillaris
n. radialis
C5-7
C5-T1
C8-T1
C5-6
C5-C8 (T1)