Download Nerve Tissue

Nerve tissue
1. Nerve tissue – characteristics,
histogenesis and classification
2. Neurons – classes and structure:
cell body (perikaryon)
neuronal processes
3. Nerve fibers – types
4. Synapses
5. Neurotransmitters and receptors
6. Neuroglial cells
7. Nerve endings:
sensory (afferent) receptors
effector (efferent) endings
Nerve tissue
Textus nervosus:
cells – nerve and glial cells
extracellular matrix
main functions:
sensing stimuli and
creating, analyzing and
integrating information
regulates and controls
body functions
provides the unity
with the environment
properties:
irritability
capacity to respond to a stimulus –
generation of a nerve impulse
conductivity
capacity to transfer the response
throughout the neuron by the
plasma membrane
Prof. Dr. Nikolai Lazarov
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Classification of nervous system
Prof. Dr. Nikolai Lazarov
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Neurulation
embryonic origin:
neuroectoderm
formation of neural tube (neurulation)
neurulation
begin of the process – E17
neural (primary embryonic) induction –
signaling molecules (growth factors) from
the underlying notochord:
neural plate
neural groove
neural fold
neural tube CNS
neural crest ganglion ridge PNS
transverse segmentation of neural tube:
cranial neuropore – Е25
caudal neuropore – Е27
Prof. Dr. Nikolai Lazarov
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Histogenesis
undifferentiated neuroepithelial cells
(stem cells) – pluripotential:
unipotent progenitor cells:
neuroblasts (immature neurons)
unipolar, bipolar and multipolar
glioblasts (glial precursor cells)
oligodendrocytes
protoplasmic astrocytes
fibrillar astrocytes
ependymal cells
microglia mesenchymal origin?
histogenesis – zones:
ependymal layer
mantle layer
marginal layer
Prof. Dr. Nikolai Lazarov
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Nerve cells
neuron – more than 10 billion in the human NS
cell body (perikaryon)
(perikaryon
axon – Golgi type І and ІІ neurons
dendrites
Prof. Dr. Nikolai Lazarov
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Cell body
perikaryon (Gr. peri,
peri around + karyon, nucleus)
a trophic and receptive center of the neuron
diameter – 20-40 µm (4-120 µm)
composition: shape – pyramidal, stellate, fusiform, flask-shaped etc.
large, euchromatic nucleus with
a prominent nucleolus
organelles:
Nissl bodies
Golgi complex
mitochondria
microtubules
neurofilaments
lypofuscin and
neuromelanin
Prof. Dr. Nikolai Lazarov
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Nerve processes
axon (Lat. axis, axle or pivot)
structure:
length – 1 mm-100 cm
diameter – 0.2-20 µm
axon hillock
initial segment
collateral branches
axonal ending (terminal)
synapse
axolemma
axoplasm:
axoplasm
ribosomes – occasionally
absence of rER and GA
axonal transport:
transport
slow stream – 0.2 µm/day
anterograde flow
fast stream – 10-40 cm/day
anterograde and
retrograde flow
Prof. Dr. Nikolai Lazarov
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Nerve processes
dendrites (Gr. dendron, tree)
number – variable, most frequently 5-15
structure: 80-90% of the surface
short, dendritic tree
dendrite spines
dendritic cytoplasm:
cytoplasm
Nissl bodies
mitochondria
neurofilaments
microtubules
absence of Golgi complex
Prof. Dr. Nikolai Lazarov
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Basic neuronal types
morphological classes:
pseudounipolar neurons
bipolar neurons
multipolar neurons
Prof. Dr. Nikolai Lazarov
functional classes:
motor (efferent) neurons
sensory (afferent) neurons
interneurons
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Nerve fibers
Types of nerve fibers:
fibers
Nerve fiber:
axon
sheath derived from cells of ectodermal origin:
oligodendrocyte – CNS
Schwann cell – PNS
unmyelinated – 0.1-2 µm diameter
both in the CNS and PNS
absence of nodes of Ranvier
0.5-2 m/sec conduction velocity
myelinated – 1-20 µm
both in the CNS and PNS
mesaxon
nodes of Ranvier
internodal segment – 1-2 mm
SchmidtSchmidt-Lanterman clefts
4-120 m/sec velocity
Prof. Dr. Nikolai Lazarov
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Myelination
myelination in humans:
begin – fetal period
end – 7 years
regulation – neuroregulin NRG1
Myelin-forming cells:
oligodendrocytes – CNS
Schwann cells – PNS
myelin:
lipids – 70%
proteins – 30% in CNS
MBP (myelin basic protein)
P0 – peripheral axons
PMP-22 – peripheral axons
Prof. Dr. Nikolai Lazarov
myelin sheath:
major dense lines
intraperiod lines
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Synapses
synapse (Gr. synaptein, to join together)
structure:
presynaptic component,
axon terminal
presynaptic membrane
presynaptic grid
mitochondria
synaptic vesicles –
(20-65 nm) transmitters C.S. Sherrington
synaptic cleft (20-30 nm)
postsynaptic membrane
1857–1952
postsynaptic thickening
receptors
Prof. Dr. Nikolai Lazarov
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Types of synapses
way of transmission:
electrical synapses
chemical synapses
contacting structures:
axosomatic synapses
axodendritic
axoaxonic
dendrodendritic
somatodendritic etc.
morphologically:
asymmetrical (type I) – Glu
symmetrical (type IІ) – GABA
functionally:
excitatory synapses
inhibitory synapses
atypical synapses:
reciprocal dendrodendritic
serial synapses
“ribbon” synapse
synaptic glomeruli
Prof. Dr. Nikolai Lazarov
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Neurotransmitters
neurotransmitters – criteria
neuromodulators
types of neurotransmitters:
classical transmitters
amino acids
biogenic amines
other major transmitters – ACh
neuroactive peptides (neuropeptides)
atypical neural messengers:
arachidonic acid derivatives
purines
adenosine, ATP
gaseous – NO, CO
postsynaptic effect:
excitatory
acetylcholine
glutamate
aspartate
inhibitory
monoamines
GABA and glycine
Prof. Dr. Nikolai Lazarov
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Transporters and receptors
Transporters:
Transporters
Acetylcholinesterase (AChE)
integral proteins –
Na+ transport symporters
Transmitter receptors:
receptors
ionotropic – transmitter-gated ion channels
for ACh, GABA, Gly, SER
for glutamate
• NMDA-receptors
• non-NMDA-receptors (AMPA and kainate)
metabotropic receptors
G-protein-coupled receptors
• muscarinic ACh receptors
• α- and β-adrenergic receptors
• receptors for Glu, SER, GABA, neuropeptides
tyrosine kinases receptor family
guanylate cyclase receptors
cytokine receptors
autoreceptors
Prof. Dr. Nikolai Lazarov
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Arvid Carlsson,
Carlsson Paul Greengard and Eric Kandel for their discoveries
concerning "signal transduction in the nervous system"
Arvid Carlsson,
Carlsson Department of Pharmacology, Göteborg University, Sweden,
is rewarded for his discovery that dopamine is a brain transmitter of great
importance for our ability to control movements that has led to the realization
that Parkinson's disease is caused by a lack of dopamine in certain parts of the
brain.
Paul Greengard,
Greengard Laboratory of Molecular and Cellular
Science, Rockefeller University, New York, USA, is
rewarded for his discovery of how dopamine and a
number of other transmitters exert their action in the
nervous system.
Eric Kandel,
Kandel Center for Neurobiology and Behavior, Columbia
University, New York, USA, is rewarded for his discoveries of how
the efficiency of synapses can be modified, and which molecular
mechanisms that take part.
Prof. Dr. Nikolai Lazarov
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Neuroglia
Glial cells – glioblastic origin:
central – macroglia and microglia (in CNS)
peripheral – in PNS
central gliocytes
– neural tube:
astrocytes
oligodendrocytes
ependymal cells
microglial cells
peripheral gliocytes – neural crest:
Schwann cells (neurolemmocytes)
satellite cells of Cajal
(syn: mantle cells or amphicytes)
Prof. Dr. Nikolai Lazarov
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Central gliocytes
astrocytes
(Gr. astron
– star)
protoplasmic
fibrous astrocytes
oligodendrocytes
(Gr. oligos
– small)
large light
medium-sized
small dark – ¼ of the light cells
myelin-forming cells in the CNS
ependymal cells – neural crest
line the ventricles of the brain
and central canal of the spinal cord
absorption and secretion of
cerebrospinal fluid (liquor)
tanycytes (ependymal astrocytes)
microglia – 15% of the total cells of CNS
non-dividing cells
derived from monocytes
role of macrophages (mononuclear phagocyte system in nervous tissue)
Prof. Dr. Nikolai Lazarov
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Peripheral gliocytes
Schwann cells (neurolemmocytes)
neural crest origin
myelin-forming cells in the PNS
maintenance of the axon integrity
phagocytotic activity and cellular debris
that allows for regrowth of PNS neuron
satellite cells (amphicytes)
in sensory and autonomic ganglia
help regulate
the external chemical environment
Prof. Dr. Nikolai Lazarov
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Sensory receptors – classification
3 main groups – Sherrington, 1906:
exteroceptors
proprioceptors
interoceptors
by sensory modality:
C.S. Sherrington
1857–
1857–1952
baroreceptors – respond to pressure
chemoreceptors – chemical stimuli
mechanoreceptors – mechanical stress
nociceptors – pain perception
thermoreceptors – temperature
(heat, cold or both)
by location:
cutaneous receptors – in the skin
muscle spindles – in the muscles
by morphology:
morphology
free nerve endings
encapsulated receptors
Prof. Dr. Nikolai Lazarov
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Sense of touch
four kinds of touch sensations:
light touch (contact)
cold
heat
pain
free nerve endings:
endings
unencapsulated
unspecialized, detect pain
most widely distributed,
most numerous in the skin,
mucous&serous membranes,
muscle, deep fascia, viscera walls
peritrichal endings of hair follicles
tactile discs of Merkel:
Merkel
mechanoreceptors –
pressure and texture
superficial layers of
glabrous and hairy skin
Prof. Dr. Nikolai Lazarov
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Encapsulated receptors
tactile corpuscles of Meissner – glabrous skin
end bulbs (of Krause) – responds to pressure,
genital corpuscles
Pacinian (Vater-Pacini) corpuscles – vibration
Golgi-Mazzoni corpuscles – in the fingertips
Ruffini endings – responds to pressure
neurotendinous organs (Golgi tendon organs)
neuromuscular spindles – proprioceptors:
intrafusal fibers
extrafusal fibers
Prof. Dr. Nikolai Lazarov
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Effector nerve endings
myoneural junction – motor end plate:
structure:
myelinated axon collaterals
~50 axon terminals (boutons)
• synaptic vesicles – ACh
• presynaptic membrane
sarcolemma junctional folds
postsynaptic membrane
• nicotinic ACh receptors
autonomic effector endings:
sympathetic – adrenergic (NA)
parasympathetic – cholinergic (ACh)
purinergic – ATP and adenosine
do not make
specialized synaptic contacts
Prof. Dr. Nikolai Lazarov
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Thank you…
Prof. Dr. Nikolai Lazarov
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