Transcript
Nervous Tissue
Lecturer – professor Boronikhina Tatiana Vladimirovna
Nervous tissue forms organs of the nervous system
nerve
ganglion
brain
Nervous tissue is cellular tissue
consists of cellsneurons glial cells
lacks extracellular material
All nervous tissue cells have processes
Nervous tissue cell functions
Neurons 1. generation, conduction, and transmission of nerve impulses2. accumulation, processing, and reproduction of information
Glial cells
attending functions
Nervous tissue embryonic origins
Neural tube neurons and glial cells of CNC
Neural crest neurons and glial cells of PNS
Mesenchyme microglial cells of CNS
Neuron consists of a cell body and processes
Neuron cell bodies form ganglia of PNSgray matter of CNS
Neuron processes form nerves of PNSwhite matter of CNS
Morphologic neuron classification
Bipolar
Multipolar
Pseudounipolar
Neuron cytology
Nucleus is large and euchromatic with well-developed nucleoli
Cytoplasm is rich in organelles rER mitochondria Golgi apparatus microtubules and filaments sER lysosomes
Neuron cell body (soma, perikaryon)
Neurons are obligatory aerobic cells
contain numerous mitochondria
use O2 - 25% in adults
50% in children blood glucose is a substratum of respiration
Time of revivification in clinical death is limited
5 – 6 minutes
15 – 16 minutes in hypothermia or pharmacologic defence
Basophilic clumps or Nissl bodies
rER
Nissl bodies
Neuron rER synthesizes membrane proteins
proteins are necessary forsynaptic vesicle formationneuron growth and differentiationintracellular regeneration
Golgi apparatus takes part in synaptic vesicle formation
Golgi apparatus in neuron cell bodies
synaptic vesicles
“Neurofibrils” are aggregated microtubules and filaments
Silver impregnation
electron micrographof axon cytoplasm
Neuron processes
Dendrites
are numerous or singlebranch dichotomically directly from the soma (arborization)contain all organellespossess spines to increase the synaptic surface may form receptors
Axon
is always a singlebranches forming collaterals and at the terminal lacks rER and ribosomescontains many microtubules and filamentslacks spines may form effectors
Axonal transport
Transport direction: anterograde – away from the neuron soma retrograde – towards the neuron soma
Transport velocity: fast (200-400mm/day) synaptic vesicles slow (0,2-1mm/day) tubulin, actin intermediate (2-50mm/day) enzymes
Neuron dynamic polarization
Dendrites conduct nerve impulses
towards the soma
Axon conducts nerve impulses
away from the soma
neurons are polarized by synapses
Synapses are specialized neuron junctions to transmit nerve impulses
Synapse classifications
Depending on transmission mechanism:• chemical• electrical (nexuses)
Depending on physiologic effect: • excitatory • inhibitory
Morphologic synapse classification
Synapses are a neuron axon terminations on the soma, dendrites, and the axon of another neurons
a - axosomatic
b - axodendritic
c - axoaxonic
Chemical synapse parts
Presynapse – axon ending (presynaptic knob)synaptic vesicles with neurotransmittersmitochondriapresynaptic membrane
Postsynapse – soma, dendrite, or axon
postsynaptic membrane receptors to neurotransmitters
Synaptic cleft filaments enzymes for neurotransmitter inactivation
Synapse electron micrographs
Parasynapse is from glial cells
functions synaptic cleft isolationneurotransmitter utilization
Synapse functioning
Neurotransmitter-receptor interaction opens ionic channels
Exitatory synapse Na+ channels open
membrane depolarization
Inhibitory synapse Cl- channels open
membrane hyperpolarization
Neurotransmitter utilization
return to presynapse by endocytosisdestruction in synaptic cleft by enzymes absorption by parasynapse
Peripheral nerve endings
Sensory nerve endings – receptors are terminals of the sensory neuron dendrites
Function: interact with stimuli and generate nerve impulses
Motor nerve endings - effectors are terminals of the motor neuron axons on muscles or glands
Function: stimulate muscle contraction or gland secretion
Histologic receptor classification
Free
dendrite terminals
Non-free
dendrite terminals
glial cells
Encapsulated
dendrite terminals
glial cells
connective tissue
Encapsulated receptor in the skin dermis
mechanoreceptor Pacinian corpuscle
Effectors are neuromuscular or neuroglandular synapses
on smooth muscle cells
on skeletal muscle fiber
Motor end plate
Presynapse – motorneuron axon Postsynapse – sarcolemmaNeurotransmitter – acetylcholineCleft enzyme - acetylcholinesteraseParasynapse - lemmocytes
Functional neuron classification
Sensory neuronspseudounipolarbipolarmultipolar (rarely)
Motor neurons multipolar
Associative neurons multipolar or bipolar
Neuron capacity for regeneration
Physiologic regeneration intracellular level (static population)
Reparative regenerationsoma damage cell deathprocess damage processes are repaired
Nervous stem cells
be discovered in the brain
Glial cell classification
Macroglial cells arise from neuroectoderm oligodendrocytes astrocytes ependymal cells
Microglial cells arise from mesenchyme are blood monocyte derivatives are macrophages of the CNS belong to the mononuclear phagocytic system
Glial cell common features
possess processesare capable of migration
(except for ependymal cells)can proliferateare capable of phagocytosis
(except for ependymal cells)perform attending functions for neurons
Oligodendrocytes
are found in the CNS and PNS possess a few short processescontain numerous organellesenclose the neuron cell bodies and processeslive symbiotically with neurons
Functions: neuron insulation and protection neuron nutrition nerve fiber formation nerve fiber regeneration
Astrocytes
are found only in the CNS:protoplasmic astrocytes in the gray matterfibrous astrocytes in the white matter
contain numerous microfilaments and microtubulestheir processes sheathe blood vesselsform glial membrane beneath the pia mater
Functions: • neuron support• neuron isolation• nutrient transport• electrolyte balance maintenance • repair (scar formation)
Ependymal cells
are found in the CNS: line the spinal canal and brain ventricles
form epithelium-like layerare cylindrical or cuboidal in shapeapical cell pole possesses ciliabasal cell pole form process
Functions:• production of cerebrospinal fluid (CSF)• exchange between CSF and nervous tissue• neuron support
Ependymal cells line the spinal canal
Nerve fibers are neuron processes enveloped by
oligodendrocyte sheaths
Unmyelinated nerve fiberscontain dendrites (except for ANS motor neuron axon)untreated fibers are grey in colourare slow - nerve impulse conduction velocity is 8-10 m/sec
Myelinated nerve fiberscontain axons (except for sensory neuron dendrites)untreated fibers are white in colourare fast - nerve impulse conduction velocity is 80-120 m/sec
Function of sheaths – electric insulation of neuron process
Unmyelinated nerve fibers
contains several (15-20) axis cylinders or neuron processes the so-called “cable-type fibers”
axis cylinders are enclosed by cytoplasm and plasmalemma of oligodendrocytes (lemmocytes or Schwann cells in the PNS)
Myelinated nerve fibers
contain the only axis cylinderaxis cylinder is enclosed by the myelinated sheath (myelin) and neurilemma (cytoplasm, nucleus, and plasmalemma of lemmocyte)
Myelinated sheath (myelin)
consists of oligodendrocyte plasmalemma (mesaxon) several layers has lipoprotein organization with lipid predominance
Myelinated sheath structures
Node of Ranviersites between adjacent lemmocytes
lacked myelin
Schmidt-Lanterman clefts (only in PNS)sites where the Schwann cell cytoplasm is preserved to function like nutritious canals
Myelinated fiber light and scanning appearance
• nodes of Ranvier provide saltatory impulse conduction
PNS nerve fibers are enclosed by endoneurium
Includesbasal lamina collagen fibers
Is produced by lemmocytes
Myelinated fiber formation in the CNS
an oligodendrocyte produces myelin of several axis cylinders
Myelinated fibers in the CNS
neurilemma is minimalmyelin lacks Schmidt-Lanterman cleftsnodes of Ranvier are bare
Demyelinization
Nerve fiber regeneration
Thank you for attention!
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