Nervous tissue

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!