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Nervous tissue
Morphology examplesMorphology examples
Conducts electrical impulses (signals) to the CNS & transmits impulses from the CNS to various structures of the body
Conveys information from one area to another
Neural tissue
Morphogenesis of the neural tissue includes:
Proliferation; Determination & differentiation; Address migration of cells; Address growth of processes of neurons; Formation of intercellular junctions -
synapses; Apoptosis.
Neurulation
Cells in the neural tube
Ependymal (inner) layer
Cambial cells
Ependymal cells
Mantle layer
Neuroblasts
Glioblasts
Neurons
Astrocytes
Oligodendrogliocytes
Marginal layer
White matter of CNS organs
Gray matter (cell bodies)
White matter (myelinated axons)
Neural tube• CNS (brain
&spinal cord) Retina of the
eye Olfactory
organ Neural crest• Neural ganglia
(spinal &cranial; autonomic)
• Neurolemmocytes Adrenal medulla Diffuse endocrine
cells Pigmental cells Cells of arachnoid &
pia mater
Placodes • Sensoepithelial cells
of organ of Corti & equilibrium
Receptor cells of taste organ
Epithelium of lens
NeuronsGenerate &Transmit nerve impulses
NeurogliaSupport neural tissueHelp supply nutrients to neuronsProtect neuronsForm barriers
Neural tissue cells
Morphological classification of neurons - based on number of processes found on cell body
Unipolar Bipolar Multipolar Pseudounipolar
Unipolar neurons
Have only one axon Rare
Pseudounipolar neurons Have a single process that
extends from the cell body & subsequently branches into an axon & dendrite
Sensory neurons – located mainly in spinal & cranial ganglia
Bipolar neurons 2 processes. Have a
single dendrite and an axon
Are present in some sense organs: retina, spiral ganglion.
Multipolar neurons
>2 processes. Have two or more dendrites and one axon
Most common type of neuron. >99% of neurons
Functional classification of neurons motor neurons - efferent (conduct impulses from CNS
to other neurons, muscles or glands); sensory neurons - afferent (receive stimuli from the
internal & external environment). Conduct nerve impulses to the CNS.
interneurons act as connectors of neurons in chain. They most commonly connect sensory & motor neurons.
secretory neurons - neurons of hypothalamus: supraoptic & paraventricular nuclei – neurons produce hormones: vasopressin & oxytocin);- all neurons produce neurotransmitters of synapses.
Nervous Tissue
Sensory – interneuron – motor neuron
Neurons Functional unit of nervous system Special neuronal characteristics
Convey APs (excitable)LongevityDo not divideHigh metabolic rate
Neuron structure
Cell membrane with Na+-K+ pumps, that maintain the necessary ion gradients.
Nucleus with one prominent nucleolus (“owl-eye” nucleus)
Cytoplasm with various cytoplasmic organelles & inclusions, & cytoskeletal components
Neuron has
Cell body (perikaryon, soma) Processes: Only one axon One & more dendrites
Nucleus with Nucleolus
Parts of a Neuron
Axons or Dendrites
Cell body
Neuroglial cells
Neuron structure Cell body (perikaryon or soma)single nucleus with
prominent nucleolusNissl bodies
(chromatophilic substance) are stained basophilic
rough ER & free ribosomes (polysomes) for protein synthesis
Golgi complexMitochondriaLysosomes
Microtubules (neurotubules) move material inside cell
Neurofilaments (specific type of intermediate filaments) give cell shape and support
Microfilaments (actin) associated with the cell membrane
Neurofilaments & neurotubules form neurofibrils – is artefact. Neurofibrils appear at time of slide preparing & can be distinguish inside of neurons
Lipofuscin pigment clumps (harmless aging)Lipid inclusions
Cell processes = dendrites & axon
Perikaryon or somaPerikaryon or soma
Cell body is location for most protein synthesis neurotransmitters & repair proteins
Dendrites Conduct impulses towards the cell
body Typically short, highly branched Surfaces specialized for contact with
other neurons (spines) – increase the area useful for synapse formation
Have arborized terminals – permit a neuron to receive stimuli at the same time from many other neurons
Contains neurofibrils & Nissl bodies
Axon Conducts impulses away from cell
body Long, thin cylindrical process of cell Arises at axon hillock – a region of
the soma that lacks rER & ribosomes but contains many neurotubules & neurofilaments
May has collaterals (branching at right angles from the main trunk)
Axon terminals (many small branches from which impulses are passed to another neuron or other type of cell)
Swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters
Synaptic boutons
Transport
Dendritic – the movement of substances & organelles through the dindrites
Axonal - the movement of substances & organelles through the axon
Axonal Transport
Axonal transport system moves substances slow axonal flow
movement in one direction only -- away from cell body movement at 1-5 mm per day
fast axonal flow transports in either direction at 100-500 mm per day moves organelles & materials along surface of
microtubules for use or for recycling in cell body
•Anterograde transport – carries material away from the soma
•Retrograde transport – carries material toward the soma for reutilization, recycling, or degradation
Neuroglia
Macroglia Astrocytes Oligodendrocytes Ependymal cells
Microglia
Neuroglia of CNS: astrocytes, oligodendrocytes, ependymal cells, microglia
Neuroglia of PNS: neurolemmocytes (Schwann cell), satellite cells
Neuron and Neuroglia
CNS Neuroglia
Astrocytes protoplasmic (CNS gray
matter) fibrous (CNS white
matter)Function:
1. scavenge ion & debris (wastes) from neuron metabolism & supply energy for metabolism.
2. Provide structural support for nervous tissue
3. Form a protective barrier between pia mater & the nervous tissue of the brain & spinal cord
4. Form scar tissue after injury to the CNS
Neuroglia of CNS Astrocytes
Promote tight junctions to form blood-brain barrier
1. Endothelium of the capillary (between endothelial cells there are tight junctions)
2. basement membrane of endothelium
3. perivascular membrane – is formed by foot processes of astrocytes
Blood-brain barrier
1 – endothelium; 2- basement membrane; 3 – astrocyte’s body, 4 – foot processes of astrocyte; 5 – neuron, 6 – neuron’s processes; 7- oligodendroglial cell
Neuroglia of CNS Ependymal Cells
Line ventricles of the brain, spinal cord central canal, choroid plexus
Secrete & move liquor Form blood-liquor barrier: 1. Endothelium of capillary2. Basement membrane of
endothelium3. Loose connective tissue4. Basement membrane of
ependymal cells5. Ependymal cells
Oligodendrocytes Produce the
myelin sheath which provides the electrical insulation for certain neurons in the CNS
Neuroglia of CNS
Neuroglia of CNS
MicrogliaSpecialized macrophagesAg-presentationHas mesenchymal origin
Supporting cells in the PNS Satellite cells Schwann cells / neurolemmocytes
Neuroglia of PNS
Schwann cells or neurolemmocytes Wrap around portion of only one axon to form myelin sheath
Satellite cells are flattened cells Surround neuron cell bodies in ganglia, provide support and
nutrients
Satellite Cells
The End
Nerve fibers
Myelinated fibers
Unmyelinated fibers
Unmyelinated Myelinated
Localization
Mostly in the autonomic NS In the CNS and PNSSpeed of the conduction of the nerve impulse
low (0,5-2 m/s) High (5-120 m/s)
Nerve fiber of the cable type (cytoplasm of the Schwann cell can contains 10-20 axons of different neurons)
Nerve fiber contains only 1 axon. But in tne CNS 1 oligodendrocyte can takes part in the process of myelinization until 40-50 nerve fibers.
Structural components
1.axon (many axons)2.cytoplasm of the Schwann cell + mesaxon (mesaxons)3.basement membrane
1.axon2.myelin sheath with Schmidt-Lanterman clefts and node of Ranvier.3.cytoplasm and nucleus of the Schwann cell.4.basement membrane.
Conduction of the nerve impulse is continuous.
Conduction of the nerve impulse is salutatory (from the node to node of Ranvier – nerve impulse jumps)
Myelinated and Unmyelinated Axons
Unmyelinated nerve fibers
Axons surrounded by a lipid & protein covering (myelin sheath) produced by Schwann cells.
Myelin sheath is composed of multiple layers of Schwann cell membrane wrapped concentrically around the axon.
The myelin sheath is segmented because it is formed by numerous Schwann cells.
The junctions where two adjacent Schwann cells meet is devoid of myelin. gaps called nodes of Ranvier
Areas of incomplete fusion of the Schwann cell membrane occur, & small amounts of Schwann cell cytoplasm are trapped between the membranes – Schmidt-Lanterman clefts (defects in the myelin formation)
Myelinated nerve fiber
Schmidt-Lanterman clefts
Myelin sheath
Myelination in the CNS
Myelin sheaths are formed by oligodendrocytes
Myelination in the PNS
Myelin sheaths are formed by Schwann cell
Myelin Sheath Whitish, fatty (protein-lipid), segmented sheath
around most long axons It functions in:
Protection of the axonElectrically insulating fibers from one another Increasing the speed of nerve impulse transmission
Myelin Sheaths
Nodes of Ranvier
Gaps in the myelin sheath between adjacent Schwann cells
They are the sites where collaterals can arise
Nodes of Ranvier
Conduction of nerve impulse
A – in the unmyelinated nerve fiber (continuous)
B – in the myelinated nerve fiber (salutatory)
Nerve endings Functionally they can be divided into 3 groups:
synapses – provide the connection between neurons;
efferent (motor) endings – transmit signals from the NS to the working organs (muscles, glands); are present on the axons.
receptor (sensitive) endings – receive the irritation from the external environment and from the internal organs; are present on the dendrites.
Electrical
In mammals are rarely present. They are as nexus – provide the passive transport of the electric current through the cleft from the cell to other in the both directions and without delay.
Chemical Mostly distributed. The conduction of the nerve impulse is determined by the special substance - neurotransmitters.The conduction of the nerve impulse is only in the one direction and with delay. The are divided into:Axodendritic, occurs between axons and dendrites Axosomatic, occurs between axons and the cell bodyAxoaxonic, occurs between axons and axonsDendrodendritic, occurs between dendrites and dendrites.
Synapses are divided into:
Synapses
Presynaptic neuron Postsynaptic neuron
Synapses
Axodendritic synapses Axosomatic synapses Axoaxonic synapses Dendrodendritic synapses
Synapse structure Presynaptic element
Axon terminalSynaptic vesiclesNeurotransmittersMitochondria
Synaptic cleft Postsynaptic
elementsNT receptorsMay generate AP
Synaptic Transmission
An AP reaches the axon terminal of the presynaptic cell and causes V-gated Ca2+ channels to open.
Ca2+ rushes in, binds to regulatory proteins & initiates NT exocytosis.
NTs diffuse across the synaptic cleft and then bind to receptors on the postsynaptic membrane and initiate some sort of response on the postsynaptic cell.
Efferent nerve endings
Motor Are present in the striated and smooth muscles. By structure they are like synapses, but there are some features: nearly to the muscle fiber the axon loses the myelin sheath and gives some small branches. They are covered by the Schwann cells and basement membrane.The transmission of the excitation is provided by the neurotransmitter - acetylcholine.
Secretory Are present in the glandsCan make next influences:- hydrokinetic (mobilization of the water);- proteokinetic (secretion of the proteins);- synthetic (to increase the synthesis);- trophic (to maintain the normal structure and function).
Motor unit One neuron Muscle cells stimulated
by that neuron• Neuromuscular
junctions – association site of nerve and muscle
Receptor nerve endings
exteroreceptors (receive the signals from the external environment). They are: visual, auditory, olfactory, taste, tactile receptors.
interoreceptors. They are divided into visceroreceptors – receive signals from the inner organs; and proprioreceptors – receptors of the locomotor system.
Physiological classification of the receptor nerve endings
mechanoreceptors (pressure, vibration) chemoreceptors (taste, smell) thermoreceptors (cold, warm) pain receptors
Morphological classificationReceptor nerve endings
Free (simple)They are consists of terminal branches of the dendrites of the sensory neuron.They provide the perception of the pain, cold, warm, tactile signals. They are present inside of the epithelium and in the loose connective tissue, which is located beneath.It is consists of only of the dendrite.
Restricted (compound)
Encapsulated They are surrounded by the connective tissue capsule.Structure:branches of the dendritesurrounding Schwann cellsconnective tissue capsule.Examples:Vater-Pacini corpusclesMeissner’s tactile corpusclesRuffini’s curpusclesBulb of KrauseNeuromuscular spindlesTendon organ of Golgi
Unencapsulated They are consist of the branches of the dendrites that are surrounded by the Schwann cells.They are present in the dermis of the skin and in the lamina propria of the tunica mucosa.
Free nerve endings (pain, temperature, light touch)
Merkel endings (touch)
Pacinian corpuscle (vibration, deep pressure)
Krause’s end bulb (touch)
Meissner’s corpuscle (touch)
Ruffini’s corpuscle (stretch)
(Fibroblasts, collagen, fluid)
(Collagen fibers)
Receptor nerve endings
Free nerve endings
Meissner corpuscle
Vater-Pacini corpuscle
Pacinian corpuscle
Neuromuscular spindle
Vater-Pacini corpuscles – are present on the connective tissue of the skin and inner organs. They are responsible for the sensation of the pressure and vibration. Meissner’s tactile corpuscles - are located in the papillary layer of the dermis in skin, mostly: tips of fingers, lips, nipple and area which is around. Ruffini’s curpuscles – are located in the connective tissue of the skin and in the capsules of the articulations. Take in pressure.Bulb of Krause – is present in the papillary layer of the dermis, lamina propria of the tunica mucosa in the oral cavity. It is mechanoreceptor. Neuromuscular spindle – receptors of the sprain of the muscle fibers. It has motor and sensory innervations.Tendon organ of Golgi – receptor of the sprain. It is located in the places where the skeletal muscle fibers join to the tendon.
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