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.

Good bye! ☻