1. HISTOLOGY 1.13.: NERVOUS TISSUE Nervous tissue is specialized to generate and conduct impulses. Origin: neuroectoderm Tissue components: nerve cells, glial cells and their processes Blood supply: densely capillarized

2. The neuron: Generalized schematic drawing of a multipolar neuron Nissl staining Silver impregnation

3. Classification of neurons: on the basis of their processes Unipolar neuronsPseudo-unipolar neurons Bipolar neurons

4. Classification of neurons: on the basis of their processes MULTIPOLARNEURON-TYPES Motoneuron in the spinal cord (Nissl staining) Cortical pyramidal cell (silver impregnation) Cerebellar Purkinje cell

5. Classification of neurons: on the basis of their activity Excitatory cell type: it has spiny dendrites, its axon makes asymmetrical synapses using excitatory neurotransmitters Inhibitory cell type: it has non-spiny beaded dendrites, its axon makes symmetrical synapses using inhibitory neurotransmitters

6. Model of a multipolar neuron within the nervous tissue: 1.Dendrite 2.Axon (myelinated) 3.Nucleus 4.Nucleolus 5.Golgi apparatus 6.rER 7.Axon hillock and initial segment 8.Synaptic boutons terminating on the membrane of the neuron on the membrane of the neuron 9. Glial cell endfeet 10.Capillary with erythrocytes 11. Compact neural tissue (neuropil)

7. Cell body (perikaryon) of the neurons (electron micrograph) N=nucleusn=nucleolus Asterisks label stacks of rER (Nissl bodies) M=mitochondrionL=lipofuchsin G=Golgi apparatus Non-visible on the picture:microtubulesneurofilamentssER M L G LM EM

8. Processes of the neurons: dendrites Highly branched processes. Dendrites may contain microtubules, neurofilaments, sER, free ribosomes and mitochondria. Their membranes exhibit postsynaptic densities (arrows), the sites of synaptic transmission, thus: dendrites are the „receiving” processes, accepting impulses from other neurons. Cross-section Transverse section

9. Processes of neurons: axons Axon hillock Telodendrion Axon LM EM Long, cylindrical process with few branches along its course and multiple terminal branches (telodendrion). Axons originate from axon hillock. Initial segment: free of myelin sheath, receive synapses from other neurons. Initial segment Terminal bulb, or synaptic bouton

10. Characteristics of dendrites and axons: a summary Axon:Dendrite: 1.Extends from cell body or dendriteextends from cell body 2.Begins with initial segmentin proximal portion continues cytoplasm 3.May be absent (amacrine cells)May be absent (dorsal root ganglion) 4.Unique in most cellsUsually multiple 5.May be myelinated or noRarely myelinated 6.Never contains ribosomesContain rER, or ribosomes 7.Smooth contours, cylindrical shapeIrregular contours, appendages (spines) 8.The thinnest process at the originOriginates as thick, tapering process 9.Ramifies by branching at obtuse anglesRamifies by branching at acute angles 10.Gives rise to branches of same diameterSubdivides into smaller branches 11.May extend long distances from somaConfined to the vicinitiy of cell body 12.Neurofilaments predominate in axonsMicrotubules predominate in dendrites 13.Capable of generating action potentialsConduct in a decremental fashion propagating them and synapticbut may be capable of generating transmissionaction potentials 14.Primarily engaged with conductionPrimarily engaged with receiving and transmissionsynapses

11. Synapses A synapse between neurons is a site of morphological specialization where one neuron is able to influence the excitability of another neuron. Types of synapses: 1./ Electrical synapse: is a gap junction between the membranes of two adjacent neurons 2./ Chemical synapse: changes the membrane potential of the postsynaptic neuron by releasing neurotransmitter molecules. Electrical synapse (gap junction) Chemicalsynapse

12. Types of chemical synapses: A./ On the basis of the postsynaptic site: Axo-dendritic Axo-spinous Axosomatic (Less frequent types /not shown here/: Axo-axonic synapse, Dendro-dendritic synapse, Dendro-axonic type Reciprocal synapse)

13. Types of chemical synapses: A./ On the basis of the function: 1./ Excitatory (arrow): Usually asymmetrical 2./ Inhibitory („hands”): Usually symetrical

14. Neurotransmitters of the chemical synapses: Acetyl choline (ACh) Amino acids:glutamate (Glu)Amino acid derivatives: serotonin (5-HT) aspartate (Asp)dopamine (DA) glycine (Gly)  -amino butyric acid (GABA) histamine (His) Peptides:opioids (enkephalins, endorphins, dynorphins, etc.) neurohypophyseal (vasopressin, oxytocin, neurophysin) tachikinins (substance P and K, neurokinin, etc.) gastrins ( gastrin, cholecystokinin-CCK) Somatostatin (SOM) Vasoactive intestinal polypeptide (VIP) Neuropeptide Y (NPY) etc. Purins:adenosin