Year 1 Med School Nervous Tissue Slidess

Nervous Tissue Slides

1. NERVOUS TISSUE

2. LECTURE OVERVIEW TISSUES EPITHELIAL TISSUE CONNECTIVE TISSUE MUSCLE TISSUE NERVOUS TISSUE N e urons Supporting cells Soma (cell body) Neurites (proc e sse s ) Dendrites Axon Neurogl i a Microglia Schwann cells Satellite cells Astrocytes Ependymal cells Oligodendrocytes

3. Nervous tissue Nervous system have highly complex intercommunicating network of nerve cells Receive & conduct impulses along their neural pathway to & from the CNS 2 types : Neurons (nerve cells) Supporting cells

4. Structural & functional unit of the nervous system 3 general categories: Sensory neurons Convey impulse from receptor to CNS Motor neurons Convey impulses from CNS or ganglia to effector cells Interneurons Form a communicating & integrating network btwn the sensory & motor neurons Neuron Inter- neuron Sensory neuron Motor neuron

5. Neuron: structure Excitable cell – specialized to receive stimuli from other cell and conduct the electrical impulse to other parts of the system Consist of : Cell body (soma) Dendrites Axon Dendrites Cell body Axon

6. Contain nucleus surrounded by cytoplasm (perikaryon) In general, located in the CNS , EXCEPT for most primary sensory neurons & terminal effector neurons for ANS - in aggregation at peripheral sites → ganglia Nucleus : large, round or ovoid usually centrally located prominent nucleolus Neuron: Cell body Nucleolus Nucleus Perikaryon

7. Neuron: Cell body Cytoplasm : contain large aggregation of rough endoplasmic reticulum ( Nissl bodies ), extend into dendrites but NOT axon hillock or axon Other organelles Numerous mitochondria Large Golgi apparatus Microtubules Intermediate filaments Rough endoplasmic reticulum (Nissl body) Axon hi l lock Nucleus Nucleolus

8. Neuron: Dendrites Highly branched, tapering processes extend from cell body → dendritic tree (increase receptor surface area) Specialized sensory receptors – receive stimuli from other neurons or external environment Form synapses with other neurons Dendrite Synapse

9. Neuron: Axon Single process arise from cone-shaped portion of cell body → axon hillock Cylindrical process terminating on other neurons or effector organs Minimal terminal branches end in small swelling → terminal boutons Conducts impulse away from cell body to another neuron or effector cell Axon hi l lock Axon T erm i nal boutons

10. Neuron: H&E slide diagram

11. Types of neuron Base on number of dendrites and axons that originate from cell body 3 major types: Multipolar neuron Bipolar neuron Unipolar neuron (pe u d o -u n ipolar)

12. Types of neuron: Multipolar Multipolar neuron Numerous branched dendrites& single axon Most common Include motor neurons & interneurons of brain, cerebellum and spinal cord

13. Types of neuron: Bipolar Bipolar neuron Single dendrite & single axon Not common Purely sensory neurons Found in retina of the eye, vestibulo- cochlear nerve in the inner ear, and olfactory epithelium retina

14. Types of neuron: Unipolar Unipolar neuron P s e u d o u n ipolar neuron Only single process from cell body – divides into 2 long processes Purely sensory Found in numerous sensory ganglia of cranial and spinal nerves ( dorsal root ganglia )

15. TYPES OF NEURONS SENSORY INTERNEURON MOTOR PSEUDO- U N IP O L A R BIPOLAR MULTIPOLAR

16. EXAMPLES OF MULTIPOLAR NEURONS

17. Neurons: H&E photomicrographs neuron neuron dendrite axon Nissl bod i es neucleolus nucleus Nucleus of Schwann cell Nuclei of supporting cells

18. Neurons: Different staining methods Silver impregnation: purkinje cell in cerebellar cortex Spread preparation: neurons in small peripheral ganglion Gold/toludine blue method: detail of neuronal shape Heavy metal impregnation (gold): highlight axon, terminal boutons

19. Myelination In PNS , all axons enveloped by specialized cells → Schwann cells Provide structural and metabolic support Small diameter axons: enveloped by cytoplasm of Schwann cells → non-myelinated Large diameter fibre wrappedby variable number of concentric layers of Schwann cell plasma membrane forming myelin sheath → myelinated In CNS : similar myelination by oligodendrocytes Axon Nucleus of schwann cell Myelin shea t h

20. Non-myelinated nerve fibres One or more axon become longitudinally invaginated into Schwann cell Each axon embedded in a channel, invested by Schwann cell plasma membrane & cytoplasm At opening of channel, plasma membrane opposed → mesaxon Only one axon in a channel, within extracellular compartment of Schwann cell Include ANS & small pain fibres Mesaxon Axons

21. Myelinated nerve fibres In peripheral nerves, myelination begins with invagination of a single axon into a Schwann cell Form mesaxon Mesaxon rotates around axon → enveloping axon in a concentric layer of Schwann cell cytoplasm & plasma membrane Cytoplasm excluded, plasma membrane fused with each other forming multiple layers of membrane → myelin sheath Mesaxon Myelin shea t h

22. Nodes of Ranvier Myelin sheath of an axon provided by many Schwann cells Each Schwann cell covering a segment of axon Short interval not covered by myelin sheath → nodes of Ranvier At certain point within myelin sheath, narrow channel of cytoplasm retained → Schmidt- Lanterman cleft Myelin sheath Node of Ran v ier Nucleus of Schwann cell Axon Schmidt- Lanterman cleft

23. Nodes of Ranvier : H&E slide

24. Synapse Specialized intercellular junction – allow communication btwn linking neurons of each nervous pathway Axon of one neuron may synapse with dendrites/ cell bodies/ axons of other neuron Structure: Terminal bouton (not myelinated) Synaptic cleft (gap) Synaptic vesicles (contain neurotansmitter) Presynaptic membrane Postsynaptic membrane

25. Synapse: simplified diagram

26. Motor end plate Similar intercellular junction link neuron & effector cells (eg: skeletal muscle) Neuromuscular junction A motor neuron & muscle fibre it supplies constitute a motor unit Terminal boutons – clusters of small bulbous swelling Plate covered by extension of Schwann cell cytoplasm Post synaptic membrane deeply fold to form secondary synaptic cleft

27. Sensory receptors Nerve endings or specialized cells – convert stimuli from external / internal environment into afferent nerve impulse Free nerve endings Meissne r ’ s corpuscles Neurom u scular spindle Pacinian corpuscles

28. Peripheral nerve May contain afferent ( sensory ) & efferent ( motor ) nerve fibres of either somatic or ANS Each nerve composed of one or more bundles (fascicles) of nerve fibres Individual nerve fiber (generally axon)with the myelin sheath surrounded by endoneurium Fascicles - by perineurium Peripheral nerve - by epineurium - form a strong epineurial sheath Epineurium Perineurium Endoneurium

29. STRUCTURE OF PERIPHERAL NERVE (eg: SPINAL NERVE)

30. Peripheral nerve: transverse section E : Epineurium F : Fascicle P: Perineurium PERIP H ER A L NERVE Endoneurium

31. Peripheral nerve: transverse section

32. Peripheral nerve: longitudinal section

33. Peripheral nerve: longitudinal section

34. Supporting cells Non-conducting cells In close apposition to neurons Includes : Neuroglia (CNS) Schwann cells Satellite cells Provides: Physical support Electrical insulation Metabolic exchange pathways btwn vascular system & neurons

35. Neuroglia Supporting cells in the CNS (form half of the total mass) Highly branched cells occupy spaces btwn neurons 4 principle type: Astrocytes Oligodendrocytes Microglia Ependymal cells Oligo- dendrocytes Ependymal cells Microglia Astrocytes

36. Neuroglia

37. Neuroglia: Astrocytes Most numerous glial cells in grey matter Long branched processes occupy most of interneuronal spaces Processes end at: Terminal non-synaptic region of neurons Capillaries (form blood- brain barrier) Pia mater of the meninges Mediate metabolic exchange btwn neuron & blood, regulate intercellular environment of CNS

38. Neuroglia: Astrocytes Fibrous astrocytes More common in white matter Have fewer processes Relatively straight Protoplasmic astrocytes Prominent in grey matter Numerous short highly branched processes

39. Neuroglia: Oligodendrocytes Small number of short, branched processes Responsible for myelination of axons in CNS A single oligodedrocyte can contribute to myelination of 50 axons Formation of myelin sheath similar to Schwann cells Predominant in white matter

40. Neuroglia: Microglia Small cells with elongated nuclei & little cytoplasm Form fine, highly branched process In response to tissue damage, microglia transform into large ameboid phagocytic cells (as macrophage- monocyte defence system )

41. Neuroglia: Ependymal cells Form the epithelial lining of ventricles & spinal canal Cuboidal or low columnar in shape Do not rest on basement membrane but the base of cells break up into small branches and connected to processes from astrocytes

42. Schwann cells & Satellite cells Schwann cells produce myelin sheath in PNS Satellite cells small cuboidal cells surrounded neuronal cell bodies of ganglia (for electrical insulation & metabolic exchange)

43. THANK YOU