Nervous System

1. Nervous System Myelin sheath in H and E slides Spinal cord Myenteric ganglion Pacinean Corpuscle

2. Nervous Tissue: The organization of cells in nervous tissue The organization of organelles in neurons.

5. Nervous System Organisation: • Central nervous system (CNS) • Brain & spinal cord • Peripheral nervous system (PNS) • Outside CNS • Cranial & spinal nerves and associated ganglia • - PNS • > sensory • > motor - somatic: impulses transmitted directly to skeletal muscle via one neuron • - autonomic: impulse  one neuron  autonomic ganglion  SM, CM, glands

6. Cells of the nervous system: Glia Neurons - perikaryon (soma, cell body) - dendrites - axon - axon terminals

7. Neurons: - many shapes (unipolar, bipolar, pseudounipolar, multipolar) Usually polarized - cell body - dendrites - axon - axon terminal

9. Dendrites: Receive and integrate synaptic signals. **Dendritic spines** Some neurons have many dendrites. Some dendrites have many branches. Ultrastructure similar to cell body.

14. Axon: one process, some have collateral branches. -can be long in the PNS -NO ribosomes -Yes, neurofilaments, microtubules, mitochondria > believed to serve in regulation of diameter

15. Axon ensheathing cells are glia. • Oligodendrocytes in the CNS. • Schwann cells in the PNS. • Ensheathing cells responsible for maintaining myelin sheath

19. In the CNS, white matter contains myelinated axons gray matter, no myelination

20. Other types of glia (neuroglia): Astrocytes: protoplasmic - gray matter fibrous - white matter - regulate ions and other molecules around neurons - release glucose from glycogen - have processes around blood vessels - form scar tissue

21. astrocyte

22. Oligodendrocytes: smaller than astocytes -some produce myelin Microglia: small phagocytic cells -originate from bone marrow Ependymal cells: - cuboidal or low columnar simple epith. - line the ventricles

23. Astrocytes – green Microglia – red

26. Morphological reactions of injured axons in the PNS: PAGE 216 • Chromatolysis: may last several months. • Nissl bodies disperse, peripheral nucleus. • Soma producing: Free ribosomes, protein, RNA and other molecules. • The axon and myelin sheath distal to the lesion degenerates as far as the axon collateral • sprouting of the axon into endoneurium • guiding by proliferating Schwann cells toward the target • regeneration in the presence of macrophages, fibroblasts, Schwann cells and basal lamina. These express growth factors, cytokines, up-regulate expression signal receptors.

27. Chromatolysis cont’d • Schwann cells form a sheath that guides the sprout to the target • Sprout makes synaptic contact with target • Other sprouts degenerate If no synaptic contact is made, the target cell degenerates. Need connective tissue sheaths for the regeneration. These are absent in the CNS generally, no regeneration In the CNS, microglia phagocytose the injured cells • Glial scar occupies the space.

31. Location of synapses: Axodendritic synapses Axosomatic synapses Axoaxonic synapses Dendrodendritic synapses

33. Ultrastructure of neurons: Cell body - nucleus - rER and polyribosomes (Nissl bodies) - Golgi complex - mitochondria - lipofuscin granules (considered ‘aging’ pigment) - cytoskeleton: neurofilaments, microtubules Axon hillock - no rER

35. Pacinian Corpuscle

36. Nerve ending