Transcript nervous07
Nervous System Myelin sheath in H and E slides Spinal cord Myenteric ganglion Pacinean Corpuscle Nervous Tissue: The organization of cells in nervous tissue The organization of organelles in neurons. 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 Cells of the nervous system: Glia Neurons - perikaryon (soma, cell body) - dendrites - axon - axon terminals Neurons: - many shapes (unipolar, bipolar, pseudounipolar, multipolar) Usually polarized - cell body - dendrites - axon - axon terminal Dendrites: Receive and integrate synaptic signals. **Dendritic spines** Some neurons have many dendrites. Some dendrites have many branches. Ultrastructure similar to cell body. 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 Axon ensheathing cells are glia. o Oligodendrocytes in the CNS. o Schwann cells in the PNS. Ensheathing cells responsible for maintaining myelin sheath In the CNS, white matter contains myelinated axons gray matter, no myelination 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 astrocyte 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 Astrocytes – green Microglia – red 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. 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. Location of synapses: Axodendritic synapses Axosomatic synapses Axoaxonic synapses Dendrodendritic synapses 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 Pacinian Corpuscle Nerve ending