Nervous System Myelin sheath in H and E

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

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

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

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

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

Neurons: - many shapes (unipolar, bipolar, pseudounipolar, multipolar) Usually polarized - cell body -

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

Dendrites: Receive and integrate synaptic signals. **Dendritic spines** Some neurons have many dendrites. Some

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

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

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

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

Other types of glia (neuroglia): Astrocytes: protoplasmic - gray matter fibrous - white matter

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

astrocyte

Oligodendrocytes: smaller than astocytes -some produce myelin Microglia: small phagocytic cells -originate from bone

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

Astrocytes – green Microglia – red

Morphological reactions of injured axons in the PNS: PAGE 216 Chromatolysis: may last several

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

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

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

Ultrastructure of neurons: Cell body - nucleus - r. ER and polyribosomes (Nissl bodies)

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

Pacinian Corpuscle

Pacinian Corpuscle

Nerve ending

Nerve ending

Nervous System Nervous System Nervous system Central NervousNervous System Nervous System Nervous system Central Nervous
Myelin Components Central and peripheral myelin also containMyelin Components Central and peripheral myelin also contain
MYELIN SHEATH AND ITS FORMATION Adapted from internetMYELIN SHEATH AND ITS FORMATION Adapted from internet
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Myelination n Axons covered with a myelin sheathMyelination n Axons covered with a myelin sheath
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