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Neurons, neuroglia and organization of the nervous system

Neurons, neuroglia and organization of the nervous system. Overview of the nervous system. General definitions. Central nervous system (CNS)- brain and spinal cord Peripheral nervous system (PNS)- links the CNS to target systems, including sensory organs

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Neurons, neuroglia and organization of the nervous system

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  1. Neurons, neuroglia and organization of the nervous system

  2. Overview of the nervous system

  3. General definitions • Central nervous system (CNS)- brain and spinal cord • Peripheral nervous system (PNS)- links the CNS to target systems, including sensory organs • Autonomic nervous system (ANS)- spans CNS and PNS; controls visceral functions

  4. Functions of the nervous system • Sensory- detection of internal and external stimuli (sensory neurons) • Integrative- processing of sensory information (interneurons) • Motor- response to integrated “decision” (motor neurons)

  5. Organization of the nervous system

  6. Structure and function of neurons • Act through propagation of action potentials • Vary considerably in size • Dendrites, cell body and axons • May be myelinated • Synapse with other neuron or muscle cell; release neurotransmitters

  7. Neurotransmitter action • About 100 neurotransmitters known • Amino acids, polypeptides, gases • Released into synaptic cleft, bind to membrane of target cell

  8. Structural diversity in neurons • Multipolar- many dendrites, one axon • Most neurons in CNS • Bipolar- one dendrite, one axon • Sensory organs • Unipolar- sensory • Axon termini extend into CNS

  9. Neuroglial cells • Much smaller than neurons and more numerous • Do not propagate action potentials • Can replace themselves

  10. Four types of neuroglia in CNS • Oligodendrocytes • Myelinating cells • Astrocytes • Blood-brain barrier (BBB) • Microglia • Phagocytes (from bone marrow) • Ependymal cells • Line ventricles of brain; produce cerebrospinal fluid (CSF)

  11. Neuroglia of the CNS

  12. Neuroglia of the PNS • Schwann cells • Myelinating cells • Help direct axon regeneration • Satellite cells • Support, protection, regulation of molecular exchange • “Filter out” other stimuli

  13. Why myelin? • Increases speed of nerve impulse transmission • Myelinating cells leave gaps on axons (nodes of Ranvier) • Schwann cells can help regenerate axons • Demyelination can lead to loss of function (MS)

  14. Classification of neurons • Exteroreceptors- deal with “external environment” • Interoreceptors- deal with internal environment • Proprioreceptors- position and movement

  15. Neuronal circuits

  16. Neural circuits in CNS vary in direction and complexity • One presynaptic→one postsynaptic is simplest • One presynaptic→ many postsynaptic (divergence) amplifies a sensory signal • Many presynaptic →one postsynaptic (convergence) brings information from many sources into one pathway • May move repeatedly through circuit (reverberating)- repeated or learned activities • Parallel-discharge- pathways diverge and then converge- complex activities requiring concentration?

  17. Repair and regeneration of neurons • Neurons can grow new dendrites or axon termini • Repair is limited to certain neurons in the PNS • Growth factors promote formation of new neurons; limited to specific regions of brain (hippocampus) in human adults • Growth does occur in fetal and juvenile stages- what turns it off?

  18. Synapses (chemical)

  19. Electrical synapses • Membranes of presynaptic and postsynaptic cells are fused • Transmission is faster • Can be bidirectional • Generally associated with defensive reflexes

  20. Gray matter and white matter in the nervous system

  21. Medically significant conditions • Multiple sclerosis (demyelination) • Epilepsy (uncontrolled electrical discharges) • Tumors • Neuropathies- affect specific nerves • Infectious disease

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