neurons neuroglia and organization of the nervous system
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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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general definitions
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
functions of the nervous system
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)
structure and function of neurons
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
neurotransmitter action
Neurotransmitter action
  • About 100 neurotransmitters known
  • Amino acids, polypeptides, gases
  • Released into synaptic cleft, bind to membrane of target cell
structural diversity in neurons
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
neuroglial cells
Neuroglial cells
  • Much smaller than neurons and more numerous
  • Do not propagate action potentials
  • Can replace themselves
four types of neuroglia in cns
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)
neuroglia of the pns
Neuroglia of the PNS
  • Schwann cells
    • Myelinating cells
    • Help direct axon regeneration
  • Satellite cells
    • Support, protection, regulation of molecular exchange
    • “Filter out” other stimuli
why myelin
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)
classification of neurons
Classification of neurons
  • Exteroreceptors- deal with “external environment”
  • Interoreceptors- deal with internal environment
  • Proprioreceptors- position and movement
neural circuits in cns vary in direction and complexity
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?
repair and regeneration of neurons
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?
electrical synapses
Electrical synapses
  • Membranes of presynaptic and postsynaptic cells are fused
  • Transmission is faster
  • Can be bidirectional
  • Generally associated with defensive reflexes
medically significant conditions
Medically significant conditions
  • Multiple sclerosis (demyelination)
  • Epilepsy (uncontrolled electrical discharges)
  • Tumors
  • Neuropathies- affect specific nerves
  • Infectious disease