Nature of the Nervous System n Camillo Golgi n The Synctium l continuous network l no gaps ~
Nature of the Nervous System n Santiago Ramon y Cajal n The Neuron Doctrine l discrete cells l communication across gaps l synapses ~
Nature of the Nervous System n Golgi won l Proved himself wrong l Golgi Stain - silver chromate Supported Neuron Doctrine Golgi & Cajal shared Nobel Prize (1906) ~
Classification of Neurons l Structural – based on the number of cytoplasmic processes Multipolar neurons Bipolar neurons Unipolar neurons l Functional – based on the direction of impulse transmission Sensory neurons Motor neurons Interneurons (association)
Histology of Nervous Tissue l 2 types of cells Neurons –Structural & functional part of nervous system –Specialized functions Neuroglia (glial cells) –Support & protection of nervous system
NEURONS n Basic functional unit of N.S. n Specialized cell l All cells have same basic properties n information processing Transmits Integrates Stores n Regulation of behavior ~
Neurons l Function Conduct electrical impulses l Structure Cell body –Nucleus with nucleolus –Cytoplasm (perikaryon) Cytoplasmic processes –Dendrites –Axon
Application n In Multiple Scleroses the myelin sheath is destroyed. n The myelin sheath hardens to a tissue called the scleroses. n This is considered an autoimmune disease. n Why does MS appear to affect the muscles?
Types of Neurons n Functional classification l Sensory or afferent: Action potentials toward CNS l Motor or efferent: Action potentials away from CNS l Interneurons or association neurons (CNS) l Principle neurons / projection neurons (CNS) n Structural classification l Multipolar, bipolar, unipolar
Neuroglia l Neuroglia of CNS Astrocytes –Form the blood-brain barrier –Form a structural framework for the CNS –Repair damaged neural tissue –Control the interstitial environment of the CNS Oligodendrocytes –Form myelin sheaths CNS Microglia –Phagocytose foreign microbes, etc. Ependymal –Line ventricles of the brain, secrete cerebrospinal fluid l Neuroglia of PNS Schwann cells –Form myelin sheaths of PNS Satellite cells
Nerve Fibers of the PNS l An axon and its sheaths Myelinated axon –Axon is surrounded by a myelin sheath Unmyelinated axon –Axon has no myelin sheath
Myelin l White matter of nerves, brain, spinal cord l Composed primarily of phospholipids l Production Developing Schwann cells wind around axon l Function Increases speed of impulse conduction Insulation and maintenance of axon
Neuronal Communication: n Within a neuron, electrical signals called action potentials travel along the axon. n Communication between neurons is mediated via synaptic transmission (e.g. by means of neurotransmitters such as glutamate, GABA, acetylcholine). n Transfer of information from one part of body to another.
Neuroglia vs. Neurons n Neuroglia divide. n Neurons do not. n Most brain tumors are “gliomas.” n Most brain tumors involve the neuroglia cells, not the neurons. n Consider the role of cell division in cancer!
BBB: Function n Maintains stable brain environment large fluctuations in periphery n Barrier to poisons n Retains neurotransmtters & other chemicals n Regulates nutrient supplies glucose levels active transport ~
Myelin n Wrap around axon n Saltatory Conduction l faster transmission n CNS: oligodendroglia or oligodendrocytes n PNS: Schwann cells ~
Myelinated and Unmyelinated Axons n Myelinated axons l Myelin protects and insulates axons from one another l Not continuous Nodes of Ranvier n Unmyelinated axons