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Neurons

Neurons. Vary in size and structure, but have common features: Cell Body Dendrites Axon Mature neurons do not divide, but neural stem cells can divide and form neurons or neuroglial cells. 1. Cell Body.

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Neurons

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  1. Neurons • Vary in size and structure, but have common features: • Cell Body • Dendrites • Axon • Mature neurons do not divide, but neural stem cells can divide and form neurons or neuroglial cells.

  2. 1. Cell Body • Contains normal cellular structures (golgi apparatus, mitochondria, cytoplasm, cell membrane, etc.) • Neurofibrils – fine threads that extend into the axon • Nissl bodies (chromatophilic substances) • Membranous sacs in the cytoplasm • Similar to rough ER • Ribosomes on Nissl bodies synthesize ______

  3. 2. Dendrites • Usually short and highly branched (dendr = ?) • The main receptive surfaces for receiving communication from axons of other neurons

  4. 3. Axons • Arise from a slight elevation of the cell body, called the axonal hillock. • Conduct nerve impulses away from the cell body • Contains many mitochondria, microtubules, and neurofibrils • Originates as a single structure, but may have branches, especially at the end to interact with receptive surfaces of other cells

  5. PNS Axons • Enclosed in myelin sheaths composed of many Schwann cells • Myelin is a lipoprotein. • Neurilemma sheath surrounds the myelin sheath • Nodes of Ranvier – narrow gaps in the myelin sheath between the Schwann cells

  6. Classification of Neurons • Classification based on Structural differences: • Bipolar neurons • Unipolar neurons • Multipolar neurons • Classification based on Functional differences: • Sensory neurons (afferent neurons) • Interneurons (association or internuncial neurons) • Motor neurons (efferent neurons)

  7. Structural Differences • Sketch the neurons below. Notes on the next 3 slides:

  8. Structural Differences, cont….. • Bipolar: • 2 processes • Axon • Dendrite • Found in specialized parts of the eyes, nose, and ears

  9. Structural Differences, cont….. • Unipolar: • 1 process divides into 2 branches, which function as a single axon • 1 branch (peripheral process) associated with dendrites • Other branch (central process) enters brain or spinal cord

  10. Structural Differences, cont….. • Multipolar: • Many processes arising from cell body: • 1 axon • Many dendrites • Most neurons whose cell bodies lie in the brain or spinal cord are multipolar. • Direction of impulse is ALWAYS from dendrites to axon.

  11. Functional Differences • Sensory (afferent) neurons • From peripheral body parts to the brain or spinal cord • Have specialized receptor ends at the tips of their dendrites OR • Dendrites closely associated with receptor cells in the skin or sensory organs. • Most are unipolar, but some are bipolar.

  12. Functional Differences, cont….. • Interneurons (association or internuncial neurons) • Lie entirely in the brain or spinal cord • Multipolar and link other neurons • Transmit impulses from one part of the brain or spinal cord to another • Motor (efferent) neurons • Multipolar • Carry nerve impulses from brain or spinal cord to effectors • Stimulate muscles or glands

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