Lecture 6: Nervous Tissue

• What are the two categories of cells found in nervous tissue?

  Neurons and Neuroglia
• What role do neurons play in nervous tissue?

  They generate electrical impulses and transfer them
• How do neurons transfer impulses?

  Via synapses, specialized contact areas
• What percentage of nervous tissue is made up of neuroglia?

  Over 90%
• What functions do neuroglia serve?

  Provide structural, metabolic, and protective support
• What is a distinctive feature of neurons?

  Variety of shapes and sizes
• What is the axon hillock also known as?

  The trigger zone for action potentials
• What is the cell body of a neuron also called?

  Soma or Perikaryon
• What organelles are abundant in the perikaryon?

  Endoplasmic reticulum and polysomes
• Why do neurons lack centrioles?

  They are amitotic and do not divide
• What are the parts of a neuron?

  • Cell body (Soma/Perikaryon)
  • Axon
  • Dendrites
• What are unipolar neurons also known as?

  Primary sensory neurons
• How do unipolar neurons function?

  They innervate peripheral tissues for sensory information
• Where are bipolar neurons located?

  In the retina, cochlea, and olfactory epithelium
• What characterizes multipolar neurons?

  Numerous processes with one axon and many dendrites
• What type of neurons are sensory or afferent neurons?

  Neurons that respond to sensory stimuli
• What do motor or efferent neurons do?

  Transmit signals from CNS to muscles or glands
• What are interneurons also known as?

  Association neurons
• Where are interneurons primarily located?

  In the brain and spinal cord
• What neurotransmitter do cholinergic neurons release?

  Acetylcholine
• What do adrenergic neurons release?

  Norepinephrine or epinephrine
• What is the synapse?

  Where the axon terminal meets another cell
• What are the components of a synapse?

  • Presynaptic membrane
  • Synaptic cleft
  • Postsynaptic membrane
• What is the difference between electrical and chemical synapses?

  Electrical synapses allow rapid signal passage
• How does a neurotransmitter function in a chemical synapse?

  It carries the signal to the postsynaptic cell
• Where is the neurotransmitter stored?

  In synaptic vesicles
• What percentage of nervous tissue is made up of neurons?

  10%
• What is the role of neuroglia in the nervous system?

  Support, protect, and nourish neurons
• What are the types of neuroglia in the CNS?

  Ependymal cells, astrocytes, oligodendrocytes, microglia
• What are the types of neuroglia in the PNS?

  Satellite cells and Schwann cells
• What is the function of satellite cells?

  Surround neuronal cell bodies in ganglia
• What do Schwann cells do in the PNS?

  Support axons and form myelin sheaths
• How do Schwann cells form myelin sheaths?

  By wrapping their plasma membrane around axons
• What is the length range of internodes formed by Schwann cells?

  25–1000 μm
• What is the node of Ranvier?

  The junction between each internode of myelin
• What do oligodendrocytes do in the CNS?

  Form myelin sheaths around adjacent axons
• What size axons do oligodendrocytes typically myelinate?

  Most axons over 1 μm in diameter
• What percentage of neuroglia do microglia comprise?

  10–20%
• What is the primary function of microglia?

  Act as macrophages in the CNS
• What do astrocytes provide for neurons?

  Structural and metabolic support