12.2

• neurons

  basic functional units of the nervous system

  send and receive signals

  communication, information processing, control
• cell body (soma)

  • large nucleus and nucleolus
  • perikaryon (cytoplasm)
  • free fluid inside cell body
  • mitochondria (produce energy)
  • RER and ribosomes (synthesize proteins)
• cytoskeleton of perikaryon

  • neurofilaments and neurotubules
  • intermediate filaments and microtubules
  • neurofibrils
  • bundles of neurofilaments
  • support for dendrites and axon
• dendrites

  • short and highly branched
  • extending from cell body
  • dendritic spines
  • find processes on dendrites
  • receives information from other neurons
  • 80-90% of neuron surface area
• nissl bodies

  • dense areas of RER and ribosomes
  • makes nervous tissue grey (grey matter)
• axon

  • single, long cytoplasmic process
  • propagates electrical signals
  • action potential happens here
• axoplasm

  • cytoplasm of axon
  • neurofibrils, neurotubules, enzymes, organelles
• axolemma

  • plasma membrane of axon
  • covers axoplasm
• initial segment

  • base of axon
• axon hillock

  • thick region
  • attaches initial segment to cell body
  • PRIOR to initial segment
• collaterals

  • branches of the axon
• telodendria

  • fine extensions of the distal axon
• axon terminals (synaptic terminals)

  • tips of telodendria
• anaxonic neurons

  • small
  • all cell processes look similar
  • found in brain and special sense organs
• bipolar neurons

  • small (and rare)
  • one dendrite, one axon
  • special sense organs
• unipolar neurons (pseudounipolar neurons)

  • axon and dendrites are fused
  • cell body to one side
  • most sensory neurons of PNS
• multipolar neurons

  • one long axon or 2+ dendrites
  • common in CNS
  • all motor neurons that control skeletal muscles
• sensory neurons (afferent neurons)

  • uni polar
  • cell bodies grouped in sensory epithelia
• somatic sensory neurons

  • monitor external environment (skeletal muscles)
• visceral sensory neurons

  • monitor internal environment (organs)
• type of sensory receptor

  interocepters

  monitor internal systems

  internal senses
• type of sensory receptor

  extroceptors

  monitor external systems

  complex senses
• type of sensory receptor

  proprioceptors

  monitor position and movement of skeletal muscle joints
• motor neurons

  carry instructions from CNS to peripheral effectors

  made of efferent fibers (axons)
• anaxonic neuron

  A) cell body

  
• bipolar neuron

  
• unipolar neuron

  
• multipolar neuron