Chapter 48 - Neurons, Synapses, & Signaling

Question 1

Describe types of neurons and their role in information processing.

Answer 1

• Sensory
  
  • Receives info. from internal/external environment
  • Send info from receptors to brain or ganglia (clusters of nerve cell bodies)
• Interneurons
  
  • Analyze and interpret input
• Motor neurons
  
  • Transmit signals to motor cells (muscle or glands)

Question 2

Describe neuron structure.

Answer 2

• Cell body:
  
  • Part of the neuron that houses the nucleus and other organelles
• Dendrites:
  
  • Receive messages from other cells
• Axons:
  
  • Send messages to other cells
• Myelin sheath:
  
  • Type of fat which covers the axon of some neurons and helps speed neural impulses
• Terminal branches of axons:
  
  • Forms junctions with other cells

Question 3

Define and describe how membrane potential is maintained.

Answer 3

• Membrane potential is the electrical difference in versus outside of the cell:
  
  • Intracellular fluid is negative (excess anions)
  • Extracellular fluid is positive (excess cations)
• Resting potential of the neuron is maintained by sodium-potassium pump.

Question 4

Describe how action potentials (nerve impulses) are generated.

Answer 4

Membrane potential changes in response to opening & closing ion channels

• Hyperpolarization:
  
  • When inside becomes more negative
  • ex: opening of potassium (K⁺) channels and cations move out
• Depolarization:
  
  • When inside becomes less negative
  • ex: opening of sodium (Na⁺) channels and cations move in
  • If enough, action potenial will occur
    
    • Positive feedback reaction occurs and positive charge flows down axon (sodium channels opening up down the axon)
    • Followed by potassium channels opening slowly and cations flow out restoing negative charge inside and prevents action potential from moving backwards.

Question 5

Describe how communication (synaptic transmission) occurs.

Answer 5

• Action potential depolarizes membrane at synaptic terminal
  
  • Some synapses are electrical:
    
    • gap junctions allow current to flow between cells for rapid, unvarying behavior
  • Most neurons transmit information via chemical synapses:
    
    • Calcium channels open and cations flow in
    • Synatpic vesicles cell fuse with membrane and release neurotransmitters via exocytosis
    • Neurotransmitters directly/indirectly control ion channels to cause post-synatpic potential:
      
      • Excitatory PSP: sodium cation in
      • Inhibitory PSP: potassium cation out
    • Neuron gets 1000’s of PSPs that derine if action potential is generated:
      
      • Temporal summation: occurs at single synapse
      • Spatial summation: occurs at different synapses