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Flashcards in Chapter 8 Neurons Deck (31):

What are the 4 CNS Glial supporting cells?

  1. Astrocytes
    Blood-brain barrier
  2. Oligodendrocytes
    Myelin sheaths
  3. Ependymal cells
    Line ventricles
  4. Microglia


What are the two PNS Glial supporting cells?

  1. Schwann cells
    Also called neurolemmocytes
    Myelin sheaths
  2. Satellite cells
    Support cell bodies


What are neurons? 

  • Neuron is Functional unit of Nervous System
    Carries out primary function of NS
  • Classified functionally 3 types
    -Sensory Afferent neurons
    -Motor Efferent neurons 
  • Amitotic neurons do not rgenerate


What is the axonal transport?

  • Slow axonal transport

Moves material by cytoplasmic flow 0.2–2.5 mm/day

  • Fast axonal transport

Moves organelles at rates of up to 400 mm/day
Forward transport: from cell body to axon terminal
Retrograde transport: axon terminal to cell body


What are myelin sheats and how are they formed? 

  1. Myelinated axons conduct impulses more rapidly
    -Myelin gives tissues white color = white matter
    -Cell bodies and axons = grey matter
    -Node of Ranvier is left open
  2. In PNS, Schwann cells wrap around axons to form the myelin sheath
  3. In CNS, oligodendrocytes myelinate several axons
  4. Grey matter is unmyelinated while white matter is myelinated


Can neurons regenerate? 

  • When an axon in PNS is cut, the severed part degenerates, and a regeneration tube forms
  • CNS axons are not as able to regenerate


What is memebrane potential? 

  • Neurons have a resting potential of −70mV

Na+/K+ pumps
Negative molecules inside the cell
Permeability of the membrane to ions

  • At rest, there is a high concentration of K+ inside the cell and Na+ outside the cell


What is it called when membrane potential changes? 

  • Neurons and muscle cells can change their membrane potentials
    -Called excitability
    -Caused by changes in permeability to certain ions
    -Ions follow electrochemical gradient = concentration gradient and attraction to opposite charges
    -Flow of ions is called ion current


What is the name of neurons at rest? What are the three other membrane potential phases? 

  1. At rest, a neuron is considered polarized when the inside is more negative than the outside
  2. When the membrane potential inside the cell increases = depolarization
    Occurs when positive ions enter the cell, is excitatory
  3. A return to resting potential = repolarization
  4. When the membrane potential inside the cell decreases = hyperpolarization
    Occurs when positive ions leave the cell, is inhibitory. -85mV


What are the two types of electrical signals? 

Graded and action potential


What is graded potential? 


  • Graded potentials
    -Variable strength
    -Decreases with distance
    -Can sum to cause an AP
    -Short distance communication


What is action  potential?

  • Action potentials
    -Constant strength
    -All or none
    -Generated at axon hillock
    -Long distance rapid communication




What are the three thresholds of graded potential? 

  1. Threshold
    -Minimum depolarization
    needed to cause an AP
  2. Subthreshold
    -Graded potential
    below threshold

    -55mV so no action potential sent
  3. Suprathreshold
    -Graded potential
    above threshold so action potential is sent


What are Excitory postsynaptic potential and inhibitory postsynaptic potential? 

Membrane potential changes depending on which ion channels open

  1. Na+ or Ca2+  channels - graded depolarization
    Excitatory postsynaptic potential (EPSP)
  2. K+ or Cl− channels – graded hyperpolarization
    Inhibitory postsynaptic potential (IPSP)


What is spatial summation? 

Spatial summation occurs when excitatory potentials from many different presynaptic neurons cause the postsynaptic neuron to reach its threshold and fire. 


How does temporal summation work? 

  • Two stimuli that follow one another in succession
  • Graded potentials that arrive at trigger zone overlapping in time may sum to threshold and trigger AP


How do gated channels regulate ion movement? 

  • Changes in membrane potential are due to the flow of ions through ion channels
    Closed at rest but open when ____

3 Types gated ion channels:

  1. Mechanically gated
    Open in response to physical force
  2. Chemically gated
  3. Voltage-gated
    Respond to electrical signals


How do voltage gate Na+ channels work? 

  • Na+ channels open if membrane potential depolarizes to -55mV
  • This is called threshold

Sodium rushes in due to electrochemical gradient
Membrane potential increases until channels become inactivated +30mV 


How does action potential work?

  • Occurs at threshold (−55mV)
  • Voltage-gated Na+ channels open, Na+ rushes in
  • As cell depolarizes more Na+ channels open, Na+ enters cell
  • At +30mV repolarization as   Na+ channels close and K+ channels now fully open
  • Actually overshoots resting potential to -85mV which is hyperpolarization
  • Na+/K+ pumps reestablish resting potential of -70mV



What is the all or nothing law? 

Once threshold is reached, an action potential will happen
Size of stimulus will not affect the size of AP
Size of stimulus will not affect AP duration


How does stimulus intsnsit effect action potential? 

A stronger stimulus will make action potentials occur more frequently
A stronger stimulus may also activate more neurons – called recruitment


How conduction work for unmyelinated sheaths? 

  • When an AP occurs on a neuron membrane, voltage- gated Na+ channels open as a wave down the entire axon
  • The conduction rate is slow because so many APs are generated 


How does conduction work for myelinated sheaths? 

  • Myelin provides insulation, increasing speed
    Nodes of Ranvier allow Na+  and K+ across membrane  every 1−2 mm
    Action potentials “leap” from node to node
  • In demyelinating diseases, ions leak slowing conduction


What influences the speed of action potential? 

  1. Myelination
    Myelinated axons  faster
    Less ion leakage out of cell
  2. Diameter of axon
    Larger diameter  faster
    Reduces resistance


What is a synapse? 

Communication point between a neuron and the cell it is signaling 
In the CNS, this second cell will be another neuron
In the PNS, the second cell will be a muscle or gland
If two neurons in pathway
Presynaptic neuron is before synapse;  postsynaptic neuron is after synapse


What are the two types of synapses? 

  1. Electrical
  2. Chemical


What is an electrical synapse?

  • Electrical synapses occur in smooth muscle, cardiac muscle, and some neurons in brain
  • Cells are joined by gap junctions


What are chemical synapses? 


What is ACh or Acetylcholine? 

  • ACh is a neurotransmitter that opens ion channels when it binds to its receptor
  • Can be excitatory or inhibitory, depending on the receptor and which ion channel it opens

-Excitatory in all somatic motor neurons
-Excitatory or Inhibitory in autonomic motor neurons


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