Chapter 8 Neurons

Question 1

What are the 4 CNS Glial supporting cells?

Answer 1

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

Question 2

What are the two PNS Glial supporting cells?

Answer 2

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

Question 3

What are neurons?

Answer 3

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

Question 4

What is the axonal transport?

Answer 4

• 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

Question 5

What are myelin sheats and how are they formed?

Answer 5

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
   

Question 6

Can neurons regenerate?

Answer 6

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

Question 7

What is memebrane potential?

Answer 7

• 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
  

Question 8

What is it called when membrane potential changes?

Answer 8

• 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

Question 9

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

Answer 9

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

Question 10

What are the two types of electrical signals?

Answer 10

Graded and action potential

Question 11

What is graded potential?

Answer 11

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

Question 12

What is action potential?

Answer 12

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

Question 13

IDK

Answer 13

Question 14

What are the three thresholds of graded potential?

Answer 14

1. Threshold
   -Minimum depolarization
   needed to cause an AP
   -55mV
2. Subthreshold
   -Graded potential
   below threshold
   
   -55mV so no action potential sent
3. Suprathreshold
   -Graded potential
   above threshold so action potential is sent
   

Question 15

What are Excitory postsynaptic potential and inhibitory postsynaptic potential?

Answer 15

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)

Question 16

What is spatial summation?

Answer 16

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

Question 17

How does temporal summation work?

Answer 17

• 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
  
  

Question 18

How do gated channels regulate ion movement?

Answer 18

• 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
   Neurotransmitters
3. Voltage-gated
   Respond to electrical signals

Question 19

How do voltage gate Na+ channels work?

Answer 19

• 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

Question 20

How does action potential work?

Answer 20

• 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

Question 21

What is the all or nothing law?

Answer 21

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

Question 22

How does stimulus intsnsit effect action potential?

Answer 22

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

Question 23

How conduction work for unmyelinated sheaths?

Answer 23

• 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

Question 24

How does conduction work for myelinated sheaths?

Answer 24

• 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
  

Question 25

What influences the speed of action potential?

Answer 25

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

Question 26

What is a synapse?

Answer 26

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 ![]()

Question 27

What are the two types of synapses?

Answer 27

1. Electrical 2. Chemical

Question 28

What is an electrical synapse?

Answer 28

* Electrical synapses occur in smooth muscle, cardiac muscle, and some neurons in brain * Cells are joined by gap junctions ![]()

Question 29

What are chemical synapses?

Answer 29

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Question 30

What is ACh or Acetylcholine?

Answer 30

* 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 ![]()

Question 31

Know this table!

Answer 31

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