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Physiology > Chapter 7 > Flashcards

Chapter 7 Flashcards

1
Q

What is the nervous system divided into?

A
  • central nervous system (brain and spinal cord)
  • peripheral nervous system (cranial and spinal nerves)
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2
Q

What are the 2 cells of the nervous system?

A

neurons and supporting cells (glial cells)

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3
Q

What are neurons?

A

functional units of the nervous system

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4
Q

What do glial cells do?

A

maintains homeostasis
- 5x more common than neurons

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5
Q

How do neurons gather and transmit information?

A
  • responds to stimuli (sensory)
  • produces and sends electrochemical impulses (electrical conduction)
  • releases chemical messages (neurotransmitters)
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6
Q

What are neurons made of? Where’s the nucleus?

A

1) cell body (with nucleus)
2) dendrites
3) axon

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7
Q

What is the cell body and it’s function?

A

nutritional center
- makes macromolecules

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8
Q

What are groups of cell bodies called in the CNS? PNS?

A

CNS: nuclei
PNS: ganglia

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9
Q

What do dendrites do? How?

A

receive information and convey it to cell body through ligand gated channels

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10
Q

What do axons do? How?

A

conduct impulses away from cell body through voltage gated channels

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11
Q

What are the 2 special transports provided by long axon length?

A

1) axoplasmic flow: moves soluble compounds toward nerve endings via rhythmic contractions of axon
- protein transportation
2) axonal transport: transport of vesicles, mitochondria, ion channels

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12
Q

What does axonal transport move? Which way?

A

large and insoluble compounds
- bidirectionally along microtubules
- FAST!

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13
Q

What does anterograde transport move? How?

A

moves materials away from cell body
- uses molecular motor kinesin

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14
Q

What does retrograde transport move? How?

A

moves materials toward cell body
- uses molecular motor dynein

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15
Q

How do viruses and toxins enter the CNS?

A

through retrograde transport

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16
Q

What are afferent neurons? Where do impulses go?

A

sensory neurons
- impulses INTO CNS

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17
Q

What are efferent neurons? Where do impulses go?

A

motor neurons
- impulses OUT of CNS

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18
Q

What are interneurons? Where are they located?

A
  • association
  • integrate nervous system activity
  • inside CNS only
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19
Q

What is a pseudounipolar neuron? Example?

A

cell body sits along side of single process
- sensory neurons

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20
Q

What is a bipolar neuron? Example?

A

dendrite and axon arise from opposite ends of cell body
- retinal neurons

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21
Q

What are multipolar neurons? Example?

A

have many dendrites and one axon
- motor neurons

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22
Q

What is the PNS equivalent of the supporting/glial cells?

A

Schwann cells: myelination of PNS axons
Satellite cells

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23
Q

How big are Schwann cells? What do they do?

A

1mm of 1 axon and wraps around
- electrically insulates axon

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24
Q

What are the supporting cells of the CNS?

A

oligodendrocytes, microglia, astrocytes, ependymal cells

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25
Q

What do oligodendrocyte do?

A

myelinates several CNS axons

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26
Q

What do ependymal cells do?

A

neural stem cells

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27
Q

What cells are involved in nervous system mantenance?

A

glial cells

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28
Q

What is the node of Ranvier?

A

unmyelinated gap between Schwann cells

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29
Q

Which nervous system does axon regeneration occur? Why?

A

PNS easier than CNS
- oligodendrocytes produce proteins that block regrowth

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30
Q

What happens when an axon in PNS is cut?

A
  • distal part degenerates
  • Schwann cells survive and form regeneration tube
  • tube releases chemical to attract growing axon
  • tube guides regrowing axon to synaptic site
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31
Q

What do neurotrophins do?

A
  • promote fetal nerve growth
  • required for survival of many adult neurons
  • important for regeneration
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32
Q

What is the most common glial cell?

A

astrocytes

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33
Q

What do astrocytes do?

A
  • buffering K+ levels
  • recycling neurotransmitters
  • regulating adult neurogenesis
  • releasing transmitters that regulate neuronal activity
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34
Q

What is the blood-brain barrier?

A

allows only specific compounds to enter brain

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35
Q

What makes up the blood-brain barrier?

A

capillary specializations in brain
- astrocyte induction
- gaps between adjacent cells are closed by tight junctions

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36
Q

What is resting membrane potential?

A

all cells have a negative internal charge and unequal distribution of ions

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37
Q

What causes the resting membrane potential?

A
  • large anions trapped inside cell
  • Na+/K+ pump keeps Na+ high outside the cell
  • K+ is very permeable and high inside cell (attracted by negative charges inside)
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38
Q

What affects resting membrane potential?

A

excitable cells
- rapid changes in permeability to ions
- neurons and muscles activate to generate and conduct electrical impulses

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39
Q

How is membrane potential measured?

A

1 electrode in the cell and 1 electrode outside

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40
Q

What is depolarization?

A

membrane potential is more positive

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41
Q

What is hyperpolarization?

A

membrane is more negative than resting potential

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42
Q

What is repolarization?

A

membrane returns to resting potential

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43
Q

Which leak channels are always open?

A

potassium (K+)

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44
Q

How are voltage-gated channels regulated?

A

opened by depolarization

45
Q

Are K+ and Na+ channels open in resting cells?

A

No they’re closed
- both voltage-gated

46
Q

How does the action potential graph look?

A

wave formed by rapid depolarization by Na+ influx and repolarization by K+ efflux

47
Q

Which way does action potential travel in an axon

A

axon hillock to synapse

48
Q

What happens during depolarization?

A
  • voltage-gating Na+ channels open
  • Na+ driven inward by electrochemical gradient -> depolarization = more channels open
  • positive feedback loop
  • causes rapid change from -70 to 30mV
49
Q

What happens during repolarization?

A
  • voltage-gated Na+ channels close and K+ opens
  • electrochemical gradient drives K+ outward
  • repolarizes axon back to RMP
50
Q

How does depolarization and repolarization occur?

A

diffusion
- after action potential, sodium-potassium pump extrudes Na+ and recovers K+

51
Q

What does it mean for an action potential to be all-or-none?

A

Once membrane potential reaches threshold, action potential is irreversibly fired

52
Q

What is true about action potentials?

A
  • propagate without decrement
  • produced by voltage gated channels
  • cannot summate
  • constant amplitude
53
Q

Where are voltage-gated channels found?

A

plasma membrane of axons

54
Q

What does increased stimulus intensity cause?

A

more action potentials are fired
- size of APs remain constant

55
Q

What is the absolute refractory period?

A

membrane cannot produce another action potential because Na+ channels are inactivated

56
Q

What is the relative refractory period?

A

voltage-gated K+ channels are open
- harder to depolarize to threshold

57
Q

How does a new action potential get generated?

A

process repeats all along axon
- amplitude is the same throughout

58
Q

How fast is conduction of an unmyelinated axon?

A

2 mph

59
Q

How fast is conduction in myelinated membranes?

A

0! Ions can’t flow through myelination

60
Q

Where do action potentials occur in myelinated axons?

A

in Nodes of Ranvier
- voltage-gated Na+ channels are present in the nodes

61
Q

How does action potential work in myelinated axons?

A

current from action potential at one node can depolarize next node to threshold
- saltatory conduction

62
Q

What is synapse?

A

connection between neuron (presynaptic) and another cell (postsynaptic)

63
Q

What is the common synapse in the nervous system?

A

chemical synapses via neurotransmitters
- electrical synapses are rare

64
Q

Where does depolarization flow in an electrical synapse?

A

presynaptic into postsynaptic cell through gap junctions

65
Q

What are gap junctions formed by? Where are they found?

A

connexin proteins
- found in smooth and cardiac muscles, brain, and glial cells

66
Q

What does the synaptic cleft separate?

A

terminal bouton of presynaptic from postsynaptic cell

67
Q

What is found in synaptic vesicles?

A

neurotransmitters

68
Q

How do neurotransmitters get released?

A

vesicles fuse with bouton membrane
- exocytosis

69
Q

What affects how much neurotransmitter is released?

A

directly related by frequency of action potentials

70
Q

How does synaptic transmission work?

A
  • action potential travels down axon to depolarize bouton
  • opens voltage-gated calcium channels in bouton (driven inward by gradient)
  • triggers exocytosis of vesicles and releases neurotransmitters
71
Q

How does calcium trigger exocytosis of vesicles?

A

activates calmodulin then protein kinase
- kinase phosphorylates regulatory proteins that promote fusion and exocytosis of vesicles

72
Q

What happens when a neurotransmitter (ligand) diffuses across the synaptic cleft?

A
  • binds to receptor proteins on postsynaptic membrane (opens ligand gated channels)
73
Q

What causes excitatory postsynaptic potentials (EPSPs)?

A

depolarization

74
Q

What causes inhibitory postsynaptic potentials (IPSPs)?

A

hyperpolarization

75
Q

Why are EPSPs and IPSPs graded potentials?

A
  • ligand gated channels
  • dendrite and neuron cell body only
  • variable in amplitude
  • propagate with decrement
  • summation
76
Q

What is the most widely used neurotransmitter?

A

acetylcholine
- used in brain and autonomic nervous system and all neuromuscular junctions

77
Q

What are the acetylcholine receptor subtypes?

A

nicotinic and muscarinic

78
Q

What do ligand-gated channels have?

A

a neurotransmitter receptor site and an ion channel

79
Q

How do ligand-gated channels open?

A

when a ligand/neurotransmitter binds

80
Q

What is a nicotinic acetylcholine channel formed by?

A

5 polypeptide subunits

81
Q

How does a nicotinic acetylcholine channel work?

A

opens when 2 acetylcholines bind (only 2 subunits contain binding sites)
- permits diffusion of sodium in and potassium out of postsynaptic cell
- inward flow of sodium dominates

82
Q

What signal do nicotinic channels produce?

A

EPSPs

83
Q

What are g protein-coupled channels?

A

1 subunit membrane polypeptide
- activates ion channel indirectly through g-proteins

84
Q

How do muscarinic acetylcholine channels work?

A
  • binding of 1 ACh activates g-protein cascade and affects gated potassium channels
  • open = hyperpolarization
  • close = depolarization
85
Q

What do acetylcholinesterase do?

A

inactivates acetylcholine
- stops action
- located in cleft

86
Q

What are the large synapses on skeletal muscles called?

A

end plates or neuromuscular junctions

87
Q

What do end plates produce?

A

large EPSPs (end-plate potentials)
- opens voltage gated channels beneath end plate
- cause muscle contraction

88
Q

What blocks ACh action at neuromuscular junctions?

A

curare

89
Q

What are examples of monoamine neurotransmitters?

A

serotonin
norepinephrine
dopamine

90
Q

What is serotonin derived from?

A

tryptophan

91
Q

What can tyrosine make?

A

norepinephrine and dopamine
- catecholamines

92
Q

What are monoamine neurotransmitters inactivated by?

A

presynaptic reuptake
- breakdown by monoamine oxidase (MAO)

93
Q

What are MAO inhibitors?

A

antidepressants

94
Q

What is serotonin involved in?

A

regulation of mood, behavior, appetite, and cerebral circulation

95
Q

What are SSRIs?

A

serotonin-specific reuptake inhibitors (antidepressants)
- block reuptake of serotonin, prolonging its action

96
Q

What are the 2 major dopamine systems in brain?

A

1) nigrostriatal dopamine system
2) mesolimbic dopamine system

97
Q

Where does nigrostriatal dopamine system originate from? What is it involved in? Degeneration causes what?

A
  • substrantia nigra
  • motor control
  • Parkinson’s disease
98
Q

What is the mesolimbic dopamine system involved in? Overactivity leads to what?

A
  • behavior and emotional reward
  • schizophrenia (treated by anti-dopamine drugs)
99
Q

What is norepinephrine used for in PNS? CNS?

A

PNS: sympathetic neurotransmitter
CNS: affects general level of arousal
- amphetamines stimulate pathways

100
Q

What are the main CNS excitatory neurotransmitters?

A

glutamate and aspartate (acidic)

101
Q

What is an example of an inhibitory neurotransmitter?

A

glycine

102
Q

How does glycine work as inhibitor? What inhibits glycine?

A
  • opens Cl- channels to hyperpolarize
  • Strychnine blocks glycine receptors
103
Q

What happens when strychnine works?

A

causes spastic paralysis

104
Q

What is GABA and its function? Degeneration can cause what?

A

gamma-aminobutyric acid (most common in brain)
- inhibitory
- opens Cl- channels
- Huntington’s disease

105
Q

What is true about EPSPSs?

A
  • graded in magnitude
  • no threshold
  • depolarization
  • summate
  • no refractory period
106
Q

What is spatial summation?

A

EPSPs from different synapses occur in postsynaptic cell at the same time

107
Q

What is temporal summation?

A

EPSPs that occur closely in time can summate before they fade

108
Q

What is postsynaptic inhibition?

A

GABA and Glycine produce IPSPs
- IPSPs dampen EPSPs
- hard to reach threshold

109
Q

When does presynaptic inhibition occur?

A

1 neuron synapses onto axon or bouton of another neuron
- inhibits release of its neurotransmitter

Physiology (18 decks)

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