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)
2
Q
What are the 2 cells of the nervous system?
A
neurons and supporting cells (glial cells)
3
Q
What are neurons?
A
functional units of the nervous system
4
Q
What do glial cells do?
A
maintains homeostasis
- 5x more common than neurons
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)
6
Q
What are neurons made of? Where’s the nucleus?
A
1) cell body (with nucleus)
2) dendrites
3) axon
7
Q
What is the cell body and it’s function?
A
nutritional center
- makes macromolecules
8
Q
What are groups of cell bodies called in the CNS? PNS?
A
CNS: nuclei
PNS: ganglia
9
Q
What do dendrites do? How?
A
receive information and convey it to cell body through ligand gated channels
10
Q
What do axons do? How?
A
conduct impulses away from cell body through voltage gated channels
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
12
Q
What does axonal transport move? Which way?
A
large and insoluble compounds
- bidirectionally along microtubules
- FAST!
13
Q
What does anterograde transport move? How?
A
moves materials away from cell body
- uses molecular motor kinesin
14
Q
What does retrograde transport move? How?
A
moves materials toward cell body
- uses molecular motor dynein
15
Q
How do viruses and toxins enter the CNS?
A
through retrograde transport
16
Q
What are afferent neurons? Where do impulses go?
A
sensory neurons
- impulses INTO CNS
17
Q
What are efferent neurons? Where do impulses go?
A
motor neurons
- impulses OUT of CNS
18
Q
What are interneurons? Where are they located?
A
- association
- integrate nervous system activity
- inside CNS only
19
Q
What is a pseudounipolar neuron? Example?
A
cell body sits along side of single process
- sensory neurons
20
Q
What is a bipolar neuron? Example?
A
dendrite and axon arise from opposite ends of cell body
- retinal neurons
21
Q
What are multipolar neurons? Example?
A
have many dendrites and one axon
- motor neurons
22
Q
What is the PNS equivalent of the supporting/glial cells?
A
Schwann cells: myelination of PNS axons
Satellite cells
23
Q
How big are Schwann cells? What do they do?
A
1mm of 1 axon and wraps around
- electrically insulates axon
24
Q
What are the supporting cells of the CNS?
A
oligodendrocytes, microglia, astrocytes, ependymal cells
25
What do oligodendrocyte do?
myelinates several CNS axons
26
What do ependymal cells do?
neural stem cells
27
What cells are involved in nervous system mantenance?
glial cells
28
What is the node of Ranvier?
unmyelinated gap between Schwann cells
29
Which nervous system does axon regeneration occur? Why?
PNS easier than CNS
- oligodendrocytes produce proteins that block regrowth
30
What happens when an axon in PNS is cut?
- distal part degenerates
- Schwann cells survive and form regeneration tube
- tube releases chemical to attract growing axon
- tube guides regrowing axon to synaptic site
31
What do neurotrophins do?
- promote fetal nerve growth
- required for survival of many adult neurons
- important for regeneration
32
What is the most common glial cell?
astrocytes
33
What do astrocytes do?
- buffering K+ levels
- recycling neurotransmitters
- regulating adult neurogenesis
- releasing transmitters that regulate neuronal activity
34
What is the blood-brain barrier?
allows only specific compounds to enter brain
35
What makes up the blood-brain barrier?
capillary specializations in brain
- astrocyte induction
- gaps between adjacent cells are closed by tight junctions
36
What is resting membrane potential?
all cells have a negative internal charge and unequal distribution of ions
37
What causes the resting membrane potential?
- 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)
38
What affects resting membrane potential?
excitable cells
- rapid changes in permeability to ions
- neurons and muscles activate to generate and conduct electrical impulses
39
How is membrane potential measured?
1 electrode in the cell and 1 electrode outside
40
What is depolarization?
membrane potential is more positive
41
What is hyperpolarization?
membrane is more negative than resting potential
42
What is repolarization?
membrane returns to resting potential
43
Which leak channels are always open?
potassium (K+)
44
How are voltage-gated channels regulated?
opened by depolarization
45
Are K+ and Na+ channels open in resting cells?
No they're closed
- both voltage-gated
46
How does the action potential graph look?
wave formed by rapid depolarization by Na+ influx and repolarization by K+ efflux
47
Which way does action potential travel in an axon
axon hillock to synapse
48
What happens during depolarization?
- 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
What happens during repolarization?
- voltage-gated Na+ channels close and K+ opens
- electrochemical gradient drives K+ outward
- repolarizes axon back to RMP
50
How does depolarization and repolarization occur?
diffusion
- after action potential, sodium-potassium pump extrudes Na+ and recovers K+
51
What does it mean for an action potential to be all-or-none?
Once membrane potential reaches threshold, action potential is irreversibly fired
52
What is true about action potentials?
- propagate without decrement
- produced by voltage gated channels
- cannot summate
- constant amplitude
53
Where are voltage-gated channels found?
plasma membrane of axons
54
What does increased stimulus intensity cause?
more action potentials are fired
- size of APs remain constant
55
What is the absolute refractory period?
membrane cannot produce another action potential because Na+ channels are inactivated
56
What is the relative refractory period?
voltage-gated K+ channels are open
- harder to depolarize to threshold
57
How does a new action potential get generated?
process repeats all along axon
- amplitude is the same throughout
58
How fast is conduction of an unmyelinated axon?
2 mph
59
How fast is conduction in myelinated membranes?
0! Ions can't flow through myelination
60
Where do action potentials occur in myelinated axons?
in Nodes of Ranvier
- voltage-gated Na+ channels are present in the nodes
61
How does action potential work in myelinated axons?
current from action potential at one node can depolarize next node to threshold
- saltatory conduction
62
What is synapse?
connection between neuron (presynaptic) and another cell (postsynaptic)
63
What is the common synapse in the nervous system?
chemical synapses via neurotransmitters
- electrical synapses are rare
64
Where does depolarization flow in an electrical synapse?
presynaptic into postsynaptic cell through gap junctions
65
What are gap junctions formed by? Where are they found?
connexin proteins
- found in smooth and cardiac muscles, brain, and glial cells
66
What does the synaptic cleft separate?
terminal bouton of presynaptic from postsynaptic cell
67
What is found in synaptic vesicles?
neurotransmitters
68
How do neurotransmitters get released?
vesicles fuse with bouton membrane
- exocytosis
69
What affects how much neurotransmitter is released?
directly related by frequency of action potentials
70
How does synaptic transmission work?
- 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
How does calcium trigger exocytosis of vesicles?
activates calmodulin then protein kinase
- kinase phosphorylates regulatory proteins that promote fusion and exocytosis of vesicles
72
What happens when a neurotransmitter (ligand) diffuses across the synaptic cleft?
- binds to receptor proteins on postsynaptic membrane (opens ligand gated channels)
73
What causes excitatory postsynaptic potentials (EPSPs)?
depolarization
74
What causes inhibitory postsynaptic potentials (IPSPs)?
hyperpolarization
75
Why are EPSPs and IPSPs graded potentials?
- ligand gated channels
- dendrite and neuron cell body only
- variable in amplitude
- propagate with decrement
- summation
76
What is the most widely used neurotransmitter?
acetylcholine
- used in brain and autonomic nervous system and all neuromuscular junctions
77
What are the acetylcholine receptor subtypes?
nicotinic and muscarinic
78
What do ligand-gated channels have?
a neurotransmitter receptor site and an ion channel
79
How do ligand-gated channels open?
when a ligand/neurotransmitter binds
80
What is a nicotinic acetylcholine channel formed by?
5 polypeptide subunits
81
How does a nicotinic acetylcholine channel work?
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
What signal do nicotinic channels produce?
EPSPs
83
What are g protein-coupled channels?
1 subunit membrane polypeptide
- activates ion channel indirectly through g-proteins
84
How do muscarinic acetylcholine channels work?
- binding of 1 ACh activates g-protein cascade and affects gated potassium channels
- open = hyperpolarization
- close = depolarization
85
What do acetylcholinesterase do?
inactivates acetylcholine
- stops action
- located in cleft
86
What are the large synapses on skeletal muscles called?
end plates or neuromuscular junctions
87
What do end plates produce?
large EPSPs (end-plate potentials)
- opens voltage gated channels beneath end plate
- cause muscle contraction
88
What blocks ACh action at neuromuscular junctions?
curare
89
What are examples of monoamine neurotransmitters?
serotonin
norepinephrine
dopamine
90
What is serotonin derived from?
tryptophan
91
What can tyrosine make?
norepinephrine and dopamine
- catecholamines
92
What are monoamine neurotransmitters inactivated by?
presynaptic reuptake
- breakdown by monoamine oxidase (MAO)
93
What are MAO inhibitors?
antidepressants
94
What is serotonin involved in?
regulation of mood, behavior, appetite, and cerebral circulation
95
What are SSRIs?
serotonin-specific reuptake inhibitors (antidepressants)
- block reuptake of serotonin, prolonging its action
96
What are the 2 major dopamine systems in brain?
1) nigrostriatal dopamine system
2) mesolimbic dopamine system
97
Where does nigrostriatal dopamine system originate from? What is it involved in? Degeneration causes what?
- substrantia nigra
- motor control
- Parkinson's disease
98
What is the mesolimbic dopamine system involved in? Overactivity leads to what?
- behavior and emotional reward
- schizophrenia (treated by anti-dopamine drugs)
99
What is norepinephrine used for in PNS? CNS?
PNS: sympathetic neurotransmitter
CNS: affects general level of arousal
- amphetamines stimulate pathways
100
What are the main CNS excitatory neurotransmitters?
glutamate and aspartate (acidic)
101
What is an example of an inhibitory neurotransmitter?
glycine
102
How does glycine work as inhibitor? What inhibits glycine?
- opens Cl- channels to hyperpolarize
- Strychnine blocks glycine receptors
103
What happens when strychnine works?
causes spastic paralysis
104
What is GABA and its function? Degeneration can cause what?
gamma-aminobutyric acid (most common in brain)
- inhibitory
- opens Cl- channels
- Huntington's disease
105
What is true about EPSPSs?
- graded in magnitude
- no threshold
- depolarization
- summate
- no refractory period
106
What is spatial summation?
EPSPs from different synapses occur in postsynaptic cell at the same time
107
What is temporal summation?
EPSPs that occur closely in time can summate before they fade
108
What is postsynaptic inhibition?
GABA and Glycine produce IPSPs
- IPSPs dampen EPSPs
- hard to reach threshold
109
When does presynaptic inhibition occur?
1 neuron synapses onto axon or bouton of another neuron
- inhibits release of its neurotransmitter
