Exam 3 Flashcards
(194 cards)
1
Q
Audible range for humans
A
20 Hz- 20 kHz
2
Q
changes in air pressure from a sound wave change in a ______ manner
A
sinusoidal
3
Q
Main function of outer ear is to
A
capture sound and rout it to tympanic membrane
4
Q
Main function of middle ear is
A
amplification (~200x).
5
Q
Impedance mismatch -
A
relative difficulty that sound waves have moving through different media. This problem overcome by different mechanisms
6
Q
ossicles-
A
middle ear bones (malleus, incus, stapes)
7
Q
pressure on tympanic membrane is transferred to smaller surface area of _____
A
the oval window
8
Q
organ of corgi consists of the ______ membrane, ______ membrane, nerve cells and stereocilia
A
tectorial
basilar
9
Q
what 2 groups of stereo cilia are there?
A
inner hair cells and outer hair cells
10
Q
what are the relative shapes of the groups of inner and outer hair cells?
A
inner hair cells are in a line, outer hair cells are grouped in U shapes
11
Q
Which hair cells are most important in transducing and sending afferent signals?
A
inner hair cells
12
Q
Tonotopy –
A
different frequency information conveyed because of maximal displacement variability due to frequency
13
Q
who discovered tonotopy.
what theory did he propose?
A
Von Bekesy
Tonotopic theory of frequency discrimination
14
Q
Scala media
A
fluid that is in direct contact with the hair cells.
15
Q
Outer hair cells receive signal from the brain – have a motor response and can change their length and alter the properties of the ________. This increases the ___________ of the auditory system.
A
- tectorial membrane
- frequency discrimination capabilities
16
Q
Which end of cochlea is most flexible?
A
apex
17
Q
High Freq. generate max displacement at the _____, Low Freq max is as _____. This physical map of freq is called Tonotopy
A
- base
- Apex
18
Q
when sound vibrates the basilar membrane, there are 2 phases. In the upward phase, the shear force is towards:
In the downward phase the shear force is towards:
A
- tallest stereocilia
- shortest stereocilia
19
Q
hair cells are highly specialized ______ cells. Their apical surface contains _________, while the basal surface has the ___________
A
- epithelial
- The stereocilia
- synaptic end of the cell
20
Q
Hair cells detect changes in water pressure on _______
A
cupula
21
Q
Ampullae of Lorenzini –
A
electrodetectors that are used to detect electric fields in the environment (the head of a hammerhead shark)
22
Q
What do vestibular hair cells help do and how do they do it?
A
they are oriented in different ways in a liquid medium to help with balance
23
Q
what is the really long hair cell in stereocilia bundles?
A
kinocilium
24
Q
how are stereocilia in hair bundles oriented?
A
stairstep
25
how does a kinocilium differ from other hair cells?
it contains concentric rings of microtubules
26
shorter hair cells are connected to longer hair cells via
tip links
27
side to side movement does not depolarize. For hair cells to depolarize, movement in what plane must happen?
in the plane of shortest-longest cells
28
Mechanoelectrical transduction –
connecting proteins are thought to act as a ‘spring’ and expand/contract upon movement of hair cells. Expansion opens K+ channels
29
Bundle deflected toward shortest one –
| Deflected toward longest one –
- hyperpolarization
| - depolarization
30
how many channels does each stereo cilium have?
2
31
Special adaptation to facilitate high activity in stereocilia:
Potassium cycling – potassium depolarizes and repolarizes hair cell
32
hair cells can only directly report frequencies up to ___ kHz. After this point, the cells can't oscillate fast enough and the voltage is ______
- 3
| - continuous
33
What provides the high K+ content of the scala media?
Stria vascularis
34
How are hair cells able to keep solutions from opposite ends of the cell separate?
tight junctions
35
Hair cells:
| what solutions are the apical and basal side in contact with?
apical- endolymph
| basal- perilymph
36
which chambers are in contact with the apical and basal sides of hair cells
apical- scala media
| basal- scala tympani
37
Explain how a hair cell sends a signal to neurons in 3 basic steps.
1.
2.
3.
1. mechanical movement on apical side opens K+ channels, causing a depolarization
2. depolarization opens Ca++ channels on basal side.
3. Ca++ influx causes NT release
38
How does a hair cell depolarize after an action potential?
V gated and Ca++ gated K+ channels on basal side release K+ into the perilymph
39
_________ receive oscillatory pattern of NT from the hair cells up to (3Khz) and produce oscillatory patters of action potentials. The action potentials are “phase-locked” to oscillatory.
oscillatory nerve fibers
40
K+ levels in hair cells are mostly maintained ______
passively
41
why is it beneficial for hair cells to use only K+ for action potentials?
they would not have to constantly use ATP to pump Na+ back out of cells
42
action potentials from sound waves are considered ________, as they fire at the same point in a wave oscillation over and over.
phase-locked
43
Characteristic frequency-
freq at which an ANF can respond to lowest intensity sound
44
the higher a frequency gets, the _____ action potentials are produced
more
45
Labeled line system –
mechanism for distinguishing different frequencies.
46
above 3 kHz, frequency information comes not from oscillation information but from ___________
location of nerve on cochlea that picks up the frequency strongest.
47
the primary auditory complex interprets sound based on
the location of stimulation within the complex
48
sound localization is achieved through the _____
medial superior olive (MSO)
49
MSO has neurons that are _____ detectors.
coincidence
50
sound localization at frequencies greater than 3 kHz is determined by:
interaural intensity differences (head produces an acoustical shadow; lower intensity on opposite side of head from sound)
51
LSO-
lateral superior olive
52
MNTB-
medial nucleus of the trapezoid body
53
Explain how the source of sounds greater than 3 kHz in frequency are specially determined.
LSO's on both sides of the head will fire and MTNB's from both sides of the head will inhibit the opposite LSO's excitation. Whichever side the sound came from will be more intense on that side, leading to a net excitation from the side that the sound came from, canceling out the MNTB inhibition from the other side and producing a net excitation from the LSO closer to the sound. The MNTB on the side closer to the sound will also produce a net inhibition of the LSO opposite the sound.
54
the trigeminal system detects:
irritants in the environment
55
Two physical routes for olfactory information:
Orthonasal – via nostrils
| Retronasal – via oral cavitiy
56
Olfactory neurons detect signals in the ______ and transmit information through the ______ to the _______
- nasal cavity
- cribriform plate
- olfactory bulb
57
ar olfactory nerve axons myelinated?
| Why is this ok?
- No
| - because they do not have to send signals that far.
58
```
Amygdala –
Entorhinal cortex –
Orbitofrontal cortex –
Hypothalamus –
Hippocampal formation –
```
- aggression
- emotions
- taste + olfactory info is combined
- regulates feeding
- learning and memory
59
does concentration of an odorant matter?
yes, some odors are pleasant at one concentration and not pleasant at another
60
Which system is least acute in humans?
olfactory
61
How does the relative size of olfactory bulb in humans compare to rats?
rats' are much larger relatively
62
Bloodhounds have _____ ORC's
| Humans have _____ ORC's
4 billion
| 12 million
63
Where are olfactory receptor proteins located?
cilia of ORCs
64
Bowmans gland –
responsible for secreting mucus
65
ORC cilia-
actin filled projections that increase surface area.
66
Supporting cell (sustinacular) protection/defense cells near ORCs can:
detoxify airborne compounds.
67
Mucus contains _____ and _______ to fight off pathogens
- MACS
| - antibodies
68
ORCs are very vulnerable due to:
| Can they regenerate?
- being in direct contact with environment.
| - Yes
69
How often can rodents renew their entire olfactory system?
6-8 weeks
70
Nobel prize in 2004 – __________ in 1991 discovered a lot about odorand receptor genes. All of them are _____, encoded by a huge (__%) chunk of the genome
- Linda Buck and Richard Axel
- GPCR
- 5
71
When comparing the membrane current of an ORN after odorant is sprayed on the cilia vs the cell body, which is stronger?
sprayed on cilia
72
What allows odorant receptor proteins to be so variable and specific to certain compounds?
variable amino acids
73
How many receptor genes/receptor proteins are expressed per ORN?
one
74
How specific are ORN receptor proteins?
they can be sensitive to 1 compound or sensitive to several
75
how do particular receptors in the olfactory epithelium tend to be distributed.
they tend to be grouped in distinct zones. The zones overlap, but the receptors tend to not disperse outside of their particular zone
76
alpha subunit of olfactory g proteins called-
Golf
77
odorant transduction is not as simple as stimulus depolarization. Explain the steps involved:
Odorant binds to receptor protein, activating Golf--> activates AC III---> makes cAMP--> activates Na+/Ca++ channel (which mildly depolarizes). The Ca++ influx activates Ca++ gated Cl- channels that do the major depolarizing.
78
NKCC
Na/K/Cl cotransporter that move Cl- into the cell for a high cytosolic Cl- level. Needed to achieve Cl- efflux to depolarize
79
Knocking out any component of the odorant transduction pathway leads to:
no sense of smell
80
Are there interneurons in the odorant pathway?
nope
81
How is the strength of an odorant signal conveyed?
frequency of AP
82
How are ORNs able to all sort themselves into their specific glomeruli?
during development, the axons display specific traits that guide them to the right spot. As new ORN's regenerate, they follow their brothers to the right glomerulus
83
How much convergence happens from ORN's onto mitral cells?
tons. 25,000 ORN axons converge onto 25 mitral cells.
84
using fluorescent proteins expressed in glomeruli, researchers testing on drosophila were able to determine that:
specific odorant would activate specific glomeruli. (the application of 1 odorant would activate maybe 1 or 2 glomeruli exclusively)
85
Vomeronasal system-
pheromone detection system. found primarily in rodents and carnivores
86
location of vomeronasal system-
opening is on top of the gum line
87
where does the vomeronasal organ transmit it's information?
to the accessory olfactory bulb. (found in the brain of rodents and carnivores. Primate vomeronasal system is pseudogenes)
88
```
What is the importance in our ability to detect these tastes?
Salt-
Sweet-
Umami-
Sour-
Bitter-
```
Salt: Ability to detect salt is important for osmoregulation
Sweet: Detection of sweet foods helps detect high-energy carbohydrates
Umami: (Japanese for delicious) – allows for the detection of proteins, amino acids, and nucleotides
Sour: some sour tastes are desirable (citrus), but a sour flavor can also indicate spoiled food
Bitter: because many bitter compounds are toxic) – plant alkaloids
89
Salty, sweet, umami, and sour are detectable in the ___ range, while bitter is detectable in the ___ range
mM
| micromolar
90
Papilla-
infoldings of tongue
91
3 types of papillae and their location on tongue:
Foliate are on the back and sides of tongue. Front is Fungiform. Circumvallate are on back of oral cavity.
92
Taste buds on back of oral cavity send signals through the ______
vagus nerve (cranial nerve X)
93
Circumvallate papillae send info to brain via ______
| Fungiform papillae send info to brain via _______
- cranial nerve IX (glossopharyngeal)
| - cranial nerve VII (facial nerve)
94
Taste responses are localized.
Bitter and Sour-
Salty and Sweet-
- back and sides
| - front and sides
95
Taste buds stimulate stimulate salivary glands and trigger ________
the rest of digestive system to get ready for food.
96
humans have approx ____ taste buds, each containing approx _____ cells.
- 4000
| - 50-150
97
The 4 types of cells in a taste bud:
Type 1 – support cells (aka glial cells)
Type 2 – taste receptor cells for bitter, sweet, and umami.
Type 3 – taste receptor cells for salty and sour
Type 4 – basal cells – stem cell population that regenerates TRCs (TRCs last ~ 2 weeks)
98
flavor molecules are recieved by ____ at the ____. Information is transferred by the taste cells to _______
- microvilli
- taste pore
- gustatory afferent axons
99
Cranial nerve VII – facial nerve – innervates ______ papillae
Cranial nerve IX – glossopharyngeal – takes information from ________ papillae
Cranial nerve X – vagus nerve – takes information from ___________
- fungiform
- circumvallate + folliate
- pharynx and esophagus
100
Denatominum benzoate –
bitter compound used in research
101
salts and acids, being ions, are able to trigger action potentials via ______.
Sweet, bitter, and umami tastes trigger action potentials via _______.
- ion channels
| - G-protein coupled receptors
102
It is thought that the NT involved in gustatory is:
serotonin
103
Na+ channel of taste receptors is not voltage gated, but rather _______
amiloride-sensitive. (an increase in Na+ opens channels)
104
The H+ sensitive TRP channel in gustatory cells opens in response to _____
increases in H+ nearby
105
What proteins make up these receptors?
Bitter:
Sweet:
Amino acids (umami):
- T2R
- T1R2 + T1R3
- T1R1 + T1R2
106
Describe the pathway for taste transduction (the bitter receptor example)
mT2R8: (bitter receptor) Alpha subunit (gustducin) when activated separates and activates PDE (not sure why). Beta/Gamma interacts with PLC which cleaves IP3 off of PIP2, IP3 binds receptors on endoplasmic reticulum which opens Ca+ channels leading to an increase of cytosolic Ca+. High Ca+ activates TRPM5 channels which lets Na+ into the cell and depolarizes cell. Pannexins (ATP channel) require increased Ca+ and depolarization to be open. ATP diffuses out of this channel. Hemichannel (gap junction). Can be described as a Neurotransmitter release channel (the neurotransmitter being ATP).
ATP--> gustatory afferent P2XRs (ligand-gated ion channels)
107
Gustatory cortex is also called _________. Its function is to ______________
- orbitofrontal cortex
| - combine taste, olfactory, and trigeminal (detection of irritants) to form flavors.
108
Acid-sensing TRCs can also detect _____
Carbon dioxide
109
Acetolamide –
medication to help alleviate altitude sickness. When you take it and then drink a carbonated drink, it will taste flat/not right. It is a carbonic anhydrase inhibitor
110
CAR4 –
catalyzes reaction from CO2 to protons. Enough protons build up and activate TRP channel
111
The GI tract can detect what 3 tastes:
sweet, bitter, and umami
112
The development of the nervous system generally occurs in this order, with some overlap:
```
Proliferation
Patterning
Differentiation
Migration
Axon Outgrowth
Pathfinding, targeting
```
113
Blastula –
hollow ball of cells
114
Gastrulation –
three germ layers originate from the process of gastrulation and major axes of the organism are established
115
First steps in development:
1.
2.
3.
1. cell division to increase cell number
2. gastrulation to establish 3 germ layers
3. neurulation establishes rudiments of CNS
116
Nervous system is derived from what germ layer?
ectoderm
117
_____ is important in development for signaling, but degenerates upon maturity.
notochord
118
Signals coming from _______ cause portions of ectoderm to form into _______ (what will make the brain)
- mesoderm
| - neural plate
119
____________: specialized cells formed from mesoderm, organizing centers that send signals to surrounding cells and cause them to differentiate.
Floor Plate & Roof Plate
120
blocks of epidermal tissue, give rise to vertebrate of spinal chord.
Somites:
121
```
timeline of CNS development
Day 18-
Day 20-
Day 22-
Day 24-
```
- Neural plate forms
- neural groove and neural crest form
- neural tube formed; neural crest still present. Somites formed
- neural fold remnants still present, neural tube now spinal chord; sensory ganglion formed
122
Once the neural tube is totally formed, the part that will eventually become the brain is subdivided into 3 parts:
prosencephalon, mesencephalon, and Rhombencephalon
123
Cranial and spinal ganglia along the neural tube will give rise to:
nerves
124
the 3 portions of an early neural tube will again subdivide into what 5 sections?
telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon
125
______ forms the cortex of the brain (massive growth)
telencephalon
126
Determination –
the process of acquiring cell fate. Typically, a cell’s fate is determined before it looks any different than other cells. This is due to genomic control of development.
127
Induction:
one group of cells sends a signal that influences
| the fate of another group of cells
128
Differentiation:
the acquisition of a cell’s phenotype
129
Key factors affecting neural development: (6 things)
Segregation of proteins at cell division
Diffusible signaling molecules and their receptors
Cell-cell interactions (receptor-mediated)
Cell-substrate interactions (extracellular matrix)
Signaling pathways leading to expression of transcription
factors
Transcription factor activity leading to regulation of gene
expression
130
in development, when you need a stem cell to divide, not only must the cleavage plane be determined, ____________ must also be separated
proteins involved in differentiating cells into different types
131
list 5 proteins that must be separated during stem cell cleavage during development
Ecm, Collagen, proteoglycans, laminin, fibronectin
132
Precursor cells –
stem cells with unlimited mitotic potential
133
Progenitor cells –
limited mitotic potential
134
Neuroblasts + glioblasts –
post-mitotic
135
Precursor cells in vertebrate neuroepithelium are connected to both the _____ and _____ surfaces during G1, S, G2
neural tube lumen and pial surface
136
When precursor cells in vertebrate neuroepithelium undergo mitosis, they disconnect from the pial and neural tube lumen surfaces. They will either divide with a horizontal or vertical plane of division. What are the differences between how they divide.
Horizontal plane- asymmetrical division that leads to a progenitor cell and a neuroblast or glial cell
Vertical plane- symmetrical division that leads to precursor and/or progenitor cell(s)
137
______ protein inhibits neuronal fate
Notch
138
. In horizontal plane, cells don’t get equal notch distribution so _______ can be formed. In vertical plane, both cells get notch and they __________
- neuroblasts
| - continue to differentiate
139
Bone morphogenetic protein –
group of secreted factors that are a subgroup of a larger group of factors called transforming growth factor proteins (TGF).
140
Describe the mechanism by which neuronal and glial differentiation occurs from ectoderm.
1. Presence of BMP causes ectoderm to remain so. Presence of Noggin/chordin turns ectoderm into neuroectoderm
2. TGF-betas and Sonic hedgehog then establish organizing centers and gradients for further development. (TGF-beta forms roof plate, sonic hedgehog forms floor plate)
3. bHLH transcription factors promote formation of proneural genes (neuronal fate), but if notch is present these TF's aren't encoded and tissue remains precursor.
4. Next, if Olig 1/2 or Nkx2.1 is present, oligodendrocytes form, but if proneural bHLHs are present they will not form.
5. Then, if Notch/Nrg is present, astrocytes form, but if Proneural bHLHs are present they will not develop and the precursor cells will become ependyma.
141
In a cross section of spinal chord, what mRNAs can be seen expressed and where?
sonic hedgehog is expressed in the NC and FP. Noggin is expressed in the RP and slightly in the FP and NC. The noggin in RP interferes with BMP signaling.
142
In a general sense, how is the nervous system able to organize and develop itself with such complexity?
Different signaling molecules have different localizations and gradients that drive different transcription factors in different zones. All these factors combine to give rise to cells of different fates
143
2 stages of embryo development:
1. Regional specification
| 2. segment identity
144
____ genes contribute to segment identity
Hox
145
In humans the most strict anterior--> posterior expression of developing tissues occurs in the ______
hindbrain and spinal chord
146
If you misexpress Antp in drosophila, you get:
legs in the fly's head. Take home is that TFs are responsible for encoding a lot
147
Repeating segments called _______ express different combinations of _____ genes to create differential neuronal expressions
rhombomeres
| Hox
148
Fusion of neural tube leads to expression of:
Basic Helix-Loop-Helix (BHLH)
149
Snail 1 + Snail 2 –
downregulate the expression of cell adhesion proteins. This causes the neural crest cells to dissociate or become ‘mesenchymal’, free to migrate along different pathways in the developing embryos.
150
Guiding the migration of neural crest cells includes: (3 things)
1. Secreted molecules
2. Surface of other cells
3. Interaction with extracellular matrix (ECM molecules) – Fibronectin, Laminin
151
Four populations of neural crest cells (labeled in diagram):
1. Sensory ganglia
2. Autonomic ganglia – some parasympathetic, but mostly sympathetic ganglia that sits close to spinal chord
3. Adrenal medulla – have cromaffin cells that release epinephrine
4. Melanocytes – give rise to pigment cells of the skin
152
TFs first tell neural crest progenitor cells to ______, then other sets of TFs tell migrated cells _________
- migrate
| - what to become
153
Radial Glial-
These cells function as a scaffold for other cells to migrate. Forms in an inside out fashion. Newer cells migrate to the surface.
154
new neurons in CNS migrate from their site of origin, down the axons of ______ towards the ________ surface.
radial glia
| pial
155
Signaling is extremely important to neuron migration, as a neuron traversing a radial glia must be able to _______, _______, and ______ in order to successfully migrate
associate, migrate, and detach
156
Reelin-
large glycoprotein secreted by cells at pial surface. Tells neurons to hop off radial glia
157
A neuron's key structure in sensing embryonic environment
growth cones
158
Pioneer axon-
lays down pattern of later growing axons.
159
growth cone is a ______ structure.
| Where is it located on a neuron?
- sensory
| - end of the growing axon
160
the ends of growth cones are made of:
actin
161
the pointed extensions at tips of growth cones are called:
| the flattened portions are called:
- filopodia
| - lanellipodia
162
growth cone receptors are found on ______
filopodium at surface of leading edge
163
_____ has a very sensitive, concentration dependent effect on growth cone activity.
Ca++
164
Tropic factors-
| Trophic factors-
- guidance molecules
| - general growth and survival of neurons
165
Tropic interactions: (3 types)
Chemo-attraction
Chemo-repulsion
Contact repulsion
166
Contact-mediated attraction-
because of protein interactions, axons stick together
167
Contact-mediated repulsion–
a pioneer axon has particular proteins that repel it from other axon; it explores the embryonic environment. Other axons follow.
168
_______ growth cones have no filopodia.
fasiculated
169
Target Trophic support –
The targets of the outgrowing molecule often provide the trophic signal
170
list the 6 major classes of axon guidance molecules:
Extracellular matrix molecules, Cell Adhesion Molecules, Cadherins, Netrin/slit family, semaphorins, Ephrins
171
What happens if a growing axon never reaches it's target?
the neuron dies
172
Extracellular Matrix Molecules include _____, _____, _____. Receptors are called _____ receptors. Signal produced could be _____ , _____, or _____. Patterns of ECM differ throughout the embryo, resulting in the varying signals received by this receptor class.
- Fibronectin, Laminin, Collagen
- Integrin
- repulsive, attractive, permissive
173
CAMs (Cell Adhesion Molecules) – big family of proteins. Generally promote_______. These receptors bind to _______ and adhere cells together
- interactions
| - each other
174
Cadherins – also cell adhering molecules, but these are _____ dependent. If an embryo lacks _____, it will just fall apart.
- Ca++
| - Ca++
175
Netrin/slit family – mediate _______ and _______. Secreted molecules have specific receptors that guide the developing neuron.
- chemoattraction
| - chemosecretion
176
Semaphorins – promote ______
inhibition
177
Ephrins – when they interact with ____, they signal in their cells. This is important for extremely specific geographic targeting (i.e. specific cells to make synapses with).
-Eph's
178
Netrin receptors:
DCC and Unc5
179
Netrin is a chemo_____.
attractant
180
The slit receptor is:
Robo
181
Slit receptors mediate chemo_______.
repulsion
182
Netrin is released from the _____ cells, and the crossing axons have to display _____. This ensures that axonal crossing happens at the right time in the developing embryo.
- midline
| - DCC
183
One Drosophila mutant had axons that kept crossing over the midline, meaning there had to be another signal that allowed the axon to ‘ignore’ the Netrin signal after crossing over. The axons begin to express _____, which is repulsed by the protein ____. The _____ repulsion wins over the _____ attraction.
- Robo
- Slit
- Slit
- DCC
184
Who won the nobel prize for identifying the first neurotropic factor?
Rita Levi-Montalcini and Stanley Cohen
185
Describe what occurs when a growth cone encounters each of these chemicals.
1. Cams/cadherins
2. semaphorins
3. neurotrophins
4. slit/Robo
5. Netrins/DCC
1. contact mediated attraction
2. contact mediated repulsion
3. target trophic support
4. chemorepulsion
5. chemoattraction
186
NGF is a member of a protein family called:
neurotrophins
187
The variable selectivity of tyrosine kinase receptors allows various neurons to respond selectively to different ________
neurotrophins
188
neurotrophin signaling can inhibit _____ and promote _____
- programmed cell death
| - outgrowth
189
during development, motor neurons are over produced as an "_________"
insurance policy
190
what regulates survival of motor neurons that innervate body parts during development.
Target-derived trophic support
191
Explain how target derived trophic factor discovery explained motor neuron development
motor neurons are over produced, and once an area is innervated the extra ones die off. If a limb bud is chopped off, all the neurons will die. If an extra limb bud is attached at a limb site, more motor neurons than normal will survive.
192
What method was used to determine the kind of macromolecules neurotrophins were?
halo assay
193
How was the halo assay carried out?
dorsal root ganglion were cultured and several experiments were carried out, destroying 1 macromolecule at a time until they found that snake venom actually enhanced growth. From mouse saliva (analogous to snake venom) they extracted the protein NGF.
194
NGF was experimentally shown to increase the survival rate of neurons and when NGF was inhibited in a developing mouse, it's sensory ganglia were:
atrophied, shriveled, and underdeveloped.
