Chapter 15 Axon guidance and selection Flashcards
the _______ on the end of the axon is its locomotory apparatus
- has been called a neural crest cell on a leash
growth cone
Neurons are determined by position in the neural tube and its “Birthday”
1) ventrolateral margin of the neural tube become _______
2) dorsal neural tube neurons become _______ and _______
1) motor neurons
2) interneurons; sensory inputs
Every muscle cell in the body is innervated by a _______
single neuron
Early neurons towards the ________, while later neurons towards the _______
inside
outside
- Later neurons must travel past “older” neurons and are exposed to new TF’s
As each wave of neurons develops, it is influenced by those already present:
- expression of a series of _______ and _______ transcription factors
Hox
Lim
_______ genes are involved in controlling cell surface molecules that interact with ECM components to either attract or repel neuronal growth
Lim
Axonla targets are determined _______ the axon even begins to extend
before
_______ don’t require axonal signal transduction to find targets
motor neurons
The newt, Taricha torso (california newt), produces a neurotoxin, _______, that blocks neural transmission. Pieces of T. torosa embryos were grafted onto the embryos of other newt species during early development, and they still produced fully developed, normal adults
tetrodotoxin
The newt experiment showed that axons do not rely on ________ to travel, identify, or connect with their target cells. Other signals must be involved
signal transduction
Axons are guided by _______ signals, both diffusible and ECM components
chemical
Axon growth cones prefer to travel on surfaces that are “sticky” to them. usually ECM ligands bound by axon cell surface receptors. Axons show _______ and _______ contact guidance
adhesion and repulsion
What are the 4 major classes of ECM/Guidance molecules?
1) ephrin
2) semaphorin
3) netrin
4) slit
_______ and _______ are ECM molecules
Ephrin
semaphorin
_______ and _______ are diffusible molecules
netrin
slit
EX) guided by ECM components:
In the developing vertebrate limb, the Ti1 sensory neuron extents its axon towards the CNS. Upon reaching a band of _______ expressing cells it is inhibited and reorients its growth. When filopodia of its grwowth cone near _______ expressing cells, they turn and grow toward them
Semaphorin1
Cx1
EX) guided by diffusible molecules:
1) Commissural neurons in the spinal cord are guided by _______, ______, and _______ gradients
2) Netrins are bound by _______ and _______ receptors on the axon growth cone
3) ______ binds to _______ receptors and repels neurons from crossing the midline
1) Netrins, Shh, Slit
2) DCC and DSCAM
3) Slit; Robo
Guided diffusible molecules:
_______ forms a steep gradient produced by the floor plate cells
Netrin-1
Guided diffusible molecules:
_______ is produced by the lower region of the spinal cord, not in the floor plate
Netrin-2
________: to guide neural growth
neurotropic
_______: to keep neurons alive
neurotrophic
Target cells secrete specific chemical signals called _______
neurotropins
- work over short distances as chemo-attractants and chemo-repulsives
What are some examples of neurotropins? (3)
1) Nerve Growth Factor
2) Brain-derived neurotrophic factors (BDNF)
3) Neurotrophins 3 and 4/5
________: bind to cannabinol receptors during development regulating the development of neurons in the cerebrum and cerebral cortex
Endocannabinoids
_______ cannabinoids (marijuana) can also bind to these receptors regulating the development of neurons in the cerebrum and cerebral cortex
exogenous
What are the 3 main branches of the trigeminal ganglion?
1) ophthalmic (eyes)
2) Maxillary (upper jaw)
3) Mandibular (lower jaw)
Growth of neurons to the trigeminal targets is regulated by _______ from the target tissues and differential expression of the _______ on the neurons
BMP’s
BMP receptors
Once the target cell is identified, a _______ is constructed
- allows specialized cell-cell connection
- specialized membranes on both neuron and target cell
synapse
the synapse is a junction for the transmission and reception of _______
neurotransmitters
Synaptic cleft fills with a specific form of _______
laminin
- may serve as a stop signal for axonal growth
Junctions of the synaptic cleft are often stabilized by _______
N cadherins
More than half of the neurons produced during development _______ as a result of competition between neurons for limited _______
apoptose
neurotrophins
_______: is a disease caused by decreased production of BDNF
Huntington’s disease
_______: is a disease characterized by GDNF and CDNF reductions and reduced survival of midbrain dopaminergenic neurons
Parkinsons disease
- (CDNF: cerebral dopamine neurotrophic factor)
