The placodes, the neural crest and their derivatives. Development of the peripheral nervous system

what is a placode?

a thickening of ectoderm which develops into a sensory organ or ganglion

when does the lens placodes appear?

by the time neurulation is finished

when do the otic vesicles appear?

same time as lens placodes

what will the otic placodes give rise to?

structures of the inner ear

what will the nasal placodes give rise to?

olfactory epithelium of the nose

where will the trigeminal placodes arise?

close to the 1st pharyngeal groove

what will the trigeminal placode give rise to?

trigeminal ganglion

where will the epibranchial placodes arise?

close to the pharyngeal arches

how many epibranchial placodes do we have?

4

what will the epibranchial placodes give rise to?

inferior (geniculate) ganglion of facial nerve

inferior (petrosal) ganglion of glossopharyngeal nerve

inferior (nodose) ganglion og vagus nerve

which placode is unpaired?

adenohypophyseal placode

what will the adenohypophyseal placode form?

rathke’s pouch

describe the formation of the neural crest

during fusion of the neural folds many cells dissociate from the neural folds.

these folds deposit between the neural tube and the surface ectoderm, forming the neural crest

which structures do the neural crest cells give rise to? (16)

* CT and bones of face and skull
* dermis of face and neck
* melanocytes
* odontoblasts
* meninges of the forebrain
* smooth muscle cells of vessels of face and forebrain
* cranial nerve ganglia
* schwann cells
* glial cells
* dorsal root ganglia
* sympathetic chain
* parasympathetic ganglia of GI tract
* aorticopulmonary septum in the heart
* preaortic ganglia
* c-cells of thyroid gland
* adrenal medulla

SOMATIC NS: what are the peripheral afferent nerves peripheral branches of? where does it originate from?

peripheral branches of the axons of the pseudounipolar cells of the dorsal root ganglia

neural crest cells

SOMATIC NS: what are the peripheral efferent nerves axons of? where does it originate from?

axons of the motor neurons in the ventral horn of the spinal cord

originate from basal plates of the neural tube

what do the sympathetic and parasympathetic ganglia arise from?

neural crest and neural tube

what do the enteric NS arise from?

neural crest cells which migrate to GI tract