PNS Development (soft chalk)

At paravertebral ganglion they may

1) synapse with neurons or ascend or 2) descend in the sympathetic trunk to synapse at other levels.

Trunk neural crest cells differentiate into the following structures:

1. melanocytes 2. Schwann cells *3. glial cells in peripheral ganglia 4. chromaffin cells of adrenal medulla* 5. dorsal root ganglia 6. sympathetic chain ganglia 7. prevertebral sympathetic ganglia 8. enteric parasympathetic ganglia of gut 9. abdominopelvic parasympathetic ganglia

Cranial neural crest cells differentiate into the following structures:

1. pharyngeal arch skeletal and connective tissue components 2. bones of neurocranium 3. pia and arachnoid *4. parafollicular cells of thyroid* 5. odontoblasts 6. sensory ganglia of CN V, VII, IX, and X *7. parasympathetic ganglia of the head* 8. aorticopulmonary septum (outflow tract)

They are classified into three groups, according to their embryologic origins:

A. Somatic Efferent Cranial Nerves B. Nerves of Pharyngeal Arches C. Special Sensory Nerves

The nervous system has two main components:

A. The central nervous system (CNS) B. The peripheral nervous system (PNS)

Special Sensory Cranial Nerves

The olfactory nerve (CN I) The optic nerve (CN II) The vestibulocochlear nerve (CN VIII)

The PNS and its central pathways are traditionally divided into two functional systems:

The somatic nervous system The autonomic nervous system

Somatic Efferent Cranial Nerves

The trochlear (CN IV), abducent (CN VI), hypoglossal (CN XII), and the greater part of the oculomotor (CN III)

___ pairs of cranial nerves form during the _____ weeks

Twelve fifth and sixth

All these segmentally arranged sympathetic ganglia are connected in

a bilateral chain by longitudinal nerve fibers forming the sympathetic trunks.

The fibers destined for a particular developing muscle group become arranged in

a bundle, forming a ventral nerve root.

The central processes of neurons in the spinal ganglion form

a single bundle - dorsal sensory root - that grows into the spinal cord, opposite the apex of the dorsal horn of gray matter.

During the fifth week, neural crest cells in the thoracic region migrate

along each side of the spinal cord and form paired cellular masses (ganglia) dorsolateral to the aorta.

The abducent nerve (CN VI)

arises from nerve cells in the basal plates of the metencephalon.

The trochlear nerve (CN IV)

arises from nerve cells in the somatic efferent column in the posterior part of the metencephalon.

The oculomotor nerve (CN III)

arises from the basal plates of the mesencephalon.

The olfactory nerve (CN I)

arises from the nasal ectodermal placode. The ectodermal epithelium in the roof of each nasal cavity becomes specialized to form the olfactory epithelium. Some epithelial cells differentiate into olfactory receptor cells (neurons). The axons of these cells constitute the olfactory nerves.

The nerve fibers of the dorsal nerve root are formed by

axons derived form neural crest cells that migrate to the dorsolateral aspect of the spinal cord, where they differentiate into the cells of the spinal ganglion (dorsal root ganglia).

This process occurs when?

before, during and after the closure of the neuropores.

The axons of cells in the spinal ganglia are at first ___ but ___

bipolar, but the two processes soon unite in a T-shaped fashion.

Motor nerve fibers arise from

cells in the basal plates of the developing spinal cord (axons of the ventral horn cells) as rootlets along its ventrolateral surface

The somatic nervous system

conscious sensations + innervation of the voluntary (striated) muscles of the body

The peripheral nervous system (PNS)

consists of all components of the nervous system outside of the CNS. Thus, the PNS consists of cranial nerves and ganglia, spinal nerves and ganglia, autonomic nerves and ganglia, and the enteric nervous system.

The central nervous system (CNS)

consists of the brain and spinal cord.

The PNS develops as an integrated system, essentially in _____ sequence.

cranial-to-caudal

Detachment and migration of the neural crest cells occur in a

craniocaudal wave, from the mesencephalon to the caudal end of the spinal neural tube.

Separation of the neural crest from the neural folds or neural tube is referred to as

delamination of neural crest cells.

Immediately after being formed, a mixed spinal nerve divides into

dorsal and ventral primary rami

Neural crest cells are a unique population of cells that arise from

dorsal part of the forming neural tube during neurulation

These cells undergo an ____ transformation as ______

epithelial-to-mesenchymal transformation (different than that occurring as cells undergo ingression through the primitive streak) as they detach from the neural tube.

The vagus nerve (CN X)

is formed by fusion of the nerves of the fourth and sixth pharyngeal arches. Originates in myelencephalon.

The optic nerve (CN II)

is formed by more than a million nerve fibers that grow into the diencephalon from neuroblasts in the primordial retina. Because the retina develops from the evaginated wall of the forebrain, the optic nerve actually represents a fiber tract of the brain.

The trigeminal nerve (CN V)

is the nerve of the first pharyngeal arch, but it has an ophthalmic division that is not a pharyngeal arch component. Originates in metencephalon.

The facial nerve (CN VII)

is the nerve of the second pharyngeal arch. Originates in metencephalon.

The glossopharyngeal nerve (CN IX)

is the nerve of the third pharyngeal arch. Originates in myelencephalon.

After the sympathetic trunks have formed, axons of sympathetic neurons, located in ______ pass to a ____

located in the intermediolateral cell column (lateral horn) of the thoracolumbar segments T1-L3 of the spinal cord paravertebral ganglion

Their axons are distributed to

muscles derived from the head myotomes (preotic and occipital).

The unipolar neurons in the spinal ganglia (dorsal root ganglia) are derived from

neural crest cells that migrate to the dorsolateral aspect of the spinal cord.

The PNS arises from the

neural tube + two groups of cells outside of the neural tube: neural crest cells and ectodermal placodes.

The presynaptic parasympathetic fibers arise from

neurons in nuclei of the brainstem and in the sacral region of the spinal cord

The fibers from the brainstem leave through the

oculomotor (CN III), facial (CN VII), glossopharyngeal (CN IX), and vagus (CN X) nerves.

The vestibulocochlear nerve (CN VIII)

originates in the otic placode. It consists of two kinds of sensory fiber in two bundles; these fibers are known as the vestibular and cochlear nerves. The vestibular nerve originates in the semicircular ducts, and the cochlear nerve proceeds from the cochlear duct, in which the spiral organ (of Corti) develops.

The fibers of the traditional cranial root (of CN XI) are now considered to be

part of CN X.

The postsynaptic neurons are located in

peripheral ganglia or in plexuses near or within the structure being innervated (e.g., the pupil of the eye and salivary glands).

The neural crest gives rise to cells that form most of the

peripheral nervous sytem and autonomic nervous sytem.

The cells of origin of these nerves are located in the

somatic efferent column (derived from the basal plates) of the brainstem.

The hypoglossal nerve (CN XII)

somatic motor fibers originate from the myelencephalon.

Other presynaptic fibers pass through the paravertebral ganglia without synapsing, forming

splanchnic nerves to the viscera.

The autonomic nervous system

strictly motor - controls most of the involuntary, visceral activities of the body.

trigeminal (CN V), facial (CN VII), glossopharyngeal (CN IX), and vagus (CN X)

supply the embryonic pharyngeal arches; thus, the structures that develop from these arches are innervated by these CNs

Functionally, the ANS can be divided into

sympathetic (thoracolumbar) and parasympathetic (craniosacral) parts.

The neural tube differentiates mainly into

the CNS

The sympathetic nervous sytem originates from

the basal plate of the neural tube and the neural crest cells.

The gut contains its own nervous system called

the enteric nervous system.

nuclei for all cranial nerves are present by...

the fourth week of development

The ventral primary ramus

the major division of each spinal nerve, contributes to the innervation of the limbs and ventrolateral parts of the body wall. The major nerve plexuses (cervical, brachial, and lumbosacral) are formed by ventral primary rami.

The spinal accessory nerve (CN XI) emerges from

the myelencephalon

The autonomic system itself consists of two divisions:

the parasympathetic division - promotes the anabolic visceral activities characteristic of periods of peace and relaxation the sympathetic division - controls the involuntary activities that occur under stressful "fight or flight" conditions

The dorsal primary ramus

the smaller division, innervates the dorsal axial musculature, vertebrae, posterior intervertebral joints, and part of the skin of the back.

The fibers of the CN XI supply

the sternocleidomastoid and trapezius muscles.

The trochlear (CN IV), abducent (CN VI), hypoglossal (CN XII), and the greater part of the oculomotor (CN III) are homologous with

the ventral roots of spinal nerves. Sensory roots, corresponding to the dorsal roots of spinal nerves, are absent.

Neural crest cells are traditionally grouped based on

their specific regional contributions to structures of the embryo.

Other neural crest cells migrate to

to the area of the heart, lungs, gastrointestinal tract, adrenal medulla, where they form terminal ganglia in sympathetic organ plexuses, located near or within these organs.

The distal processes of spinal ganglion cells grow

toward the ventral nerve root and eventually join it to form a mixed spinal nerve.

Cranial nerves of Pharyngeal Arches

trigeminal (CN V), facial (CN VII), glossopharyngeal (CN IX), and vagus (CN X)

Each of these systems are composed of

two-neuron pathways consisting of preganglionic and postganglionic neurons.

what type of cells make up the dorsal root ganglion

unipolar neurons

Some neural crest cells migrate

ventral to the aorta and form neurons in the preaortic ganglia, such as the celiac and mesenteric ganglia.

Subsequently, they migrate to many specific locations in the body,

where they differentiate into a remarkable variety of structures.