Neuroscience

The Peripheral Neuropathy Solution

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Peripheral Nervous System

Spleen Surface MesodermPineal Gland Ectoderm Frog

Clinical Correlate

Neural plate

Neural fold Neural \ fold

Reduced levels of alpha-feto protein are seen in mothers of fetuses with Down syndrome.

Notochordal process

Ectoderm Mesoderm Endoderm

Notochord

Neural groove

Neural crest

Neural fold

Neural tube

Rostral" '?. J neuropore

Failure to close results in ancephaly causing polyhydraminos and increased alpha-feto protein

Neural crest

Neural crest

Caudal neuropore (closes at 27D)

Failure to close results in spina bifida alpha-feto protein

Figure IV-1-1. Third Week Neurulation

Table IV-1-1. Germ Layer Derivatives

Ectoderm

Mesoderm

Endoderm

Surface ectoderm

Muscle

Forms epithelial parts of:

Epidermis

Smooth

Tonsils

Hair

Cardiac

Thymus

Nails

Skeletal

Pharynx

Inner ear

Connective tissue

Larynx

Enamel of teeth

All serous membranes

Trachea

Lens of eye Anterior pituitary Parotid gland

Bone and cartilage

Blood, lymph, cardiovascular organs

Bronchi Lungs

Urinary bladder Urethra

Tympanic cavity Auditory tube GI tract

Neuroectoderm Neural tube Central nervous system Retina S> N^VC

Adrenal cortex

Gonads and internal reproductive organs

Spleen

Pineal gland Neurohypophysis Glial Cells

Kidney and ureter Dura mater

Forms parenchyma oh

Liver

Pancreas

Tonsils

Neural crest

Thyroid gland

Adrenal medulla

Parathyroid glands

Ganglia

Glands of the GI tract

Sensory

Submandibular gland

Autonomic

Sublingual gland

Pigment cells

Schwann cells

Satellite cells

Meninges

Pia and arachnoid mater

Pharyngeal arch cartilage

Odontoblasts

Parafollicular (C) cells

Aorticopulmonary septum

Endocardial cushions

Primordial germ cells

Early blood and blood vessels

Epithelia of the gut not derived from endoderm

medical 309

Dura Mater Head Pelvic

To viscera of w head and neck

Superior cervical ganglion

Prevertebral Ganglia

Prevertebral ganglia

Smooth muscle ' and glands of • the hindgut and pelvic viscera

Lumbar splanchnic nerves

*Erector pili muscle, sweat glands, cutaneous smooth muscle

Thoracic splanchnic nerves

Prevertebral ganglia

Sympathetic chain

To viscera of w head and neck

Superior cervical ganglion

Middle cervical ganglion Vertebral ganglion Cervicothoracic ganglion

1 r Heart, trachea, bronchi, lungs (thorax)

Thoracic splanchnic nerves

Prevertebral ganglia

Smooth muscle ' and glands of • the hindgut and pelvic viscera

Lumbar splanchnic nerves

Prevertebral ganglia

*Erector pili muscle, sweat glands, cutaneous smooth muscle

Sympathetic chain

Clinical Correlate

Lesions at arrows result in Homer syndrome (ptosis, miosis, and anhydrosis),

Figure IV-1-3. Overview of Sympathetic Outflow

Figure IV-1-5. Overview of Parasympathetic Outflow

Parasympathetic Terminal Ganglia

Terminal ganglia

o>4ATerrrilnal I ganglia

Terminal ganglia

Hindgut and pelvic viscera (Including the bladder^, and erectile tissue)

Ciliary ganglion

Ciliary m.

Submandibular V"

Sublingual gland

Pterygopalatine Lacrimal gland ganglion Nasal mucosa'*"" Oral mucosa

Otic ganglion

Viscera of the thorax and abdomen (foregut and midgut)«------/o;

Midbrain

«A^MHMMfln

Pons

J Medulla I

Table IV-1-3. Parasympathetic = Craniosacral Outflow

Origin

She of Synapse

Innervation

Cranial nerves III, VII, IX

4 cranial ganglia

Glands and smooth muscle of the head

(in or near the walls of viscera)

Viscera of the neck, thorax, foregut, and midgut

Pelvic splanchnic nerves S 2, 3,4

Terminal ganglia

(in or near the walls of viscera)

Hindgut and pelvic viscera (including the bladder and erectile tissue)

Chapter Summary

The peripheral nervous system (PNS) consists of 12 pairs of cranial nerves, 31 pairs of spinal nerves with their related sensory and motor ganglia, and the peripheral part of the autonomic nervous system. The afferent and efferent neurons in the PNS convey somatic and visceral (autonomic) functions to and from the central nervous system (CNS).

Cells of Nervous System

The basic functional cell for conducting motor and sensory functions within the nervous system is the neuron. Neurons in the CNS are myelinated by oligodendrocytes, and in the PNS neurons are myelinated by Schwann cells. Oligodendrocytes myelinate multiple axons but Schwann cells myelinate only a segment of one neuron.

The skeletal motor neurons and preganglionic motor neurons in the CNS develop from the neural tube, whereas the sensory neurons and postganglionic neurons located in sensory or motor ganglia, respectively, in the PNS derive from neural crest cells.

Neurulation and the development of the nervous system begin in the third week of development As the primitive streak regresses caudally, the notochord develops in the midaxis of the embryo between the buccopharyngeal membrane and the doacal membrane. The appearance of the notochord then induces the ectoderm overlying the notochord to form the neural plate composed of neuroectoderm cells. The neural plate is wide at the cranial end and tapers caudally. By the end of the third week, the lateral margins of the neural plate thicken and become elevated to form the neural folds with the neural groove located centrally between the two folds. The neural folds then grow over the midline and begin to fuse to form the neural tube. Closure of the neural tube begins in the cervical region and continues aanially and caudally. The cephalic (cranial neuropore) and the caudal (caudal neuropore) ends of the neural tube dose last. Failure of closure of the cranial and caudal neuropores results in anencephaly and spina bifida (see following chapter). Alpha-feto protein levels are increased with the neural tube defects. During closure of the neural tube, neural crest cells are formed from neuroectoderm at the margins of the neural folds. The neural crest cells migrate throughout the embryo and form a number of cell types (Table IV-1-1).

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