Principles of Human Anatomy & Development: Embryonic Folding to Somatic PNS

Flashcards covering embryonic trilaminar disk development, germ layer derivatives, embryonic folding, somite differentiation, vertebral formation, and somatic PNS structure.

Surface Ectoderm

The outermost primordial germ layer derivative that gives rise to the epidermis of the skin, hair, nails, sweat and mammary glands, half of the pituitary gland, tooth enamel, membranous structures of the inner ear, and the lens of the eye.

Neural Tube

A primordial structure derived from ectoderm that gives rise to the brain, spinal cord, retina, and half of the pituitary gland.

Neural Crest

Cranio-caudally segmented tissue derived from ectoderm that gives rise to ganglia of the peripheral nervous system, part of the adrenal gland, pigment cells, pharyngeal arches, and some soft tissues of the head.

Notochord

The flexible midline rod (from Greek noton, back + chorde, cord) that induces the neural tube and later becomes the nucleus pulposus of the intervertebral discs.

Somite

A segmented block of paraxial mesoderm (from Greek soma, body) representing the body's earliest visible segmentation; gives rise to skeletal muscle, the skeleton except the skull, dermis of the skin, and connective tissue of the body wall.

Intermediate Mesoderm

A region of mesoderm lateral to the somites that gives rise to the urogenital system, including kidneys, gonads, ovaries, and associated ducts and glands.

Lateral Plate Mesoderm

The lateral region of mesoderm that gives rise to visceral smooth muscle and connective tissue, serous membranes (pleura, pericardium, peritoneum), cardiovascular and lymphatic systems, the spleen, and part of the adrenal gland.

Endoderm

The innermost germ layer that gives rise to the epithelium lining internal organs, including the trachea, bronchi, lungs, GI tract, pharynx, thyroid gland, tympanic cavity, auditory tube, tonsils, and parathyroid glands.

Somatopleure

The body-wall layer formed by the fusion of the dorsal portion of lateral plate mesoderm (somatic mesoderm) with the deep surface of the ectoderm.

Splanchnopleure

The gut-wall layer formed by the fusion of the ventral portion of lateral plate mesoderm (splanchnic mesoderm) with the endoderm.

Coelom

A body cavity (from Greek koiloma, cavity); specifically, the space that opens between the somatopleure and splanchnopleure.

Septum Transversum

A crosswise partition (from Latin septum, partition + transversus, crosswise) that grows around the gut tube, separating the pleural cavity from the peritoneal cavity, and becomes the adult diaphragm.

Mesentery

The double-layered membrane (from Greek mesos, middle + enteron, intestine) formed by meeting mesoderm that suspends the gut tube in the body cavity.

Sclerotome

The medial part of a somite (from Greek skleros, hard + tome, segment/cutting) that separates from the dermomyotome and goes on to form the vertebrae.

Somitomere

Undifferentiated paraxial mesoderm surrounding the neural tube that fuses with the cranial half of each sclerotome during vertebral formation.

Dermomyotome

The lateral part of a somite (from Greek derma, skin + mys, muscle + tome, segment) that splits into epaxial and hypaxial portions to form skin and skeletal muscle.

Epaxial

Referring to structures located above the body's axis (from Greek epi, above + Latin axis, axis); epaxial dermomyotome forms deep back muscles and overlying skin.

Hypaxial

Referring to structures located below the body's axis (from Greek hypo, below + Latin axis, axis); hypaxial dermomyotome forms the rest of the body's skeletal muscle and skin.

Intervertebral Foramen

An opening between adjacent vertebrae (from Latin forare, to bore or pierce) created because vertebrae form intersegmentally, through which a spinal nerve passes.

Cervical Region Segment Count

Region containing 7 vertebrae and 8 segments; the segment count runs one ahead because the top of the topmost sclerotome is absorbed into the skull.

Coccygeal Region Segment Count

Region with a variable number of vertebrae (usually 4, fused into the coccyx) and a matching number of segments (variable, usually 4).

Afferent

Carrying a sensory signal toward the central nervous system (from Latin ad-, toward + ferre, to carry).

Efferent

Carrying a motor signal away from the central nervous system (from Latin ex-, out of + ferre, to carry).

Somatic

Structures or innervation derived from or associated with somites (from Greek soma, body).

Visceral

Structures or innervation reaching internal organs and non-somite derivatives (from Latin viscera, internal organs).

Ventral Horn

The region of spinal cord gray matter containing the cell bodies of somatic motor neurons.

Spinal Ganglion (Dorsal Root Ganglion)

A cluster of somatic sensory nerve cell bodies (from Greek ganglion, knot) located outside the spinal cord, just deep and slightly dorsal to the intervertebral foramen.

Peripheral Process

The branch of a somatic sensory neuron axon that extends outward from the cell body in the spinal ganglion toward the body periphery.

Central Process

The branch of a somatic sensory neuron axon that carries sensory signals from the spinal ganglion through the dorsal root into the dorsal horn of the spinal cord.

Allantois

A sausage-shaped extraembryonic membrane (from Greek allas, sausage) located at the caudal end of the embryo near the cloacal membrane.

Ramus

A branch of a spinal nerve (from Latin ramus, branch), such as the dorsal ramus (supplying epaxial derivatives) or ventral ramus (supplying hypaxial derivatives).