1Introduction KEY POINTS Ontogeny is the series of steps that leads to a mature state. The human being is precocious with regard to hearing. Although humans may be considered precocious with respect to vestibulo-ocular reflexes and other vestibular reflexes, we certainly are altricial with respect to upright posture and balance. Several animal models have been used to understand molecular, structural, and functional development of auditory and vestibular systems including Drosophilia, zebrafish, -- 2Nature of Cells and Tissues KEY POINTS Within each cell is a complex environment containing many organelles to carry out the cell's functions. The human body contains 80 to 100 trillion cells, most of which are immersed in a fluid environment that is strictly regulated to maintain homeostasis. Cells combine to form connective, epithelial, neural, and muscle tissues. Tissues combine to form the organ systems in the human body. Cell signaling pathways control the development of tissues and organs -- 3Basic Concepts in Genetics KEY POINTS The nucleus of the cell holds the chromosomes. Normally, humans have 46 chromosomes, half of which (i.e., 23) are inherited from your mother and half from your father. Chromosomes contain deoxyribonucleic acid (DNA), which hachromosomes is known as thes approximately 3 billion base pairs that code for 25,000 to 30,000 genes in humans. Genes are the fundamental units of heredity. A gene contains the necessary information for the cell to generate a functional.

4Basic Concepts in Embryology KEY POINTS Embryology is the study of the embryo. Embryologists are experts in development. Human development begins with fertilization of the egg by sperm. Cell fate (what a cell will become) is influenced by several mechanisms including cell lineage, restriction, and induction. The embryonic period of development begins at fertilization and lasts until the end of the eighth week after fertilization. Many events occur during the embryonic period leading to the morp -- 5Embryogenesis of the Outer and Middle Ear KEY POINTS The temporal bone develops from mesodermal and neural crest mesenchyme via intramembranous and endochondral ossification. Once developed, it will continue to ossify throughout childhood up to puberty. The pinna develops from six auricular hillocks that form around the first pharyngeal groove during the fifth week after fertilization. The first pharyngeal groove invaginates to form the external auditory meatus. The invaginating first pharyngea -- 6Embryogenesis of the Inner Ear KEY POINTS The inner ear will develop from the otic placode, which appears during week three postfertilization. The otic placode and eventual otocyst are influenced by several molecular pathways that pattern the otocyst into various regions of genetic expression (e.g., distinguishing dorsal from ventral, anterior from posterior, medial from lateral). Semicircular canals and cristae will develop from dorsal regions of the otocyst, macular structures at or near the -- 7Emergence of Inner Ear Function KEY POINTS The human is precocious with regard to auditory and vestibular functional development.

however, final maturation of function occurs after birth. Membranes overlying the inner ear sensory receptors are first present between 8 to 10 weeks of age before hair cells have fully differentiated. The overlying membrane is critical for adequate stimulation of the sensory hair cells. Hair cells become active upon the appearance of ion channels and membrane curren.