Anatomy & Physiology I and II

Anatomy & Physiology Study Guide • The two kinds of photoreceptors are rods, which respond to almost any photon regardless of its energy content, and cones, which have characteristic ranges of sensitivity. • Each photoreceptor contains an outer segment with membranous discs. A narrow stalk connects the outer segment to the inner segment. Light absorption occurs in the visual pigments, which are derivatives of rhodopsin (opsin plus the pigment retinal, which is synthesized from vitamin A). • Color sensitivity is dependent upon the integration of information from red, green, and blue cones. Color blindness is the inability to detect certain colors. • In the dark-adapted state, most visual pigments are fully receptive to stimulation. In the light- adapted state, the pupil constricts, and bleaching of the visual pigments occurs. • The ganglion cells that monitor rods, called M cells (magnocells), are relatively large. The ganglion cells that monitor cones, called P cells (parvo cells), are smaller and more numerous. • Visual data from the left half of the combined field of vision arrive at the visual cortex of the right occipital lobe; data from the right half of the combined field of vision arrive at the visual cortex of the left occipital lobe. • Depth perception is obtained by comparing relative positions of objects between the left and right eye images. • Visual contributions of the hypothalamus’ suprachiasmatic nucleus affect the function of other brainstem nuclei. This nucleus establishes a visceral circadian rhythm, which is tied to the day–night cycle and affects other metabolic processes. Equilibrium sensations originate within the inner ear, while hearing involves the detection and interpretation of sound waves: • Equilibrium and hearing are supplied by the inner ear’s receptors. • The ear is categorized into the external ear, the middle ear, and the inner ear. • The external ear includes the auricle, or pinna, which surrounds the entrance to the external acoustic meatus, which ends at the tympanic membrane (eardrum). • The middle ear communicates with the nasopharynx via the auditory (pharyngotympanic) tube. The middle ear encloses and protects the auditory ossicles. • The membranous labyrinth (the chambers and tubes) of the inner ear contains the fluid endolymph. The bony labyrinth surrounds and protects the membranous labyrinth and can be subdivided into the vestibule, the semicircular canals, and the cochlea. • The vestibule of the inner ear encloses the saccule and utricle. The semicircular canals contain the semicircular ducts. The cochlea contains the cochlear duct, an elongated portion of the membranous labyrinth. • The round window separates the perilymph from the air spaces of the middle ear. The oval window is connected to the base of the stapes. • The basic receptors of the inner ear are hair cells, which provide information about the direction and strength of mechanical stimuli. • The anterior, posterior, and lateral semicircular ducts are continuous with the utricle. Each duct contains an ampulla with a gelatinous cupula and associated sensory receptors. ©2018 Achieve Test Prep Page 203 of 367