A dark, often irregular spot on the surface of a planet or satellite; pl. maculae. The name is not a geological term but is used in the nomenclature of individual features, for example Thrace Macula on Europa and Elpis Macula on Titan.
1. A patch of sensory hair cells in the utriculus and sacculus of the inner ear that provides information about the position of the body in relation to gravity. The hairs of the cells are embedded in an otolith, a gelatinous cap containing particles of calcium carbonate. Movement of the particles in response to gravity pulls the gelatinous mass downwards, which bends the hairs and triggers a nerve impulse to the brain (see illustration).
2. An area of the retina of the vertebrate eye with increased visual acuity. Maculae occur in some animals that lack foveae and often surround foveae in those animals that possess them.
Macula (when the head is positioned at 90° to the direction of the force of gravity)
A dark spot on the surface of an extraterrestrial body.
- psychophysical parallelism
- psychrometer
- psychrometric chart
- psychrometry
- psychrophile
- psychrophilic
- ptarmigan
- Pteraspida
- Pteraspis
- Pteridophyta
- pteridophyte
- pteridophytes
- Pteridospermales
- pterobranch
- Pterobranchia
- pterodactyl
- pterodactyls
- pteropod ooze
- Pteropsida
- Pterosauria
- Pterygota
- PTFE
- PTH
- PTI
- Ptilograptidae