General Biology/Tissues and Systems/Sensory Systems
From Wikibooks, the open-content textbooks collection
General Biology | Getting Started | Cells | Genetics | Classification | Evolution | Tissues & Systems | Additional Material
Contents |
[edit] Sensory systems
Categorized by
- nature of stimulus, such as mechanical, chemicalor light stimulus, and
- where stimulus received, such as outside (exteroceptors,such as the eye and skin temp receptors) or insidebody (interoceptors, such as blood body temperature receptors).
Transduction of sensory input into signal. Means to “carry across”,signal transduced, or carried, from environment into nervous signal.
Three sensory processes we cover
- taste and smell (chemoreception)
- gravity and movement
- light
[edit] Taste and smell (chemoreception)
Found in mammal nose and mouth, fly feet, fish bodies, moth antennae.
Papilla: bumps on tongue, contain taste buds down between. Sweet, sour,salty and bitter. Some act directly by ion channels, others act indirectly.Other “taste” sensations really smell.
Smell: received in nasopharynx. Airborne molecules go into solution on moist epithelial surface of nasal passage. Approximately 1000 genescode for sensory neuron receptors. “Fried onions” odor not one receptorbut a mixture of many odors registered in our mind as one. Very sensitive,habituates rapidly (don’t notice a smell after a bit). Odor sensation hasrelatively unfiltered root to higher brain centers.
Snakes more chemosensory focused than us.
[edit] Response to gravity and movement
Registered in inner ear. Three semicircular canals loop in threeplanes at right angles to each other, responsible for transduction of movementmessages. Method: hair cells deformed by gelatinous membrane. Vestibularapparatus, gives us perception of gravity and movement. Due to physicalresponse, not chemical binding.
Cochlea: bony, coil shaped part of inner ear, where hearing occurs.
Sound enters thru auditory canal, vibrates tympanic membrane,moving three bones of middle ear (malleus, incus, and stapes)against oval window opening in front of cochlea. Cochlea has three fluidfilled ducts, one of these the organ of Corti. Sound waves in airgo to vibration in organ of Corti; fluid tickles hair cells, whichregister the movement along basilar membrane in cochlea. Differentsound frequencies move different portions of basilar membrane. Hearingloss due to loss of hair cells.Humans normally smell more than 300 odors in a day(Facts and Truth).
Transduction of sound accomplished thru physical deformation,not chemical binding.
[edit] Vision
Light enters pupil', focused by lens onto retina.'
Sclera: hardened part behind retina.
Optic nerves and neurons attached to retina. Blind spotwhere optic nerve attaches, has no receptors.
Two types of photoreceptors
- rods - black and white low-light vision, 100 million in each retinain humans.
- cones - color vision, work best under better illumination. 3 millionin each retina.
Fovia: region of most acute vision, has most of the cones, few rods.
Transduction process of light to signal a molecular change, to lightabsorbing molecule called photopigment. Located in outer parts of rodsand cones in pigment discs. The rod photopigment is called rhodopsin,cone has three photopigments, called photopsins. This molecularchange initiates pathways to result in action potential in downstream neuronleading to vision center in brain.Parul Godika
Each of the three photospsins has a different peak of sensitivity: blue,green or red, and changes isometric form (from cisto trans) based on light from a particular wavelength range. Color blindness:inherited lack of one or more types of these cones. Gene carried on X chromosome,therefore more common in men than women.
General Biology | Getting Started | Cells | Genetics | Classification | Evolution | Tissues & Systems | Additional Material
