The Senses Special vs General Special characterized by

The Senses

Special vs General Ø Special: characterized by Ø Large and complex organs Ø Localized grouping of specialized receptors Ø Eye Ø Nose Ø Ears Ø Taste buds

General Ø Exist as individual cells or receptor units Ø Widely distributed throughout the body Ø Free nerve endings Ø Messiners corpusles Ruffini’s corpusles Ø Pacinian corpuscles Ø Krause’s End Bulbs Ø Golgi tendon receptors Ø Muscle spindles Ø

Converting Stimulus into Sensation Ø Stimuli: light, sound, temperature change, mechanical pressure, or taste & smell Ø Changed into an electrical signal or nerve impulse transmitted over a nervous system pathway Ø To the Brain, where interpretation takes place

Special Sense Organs: Eye Ø Ø Ø 3 layers form eyeball: sclera, choroid, retina Cornea, is part of the sclera: window of the eye Iris: colored part of the eye, Conjunctiva: mucous membrane that lines the eyelids and covers the sclera in front Lacrimal gland: located in upper lateral portion of the orbit

EYE cont’ Ø Choroid: middle layer of the eyeball: contains dark pigment to prevent scattering of incoming light rays Ø 2 involuntary muscles: Ø Ciliary muscle and Iris Ø Pupils dilate and constrict according to light. Ø Lens: lies directly behind the pupil, held in place by a ligament attached to ciliary muscle. (responsible for focus)

Retina Ø Innermost layer of the eye Ø Contains rods and cones Ø Rods: receptors for night vision Ø Cones: receptors for day and color vision Ø Connected to the Optic nerve Ø Visual perception occurs in the visual cortex of the cerebrum

Ear Ø Ø Functions in hearing and equilibrium Divided into 3 sections: Inner, middle and outer ear Outer: Auricle: pinna l External auditory canal: 2. 5 cm in length l Contains ceruminous glands=ear wax l Ends at tympanic membrane

Ear: cont’ Ø Middle Ear: Houses ossicles, that is Ø Malleus (hammer) Ø Incus (anvil) Ø Stapes (stirrup) Ø Ends in the oval window Ø Auditory (eustachian) tube connects the middle ear to the throat Ø Inflammation: Otitis Media

Ear…. cont’ Ø Inner ear: Bony Labrinth filled with perilymph(fluid) Ø Subdivided into: vestibule, semicircular canals, and cochlea Ø Specialized hair cells in the “organ of Corti” respond when bent by movement of the endolymph(fluid)set in motion by sound waves.

Taste Tongue: covered with tiny, different sized bumps, known as papillae. Ø approximately 10, 000 of these papillae, which are made up of taste buds. Ø Taste buds contain the specialized receptor cells which allow us to distinguish the different tastes that we know. Ø Four different taste-sensitive areas on the surface of the tongue: Ø sour, salt, bitter and sweet. Ø

Areas of Taste

Smell Ø Smells are detected in the nose by the specialized receptor cells of the olfactory epithelium. Ø These are called olfactory receptor neurones. Ø Neurones send chemical message to olfactory nerve, which in turn is sent to the brain for analysis.