THE NERVOUS SYSTEM: SPECIAL SENSES

THE NERVOUS SYSTEM: SPECIAL SENSES

Special senses allow the human body to react to the environment. Eye (sight) Ear (hearing) Tongue (taste) Nose (smell) Skin (touch and general senses)

Your sense of sight THE EYE

THE EYE Receives light rays and transmits impulses from the rays to the optic nerve. The optic nerve carries the impulses to the brain, where they are interpreted as sight. The eye is well protected: Bony socket of the skull Eyelids and eyelashes Lacrimal glands produce tears to moisten and cleanse Conjunctiva lines the eyelids to provide additional protection

THREE MAIN LAYERS OF THE EYE Sclera Outermost layer; tough connective tissue the white of the eye Maintains the shape of the eye The muscles which move the eye are connected to the outside of the sclera Cornea transparent part of the front of the sclera

THREE MAIN LAYERS OF THE EYE Choroid Coat Middle layer Contains many blood vessels that nourish the eyes Retina Innermost layer Has many nerve cells which transmit light images to the optic nerve Special nerve cells: Cones see color when there is light Rods vision when it is dark

OTHER PARTS OF THE EYE Iris Pupil Colored part of the eye Located behind the cornea in front of the choroid coat Opening in the center of the iris Two muscles in the iris control the size of the pupil to regulate the amount of light that enters Lens Circular structure behind the pupil Refracts light rays so the rays focus on the retina

Your ability to hear and balance THE EAR

THE EAR Controls the special sense of hearing and balance. Transmits impulses from sound waves to the auditory nerve which carries them to the brain which allows for hearing.

THE EAR IS DIVIDED INTO THREE SECTIONS Outer Ear The visible part of the ear, called the pinna or auricle Leads to a tube called the auditory canal, which sound waves travel thru Sound waves will then hit the tympanic membrane ( eardrum ) The tympanic membrane vibrates when the sound waves hit it and transmits them to the middle ear

THE EAR IS DIVIDED INTO THREE SECTIONS Middle Ear Contains three small bones (ossicles): malleus, incus, stapes The bones are connected and transmit sound from the tympanic membrane to the inner ear The middle ear is connected to the pharynx (throat) through the Eustachian tube which helps to equalize pressure on both sides of the tympanic membrane.

THE EAR IS DIVIDED INTO THREE SECTIONS Inner Ear Separated from the middle ear by the oval window The first section is the vestibule, which acts as the entrance to the other two parts: Cochlea: shaped like a snail shell, contains hair-like cells which make up the Organ of Corti Organ of Corti: receptor of sound waves, transmits impulses to the auditory nerve Semicircular Canals: contain liquid and hair like cells that bend when the liquid moves with head and body movements Impulses sent from these cells help to maintain sense of balance and equilibrium.

Your sense of taste THE TONGUE

THE TONGUE Is a mass of muscle tissue with projections called papillae. Papillae contain taste buds that are stimulated by the flavors of food moistened by saliva. Four main tastes: Sweet and Salty (at the tip of the tongue) Sour (at the sides of the tongue) Bitter (at the back of the tongue) Taste is influenced by your sense of smell.

Your sense of smell THE NOSE

THE NOSE The organ of smell. Olfactory receptors are located in the upper part of the nasal cavity. Impulses from these receptors are carried to the brain through the olfactory nerve, which makes the sense of smell possible. The human nose can detect over 6,000 different smells. The sense of smell is more sensitive than taste, and it is very closely related to taste.

Your sense of touch THE SKIN AND GENERAL SENSES

THE SKIN (AND GENERAL SENSES) General sense receptors for pressure, heat, cold, touch, and pain are located throughout the body in the skin and connective tissue. Each of these receptors perceives only one type of sense. Ex. heat receptors only perceive heat; cold receptors only perceive cold. Messages from these receptors allow the human body to respond to its environment and help it to react to conditions that could cause injury.