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The Five Senses. The 5 Senses. Sight (Eye) Hearing (Ear) Taste (Tongue) Smell (Nose) Touch (Skin). The Sixth Sense. Sight – the Eye. The Eye. About 25mm (1 inch) in diameter Consists of: 3 tunics (layers) A lens 2 principal cavities. Fibrous Tunic (Outer Layer). 2 parts: Sclera
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The 5 Senses • Sight (Eye) • Hearing (Ear) • Taste (Tongue) • Smell (Nose) • Touch (Skin)
The Eye • About 25mm (1 inch) in diameter • Consists of: • 3 tunics (layers) • A lens • 2 principal cavities
Fibrous Tunic (Outer Layer) • 2 parts: • Sclera • Made of dense connective tissue • White part of the eye • Cornea • Forms the anterior surface of the eye • Transparent
Vascular Tunic (Middle Layer) • 3 Parts: • Choroid • Thin, vascular layer • Supplies nutrients and oxygen to the eye • Absorbs light • Ciliary Body • Thickened, anterior portion of the vascular tunic • Contains muscle fibers that regulate the shape of the lens • Iris • Forms the most anterior part of the vascular tunic • Consists of pigment (gives the eye color) and regulates the diameter of the pupil
Internal Tunic (Inner Layer/Retina) • 2 Types of Photoreceptors • Rods • Approximately 100 million per eye • Responsible for night (black and white) vision • Cones • Approximately 7 million per eye • Responsible for daytime (color) vision • Optic Disk • “Blind spot” of the eye – no rods or cones • Forms the start of the optic nerve • Optic Nerve (cranial nerve II) • Transmits information from the retina to the brain
Cow Eye • Tapetum • Extra layer between retina and choroid • Night Vision
Lens • Focuses light rays for near and far vision • Biconvex structure • Composed of tightly arranged proteins • Held in place by the suspensory ligament that attaches to the ciliary body
Cavities of the Eye • Interior of the Eye is separated by the lens into: • Anterior cavity • Further divided into an anterior and posterior chamber by the iris • Contains a watery substance called aqueous humor • Posterior cavity • Contains a jellylike substance called vitreous humor
Vision • The lens must change shape to focus light on the retina • The farther away an object, the flatter the lens must become • Adjustments in shape are controlled by the ciliary muscles in the ciliary body • Light rays hit the photoreceptors in the retina • Nerve impulses are carried along the optic nerve to the optic chiasma and to the occipital lobe of the cerebrum
The Ear • Organ of hearing and equilibrium (balance) • Three regions: • Outer Ear • Middle Ear • Inner Ear
The Outer Ear • Open to the external environment • Directs sound waves to the middle ear • Consists of: • Auricle (pinna) • Directs sound waves to the external auditory canal • External auditory canal • A 2.5cm fleshy tube that fits into the bony external acoustic meatus • Tympanic membrane (eardrum) • Conducts sound waves to the middle ear
The Middle Ear • The air-filled space medial to the tympanic membrane • Structures include: • Auditory ossicles • Three small bones that extend from the tympanic membrane to the vestibular window • Hammer, anvil, and stirrup (amplify sound waves) • Auditory muscles • Two tiny muscles that function to reduce the pressure of loud sounds • Auditory (eustachian) tube • Connects the middle ear cavity to the pharynx • Drains moisture from the middle ear cavity to equalize pressure on both sides of the eardrum
The Inner Ear • Contains the organs of hearing, balance, and equilibrium • Bony labrynth • Semicircular canals (3) & Ampulla: contain receptors that are sensitive to the rotation of the head • Vestibule: contains receptors that are sensitive to gravity and linear motions of the head • Contains fluids called endolymph and perilymph • Vestibular window: membrane covered opening from the middle ear to the inner ear; transfers sound waves from the auditory ossicles to the cochlea • Cochlea: contains hair cells that vibrate and send nerve impulses to the cochlear nerve (cranial nerve VIII)
Hearing • Sound waves are funneled by the auricle into the external auditory meatus • The sound waves strike the tympanic membrane, causing it to vibrate • Vibrations of the tympanic membrane are amplified as they pass through the hammer, anvil, and stirrup • The vestibular window is pushed back and forth by the stirrup setting up pressure waves in the perilymph of the cochlea • The pressure waves are propagated to the endolymph contained within the cochlear duct • Stimulation of hair cells within the spiral organ of the cochlea causes the generation of nerve impulses in the cochlear nerve, which pass to the pons of the brain
Tongue/Taste • Taste buds • Peglike projections of the tongue called lingual papillae • One taste bud contains a cluster of 40-60 gustatory cells, each innervated by a sensory neuron • Taste sensations • Sweet (front) • Sour (sides) • Bitter (back) • Salty (front sides) • Taste • Sensations are transmitted to the brain stem, then to the thalamus, and finally to the cerebral cortex
Smell • Receptors for smell are located in the nasal mucosa of the superior nasal concha • Airborne chemicals become dissolved in the mucous layer lining the superolateral part of the nasal cavity • The olfactory nerve (cranial nerve I) transmits impulses related to smell • Sensations are conveyed along each olfactory tract to the olfactory portions of the cerebral cortex