The Senses Help to maintain homeostasis General senses receptors located throughout the body

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1 The Senses Help to maintain homeostasis General senses receptors located throughout the body Within the skin, organs & joints Sense of touch Special senses receptors in the head Sight Smell Taste Hearing Equilibrium Receptors Receptors specialized cells that collect info from the environment & pass info to the nervous system Chemoreceptors receptors for smell & taste; respond to chemicals in solution Pain receptors (nociceptors) Thermoreceptors respond to temp. Mechanoreceptors Proprioceptors sense changes in tension of muscles & tendons Baroreceptors detect changes in pressure Stretch receptors detect changes in length or volume Photoreceptors respond to patterns made by light; sight 1

2 Chemical Senses Taste & Smell Chemoreceptors; respond to chemicals in a solution Chemicals dissolved in saliva & fluids in nasal membranes Both senses complement each other; 80% of taste depends on smell Olfaction Olfactory receptors are located in the roof of the nasal cavity Chemicals must be dissolved in mucus Sniffing intensifies smell; pulls molecules across olfactory receptor cells Olfactory cells surrounded by supporting cells Olfactory hairs increase the surface area of receptor cells Olfaction closely related to taste & memories Olfaction Impulses are transmitted from receptor cells to the olfactory nerve Olfactory nerve passes thru ethmoid bone to the olfactory bulb. Interpretation of smells is made in the cortex but passes through the limbic system, the part of the brain that stores memories and emotions 2

3 The Sense of Taste Gustation Taste buds receptor organs for taste Location of taste buds Most are on the tongue Hard & soft palate Cheeks The Tongue and Taste Tongue is covered w/projections called Taste buds are found on the sides of papillae Taste buds are constantly being replaced due to wear and tear 3

4 Structure of Taste Buds Taste buds consist of 3 types of cells; gustatory cells, supporting cells, & basal cells Gustatory cells (taste cells) are the receptors Supporting cells surround taste cells Gustatory hairs (long microvilli) protrude from TASTE PORE Hairs are stimulated by chemicals dissolved in saliva Basal cells are located at the base & are the source for new taste cells Anatomy of Taste Buds Taste Sensations Sweet receptors Sugars, carbohydrates Sour receptors Acids (lemon, vinegar) Salty receptors Metal ions (NaCl) Bitter receptors Alkaloids (aspirin), many poisons Umami 4

5 Taste Pathway Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas Facial nerve transmits impulse from taste buds in anterior 2/3 of tongue Glossopharyngeal nerve from taste buds in posterior 1/3 of tongue Vagus nerve - from the few taste buds at the base of the tongue & pharynx The Ear Houses 2 senses Hearing Equilibrium Receptors are mechanoreceptors respond to vibrations & movement of fluids in ear Different organs house receptors for each sense Anatomy of the Ear The ear is divided into 3 areas Outer (external) ear Middle ear Inner ear 5

6 The External Ear Involved in hearing only Structures of the external ear Pinna (auricle) shell shaped structure; directs sound waves into canal External auditory canal w/in temporal bone external acoustic meatus Tympanic membrane transfers sound waves The External Auditory Canal Ceruminous glands secrete ear wax (cerumen) External ear ends at the tympanic membrane or eardrum Middle Ear or Tympanic Cavity Air-filled cavity within the bone Only involved in the sense of hearing 6

7 Middle Ear or Tympanic Cavity 2 tubes are associated with the middle ear The opening from the auditory canal is covered by the tympanic membrane The auditory tube or eustachian tube connects middle ear w/throat Allows for equalizing air pressure during yawning, swallowing or flight This tube is otherwise collapsed Bones of the Tympanic Cavity 3 bones of the cavity (ossicles) Malleus ( ) Incus ( ) Stapes ( ) Vibrations from eardrum moves the malleus Bones transfer sound to the inner ear Inner Ear or Labyrinth Includes organs for hearing & balance Osseous labyrinth bony canal in temporal bone Membranous labyrinth within osseous labyrinth Perilymph inner ear fluid between osseous & membranous labyrinth Endolymph fluid within the membranous labyrinth 7

8 Inner Ear Inner Ear A maze of bony chambers within the temporal bone Cochlea snail shell organ used in hearing Semicircular canals Vestibule contains oval & round window, saccule, & utricle for hearing & equilibrium Inner Ear 8

9 Cochlea Organ of Corti Located within the cochlea Receptors or hair cells on the basilar membrane Gel-like tectorial membrane is capable of bending hair cells Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe Organs of Hearing Figure 8.13 Mechanisms of Hearing Vibrations from sound waves move tectorial membrane Hair cells are bent by the membrane Continued stimulation can lead to adaptation 9

10 Organs of Equilibrium Receptor cells are in 2 structures Vestibule Semicircular canals Organs of Equilibrium Equilibrium has 2 functional parts Static equilibrium- Dynamic equilibrium Static Equilibrium Maculae receptors in the vestibule Report on the position of the head Send information thru vestibular nerve Anatomy of the maculae Hair cells are embedded in the otolithic membrane Otoliths ( the hair cells ) float in a gel around Movements cause otoliths to bend the hair cells 10

11 Function of Maculae Macula of utricle Otoliths Hairs of hair cells bend Gelatinous material sags Hair cells Sensory (afferent) nerve fiber Supporting cells Gravitational force (a) Head upright (b) Head bent forward Dynamic Equilibrium Crista ampullaris receptors in the semicircular canals Tuft of hair cells Cupula (gelatinous cap) covers the hair cells With angular head movements, the cupula stimulates the hair cells An impulse is sent via the vestibular nerve to the cerebellum Dynamic Equilibrium Action of angular head movements The cupula stimulates the hair cells An impulse is sent via the vestibular nerve to the cerebellum 11

12 The Eye Visual perception based on photoreceptors that sense patterns made by Eye Protection Enclosed in a bony orbit Fat surrounds & cushions eye Accessory Structures of the Eye Eyebrow prevent sweat from entering eye Eyelids Thinnest skin in the body Protects & lubricates Medial canthus inner corner Lateral canthus outer corner Eyelashes Blinking protects eye from foreign objects Accessory Structures of the Eye Tarsal glands produces an oily secretion to lubricate the eye& eyelid Ciliary glands modified sweat glands between the eyelashes; Sty inflammation of ciliary gland Conjunctiva Membrane lining eyelids Connects to the surface of the eye Secretes mucus to lubricate the eye 12

13 Accessory Structures of the Eye Conjunctivitis inflammation of conjunctiva; Accessory Structures of the Eye Accessory Structures of the Eye Lacrimal apparatus Lacrimal gland produces tears (saline solution) Lacrimal puncta pore that tears drain into Superior & inferior lacrimal canaliculi drains lacrimal fluid from eyes to lacrimal sac Lacrimal sac empties lacrimal fluid into nasal ducts Nasolacrimal duct empties lacrimal fluid into the nasal cavity 13

14 Function of Lacrimal Apparatus Properties of lacrimal fluid (tears) Dilute salt solution Contains antibodies & lysozymes to reduce eye infections Protects, moistens, & lubricates the eye Extrinsic Eye Muscles Muscles attached to the outer surface of eye Control eye movements Extrinsic Eye Muscles 4 rectus muscles originate from annular ring located in back of orbit Superior rectus top muscle, upward movement Inferior rectus lower muscle, downward movement Lateral rectus outer muscle, outward movement Medial rectus inner muscle, inner movement Superior Oblique originates at annular ring & runs through trochlea loop; attaches to top; helps rotate eye down & out Inferior Oblique originates at medial orbit; runs laterally to inferior surface; helps rotate eye up & out Trochlea loop supporting superior oblique 14

15 Eyelid Muscles Orbicularis occuli Levator palpebrae Structure of the Eye The eye is a fluid filled sphere surrounded by several layers called tunics Humors fluids that help maintain shape of eye 3 Tunics (layers) Fibrous tunic outside layer Vascular tunic (uvea) middle layer Sensory tunic (retina) inside layer 15

16 Fibrous Tunic outer layer 1. Cornea Transparent window; bulges from sclera Allows light to pass through Repairs itself easily The only human tissue that can be transplanted without fear of rejection 2. Sclera White connective tissue layer Site of muscle attachment Optic nerve emerges from back of sclera Vascular Tunic - middle layer Choroid - highly vascular layer that is loosely attached to sclera Dark pigment helps absorb light Ciliary body smooth muscles that control lens shape; secretes aqueous humor Suspensory ligaments hold the lens in place & may change the shape of the lens as the eye focuses on near or far objects. Accommodation Lens Accommodation Light must be focused to a point on the retina for optimal vision The eye is set for distance vision (about 20 ft away) The lens must change shape to focus for closer objects; suspensory ligaments contract 16

17 Vascular Tunic - middle layer Iris - gives eye color; located between cornea & lens; smooth muscles control size of pupil Pupil opening in the iris; allows light to enter the circulation of aqueous humor Smooth muscles of iris act as diaphragm to change size of pupil Bright light pupil Dim light pupil Sensory Tunic (Retina) inner layer Retina - contains photoreceptors cells that respond to light Thin, delicate inner lining of the eye Rods dim light vision & peripheral vision; grays Cones Signals pass from photoreceptors via a 2- neuron chain Bipolar neurons receive impulse from cones & rods Ganglion cells receives impulse from bipolar cells; sends message to optic nerve 3 parts of Retina Optic nerve carries impulse to brain for interpretation Fovea centralis area of greatest visual acuity; point of sharpest vision; contains only cones Optic disc blind spot; no photoreceptors are present Site of where 17

18 Neurons of the Retina Lens Biconvex crystal-like structure Held in place by suspensory ligaments attached to ciliary body Internal Eye Chamber Fluids Anterior cavity in front of lens,contains aqueous humor Watery fluid Helps maintain proper pressure Provides nutrients for the lens & cornea 18

19 Internal Eye Chamber Fluids Vitreous humor Gel-like substance behind the lens Keeps the eye from collapsing Helps hold retina against chroid coat Helps transmit light Visual Diorders Emmetropic Astigmatism unequal curves w/in lens; object appears clear in some areas and blurry in others Hyperopic far sighted Eye too short Objects focused behind retina Corrected w/ convex lens Myopic nearsightedness Eye too long Objects focused in front of retina Corrected w/concave lens Visual abnormalities Presbyopia deterioration of lens as one ages Amblyopia lazy eye Strabismus crossed eye Colorblindness lack of certain cones Retinal detachment retinal & neural layers separate Caused by traumatic blows, diabetes May cause blindness Glaucoma increase pressure to eye Due to excess aqueous fluid Compresses retina & optic nerve Cataracts clouding of lens Lens transplants 19