The Senses

Introduction Sensory receptors detect environmental changes and trigger nerve impulses that travel on sensory pathways. The body reacts with a particular feeling or sensation. Sensory receptors detect environmental changes and trigger nerve impulses that travel on sensory pathways. The body reacts with a particular feeling or sensation. Two major categories: Two major categories: Somatic senses: touch, pressure, temperature, and pain Somatic senses: touch, pressure, temperature, and pain Special senses: smell, taste, hearing, equilibrium, and vision Special senses: smell, taste, hearing, equilibrium, and vision

Types of Receptors Chemoreceptors – changes in the chemical concentration Chemoreceptors – changes in the chemical concentration Pain receptors – tissue damage Pain receptors – tissue damage Thermoreceptors – change in temperature Thermoreceptors – change in temperature Mechanoreceptors – changes in pressure or movement Mechanoreceptors – changes in pressure or movement Photoreceptors – light energy Photoreceptors – light energy

Somatic Senses Associated with receptors in the skin, muscles, joints, and viscera Associated with receptors in the skin, muscles, joints, and viscera Includes touch, pressure, temperature, and pain Includes touch, pressure, temperature, and pain Touch/Pressure Senses Touch/Pressure Senses Sensory nerve fibers – epithelial tissues Sensory nerve fibers – epithelial tissues Connective tissue; lips, fingertips, palms, soles, nipples, external genitals Connective tissue; lips, fingertips, palms, soles, nipples, external genitals Connective tissue in subcutaneous tissues; tendons and ligaments; deep pressure sensation Connective tissue in subcutaneous tissues; tendons and ligaments; deep pressure sensation

Temperature Senses Temperature Senses Depends on free nerve endings in skin; warm receptors and cold receptors Depends on free nerve endings in skin; warm receptors and cold receptors Warm receptors sensitive above 25C (77F), unresponsive above 113F Warm receptors sensitive above 25C (77F), unresponsive above 113F Cold receptors sensitive between 10C (50F) and 20C (68F); below 10C produces freezing sensation Cold receptors sensitive between 10C (50F) and 20C (68F); below 10C produces freezing sensation Sense of Pain Sense of Pain Receptors protect body from tissue damage Receptors protect body from tissue damage Widely distributed throughout skin and internal tissues, except tissues of brain Widely distributed throughout skin and internal tissues, except tissues of brain Visceral pain may not elicit pain sensations Visceral pain may not elicit pain sensations Referred pain may happen when the pain sensation feels as if its coming from another part than whats being stimulated. Referred pain may happen when the pain sensation feels as if its coming from another part than whats being stimulated.

Special Senses Sensory receptors are within large, complex sensory organs in the head Sensory receptors are within large, complex sensory organs in the head Includes the following: Includes the following: Smell → Olfactory organs Smell → Olfactory organs Taste → taste buds Taste → taste buds Hearing, equilibrium → Ears Hearing, equilibrium → Ears Sight → Eyes Sight → Eyes

Olfactory Receptors Smell receptors are chemoreceptors Smell receptors are chemoreceptors Smell and taste function closely together and aid in food selection; we usually smell food at the same time we taste it. Smell and taste function closely together and aid in food selection; we usually smell food at the same time we taste it. Olfactory bulbs in the ethmoid bone analyze impulses Olfactory bulbs in the ethmoid bone analyze impulses The major interpreting areas are within the temporal lobes and frontal lobes The major interpreting areas are within the temporal lobes and frontal lobes

Taste Taste buds are taste organs Taste buds are taste organs Located on surface of tongue and associated with papillae Located on surface of tongue and associated with papillae Also in roof of mouth and walls of throat Also in roof of mouth and walls of throat Chemicals must be dissolved in saliva first to be tasted Chemicals must be dissolved in saliva first to be tasted Primary taste sensations: Primary taste sensations: Sweet Sweet Sour Sour Salty Salty Bitter Bitter

Hearing Ear is the hearing organ Ear is the hearing organ Also can sense equilibrium Also can sense equilibrium Three parts: External, Middle, and Inner Ear parts Three parts: External, Middle, and Inner Ear parts External Ear – two parts of auricle and external auditory meatus External Ear – two parts of auricle and external auditory meatus Auricle – collects sound waves and directs to E.A.M. Auricle – collects sound waves and directs to E.A.M.

Middle Ear – tympanic cavity, eardrum, and the auditory ossicle bones Middle Ear – tympanic cavity, eardrum, and the auditory ossicle bones Tympanic cavity – air-filled space in temporal bone Tympanic cavity – air-filled space in temporal bone Eardrum – semitransparent membrane covered by a thin layer of skin and mucous membrane; pressure changes on eardrums reproduces vibrations of sound waves Eardrum – semitransparent membrane covered by a thin layer of skin and mucous membrane; pressure changes on eardrums reproduces vibrations of sound waves Auditory Ossicles (bones) – malleus, incus, stapes Auditory Ossicles (bones) – malleus, incus, stapes Malleus – vibrates with eardrum Malleus – vibrates with eardrum Incus – vibrates as a result of the malleus vibrating Incus – vibrates as a result of the malleus vibrating Stapes – vibrates due to incus; vibrations moves fluid within the inner ear to stimulate hearing receptors Stapes – vibrates due to incus; vibrations moves fluid within the inner ear to stimulate hearing receptors

Auditory ossicles also increase or amplify force of vibrations The auditory tube connects the middle ear to the throat (eustachian tube) Helps maintain equal air pressure on both sides of the eardrum for normal hearing; noticeable in rapid change in altitude

Inner Ear Inner Ear – communicating chambers and tubes called a labyrinth  The three semicircular canals provide a sense of equilibrium  Cochlea function in hearing  Organ of Corti – contains hearing receptors

Steps in Hearing  Sound waves enter the E.A.M.  Waves change the pressure on the eardrum for reproduction of vibrations  Auditory ossicles amplify and transmit vibrations to end of stapes  Stapes movement transmits vibrations to receptor cells  Receptor cells cause release of neurotransmitter to stimulate sensory neurons  Sensory impulses are triggered and auditory cortex of temporal lobe interprets them

Sense of Equilibrium Two senses: static equilibrium and dynamic equilibrium Two senses: static equilibrium and dynamic equilibrium Static equilibrium – sense head position, maintain stability and posture Static equilibrium – sense head position, maintain stability and posture Dynamic equilibrium – sense head or body movements or rotations; maintain balance Dynamic equilibrium – sense head or body movements or rotations; maintain balance

Sight Sense The eye is the organ The eye is the organ Each eyelid has four layers: skin, muscle, connective tissue, conjunctiva Each eyelid has four layers: skin, muscle, connective tissue, conjunctiva Skin covers outer surface Skin covers outer surface Conjunctiva is mucous membrane that lines inner surfaces of eyelids and covers eyeball, except for cornea Conjunctiva is mucous membrane that lines inner surfaces of eyelids and covers eyeball, except for cornea Lacrimal glands secretes tears Lacrimal glands secretes tears

Eye Structure  Hollow, spherical structure 2.5 cm in diameter  3 distinct layers:  Outer tunic – cornea, sclera, optic nerve  Middle tunic – choroid coat, ciliary body, iris  Inner tunic – retina

Outer Tunic Contains a transparent cornea that helps the eye focus entering light rays Contains a transparent cornea that helps the eye focus entering light rays Sclera is the white portion of the eye; opaque; protects the eye and is attachment for muscles Sclera is the white portion of the eye; opaque; protects the eye and is attachment for muscles Optic nerve – is in the back of the eye Optic nerve – is in the back of the eye

Middle Tunic Choroid coat – joins with the sclera; honeycombed with blood vessels to nourish tissues, contains pigments; melanin absorbs excess light to keep inside of eye dark. Choroid coat – joins with the sclera; honeycombed with blood vessels to nourish tissues, contains pigments; melanin absorbs excess light to keep inside of eye dark. Ciliary body – thickest part that forms ring around front of eye; helps hold lens in place Ciliary body – thickest part that forms ring around front of eye; helps hold lens in place Lens – behind iris and pupil, transparent, elastic Lens – behind iris and pupil, transparent, elastic Iris – thin, colored portion of eye Iris – thin, colored portion of eye

Inner Tunic Retina – transparent sheet of tissue continuous with optic nerve and inner lining of eyeball Retina – transparent sheet of tissue continuous with optic nerve and inner lining of eyeball – Macula lutea – yellowish spot of retina – Fovea centralis – provides sharpest vision – Optic disk – blind spot of the eye; nerve fibers join optic nerve – Posterior cavity – space between lens, ciliary body, and retina that is filled with jellylike fluid called vitreous humor

Light Refraction To see something, light waves are given off or reflected from the object To see something, light waves are given off or reflected from the object Light waves enter the eye and the image is focused on the retina by bending the light waves; refraction. Light waves enter the eye and the image is focused on the retina by bending the light waves; refraction. For normal eye shape, light waves focus on retina and the image on the retina is upside down and reversed from left to right. The visual cortex interprets the image in its proper position For normal eye shape, light waves focus on retina and the image on the retina is upside down and reversed from left to right. The visual cortex interprets the image in its proper position

Visual Receptors Visual receptors are modified neurons Visual receptors are modified neurons Rods and cones lie in the retina Rods and cones lie in the retina Rods – very sensitive to light and provide vision in dim light; produce colorless vision Rods – very sensitive to light and provide vision in dim light; produce colorless vision Cones – detect color; provide sharp images Cones – detect color; provide sharp images The fovea centralis lacks rods, but packed with cones The fovea centralis lacks rods, but packed with cones For details, people move their eyes so that the image falls on the fovea centralis. For details, people move their eyes so that the image falls on the fovea centralis.

Visual Pigments The wavelength of light determines the color the brain perceives from it. The wavelength of light determines the color the brain perceives from it. Color blindness results from lack of different types of cone pigments Color blindness results from lack of different types of cone pigments