Sensory Organs

Lesson 13-1 Objectives State the functions of the sensory system. Define the five types of sensory receptors. Describe the four components involved in the perception of a sensation. Describe the five general senses. State the functions of the sensory system. Define the five types of sensory receptors. Describe the four components involved in the perception of a sensation. Describe the five general senses.

Sensory System Sensory system allows us to experience the world. External information Sound of a dog barking Internal information Sudden change in blood pressure Sensory system allows us to experience the world. External information Sound of a dog barking Internal information Sudden change in blood pressure

Five Types of Sensory Receptors Receptor: Specialized area of a sensory neuron that detects a specific stimulus –Chemoreceptors (smell and taste) –Pain receptors (nociceptors) : tissue damage, O 2 Loss –Thermoreceptors: Change in temp –Mechanoreceptors: pressure or movement of fluid –Photoreceptors: Light Receptor: Specialized area of a sensory neuron that detects a specific stimulus –Chemoreceptors (smell and taste) –Pain receptors (nociceptors) : tissue damage, O 2 Loss –Thermoreceptors: Change in temp –Mechanoreceptors: pressure or movement of fluid –Photoreceptors: Light

Four Components of Sensation

Two Characteristics of Sensation Projection Adaptation Projection Adaptation

Projection Brain refers sensation back to its source A. Ordinary injury B. Phantom limb pain

Adaptation Adaptation: With continuous stimulation, sensory receptors become less responsive. Receptors vary in their ability to adapt.  Smell and temperature receptors adapt well.  Pain receptors do not adapt at all. Adaptation: With continuous stimulation, sensory receptors become less responsive. Receptors vary in their ability to adapt.  Smell and temperature receptors adapt well.  Pain receptors do not adapt at all.

Five General Senses Widely Distributed Pain Touch Pressure Temperature Proprioception Widely Distributed Pain Touch Pressure Temperature Proprioception

Pain Receptors or Nociceptors Consist of free nerve endings stimulated by tissue injury, chemicals, tissue hypoxia (not enough O 2 ) Widely distributed throughout the skin, viscera, other internal tissues Do not adapt Consist of free nerve endings stimulated by tissue injury, chemicals, tissue hypoxia (not enough O 2 ) Widely distributed throughout the skin, viscera, other internal tissues Do not adapt

Sites of Referred Pain Coming from another area Compare heart’s location with possible sites of pain during a heart attack. Gallbladder attack may present with shoulder pain.

Touch and Pressure Receptors Touch (tactile) receptors (1 st Sense to develop) –Mechanoreceptors –Found mostly in skin Pressure receptors –Mechanoreceptors –Located in the skin, subcutaneous tissue, and deep tissue Touch (tactile) receptors (1 st Sense to develop) –Mechanoreceptors –Found mostly in skin Pressure receptors –Mechanoreceptors –Located in the skin, subcutaneous tissue, and deep tissue

Thermoreceptors Receptors for cold and heat Located in free nerve endings and other specialized sensory cells in the skin Quick adaptation Temperature extremes experienced as pain Receptors for cold and heat Located in free nerve endings and other specialized sensory cells in the skin Quick adaptation Temperature extremes experienced as pain

Proprioception Proprioception: Sense of orientation or position in space Receptors –Located in muscles, tendons, joints, and inner ear –Sensory information parietal lobe, cerebellum Proprioception: Sense of orientation or position in space Receptors –Located in muscles, tendons, joints, and inner ear –Sensory information parietal lobe, cerebellum Shake head yes, and then turn head no. Shrug shoulders up and down Shrug shoulders up and down while alternating between nodding yes and turning head no.

Try another one Tap one foot on the ground (keep heel on floor). Turn the opposite foot in and out (keep heel on floor). Do both tasks at the same time. Tap one foot on the ground (keep heel on floor). Turn the opposite foot in and out (keep heel on floor). Do both tasks at the same time.

Lesson 13-2 Objectives Describe the five special senses. Describe the structure of the eye. Explain the movement of the eyes. Describe how the size of the pupils changes. Describe the five special senses. Describe the structure of the eye. Explain the movement of the eyes. Describe how the size of the pupils changes.

Five Special Senses Smell Taste Sight Hearing Balance Smell Taste Sight Hearing Balance

Gustatory Sense: Taste Taste receptors are chemoreceptors. Nerve impulses move along three cranial nerves to parietal and temporal lobes.

Olfactory Sense: Smell Chemoreceptors in nasal tissue Nerve impulses travel on Olfactory Cranial nerve to temporal lobe for interpretation

Vision: Sense of Sight Visual accessory structures Primary visual structures are the eye and visual pathway. Visual accessory structures Primary visual structures are the eye and visual pathway.

Visual Accessory Structures Eyebrows: protection (sweat, light) Eyelids: Protection (foreign objects) Conjunctiva: mucous membrane –Pink eye= Conjunctivitis's Eyelashes: trap dust, moisten Lacrimal apparatus: tears Extrinsic eye muscles: move eye Eyebrows: protection (sweat, light) Eyelids: Protection (foreign objects) Conjunctiva: mucous membrane –Pink eye= Conjunctivitis's Eyelashes: trap dust, moisten Lacrimal apparatus: tears Extrinsic eye muscles: move eye

Eye: Organ of Vision

Eyeball: Three Layers Sclera: outermost Choroid: middle Retina:inner Sclera: outermost Choroid: middle Retina:inner

Sclera Tough outer layer in posterior eyeball Forward extension becomes cornea Extrinsic eye muscles attach here Tough outer layer in posterior eyeball Forward extension becomes cornea Extrinsic eye muscles attach here

Choroid Middle layer in the posterior eyeball Forward extension becomes ciliary body and iris Iris control light –Pupil=opening Highly vascular to nourish retina Middle layer in the posterior eyeball Forward extension becomes ciliary body and iris Iris control light –Pupil=opening Highly vascular to nourish retina

Retina Inner layer in posterior eyeball Site of photoreceptors  Rods  Cones Optic disc (blind spot)  Exit of optic nerve Inner layer in posterior eyeball Site of photoreceptors  Rods  Cones Optic disc (blind spot)  Exit of optic nerve

Retinal Photoreceptors Rods –Located on periphery –Responsible for black and white or night vision Cones –Located on central part of posterior eye –Concentrated in fovea centralis in center of macula lutea –Responsible for color vision Rods –Located on periphery –Responsible for black and white or night vision Cones –Located on central part of posterior eye –Concentrated in fovea centralis in center of macula lutea –Responsible for color vision

Cavities of Eyeball Posterior cavity –Between lens and retina –Contains vitreous humor Anterior cavity –Between lens and cornea –Contains aqueous humor Posterior cavity –Between lens and retina –Contains vitreous humor Anterior cavity –Between lens and cornea –Contains aqueous humor

Formation and Drainage of Aqueous Humor Formed by ciliary body Circulates through pupil behind cornea Drains through canals of Schlemm Formed by ciliary body Circulates through pupil behind cornea Drains through canals of Schlemm

Muscles of the Eye Extrinsic muscles: Move eyeball in its bony orbit Intrinsic muscles: Move structures within eyeball –Iris –Ciliary muscles Extrinsic muscles: Move eyeball in its bony orbit Intrinsic muscles: Move structures within eyeball –Iris –Ciliary muscles

Extrinsic Muscles of the Eye Four rectus muscles Two obliques Primary innervation from oculomotor nerve Four rectus muscles Two obliques Primary innervation from oculomotor nerve

Three Intrinsic Eye Muscles Iris  Circular muscle Miosis Muscarinic receptors  Radial muscle Mydriasis Alpha 1 receptors Ciliary muscles Iris  Circular muscle Miosis Muscarinic receptors  Radial muscle Mydriasis Alpha 1 receptors Ciliary muscles

Eye Disorders

Refraction: Lens Ciliary muscles pull on suspensory ligaments. Suspensory ligaments pull on lens. Lens changes shape. Ciliary muscles pull on suspensory ligaments. Suspensory ligaments pull on lens. Lens changes shape.

Refraction Bending light rays to focus on retina Lens, primary refracting structure Focal point on retina

Errors of Refraction Myopia, focal point in front of retina Hyperopia, focal point behind retina Astigmatism, result of irregularly curved cornea

Visual Pathway Photoreceptors generate nerve impulse Nerve impulse travels along CN II to occipital lobe Occipital lobe “sees” Rover

Visual Pathway: Optic Chiasm Lateral fibers of CN II ascend to same side of brain. Medial fibers of CN II cross to opposite sides, forming the optic chiasm. The brain sees one image.

How Seeing Occurs Pathway of light  Cornea aqueous humor pupil lens vitreous humor rods and cones Pathway of nerve impulses  Rods and cones CN II occipital lobe Pathway of light  Cornea aqueous humor pupil lens vitreous humor rods and cones Pathway of nerve impulses  Rods and cones CN II occipital lobe

Lesson 13-3 Objectives Describe the three divisions of the ear. Describe the functions of the parts of the ear involved in hearing. Explain the role of the ear in maintaining the body’s equilibrium. Describe the three divisions of the ear. Describe the functions of the parts of the ear involved in hearing. Explain the role of the ear in maintaining the body’s equilibrium.

Sense of Hearing: Three Parts of Ear External to tympanic membrane Middle from tympanic membrane to oval window Inner behind oval window

Three Parts of Ear: Contents External –Auricle, external auditory canal Middle –Malleus, incus, stapes –Eustachian tube Inner –Cochlea, vestibule, semicircular canals, origin of CN VIII External –Auricle, external auditory canal Middle –Malleus, incus, stapes –Eustachian tube Inner –Cochlea, vestibule, semicircular canals, origin of CN VIII

Eustachian Tube Connects throat with middle ear Equalizes pressure across tympanic membrane In young child, short and horizontal In adults, longer and more vertical Connects throat with middle ear Equalizes pressure across tympanic membrane In young child, short and horizontal In adults, longer and more vertical

Receptors : Organ of Corti Mechanoreceptors (hairs) in cochlea of inner ear Organ of Corti in endolymph Cochlear branch of CN VIII

How Hearing Occurs Pathway of vibrations  Sound waves tympanic membrane ossicles oval window organ of Corti Pathway of nerve impulses  Organ of Corti CN VIII (cochlear branch) temporal lobe Pathway of vibrations  Sound waves tympanic membrane ossicles oval window organ of Corti Pathway of nerve impulses  Organ of Corti CN VIII (cochlear branch) temporal lobe

Recap: How Hearing Occurs

Receptors for Balance Mechanoreceptors (hairs) in vestibule and semicircular canals of inner ear Hairs in endolymph Vestibular branch of CN VIII