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Chapter 09 Lecture Outline See separate PowerPoint slides for all figures and tables preinserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 9.1 General Senses 2 A. Introduction 1. A stimulated sensory receptor sends a signal to the brain 2. Signals are interpreted in the brain 3. Receptor Potentials a. Begin with a stimulus b. Can be weak or strong (not all-or-none) c. Can add together d. Do not generate action potentials, but are part of neurons or synapse with neurons that create action potentials 3 4. Classification based on type of stimulus a. b. c. d. e. Mechanoreceptors – stimulated by changes in pressure or body movement Thermoreceptors – stimulated by changes in the external or internal temperature Pain receptors – stimulated by damage or oxygen deprivation to the tissues Chemoreceptors – stimulated by changes in the chemical concentrations of substances Photoreceptors – stimulated by light energy 4 5. Pathway to brain for general senses a. b. c. Receptor to spinal cord Spinal cord tracts to the thalamus (all senses except smell) Thalamus to the somatosensory cortex in the parietal lobe 5 B. General Senses - Proprioceptors 1. 2. 3. 4. Mechanoreceptors involved in reflex actions to maintain muscle tone Maintain equilibrium, posture, and position of limbs Muscle spindles – increase the degree of muscle contraction Golgi tendon organs – decrease the degree of muscle contraction 6 Muscle Spindle 7 C. General Senses – Cutaneous Receptors 1. Located in the deepest layer of the epidermis and the entire dermis 2. Make skin sensitive to touch, pressure, pain, and temperature 3. Three types sensitive to fine touch a. Meissner corpuscles – in dermal papillae of hairless skin b. Merkel disks – deepest epidermis c. Root hair plexus – around hair follicle 8 Cutaneous Receptors, cont 4. Three types sensitive to pressure a. Pacinian corpuscles – deep in dermis b. Ruffini endings – dermis and hypodermis c. Krause end bulbs – superficial dermis 5. Temperature receptors are free nerve endings in epidermis and superficial dermis 9 Sensory Receptors in the Skin 10 D. General Senses – Pain Receptors 1. 2. Also called nociceptors Somatic nociceptors a. Skin and skeletal muscle b. Respond to mechanical, thermal, electrical or chemical damage 3. Visceral nociceptors – react to excessive stretching, oxygen deprivation, or chemicals released by damaged tissues 4. Referred pain – brain cannot distinguish between somatic pain nociceptors and internal visceral nociceptors because they are in the same spinal cord tracts 11 9.2 Senses of Taste and Smell 12 A. Introduction 1. 2. Chemical senses Sensitive to molecules in food and in the air 3. Other chemoreceptors in the body a. Govern respiratory rate b. Sensitive to the oxygen, carbon dioxide, and hydrogen ion concentration of the blood 13 B. Sense of Taste (Gustation) 1. Sensory receptors located in the taste buds a. Primarily on the tongue b. Also present on the hard palate, the pharynx, and the epiglottis 2. Types of taste sensations a. Sweet b. Sour c. Salty d. Bitter e. Umami – meat 14 Sense of Taste, cont 3. How the brain receives taste information a. Molecules in food bind with receptor proteins on microvilli on taste cells b. Nerve impulses are generated and go to the brain c. Sensory receiving and memory areas for taste are located in the insula and parietal lobes 15 Taste Buds 16 C. Sense of Smell (Olfaction) 1. Dependent on olfactory cells a. Located in olfactory epithelium in the roof of the nasal cavity b. Modified neurons c. Olfactory cilia have receptor proteins for odor molecules 17 Sense of Smell, cont 2. How the brain receives odor information a. Nerve fibers lead to the olfactory bulb b. Combinations of activated receptor proteins account for different odors c. An odor’s signature is determined by which neurons are stimulated in the olfactory bulb d. Neurons send signals through the olfactory tract to the olfactory areas of the cerebral cortex in the temporal lobe e. Also has a direct connection to the limbic system 18 Olfactory cell location & anatomy 19 D. Senses of Taste and Smell 1. 2. 3. Both work together Smell can enhance taste Part of what is referred to as smell may actually be taste 20 9.3 Sense of Vision 21 A. Accessory organs of the eye 1. Eyebrows, eyelids, and eyelashes a. Eyebrows shade the eyes from the sun and protect eyes from perspiration or debris b. Eyelids are continuations of the skin c. Eyelashes can block debris from entering the eye d. Secretions from sebaceous glands associated with eyelashes lubricate the eye e. Eyelids help keep the eye lubricated 22 Eyebrows, eyelids, and eyelashes, cont f. g. h. Muscle that closes the eyelid – orbicularis oculi Muscle that opens the eyelid – levator palpebrae superioris Inner surface of eyelid covered by the conjunctiva; also covers the anterior surface of the eye (except the cornea) 23 Accessory structures of the orbit 24 2. Lacrimal apparatus 1. Lacrimal gland produces tears 2. Tears collect in lacrimal sac 3. Tears drain into the nose by the nasolacrimal duct 25 3. Extrinsic eye muscles 1. Contractions move the eyes; controlled by three cranial nerves 2. Superior rectus rolls eye upward – CN III 3. Inferior rectus rolls eye downward – CN III 4. Lateral rectus turns eye outward – CN VI 5. Medial rectus turns eye inward – CN III 6. Superior oblique rotates eye counterclockwise – CN IV 7. Inferior oblique rotates eye clockwise – CN III 26 Extrinsic Eye Muscles 27 B. Anatomy and physiology of the eye 1. Three layers (coats) a. Sclera – outer coat 1) White and fibrous 2) Cornea is transparent b. Choroid - middle, vascularized layer 1) Becomes the iris towards the front a) Regulates the size of the pupil b) Colored portion of eye 2) The ciliary body is behind the iris a) Contains the ciliary muscle b) Controls the shape of the lens 28 Three layers, cont c. Retina – inner coat 1) Contains photoreceptors a) Rod cells – night vision and peripheral vision b) Cone cells – distinguish colors 2) Fovea centralis – area of retina where cone cells are densely packed 3) Optic nerve – formed from sensory fibers from the retina 29 2. Lens a. b. Divides the eye into two compartments Anterior compartment contains aqueous humor c. Posterior compartment contains the retina and the vitreous humor d. Function of the lens 1) Focuses images on the retina (refraction) 2) Image produced is smaller than the object; image is inverted and reversed 30 Anatomy of the Eye 31 Functions of Parts of the Eye 32 3. Accommodation a. Process of focusing objects on the retina 1) Lens must change shape 2) Controlled by the ciliary muscle 3) Ciliary muscle is relaxed for a distant object; tightens the suspensory ligament; lens flattens 4) Ciliary muscle contracts to view a near object; loosens the suspensory ligament; lens bulges 33 Focusing 34 b. Abnormalities of refraction 1) Myopia – near-sightedness a) Have an elongated eyeball b) Light from far objects focus in front of the retina c) Correction with concave lenses 2) Hyperopia – far-sightedness a) Have a short eyeball b) Light from near objects focus behind the retina c) Correction with convex lenses 3) Astigmatism a) Have an oval-shaped cornea or irregular lens b) Correction with a lens ground to compensate 35 Common abnormalities of the eye 36 4. Vision pathway a. Function of the photoreceptors 1) Begins when light is focused on the photoreceptors 2) Rods and cones contain visual pigments called rhodopsin a) One type in rods b) Three types in cones – red, blue, and green 1) Color blindness is caused by the inherited absence of the color pigments in the cones 3) Rods and cones absorb light and rhodopsin splits into opsin and retinal 4) The light stimulus stops the release of neurotransmitter molecules from the synaptic vesicles 5) Nerve impulses travel to the visual area of the cerebral cortex 37 Photoreceptors in the eye 38 b. Function of the retina 1) Three layers of neurons a) Rod cells and cone cells are located in the deepest layer next to the choroid b) Middle layer contains bipolar cells c) Innermost layer contains ganglion cells whose sensory fibers become the optic nerve 2) Light must penetrate to the back of the retina 3) Rod cells and cone cells synapse with the bipolar cells 4) Bipolar cells synapse with the ganglion cells that initiate nerve impulses 5) Considerable processing occurs in the retina a) As many as 150 rods activate the same ganglion cell b) One cone activates one ganglion cell 39 Function of the retina, cont 6) Blind spot a) No rods and cones where the optic nerve leaves the retina b) No vision is possible in this area 40 Structure of the retina 41 c. From the retina to the visual cortex 1) The optic nerves carry impulses to the optic chiasma a) Fibers from the right half of each retina converge and continue through the right optic tract b) Fibers from the left half of each retina converge and continue through the left optic tract 2) Fibers from the optic tracts synapse with neurons in the thalamus 42 From the retina to the visual cortex, cont 3) 4) Axons from the thalamus carry impulses to the primary visual areas of the occipital lobes by way of the optic radiations The right and left visual cortex rebuilds and rights the image 43 Optic chiasma 44 C. Eye diseases and disorders 1. 2. 3. 4. 5. Cataract – clouded lens Glaucoma – increased intraocular pressure from the build-up of aqueous humor Macular degeneration – damage to the macula lutea in the fovea centralis leading to blindness Diabetic retinopathy – damage to retinal blood vessels leading to blindness Detached retina – sharp blow separates the retina from the choroid 45 Macular degeneration 46 9.4 Sense of Hearing 47 A. Introduction 1. Two sensory functions of the ear – hearing and equilibrium 2. Sensory receptors located in the inner ear a. Consists of hair cells with stereocilia b. Sensitive to mechanical stimulation (mechanoreceptors) 48 B. Anatomy of the ear 1. Outer ear a. Pinna b. Auditory canal 1) Lined with hair 2) Modified sweat glands secret cerumen 49 C. Middle ear 1) Begins at the tympanic membrane 2) Ends at bony wall with two small openings a) Oval window b) Round window 3) Three small bones (ossicles) a) Malleus b) Incus c) Stapes 4) Auditory tube (eustachian tube) extends from the middle ear to the nasopharynx 50 D. Inner ear 1) Lies in the bony labyrinth 2) Lined with membranous labyrinth 3) Filled with fluid a) Perilymph – between the bony labyrinth and the membranous labyrinth b) Endolymph – within the membranous labyrinth 4) Three areas a) Semicircular canals - equilibrium b) Vestibule - equilibrium c) Cochlea - hearing 51 Anatomy of the ear 52 C. Sound pathway 1. Through the auditory canal and middle ear a. Sound travels by the vibrations of air molecules b. Sound waves strike the tympanic membrane causing it to vibrate c. Pressure from the tympanic membrane causes the malleus, the incus, and then the stapes, to vibrate d. The stapes strikes the oval window e. Vibrations from the oval window are passed to the perilymph within the cochlea of the inner ear 53 Sound pathway, cont 2. From the cochlea to the auditory cortex a. Cochlea has three canals 1) Vestibular canal – with perilymph 2) Cochlear canal – with endolymph 3) Tympanic canal – with perilymph b. The spiral organ (organ of Corti) is the sense organ for hearing 1) Located in cochlear canal 2) Consists of hair cells and the tectorial membrane 3) Hair cells sit on the basilar membrane and their steriocilia are embedded in the tectorial membrane 54 Spiral organ, cont 4) Each part of the spiral organ is sensitive to different wave frequencies or pitches a) Tip – low pitches; base – high pitches b) Pitch sensation depends of which region of the basilar membrane vibrates 5) Volume is the amplitude of the sound wave; louder sound create more pressure and then faster vibrations of the basilar membrane 55 Sound pathway, cont c. d. e. Pressure waves move across the basilar membrane The steriocilia bend Nerve impulses begin in the cochlear nerve and travel to the brain stem, the thalamus, and then the auditory cortex in the temporal lobe 56 Mechanoreceptors for hearing 57 D. Hearing damage and deafness 1. 2. Conduction deafness – occurs from mechanical blockage of the sound waves Nerve deafness – disruption of the neural pathway; most often because stereocilia have been worn away 58 9.5 Sense of Equilibrium 59 A. Introduction 1. Mechanoreceptors in the semicircular canals are responsible for rotational equilibrium 2. Mechanoreceptors in the vestibule are responsible for gravitational equilibrium 3. Other structures in the body are involved with equilibrium a. Proprioceptors in muscles and joints b. Photoreceptors in the eye c. Cerebellum 60 B. Rotational (dynamic) equilibrium 1. 2. Involves the three semicircular canals The ampulla is the enlarged base of the three canals a. Contains hair cells with steriocilia embedded in the cupula b. Each ampulla responds to head rotation in a different plane of space 3. Displaced cupula causes the stereocilia to bend 4. Creates changes in nerve impulses traveling through the vestibular nerve to the brain 61 Rotational equilibrium, cont 5. Motion sickness a. Continuous movement of fluid within the semicircular canals b. Sensory input from the inner ear that is different from visual sensations 6. Vertigo is dizziness and a sensation of rotation 62 Rotational Equilibrium 63 C. Gravitational (static) equilibrium 1. 2. 3. 4. 5. Depends on the utricle and saccule located in the vestibule a. Utricle is sensitive to horizontal movements b. Saccule is sensitive to vertical movements Contain hair cells with steriocilia embedded in the otolithic membrane Otoliths of calcium carbonate rest on the membrane When the head moves the otoliths are displaced and the membrane is disturbed and the steriocilia are bent toward or away from the kinocilium The cerebellum and other brain centers use sensory input to maintain balance 64 Gravitational equilibrium 65 Functions of the parts of the ear 66 9.6 Effects of Aging 67 A. Vision 1. The lens of the eye does not accommodate as well – need for corrective lenses and/or Lasix 2. Three visual disorders seen frequently: a. Cataracts b. Age-related macular degeneration c. Glaucoma 68 B. Hearing and equilibrium 1. The need for a hearing aid increases with age a. Presbycusis (age-related hearing decline) b. Otosclerosis is the most frequent cause of conduction deafness in adults 2. Dizziness and the inability to maintain balance 69