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Chapter 19, sp 10 Chapter 19, sp 10 Presentation Transcript

  • Human Anatomy, Second Edition McKinley & O'Loughlin Chapter 19 Lecture Outline: Senses: General and Special
  • Senses: General and Special
    • Sensation is the conscious or subconscious
    • awareness of incoming sensory information .
    • Perception is the conscious awareness of
    • sensation.
    • Stimuli are detected by two classes of
    • receptors.
      • general senses distributed throughout the skin and organs.
      • special senses within complex organs in the head.
    19-
  • Receptors
    • Range from simple dendritic endings of a neuron to complex sense organs.
    • Monitor both external and internal environmental conditions.
    • A stimulus, a change in the environment, must be converted into a nerve impulse.
    • The receptive field is the entire area through which the sensitive ends of the receptor cell are distributed.
    19-
  • Tonic vs. Phasic Receptors
    • Sensory receptors may act
      • continuously ( tonic receptors ) or
      • merely detect changes in a stimulus ( phasic receptors )
    19-
  • Adaptation
    • Phasic receptors can undergo a reduction in sensitivity to a continually applied stimulus.
    19-
  • Classification of Receptors
    • Three criteria are used to describe receptors:
      • receptor distribution
      • stimulus origin
      • modality of stimulus
    19-
  • Receptor Distribution (Body Location)
    • General senses - structurally simple; throughout the body
      • Somatic sensory receptors (within body wall)
      • Visceral sensory receptors (within viscera)
    • Special senses - structurally complex; only in the head
    19-
    • Exteroceptors : Detect stimuli from the external environment
    • Interoceptors : Detect stimuli in internal organs (viscera). Primarily stretch receptors in the smooth muscle of these organs.
    • Proprioceptors : Located in muscles, tendons, and joints. Detect body and limb movements, skeletal muscle contraction and stretch, and changes in joint capsule structure.
    Stimulus Origin (Location) 19-
  • Modality of Stimulus (Stimulating Agent)
    • Chemoreceptors
    • Thermoreceptors
    • Photoreceptors
    • Mechanoreceptors
    • Baroreceptors
    • Nociceptors
    19-
  • Types of Pain
    • Phantom pain
      • Sensation comes from an amputated limb
    • Referred pain
      • Impulses from certain viscera are perceived as not coming from the organ but from the dermatomes of the skin
      • Use same spinal segment - same ascending pathways for numerous visceral and cutaneous sensory neurons
      • Useful for medical diagnosis
    19-
  • General Senses
    • Receptors generally simple
    • Stimuli: chemicals, temperature, pain, touch, stretch, pressure
    • Receptors: chemoreceptors, thermoreceptors, nociceptors, mechanoreceptors, and proprioceptors
    19-
  • Tactile Receptors
    • Mechanoreceptors that react to touch, pressure, and vibration stimuli.
    • Located in the dermis and the subcutaneous tissue.
    • Most numerous type of receptor.
    19-
  • Tactile Receptors
    • Unencapsulated:
      • free nerve endings : pain and temperature mainly.
      • root hair plexuses : hair movement
      • tactile (Merkel) discs : light touch
    19-
  • Tactile Receptors
    • Encapsulated : covered by either connective tissue or glial cells
      • Krause bulbs : light pressure and vibration
        • located primarily in the mucous membranes
      • Lamellated (Pacinian) corpuscles : deep pressure and vibration
      • Ruffini corpuscles : continuous pressure and distortion of the skin and in some joint capsules (tonic)
      • Tactile (Meissner’s) corpuscles : light touch in dermal papillae of hairless skin
    19-
  • Special Senses
    • Smell is the least complex
    • Vision is the most complex
    19-
  • Gustation – Sense of Taste
    • Gustatory receptors are housed in specialized taste buds on the dorsal surface of the tongue.
    19-
  • 4 Types of Papillae
    • Vallate (circumvallate) papillae are the
      • least numerous yet the largest
      • arranged in an inverted V shape on the posterior dorsal surface of the tongue
      • most of our taste buds are housed within the walls of these
    • Filiform papillae have no taste buds
      • on the anterior two-thirds of the tongue surface
    • Fungiform papillae have only a few taste buds
      • primarily located on the tip and sides of the tongue
    • Foliate papillae are not well developed in humans
    19-
  • Gustatory Discrimination
    • Five basic taste sensations:
      • salty
      • sweet
      • sour
      • bitter
      • umami - deliciousness - amino acids such as glutamate or aspartate
    19-
  • Gustatory Discrimination
    • Threshold varies
    • Taste maps have a broader region than originally believed
    • Not everyone tastes equally
    19-
  • Gustatory Pathways
    • Gustatory cells are taste receptors
      • Live 7-10 days
      • Chemoreceptors - food must be dissolved in saliva to be tasted
    • Facial nerve for anterior 2/3 of tongue
    • Glossopharyngeal for posterior 1/3 of tongue
    • Gustatory cortex is in the insula
    • The conscious perception of taste integrates taste info with those of temperature, texture, and smell
    19-
  • Olfaction
    • Sense of smell or remote chemoreception
    • Not highly developed in humans
    • Olfactory neurons (or receptor cells)
      • in 5 cm square area of nasal epithelium
    • Supporting cells
      • sandwich the olfactory neurons and sustain and maintain the receptors
    • Basal cells
      • function as stem cells to replace olfactory epithelium components
    • Lamina propria, internal to the epithelium, has olfactory glands secreting mucin and blood vessels and nerves
    19-
  • Olfactory Receptor Cells
    • Bipolar cells that are highly differentiated and modified
    • Have olfactory hairs in mucus: receptor proteins there detect molecules
    • Adaptation occurs rapidly
    19-
  • Olfactory Discrimination
    • Eight different primary odors that all smell as well as thousands of other chemical stimuli that not everyone smells
    • Undergo mitosis to replace aged cells!!!
    • As with gustatory receptors, the number decreases with age
    19-
  • Olfactory Pathway
    • The olfactory nerves are the olfactory neuron axons.
    • Project through the olfactory foramina into olfactory bulbs and synapse.
    • Olfactory tracts go to the olfactory cortex in the temporal lobe and not to thalamus initially !
    • Later, they can project to the thalamus and then to the frontal lobes for more specific discrimination.
    • Widespread olfactory associations with the hypothalamus and limbic system. Smells often initiate behavioral and emotional reactions.
    19-
  • The Sense of Vision
    • Photoreceptors in the eyes to detect light, color, and movement.
    • About 70% of all the receptors are in the eye
    • Binocular vision gives depth perception
    • 1 inch in diameter, only 1/6 visible
    19-
    • Conjunctiva - a superficial covering over part of its anterior exposed surface and blood vessels to nourish eye
    • Eyebrows, eyelashes, and eyelids protect against foreign objects
    • Lacrimal glands keep the exposed surface clean, lubricated, and helps prevent bacterial infection because of antibiotic like enzyme, lysozyme
    • Tarsal (Meibomian) glands are sebaceous glands that produce a secretion to prevent tear overflow from the open eye and keep the eyelids from sticking together
    • Ciliary glands are modified sweat glands that form the thick secretory products that contribute to “sleep”
    • Six extrinsic muscles move eye
    Accessory Structures 19-
  • Conjunctivitis
    • May be viral, bacterial, allergenic, etc.
    • Causes inflammation and redness, called “pink eye”
    • Trachoma is a chronic, contagious form caused by Chlamydia trachomatis .
      • A common cause of neonatal blindness in developing countries.
    19-
  • Corneal Transplant
    • Most common transplant. Also plastic artificial ones can be used.
    • Rejection rare because there are no blood vessels in cornea
    19-
  • Photoreceptors
    • Rods for vision in dim light (120 million)
      • Found more towards periphery
    • Cones for color vision and visual acuity (6 million)
      • Only work in bright light
      • Three types: red, green, and blue
        • Overlap of three ranges gives us all the colors
      • Color blindness is sex-linked (males)
    19-
  • Detached Retina
    • Separation of outer pigmented and inner neural layers of retina
    • Cause: trauma or may be no overt cause
    • Higher risk: nearsighted, diabetics, and older people
    • Retina gets starved of nutrients from choroid layer
    19-
  • Optic Disc
    • The optic disc lacks photoreceptors, therefore, it is the blind spot.
    • The macula lutea , lateral to the optic disc, is a rounded, yellowish region of the retina containing a pit called the fovea centralis (the area of sharpest vision with the highest proportion of cones and almost no rods.
    19-
    • A leading cause of blindness in developed countries
    • Increased risk with smoking and hypertension
    • Amsler grid: check in lab may detect loss of visual acuity, etc.
    • Laser photocoagulation may destroy abnormally proliferating blood vessels and help slow progression
    Macular Degeneration 19-
  • Cavities and Chambers of the Eye
    • The eye is subdivided by the lens into two separate cavities.
      • anterior cavity -between the lens and the cornea
        • anterior chamber between the iris and cornea
        • posterior chamber between the lens and the iris
      • posterior cavity
    19-
    • Lens becomes cloudy
    • A major cause of blindness worldwide
    • Causes: aging mainly, but other factors are diabetes, infections, UV, and glaucoma
    • Ultrasound fragments and then pieces removed and replaced with an artificial lens usually
    Cataracts 19-
  • Aqueous Humor
    • The anterior cavity contains aqueous humor.
      • removes waste products and helps maintain the chemical environment within the anterior and posterior chambers of the eye
      • secreted into the posterior chamber
      • then it flows through the posterior chamber
      • around lens
      • down through the pupil
      • into the anterior chamber
    19-
    • Increased intraocular pressure from aqueous humor
    • May dislocate lens, compress choroid layer and thereby constrict blood vessels nourishing retina and cause blindness from retinal degeneration
    • May not be noticed early
    • Early detection is important
    Glaucoma 19-
  • Vitreous Humor
    • Posterior cavity is posterior to the lens and anterior to the retina.
    • Transparent, gelatinous vitreous body which completely fills the space between the lens and the retina.
    • Does not circulate and turn over
    • Useful forensically if other fluids not available
    19-
  • Retinal Image Formation
    • For near vision:
      • Refraction (bending) of light rays
        • Cornea ->aqueous humor ->lens ->vitreous humor ->retina
      • Accommodation of the lens
      • Constriction of the pupil
      • Convergence (medial movement) of the eyes
    19-
  • Visual Pathways
    • Each optic nerve conducts visual stimulus information.
    • At the optic chiasm , some axons from the optic nerve decussate.
    • The optic tract on each side then contains axons from both eyes.
    • Visual stimulus information is processed by the thalamus and then interpreted by visual association areas in the cerebrum .
    • Note: the eye labels have been reversed!
    • (page 582 and figure on next page)
    19-
    • Emmetropia = normal vision (20/20)
    • Hyperopia = far-sightedness (short eyeball)
    • Myopia = near-sightedness (long eyeball)
    • Astigmatism = unequal curvature of the cornea or lens
    • Presbyopia (“old eyes”) = loss of the ability to accommodate for near vision
    How Vision Can Be Functionally Impaired 19-
  • Treatments
    • Glasses and contacts
    • Surgery
      • Corneal incision - radial keratotomy flattens the cornea for myopia
      • Laser vision correction changes the shape of the cornea for either myopia or hyperopia
    19-
  • Hearing and Equilibrium 19-
  • Hearing and Equilibrium
    • The external ear is located mostly on the outside of the body
    • The middle and inner areas are housed within the petrous portion of the temporal bone.
    • The external and middle ear are for hearing only
    • Movements of the inner ear fluid result in the sensations of hearing and equilibrium, or balance.
    19-
  • The Middle Ear
    • Contains an air-filled tympanic cavity.
    • Medially, a bony wall that houses the oval window and round window separates the middle ear from the inner ear.
    19-
  • The Middle Ear
    • Tympanic cavity maintains an open connection with the atmosphere through the auditory tube ( pharyngotympanic tube or Eustachian tube ).
      • opens into the nasopharynx (upper throat) from the middle ear - normally closed
      • air movement allows the pressure to equalize on both sides of the tympanic membrane
    • Tympanic cavity of the middle ear houses the auditory ossicles.
      • malleus (hammer), the incus (anvil), and the stapes (stirrup)
    19-
  • Otitis Media
    • Middle ear infection
    • Common esp. in young children: horizontal, short, and undeveloped auditory tubes
    • Fluid accumulates causing pressure, pain, and maybe impaired hearing
    • Possible complications: meningitis, fusion of the ossicles leading to impaired hearing
    • Antibiotics (not used much currently to avoid antibiotic resistance) or, if necessary, myringotomy, a small drainage tube in eardrum
    19-
  • The Inner Ear
    • In the petrous portion of the temporal bone, within a bony labyrinth, are membrane-lined, fluid-filled tubes and spaces, called the membranous labyrinth.
    19-
  • The Inner Ear
    • Vestibular complex
      • Vestibule
        • Contains two saclike, membranous labyrinth parts—the utricle and the saccule - interconnected through a narrow passageway
        • Used for static equilibrium and linear acceleration
      • Semicircular canals
        • The membranous labyrinth is called the semicircular ducts
        • Used for dynamic equilibrium
    • Cochlea houses
      • The membranous labyrinth is called the cochlear duct
      • Used for hearing
    19-
  • Equilibrium
    • Rotation of the head causes endolymph within the semicircular canal to push against the cupula covering the hair cells, resulting in bending of their stereocilia and the initiation of a nerve impulse.
    19-
  • Motion Sickness
    • The vestibular complex of the inner ear is sending impulses to the brain that conflict with the visual reference
    19-
  • Structures for Hearing
    • Housed within the cochlea in both inner ears.
      • snail-shaped spiral chambers in the bone of the inner ear
    • Membranous labyrinth houses the organ of Corti for hearing .
    19-
  • Sound Wave Pathways
    • Sound waves enter the external auditory canal and make the tympanic membrane vibrate
    • Tympanic membrane vibration causes movement by the auditory ossicles; sound waves are amplified. The stapes moves within the oval window; pressure waves are generated.
    • Pressure waves begin at the oval window and travel through the scala vestibuli.
    19-
  • Sound Wave Pathways
    • The sound waves displace one region of the basilar membrane causing hair cells in the spiral organ to distort when they push against the tectorial membrane. This stimulus is converted to a nerve impulse, which travels through the cochlear nerve.
    • Remaining pressure wave vibrations are transferred to the scala tympani and exit the inner ear via the round window.
    19-
  • Deafness
    • Conduction deafness is due to middle ear conditions
    • Sensorineural deafness is due to problems within the cochlea or along the auditory nerve pathway. Hard to treat with hearing aides.
    • Cochlear implants
      • Electronic device that compensates for damaged or nonfunctioning parts of the inner ear. May help person learn to speak.
      • Controversial
    19-