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Lab4 sensory


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Lab4 sensory

  1. 1. SPECIAL SENSESLast revised: 12/7/2011
  2. 2. The Senses Sensory receptors transduce different forms of energy in the ―real world‖ into nerve impulses. Different sensory perceptions (sound, light, pressure) arise from differences in neural pathways.  If the optic nerve delivers an impulse, the brain interprets it as light.
  3. 3. Functional Categories of Sensory Receptors Receptors can be classified according to the type of signal they transduce:  Chemoreceptors – sense chemicals in the environment  Taste, smell, or blood  Photoreceptors – sense light  Thermoreceptors – respond to cold or heat  Mechanoreceptors – stimulated by mechanical deformation of the receptor.  Touch  Hearing  Nociceptors – sense pain; damaged tissue release chemicals that excite sensory endings
  4. 4. Nociceptors Pain receptors that depolarize when tissues are damaged.  Stimuli can include heat, cold, pressure, or chemicals  Glutamate and substance P are the main neurotransmitters.  May be activated by chemicals released by damaged tissues, such as ATP.  Perception of pain can be enchanced by emotions and expectations  Pain reduction depends on endogenous opioids. Nociceptors can be myelinated or unmyelinated  Sudden, sharp pain is transmitted by myelinated neurons.  Dull, persistent pain in transmitted by unmyelinated neurons.
  5. 5. Tonic and Phasic Receptors Receptors can be categorized based on how they respond to a stimulus. Phasic: respond with a burst of activity when a stimulus is first applied but quickly decrease their firing rate—adapt to the stimulus—if the stimulus is maintained. (fast-adapting)  Alerts us to changes in the environment  Allow sensory adaptation  Smell, touch, temperature Tonic: maintain a high firing rate as long as the stimulus is applied. (slow-adapting)
  6. 6. Cutaneous Receptors Pain, cold, and heat receptors are naked dendrites  Cold receptors – located close to epidermis  Warm receptors – located deeper in the dermis.  Hot receptors – pain experienced by a hot stimulus is sensed by a special nociceptor called a capsaicin receptor. Touch and pressure receptors have special structures around their dendrites.  Meissner’s corpuscles  Encapsulated dendrites in connective tissue  Changes in texture and slow vibration  Pacinian corpuscles  Encapsulated dendrites by concentric lamellae of connective tissue structures  Deep pressure and fast vibrations  Ruffini endings  Sustained pressure  Enlarged dendritic endings with open, elongated capsule  Merkel’s discs  Expanded dendritic endings  Sustained touch and pressure  Slow adapting
  7. 7. Two-Point Threshold Test Measures the density of touch receptors The minimum distance at which two points of contact can be felt.High density of receptive fields =shorter minimum distanceLow density of receptive fields =longer minimum distance
  9. 9. Vestibular Apparatus Provides a sense of equilibrium Located in the inner ear Consists of:  Otolith organs  Linear acceleration  Utricle (horizontal)  Saccule (vertical)  Semicircular canals  Rotational acceleration Both structures in the vestibular apparatus are:  Filled with endolymph  Contain sensory hair cells which are activated by bending.
  10. 10. Sensory Hair Cells
  11. 11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hairs of hair cells bend Gelatinous Otoliths material sags Macula of utricleHair cellsSensory nerve fiber Supporting cells Gravitational force (a) Head upright (b) Head bent forward
  12. 12. Semicircular CanalsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endolymph Semicircular canal (a) Head in still position Ampulla Cupula Crista ampullaris Crista ampullaris Hairs Hair cellSupporting cellsSensory (afferent)nerve fibers (b) Head rotating (c) 12
  13. 13. Clinical ApplicationsNystagmus Vertigo Involuntary oscillations of the eyes  Loss of equilibrium with the when spinning is suddenly illusion of spinning stopped.  May be caused by anything that alters the firing rate of one of the Eyes continue to move in the vestibulocochlear nervers. direction of the spin, then jerk  May be due to spinning or rapidly back to the midline. pathologically induced by by viral  When a person begins spinning, the cupula infections. bends in the opposite direction.  If the movement suddenly stops, inertia of  Tx: Antivert® (meclizine) endolymph causes it to continue moving in  Anticholinergic action the direction of the spin.  Blocks conduction in the middle ear  This is a normal phenomenon that helps vestibular-cerebellar pathways. maintain balance during spinning, however, nystagmus can also be a symptom of certain diseases, like Meniere’s disease.
  14. 14. Anatomy of the Ear
  15. 15. Structures of the Middle Ear Cavity between the tympanic membrane and the cochlea Contains three bones called ossicles:  Malleus  Incus  Stapes  Vibrations are transmitted and amplified along the bones.  The stapes is attached to the oval window, which transfers the vibrations into the inner ear.
  16. 16. Organ of Corti Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.• Group of hearing receptor cells,called hair cells.• On upper surface of basilar Scala vestibuli (contains perilymph)membrane Vestibular membrane• Different frequencies of Cochlear duct (contains endolymph)vibration move different parts of Branch of cochlear Spiral organ (organ of Corti) Basilar membranebasilar membrane nerve Scala tympani• Particular sound frequencies (contains perilymph)cause hairs of receptor cells to (a) Tectorialbend membrane Hair cells• Nerve impulse generated Basilar membrane Branch of Nerve 16 Supporting (b) cochlear nerve fibers cells
  17. 17. Figure 10-20 Sound transmission through the ear 1 Sound waves strike 2 The sound wave 3 The stapes is attached to the tympanic energy is transferred the membrane of the oval membrane and to the three bones window. Vibrations of the become vibrations. of the middle ear, oval window create fluid which vibrate. waves within the cochlea. Cochlear nerve Incus Oval Ear canal Malleus Stapes window 5 Vestibular duct (perilymph) 3 Cochlear duct 2 (endolymph) 6 4 1 Tympanic duct (perilymph) Tympanic Round membrane window 4 The fluid waves push on the 5 Neurotransmitter release 6 Energy from the waves flexible membranes of the onto sensory neurons transfers across the cochlear duct. Hair cells bend creates action potentials cochlear duct into the and ion channels open, that travel through the tympanic duct and is creating an electrical signal that cochlear nerve to dissipated back into alters neurotransmitter release. the brain. the middle ear at the round window.Copyright © 2010 Pearson Education, Inc.
  18. 18. Clinical ApplicationsConduction deafness Sensorineural deafness Sound waves are not conducted  Nerve impulses are not conducted from the outer to inner ear. from the cochlea to the auditory  May be due to a buildup of earwax, cortex. too much fluid in the middle ear,  May be due to damaged hair cells. damage to eardrum, or  May only impair hearing of a overgrowth of bone in the middle particular sound frequency. ear.  May be helped by cochlear  Impairs hearing of all sound implants. frequencies.  Can be helped by hearing aids.
  19. 19. The EyesVISION
  20. 20. Functional Anatomy of the Eye Image is inverted on retina due to refraction of light. Degree of refraction depends on:  Refractive index (RI) of media  RI of air = 1.00  RI of cornea = 1.38  Curvature of the interface between the two media.
  21. 21. Functional Anatomy of the Eye
  22. 22. Photoreceptors Rods: Provide black and white vision under low light intensities Cones: Provide sharp color vision when light intensity is great  Humans have trichromatic vision due to the presence of three different types of cones: Blue, Green, and Red.
  23. 23. Visual Acuity Sharpness of vision Depends upon resolving power  Ability of the visual system to resolve two closely spaced dotsVisual Abnormalities  Myopia (nearsightedness)  Hyperopia (farsightedness)  Astigmatism  uneven cornea or lens  Presbyopia  hardening of the lens  impedes accommodation