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Chapter 9 Lecture Notes page 1 Chapter 9 - General and Special Senses I. receptor structure and physiology A. receptors are specialized cells or nerve endings that detect changes in the external or internal environment (stimuli) they are able to convert stimuli into action potentials B. not all sensory information reaches the cerebral cortex stimulus receptor is activated action potential in sensory/afferent neuron subconscious regions of brain and spinal cord cerebral cortex 1. adaptation is decreases sensitivity of the receptor to a constant stimulus 2. sensory input is screened by the reticular formation in the brain stem 3. input from some receptors goes to subcortical regions of the brain C. receptor classification 1. nocireceptors detect tissue damage and warn us about the damage by making us feel pain nocireceptors can be activated by pressure, extreme temperatures, or chemicals released by damaged cells 2. thermoreceptors detect changes in temperature located in skin, muscles, liver and hypothalamus BIOL 2404 Strong/Spring 2007 Chapter 9 Lecture Notes page 2 3. mechanoreceptors detect stretch, pressure and bending used for hearing and equilibrium, touch in skin, blood pressure monitoring in arteries, body position in joints, and muscle length in skeletal muscles 4. chemoreceptors detect chemicals used for taste, smell, and monitoring of oxygen and pH of the blood 5. photoreceptors detect light used for vision II. general senses A. pain - nocireceptors 1. located in the skin, joint capsules, periosteum, and around blood vessels 2. do not adapt 3. analgesia prevents the perception of pain a. intrinsic analgesic system blocks transmission from the sensory neuron to interneurons b. extrinsic analgesia can be applied at the level of the receptor (aspirin), the afferent pathway (benzocaine blocks the transmission of action potentials in the afferent neuron) or the CNS (morphine blocks transmission from the sensory neuron to interneurons) 4. referred pain is the perception of pain coming from uninjured body parts due to convergence in the afferent pathway BIOL 2404 Strong/Spring 2007 Chapter 9 Lecture Notes page 3 B. touch and pressure: free and encapsulated nerve endings C. temperature D. proprioception: 1. free nerve endings in joint capsules detect stretch on the capsule 2. Golgi tendon organs detect tension in tendons 3. muscle spindles detect skeletal muscle length III. special senses A. olfaction 1. olfactory receptors are located in the olfactory epithelium in the superior nasal cavity just inferior to the cribriform plate of the ethmoid bone 2. olfactory receptors are neurons that have dendrites called cilia that project from the surface of the olfactory epithelium 3. molecules from inhaled air dissolve in mucus covering the olfactory epithelium and bind with membrane receptors in olfactory cilia, initiating action potentials in olfactory receptor cells 4. the receptor cell axon (cranial nerve I) projects upward through the olfactory foramina of the cribriform plate and synapses with other neurons in the olfactory bulb BIOL 2404 Strong/Spring 2007 Chapter 9 Lecture Notes page 4 5. the olfactory tract goes from the olfactory bulb to the olfactory cortex, the hypothalamus, and the limbic system B. gustation 1. gustatory receptors are located in taste buds in the epithelium of the tongue papillae, mouth and pharynx 2. gustatory receptors have microvilli that project to the surface of the epithelium 3. molecules dissolved in saliva bind with membrane receptors in the gustatory microvilli, changing its membrane potential and causing the release of a neurotransmitter 4. there are at least 5 types of gustatory membrane receptors: sweet, sour, bitter, salty, and umami (detects glutamate, which is present in high protein foods such as meat) 5. the neurotransmitter initiates action potentials in the sensory neuron innervating the cell; these neurons are located in cranial nerves VII, IX, X 6. information from these neurons is routed via the thalamus to the gustatory cortex, where information from smell and pain receptors is integrated with gustatory input BIOL 2404 Strong/Spring 2007 Chapter 9 Lecture Notes page 5 C. vision 1. accessory structures: a. eyelids and glands - protect eyes, keep surface of eye clean and moist b. conjunctiva - a layer of epithelium lining the eyelids and covering the exposed surface of the eye except the cornea c. lacrimal apparatus - lacrimal gland is in orbit (eye socket in skull) superior and lateral to eyeball; tears contain lysozyme; tears drain through lacrimal pores at medial canthus into nasolacrimal duct which opens into the nasal cavity d. extrinsic muscles - 6 skeletal muscles attached to the outside of the eyeball that move it BIOL 2404 Strong/Spring 2007 Chapter 9 Lecture Notes page 6 2. structure of eyeball a. fibrous tunic: sclera (white) cornea (anterior, clear, curved) b. vascular tunic: iris - muscle that controls the amount of light entering the eye by constricting or dilating; controlled by oculomotor nerve ciliary body - contains a muscle that controls the lens for focusing and holds the lens in place via suspensory ligaments choroid - distributes blood vessels to retina c. neural tunic pigmented layer absorbs light neural layer contains photoreceptors (rods and cones), bipolar cells and ganglion cells rods no color discrimination more sensitive - used in dim light lower acuity (sharpness of image) peripheral BIOL 2404 cones color discrimination less sensitive - used in bright light higher acuity central (fovea centralis) Strong/Spring 2007 Chapter 9 Lecture Notes page 7 optic disc where optic nerve leaves eye has no photoreceptors - blind spot fovea centralis - indentation in center of retina where images are focused d. lens - used to focus light on the retina held in place by suspensory ligaments attached to ciliary body elastic clear shape adjusted by ciliary muscle ; controlled by oculomotor nerve e. chambers BIOL 2404 anterior cavity anterior to lens - contains aqueous humor anterior chamber between cornea and iris posterior chamber between iris and lens aqueous humor: produced by ciliary body reabsorbed into canal of Schlemm produces intraocular pressure posterior cavity posterior to lens - contains vitreous body (gelatinous) holds retina in place Strong/Spring 2007 Chapter 9 Lecture Notes page 8 3. vision a. refraction - light entering the eye is bent inwards by the curved surfaces of the cornea and lens b. accommodation - the lens changes shape to focus the image on the retina near vision far vision c. convergence - the eyes move medially to focus on close objects d. photoreception - BIOL 2404 rods and cones contain visual pigment molecules that have two components: retinal and opsin retinal is sensitive to light and changes shape when exposed to light Strong/Spring 2007 Chapter 9 Lecture Notes page 9 when retinal changes shape it separates from opsin, activating photoreceptor cell 4. afferent pathway a. photoreceptor activates bipolar cell, which activates ganglion cell b. axons of the ganglion cells leave eyeball at optic disc to form optic nerve c. left and right optic nerves meet at the optic chiasm, where axons from half of each eye cross to opposite sides of the brain d. optic tract contains axons from both eyes and projects to thalamus and midbrain (origin of the oculomotor nerve) e. from thalamus, other neurons carry visual information to visual cortex D. hearing 1. structure of ear a. outer or external ear BIOL 2404 pinna directs sound waves into external auditory canal which ends at tympanic membrane sound waves make tympanic membrane vibrate Strong/Spring 2007 Chapter 9 Lecture Notes page 10 b. middle ear ossicles (malleus, incus, stapes) are attached to tympanic membrane and oval window of inner ear ossicles amplify vibrations from tympanic membrane and transmit them to the inner ear two small skeletal muscles can adjust the level of amplification to somewhat protect the ear from loud noises the auditory tube runs from the middle ear to the pharynx and equalizes air pressure across the tympanic membrane c. inner ear 3-part cavity in temporal bone; contains a fluid-filled membrane complex suspended in fluid vestibule - contains two membrane compartments: utricle and saccule cochlea - contains one coiled membrane compartment: cochlear duct in the cochlear duct is the organ of Corti BIOL 2404 Strong/Spring 2007 Chapter 9 Lecture Notes page 11 basilar membrane hair cells - stereocilia tectorial membrane fibers of cochlear branch of VIII semicircular canals (3) - each contains a horseshoe-shaped membrane compartment: semicircular ducts 2. hearing the stapes causes vibrations in the perilymph that spread into the cochlea and vibrate the basilar membrane this vibrates the hair cells up and down; as they go up the tectorial membrane stops them and bends the “hairs” bending the hairs changes their rate of neurotransmitter release and stimulates the afferent neuron a. pitch - each frequency of sound stimulates a different area of the organ of Corti BIOL 2404 Strong/Spring 2007 Chapter 9 Lecture Notes page 12 b. loudness - the louder the sound, the more hair cells in a given pitch area are activated 3. afferent pathway cochlear branch of VIII medulla oblongata inferior colliculus - motor response thalamus primary auditory cortex E. equilibrium 1. static - utricle and saccule contain maculae that monitor: a. body position with respect to gravity “hairs” are bent downwards by the pull of gravity BIOL 2404 Strong/Spring 2007 Chapter 9 Lecture Notes page 13 b. linear acceleration inertia bends the “hairs” small crystals of calcium carbonate act like gravity and inertia “detectors” 2. dynamic - semicircular ducts contain cristae that monitor rotational movement when the head or body turns, the fluid in the duct lags behind and bends the crista, bending the “hairs” of the embedded hair cells BIOL 2404 Strong/Spring 2007