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45 Cards in this Set
- Front
- Back
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Sensory Physiology |
* Brain is biased in interpreting
* Based on past experiences |
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Senses
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Sensory receptors transduce different forms of energy in the “real world” into nerve impulses.
Sensory modalities: * -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. |
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-Receptors -Sensory Receptors |
-vision, hearing, smell, taste, etc. sensing the world around us… and within us
-characterized by FUNCTION |
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Law of Specific Nerve Energies
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Information from a given sensory nerve can only be experienced as one stimulus type. (ex: 1 photoreceptor can only be perceived as light) AKA The sensation produced by the “adequate” or normal stimulus is the one the brain will perceive. (ex: a punch to the eye is perceived as a flash of light) |
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Generator Potentials |
Sensory receptors behave very similarly to neurons. Stimulus causes increase in ion permeability of membrane leading to the production of a depolarization: receptor or generator potentials.
Increasing the intensity of that stimulus increases the magnitude of the generator potential until threshold is met and an action potential occurs.
SIMILAR TO EPSP (BEHAVE LIKE NEURONS) |
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Sensory Receptor Responses (Tonic vs. Phasic) |
(why some sensations go away and some never leave) * Tonic receptors respond at constant rate as long as stimulus is applied * -e.g. pain * Phasic receptors respond with burst of activity but quickly reduce firing rate to constant stimulation (=adaptation) * -e.g. smell, touch |
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Generator Potential: (HEP) |
In tonic receptors, the generator potential is proportional to the intensity of the stimulus.
-Increased intensity results in increased frequency of action potential after threshold is reached. Magnitude of AP does not change! |
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Sensory neurons of touch – |
Cutaneous receptors -Free nerve endings: light touch, hot, cold, PAIN -Merkel’s disk: sustained touch, pressure -Ruffini corpuscles: Sustained pressure -Meissner’s corpuscles: Texture, slow vibrations -Pacinian corpuscles: Deep pressure, fast vibrations |
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Taste |
(Also called gustation) -Receptors are taste buds -Located in bumps on the tongue called papillae
Specialized endothelial cells: -Cells behave like neurons by depolarizing and producing action potentials. -Cells release neurotransmitters onto sensory neurons. -Microvilli come into contact with chemicals.(expand surface area) -Each taste bud has taste cells sensitive to each category of tastes. |
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Five categories of taste |
1 salty 2 sour 3 sweet 4 bitter(relys on 2nd messenger) 5 n (relys on 2nd messenger) ex: if something taste salty, contain Sodium depolarizes, fires neuron |
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Smell |
(Smell is also called olfaction) Olfactory receptors are located in the olfactory epithelium of the nasal cavity.
-Olfactory receptors are bipolar neurons with ciliated dendrites projecting into the nasal cavity. -Proteins in the cilia bind odors.
-Basal stem cells replace receptors damaged by the environment (~ 2 months). -G-protein coupled -Odor binding activates adenylate cyclase to make cAMP. -Opens Na+ and Ca2+ channels -Neural convernage/diverenage
(much more complicated than taste) |
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Inner Ear |
Consists of a bony labyrinth surrounding a membranous labyrinth -Between the two is fluid called perilymph. -Within the membranous labyrinth is fluid called endolymph. -Endolymph has an unusually high K+ concentration (!!) |
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Vestibular Apparatus |
Provides a sense of equilibrium Located in the inner ear(component of inner ear)
Consists of: 1.Otolith organs |
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Vestibular apparatus and linear accelaration
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Utricle and Saccule provide a sense of linear acceleration
Utricle = horizontal Saccule = vertical
(Within each of them is a macula): -Specialized epithelium consisting of hair cells and supporting cells -Hair cells project into endolymph, but are embedded in otolithic membrane -Motion of otolithic membrane bends the hair cells and causes firing of action potentials onto nerve ending |
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macula |
Sensory hair cells * Macula: Composed of modified epithelial cells with 20−50 hairlike extensions called stereocilia (not true cilia) and one kinocilium (true cilium)
(monters movement in vertical or horizontal movement--- sends info to brain) |
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Sensory Hair Cells (process)
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-When stereocilia bend toward the kinocilium, K+ channels open, and K+ rushes into the cell. (big exception, more K+ outside cell)
Bending away from the kinocilium hyperpolarizes sensory dendrites.
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Horizontal movement
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* Utricle sensitive to horizontal acceleration |
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Vertical movement |
Saccule: sensitive to vertical acceeration -hair push upward when person descends |
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Semicircular Canals |
Hair cell processes are embedded in cupula of crista ampullaris
When endolymph moves cupula moves --Sensory processes bend in opposite direction of angular acceleration
Senses complex 3-dimensional movement |
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Nystagmus |
When a person’s body is spinning, eye movements are toward the opposite direction of the spin to maintain a fixation point.
When the body comes to a stop, the cupula is bent by fluid inertia and eye movements are still affected. The jerky eye movement produced is called nystagmus. |
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Ears & Hearing |
Hearing: the neural perception of sound waves -Sound waves are pressure waves
Sound waves travel in all directions from source
Waves characterized by frequency & intensity -Frequency is measured in hertz (cycles/sec) -Pitch is directly related to frequency -Intensity (loudness) is directly related to amplitude of waves (Measured in decibel) |
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Ears & Hearing
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* Sound waves funneled by pinna (auricle) into external auditory meatus |
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Middle Ear |
Middle ear is between tympanic membrane & cochlea; holds auditory ossicles(3 bones):
-Malleus (hammer) is attached to tympanic membrane -Carries vibrations to incus (anvil) -Stapes (stirrup) receives vibrations from incus, transmits to oval window
(taking large surface area, amplifying to small area, increasing stimulus) |
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The inner ear |
Cochlea: Consists of a tube wound 3 turns & tapered so looks like snail shell |
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Cochlea |
Endolymph: Tube is divided into 3 fluid-filled chambers (1. Scala vestibuli, 2.cochlear duct, 3.scala tympani)(perilymph) |
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Spiral Organ (Organ of Corti)
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Where sound is transduced
Sensory hair cells located on the basilar membrane
Pressure waves moving thru cochlear duct create shearing forces between basilar & tectorial membranes, moving & bending stereocilia
Causing ion channels to open, depolarizing hair cells
The greater the displacement, the greater the amount of NT released & APs produced
what is responsible for hearing and signal transduction? -organ of corti!!!!! |
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Ears & Hearing - Cochlea (Low) |
-Low frequencies can travel all way thru vestibuli & back in tympani -As frequencies increase they travel less before passing directly thru vestibular & basilar membranes to tympani see figure |
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Ears & Hearing - Cochlea (High) |
High frequencies produce maximum stimulation of Spiral Organ closer to base of cochlea & lower frequencies stimulate closer to apex |
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Hearing Impairment: Conduction deafness
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Conduction deafness: Sound waves are not conducted from the outer to the inner ear. -May be due to a buildup of earwax, too much fluid in the middle ear, damage to the eardrum, or overgrowth of bone in the middle ear -Impairs hearing of all sound frequencies
-Can be helped by hearing aids |
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Hearing Impairment: Sensorineural/perceptive deafness |
Sensorineural/perceptive deafness: Nerve impulses are not conducted from the cochlea to the auditory cortex. -May be due to damaged hair cells (from loud noises) -May only impair hearing of particular sound frequencies and not others
-May be helped by cochlear implants |
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The Eyes |
Transduce light energy into nerve impulses |
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Structures of the Eye
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see figure (know it!) -Photoreceptors are in retina -Retina absorbs some light -Rest is absorbed by dark choroid layer -Axons of retinal neurons gather at optic disc (blind spot) & exit eye in optic nerve |
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Basics of photoreception (sight)
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1. Light passes through the cornea and into the anterior chamber of the eye. 2. Next, it passes through the pupil, which can change shape to allow more or less light in. 3. Then it passes through the lens, which can change shape to focus the image. 4. Finally, it hits the retina, where photoreceptors are found. |
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Pupil and Iris
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The iris can increase or decrease the diameter of the pupil(where light enters).
Constriction: contraction of circular muscles via parasympathetic stimulation
Dilation: contraction of radial muscles via sympathetic stimulation |
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Retina |
* Neuron axons in the retina are gathered at a point called the optic disc (blind spot). |
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The retina |
Extension of the brain -Multilayered epithelium. Composed of neurons, pigmented epithelium, and photoreceptors (rods and cones). 3 layers: 1. Rods and cones 2. Bipolar cells 3. Ganglionic cells
Light passes through 3 layers and stimulates cones and rods -Stimulation is then passed to bipolar cells and ganglionic cells -Ganglion cells combine to form optic nerve, leaves eye at blind spot |
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Photoreceptors: rods and cones
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3 parts: 1. Outer segment: -Faces choroid, -Contains photopigment (light absorbing protein), -Structured in stacks of discs 2. Inner segment -nucleus, metabolic center 3. Synaptic terminal -Synapses to bipolar cell |
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Photoreception: how it works (Rods)
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Rods: Photopigment: opsin -Combines with retinene (derivative of vitamin A) Photopigment is rhodopsin -Only absorbs light at one wavelength -Cannot distinguish color (Vision is shades of gray) -Important for peripheral vision and night vision -About 125 million rod cells in human retina
Reaction -Light causes chemical change in rhodopsin (opsin goes from 11 cis-retinene, to all trans-retinene) -Dissociates into retinene and opsin (bleaching reaction) -Causes change in cell permeability, resulting in change in cell membrane potential |
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Photoreception: how it works (Cones) |
Cones: Photopigment is photopsin 3 types (slightly different structures that cause differences in wavelength of max absorption) 1. Blue 2. Green 3. Red
-Color vision -High acuity -Less sensitive to light -Highly concentrated at fovea -About 6 million cones in eye
Reaction -Light causes chemical change in photopsin (B, G, or R) -Dissociates into retinene and opsin (bleaching reaction) -Causes change in cell permeability, resulting in change in cell membrane potential |
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Cones |
Cones are less sensitive to light, but allow color vision and greater visual acuity.
Trichromatic vision involves three types of cones. S: short wavelengths, blue M: medium wavelengths, green L: long wavelengths, red |
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Electrical Activity of Retinal Cells
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Visual transduction is inverse of other sensory systems
-In dark, photoreceptors release inhibitory NT that hyperpolarizes bipolars -Light inhibits photoreceptors from releasing inhibitory NT, thus stimulating bipolars |
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Phototransduction: Dark current (in dark conditions)
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In dark conditions: -Na, Ca channels are OPEN -Are gated by cGMP (cGMP is required to keep open) -Open channels means depolarization and release of NT
But, this NT (glutamate) is used to INHIBIT the bipolar cells |
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Phototransduction: Dark current (in light conditions)
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In light conditions: -Na/Ca channels are closed -Due to cascade that ultimately causes the conversion of cGMP to GMP which causes Na/Ca channels to close
This causes the removal of inhibition on the bipolar cell and starts the nerve impulse from the bipolar to the ganglionic cell |
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Visual Acuity and Sensitivity
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Visual acuity is best at one point in the retina, called the fovea centralis. * Here, other layers of the retina are pushed aside, so light falls directly on a group of cones. |
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Retinal Convergence and Light Sensitivity |
Each cone has a 1:1 relationship with a ganglion cell (usually it is 105:1), which allows great visual acuity.
-Cones only work in good light.
-Convergence of lots of rods onto a single ganglion cell increases light sensitivity. |
