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Chapter 10 Sensory Part 1

Chapter 10 Sensory Part 1 - Ch 10 Sensory Physiology Part 1...

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Unformatted text preview: Ch 10: Sensory Physiology, Part 1 Ch Key Points Receptor transduction Receptor Receptive fields and perception Phasic and tonic receptors Different somatosensory modalities Five special senses Classification of Sensory System by Structural Complexity by Somatic (= general) Somatic senses senses 1. 2. 3. 4. 5. 5. Touch Temperature Nociception Itch Itch Proprioception Conscious vs. Unconscious Special senses 1. 2. 3. 4. 5. Vision Vision Hearing Hearing Taste Taste Smell Smell Equilibrium Equilibrium Sensory Receptors Overview Overview are transducers → convert stimuli into graded are potential (receptor potential) potential are of various complexity Fig 10-1 react to particular forms of stimuli Chemoreceptors _____________ _____________ _____________ Sensory Transduction Sensory Converts Stimulus into graded potential = Converts receptor potential. Threshold If receptor potential above threshold ⇒ AP If “Adequate Stimulus” Receptor potential in non-neural receptors ⇒ Receptor change in membrane potential influences NT release release Complexity Range of Receptors Receptors Receptor is part of Receptor neuron: neuron: AP triggered if receptor potential above threshold threshold Specialized receptor Specialized cell: Simple neural receptor Complex neural receptor Fig 10-1 Special senses receptor Amount of NT released ∝ stimulus strength stimulus 4 Types of Sensory Receptors Types 1. Chemo- (specific ligands) and OsmoChemo- (specific (conc. of solutes) (conc. 2. Mechano- (touch, pressure, vibration, 2. Mechanostretch) stretch) 3. Thermo- (temp. change) 3. Thermo- (temp. s s Cold receptors lower than body temp. Warm receptors (37 - 45oC) > 45oC ? 1. Photo- (light) Photo- (light) How could you create an excitatory signal in a neuron? . . . an inhibitory signal? an Receptive Fields Receptive Each 1° sensory neuron picks up Each information from a receptive field information Often convergence onto 2° sensory neuron Often ⇒ summation of multiple stimuli Size of receptive field determines Size sensitivity to stimulus → Two point discrimination test (see lab) discrimination Fig 10-3 Fig 10-2 Sensory Pathway Sensory Stimulus Stimulus Sensory receptor (= transducer) Sensory Afferent sensory neurons CNS Integration, perception CNS Distinguishes 4 Stimulus Properties Modality (nature) of stimulus Modality Type of receptor Location Location lateral inhibition (fig 10-6) population coding) Intensity Fig 10-10 Duration Somatosensory cortex Intensity & Duration of Stimulus Intensity Intensity is coded by # of receptors activated and frequency of AP coming from receptor and Duration is coded by duration of APs in sensory neurons sensory Sustained stimulation leads to adaptation Tonic receptors Phasic receptors (p 334) Tonic Receptors Receptors Phasic Phasic Receptors Receptors Slow or no adaptation Slow Rapid adaptation Rapid Continuous signal transmission for duration of stimulus of Cease firing if strength Cease of a continuous stimulus remains constant remains Monitoring of Monitoring parameters that must be continually evaluated, e.g.: baroreceptors Allow body to ignore Allow constant unimportant information, e.g.: information, Smell Somatic Senses Somatic Primary sensory neurons from receptor to spinal cord or medulla to Secondary sensory neurons always cross over (in spinal cord or medulla) → thalamus thalamus Tertiary sensory neurons → somatosensory cortex (post central gyrus) (post Touch Receptors Touch Free or encapsulated dendritic endings In skin and deep organs, e.g.: Pacinian corpuscles corpuscles concentric layers of c.t. ⇒ large receptive field concentric detect vibration detect opens mechanically gated ion channel rapid adaptation ⇒ receptor type? receptor Temperature Receptors Temperature AKA thermoceptors or thermorecetors Free dendritic endings in hypodermis Function in thermoregulation Cold receptors (< body temp.) Warm receptors (> body temp.) Test if more cold or warm receptors in lab Adaptation only between 20 and 40°C Nociceptors activated if T > 45°C Nociceptors Nociceptors Free dendritic endings Free Activation by strong, noxious stimuli Function? Function? 3 categories: Mechanical Mechanical Thermal (menthol and cold / capsaicin and hot) Thermal (menthol Chemical (includes chemicals from injured tissues) Inflammatory Pain May activate 2 different pathways: Reflexive protective – integrated in spinal cord Ascending to cortex (pain or pruritis) Pain Pain Aβ, and AΔ fibers mediate pain C fibers mediate pruritis Fast (Aδ fibers) pain is sharp Slow pain (C) is throbbing Ascend to limbic system and hypothalamusEmotional Distress Modulation Gate Control Theory: We can inhibit the pain response (fig 10-12c) Pain control NSAIDs (inhibit COX) Opiates (inhibit NT release) Referred Pain Referred Pain in organs is Pain poorly localized poorly May be displaced if Multiple 1° sensory Multiple neurons converge on single ascending tract tract Fig 10-13 Referred Pain: Heart Referred Special Senses: Smell Smell and Taste 2 of the five special senses Very old (bacteria use to sense environment) Olfaction Olfactory epithelium has > 1,000 different Olfactory odorant receptors odorant Bipolar neurons continuously divide! G-protein – cAMP mediated G-protein Brain uses “population coding” to Brain to discriminate 1,000s of odors discriminate Fig 10-14 Special Senses: Gustation Gustation Organ for taste = ? See Fig 10-15 Taste buds located in papillae located contain group of taste contain and support cells and Sour and Salt Ligands Sour Special Senses: Hearing Balance Balance Review Ear anatomy Review Ear (fig 10-17) (fig Outer Pinna or auricle Middle Incus, malleus, stapes Inner Cochlea Organ of Corti Semicircular Canals Macula and crista Macula ampullaris ampullaris & Special Senses: Sound Transmission and Transduction and Sound waves Tympanic membrane vibrations Ossicles transmit & amplify vibration Via oval window to perilymph then endolymph Interpretation of Sound Waves: Interpretation Pitch Perception Sound wave frequency expressed in Hertz (Hz) = Sound wavelength / sec wavelength Human can hear between 20 and 20,000 Hz High pitch = high frequency Low pitch = low frequency Loudness = amplitude Relative to the rate of AP released Decibels (Db) is a logarithmic scale, i.e., each 10 Db Decibels increase is a 10X increase in intensity increase noisy restaurant ~ 70 dB rock concert ~ 120 dB Tone = pure sound of 1 frequency (e.g. tuning fork) fork) Sound Transmission cont. Sound Transmission Vibrations in perilymph are Vibrations transferred across the basilar membrane to the cochlear duct membrane Vibrations in endolymph stimulate Vibrations sets of receptor cells sets Receptor (hair) cells release NT which stimulates nearby sensory neuron stimulates Impulse to auditory cortex of Impulse temporal lobe via Cochlear nerve to Vestibulocochlear N. (VIII) to Movement of Tectorial Membrane Movement Fig 10-20 Hearing Transduction Hearing = multi-step process: multi-step air waves → mechanical vibrations → fluid waves → chemical signals → APs At rest ~ 10% of ion channels open Fig 10-21 More voltagegated Ca2+ ion channels open: Excitation All channels closed: Inhibition Signal Transduction cont. Signal At rest Excitiation Inhibition Basilar Membrane Basilar Pitch perception is Pitch function of basilar membrane membrane BM stiff near oval window BM more flexible near distal BM end end Brain translates location on Brain membrane into pitch of sound membrane Fig 10-22 2 (3) types of Hearing Loss (3) 1. Conduction deafness 1. 2. External or middle ear Many possible etiologies 1. Cerumen, Otitis media, otosclerosis etc…. 2. Sensorineural deafness 1. 2. 3. Damage to neural structures (from receptors, i.e., hair Damage cells, to cortical cells) cells, Most common: gradual loss of receptor cells Need for hearing aids and cochlear implants 3. Central 1. 2. Damage to neural pathways Not common Special Senses: Equilibrium State of Balance State s Utricle and saccule (otolith organs) with Utricle maculae (sensory receptors) for linear acceleration and head position acceleration s Semicircular canals and ampullae with Semicircular cristae ampullaris (sensory receptors) for rotational acceleration rotational s Equilibrium also interpreted with input Equilibrium from vision & stretch receptors in muscle from Otolith Organs of Maculae Otolith Maculae and Crista Maculae ampullaris receptors ampullaris similar to organ of corti receptors However: gravity & acceleration provide force to move stereocilia force Fig 10-25 Not in book Motion Sickness Motion = Equilibrium disorder Due to sensory input Due mismatch mismatch Example? Antimotion drugs (e.g.: Antimotion Dramamine): Dramamine) Depression of vestibular Depression inputs inputs Vestibular Nystagmus Nystagmus = Reflex movement via input from semicircular semicircular canals & cristae ampullaris canals As you rotate eyes slowly drift in opposite direction (due to backflow of eyes endolymph) endolymph) then rapid eye movement in direction of rotation to then establish new fixation point Continues until endolymph comes to rest Continues Sudden stop ? ...
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