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Chapters 8 and11: Nonvisual Sensory Systems. Sensory Systems. The brain detects events in the external environment and directs the corresponding behavior Afferent neurons carry sensory messages to brain Efferent neurons carry motor messages to the muscles
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Sensory Systems • The brain detects events in the external environment and directs the corresponding behavior • Afferent neurons carry sensory messages to brain • Efferent neurons carry motor messages to the muscles • Stimulus: any energy capable of exciting a receptor. This defines broad categories of sensory systems • Mechanical • Chemical • Thermal • Photic
Introduction • Sensory Systems • What is the energy and how is it transduced? • What is the pathway to brain? • What common features does it share with other sensory systems?
Introduction: Chemoreceptors (gustatory and olfaction) • Animals depend on the chemical senses to identify nourishment • Chemical sensation • Oldest and most common sensory system • Chemical senses • Gustation • Olfaction • Chemoreceptors
Taste • The Basics Tastes • Saltiness, sourness, sweetness, bitterness, and umami • Examples of correspondence between chemistry • Sweet—sugars like fructose, sucrose, artificial sweeteners (saccharin and aspartame) • Bitter—ions like K+ and Mg2+, quinine, and caffeine • Advantage – Survival • Poisonous substances - often bitter
Taste • The Basic Tastes • Steps to distinguish the countless unique flavors of a food • Each food activates a different combination of taste receptors • Distinctive smell • Other sensory modalities
Taste • The Organs of Taste • Tongue, mouth, palate, pharynx, and epiglottis
Taste • The Organs of Taste • Areas of sensitivity on the tongue • Tip of the tongue • Sweetness • Back of the tongue • Bitterness • Sides of tongues • Saltiness and sourness
Taste • The Organs of Tastes • Taste receptors • Threshold concentration • Just enough exposure of single papilla to detect taste
Taste • Tastes Receptor Cells • Apical ends Microvilli Taste pore • Receptor potential: Voltage shift
Taste • Taste Receptor Cells
Taste • Mechanisms of Taste Transduction • Transduction process • Taste stimuli (tastants) • Pass directly through ion channels • Bind to and block ion channels • Bind to G-protein-coupled receptors
Taste • Mechanisms of Taste Transduction • Saltiness • Salt-sensitive taste cells • Special Na+ selective channel • Blocked by the drug amiloride
Taste • Mechanisms of Taste Transduction • Sourness • Sourness- acidity – low pH • Protons causative agents of acidity and sourness
Taste • Mechanisms of Taste Transduction • Bitterness • Families of taste receptor genes - TIR and T2R
Taste • Mechanisms of Taste Transduction • Sweetness • Sweet tastants natural and artificial • Sweet receptors • T1R2+T1R3 • Expressed in different taste cells
Taste • Mechanisms of Taste Transduction • Umami • Umami receptors: • Detect amino acids • T1R1+T1R3
Taste • Central Taste Pathways • Gustatory nucleus • Point where taste axons bundle and synapse • Ventral posterior medial nucleus (VPM) • Deals with sensory information from the head • Primary gustatory cortex • Receives axons from VPM taste neurons
Taste • Central Taste Pathways (Cont’d) • Localized lesions • Ageusia- the loss of taste perception • Gustation • Important to the control of feeding and digestion • Hypothalamus • Basal telencephalon
Taste • The Neural Coding of Taste • Labeled line hypothesis • Individual taste receptor cells for each stimuli • In reality, neurons broadly tuned • Population coding • Roughly labeled lines • Temperature • Textural features of food
Difference between smell and pheromones? Smell (Olfactory)— a mode of communication • Important signals • Reproductive behavior • Mate Selection • Territorial boundaries • Identification • Aggression • Pheromones • Mate Selection • Territorial boundaries • Identification • Aggression • Role of human pheromones
Pheromone Actions in Animals • Pheromones are chemicals that transmit a message from one animal to another • Pheromones can alter reproduction • Lee-Boot effect: the estrous cycle stops when groups of female mice are housed together • Whitten effect: the estrous cycle restarts in synchrony when a group of female mice are exposed to the urine of a male mouse • Bruce effect: involves the failure of pregnancy when a recently impregnated mouse is exposed to a normal male mouse (other than the one with which she mated) • The vomeronasal organ detects nonvolatile chemicals in urine • The vomeronasal organ projects to the accessory olfactory bulb which in turn projects to the amygdala which has connections with the hypothalamus • Lesions of the accessory olfactory bulb disrupt the Lee-Boot, Whitten and Bruce effects
Pheromone Actions in Humans • Humans possess a vomeronasal organ • Exposure to chemical present in sweat can alter human behavior • McClintock studied the menstrual cycles of women who attended an all-female college • Women who spent time together showed synchronization of their menstrual cycles • Women who spent time with men showed shorter cycles • Exposure to underarm sweat elicited synchronization • Pheromones present in human sweat can alter social behavior • Androstenol placed on a necklace had no effect on the social interactions of men, but women exposed to androstenol showed more interactions with me
Smell • The Organs of Smell • Olfactory epithelium • Olfactory receptor cells, supporting cells, and basal cells
Smell • The Organs of Smell • Odorants: Activate transduction processes in neurons • Olfactory axons constitute olfactory nerve • Cribriform plate: A thin sheet of bone through which small clusters of axons penetrate, coursing to the olfactory bulb • Anosmia: Inability to smell • Humans: Weak smellers • Due to small surface area of olfactory epithelium
Smell • Olfactory Receptor Neurons • Olfactory Transduction
Smell • Olfactory Signal • Adaptation: Decreased response despite continuous stimulus
Smell • Central Olfactory Pathways
Smell • Central Olfactory Pathways (Cont’d)
Smell • Central Olfactory Pathways (Cont’d) • Axons of the olfactory tract: Branch and enter the forebrain • Neocortex: Reached by a pathway that synapses in the medial dorsal nucleus
Smell • Spatial and Temporal Representations of Olfactory Information • Olfactory Population Coding • Olfactory Maps (sensory maps) • Temporal Coding in the Olfactory System • Olfaction paradox
Concluding Remarks • Transduction mechanisms • Gustation and olfaction • Similar to the signaling systems used in every cell of the body • Common sensory principles - broadly tuned cells • Population coding • Sensory maps in brain • Timing of action potentials • May represent sensory information in ways not yet understood
The Nature of Sound • Sound • Audible variations in air pressure • Sound frequency: Number of cycles per second expressed in units called Hertz (Hz) • Cycle: Distance between successive compressed patches • Range: 20 Hz to 20,000 Hz • Pitch: High and Low • Intensity: Difference in pressure between compressed and rarefied patches of air
The Structure of the Auditory System • Auditory System
The Structure of the Auditory System • Auditory pathway stages • Sound waves • Tympanic membrane • Ossicles • Oval window • Cochlea fluid • Sensory neuron response • Brain stem nuclei output • Thalamus to MGN
The Middle Ear • Components of the Middle Ear
Sound Force Amplification by the Ossicles Pressure: Force by surface area Greater pressure at oval window than tympanic membrane, moves fluids The Attenuation Reflex Response where onset of loud sound causes tensor tympani and stapedius muscle contraction Function: Adapt ear to loud sounds, understand speech better The Middle Ear
The Inner Ear • Physiology of the Cochlea • Pressure at oval window, pushes perilymph into scala vestibuli, round window membrane bulges out • The Response of Basilar Membrane to Sound • Structural properties: Wider at apex, stiffness decreases from base to apex • Research: Georg von Békésy • Endolymph movement bends basilar membrane near base, wave moves towards apex
The Inner Ear • The Organ of Corti and Associated Structures
The Inner Ear • Transduction by Hair Cells • Research: A.J. Hudspeth. • Sound: Basilar membrane upward, reticular lamina up and stereocilia bends outward
Central Auditory Processes Auditory Pathway • Primary pathway: Ventral cochlear nucleus to superior olive to inferior colliculus to MGN to auditory cortex
Auditory Cortex • Principles in Study of Auditory Cortex • Tonotopy, columnar organization of cells with similar binaural interaction • The Effects of Auditory Cortical Lesions and Ablation • Lesion in auditory cortex: Normal auditory function (like vision?) • Lesion in striate cortex: Complete blindness in one visual hemifield • Different frequency band information: Parallel processing, localization deficit
Concluding Remarks • Hearing and Balance • Auditory Parallels Visual System • Tonotopy (auditory) and Retinotopy (visual) preserved from sensory cells to cortex code • Convergence of inputs from lower levels Neurons at higher levels have more complex responses
Introduction • Somatic Sensation • Enables body to feel, ache, chill • Sensitive to stimuli • Responsible for feeling of touch and pain • Somatic sensory system: Different from other systems • Receptors: Distributed throughout • Responds to different kinds of stimuli
Touch • Types and layers of skin • Hairy and glabrous (hairless) • Epidermis (outer) and dermis (inner) • Functions of skin • Protective function • Prevents evaporation of body fluids • Provides direct contact with world • Mechanoreceptors • Most somatosensory receptors are mechanoreceptors
Touch • Mechanoreceptors (Cont’d) • Pacinian corpuscles • Ruffini's endings • Meissner's corpuscles • Merkel's disks • Krause end bulbs
Touch • Mechanoreceptors (Cont’d) • Receptive field size and adaptation rate
Touch • Mechanoreceptors (Cont’d) • Two-point discrimination • Importance of fingertips over elbow • Primary Afferent Axons • Aa, Ab, Ad, C • C fibers mediate pain and temperature • Ab mediates touch sensations