Bio 103 Exam 3 - Chapter 43 Lecture Notes Dr Yost Bio 103 PDF

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Chapter 43 Lecture Notes Dr Yost Bio 103...

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Chapter 43 Sensory Systems How sensory systems work: ● Sensory Receptors ○ Specialized neuron endings ○ Specialized cells in close contact (synapse) with neurons ● Sense organs incuse sensory receptors and other cell types ● Exteroreceptors: Respond to external stimuli (temp, surface pain) ● Interoceptors: Respond to internal stimuli (stomach acid) Sensory Processing Pathway: ● Stimulus: modality ● Receptor: most sensitive to one modality (light, sound pressure) ○ Response to internal or external stimuli ● Reception: binding to receptor and receptor is stimulated Energy Transduction: ● Energy transduction: occurs at level of receptor ● Nervous System: stimulus changed to electrical signal (current focus) ● If receptor is a separate cell: ○ Receptor potential stimulated neurotransmitter release ○ Flows across synapse and binds receptors on sensory neuron ● If receptor is a specialized neuron: ○ Current generated by receptor potentials flows to a region along axon to where an AP can be generated ● All sensory receptors transduce stimulus into either a generator or a receptor potential ● Generator potential: ○ Location: somatic sense, visceral senses (internal organs) ○ Receptor Location: End of nerve ○ Function: releases neurotransmitter which stimulates sensory neuron Graded Potential: ● Generator or receptor potential ● By ligand-gated channels ● It can be summed, can lead to generation of an AP ● Characteristics: ○ Magnitude varies with stimulus strength (amount of Na+ entering the cell) ○ No refractory period

● Stimulus Intensity: ○ Determined by number of APs generated which is determined by intensity of graded potential up to a maximum level Sensing stimulus strength: ● Action potentials do not change in size, only frequency. ● Frequency code: Frequency of nerve impulses received by brain change ● Population code: Greater stimulus, greater number of receptors responding equals more impulses to CNS Sensory adaptation: ● Many sensory receptors do not continue to respond at the same rate (even if stimulus continues at same intensity) Sensory adaptation occurs for two reasons: ● During sustained stimulus: receptor sensitivity decreases resulting in lower frequency of action potentials in sensory neuron ● Changes occur at synapse in neural pathway activated by receptor (ex: amount of neurotransmitter released) Two groups of receptors: ● Tonic: slow response, gradual decrease in frequency ● Phasic: fast response, aware at beginning of stimulus and at end of stimulus. Post Transduction: Transmission: Information into the CNS (afferent) Projection: Information sent to specific part of the brain Interpretation and Perception: - Processing information by brain - Receptor pathway connects to CNS (vision, taste centers, etc) - Brain uses information from past experiences during processing (influenced by state of mind) - It can interpret sensory stimuli, or modify stimuli to make them more complete, familiar, or logical (ex: replaying of past experiences) Classification of Sensory Receptors: ● According to location of stimuli to which they respond ○ Exteroceptors and interoceptors ● Others: ○ Visceral: associated with internal organs specifically ○ Somatic: Internal organs other than viscera ■ Skin (touch, pressure, temp)

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■ Muscle Proprioceptors: Indicates body orientation and muscle/joint composition ■ Muscles, tendons, joints Mechanoreceptors: Shape change ■ Touch, pressure, gravity, stretching, movement Chemoreceptors: chemical changes Photoreceptors: light energy Thermoreceptors: temp (internal & external) ■ Used by parasites to find endothermic host ■ Predators use it to locate prey Electroreceptors: Sense electric potentials (currents) ■ Earth's magnetic field (sea turtles) Nocireceptors: Pain ■ Free nerve endings on certain sensory neurons ■ Respond to: ● Strong tactile (mechanical) stimuli ● Temperature extremes ● Certain chemicals ■ Glutamate and substance P are neurotransmitters released by sensory neurons that transmit pain signals

Mechanoreceptors: ● Action: Transduce mechanical energy into electrical (ex: sound, lungs, stomach) ● Activation: upon changing orientation and shape ● Result: ○ Provides info about shape, texture, weight, and topographic relations of objects in the external environment ○ Enable organism to maintain body position ● Tactile Receptors: (meisner’s corpuscles) ○ Simplest mechanoreceptors ■ Free nerve endings in skin ■ Detect touch, pressure, vibration, and pain ○ Many tactile receptors lie at base of hair ■ Stimulated indirectly when hair is bent or displaced ○ May be encapsulated or unencapsulated ■ Unencapsulated: Merkel cells (in skin) ● Sense light touch and adapt slowly (tonic) ● Only touch receptors in the epidermis ■ Encapsulated: ● Structure: consists of a receptor surrounded by connective

tissue layers ● Location: on a nerve ending ● Statocyst: ○ Structure: infolding of epidermis lined with receptors (hair cells) ■ Statoliths (granules) located in central surrounded by sensory hair cells ○ Function: gravity receptors (body position) ■ Gravity pulls on statoliths causing mechanical displacement at receptor, initiating receptor and action potentials ● Hair cells: ○ Functions: ■ Maintenance of body position ■ Equilibrium ■ Hearing ■ Motion detection (lateral line system) ○ Structure: ■ Surface has hairlike projections (a long kinocilium and many shorter stereocilia) ■ Mechanical stimulation of stereocilia causes positive or negative voltage changes ■ Hair cell either hyperpolarizes or depolarizes affecting release of neurotransmitter ○ Lateral line system: ■ Receptors (hair cells) embedded in gelatinous matrix location in canals along body surface ■ Water movement causes bending of cupula (dome shape) and displacement of receptors ■ Mechanical stimulation of stereocilia causes positive or negative voltage changes ■ Bending towards shorter hair hyperpolarizes hair cells and reduces neurotransmitter release. ■ Bending towards longer hair depolarizes cell and increase neurotransmitter release The Ear ● Middle ear: ○ Structures: ■ Malleous, incus, stapes ■ Auditory tube ■ Muscles and joints ○ Function:

■ Bones amplify vibrations passing from tympanic membrane through oval window and perilymph in the vestibular canal ■ Auditory tubes balances pressure and drains middle ear ■ Muscles alter tension or bones ● Inner ear: ○ Membranous labyrinth that includes: ■ Saccule and utricle ■ Three semicircular canals ○ Vestibular canal and tympanic canal connect at apex of cochlea and are filled with perilymph ○ Perilymph movement stimulated receptors in a semicircular canals and cochlea ○ Saccule and utricle ■ Stucure: hair cells covered by gelatinous cupula in which calcium carbonate ear stones (otoliths) are embedded ■ Function: static equilibrium, linear acceleration ■ Orientation: ● Saccule: Vertical acceleration, front to back tilt ● Utricle: horizontal acceleration, left to right tilt ○ Semicircular cancels: ■ Structure: each semicircular canal lies in different plane ● Ampulla: enlargement at end of each semicircular canal ○ Houses a sensory unit, the crista ampullaris ● Crista: receptor hair cells imbedded in jelly-like cupula (cup or dome) ■ Function: detecting angular acceleration ● Cochlea ○ Structure: ■ Spiral tube: connects to middle ear via oval window ■ Three canals separated by membranes ● Scala vestibuli- sound enters the cochlea at oval window ● Scala media ● Scala tympani- sound exits cochlea at round window ■ Organ of corti (mechanoreceptor) ● Uses hair cells to detect sound (pressure) waves ● Organ of corti ○ Location: entire length of scala media ○ Structure: ■ Hair cells rest on basilar membrane between scala media and scala tympani

■ Tectorial membrane above organ and in contact with the hair cells ○ Function: Hears sound ○ How: ■ Pressure waves make the oval window bulge inward ■ Vestibular fluid waves occur in vestibuli ■ Waves in vestibulo causes waves in tympani ■ Basilar membrane and organ of corti move upward ■ Receptors (hairs) contact tectorial membrane ■ Receptors flex which stimulates them ■ Receptor potential and possible action potential initiated ○ Pitch, loudness, & tone: ■ Loudness depends on wave amplitude ● Hair cells more intensely stimulated ○ Cochlear nerve transmits greater number of impulses per second ■ Tone depends on harmonics produced ● Differences in tone quality are recogonized in patterns of many hair cells being stimulated simultaneously ■ Distinguishing pitch: Basilar membrane has different thickness and stiffness in its length, variation in what areas vibrate due to changes in frequency ● Vestibulocochlear nerve: ○ Mixed functions ■ Some neurons in nerve carry info about position ■ Some neurons carry sound info Chemoreceptors ● Gustation: taste receptors ● Mammals have taste buds in papillae on tongue, each contains about 50 taste receptor cells ○ Life span: 10 days ○ Humans: sweet, soup, salt, bitter, unami (glutamate) ○ Receptors are often localized in specific areas of the tongue ● Tasting food ○ G protein pathway ■ Sweet: blocks out K+ outflow ■ Bitter: stimulates Ca2+ influx ■ Unami ○ Ion channel pathways

■ Salt: Na+ influx ■ Sour: influx of H+form substance and block K+ outflow ○ Involves cranial nerves 7, 9, 10 ○ Genetic component to taste ■ 25% supertasters, 25% nontasters

Smell ● In humans, olfaction occurs in olfactory epithelium ● Each olfactory receptor cell has an axon contributing to olfactory nerve (cranial nerve 1) which extends to olfactory bulb ● Cranial Nerve 1 ● Goes through cribiform plate in ethmoid bone ○ Bipolar cells replace every 60 days ○ Smells must be double in the mucous layer ● Sense of smell: ○ Odorant binds a receptor on cilum of an olfactory receptor cell ○ G protein is activated ● Direction of odor from which nostril the smell reaches first Photoreceptors: ● Most animals have photoreceptors that use pigments such as rhodopsins to absorb light energy ● Cnidarians, platyhelminthes, some mollusks, echinoderms ○ Light-sensitive eyespots (ocelli) detect light but do not form images ● Image formation: ○ Lens: concentrates light and focus image on photoreceptors ■ Lens not required in pin-whole eye ○ Brain: interprets image coming in along optic tract ○ At the moment, image forming eyes are categorized as: ■ Compound ■ Camera ● Direct - cephalopod mollusks ● Indirect - vertebrates ● Compound eye ○ Ommatidium ■ Individual visual nit ■ Biconvex lens and crystalline cone focus light onto photoreceptors ■ Retinular Cells: photoreceptors cells with membrane containing rhodopsin

■ Nerves from receptor cells form optic nerve ■ Final image is a mosaic Vertebrate Eye ● 3 major tissue layers ○ Sclera ■ Outer tunic (layer) ■ Protection and rigidity ○ Choroid ■ Middle tunic; pigmented (two layers) ● Components: ○ Cornea ■ Thinner, transparent sclera (fibers aligned); initial focusing ○ Iris: smooth muscle, regulates pupil size and light entry ○ Pupil ○ Lens: transparent, elastic; focuses image on retina ○ Ciliary body ■ Ciliary processes secrete fluid ■ Ciliary muscles change lens’ shape ○ Aqueous humor: liquid; in anterior cavity between cornea and lens ○ Vitreous humor: thicker fluid; posterior cavity between lens and retina ○ Fovea: concentration of cones; keenest vision ○ Blind spot: no receptors; optic nerve exits- cranial nerve 2 ● Accommodation: ○ Change in lens shape to focus image on retina ○ Method: ■ Ciliary muscle attached to suspensory ligaments attached to lens ■ Contraction and relaxation cause lens to change shape, which charges the focal length by making the lens thicker or thinner ○ Irregularities: ■ Emmetropia: normal ■ Myopia: nearsighted, image in front of retina ■ Hypermetropia: far sighted, image behind retina ■ Astigmatism: irregularities on cornea or lens ■ Presbyopia (old age): loss of near vision as accommodation decreases

● Retina: ○ Extension of CNS

○ During development receptors back out of CNS so are facing backward ○ Rods and Cones Phototransduction ● Rod cells ○ In light, glutamate hyperpolarize, reducing neurotransmitter ■ cGMP is broken down, channels close, reducing Na+ in cell ○ In dark, ospin binds to retinal in the cis form ■ cGMP opens channels that permit passage of Na+ ■ Depolarization, increased neurotransmitter ● Adaptation in rod cells ○ During exposure to bright light, rhodopsin breaks down, decreasing sensitivity ○ Dark adaptation occurs as enzymes restore rhodopsin ● Modality and color ○ 4 types of receptors: blue cones, green cones, red cones, rods ○ Color blindness occurs when there is a deficiency of one or more types of cones , usually an inherited X-linked condition Visual Fields ● Binocular vision ○ Information enters both eyes at same time ○ Important in judging distance and in depth perception ● Monocular vision (rabbits, horses, etc) ○ Eyes further apart, wider visual field Integration of visual information ● Axons of optic nerves end in thalamus, which connects to primary visual cortex in occipital lobe of cerebrum ● Optic nerve ● Crossing over occurs at optic chiasm ● Optic tract: after chiasm...