Special Senses Mechanoreception Electroreception Chemoreception Others
Recall our receptor types Chemically regulated: Respond to particular chemicals Voltage regulated: respond to changing membrane potential Mechanically regulated All will produce graded potentials If graded potential produces large enough depolarization, an Action Potential will fire
Sensation & Perception Mechanical Pressure waves physical deformation Electromagnetic (voltage) Photons, electromagnetic fields Chemical Solutes or specific odorants, neurotransmitters, pheromones Mechanical Hearing, balance Nociceptors (pain), Proprioception, (movement & position), touch, vib. Electromagnetic Sight, orienting Chemical Smell, taste, temp, pain
Equilibrium Body position, movement, balance (kinetic & static) General mechanism of stimulation Movement of hair cells buried in a liquid or jelly matrix
Equilibrium & hearing
Inner Ear Sensory structures monitoring balance, position & movement contained within vestibule Internal stimulus; external stimulus kinetic equilibrium static equilibrium Vestibule
Equilibrium Static Maculae in saccule & utricle evaluates position of head relative to gravity Kinetic Crista ampullaris of Semicircular canals in utricle evaluate change in direction & rate of head movement Innervation: Vestibulocochlear Nerve (VIII)
Vestibule: Static
Semicircular: Kinetic Aligned @ right angles
Hair cell simulation Cupula behaves as a float Imagine pulling a buoy through the water Body moves & crista ampularis follows Endolymph stays put Cupula is dragged backward, then forward as movement continues, stimulating hair cells
Hearing
Cochlea
Organs of Corti in cochlea Along its entire length Sound waves displace hair cells
Hair cells of organ of corti Stimulated by pressure waves Wave displaces basilar membrane & vibrates hair cells Their anchored microvilli bend & stimulate cochlear nerve, which fires AP
Organ of Corti; ~400X
Middle ear transmits vibes External auditory meatus transmits sound waves to tympanic membrane Tympanic membrane transmits sounds to auditory ossicles Malleus, incus, stapes Stapes attaches to oval window, transmits sound to inner ear
Innervation Cochlear nerve (VIII) sends axons to cochlear nucleus in brainstem Project to midbrain -> thallamus -> auditory cortex of cerebrum
Sight: Photoreception Stimulus: Electromagnetic Photons: Detection of light Wavelength: Determination of color Ancient proteins allow transmission of signal and signal reception Crystalins in lens Opsins in photoreceptors
Gathering & projecting signal Cornea Iris; pupil Lens (crystallins) Retina Photoreceptors (opsins) Fovea
Pathway Lens projects incoming light on to retina Crystalin orientation refracts light Opsins respond to reflected light
Retina Anatomy Sensation & propagation Rods & cones; Bipolar cells; ganglion cells
Rods & Cones Rods: Ultra-sensitive to any light 20x more common than cones Cones: Sensitive to particular wavelengths Absorb blue, green or red Require much light
Rods & Cone Anatomy Outer PM folded into discs Discs loaded with Rhodopsin (pigment) Opsin + retinal in loose chemical association Manufacture of retinal requires vitamin A
Rod & Cone Signal Transduction Sensation produces reduction in neurotransmitter release Rod cells are hyperpolarized Bipolar cell is hyper or depolarized, depending on receptors
Refraction angle is constant Lens must change shape to ensure that light arriving at different angles, is projected onto the same retinal location (fovea) Ciliary muscles Focusing
Innervation Optic nerve (II): left visual field projects to right brain & vice versa Optic tectum
Chemoreception Smell (olfaction) Odorants bind to receptors on PM Produce depolarizations in sensory neurons of Olfactory Nerve (I)
Mammalian taste (Gustation) 1. Food chemical (tastant) binds to receptor in gustatory cell membrane 2. Produces graded depolarization 3. Synaptic vesicles release neurotransmitter 4. Neurotransmitter binds to sensory dendrites of nerve, eliciting AP!
Gustation Receptor organs are Taste buds Respond to solutes dissolved in saliva Occur all across tongue (and to limited extent in pharynx) in papillae
Gustatory cells Gustatory hairs project from taste cells through taste pore to epithelial surface
Taste Chemoreceptor binds sugar 2 nd messenger pathway results in Ca 2+ release and Na + channels open Cells release neurotransmitter which binds to neuron, fires AP
Signal transduction Various methods; All Chemical Salty: Na + enters cell through Na + channels Sour: H + enters cell, causes other cations to enter cell, or blocks K + channels Bitter, sweet, umami: G-protein mediated Bitter: Ca + release from intracellular stores Sweet: K + channels open
Gustatory innervation Facial (VII) - Anterior 2/3 of tongue Glossopharyngeal (IX) - Posterior 1/3 & pharynx Vagus (X) - Epiglottis & lower pharynx Taste impulses passing through brainstem trigger cranial, visceral reflexes Digestion: saliva & gastric juice secretion OR Regurgitation: gag & vomit reflex