Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Subventricular zone wikipedia , lookup
Endocannabinoid system wikipedia , lookup
Synaptogenesis wikipedia , lookup
Electrophysiology wikipedia , lookup
Optogenetics wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Signal transduction wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Molecular neuroscience wikipedia , lookup
BIOL 2305 Peripheral Nervous System - Afferent Division - Part II Peripheral Nervous System – Afferent – Special Senses Peripheral Nervous System (PNS) – all neural structures outside the brain and spinal cord Includes sensory receptors, peripheral nerves, associated ganglia, and motor endings PNS provides links to and from the external environment Special Senses – External Stimuli Vision Hearing Taste Smell Equilibrium 1 Cross-Section of the Eye Organization of the Retina Vision Overview Light enters the eye through the pupil; diameter of pupil modulates light Shape of lens focuses the light on the retina Retinal rods and cones are photoreceptors Reflected light is translated into mental image 2 Fovea centralis Fovea centralis in macula lutea contains high density of cones (responsible for sharp central vision) Retina is a neural layer composed of: Ganglion cells Bipolar cells Photoreceptor cells Pigment epithelium contains pigment cells that absorb excess light Pupils In bright light, they constrict to ~ 1.5 mm In the dark, they dilate to ~ 8 mm Controlled by the autonomic nervous system, pupillary reflex 3 Image Projection The image projected onto the retina is inverted or upside down. Visual processing in the brain reverses the image Convex structures of eye produce convergence of diverging light rays that reach eye Refraction of Light 4 Optics Mechanism of Accommodation Accommodation – the process by which the eye adjusts the shape of the lens to keep objects in focus Zonule of Zinn - ring of fibrous suspensory ligaments that connect the ciliary body to the crystalline lens of the eye 5 Mechanism of Accommodation Common Visual Defects 6 Retina Photoreceptors – rods & cones are first to detect light stimulus Bipolar – generates action potentials Amacrine & Horizontal cells – integrate and regulate input from multiple photoreceptor cells Ganglion cells’ axons converge to form the optic nerve (cranial nerve II) and exit the eye, creating the optic disc (blind spot) 7 Photoreceptors Rods Light-sensitive Don’t distinguish colors- are monochromatic, night vision High sensitivity (low light, night vision) Low Acuity Cones Three types: red cones green cones blue cones Distinguish colors Lower sensitivity (daylight, day vision) High acuity Photoreceptors 8 Phototransduction Rods contain the pigment rhodopsin, which changes shape when absorbing light Rods: Rhodopsin = opsin + retinal Cones contain a close analog called iodopsin Cones: Iodopsin = photopsin + retinal Phototransduction Each rod contains visual pigments consisting of a light-absorbing molecule called retinal bonded to a protein called opsin, forming rhodopsin. 9 Phototransduction Absence of light: retinal is bound to opsin Presence of light: retinal alters conformation from cis (bent) to trans (straight) isomer Trans retinal isomer no longer binds to opsin and is released from the pigment molecule in the process known as bleaching. Bleaching of opsin activates a G protein called Transducin, which activates Phosphodiesterase (PDE), which breaks down cGMP (cyclic GMP) into GMP (guanosine monophosphate), inactivating it. With less cGMP, Na+ channels begin to close, causing the photoreceptor cell to hyperpolarize. Hyperpolarization of the photoreceptor (rod or cone) causes a decrease in the release of the inhibitory neurotransmitter glutamate. Bipolar cells are now allowed to depolarize, sending action potentials to ganglion cells whose axons converge as the optic nerve and exit the posterior of the eye at the optic disc. 10 Phototransduction Phototransduction In the dark, rods and cones release the neurotransmitter glutamate into synapses with neurons called bipolar cells Bipolar cells become hyperpolarized and are unable to “fire” In light, rods and cones hyperpolarize, shutting off release of the inhibitory neurotransmitter glutamate. The bipolar cells are allowed to self-depolarized 11 Convergence and Ganglion Cell Function The Retina & Visual Acuity 12 Visual Integration/Pathway Vision Integration / Pathway Optic nerve Optic chiasm Optic tract Thalamus Visual cortex 13 The Ear / Auditory Physiology External Ear Structures & Functions Pinna - Collects sound waves and channels them into the external auditory canal. External Auditory Canal - Directs the sound waves toward the tympanic membrane. Tympanic membrane - Receives the sound waves and transmits the vibration to the ossicles of the middle ear. Sound and Hearing Sound waves vibrate tympanic membrane Auditory ossicles conduct and amplify the vibration, stapes moves oval window Movement at the oval window applies pressure on the perilymph of the vestibular duct Pressure waves move through vestibular membrane through endolymph to distort basilar membrane Hair cells (stereocilia) of the Organ of Corti are pushed against the tectorial membrane 14 Cochlea and Organ of Corti Organ of Corti Ion channels open, depolarizing the hair cells, releasing glutamate that stimulates a sensory neuron Greater displacement of basilar membrane, bending of stereocilia; the greater the amount of NT released Increases frequency of APs produced 15 Signal Transduction in Hair Cells The apical hair cell is modified into stereocilia Pitch Discrimination Different frequencies of vibrations (compression waves) in cochlea stimulate different areas of Organ of Corti Displacement of basilar membrane results in pitch discrimination 16 Sensory Coding for Pitch Waves in basilar membrane reach a peak at different regions depending upon pitch of sound. Sounds of higher frequency cause maximum vibrations of basilar membrane. Vestibular Apparatus 17 Vestibular Apparatus Cristae are receptors within ampullae that detect rotational acceleration Maculae are receptors within utricle and saccule that detect linear acceleration and gravity Vestibular Apparatus: Semicircular Canals Provide information about rotational acceleration. Project in 3 different planes. 18 Semicircular Canals At the base of the semicircular duct is the crista ampullaris, where sensory hair cells are located. Hair cell processes are embedded in the cupula. Semicircular Canals Endolymph provides inertia so that the sensory processes will bend in direction opposite to the angular acceleration. Rotational Forces in the Cristae 19 Vestibular Apparatus Cristae are receptors within ampullae that detect rotational acceleration Maculae are receptors within utricle and saccule that detect linear acceleration and gravity Otolith Organs: Maculae The otolith organs sense linear acceleration and head position 20 Otolith Organs Stereocilia and Kinocilium When stereocilia bend toward kinocilium; membrane depolarizes, and releases NT When bends away from kinocilium hyperpolarization occurs Frequency of APs carries information about movement Maculae of the Utricle and Saccule Utricle: More sensitive to horizontal acceleration. During forward acceleration, otolithic membrane lags behind hair cells, so hairs pushed backward. Saccule: More sensitive to vertical acceleration. Hairs pushed upward when person descends. 21 Taste (Gustation) Taste Receptors - Clustered in taste buds Associated with lingual papillae Taste buds Contain basal cells which appear to be stem cells Gustatory cells extend taste hairs through a narrow taste pore Taste (Gustation) Epithelial cell receptors clustered in barrelshaped taste buds Each taste bud consists of 50-100 specialized epithelial cells. Taste cells are not neurons, but depolarize upon stimulation and if reach threshold, release NT that stimulate sensory neurons. Taste (Gustation) Each taste bud contains taste cells responsive to each of the different taste categories. A given sensory neuron may be stimulated by more than 1 taste cell in # of different taste buds One sensory fiber may not transmit information specific for only 1 category of taste Brain interprets the pattern of stimulation with the sense of smell; so that we perceive complex tastes 22 Taste Receptor Distribution Salty: Na+ passes through channels, activates specific receptor cells, depolarizing the cells, and releasing NT Sour: Presence of H+ passes through the channel, opens Ca2+ channels Sweet and Bitter: Mediated by receptors coupled to G-protein (gustducin). 23 Summary of Taste Transduction Smell (Olfaction) Olfactory epithelium with olfactory receptors, supporting cells, basal cells Olfactory receptors are modified neurons Surfaces are coated with secretions from olfactory glands Olfactory reception involves detecting dissolved chemicals as they interact with odorant binding proteins 24 Olfactory Receptors Bipolar sensory neurons located within olfactory epithelium Dendrite projects into nasal cavity, terminates in cilia Axon projects directly up into olfactory bulb of cerebrum Olfactory bulb projects to olfactory cortex, hippocampus, and amygdaloid nuclei Olfaction Neuronal glomerulus receives input from 1 type of olfactory receptor Odorant molecules bind to receptors and act through G-proteins to increase cAMP Open membrane channels, and cause generator potential; which stimulate the production of Aps Up to 50 G-proteins may be associated with a single receptor protein G-proteins activate many G- subunits - amplifies response 25