Summary Sensory Physiology (c) 2001-07-10 F.M.Suchanek http://www.mpi-inf.mpg.de/~suchanek/personal/texts/summaries/sensphys.txt This is a summary of the lecture "Sensory Physiology" held by Prof. Gunnar Jeserich at the University of Osnabrueck in the summer semester 2001. The lecture is based on the preceding "Introduction to Neurobiology" (see NeuroBio.txt). DO NOT PRINT (or read) this file unless you see the OK sign: ___ | / \ | / ( ) |< \___/ | \ This is important for the "pictures". You need a fixed font (e.g. FixedSys or CourierNew) and at least 72 chars per line (just pull the window larger). You are of course invited to help correcting and extending this summary. Just send an e-mail to f.m.suchanek@zweb.de (remove the letter 'z') . By reading the following text, you accept that the author does not accept any responsibility for the correctness or completeness of this text. If you have any corrections or remarks, please send me a mail. This is the only way to make the publication of this summary useful for me, too. My e-mail address is f.m.suchanek@zweb.de, but the letter 'z' has to be removed from the address. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Stimuli ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 4 attributes of a stimulus: * modality * location * intensity * timing Modalities: * entero receptors, measure state of internal organs * chemo receptors (taste & smell) * somatosensory & mechanical receptors (hearing & muscles) * photo-receptors (vision) Reception: Detecting stimuli, takes place in sensory cells Perception: Creative process of information generation from sensory inputs, takes place in the brain. Sensory transduction: Conversion of a graded stimulus (as represented by a graded receptor cell potential) to a series of APs. Sensitivity: When sensitivity is increased, the working range is decreased, because AP frequency must be above a threshold and below a limit (due to the refractory period). Multiple sensory cells with different working ranges expand the overall working range ("recruitment"). ^ Response |....____..... upper limit (refractory limit) | / | / |_/........... lower limit (threshold) | +-------------> Stimulus intensity Sensory cells: ... do not measure duration but * fire during the stimulus (tonic|proportional transducers) Stimulus |---********----| Response |---||||||||----| * fire on the onset of a stimulus (onset differential|phasic transducers) Stimulus |---********----| Response |---|||---------| * fire on the offset of a stimulus (offset differential transducers) Stimulus |---********----| Response |-----------|||-| * fire strongly on the onset and continue with a decreasing intensity (differential proportional transducers) Stimulus |---********----| Response |---|||-|-|-|---| Primary and secondary sensory cells: Primary sensory cells have an own axon and generate action potentials. In humans, this type of sensory cells only occurs in the olfactory system. Secondary sensory cells just depolarize according to the stimulus. Another neuron "listens" to the depolarization by a synapse and generates the appropriate action potentials. Primary )-------O--------------( --> brain Secondary )-------O)-------O-----( --> brain Adaptation: ...of a cell means that a cell reduces its response although the stimulus persists. Spontaneous activity: Some sensory cells fire spontaneously, i.e. without a stimulus. This provides a so-called "ground activity" and permits the sensory organ to reach the working range more quickly. Steven's law: If people are to show their intensity experience of a stimulus, they judge it proportional to the frequence of APs and log-proportional to the stimulus intensity. ^ _______ | __/ Experienced | _/ intensity | / |/ +---------------> Stimulus strength Weber's law: dS = K * S dS = just noticable stimulus difference K = constant S = stimulus intensity The just noticable stimulus difference is proportional to the overall strenght of the stimulus. Weber-Fechner-Law: I = K * log(S/S0) I = Intensity as experienced by the subject K = constant S = stimulus intensity S0 = lowest threshold stimulus a person can detect Some cranial nerves: 1. Olfactory nerve 2. Optic nerve 3. Oculomotor nerve 7. Facial nerve 8. Vestibulo-cochlear nerve 9. Glossopharyngial nerve (taste) 10. Vagus nerve ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The Eye ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Constituents of the eye: * lens * iris surrounding the lens * cornea * retina (photoreceptors and neurons in the back of the eye ball) * fovea (place in the retina where the neurons are shifted aside so that the light can reach the photoreceptorss undistortedly --> best vision) * optic disc (place in the retina where the optic nerve starts towards the brain --> no vision) ____ /| \ ( cornea /-- optic disc ( O ) O lens --- optic nerve \|___/------- ) fovea | iris Accomodation: Adjustment to distance. The cilary muscles (controlled by the parasympathetic nerve) can relax (stretching the lens --> far vision) or contract (widening the lens --> close vision). Adaptation: Adjustment of the eye to light. Carried out by two muscles: * The diletator muscle opens the iris. Controled by sympathetic nervous system * The sphinctor muscle closes the iris. Controled by parasympathetic nervous system. Constituents of the retina: * photoreceptors * horizontal cells connecting the PRs * bipolar cells connecting the PRs and the ganglion cells * ganglion cells collecting information and sending it to the brain * amacrino cells lying in between and connecting bipolar cells PR bipolar cell ganglion cell ==O )-----o---------( )-------o--------( \ horizontal O O amacrino cell cell / ==O )-----o---------( )-------o--------( PR bipolar cell ganglion cell Photoreceptors (PRs): ... consist of a stack of discs which detect light, a soma with the nucleus and a synapse to the subsequent cells. New discs are build near the soma and move upwards. Old discs are popped. There are two types of PRs: Rods & Cones. _____ |||||||_____) )---- discs soma synapse Rods (vision in the dark, roD = Dark): * look like a sky scraper * sensitivity to light * high amplification (i.e. low stimuli are enlarged) * low temporal resolution (--> summing up multiple photons to one single answer) * not present in the fovea (so you cannot see stars if you fixate them directly) * achromatic (no color vision) * convergent pathways (many rods point to one single output cell) * bad spatial resolution Cones (day vision, Cone = Color): * look like triangles * lower sensitivity to light * low amplification * high temporal resolution * concentrated in the fovea * chromatic (there are 3 types of cones, each for 1 basic color) * dispersed pathways (every cone answers nearly on its own) * less numerous than rods * good spatial resolution Light detection: ... takes place in the disks of the PRs. In its basic state, a PR has a high concentration of the molecule cGMP. It keeps cGMP-gated Na+ channels open. Na+ rushes in and depolarizes the cell. Consequently, a so-called "dark current" is always present. Meanwhile, open K+ channels try to hyperpolarize the cell (K+ rushes out). When light hits the cell, the following happens: 1. the light absorbing part ("retinal") of the visual pigment ("rhodopsin") detects the light 2. the rhodopsin activates the G-protein "transducin" 3. the transducin activates a cGMP phosphodiesterase molecule (PDE) 4. This converts cGMP to 5'GMP by means of hydrolyse 5. cGMP-gated Na+ channels close 6. the open K+ channels re-hyperpolarize the cell light v Na+ =======R==================| v |======= G PDE cGMP /\ cGMP 5'GMP cGMP production: In general, a lot of cGMP is present in the dark. When light is detected, cGMP is destroyed. cGMP-gated Na+ channels close. This also prevents Ca2+ from streaming into the cell. Since it constantly pours out of the cell, the Ca2+ concentration is decreased. This activates a molecule called GCyclase, which was previously blocked by Ca2+. It now reproduces cGMP from 5'GMP, thus playing darkness again. That's how the eye adapts to bright light. Amplification: Since one rhodopsin activates ca. 500 transducins and each cGMP phosphordiesterase molecule destroys 2000 cGMPs, the stimulus is amplified in the PR by a factor of a million. Ganglion cells: ... collect visual information. Each of them has a "receptive field" (region of interest) with a center and an antagonistic surround. In the periphery of the retina, these fields are larger (i.e. lower spatial resolution). The receptive fields respond weakly to uniform light but are good at measuring changes. There are two types of ganglion cells: On-center ones (firing if light hits the center or light on the surround is disrupted) and off-center ones (firing when light hits the surround or light on the center is disrupted). PRs and ganglia: PRs send data to both on- and off-center ganglia, but via different bipolar cells. When light hits the PR, it is hyperpolarized. Connected off-center-bipolar cells also become hyperpolarized (by excitatory ionotrophic non-NMDA-receptors) and the following off-center ganglia also hyperpolarize and stop firing. In contrast, on-center bipolar cells become depolarized when the PR hyperpolarizes (by inhibitory glutamate recpetors). Following on-center ganglia also depolarize and sent APs. Contrast: Due to a sophisticated connection of neighboring PRs, the eye is especially sensitive to contrasts: Each light receiving PR inhibits neighboring PRs by the horizontal cells. Consequently, those PRs which lie near a light area are not inhibited from both sides and their potential is stronger. dark bright reality #########-------- _ potential _______/ ______ _/ Color vision: There are two competing theories for the ability of color vision: * The trichromacy theory (states that there are 3 types of cones for each of the basic colors blue, red & green which produce the full spectrum of colors) * The color opponency theory (states that colors are defined by their opponent colors, given evidence by the after-image experiment) Cell populations in the retina: 1. magnocellular pathway (alpha-cells): large cells for structural image, color insensitive 2. parvocellular pathway (beta-cells): small cells for details, color sensitive 3. gamma-cells: movement recognition The central visual pathway: ...carries visual information from the eye to the cortex. It passes the following areas: Retina --optic nerve--> Chiasm --optic tract--90%--> LGN ==> PVC \--> Pretectum \--> Sup. Coll. ^---> Cerebral C. Chiasm: The Chiasm is the crossing of the right optic nerve and the left optic nerve. Since both eyes send information about both the left and the right visual hemisphere, this data has to be re-ordered such that the right half of the brain only receives left hemisphere info and the left half of the brain only receives right hemisphere info. Lateral Geniculate Nucleaus (LGN): Two areas in the Thalamus, one for the left hemisphere and one for the right hemisphere, main visual input gate to the Viusal Cortex. Each of them receives a weighted projection of the retina and consists of 6 layers. These layers receive their input alternately from the left and right eye. The lower two layers send their output via the Magnocellular Pathway, while the upper 4 layers use the Parvocellular Pathway. Magnocellular Pathway: Nerve leading from the LGN to the Primary Visual Cortex. It consists of large cells (hence the name). The visual data sent has * no color information * luminance information * a low spatial frequency * a high temporal frequency The Magnocellular pathway thus carries merely structural information. Parvocellular Pathway: The second nerve from the LGN to the Primary Visual Cortex. It consists of small cells and it's data is characterized by * color information * no luminance information * a high spatial frequncy * a low temporal frequency The Parvocellular pathway thus carries more detailed information and color data. Pretectum: Controls pupillary reflexes via parasympathetic nerve fiber. Superior Colliculum: Area in mesencephalon, controls saccadic eye-movements (when the eye follows something which moves). Receives 10% of the data from the optic tract. Sends information to and receives information from the Cerebral Cortex. Primary Visual Cortex (PVC): Receives visual data from the LGN and consists of 6 layers. Layer 1: Layer 2: reveives from 4, sends to cortex Layer 3: receives from 4, sends to cortex Layer 4: receives from LGN, sends to 2 and 3 Layer 5: in contact with 2 and 3, sends to Sup. Colliculus and 6 Layer 6: receives from 5, sends to 4 and LGN Thus, Layer 4 is the input, layers 2 and 3 are the output. Layer 6 establishes a feedback loop to the LGN. All layers are subdivided into columns. Each of the columns is sensitive to a stimulus of a bar in a certain rotation position (i.e. - \ | /). Among these shape columns, there are also non-shape-sensitive color columns. Behind this first two-dimensional sheet of layers and columns, there are other layers-&-columns- sheets, thus forming a three-dimensional block. Each of these sheets receives its data from only one eye. Hence, the sheets are called "ocular dominance columns". The PVC consists of 2 types of cells: 1. Simple cells Each simple cell responds to one specially rotated bar. It gets its input from a sequence of concentric cells in the retina and just ANDs the inputs. Algorithm for a cell responding to a horizontal bar: IF retina[x,y] and retina[x+1,y] and retina[x+2,y] THEN FIRE. 2. Complex cells Each complex cell respnds to a certain bar combination. It gets its input from a sequence of simple cells and just ANDs the inputs. Algorithm for a cell responding to the pattern of a cross: IF verticalbar and horizontalbar THEN FIRE. \|/-\|/-\|/-\|/ / \|/-\|/-\|/-\|/ / / / Layer 1 \|/-\|/-\|/-\|/ / / Layer 2 \|/-\|/-\|/-\|/ / / left ocular dominance sheet Layer 3 \|/-\|/-\|/-\|/ / Layer 4 \|/-\|/-\|/-\|/ / right ocular dominance sheet Layer 5 \|/-\|/-\|/-\|/ Layer 6 \|/-\|/-\|/-\|/ left ocular dominance sheet columns for bar positions Abstraction: Visual data is constructed in the retina and is then passed to the PVC. It is transformed from pixels to structures and thus becomes steadily more abstract: Receptor cells -> Bipolar cells -> Retinal ganglion cells -> LGN cells -> Simple cells -> Complex cells Further visual processing: * Parietal pathway ("Where"-pathway) in the upper brain region Spatial information, direction of movement, spatial constancy, multisensory integration (visual+auditory+somatosensory info) * Temporal pathway ("What"-pathway") Object recognition * Gyrus angularis (parieto-temporal transition zone) Object/Color-recognition ("binding", association) Hemisperic specialisation: The left hemisphere of the brain has specialized in language abilities, reading, writing and calculating (functional processing). The right hemisphere has specialized in in pattern recognition, music and spatial orientation (intuitive processing). ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The Ear ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Constituents of the ear: * Outer ear * auricle (Ohrmuschel) * ear canal, leading to the middle ear * Middle ear * Tympanum membrane separating the ear canal from the middle ear cavity * Middle ear cavitiy air-filled area between the tympanum and the cochlea, connected to the mouth via the eustachian tube * Malleus (hammer) + incus (anvil) + stapes (stirrup) (MIS) Mechanical construction passing the vibrations of the tympanus to the cochlea * Cochlea 3 tubes formed like a snail, detects sound and sends acoustic information to cortex. All tubes are filled with fluid. Consists of * Scala vestibuli upper tube, starts from the middle ear at the "oval window" * Reissner's membrane separating the Scala vestibuli and media * Scala media middle tube, contains sensory cells (s.b.) * Basilar membrane separating the scala media and tympani * Scala tympani lower tube, starts from the middle ear at the "round window" * helicotrema inner point of the snail, the only connection of scala vestibuli and scala tympani | MIS scala vestibuli \________________/-\O====>=====>======>======\ helicotrema _______________t_ _O=<====<======<======<==/ / ear canal \ \ scala tympani | \ \ auricle \ \ eustachian tube Sound travel: * Sound is catched by the auricle * It passes through the ear canal * It makes the tympanum membrane vibrate * This vibration is transferred to the oval window via malleus (hammer) + incus (anvil) + stapes (stirrup) (MIS) * Sound travels up the scala vestibuli * it reaches the helicotrema * it travels back via the scala tympani * the scala tympani emits the vibrations via the round window to the middle ear cavity Frequency determination: Since the vibration travels up the scala vestibuli and down the scala tympani, it causes the basilar membrane, which is between them, to vibrate. But the basilar membrane is thick (unelastic) at its beginning and thin (elastic) at its end and thus each point of the membrane responds best to a specific frequency. Near the oval window, only high frequencies can vibrate the basilar membrane (up to 20000 Hz), while towards the helicotrema, low frequencies are deteced (down to 16 Hz). Scala media: The scala media is the middle tube of the cochlea and its main sensory part. Within the tube, there is a hill (the "organ of corti") running from the beginning of the scala to its end. The hill is covered by four lines of "hair cells", i.e. one line of "inner hair cells" and three lines of "outer hair cells". Above this hill, there is the tectorial membrane. All lines of hair cells have small, middle and long hairs reaching towards the tectorial membrane. The longest hairs (kinocilia) of the outer hair cells are connected to it. They consist of so-called "micro-tubuli". When sound runs through the cochlea, the basilar membrane vibrates and thus changes the position of the hill towards the tectum. The resulting stream of the fluid bends the inner hair cells, which then produce a potential. tectum _____________ | __._..._ | |__/ \ | scala media tube hill \________| ... hair cell lines The Hairs (stereocilia): The hairs of one inner cell are connected by so-called "tip-links". Whenever the hairs bend (like grass does when there is wind), the distance between their "heads" becomes larger, the tip links are stretched. They pull open a channel door in the hair and Ca2+ and K+ stream in, thus depolarizing the cell. A neurotransmitter is released (glutamate) and the afferent nerve is stimulated. At the same time, voltage-gated K+-channels at the soma of the cell open. K+ streams out because the surrounding of the cell has a low K+-concentration. Thus, the cell repolarizes. Hair cells have a spontaneous activity, i.e. they may have a potential without a stimulus. When they are bend towards the konocilium, they increase their potential. When they are bend in the opposite direction, they stop their spontaneous activity and thus decrease the potential. By this means, a hair cell can signal 3 states: Normal, bent in direction 1 and bent in direction 2. K+ | K+ v // _ open K+ door | _..// .. tip link v // // _..// // // // // // // // hairs of a hair cell Spiral ganglion cells: The inner hair cells become depolarized by the channels in the hair. Each inner hair cell sends to numerous ganglion cells, thus amplifying the signal. These diverging pathways also serve as recruitment to cover the whole spectrum of loudness: Each connection to a ganglion cell is specialized on a certain intervall of loudness. The ganglion cells pass the information on to the acoustic nerve which exits the ear region. ====######)-------O----- 120 dB ===######)-------O----- 80 dB --> brain ==######)-------O----- 40 dB hair cell ganglia Sensitivity: Each inner hair cell responds to a certain frequency, according to its position on the basilar membrane. However, high amplitudes (loud sound) of neighboring frequencies also stimulate the cell. The specific responding of a cell to a certain combination of loudness and frequency is shown by its Tuning-curve. In summary, both loudness and frequency are solely encoded by the hair cells. Complex sounds (language) are split up into their basic frequencies. Amplification: Since the cochlea is filled with (rather inert) fluid, much more energy is needed to vibrate the basilar membrane. That's why the sound is amplified by three mechanisms: 1. The tympanum is much larger than the oval window. Thus, the energy of a large area is concentrated on a small area and thereby amplified 17-fold. 2. The ear bones also vibrate and contribute a 1.3-fold amplification. 3. The outer hair cells can stretch and contract. By unknown mechanisms, they shorten and lengthen exactly accordingly to the sound frequency, thus supporting and amplifying the vibration. It is supposed that the protein "Prestin" plays a role. Sometimes, un-amplification is needed, when the sound is too loud: Muscles then tighten the malleus + incus + stapes construction, thus reducing its vibration. The acoustic pathway: spiral ganglion cells | | (auditory nerve) | dorsal ("what") and ventral ("that") cochlear nucleus |\ | \ | medial superior oliva (MSO) and | lateral superior oliva (LSO) ("where") | / |/ inferior colliculus | Medial geniculate nucleus (MGN) ------ Primary auditory cortex (PAC) The ventral cochlear nucleus projects the information, "that" there is a sound event to the inferior colliculus. This pathway employs the so-called "multipolar cells". The dorsal cochlear nucleus sends the sound information itsself ("what"). This pathway employs the "pyramidal cells". The "Where"-pathway is based on "bushy cells". Sound localization: Detecting the source of sound (the "where") is done in the oliva. 3 aspects of the sound stimulus can be used to find out the source direction: 1. Amplitude spectrum The direction of the sound relative to the head may change the amplitude spectrum (i.e. the composition of frequencies and amplitudes). 2. Temporal delay The sound arrives later at the ear which is farther away from the source. This works best with a big head (and thus a large distance between the ears). The temporal delay is measured by the MSO. 3. Intensity difference The intensity arriving at the ear wghich is farther away from the source of sound will be less. The intensity difference is measured in the LSO. Medial superior oliva (MSO): Helps locating the sound by measuring the temporal delay between the input from both ears. It consists of multiple coincidence cells which each respond to a different delay interval. This is simply implemented by nerves of different lengths from both ears to one cell. If the nerve from the left ear to the cell is longer than the nerve from the right ear, then both inputs will only arrive together (and thus stimulate the cell), if the stimulus on the left ear was earlier than the one on the right ear. from left -->--v------v------v ear O O O from ^------^------^----<-- right ear Lateral superior oliva (LSO): Helps locating the sound by measuring the intensity difference between the inputs from both ears. It consists of multiple cells which each respond to a certain relation of left ear intensity to right ear intensity. All cells receive input from both ears, but the input from one ear is always inhibitory. Suppose that the left ear projects to one LSO-cell with two inhibitory connections, while the right ear projects with only one excitatory connection. Then this cell will only fire if the intensity of the right ear is at least twice as high as the one from the left ear. - + from |>>> O <| from left -->--|>> O <|---<-- right ear |> O <| ear Inferior Colliculus: The inferior colliculus contains a detailed "map" of the sound: It consists of layers which each respond to a certain frequency. Each layer is concentrically subdivided into rings which each respond to a certain loudness. _______ / \ _______ | / \ | _______ | | / ___ \ |__/ 30 kHz layer | / \ | | | | O | |__/ 20 kHz layer | \___/ | \_______/ 10 kHz layer inner rings: quiet outer rings: loud Primary auditory Cortex (PAC): The PAC consists of 6 layers and works similarly to the PVC: The 4th layer receives input, while the 5th and 6th layer send feedback. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Proprio-reception & Vestibulary organs ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Golgi-Tendon-Organ: The Golgi-Tendon-Organ measures the stretching of a muscle. It consists of a so-called "1b-fiber" innervating the transition area between a muscle and a tendon. This transition area is a column, in which plaited connective tissue fibers hold the muscle and the tendon together. Whenever the muscle contracts, the tension stretches the connective fibers and decreases the space between them. Hence there is a pressure on the 1b-fibers which causes the neurons to fire. ######## ######## muscle ######## ######## /\/\/\/\ connective tissue fibers \/\/\/\/_____ /\/\/\/\_____\ \/\/\/\/______\_____ 1b-fiber /\/\/\/\______/ \/\/\/\/_____/ /\/\/\/\ \/\/\/\/ ######## ######## ######## tendon ######## Neuromuscular spindle: The neuromuscular spindle measures the length of a muscle. It lies within a msucle and is surrounded by the nerve endings of a so-called "1a-fiber". Whenever the muscle is stretched, the spindle is stretched, too, and the 1a-fiber is stimulated. _____________________________ | | | | 1a-fiber ##########|###|###|###|############## ####### | | | | ####### ######----(---(---(---(---(----###### spindle ####### | ####### muscle ##########################|########## |____________ gamma-motorical fiber Length stabilization: The neuromuscular spindle can be used to keep a muscle in a certain state. A reflectory control loop (feedback loop) connects the 1a-fiber to the motor neurons. Whenever the muscle becomes too long, the 1a-fiber fires and thus causes the motor neurons to contract the muscle. Length modification: The spindle works independently from the surrounding muscle. It can be prestreched by gamma-motorical efferent nerves, which only innervate the spindle. When the spindle is prestreched, the 1a-fiber "thinks" that the muscle has been stretched and activates the reflectory control loop, thus causing the motor neurons to contract the muscle. This mechanism allows for a controlled length configuration of the muscle. The sense of rotation: At the end of the cochlea, there are three tubes, called the anterior, the posterior and the lateral semicircular duct. Each is formed like an arc, filled with fluid and covers one dimension. Each arc has two bumps, called "ampullae". The ampullae contain a large, flexible structure called "cupula", which blocks the way. It is innervated by the hairs of hair cells. Whenever the head is turned, the (inert) fluid in the arcs puts pressure on the cupula and bends it. The built-in hair cells are bend together with the cupula and change their potential to signal rotation. cupula ________ ampulla _/ /##/ \_ ______/ /##/ \__________ semicircular duct (##( <<< \##\ fluid ___________\\\\______________ ^---hair cells The sense of acceleration: There are two acceleration measurement organs in the human ear: The Macula utriculi, which is located together with the semicircular ducts, measures straight acceleration. The Macula sacculi, which is located between the cochlea and the semicircular ducts, measures up and down acceleration (and thus gravitation). A macula consists of a flexible block wich is innervated by the hairs of hair-cells. The hair cells are arranged in a tringle and at one vertex of this triagle, there is a longer hair called "kinocilium". The surface of the block consists of little stones called "otoliths". Whenever the head is accelerated in a specific direction, the (inert) otoliths bend the block. The position of the hairs towards the kinocilium is changed and the hair cells change their potential. ___o_o_o_o___ otoliths <-- \ \ macula \ \\\ \ hairs Vestibular nucleus: Both the maculae and the semicircular ducts send their information together with auditory data from the cochlea via the vestibular nerve. The vestibular nucleus gathers the data from this vestibular nerve and also from the eye and the proprio-receptors. The vestibular nucleus then sends this information via the thalamus to the cortex. Furthermore, it is connected to the cerebellum. __ eye --->-------/ \ _ thalamus vestibular --->------| |-------/ \----------> cortex org's & ear | | \_/ proprio- --->-------\__/ receptors ^---------------> cerbellum The cerebellum's job in proprio-reception: The cerebellum is linked to the efferent and afferent fibers of the motorical cortex. It compares these "commands" and "results" to the data it gets from the vestibular nucleus. Whenever there is a mismatch, the cerebellum informs the cortex. The cerebellum's internal structure: There are 4 important cell populations in the cerebellum: * Purkinje cells * Climbing fibers, each climbing one Purkinje cell with numerous synapses * Mossy fibers, connecting the Purkinje cells with one synapse for each * Star cells, lying in between ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Chemical senses ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Olfactory sensory neurons: ... lie in the olfactory epithelium (the place above the mouth). They detect odorants in the air and send this information to the brain. They are surrounded by supporting cells and are covered by mucus. Each olfactory sensory neuron has hairs (cilia) which project into this mucus and do the real odorant detection. Each neuron responds to a certain feature of an odorant. The one million odors a human can distinguish are composed of about one thousand of these odorant features. Olfactory sensory neurons are continuously replaced by new neurons. They have receptors with 7 transmembrane domains. ____/\ complex odorant |_| __ __ __ __ __ __ receptors | |_| | | \_/ | | \/ | (feature detectors) | | | | | | does fit does not fit does fit Odorant detection: Whenever odorants come into the olfactory epithelium, the following happens: 1. They get caught in the mucus and plug into odorant receptors on the cilia 2. The odorant receptor activates a G-protein 3. The G-protein activates the molecule Adenylcyclase 4. Adenylcyclase produces cAMP 5. cAMP opens Na+ channels 6. The influx of Na+ and Ca2+ depolarizes the cell and it fires 7. cAMP also inactivates the odorant receptor by phosphorization 8. The odorant is destroyed by proteins in the mucus odorant v Na+ =======R================| v |======= G AC ==> cAMP Olfactory pathway: The neuron's axon passes through holes in the cibriform plate to the olfactory bulb. Here, axons of neurons responding to the same feature unite in one glomerulus area and thus amplify the signal. Each glomerulus projects to a mitral cell which then leads the signal via the lateral olfactory tract to the thalamus and the limbic system. Both then send to the frontal cortex. ~~~~~~~||||~~~~~~~~||||~~~~~~~ mucus with hairs -------| |--------| |------- olfactory neurons \__/ \__/ | | ######## | ######## | ######## cibriform plate \___ _ __/ olfactory bulb \/ \/ \_/ glomerulus | | -O- mitral cell | / \ / \ limbic thalamus system | \ / \ / | V to frontal cortex Papillae on the tongue: There are three types of surface structures on the tongue, called papillae: 1. Circumvallate, right and left in the back of the tongue, each of them holding about 100 taste buds 2. Foliate, in the back of the tongue 3. Fungiform, the most numerous surface structure, spread all over the tongue, each holding about 5 taste buds Taste buds: Taste buds are collections of gustatory sensory neurons, where taste detection takes place. Numerous of these sensory neurons lie below the surface of the tongue, surrounded by supporting cells and based on basal cells. Only the neuron's microvilli (small, hair- like structures) point into a folded plasma membrane, which is part of the surface of the tongue. Afferent nerve fibers synapse the taste cells from below. Taste neurons are continuously replaced when they become too old. A taste neuron has a receptor with 7 transmembrane domains. ~~~~~~~_____~~~~~~~~ plasma membrane /"""""\ microvilli ( ) taste bud, inside: gustatory neurons \_____/ ^-^----------------> afferent fibers Taste detection: Humans have 5 basic types of gustatory sensory neurons. Each can detect a specific type of taste: 1. Salty (NaCl): Salt taste neurons just have open Na+-channels. Whenever salt (NaCl) comes near a microvillus, the Na+ part enters the cell and depolarizes it. 2. Sour (Hydrochlorid acid, Citric acid): Sour taste is carried by H+ ions. They block K+ channels on the microvilli of sour taste cells. Thus, K+ is prevented from streaming out of the cell. Hence the cell is depolarized. 3. Sweet (Saccharose, Glucose, Saccharin): Whenever a sweet taste carrier plugs into a T1-receptor on a sweet taste cell, a G-protein (gustducin) is activated, which in turn activates adenycyclase. cAMP is produced and closes K+ channels by phosphorylation. Thus, K+ cannot stream out any longer and the cell is depolarized. 4. Bitter (Chininsulfat, Nicotin): Whenever a bitter tastant is bound on a T2-receptor, a G-protein (gustducin) is activated which stimulates phosphorlase C. This now produces IP3, which in turn causes the release of internally stored Ca2+. The cell is depolarized. 5. Umami (monosodium glutamate): A special monosodium glutamate sensitivity, detected by glu-receptors (?). In each case, an increase of Ca2+ results, which releases the tastant from the receptor. In addition, the spicy component of taste is sensed by the free nerve endings of the so-called "Trigemius". Gustatory pathway: Afferent nerve fibers transport the signal from the taste buds via the solitary tract to the nucleus of the solitary tract. Here, part of the data is send to the autonomous nervous system (stomach). Another part is send via the "Brueckenhirn" (?) to the hypothalamus and the limbic system. The remainder goes to the thalamus and cortex. taste nucleus of bud sol.tract thalamus =O)---------O---------------+--------O--------------> cortex | | | ANS O Brueckenhirn | / \ V / \ stomach limbic hypo- system thalamus Good luck for the exam! Fabian M. Suchanek