Bio 344 - Chapters 7, 8, 9, 10, 11, and 12 - PDF

**[CHAPTER 7]** ***[Introduction]*** - **Ear contains array of miniature acoustical detectors packed in space size of pea** - **Can transduce vibrations as small as diameter of an atom ** - **The acoustic detectors are usually hair cells** - **Respond 1000 times faster t...

**[CHAPTER 7]** ***[Introduction]*** - **Ear contains array of miniature acoustical detectors packed in space size of pea** - **Can transduce vibrations as small as diameter of an atom ** - **The acoustic detectors are usually hair cells** - **Respond 1000 times faster than visual photoreceptors** - **Critical for both analysis of rapidly varying sounds such as music, speech, and for sound location** - **Analysis of sound location is useful for detecting predators** - **Auditions represent very important mode of sensation ** ***[The Nature of Sound ]*** - **Sound: audible variations in air pressure** - **Waveform of sound stimulus is amplitude plotted against time** - **Cycle: distance between successive compressed patches ** - **Sound frequency (Pitch): number of cycles per second expressed in units called hertz (Hz)** - **Human range: 20 Hz to 20,000 Hz** - **Bats can hear above 20,000 Hz** - **The overall amplitude of wave corresponds to loudness (logarithmic decibel scale, dB)** ***[The Structure of the Auditory System]*** - **Auditory pathway stages** - **Sound waves** - **Gathered by pinna, concha, and the auditory canal (auditory meatus)** - **Tympanic membrane (eardrum)** - **Ossicles** - **Malleus, incus, and stapes** - **Oval window** - **Site where bones contact inner ear** - **Cochlear** - **Sensory neuron response** ***[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** - **Attenuation Reflex** - **Response where onset of loud sound causes tensor tympani and stapedius muscle contraction** - **Function: Adapt ear to loud sounds, understand speech better** ***[Central Auditory System]*** - **Stimulus reaches the inner hair cells of the cochlea and goes to the cochlear nucleus then the superior olive and then to the lateral meniscus. The information sent to the lateral meniscus is now going to decussate up to the inferior colliculus, where we\'re now going to process some of this auditory information before we send it eventually to the medial geniculate complex of the thalamus and finally up to the primary cortex.** ***[Mechanisms of Sound Localization]*** - Techniques for sound localization - Horizontal: Left-right, Vertical: Up-down - Localization of Sound in Horizontal Plane - Interaural time delay: Time taken for sound to reach from ear to ear - Sound wave hits right ear first and slight delay before reaching left ear; superior olive calculates how long it takes to reach other ear - Duplex theory of sound localization: - Interaural time delay: 20-2000 Hz - Interaural intensity difference: 2000-20000 Hz - Delay Lines and Neuronal Sensitivity to Interaural Delay - Purple line in image is the delay lines and the red balls are cells (coincidence detectors) in the superior olive - Sound from left side, activity in left cochlear nucleus, sent to superior olive - Sound reaches right ear, activity in right cochlear nucleus, first impulse far - Impulses reach olivary neuron at the same time→ summation→ action potential - Sound travels from left side on the red line and reaches the first coincidence cell which causes activity but is not strong enough to fire action potential, it travels to the second coincidence cell causes activity but no action potential, during this time sound from right side is traveling on purple line and both will reach third coincidence detector and causes summation and firing of action potential. - Damage to either superior olive causes inability to detect location of sound - Localization of Sound in Vertical Plane - Vertical sound localization based on reflections from the pinna - Human vertical plane is not as good as horizontal plane because there's only one structure to identify vertical plane of sounds - ***[Interaural Intensity Differences]*** - Use circuit (LSO) that excites superior olive (that loud noise is coming from left side) that sends information to MNTB causing inhibition; sound also ends up traveling to the right side and does the same thing but it's weaker and delayed so inhibition is weaker. ***[Auditory Cortex]*** - Primary Auditory Cortex - Axons leaving MGN project to auditory cortex via internal capsule in an array - Tonotopy, columnar organization of cells with similar binaural interaction - Cells respond more to stimulation of both ears than to either ear separately - Lesion in auditory cortex: Normal auditory function, inability to locate sound (along horizontal plane; same as if you go deaf in one ear) **[CHAPTER 8]** ***[Introduction]*** - For orientation, all animals rely on sensory cues from environment - In addition, some have **Active Orientation Mechanisms** - Where animal produces carrier signal for extracting information about environment - Two mechanisms: - Echolocation - Electrolocation ***[Echolocation]*** - Mechanism to negotiate animal's surroundings - Based upon: - Emission of sound - Reflection back from objects located within emission beam - Analysis of the returning echo - First demonstrated in bats - Also used by: - Toothed whales - Tenrecs - Some shrews - Oilbirds - Swiftlets - Based upon production of high-intensity sound and perception of corresponding echo - Ultrasound: sound in frequency range above that of human hearing; above 20kHz - Higher you can detect frequency then the better you are for detecting small objects; Very good for detection of small objects - Objects reflects echoes only if its cross section is at least\~one-third wavelength impinging on it - Also exhibits stronger atmospheric attenuation - Reduction with distance from source of the intensity of an acoustic signal propagating through the atmosphere caused by interactions with gaseous constituents found in the atmosphere - To cover more receptive acoustic field, bats must generate multiple, successive calls in different directions - Echolocation calls produce only "stroboscopic" image, so bat remains "in the dark" for most of the time - To counteract this, bats can emit enormous number of echolocation calls (11hr\~400,000 calls) ***[Model System: Bats]*** - Order: Chiroptera - 950 different species - Suborders: Megachiroptera (150) and Microchiroptera (800) - All but one genus (Rousettus) of Megachiroptera do not echolocate (are frugivorous) - Pictured: Horseshoe bat ***[Early Work on Echolocation]*** - Lazzaro Spallanzani (1729-1799) - Sealed ears of bat with candle wax - Bats collided with obstacles in flight path - Blinded bats could avoid obstacles perfectly well - Concluded ears, rather than eyes, serve to orient bat during flight - Hamilton Hartridge (1920) - Guitar strings hung across completely darkened room - Failed to find evidence that bats ran into any strings down to size of hair width - Finding excluded possibility that vision used for orientation - Proposed bats emit sound with wavelengths short enough that signals can reflect off small objects in path - Donald Griffin (1938) - Used novel device (sonic detector) to detect ultrasound - Discovered bats use ultrasound - Flying bats detect obstacles in their path by - Emitting supersonic notes - Hearing these sound waves when reflected back to them by obstacles - Detecting position of obstacle by localizing source of reflected sound - *[First to coin term Echolocation]* ***[Bat Ultrasound]*** - Sound produced by bats is divided into two major categories: - Frequency modulated (FM) signals - Short pulses - Typically last less than 5msec - Quickly sweep downward in frequency during course of pulse - Cover wide range of frequencies (Broadband Signals) - Harmonics - North American big brown bat (Eptesicus fuscus) - Constant-frequency (CF) signals - Dominate in narrow frequency range (narrowband signals) - Last much longer than FM signals (between 10-100msec) - Less homogenous than FM signals (may be followed by a downward frequency modulated sweep) - Harmonics (CF1, CF2, CF3, CF4; CF2 focus) - Greater horseshoe bat (Rhinolophus ferrumequinum) - Different types of calls reflect adaptations to foraging areas and hunting behavior - FM found in species that forage in open spaces - CF found in species that hunt near ground or in dense vegetation environment FM: Search about.5 seconds apart, then they find something and approach which decreases time between frequency signal, and terminal is where frequency lowers in FM bats. ***[Distance Estimation]*** - FM signals are well suited to measure time delay between emitted pulse and returning echo (looking for specific frequency); time of echo returning lets bats know how close the object is - Due to their short duration, make for good "time stamp" - Cover a wide range of frequencies, allowing for more precise measurement (rather than using a single frequency) - Threshold bats can discriminate two separate targets based on signal to echo delay is 60μsec; corresponds to difference in target distance of 10-15mm ***[The Echolocation Circuit]*** All right I\'m going to draw a circuit that\'s similar to this but I\'m going to show you what I want you to know cuz it\'s the main circuit involved with that echolocation and now this circuit is for the FM bat itself so keep that in mind all right what we have in the FM bat is we go back to the ear and we go back to those hair sales now sitting on top of that Vaseline membrane all right and then here is the technical membrane that sits on top that\'s going to bend his hair cells themselves that hair cell now is going to be connected to cranial nerve number 8 this is your spiral ganglion that is going to be involved all right bear with me here my sister is calling me right now I want you all at the same time the count of three to go what Hair cells to cranial nerve number 8; cranial nerve number 8 now is going to feed up into your cochlear nucleus (CN) so that is your cochlear nucleus okay from the cochlear nucleus now we are going to enter into the brainstem all right and in the brain stem we are now going to Signal send a signal to area that include the superior Olive complex or Superior Olive; of the l we\'re going to send a signal to this area here that is the nll that is the Latera meniscus we can also send a sign to the inferior colliculus is the inferior colliculus that is absolutely vital Of location of the delay between the pulsing Echo we\'re going to start to be found inside the back brain itself okay now that is what the cochlear nucleus is doing here we have some connections in between the superior Olive can connect to the the nucleus lateral and discus and we can also connect from the the nucleus or the lateral meniscus right to the inferior colliculus itself okay from here we are now going to go to your thalamus and in your Thalamus you have your medial geniculate nucleus eventually going up to all of us I blew this up inside this is now your auditory cortex the final Target okay so this right here is the auditory cortex auditory or text and there are two regions of critical importance when it comes to the FM bat and the auditory cortex this area right here let me get my math proper all right it\'s going to be organized in a tonotopic manner whereby you have different frequencies of sound that are going to be represented like so okay you have a column organization representing the different frequencies that the bat is trying to detect okay and your auditory cortex on top of that you have a region that is known as the FM-FM region in this region now is looking at calculations related to the pulse Echo delay right okay so you have one region that is detecting different frequencies in the environment that you are sending out and are coming back as the echo that is now going to be connected to this FM FM region which is doing calculations related to I send a call South how quick does the Echo come back this is doing frequency so this is kind of telling you what I\'m hunting this is telling you how far away is what I\'m hunting okay so what what am I hunting down here how far away is it up here okay that\'s all being processed in the auditory cortex itself and to get that information up here we have to send all this information up this pathway and some of these complex calculations for that distance measurement starting right here in that inferior colliculus itself okay this is for an FM back and now realize this is for the North American brown bat every brain related to different species of going to be slightly different all right so if I say draw a picture of a map of a bat you\'re drawing literally one species cuz every species is going to be slightly different but this is a nice little summary of what\'s going on in a typical FM bat brain frequency what is the item I\'m chasing fmfm how far away is it distance and that\'s what that FM frequency is meant for send out a pulse Echo comes back how long did it take that Echo to come back we know that sound travels at I think it\'s \$343 m per second the bad is basically using that calculation to figure out what the distance from its body is to whatever Target is bouncing back that Echo itself ??? FM-FM: pulse-echo delay --- Multiple measurements of the time delays can be taken, leading to precise distance between bat and target Column: how far is the item that they're chasing? Doppler effect - frequency is the same but further away sounds quieter; closer sounds louder - Can detect how fast its moving away ***[Neurophysiological Studies-Inferior Colliculus]*** - Neurons within bat auditory system (inferior colliculus, medial geniculate body, and auditory cortex) well suited to measuring delay between emission of pulse and arrival of returning echo - **Delay-tuned neurons** or **FM-FM neurons** - Each of them is tuned to rather narrow range of pulse-echo delays - Also tuned to particular frequency within the FM sweep - Allows different neurons to lock on to emitted pulse and returning echo of different frequency components - Multiple measurements of the time delays can be taken, leading to precise distance between bat and target - Individual neurons tuned to specific frequencies have just enough time to mark occurrence of sweep with single action potential - Timing of the action potentials produced across all FM-FM neurons reflects timing pattern of pulses and echoes - Different neurons respond selectively to different phases of the pursuit sequence Bat echolocation is an innate behavior, not a learned behavior ***[CF-FM Sonogram]*** - Very slight change in frequency from original pulse and pulse that comes back - FM1, FM2,... is the echo frequency coming back - Using different FM1, FM2, FM3, and FM4 to find the 83kHz of sound that comes back ***[Doppler Shift]*** ***[Analysis]*** - Greater Horshoe bat (Rhinolophus ferrumequinum) - Consists of rather long CF component with frequency of 83kHz, followed by short downward sweeping FM component - Long CF component well suited for **Doppler Shift Analysis** - Occurs when source of sound and receiver of sound are in relative motion towards one another - Bats experience Doppler Shifts under two behavioral situations: - Bat emits a pulse of 83kHz while it is flying; the perceived echo returning from the object the bat is approaching is higher than 83kHz (up to 87khz) - Bat very sensitive to 83kHz sound - To compensate, the bat lowers the frequency of sound emitted as soon as it detects a positive Doppler shift! - Known as **Doppler Shift Compensation** - During Prey Detection of Moths and Beetles - Fluttering of wings produces Doppler shifts in echo frequency around 83kHz - Bats unable to compensate for Doppler shifts produce from fluttering of targets, but can still detect and separate these echoes from background clutter b - tethered moth→moth not allowed to fly and the frequency range stays the same, peak frequency stays the same b' - untethered moth→moth allowed to fly and the flutter of the wings causes the sonogram to have a broader frequency Why 83kHz for Greater Horseshoe Bats? - Hair cells sit on top of the basilar membrane, which vibrates at different frequencies. The frequency sends a signal to the cranial nerve 8. At the 83kHz, the horseshoe bat's basilar membrane expands greatly. Cranial nerve 8 feeds up into CN, cochlear nucleus, which can feed into the superior olive (SO), NLL. From the NLL, it goes to the inferior conicullus (IC). From IC it goes to MGN. In CF-FM, bats from MGN to DSCF region, CF-CF region, FM-FM region, Azimuth. This area collectively is the auditory cortex.  ***[Adaptations of the Auditory Sensory]*** ***[System]*** - In most mammals, the frequency of sound encoded by displacement of basilar and tectorial membranes at specific places - Representation of frequencies on basilar membrane around 83kHz is greatly expanded for both length and thickness - Example of **Acoustic Fovea** - Specialized region of the inner ear with a disproportionate number of receptor cells sharply tuned to a very narrow and behaviorally important frequency range ***[Auditory Cortex of Mustached Bat]*** - FM-FM area - Processes information related to echo delays - Neurons respond poorly when a pulse, echo, CF signal, or FM sweep is presented alone - Respond vigorously when a sound pulse is followed by an echo at a particular delay - Neurons compare emitted pulse with delayed echo - Arranged in topographic fashion - Delay time increasing along one axis - Range varies from.4ms to 18msec; corresponds to 7 and 310cm target distance - Computational Map - Play key role in information processing by CNS - Values of a computed parameter (pulse echo delay) vary systematically across at least one dimension of neural structure ***[Adaptations of the Auditory Cortex]*** - Over representation by acoustic fovea accompanied by high density of innervation of cochlea by first order neurons and in auditory cortex - Cortex also contains CF area and FM area - Each part of echo represented by two distinct areas in cortex - Different types of information about echo processed separately - DSCF: Doppler Shift Constant Frequency Area: specialize in detecting rapid Doppler modulations (wing flutter); identify target - FM-FM area: respond to echo delay or target range (distance) - CF-CF area: respond to Doppler magnitude (target velocity) - Azimuthal: Vertical location **[CHAPTER 9]** ***[Introduction]*** - We are confronted with an enormous amount of information from the environment every second - Only a tiny fraction of this information flow reaches our brain, and even less is consciously perceived - Our perception of the world does not reflect the "true" and complete information present in the environment - How do organisms distinguish behaviorally relevant information from irrelevant background noise at the neural level? ***[The Umwelt]*** - Umwelt - That part of the environment which is perceived after sensor and central filtering - Honey Bees: can see ultraviolet light but not red light - They can see features of many flowers that we are unable to perceive - Bats: use ultrasonic sound for purposes of orientation ***[Releasing Mechanisms and Sign Stimulus]*** - Animals proposed to have sensory and central filter mechanisms that select those stimuli that are biologically relevant while ignoring others - Called releasing Mechanisms - Determine kind of stimuli an animal responds by producing an associated behavior - Sign Stimulus - Component of the environment that triggers a given behavior - If stimulus occurs in context of social communication, called Releaser - In nervous system, needs to be a link between processes of stimulus recognition and of triggering muscle activity responsible for behavior - Tinbergen called this Innate Releasing Mechanism ***[Barn Owl (Tyto alba) Behavior]*** - Able to localize prey solely based on noise produced by prey - Field mice forage predominately at night - Typically move through tunnels in grass or snow - Visual system limited due to these conditions - Visits number of observation perches within its territory - Upon hearing prey, barn owl turns its head in rapid flick to directly face source of sound - Must locate prey in horizontal plane (azimuth) and vertical plane (elevation) ***[Barn Owl Anatomy]*** - Eyes unable to move in socket - Flick of head in response to sound takes 60msec - Vertical asymmetry in directional sensitivity of two ears - Left ear is above midpoint of eyes and points downward - Right ear is below midpoint of eyes and points upward - Asymmetry in arrangement of facial ruff - Very efficient at reflecting high frequency sound - Helps to funnel high frequency sound into ear canals - Combined causes the left ear to be more sensitive to sounds from below and the right ear to be sensitive to sounds above ***[Accuracy of Prey Localization]*** - Head first aligned via sound from zeroing speaker - Stimulation from 2nd speaker called target speaker - Orientation to response monitored by electromagnetic angle detector system - 2 copper wires mounted on owl's head (search coils) - 2 larger coils between which owl is positioned (induction coils) - Turns of head cause changes in current flow in search coils - Can determine both azimuth and elevation of head movements - Barn owl can locate sound within one or two degrees in both azimuth and elevation - Humans are as good in azimuth, but three times worse in elevation - Error range in owl is 9cm (about size of mouse) - Accuracy of prey localization varies with several factors - Frequency range of sound important - Most accurate between 5 and 9kHz - Half of owl's basilar membrane devoted to analysis of 5kHz-10kHz (acoustic fovea) Barn owls\' basilar membrane are expanded to 5-10kHz. When sound frequencies from 5-10 are detected, they vibrate the basilar membrane. ***[Physical Parameters of Sound Involved in Orientation]*** - If one ear completely blocked, owl makes large errors in localizing source of sound - Suggests owl's ability to locate prey depends on comparison of signal in both - Plug in left ear causes the head to orient above and a little to the right of the target - Plug in right ear causes the head to orient below and a little to the left of the target - If one ear is partially blocked, results in significant errors in determining elevation, but only slight errors in azimuth - Partial blockage of one ear reduces intensity of sound but not time of arrival at both ears - Suggest **[Interaural Intensity Differences]** are principal cues for locating sound elevation - Additional experiments show locating of sound in azimuth are differences in arrival time of sound at two ears - **Interaural Time Difference** - **Barn owls analyze both interaural time difference and interaural intensity differences to locate sound in azimuth and elevation, respectively**  ***[Parallel Processing of Time and Intensity Information]*** - Auditory Nerve - Link between ear and brain - Axons originate from nerve cell bodies in inner ear - Different sound frequencies are encoded by different fibers of auditory nerve - Codes for intensity and timing of sound not segregated yet - Encoding of these parameters is achieved through variation of rate and timing of action potentials - Changing sound intensity leads to fibers responding distinctly by changing spike rate - Fibers also fire a particular phase angle of the spectral component to which it is tuned - Know as **Phase Locking** ***[Cochlear Nucleus: Parallel Processing]*** - Fibers of auditory nerve innervate cochlearl nuclei - Two subpopulations of neurons exist - **Magnocellular Nucleus** - Less sensitive to changes in intensity - Phase locking - **Angular Nucleus** - Sensitive to variations in sound intensity - No phase locking ***[Laminar Nucleus: Computation of Interaural Time Differences]*** - Receives input from ipsilateral and contralateral magnocellular nucleus - Information from both ears converges here for first time - Crucial in measuring and encoding interaural time difference - **Jeffress Model** - Delay Lines - In electric circuit, a device that introduces specific delay time in transmission of a signal - Reflect differences in arrival time at two ears of acoustic signal - ***Represented by magnocellular neurons*** - Coincidence detectors - Receive input from both ears - Time of transmission of signals varies - Fire more strongly if phase locked impulses reach detector simultaneously - Firing rate indicates direction in azimuth of sound - ***Represented by laminar nucleus neurons*** LLDA -- Anterior Lateral Lemniscal Dorsal Nucleus LLDp -- Posterior Lateral Leminiscal Dorsal Nucleus Both synapse at lateral shells on the Inferior Colliculus (IC) ***[Posterior Lateral Lemniscal Nucleus]*** - Receives excitatory input from the contralateral angular nucleus and inhibitory input from the contralateral posterior part of the dorsal lateral lemniscal nucleus - Interaural intensity differences computed here - Difference between strength of inhibitory input and that of excitatory input determines rate neurons of lemniscal nucleus fire - Neurons are arranged in an orderly fashion within the nucleus - Depends on their selectivity for different interaural intensity differences - Left nucleus, ventral neurons respond maximally when sound is louder in left ear, dorsal neurons respond maximally when sound is louder in right ear, and vice versa ***[Lateral Shell: Convergence of Timing and Intensity Information]*** - Core of central nucleus of inferior colliculus and posterior part of dorsal lateral lemniscal nucleus project to lateral shell - Where timing and intensity information converge ***[External Nucleus of Inferior Colliculus: Formation of the Auditory Map]*** - **Space Specific Neurons** - Respond to acoustic stimuli only if sound originates from a restricted area in space - Area in space in which neurons within a certain brain area respond is called **receptive field** - Neurons of left external nucleus have corresponding receptive fields primarily in right auditory space and vice versa - Neighboring space specific neurons have receptive fields representing neighboring region in space - Leads to arrangement of these neurons where sound azimuth is arrayed mediolaterally and sound elevation mapped dorsoventrally - Forms **Neural Map of Auditory Space** \*\*auditory circuit linked very closely with retina ***[Formation of an Auditory-Visual Map]*** - Neurons of external nucleus of the inferior colliculus projects to the Optic Tectum (superior colliculus of mammals) - Joint Auditory-Visual Map formed - Each neuron of this map responds to both auditory and visual stimuli arising from same point in space - In this map, representation of frontal region of space is greatly expanded (where highest accuracy in localization of prey occurs) Field L -- tells the meaning of the sound in the auditory cortex Goggles on the owl shifts the owls\' vision, which can shift which cell in the **Neural Map** in the owl will fire ICX - external nucleus; where all calculations are done which projects to the optic tectum Optic tectum is where the visual information converges to (OT is in the superior colicullus) This then synapses to the Ov (Nucleus Ovidalis) and then Field L, which is where it deciphers the meaning of the sound in the auditory cortex **[CHAPTER 10 - THE VISUAL SYSTEM]** ***[The Visual System]*** - Our ability to navigate and respond to the environment depends on the visual system - Must be capable of collecting and conveying information about: - Object location - Size - Color - Texture - Motion - Steps: 1. Eye collects and focuses visible light onto a light sensitive layer of CNS tissue 2. Photoreceptors transduce light energy into electrical signals transmitted by neurons 3. Specialized circuits in retina extract information about the visual scene and transmit it to the brain 4. Visual centers in the brain integrate feature specific information to to form a "picture" ***[Properties of Light]*** - Light - Electromagnetic radiation - Wavelength, frequency, amplitude - Energy is proportional to frequency - gamma radiation and cool colors -high energy - radio waves and hot colors - low energy - Optics - Study of light rays and their interactions - Reflection - Bouncing of light rays off a surface - Absorption - Transfer of light energy to a particle or surface - Refraction - Bending of light rays from one medium to another - Scattering - Particles forced to deviate from a straight trajectory ***[Anatomy of the Eye]*** - Gross Anatomy of the Eye - Cornea: Glassy transparent external surface of the eye - Iris: Gives color to eyes - Aqueous humor: clear, watery fluid that supplies nutrients to lens and cornea - Lens: Helps focus light to back of retina - Pupil: Opening where light enters the eye - Sclera: outermost tissue layer, white of the eye - Vitreous humor: thick, gelatinous fluid, maintains shape and phagocytes - Retina: Innermost layer of eye, part of CNS - Optic nerve: Bundle of axons from the retina ***[Image Formation by the Eye]*** - Refraction of light by the cornea - Eye collects light, focuses on retina, forms images - Accommodation by the Lens - Changing shape of lens allows extra focusing power ***[Anatomy of the Retina]*** - Direct (vertical) pathway - Ganglion cells - Bipolar cells - Photoreceptors - Retinal processing also influenced by lateral connections - Horizontal cells - Receive input from photoreceptors and project to other photoreceptors and bipolar cells - Amacrine cells - Receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells - Seemingly inside-out layers - Light passes through ganglion cells and bipolar cells before reaching photoreceptors. ***[Laminar Organization of the Retina]*** \(B) Layer of epithelial cells at the very top (this is the very back of the retina) → layer of epithelial cells regenerates some of the rods and cones; ***[Photoreceptor Structure]*** - Converts electromagnetic radiation to neural signals - Four main regions - Outer segment - Inner segment - Cell body - Synaptic terminal - Types of photoreceptors - Rods and cones ***[Microscopic Anatomy of the Retina]*** - Regional Differences in Retinal Structure - Varies from fovea to retinal periphery - Peripheral retina - Higher ratio of rods to cones - Higher ratio of photoreceptors to ganglion cells - More sensitive to light - Cross-section of fovea: Pit in retina where outer layers are pushed aside - Maximizes visual acuity - Central fovea: All cones (no rods) - 1:1 ratio with ganglion cells - Area of highest visual acuity ***[Phototransduction]*** Light energy to a nueral signal: happens in rod and cones - Rhodopsin has a molecule of 11-cis-retinal that sits in center of rhodopsin and when light is absorbed by the 11-cis-retinal it converts the 11-cis to the trans version; this then adopts transducin; transducin binds to GTP molecule with alpha...; PDE is phosphodiesterace travels in the rod and looks for a molecule of cyclic GMP (cGMP) and converts it to GMP in presence of light which closes the channel. If cGMP was bound to the channel, the channel then channel is open. A. In the Dark: K+ efflux and the cGMP is causing channel to be open for Na+ influx ***[Phototransduction]*** - Phototransduction in Cones - Like rod phototransduction - Different opsins - Red, green, blue - Theres still activity in other wavelengths, which causes overlap from these opsins, giving us the different colors (some combination of the three opsins gives us a certain color) - Red-green is on x,x chromosomes - Color detection - Contributions of blue, green, and red cones to retinal signal - Spectral sensitivity ***[Retinal Processing]*** - Research in ganglion cell output by - Keffer Hartline, Stephen Kuffler, and Horace Barlow - Only ganglion cells produce action potentials - Research in how ganglion cell properties are generated by synaptic interactions in the retina - John Dowling and Frank Werblin - Other retinal neurons produce graded changes in membrane potential - Receptive Field: "On" and "Off" Bipolar Cells - Receptive field: Stimulation in a small part of the visual field changes a cell's membrane potential - Antagonistic center-surround receptive fields - ON bipolar cells are depolarized in response to light - OFF bipolar cells hyperpolarized in response to light - Different responses to light due to different types of glutamate receptors expressed - OFF bipolar cells have ionotropic AMPA and kainite receptors (lead to depolarization when glutamate-bound) - ON bipolar cells have mGLUR6 (metabotropic; leads to hyperpolarization when glutamate bound) ***[On and Off Center Ganglion Cells]*** - LEFT SIDE PICTURE: If center is ON (and OFF in surround) then light hits center cone cell, causing hyperpolarization because GMP causes Na+ channel to be closed. Center cone cell releases less neurotransmitters being released when hyperpolarized. Because it's bound to metabotropic receptor and glutamate is not being released then mGluR6 becomes depolarized (because its a metabotropic cell). Depolarization causes more neurotransmitters, Glutamate, to be released, then causing the ON ganglion cell to depolarize. - RIGHT SIDE PICTURE: if the center is OFF (wants no light). When in light hits the center cone cell does not release neurotransmitter. Then the OFF-center bipolar cell hyperpolarizes and no neurotransmitter is released ten the OFF-center ganglion cell also hyperpolarizes. ***[Circuitry Responsible for Receptive Field Surround of ON Center Ganglion Cell]*** - Horizontal cells - Glutamate from photoreceptors causes their depolarization - GABAergic - Oppose changes in membrane potential induced by phototransduction in the outer "surround" segment - Leads to the antagonistic nature of center-surround set-up - Play role in Contrast (difference in level of illumination) Ganglion Cell Output: Off Center Color Opponency in Ganglion Cells ***[Central Projections of Retinal Ganglion Cells]*** Visual Pathway - Retina Optic Nerve Optic Chiasm - Lateral Geniculate Nucleus - Largest target of ganglion cell axons - Important for processing and relaying image forming visual information to Primary Visual Cortex - Primary Visual Cortex (Occipital Lobe) - Superior Colliculus - Second largest target of ganglion cell axons - Coordinating head and eye movements to visual targets - Suprachiasmatic Nucleus - Master regulator of circadian rhythms - Olivary Pretectal Nucleus - Pupillary light reflex ***[Magno-, Parvo-, and Koniocellular Pathways in Lateral Geniculate Nucleus]*** - Midget Cells (P Cells) - Project to four **Parvocellular** layers in LGN - Parasol Cells (M Cells) - Project to two **Magnocellular** layers in LGN - Different in response properties - M cells have larger receptive fields - M cells respond only a brief time, P cells respond in sustained fashion - P cells can transmit information about color - P cells respond poorly in detecting low contrast stimuli - Ganglion cells adjacent to each other in retina innervate thalamic relay cells adjacent to each other in LGN - Ensures orderly representations - Called **Retinotopic Map** Also have K cells which project inbetween in the koniocellular layer ***[Organization of the Primary Visual Cortex]*** - Cortex has six layers present; occipital has the first six layers of cells; layer 5 and 6 have dendrites for communication; layer 4 has starlight cells---most information from LGN is projectd into layer 4, mainly 4c. - Layer 1 has no cell bodes (very top of brain, which has meningies which rub against the brains); so if head was hit, then the first layer to go is layer 1, which has no cell bodies - Further connections from ⅔, and 4 (output) ***[Visual Areas Beyond Primary Visual Cortex]*** - The what: V1→V2→V4→Temporal Lobe: object recognition - The where: V1→V2→MT→Parietal lobe: spatial vision **[CHAPTER 11: Prey Detection in Toads]** ***[Introduction]*** - **[Sign stimulus ]** - The component of the environment that triggers a specific behavior - How does the toad visually recognize prey versus predatory objects? - What are the prey/predator sign stimuli? - How are these sign stimuli extracted by the eye and brain from other sensory information? - **[Feature detectors ]** - Neurons that respond selectively to specific features of a sensory stimulus - Much of this work (1950s) made possible by intracellular recording techniques ***[Toads: Prey Detection]*** - True toads form family Bufonidae - *Bufo* has \~250 species - Widely distributed across the world - When common toad motivated to catch prey, and small moving prey object appears in visual field (must be moving), toad responds with characteristic behaviors - Stalking the prey - Binocular fixation - Snapping - Swallowing - Wiping of mouth with forelimbs ***[Action Patterns of Toad Hunting ]*** RM0 - releasing mechanism causing them to orient toward item RMa - releasing mechanism causes thm to approach the item RMf - releasing mechanism causes fixation RMs - snap ***[Toads: Predator Detection]*** - Will try to avoid predators (snakes) - If unable to, shows characteristic avoidance response - Blows itself up - Assumes a stiff legged posture - Similar behavior can be evoked through presentation of a head-rump dummy - Leeches (depending on posture and movement) can elicit prey or predator response ***[Dummy Experiments]*** - To determine features used to distinguish prey and enemy - Toad's behavior in response to dummy then measured by rate of turning of head toward prey - Prey Stimulus: - Direction of movement - Area dimensions - Short vs. long side of rectangular shaped stripe (relative to direction of movement) ***[Worm and Anti-worm Configuration ]*** - Worm Configuration - Achieved by movement of a rectangle in direction of long axis - Anti-worm Configuration - Achieved when rectangle moves in direction of its short axis ***[Prey vs. Enemies Sign Stimulus ]*** - In toad's sensory world: - "prey" are elongated objects that move in direction of long axis - "enemies" are objects that move in direction of their short axis ***[Importance of Area Dimensions Relative to Direction of Movement ]*** - Small moving squares have releasing values like rectangles moved in "worm like" fashion - Longer squares cause releasing values to decrease until it reaches zero - Still longer squares evoke "away" turn (approaching enemy) ***[Amphibian Visual System ]*** - Toads have rods and cones; they have highly developed eyes ***[Toad Visual]*** ***[System]*** - First processing station is retina - Receptor cells linked via amacrine and bipolar cells to ganglion cells - One ganglion cell receives input from number of receptor cells - Receptive Field - Axons of retinal ganglion cells form optic nerve - Decussation at optic chiasm - Form connections with two areas - Optic Tectum - Thalamic-Pretectal area - Posterior thalamus and pretectum ***[Optic Tectum ]*** - Roof of midbrain - Analogous to superior colliculus in mammals - **Retinotectal Projection** - Link between eye and tectum mediated by axons of retinal ganglion cells - Is contralateral (left optic nerve terminates in right optic tectum and vice versa - **Retinotopic Map** - Ganglion cells project to tectum in systematic point to point fashion - Adjacent receptive fields represented by adjacently located tectum neurons Finkenstädt et al. 1985. ***[Recording Experiments: Retinal Ganglion Cells]*** - Found at least four classes of ganglion cells - R1, R2, R3, R4 - Each differ: - In the size of the receptive field - Sensitivity to broadly defined features (size, contrast, ambient illumination) - No selectivity in distinguishing between worm-like and anti-worm-like objects - \(1) worm configuration; (2) anti-worm; (3) square ***[Recording Experiments: Thalamic Pretectal Area]*** - Identified more than ten different classes of neurons - TP1 to TP11 - Different neurons become activated by various visual stimuli - TP3 and TP4 (or TH3 and TP4) - Large moving visual stimuli - Little response to elongated objects moving in worm-like fashion - Respond best when moved in anti-worm fashion ***[Recording Experiments: Optic Tectum ]*** - Different categories of cell exist - T1 to T8 - Each maximally activated by different visual stimulation - Two cellular populations defining subclasses T5(1) and T5(2) - T5(1) encode elongation of an object parallel to direction of movement, but anti-worm does not correspond to response shown by animal - T5(2) show similar response, but can differentiate between object elongation parallel to and across direction of movement ***[Stimulation Experiments ]*** - Thalamic-pretectal region - Elicits escape responses - Tectum - Elicits prey catching - Turning of head - Snapping - Swallowing ***[Connections With Other Brain Regions ]*** - T5(2) project to motor centers involved in prey catching behavior (medulla oblongata and spinal cord) - T5(2) receive inhibitory input from TP3 neurons - Important in toad's selectivity for certain configurational features of objects - Lesioning of thalamic pretectal/tectal connection produces: - Strong increase in visual responses of tectal neurons - Impairment of configurational selectivity of T5(2) neurons - Increased sensitivity of T5(1) and T5(2) neurons to moving large objects - Inability to distinguish between moving objects and self induced moving retinal images - Failure to estimate object distance - \(a) Lesion of T5(1) and measuring T5(2); causes T5(2) to lose ability to avoid large square (predator) thinking it can attack because its a prey - \(b) Lesion of TP4 and measuring T5(1); loses ability to avoid large square **[CHAPTER 12 - Somatosensory System]** ***[Somatic Sensation]*** - Enables body to feel, ache, sense temperature, pressure, vibration, and limb position - Responsible for touch and pain - Different from other systems - Receptors: wide variety and broadly distributed - Responds to many kinds of stimuli---at least four senses rather than one (touch, temperature, pain, body position) ***[Touch]*** - Skin detects mechanical forces that impinge on it - Relies on activation of sensory neurons that innervate skin, muscles, joints - Relays tactile information to CNS - These cells report to CNS what is happening on body surface, where on body it is occurring, and when - Types and layers of skin - Hairy and glabrous (hairless---e.g. palms) - Epidermis (outer) and dermis (inner) - Functions of skin - Protects from pathogens - Prevents evaporation of body fluids - Provides direct contact with world - Mechanoreceptors - Sensitive to physical distortion (bending or stretching) - Most somatosensory receptors are low threshold mechanoreceptors (LTMR) - Pacinian corpuscles - Ruffini\'s endings - Meissner\'s corpuscles - Merkel\'s disks - Krause end bulb ***[Somatosensory Afferent Properties]*** - Vary in: - Cell body size - Axon diameter - Degree of myelination - Conduction velocity - Types of stimuli they respond - Response properties to stimulation - Receptive field size ***[Small and Large Receptive Fields]*** Pacinian corpuscles have more nerve endings thus more receptive fields Meissner's corpuscles have less nerve endings thus a smaller receptive field ***[Receptive Field Size and Adaptation Rate]*** - Meissner's have small receptive fields vs Pacinian which have large receptive fields - Meissner's respond rapidly in beginning but adapt when pushed down and don't respond, once let go it fires again - Pacinian respond in beginning, adapt when pushed down to to not respond, once let go it fires again rapidly - Merkel and Ruffini both fire the entire time, however, Merkel's disk will fire a bit less/less frequently when pushed down. ***[Morphologically Distinct Mechanoreceptors]*** - Merkel Cells - Oval Shaped - Enriched in fingertips and sparse in skin regions where spatial acuity low (calf) - Anchored to other cells in epidermis via cytoplasmic protrusions and adhesion proteins - Links compression or movement of skin with mechanical changes - Contain ion channels sensitive to mechanical forces - Slowly adapting - Respond steadily to sustained indentation - Heavily myelinated afferent fibers - Very sensitive to points, edges, and curvature - Good for shape and texture - Good for detecting indentation of skin - Meissner Corpuscles - Tips of dermal papillae close to skin surface - Connective tissue capsule contains set of flattened lamellar cells (Schwann cell) - Capsule and lamellar cells suspended from basal epidermis by collagen fibers - Center of capsule has two to six sensory afferents - Rapidly adapting - Tension in collagen upon indentation provides mechanical force that triggers generator potentials - Low frequency vibrations and slippage between skin and object (grip) - Changes in tactile stimulation - Pacinian Corpuscles - Deep in dermis or subcutaneous tissue - Concentric layers of membranes surround single afferent fiber - Acts as a high pass filter that dampens low frequency stimuli - Rapidly adapting - Detect vibrations transmitted through objects - Tool use (using wrench, cutting bread, writing) - Ruffini Corpuscles - Least understood - Slowly adapting fibers - Elongated, spindle shaped, capsular specializations - Located deep within skin, ligaments, and tendons - Skin stretches (digit and limb movement) - Finger positioning and conformation of the hand ***[Morphologically Distinct Mechanoreceptors (Hairy Skin)]*** - Touch Domes - Merkel Cell-neurite complexes - Contain dozens of Merkel cells and are associated with the apical collars of specific hair follicles - Circumferential endings - Surround base of hair follicle - Sensitive to stroking of the skin - Longitudinal lanceolate endings - Surround base of hair follicle - Sensitive to deflection of hair by stroking of skin or air passing over - Gentle caress - Free Nerve Endings - Afferent fibers that lack specialized receptor cells - Critical in sensation of pain ***[Mechanosensitive Ion Channels]*** - Family of mammalian mechanosensitive channels with two members - Piezo1 - Piezo2 - Can be expressed in both specialized receptor cells and sensory afferents that innervate them - Merkel Cells and their afferents both express Piezo2 - Mechanoreceptors have unmyelinated axon terminals - Mechanosensitive ion channels convert mechanical force into change of ionic current **(called receptor or generator potential)** - Mechanical stimuli may trigger release of second messengers ***[Primary Afferent Axons]*** - Skin richly innervated by axons that course through vast network of peripheral nerves - Axons bringing information from somatic sensory receptors to spinal cord or brain are primary afferent axons - Enter spinal cord through dorsal roots - Cell bodies lie in dorsal root ganglia - Primary afferent axons - Varying diameters - Size correlates with type of sensory receptor attached to - Aα, Aβ, Aδ, C axons - C fibers mediate pain, temperature, and itch - Ab mediates touch sensations - Axons of similar size but innervating muscles and tendons are called Groups I, II, III, and IV - Aa mediates proprioception (position of limbs) ***[Segmental Organization of Spinal Cord ]*** - Each spinal nerve consists of dorsal root and ventral root axons - Pass through and between vertebrae - Spinal segments (30) - Spinal nerves within four divisions of spinal cord - Cervical (C) 1-8 - Thoracic (T) 1-12 - Lumbar (L) 1-5 - Sacral (S) 1-5 - Segmental organization of spinal nerves and sensory innervation of skin related - Area of skin innervated by right and left dorsal roots of single spinal segment called **dermatome** - To lose all sensation in single dermatome, three adjacent dorsal roots must be severed (due to adjacent dorsal roots overlapping nature) - Skin innervated by axons of one dorsal root is plainly revealed by shingles (all neurons of single dorsal root become infected with reactivation of Varicella-Zoster virus) ***[Trajectory of Touch-Sensitive]*** ***[Aβ Axons in Spinal Cord]*** - Sensory Organization of Spinal Cord: - Composed of inner core of gray matter surrounded by thick covering of white matter tracts called columns - Each half of spinal gray matter divided into intermediate zone, dorsal horn, and ventral horn - Dorsal horn - Contain neurons that receive sensory input from primary afferents from skin - Called second order sensory neurons - Typically branched structure - One branch synapses in deep part of dorsal horn on second order sensory neuron - Initiate or modify variety of rapid and unconscious reflexes - Second branch ascends straight to brain - Responsible for perception of touch ***[Dorsal Column-Medial Lemniscal Pathway]*** - Touch and proprioception - Aβ enters ipsilateral dorsal column - Carries information about tactile sensation and limb position - Synapse in dorsal column nuclei - Junction of spinal cord and medulla - Axons decussate - Gracile nucleus (lower body) - Cuneate nucleus (upper body) - Ascend within white matter tract called medial lemniscus - Rises through medulla, pons, and midbrain - Synapse upon neurons of Ventral Posterior nucleus (VP) - Thalamic neurons then project to primary somatosensory cortex (S1) ***[Trigeminal Touch Pathway]*** - Somatosensory information from face - Involves trigeminal nerves (cranial nerve V) - Enters brain at pons - Synapse on neurons in ipsilateral trigeminal nucleus - Decussate and project into medial part of the VP nucleus of thalamus - Project to somatosensory cortex ***[Somatic Sensory Areas of Cortex]*** - S1 = Brodmann's area 3b - Parietal lobe - Adjacent areas - Postcentral gyrus: 3a, 1, 2, - Posterior parietal cortex: areas 5, 7 - Layered structure - S1 inputs terminate mainly in Layer IV - Layer IV neurons project to cells in other layers - Mapping of body's surface sensations onto a structure in brain is **somatotopy** Columns in cortext separate out rapidly adapting neurons and slowly adapting neurons Homunculus- tells us where theres the most sensory receptors that will be triggered in the somatosensory system; most sensitive will be the biggest on the homunculus because most receptors Mainy 3b being looked at in the homunculus