Popular in Cellular Neuroscience
Joseph Merritt Ramsey
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Popular in Neuroscience
This 11 page Class Notes was uploaded by Joseph Merritt Ramsey on Sunday November 8, 2015. The Class Notes belongs to NSCI 3310 at Tulane University taught by Jeffery Tasker in Fall 2015. Since its upload, it has received 31 views. For similar materials see Cellular Neuroscience in Neuroscience at Tulane University.
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Date Created: 11/08/15
November 2 2015 Sensory Systems Continued 0 Specific Systems 0 1 Somatic Sensory I Assessing o I Modality Receptors 0 II Intensity 0 111 Location 0 How does the brain encode where the sensation occurred on your body 0 Two Aspects I 1 Field of Receptor 0 Your nerves a field in which they can be activated 0 Deep vs Superficial 0 Deep have a wider field but need more intensity to fire 0 Superficial are much more specific and pointed 0 Examples 0 Meissner s Corpuscles hand super cial receptors 0 Pacinian Corpuscles hand deep receptors I 2 Density of Receptors o How many receptors are present in a given area 0 Two Point Discrimination technique 0 Allows for more exact and specific response in some areas 0 Field Depth I As the neurons synapse continuing up the body to the brain each successive neuron s field is the aggregation of the previous neuron 0 Eg 0 Primary neuron from the skin has a singular relatively small field of receptor 0 Secondary neuron has multiple primary neurons synapsing on it so its field is the sum of the primaries o Dermatomes sensory areas served by each spinal nerve dorsal root and spinal segment I Divided up into segments 0 IV Duration 0 Adaptation all sensory neurons adapt in essence habituating the input getting used to it I Occurs in all sensory Neurons I Results in the decreased frequency of action potential amidst continuous stimulation I Measuring the Passive Potential entering the sensory neuron we see a small dip that occurs despite continued stimulus 0 Two Types of Adaptation I 1 Slow Adapting o Gives tonic information small and consistent 0 Diagram 0 Upon coming down fewer AP can occur I 2 Rapid Adapting o Trangent Information long and sustained o Hump and the back to baseline passive response 0 So while at baseline no AP can occur 0 Practical Application You re wearing a shirt it is constantly and always touchingyou 0 So you d think it would constantly result in Sensation 0 But in fact you become used to it and don t think about it 0 But when you move you notice it again 0 Displays the interplay of Rapid and Slow Adapting Receptors I Aspects of Touch with All Components Considered 0 Size of Receptive Field large vs small 0 Adaptation fast vs slow 0 Table 0 All aspect are represented and present I Primary Afferent Neuron Styles 0 Names 0 Myelinated Afferent Neurons are labeled quotAquot neurons with a B 8 o quotCquot are unmyelinated 0 Chart 0 Temperature and Pain 0 Done by the smaller neurons A8 and C 0 Touch and Sensation o All myelinated 0 A8 is largest has Proprioceptors that affect Skeletal Muscles 0 AB is slightly smaller has Mechanoreceptors that innervate on skin 0 Breakdown 0 Mehcano AB 0 Thermo C Delta 8 o Noci Delta 8 and C I C5 is highly involved with pain I Neural Pathways for the Somatic Sensory System 0 Pathways Overview 0 Primary Sensory Neuron Overview I These are First Order I Bodies are in the dorsal root ganglia I Peripheral Nervous System end is the receptor I Central Nervous System End is the Axon Terminal I Travels from sensory point to another neuron 0 Two Main Pathways I 1 Dorsal ColumnMedial Lemniscus Pathway o Mechanoreceptors 0 2nd Order is present in the Medulla o Tract goes through spinal cord I 2 SpinoThalamic Pathway o Thermoreceptors and Nociceptors 0 2nd Order is present in the Dorsal Horn 0 Dorsal Column Medial Lemniscus o Ipsolateral projection same side doesn t cross from Primary to Secondary o Synapses in the Medulla I Specifically the Gracile and Cuneate nuclei 0 The Second order then crosses eventually synapsing on the Thalamus I Specifically the Ventral Posterior Nucleus I Crosses contralaterally here 0 From the Thalamus a tertiary neuron synapses on the cortex I It does so on the Primary Sensory Cortex I This Cortex is contralateral to the reception region ipsilateral to the thalamus synapse o SpinalThalamic Pathway 0 Primary Neurons Synapses I Their cell bodies are in the Dorsal Root Ganglia I They synapse in the Dorsal Horn in the Spinal Cord o The Secondary neuron then crosses contralaterally and synapses on the Thalamus I Specifically the Ventral Posterior Nucleus Same spot as the Dorsal Column Medial Lemniscus o The third then goes from the Thalamus to the Primary Sensory Cortex I This is contralateral to perception location but ipsilateral to the thalamus connection 0 Commonalities o 1 The Second Order Neuron Crosses Contralaterally o 2 The Second Order Neuron Synapses on the Thalamus o 3 The Third Order Neuron goes from the Thalamus to the Primary Somatic Sensory Cortex November 4 2015 Sensory Systems Continued Somatosensory 0 Specific Systems 0 1 Somatic Sensory I Assessing o I Modality Receptors 0 II Intensity 0 III Location 0 I V Duration I Aspects of Touch with All Components Considered I Primary A erent Neuron Styles I Neural Pathways for the Somatic Sensory System I Somatic Sensory Cortex Somatatopic Organization 0 Post Central Cyrus and Central Sulcus of the Brain is where the tertiary neurons synapse in order to affect movement and sensation VII I All I I o This region is spatially represented in the brain and body with groups of neurons regionally represented in the gyrus o This is known as the somatotopic representation I Lateral Inhibition in the Somatic Sensory System 0 How does the body account for the accumulating Fields of Receptors 0 Each field of receptor increases as more neurons synapse secondary is summation of primary tertiary is summation of secondary etc 0 But the body needs to refine the signal ifall neurons were activated the signals would be overwhelming o The method for refining and limiting is called Lateral Inhibition 0 Does so through the CenterSurround Receptor Interaction I Center Receptor the excitatory targeted receptor neuron I Surround Receptor inhibitory surrounding region it 0 Diagram I Feed Forward and Feedback Inhibition through Laterally Synapsed Cells 0 2 Auditory System I Physical Aspects of Sound 0 Works with Air Compression Increased density increased pressure and Rarefication decreases density decreased pressure 0 This back and forth actions results in waves 0 Frequency pitchtone o Amplitude loudness I Physical Aspects of the Ear 0 Ear Structure 0 Rough Components I 1 Outer pinna and auditory canal I 2 Middle tympanic membrane ear drum and ossicles connect tympanic membrane to the inner ear I 3 Inner vestibular apparatus and cochlea 0 Specific Things to Note I Ossicles small bones connecting tympanic membrane to the Oval Window portion of the inner ear 0 They essentially play drumsquot on the inner ear in response to ear drum movement I Oval Window small portion of the inner ear where the tympanic membrane and inner ear are connected by the ossicles I Tympanic Membrane the ear drum first registers the auditory vibrations I Cochlea inner ear transduces physical signal 0 Cochlea o Coiled snaillike Tube 0 Contains 3 Fluid Filled Regions I Names 0 1 Scala Vestibuli large connected to Tympani contains perilymph o 2 Scala Tympani large connected to vestibule contains perilymph o 3 Scala Media smaller stands alone contains endophymph 0 Contains organ of corti 0 Organ of Corti Contained within the Smaller Chamber the Scala Media the Scala Media is isolated from the other two I 1 Attached to Basilar Membrane part of the Scala Media 0 On the bottom ofthe Scala Media I 2 Hair Cells in the Membrane react and move 0 Have specialized Cilia that are attached to the Hair Cells and the Tectorial Membrane cilia known as Stereocilia 0 These cells synapse on the Spiral Ganglia creating the Auditory Nerve I 3 Cilia interact with the Tectorial Membrane 0 Hair Cells I Outer most amplifies the sound I Inner most responsible for hearing I Transduction of Sound 0 General Process o Entering the Cochlea involves the Tympanic Membrane the Ossicles and the Oval Window 0 Fluid Waves the physical waves become part of the uid wave when it enters the Scala Vestibuli o Oscillation in Basilar Membrane basilar membrane in the Organ of Corti in the Scala Media 0 Movement of Hair Cells Hair cells just above the Basilar Membrane begin to move in response to basilar movement 0 Movement of Cilia cilia on the hair cells begin to oscillate and move in response to the hair cells in uencing the tectorial membrane a sti er membrane 0 Stereo Cilia Movement 0 Diagram 0 MechanoElectric Aspect of Transduction 3quot I i l1l l f l39 39 7 a I 39 I I Mr Lmuollp gum Y quot 39quot 139quot Vim n7 ptcw il u I h f w739s r r il CPL 39 g t r 4 r u l H zlv A L I 39 39 l i l u g I ll 39 0 I quot 39 L r H fill r39 e Mirl vquotH 4W4 v I J ruffquot i l H yl7r J I V 4 u l ll mruonv k l i m m 393 H u 39l r a K 195 I M 398 s 39 r 39 KW k yquot Wk 0 HtI1 M L w Av r 317 l KI I VK HJ l I l r v J39 I I v quot I 39 4 C J 39 U t39Llkj ll39Jl H L 39J ltquoti 7U AlthW A 31quot V T Niwg lu quot T1 y l but A 0 Presence of Mechanically Activated Potassium channels on the tips of the Stereocilia respond to movement I Causes depolarization o In this case the K equilibrium is equal and the mV is 45 so K ows in when the channels open I The Cilia Oscillate back and forth pulling the channels 0 Open when moving towards the long cilia diagram 0 Closed when open towards the shorter cilia diagram I Depolarization from Potassium opens Calcium channels which mediates the release of Glutamate o Synapsed to Afferent nerve into the brain I Concentration and Equilibrium Breakdowns o Endolymph Scala Media 0 80mV Potential 0 EK 0 mv 0 High K concentration Low Na Perilymph Vesibuli and Trampani o 0 mV potential 0 EK 0 mV 0 Low K concentration High Na Hair Cell has a 45mV Resting Potential 0 Diagram of overall structure 0 Diagram of specific Hair Cell 0 Linear Proportionality I The basilar membrane 9 Hair Cells 9 Cilia Oscillations are consistent with that of the sound waves I Because they are consistent there is a proportionality to o The Amplitude how loud 0 Frequency energy what pitch 0 Neurotransmitter release I Because release is contingent on Cilia Movement and Oscillation 0 Hair Cell Receptor Potential Generation 0 Repolarization in the auditory system 0 Interplay of Tips Channels 9 Hair Cell Ion Concentrations 45mV 9 Base Channels 9 Perilymph OmV vs Endolymph 80mV Ion Concentrations 0 So at the tip 80mV to 45mV causes the ow inward I Depolarization occurs 0 At the base the mV outside in Perilymph is O and EK is zero so to restore normal cell functioning Potassium ows out through Voltage Gated Potassium channels I Hyperpolarization occurs I Frequency Sensitivity Tonotopy 0 Hair cells run the length of the Cochlea Strips o Basilar Membrane physical description 0 1 Base narrow and rigid more energy must be inserted for a response I So it is more responsive to higher frequency sounds o 2 Apex wider and exible doesn t require as much energy I So it is more sensitive to lower frequency with less energy 0 Each hair cell synapses to the spiral ganglion o The nature of the cochlea makes it so there is a tonotopy that parallels that of the somatotopy 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