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Neuroanatomy Exam Review One Class.docx

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Gautam Ullal

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Neuroanatomy Exam Review 2. Define the following terms: CNS, PNS, cranial nerve, spinal nerve, dermatome. CNS: consists of the cortex, thalamus, brainstem and spinal cord and is protected by bone PNS: consists of the cranial and spinal nerves and extends out of the CNS Cranial Nerves: the 12 pairs of nerves that emerge directly from the brainstem and carry sensory information towards the CNS Spinal Nerves: nerves that emerge out of the spine from the spine and car motor, sensory, and autonomic signals between the spinal cord and the body Dermatome: the area of skin supplied by the sensory axons of a single spinal nerve 3. Define efferent, afferent, sagittal, coronal, horizontal, ipsilateral, contralateral, decussate, dorsal, ventral, rostral, caudal Efferent: project away from reference Afferent: project towards reference Sagittal: splits the left and right brain Coronal: splits the front and back of brain (face and back of head) Horizontal: splits bottom and top brain 4. Define, and provide at least one example of, each of the following neuroscience rules: symmetry, localization of function, topography, contralaterality. Symmetry: the fact that the left and right hemispheres of the brain are almost mirror images of each other Localization of Function: different areas of the brain are responsible for different functions Topography: adjoining parts of the cortex correspond to adjoining parts of the body. EX: Primary motor cortex. Motor areas innervating each part of the body arise from a distinct zone, with neighboring body parts represented by neighboring zones on the brain. Contralaterality: each side of the body is controlled by the opposite side hemisphere of the brain 5. Sketch the surface of the brain from memory and label each of the 4 lobes. Identify an important function of each lobe. Frontal Lobe: associated with reasoning, motor skills, higher level cognition, and expressive language Temporal Lobe: location of the primary auditory cortex and contains the hippocampus which is important for forming memories Parietal Lobe: associated with processing tactile sensory information such as pressure, touch, and pain. Contains the somatosensory cortex Occipital Lobe: associated with interpreting visual stimuli and information. Contains the primary visual cortex 6. Why is the resting potential negative? What is mean by the term "electrochemical" equilibrium? The resting potential of a neuron is negative because in resting state, a neuron is more permeable to potassium, and thus approaches the equilibrium potential of potassium which is negative (-84 mV). There is also more potassium inside the cell. Electrochemical equilibrium is the potential of a cell that would be reached if it was permeable to only one specific ion. The ion would have equal forces of electrical and concentration gradient forces acting on it. For example, if the force of diffusion forcing potassium out of a cell is equal to the electrical force bringing it back in, potassium would be in equilibrium. 7. Write out the Coulomb force law, Nernst equation, Goldman Hodgkin Katz equation, length and time constant equations, driving force equation, and Snell's law from memory. Do practice problems with these equations. For instance, use the Nernst equation to derive the sodium and potassium equilibrium potentials. Coulomb Force Law Driving Force Ix = gx (Vm – Ex) (q1)(q2) F = r2 I = current of ion (positive or negative) gx = membrane conductance q1 = inside charge of cell Ex = equilibrium potential for the ion q2 = outside charge of cell r= distance between inside and outside F= electrostatic force Nernst Equation [x]out x ∈¿ E x = ¿ 58 Z log¿ E x = equilibrium potential Z= valence [x] = ion concentrations Goldman Equation P ioioout+ion[ion]out P V M = io[io∈+Pion[ion]∈¿ 58log¿ V = voltage P = permeability Snell’s Law 8. Explain what "driving force" is, and how it can be used to determine the direction of an ion's flow across the membrane. Vm – Ex =Driving force for ion x Whether a positive or negative value is produced can indicate outward or inward flow. Positive: OUTWARD CURRENT the inside of the cell is becoming more negative by losing positive charge or gaining negative charge Negative: INWARD CURRENT the inside of the cell is becoming more positive by losing negative charge or gaining positive charge 9. Describe the sequence of ion channel events that account for the rising and falling phase of the action potential. - membrane is depolarized by a synaptic or receptive potential - voltage-gated sodium channels open and sodium begins to rush into the sell, depolarizing it even more - once the membrane potential reaches threshold (+50 mV) an action potential is fired - Sodium channels inactivate, ending the rising phase and initiating the refractory period - Voltage-gated potassium channels begin to open and potassium rushes in repolarizing the cell - potassium channels are slow to close, so there is an undershoot, but eventually the cell will reach resting potential again 10. What causes the refractory period? The refractory period is caused by the fact that sodium channels quick to inactivate and potassium channels are slow to close. This means that positive charge stops entering the cell during the falling phase and that negative charge continues to rush in until all of the voltage-gated potassium channels close. 11. Why do action potentials move slowly compared to electricity in a wire, and how does myelin work to speed up action potential conduction? An action potential moves slowly down an axon compared to wire due to “leakiness”, “stickiness” and “thinness”. Leakine Low Membrane The axon is leaky due to leaky potassium channels. ss Resistance (Rm) Potassium is constantly leaving while sodium is coming into the cell which makes it more difficult to reach threshold. Stickine High Membrane When ions try to go down the axon, they may end up ss Capacitance sticking to the membrane because they get attracted to (Cm) oppositely charged ions on the outside of the membrane. Capacitance is the ability to hold charge. Thinnes High Axoplasmic The diameter of an axon is very small and increases the s Resistance (Ra) resistance of movement down itself. 12. What is the difference between an oligodendrocyte and a schwann cell? Oligodendrocyte: a glial cell that is restricted to the CNS and myelinates specific axons Schwann Cell: a glial cell restricted to the PNS that myelinates some axons The difference is that one glial cell is responsible for the PNS and one is responsible for the CNS. Oligodendrocytes also have the ability to wrap around multiple axons at once, while the Schwann cell can wrap around only one at a time. 13. What is the difference between multiple sclerosis and Guillain Barre? Multiple Sclerosis Guillain Barre Differences: Differences: - CNS - PNS - Antibodies attack oligodendrocytes - Antibodies attack Schwann Cells - Somewhat common - Rare - Usually affected for life - Body usually defeats this sickness - Rapid onset Similarities: - Autoimmune disorders - Demyelinating diseases 14. Diagram a synapse and describe the events that trigger the release of neurotransmitter. Chemical Synapse: enable cell-cell communication via the secretion of neurotransmitters - An action potential reaches the presynaptic terminal - Depolarization of the presynaptic termical causes the voltage-gated calcium ion channels to open - Because of the steep concentration gradient of calcium, (10,000 on the outside to one), calcium moves into the positively charged cell - Calcium causes vesicles to fuse with presynaptic membrane - Neurotransmitter is release into the presynaptic cleft via exocytosis 15. What are EPSPs and IPSPs? Describe how glutamate produces an EPSP, and how GABA produces an IPSP. PSPs alter the probability that an action potential will be produced in the postsynaptic cell. At the neuromuscular junction, synaptic action increases the probability that an action potential will occur in the postsynaptic muscle cell. Specifically, EPSPs increase the likelihood of a postsynaptic action potential occurring and IPSPs decrease this likelihood. Glutamate Receptor Channel: - Two molecules of glutamate bind to the channel - Since the channel is equally permeable to sodium and potassium, potassium leaves and sodium enters - The net charge is negative and so the cell becomes more positive because there is more sodium entering the cell - The cell depolarizes and goes towards threshold where an action potential can be fired GABA Receptor Channel: - No binding sites for glutamate - Selectively permeable to chloride - GABA binds to the ligand-gated chloride channel - Inside of the cell is at -65 so Cl is repelled by the negativity but the concentration gradient overpowers that - Chloride flows inside and hyperpolarizes the cell, bringing it away from threshold and therefore preventing an action potential 16. Define the following types of potentials: equilibrium potential, resting potential, receptor potential, action potential, synaptic potential. Equilibrium Potential: the electrical potential that is generated across the membrane at electrochemical equilibrium Resting Potential: the inside-negative electrical potential that is normally recorded across all cell membranes at rest Receptor Potential: due to activation of sensory neurons by external stimuli (sensory transduction), it is the change in membrane potential Action Potential: the electrical signal conducted along axons by which information is conveyed from one place to another in the nervous system Synaptic Potential: activation of synapses generates this potential, a transmission of information from one neuron to another 17. What is the value of the resting potential of a typical neuron? What is the value of the action potential threshold? Resting Potential: -65 mV Threshold: +50 mV 18. Which of these ions has a higher inside concentration than outside concentration: Na+, K+, Ca++, Cl- Potassium is the only ion with a high inside concentration that outside concentration. Chloride has a much higher outside concentration. Calcium has a 10,000:1 ration on the outside. Sodium also has a high concentration on the outside. 21. Define the terms ganglion and nucleus. Ganglion: collection of hundreds to thousands of neurons found outside the brain and spinal cord along the course of the peripheral nerves.Amass of nerve cell bodies. Nucleus: collection of nerve cells in the brain that are anatomically distinct and separate, and which typically serve a particular function 19. Diagram an example of spatial summation and an example of temporal summation. Spatial Summation: - A summation of EPSPs from multiple presynaptic cells occurring at the same time Temporal: - A summation of EPSPs from a single presynaptic cell over a length of time 20. Define the terms transduction, conduction, and synaptic transmission. Sensory Transduction: process by which the energy of a stimulus is converted into electrical signals by peripheral sensory receptors and then processed by the central nervous system Conduction: the movement of an action potential along an axon Saltatory Conduction: the propagation of action potentials along myelinated axons from one node of Ranvier to another node Synaptic Transmission: the chemical and electrical process by which the information encoded by action potentials is passed from a presynaptic cell to a postsynaptic cell 22. Describe the locations in the skin, and response properties of Merkel, Meissner, Ruffini, and Pacinian receptors. Receptor Location Response Properties Meissner Lie in the tips of the dermal Transduce information papillae adjacent to the about low-frequency primary ridges and closest objects moved across the to the surface of the skin skin. Ex: textured object across the skin, slippage between the skin, detecting an object in hand, feedback for grip Merkel Lie in the tips of the primary Have the highest spatial epidermal ridges resolution. Ex: sensitive to points, edges, and curvature. Good for processing form and texture Ruffini Located in the dermis Least understood, but are sensitive to stretching done by our own hands. Responsive to internally generated stimuli Pacinian Located deep in the dermis Detect vibrations and subcutaneous layer transmitted through objects making contact with the hand. Good for using tools like a knife, cutting, wrench etc... 23. Diagram the dorsal column medial lemniscal pathway, all the way from the hand to the cortex. Label all parts of the pathway. Do the same for the spinothalamic pathway. 24. Draw the topographic arrangement of axons in the dorsal columns and in the spinothalamic tract. 25. Describe the sensory deficits that occur from damage to one side of the spinal cord (Brown Sequard syndrome). Why do these specific deficits occur? Brown Sequard Syndrome: - Eliminates touch sensation on the right side and pain/temperature sensation on the left side - Touch is affected on the right side because the right dorsal column is cut, but pain is affected on the left side because there can be no decussation through the spinothalamic tract from the left to the right 26. Describe how pain is reduced according to the gate control theory. - To explain why thoughts and emotions influence pain perception, Ronald Melzack and Patrick Wall proposed that a gating mechanism exists within the dorsal horn of the spinal cord - When there is pain reception (more small fibre stimulation), nociceptive fibres release glutamate onto the projection neuron, allowing sodium into the cell to depolarize, an EPSP. - When a mechanoreceptor is stimulated, it goes up to the dorsal column, but also to the inhibitory local circuit neuron. The A-beta fibre sends glutamate to the interneuron (circuit neuron) which then releases GABA onto the projection neuron. This lets chloride into the projection neuron so that it becomes more negative, an IPSP. - If you rub an area right after you have caused pain to it, you stimulate somatosensory neurons and pain neurons which means that it is harder for the projection neuron to fire an action potential as it is receiving not only EPSPs from the pain, but IPSPs from the rubbing. 27. Explain how enkephalin acts within the spinal cord to reduce pain. - Enkephalin opens up voltage-gated potassium channel (increases potassium conductance) which also prevents calcium channels from opening in the terminal of C fibres - This reduces the amount of neurotransmitters that can be released by C fibres and reduces the pain signal 28. Diagram the structures of the eye and show how light comes to focus on the retina. Describe two problems that can occur in focusing light. Light first enters the eye through the cornea to the aqueous humor, from the aqueous humor to the pupil, and from the pupil to the lens. Most refraction is done by the cornea because it is exposed to air, as opposed to the lens which is exposed to fluid. The lens is responsible for focusing light as it is adjustable while the cornea is not. Nearsighted: The greater the curvature, the closer the focal plane will be causing the light rays to come together before the retina. Farsighted: The cornea is too flat, not curved enough, so it can’t focus the light quickly enough. Light rays meet behind the retina. 30. What are the different cell types in the retina, and how are they connected? Three Neuron Chain: photoreceptor to bipolar cell to ganglion cell is the most direct pathway of information from the photoreceptors to the optic nerve. Absorption of light by the photopigment in the outer segment in the photoreceptors initiates a cascade of events that changes the membrane potential of the photoreceptor, and therefore the amount of neurotransmitter released by the photoreceptor terminals. Photoreceptors: cones and rods both have an outer segment composed of membranous disks containing light-sensitive photopigment, and an inner segment that contains the cell nucleus and synaptic terminals that contact bipolar or horizontal cells in the outer plexiform layer Bipolar Cells: make synaptic contact with ganglion cells in the inner plexiform layer Retinal Ganglion Cells: the large axons of the ganglion cells form the optic nerve and carry information to the CNS Horizontal Cells/ Amacrine Cells: have processes that are limited to the inner and outer plexiform layers. The processes of the horizontal cells allow lateral interactions between photoreceptors and bipolar cells that are thought to maintain the visual system’s sensitivity to contrast or luminance. Amacrine cells are postsynaptic to bipolar cells and presynaptic to the dendrites of ganglion cells. 29. Where in the retina are there more cones? Where are there more rods? What are the important functional differences between the rod system and the cone system? Photorecept Function Location or Cone - Three types of cones due to three - Central types of photopigment (sensitive to - Most dense in the different wavelengths of light) fovea - Blue, red and green cones are why - High density is we see colour achieved by - Because of the high concentration decreasing the of cones at the fovea there is high diameter of the visual acuity when we look cones something straight on - Good spatial resolution because cones are densely packed at the fovea, which lacks overlying axons and blood vessels, reducing light scattering and less convergence Rod - Contain a single photopigment so - Eccentric we cannot see colour with rods - The density of rods - More sensitive to dim light because is much greater they are longer and contain more throughout the retina photopigment, have a greater than cones except amplification, and more for at the fovea convergence (many rods connecting to a single bipolar cell) - Peripheral vision falls on the rods and we are better at seeing dim lights out of the corner of our eyes 31. Which retinal cell type is the only one that can fire an action potential? Ganglion cells! 32. Draw a photoreceptor and show the ionic currents that flow in the dark. - Sodium and calcium leave - Potassium enters - There is depolarization - In the dark, there are ligand-gated channels in the outer segments that are permeable to both calcium and sodium - There are potassium leak channels on the inner segments - Sodium is always entering and potassium is always leaving which is why it depolarized in the dark 33. Explain the sequence of events that occur when light hits the receptor. - Little calcium and sodium enters - Potassium still leaves - Hyperpolarization - Light degrades cyclic cGMP which closes the calcium/sodium channel - Potassium leaky channels remain open so potassium leaves the cell, hyperpolarizing it - The brighter the light, the fewer channels 34. Explain how adaptation occurs in photoreceptors, and how this produces retinal afterimages. - When a light is first seen by the eye, light is absorbed by opsin, which activates the enzyme transducin, which activates phosphodiesterase and phosphodiesterase degrades cGMP, so cGMP-gated channels close (phototransduction) - Guanylate cyclase enzyme produces cGMP - Calcium normally inhibits guanylate cyclase - In the light there is less calcium and guanylate cyclase activity rises and cGMP is produced - The light stimulus is continuing and so cGMP begins to rise in concentration again and it is as if the light is not there chemically even though it is visually 35. Explain the retinal circuitry that results in on-center and off-center ganglion cell responses. On –Center Ganglion Cell: - Light strikes the center of the receptive field - Cone hyperpolarizes due to the degradation of cGMP and Ca/Na channels are closed - No action potential can be fired and therefore no neurotransmitters will be released - less glutamate is released onto the on-center bipolar cell - since glutamate causes the metabotropic glutamate receptor to close sodium channels , they will open as there is very little glutamate - the bipolar cell will then depolarize due to sodium rushing in and release glutamate onto the ganglion cell Off Center Ganglion Cell: - light strikes the center of the receptive field - cone hyperpolarizes due to the degradation of cGMP and Ca/Na channels are closed - no action potential can be fired and therefore no neurotransmitters are released - little glutamate is released onto the off-center bipolar cell - since glutamate causes the AMPA to open sodium channels, they will be closed as there is very little glutamate - the bipolar cell will hyperpolarize due to no sodium rushing in and no neurotransmitters will be released onto the ganglion cell Numerical Aspects and Random Facts of the Nervous System Neurons in the human brain: 100 billion Brain’s power in watts: 20 W (entire body is 100 W) Size of a neuron: 10 microns (diameter) Most Common Neurotransmitter: glutamate Threshold: -50 mV Resting: -65 mV Average time of an action potential: 2 ms Ipsilateral: same side Contralateral: opposite side Width of synaptic cleft: 20-40 nm Driving Force: - Positive Number: inside of cell is becoming more negative by either losing positive charge or gaining negative charge - Negative Number: inside of the cell is becoming more positive by either losing negative charge or gaining positive charge Strength of stimulus at which we “max out”: 500 AP per second Inside (mM) Outside (mM) Ex (mV) + Potassium K 140 5 -84 + Sodium Na 10 145 +67 Sensory Function Receptor Afferent Axon Conduction Type Axon Diameter Velocity Proprioception Muscle spindle Ia, II 13-20 80-120 m/s microns Touch Merkel, Aβ 6-12 35-75 m/s Meissner, microns Pacinian, and Ruffini cells Pain/Temperature Free nerve Aδ 1-5 microns 5-30 m/s endings Paint/temperature/itc Unmyelinated C 0.2-1.5 0.5/2 m/s h free nerve microns endings Receptor RF Size Adaptation Responds best to Merkel Small Slow Static indentation Meissner Small Rapid Low frequency vibration (2-50 HZ) Ruffini Large Slow Skin stretch Pacinian Large rapid High frequency vibration (>50 Hz) 36. Explain the retinal circuitry that results in the surround receptive fields of the on- center and off-center retinal ganglion cells. Surround Receptive field of the On-center: - On-centre ganglion cells fire the most when the centre is bright AND the surround is dark - When the surround is dark: - Surround cones are depolarized due to cGMP not being degraded which allows Na/Ca channels to remain open - Surround cones release glutamate onto the horizontal cells - Horizontal cells depolarize when they receive glutamate and open ligand-gated sodium channels. Then release GABA onto the center cone which allows Cl to flow in - Center cone hyperpolarizes and little glutamate is released onto the bipolar cell, so mGluR6 opens and allows sodium to rush into the bipolar cell - The bipolar cell depolarizes and glutamate is released onto the ganglion cell Surround Receptive field of the Off-center: - Off-center ganglion cells fire the most when the center is dark and the surround is bright - When the surround is bright: - Surround cones are hyperpolarized due to the degradation of cGMP and Ca/Na channels are closed - Surround cones release less glutamate onto the horizontal cells - Horizontal cells do not depolarize and release less GABA onto the center cone, so no Cl - The center cone is less hyperpolarized and releases glutamate onto the bipolar cell - Glutamate causes AMPA sodium channels to open and sodium rushes in depolarizing - The bipolar cell releases glutamate onto the ganglion cell 37. Diagram the pathway from the retina to the thalamus to the cortex, from both eyes. Using your diagram, figure out what visual deficits will result from the following lesions: a lesion in the optic nerve on the right side; a pituitary tumor pressing up on the optic chiasm; a stroke in the left side of the visual cortex. 38. What are the differences between the receptive fields of retinal ganglion cells and those of neurons in the primary visual cortex? Retinal Ganglion Cells Neurons in the PVC - Respond to light on the center or - Respond selectively to oriented surround edges - One receptive field - The combination of many RGC receptive fields 39. Describe the phenomenon of ocular dominance plasticity. - The normal distribution of ocular dominance at the level of single cortical neurons can be altered by visual experience - When one eye of a kitten was sutured close, by the time the kitten had reached adulthood, ocular dominance distribution in the visual cortex had shifted mostly to the open eye - The loss of sight in the other eye was not due to retinal degeneration or loss of retinal connections to the thalamus - Instead, the deprived eye had been functionally disconnected from the visual cortex - This is “cortical blindness” or “amblyopia” 40. Describe all steps in the process leading from sound waves in the outer ear to action potentials in the auditory nerve. Outer Ear - Sound waves hit the outer ear - Sound waves are reflected and attenuated when they hit the pinna which helps to provide directional information to the brain - The sound waves then enter the auditory canal that amplifies sounds between 2 and 12 kHz - Sound waves then hit the tympanic membrane Middle Ear - This wave information travels across the air-filled tympanic cavity via the ossicles: malleus, incus and stapes - Pressure Amplification: - 1) The ossicles convert lower-pressure sound vibrations into higher-pressure sound vibrations by the stapes displacing the oval window (opening into the cochlea) - 2) The oval window is also much smaller than the tympanic membrane so force is funnelled which increases pressure also - Sounds is delivered selectively to the oval window, and the round window moves in a reciprocal fashion, bulging outward in response to an inward movement of the stapes and bulging inwards when the stapes moves away from the oval window Inner Ear - Mechanical vibrations of the stapes at the oval window, creates pressure waves in the perilymph of the scala vestibuli and mixes with the perilymph of the scala tympani - From here, sound moves to the round window - The pressure waves propagate from the base of the cochlea to the apex - The basilar membrane is wider and flexible at the apical end (low frequencies) and narrower and stiffer at the basal end (high frequencies) - Because the basilar membrane and the overlying tectorial membrane are anchored at different positions, the vertical component of the travelling wave is translated into a shearing motion between these two membranes (organ of corti). This motion bends the stereocilia on the basilar membrane, leading to voltage changes across the hair-cell membrane. This initiates sensory transduction Mechano-Transduction - Tip links are fine, filamentous structures that connect the tops of adjacent stereocilia. They can compresses or stretch with reference to different forces. They provide a means for rapidly translating hair bundle movement into receptor potentials - BASILAR MEMBRANE MOVING UP (tectorial membrane displaced to the right, bends stereocilia) - When the tip links are stretched (deflected towards tallest stereocilium), they directly open cation-selective channels which allow potassium inside. The resulting depolarization opens voltage-gated calcium channels and calcium enters (receptor potential) - This leads to the release of glutamate onto the nerve endings of the auditory nerves where an action potential occurs and information is sent to the brain - BASILAR MEMBRANE MOVING DOWN (tectorial membrane displaced to the left, bends stereocilia) - Compression of the tip link (deflected away from tallest stereocilium) closes the channels and
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