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Michael Claffey

Unit 1 1. What structures/resources are necessary for keeping the neuron alive and healthy? a. Nucleus contains the DNA of the neuron. b. Mitochondria are the sites of cellular respiration. Glucose + Oxygen are needed. c. Endoplasmic Reticulum is a system of folded membranes. Rough ER has ribosomes which play a role in synthesis of proteins. Smooth ER is involved in the synthesis of fats. d. Golgi Complex is a connected system of membranes that packages molecules into vesicles. e. Microtubules are responsible for the transport of material throughout neurons 2. What are the structures of a neuron that support communication? a. Cell Body: Metabolic center of neuron, also called soma b. Cell membrane: Semipermeable membrane, responsible for membrane potentials c. Dendrites: short processes emanating from cell body, receive synaptic contacts from other neurons d. Axon: Long narrow process that projects from cell body e. Myelin: Fatty insulation around many axons f. Nodes of Ranvier are gaps between Myelin g. Buttons: Endings of axon branches, release chemicals into synapses. h. Synapses: gaps between neurons which chemical signals are transmitted. 3. How does the neuron use electrical and chemical signals to communicate? a. Electrical signals are used via action potentials. The electrical potential across the membrane is about -70mV, a result of the membrane being leaky to K+ ions. When the action potential is triggered by a stimulus, depolarization begins. Na+ channels open and Na+ moves down the concentration gradient, making the inside of the cell positive and the outside negative. Afterward, the K+ channels open and Na+ channels close, until inside becomes negative. The opening of the NaK channels triggers opening of the next NaK channel. In this way, the signal travels down the axon. The moving of negative charge = electrical signal. b. When the signal reaches the axon terminals, neurotransmitters are released from vesicles into the synapse. They can be either excitatory (EPSP) or inhibitory (IPSP). These then bind to the dendrites of the next neuron, and if the accumulation of these molecules causes the neuron to depolarize past the threshold, another action potential will fire. 4. How is the action potential a unit of communication among neurons? a. Stimulus applied to a neuron will cause an action potential. As the AP travels down the axon, it’ll release neurotransmitters from the terminal buttons, which then cross the synapse and bind to the postsynaptic receptors on a different neuron, which may then cause another action potential. 5. What biochemical processes does a neuron use to prepare for an action potential? a. A neuron prepares for an AP by first having a membrane potential. This is the result of a lot of Na+ outside of the cell, and K+ inside the cell. However, the membrane is leaky to K+, and therefore, some K+ leaks out due to the different concentrations of Na+ and K+ outside and inside the cell. But since Na+ can’t cross the membrane, there is electrostatic pressure on the K+, making the inside of the cell negative. When AP fires, Na channels open, depolarizing the neuron. When K channels open, the neuron returns to normal. 6. What is the resting potential? -70mV 7. What ions are involved in establishing the resting potential? Na+ and K+ 8. How is an action potential triggered or inhibited? a. An action potential is triggered when there is enough stimulus to cause the neuron to depolarize past the threshold potential. Certain neurotransmitters are excitatory, and therefore cause the neuron to depolarize. Others are inhibitory, and they hyperpolarize the neuron, therefore making it harder for an action potential to fire. 9. How is a postsynaptic potential generated? a. Postsynaptic potentials are generated from neurotransmitters from the presynaptic neuron binding to the postsynaptic receptors. Neurotransmitters like glutamate are EPSPs, which depolarize the neuron. When the depolarization passes the threshold, an action potential occurs. 10. How are postsynaptic potentials integrated? a. Integration is the adding a number of individual signals into one overall signal. Two types: spatial and temporal. Spatial occurs when EPSPs are produced simultaneously on different parts of the receptive membrane to form a sum of a greater EPSP. The same occurs for IPSPs. Temporal is if two postsynaptic potentials occur in rapid succession to form a greater signal. 11. How is the synapse an interface between electrical and chemical signals? a. The electrical signal results in the release of chemical signals (neurotransmitters). When the neurotransmitters are released from the axon terminals via exocytosis, they go into the synaptic cleft. Crossing the synaptic cleft, they bind to receptors on the postsynaptic neuron, which then causes an action potential. 12. What is the role of neurotransmitters in the synapse? a. Neurotransmitters help to either excite or inhibit the postsynaptic neuron. They bind to either ionotropic or metabotropic receptors. Ionotropic receptors opens/ closes ion channels, while metabotropic receptors bind to membrane signal proteins. These usually cause changes in protein expression. 13. What is the sequence of steps that a neurotransmitter goes through? a. Small neurotransmitters are synthesized in the cytoplasm of the cell, while large neurotransmitters are neuropeptides and therefore synthesized by ribosomes. They are packaged into vesicles by the golgi complex. The small neurotransmitters are typically synthesized in the terminal button, as opposed to the cell body for neuropeptides. Small neurotransmitters are stored in clusters next to the presynaptic membrane. The large ones are transported to the terminal buttons via microtubules, ~40 cm a day. Exocytosis is the mechanism of release. Small NT is released in pulses each time the AP triggers an influx of Ca ions. Neuropeptides are released gradually to increases in level of intracellular Ca. 14. What is the role of receptors in the synapse? a. The role of the receptor is to produce signals in the postsynaptic neuron. There are two different types of receptors. Ionotropic receptors close and open ion channels when a neurotransmitter binds onto them. This produces an immediate postsynaptic potential. Metabotropic receptors are more prevalent and their effects are slower, longer-lasting, more diffuse and varied. This mechanism may influence the neuron in a variety of ways, including and influence in the neuron’s genetic expression. 15. What are the different types of neurotransmitters? a. Small NT: tend to be released into directed synapses and to activate either ionotropic receptors or metabotropic receptors that act directly on ion channels. Rapid, brief excitatory or inhibitory signals to adjacent cells. b. Large NT: tend to be released diffusely and virtually bind to metabotropic receptors that act through second messengers. 16. How do drugs affect the synapse? a. Antagonists: decrease the effect of a neurotransmitter b. Agonists: increase effects of NT c. They affect the synapse by acting as receptor agonists, receptor blockers, and reuptake blockers. 17. How can a synapse be changed by experience? a. As a neuron fires together with another neuron, they will grow new receptors (AMPA). This results in a stronger connection between the two neurons. 18. What is long term potentiation (LTP)? a. LTP is a laboratory technique that is used to simulate neurons, providing high frequency, high intensity simulation. 19. What mechanisms are necessary for LTP? a. It requires NMDA receptors. These receptors are excited by glutamate, and also require the post synaptic neuron to already be partially depolarized. 20. How do synaptic changes produce changes in the performance of a neuron? a. As more AMPA receptors are created, the more places neurotransmitters can bind. Therefore, the synapse is becoming stronger. 21. How can these synaptic changes be considered learning? a. The synapses change depending on the condition. For example, with habituation the neurons contain less and less dopamine each time. While with sensitization, there is more serotonin release, causing more response. 22. How is protein synthesis involved in synaptic changes? a. Building of new AMPA receptors requires protein synthesis. 23. What neuronal changes underlie habituation and sensitization in Aplysia? a. Habituation: neurons contain less dopamine and release less dopamine each time. Eventually gill withdrawal stops. b. Sensitization results in the facilitating interneuron to release more serotonin onto sensory neuron. This causes the sensory neuron to release more neurotransmitter when the siphon is stimulated, causing the motor neuron to react more vigorously. 24. What role do glial cells play in the nervous system? a. They “support” the neurons Unit 2 How is light turned into a neural signal? Light -> neural signal = visual transduction: conversion of light to neural signals by the visual receptors. Rods and cones (photoreceptors) contain visual pigments that are capable of absorbing the energy of the visible spectrum. One such pigment is rhodopsin. Rhodopsin is a G-protein coupled receptor that responds to light instead of neurotransmitters. When rhodopsin receptors are bleached by light, it causes sodium channels to close. This prevents sodium ions from entering rods, and this causes the rods to hyperpolarize. This causes glutamate release to be reduced. Signals are often transmitted through neural systems by inhibition. What are the physical (as in relating to physics) characteristics of light that the retina is sensitive to? The retina is sensitive to wavelength and the number of photons (particles of energy) produced. Visible light between 380 and 760 nm is what the human visual system responds to. Wavelength plays a role in the perception of color. Intensity (# of photons) plays a role in the perception of brightness. What can the eye do to tailor the image that is reaching the retina? The eye can focus an image through accommodation, which is the process of contracting the ciliary muscles to deform the lens and change the focus. Furthermore, having two eyes in front allows us to create 3D perceptions (depth). When we look at something, our eyes turn inward slightly, which is called convergence. When we look at something, the two eyes produce different images, called binocular disparity. The difference in the position of the images is greater for close objects than for farther objects. This allows the visual system to construct depth perception. What are the cells in the retina that support vision? 5 layers of different neurons. -receptors (cones and rods). Cones detect color, rods are for low light situations. -horizontal cells: used for lateral inhibition. Typically connected to multiple rods/cones -bipolar cells: they act to transmit signals from the photoreceptors to the ganglion cells. ON bipolar cells hyperpolarize to glutamate, so inhibition = depolarization of neuron. -amacrine cells: involved in lateral inhibition. Typically connected to multiple rods/cones -retinal ganglion cells: carries the signal from retina out of eye. Axons form the optic nerve. May receive input from multiple rods/cones Visual pathway What is the pathway from the retina to the visual cortex? From the optic nerve -> optic chiasm (fields of view switched) -> left and right optic tracts -> Right and left Lateral geniculate nuclei (LGN) -> Primary visual cortex (simple visual processing: edges, etc) How are the left/right sides of vision organized? (by eye, by visual field, by cortical hemisphere) Left and right sides of vision are organized by visual fields of each eye. The left visual field of the left eye will be on the right side of the retina, and vice versa. At the optic chiasm, the left visual fields from both eyes will go to the right optic tract and to the right visual cortex, and vice versa. What is retinotopic organization? Adjacent areas of the retina excite adjacent neurons at all levels of the system. Visual processing What are receptive fields and how do they perform? Receptive fields are areas of visual space that stimulates or inhibits a neuron (or neural tissue). They perform by having on and off sites in the visual field, such as with the neurons of Lower Layer IV (circular fields of vision). When a light is fired onto the "on" portion of the visual field, it will cause a response by the neurons (bipolar to ganglion cells), while if the light is fired onto the "off" portion of the visual field, there is an inhibition (bipolar to horizontal/amacrine cells). Simple cells of other layers have straight borders, rather than circles of the on/off center cells. The same applies for complex cells. Complex cells have larger receptive fields, don't have set "on"/ "off" regions, and are binocular (response to both eyes) instead of monocular (respond to stimulation of only one eye). Complex also respond better to movement, and play a role in depth perception due to its binocularity. How does lateral inhibition affect the way we see edges? Lateral inhibition is involved when neurons fire. When a neuron fires, it inhibits neurons around it. Therefore, this creates a contrast between shades to create edges. For example, when intensity is the same, each of the neurons are receiving the same amount of stimulus and inhibition. When the edge between intense and less intense is approached, the neuron is receiving more stimulus and less inhibition because the other side has less stimulation. On the less intense side, it is receiving more inhibition from the intense side, and less excitation. This causes it to be even more inhibited. Thus, one side is excited more and the other is inhibited more, creating edges. How is color processed by the visual system? Color is processed by three different cones, each with a different photo-sensitive pigment (iodopsins). Each one is sensitive to different wavelengths of light. Where can the visual system be damaged and what are the corresponding deficits? Damage to the primary visual cortex can result in scotomas, or areas of blindness in contralateral visual fields. This means that part of the visual field may be blind, but the person may not even know it, due to completion, when the brain tries to fill in the missing details based on what's there. However, these people may still experience blindsight, which is a response to visual stimuli outside of conscious awareness (ie. reaching to grab object in scotoma). This may be b/c of connections between subcortical structures and secondary visual cortex not available to conscious awareness. Visual Cortex What are the areas of the cortex that process visual information? Posterior parietal cortex, prestriate cortex, primary visual (striate) cortex, and the inferotemporal cortex. What is the difference between the dorsal and ventral stream? Dorsal: prestriate cortex to posterior parietal cortex. This is the "where" pathway (location and movement) or pathway for control of behavior Ventral: prestriate cortex to inferotemporal cortex. This is the "what" pathway (color and shape), and pathway for conscious perception How is motion processed by the visual system? Movement across a visual field is detected by complex cells. Then, the dorsal stream is involved in the perception of where the object is. How are faces special to the visual system? In the Ventral stream, there are specific neurons that respond to faces. If these neurons in the ventral stream are damaged, a person will have prosopagnoscis, or the inability to recognize faces. Principles of the Visual System What is an example of hierarchical organization? Retina -> Thalamus -> Visual Cortex. Stages, High/Low, Greater and Greater complexity. Receives input from lower levels and adds another layer of analysis. What is an example of functional segregation? Rods and Cones. M & P. Dorsal/ Ventral. Each part does different parts. What is an example of parallel processing? Dorsal and Ventral streams. They are working simultaneously. Hearing How is sound turned into a neural signal? Sound travels down the auditory canal and causes the tympanic membrane, or eardrum, to vibrate. Then, the vibrations are transferred to the three ossicles, which are the bones of the middle ear. The last bone, the stapes, trigger vibrations in the oval window (another membrane). This transfers the vibrations to the fluid of the cochlea (internal membrane called the organ of Corti). A deflection of the organ of Corti produces a shearing force on the hair cells, which results in firing of axons of the auditory nerve. tympanic membrane -> ossicles -> oval window -> cochlea -> hair cells -> auditory nerve -> cochlear nuclei (hindbrain) -> superior olives (input from both ears) -> thalamus (medial geniculate nucleus) -> primary auditory cortex. What are the physical (as in related to physics) characteristics of sound that the cochlea is sensitive to? Amplitude of the wave = loudness of sound. Frequency = pitch. Combination of frequencies (complexity) = timbre. What is the pathway from the cochlea to the auditory cortex? From the cochlea, the signal goes to the auditory nerve, and then to the cochlear nuclei which is in the hindbrain. The cochlear nuclei receives input from only one ear, but afterwards the inputs combine at the superior olives (also where sound localization occurs). Then the signal goes to the medial geniculate nucleus (in the thalamus), and then it is received at the primary auditory cortex. How is sound localized? Sound is localized based on the differences of the two ears. Waves hit the first ear sooner than they hit the second ear. This causes a difference in time. In addition, there is a difference in the loudness of sound. The closer ear hears it louder than the second year. Using this information, the brain can localize where the sound is. What is known about cortical processing of auditory information? There are two pathways leaving the auditory cortex, the anterior auditory pathway, toward the prefrontal cortex, and the posterior auditory pathway towards the parietal lobe. The anterior auditory pathway includes information about what a sound is, and the posterior auditory pathway is where a sound is. How can the auditory system be damaged? Damage to ossicles result in conductive deafness, where the signal isn't getting to the cochlea. Nerve deafness is damage to cochlea or auditory nerve. Age related deafness is nerve deafness, as hair cells are less responsive. Somatosensory system What physical/tactile characteristics are somatosensory receptors sensitive to? Somatosensory receptors are sensitive to vibration (surface texture), sudden skin indentations, fine skin indentations, and skin stretch/ joint displacement. The Pacinian corpuscles adapt rapidly, do not respond to constant pressure, and have large receptive fields. Merkel's disks adapt slowly, and have small receptive fields. Ruffini endings adapt very little. Thermoreceptors (typically free nerve endings) detect changes in temperature. Nociceptors detect stimuli that could be damaging to tissue. There are fast and slow conducting channels: immediate and chonic pain. What are the pathways for somatosensory information? The dorsal-column medial-lemniscus system has information about touch and proprioception, or the position of body. It goes to the spinal cord, dorsal column nuclei, ventral posterior nucleus (thalamus), and finally the primary/secondary somatosensory cortex (posterior parietal cortex). The anterolateral system detects pain and temperature. They typically synapse right at the spinal cord. There are 3 different tracts to different areas of the brain. -spinothalamtic tract: touch & acute pain -spinoreticular tract: chronic pain How is somatosensory processing organized in the cortex? They are organized somatotopically in the brain. Areas that are close together are close together in the brain, similar to vision and hearing. In addition, there is somatosensory homunculus, which there is a representation of the body in the somatosensory cortex. Larger areas of cortex are dedicated to areas with greater sensitivity, so essentially there is a "little man." The somatosensory input is also contralateral-- the secondary somatosensory cortex receives input from both sides of the body. The cortical organization is in columns. All columns respod to the same area of body. When moving in strips, there are different areas of body. As you go deeper in the columns, there are different stimulus types, such as temperature, touch, pain, etc. Bimodal neurons (response to two senses) are in the posterior parietal cortex, which receives information from the primary and secondary cortex. It also receives input from visual and auditory cortexes. How is physical pain processed in the brain? Physical pain has no obvious cortical representation. The anterior cingulate cortex may be associated with the emotional reaction to pain. The periaqueductal gray (PAG) produces electrical stimulation that causes pain blocking effects. They also contain receptors for opiods (such as morphine). Endogenous analgesics are pain killers, such as endorphins & enkaphalins. Neuropathic pain originate in the CNS, with no obvious cause. Cutting nerves don't help with the pain. Chemical senses How are olfactory signals turned into a neural signal? Chemicals are detected by receptors on the membrane of dendrites in the nose. The signal then goes to the olfactory bulb, where the signal goes to the piriform cortex/ amygdala. How is the olfactory pathway different form other senses? There is no thalamus involvement in the olfactory pathway. In addition, there is no known principle for how odors are organized across the olfactory bulbs. Lastly, there is neurogenesis of the olfactory receptors, which are replaced every few weeks. This is only one of the few brain areas with noticeable neurogenesis. How are taste signals turned into a neural signal? There are 5 major tastes: sweet, sour, bitter, salty, and unami (meaty). Sweet is created by 2 known receptors that detect carbohydrates. Sour and Salty influence ion channels directly, H+ and Na+ respectively. Unami has one known receptor that reacts to glutamate. These leave the tongue via 4 nerves -> thalamus, or the ventral posterior nucleus -> primary gustatory cortex and secondary gustatory cortex. Which has more distinct categories that can be detected, the olfactory or taste system? The olfactory system, because it has over 1000 distinct receptor proteins, while the taste system only has about 50 taste receptors and 33 receptor proteins. Nervous System Organization What are the protective tissues, spaces and fluids for the brain? -Meninges act like a wrapper around the brain and creates a buffer zone. -Duramatter is the outermost layer. The arachnoid lies beneath the duramatter. Underneath the arachnoid is the piamatter, which is the innermost meninges. -Cerebral Spinal Fluid acts as a cushion for the cortex, found between arachnoid and piamatter (subarachnoid space), and also the ventricles of the brain. What are the structural and functional differences between the central & peripheral nervous system? -The CNS contains the Brain and Spinal Cord, while the PNS contains the somatic and autonomic nervous systems, each containing aafferent and efferent nerves. The efferent nerves of the autonomic nervous system also contains the sympathetic/ parasympathetic nervous system. -The CNS receives and organizes information from the body and coordinates activity of the body. The PNS carries signals to and from the body. What is the difference between the autonomic and somatic systems? -Autonomic: part of acts as a control system that functions below the conscious level. It controls visceral functions (internal organs) -Somatic: Associated with the voluntary control of body movements. Made up of afferent and efferent nerves. -Both are located in the PNS What is the difference between the sympathetic and parasympathetic nervous system? -Sympathetic: fight/flight response. -Parasympathetic: rest/digest response What are the terms for planes & directions within the brain? - Frontal: Splits it between front and back. -Sagittal: Splits it between left and right hemispheres - Horizontal: Splits it top and bottom - If a person was on all fours, and put their head up looking forward, the dorsal would be pointing up, anterior pointing forward, ventral pointing down, posterior pointing back. How is the spinal cord organized? -White matter: makes up outside of spinal cord and has highly myelinated axons that carry information either up or down the spinal cord. -Gray matter: inner component of the spinal cord. Primarily made up of cell bodies and interneurons that allow motor and sensory neurons to communicate. -The dorsal has afferent neurons (carrying info to brain) -Ventral has efferent neurons (carrying info away from brain) What are the -encephalonic divisions on the brain? -Tel-encepholon: Most recent part of the brain. Complex behavior such as voluntary movement, sensory input, speaking, memory, etc. -Di-encephalon: Consists of the Thalamus (regulatory gateway. Visual and auditory processed through Thalamus (LGN and MGN), and hypothalamus (links nervous system to endocrine system via pituitary gland. Regulates body temp, hunger, thirst, other autonomic processes). -Mes-encephalon: Contains tectum (dorsal/ upper region of midbrain), superior colliculi (preliminary vision), inferior colliculi (auditory processing), tegmentum (lower and larger portion of midbrain), substantia nigra (movement and reward, rich in dopaminergic neurons), red nucleus (motor coordination and communicating w/ cerebellum and motor cortex), periaqueductal gray (processing pain) -Met-encephalon: Contains the medulla (various autonomic processes in the body, such as respiratory and cardiac functioning), reticular formation (sleep-wake cycle and habituation), pons (autonomic function such as regulation of breathing), cerebellum (motor behavior, balance, movement and coordination, fine motor control). -Myel-encephalon: Where the spinal cord meets the brain. What are the components of the diencephalon? -Thalamus: highly mylinated. Is a regulatory gateway as all sensory input goes through the Thalamus. Visual system goes through Lateral Geniculate Nucleus while auditory goes through the Medial Geniculate Nucleus, both are in the Thalamus. -Hypothalamus: links endocrine system and nervous system via pituitary gland. Also regulates body processes. Cortical Organization What are the landmark fissures of the brain? -Longitunal Fissure: divides right and left hemisphere -Central: divides frontal and parietal lobe -Lateral: divides frontal and parietal lobe from temporal What are the lobes of the brain? -Occipital Lobe, Parietal Lobe, Temporal Lobe, Frontal Lobe What is the primary function(s) of each lobe? -Occipital Lobe: Processes visual -Parietal Lobe: somatosensory cortex, and association cortex- Integrates vision (dorsal stream - where)/ hearing/ touch, attention, sense of space and our bodies relation to space -Temporal Lobe: Hearing, Language, Ventral (what) stream of vision, and memory. -Frontal Lobe: Primary motor cortex (simple movement control), secondary motor areas (complex movement), prefrontal cortex (advanced cognitive functions, personality) How are neurons organized in the cortex? Column Organization, consists of synapses from afferent neurons, interneurons, and cell bodies. Subcortical Organization What are the components of the limbic system? Hippocampus: declarative memory (can be declared a
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