Study Guide for exam

Identify four different practical reasons for studying the brain.

1) Compared to even a century ago, modern medicine has made tremendous strides in its ability to heal common forms of illness. Effective antibiotics and antiviral agents have driven many once-fearsome infectious diseases into the background. Yet for many brain diseases, effective treatments remain elusive. One of the major payoffs expected from neuroscience research is in the development of new, effective treatments for disorders of the brain. For example, studies of learning and memory have shed light on the cellular and molecular mechanisms that go awry in Alzheimer's disease and other forms of dementia. The ability to regrow damaged neurons would open up a whole new avenue of treatment for patients with stroke, spinal cord injury, traumatic brain injuries, or degenerative diseases of the nervous system. brain stimulation also offers a potentially powerful new avenue for treating neurological and psychiatric disorders. Deep brain stimulators have now been used for several decades to treat movement disorders such as Parkinson's. Less invasive forms of brain stimulation such as rTMS and tDCS are also emerging as treatments for a variety of neurological and psychiatric conditions. The enterprise of mapping out abnormally active circuits in brain disorders and then targeting them for stimulation will likely be one of the more powerful applications of neuroscience in the near future. 2) Cognitive neuroscience research also offers the possibility of enhancing the existing abilities of the healthy human brain. Brain stimulation techniques such as rTMS or tDCS could be used to strengthen pathways that promote long-term over short-term thinking or to improve our ability to inhibit our counterproductive impulses. New classes of medication might be found to accomplish the same goal pharmacologically rather than electrically. There is also the development of human brain interface devices, which could provide for more seamless connections between our brain and external devices. Memory, like any other sense, may also be amenable to interfaces. 3) Another payoff from cognitive neuroscience will come from borrowing the brain's best tricks to improve the abilities of our computing devices. Recognizing and interpreting speech, balancing a moving body on two legs, recognizing thousands of different classes of objects from a visual scene, distinguishing familiar from unfamiliar faces when viewed from almost any angle, finding efficient routes through a series of destinations, retrieving relevant memories from a large database: for each of these problems, evolutionary processes have endowed the brain with algorithms far more efficient than the best we have managed to engineer in computers. 4) In the realm of social policy, cognitive neuroscience can play a huge role. Understanding the brain better has led to improvement in eyewitness testimony because it's so unreliable. The illumination of such problems has led to better guidelines for police who conduct lineups - these include using investigators who are blind to the suspects in the case, separating witnesses as soon as possible, and not publishing photos of suspects in the news. Nearly 7 out of 10 jail inmates met the criteria for substance abuse or dependence in the year before their admission, and understanding the brain and the process of addiction better can help us treat these people instead of allowing their problems to continue unfixed. Also, understanding the brain has changed our idea of blameworthiness, as it has become nuanced.

Describe the four core aspects of the scientific method

A new tradition of inquiry has gradually emerged to approach the universe's many puzzles in a more systematic way: the scientific method. The first step is to begin with an observation of some kind: typically an observation that is puzzling, or novel, or especially salient n some other way. To make further headway, ideally the observation must be well characterized: careful, repeated measurements using standardized techniques and well-defined units of measurement help to improve the richness of the observation and ensure that it holds up against the perils of anchoring, illusory correlation, perceptual errors, and other similar pitfalls. The next step is to develop a hypothesis: a proposed explanation for the observation in question. A good hypothesis should be capable of being verified, or ideally falsified, through some sort of experimental test. Useful hypotheses also tend to be parsimoniuous (i.e. as simple as possible while still fitting the observation), fit with the existing knowledge base, and be generalizable to other similar classes of observations. The third step is to generate specific and testable predictions from the hypothesis: if our hypothesis X is true, then we ought to be able to observe other phenomena A, B, and C. Negative predictions are especially helpful: if our hypothesis X is true, we should not see phenomena D, E, or F. The fourth step is experimental testing of the predictions. Here, rather than relying solely on our intuitions about the plausibility of the hypothesis or on our even more distorted intuitions about the plausibility of the predictions, we put them to the empirical test. The experimental phase requires careful measurement and comprehensive efforts to control for any additional factors that could influence the observations, thus interfering with the predicted effects. A key point about the scientific method is that it is iterative: the results of one experiment count as observations that can then be fed back into the process to generate new hypotheses, predictions, and experimental tests. The progression, or evolution, of scientific knowledge arises from successive iterations of experiments. An important practice is replication and extension of findings: confirming preliminary findings with additional observations by other methods, or other groups of investigators, often using more rigorous approaches or more careful controls or a larger number of overall observations. Also, statistic and peer review are helpful.

What is meant by unmasking connections? How is this different from long-term changes to the brain?

A popular model suggests that there are many neural connections that already exist, but they are inhibited so that they have no effect, functionally speaking. When the original connections lose their active input - say, because of an anesthetized arm or a blindfolding - fast changes in receptive fields can result from the disinhibition of covert, existing connections from other sensory regions of the thalamus to the cortex. Longer-term changes are thought to involve the growth of axons into new areas and the sprouting of new connections. With enough time, deafferented areas sprout new connections. The brain seems to put into place many "silent" connections that are inhibited during everyday neural conversation - but are there if needed in the future. With these, the brain can respond rapidly to changes in input. However, these silent connections are limited in number, and for longer, more widespread change, a different approach is used. Essentially, if short-term changes (such as unmasking) are found to be useful to the animal, then long-term changes (such as growth of new axons and sprouting of new synapses) will eventually follow. Think of the neocortex as a data-processing engine that accepts whatever input is plugged into it and performs the same basic algorithms on all input. The inputs will compete for space, and downstream neural populations will learn how to interact with them.

What happens when an action potential reaches an axon terminal?

Action potentials travel down axons until they invade the axon terminals. The sudden voltage change in the terminal causes the opening of voltage-gated calcium channels, causing a rapid entry of calcium ions from the outside. The calcium ions cause the vesicles packed with neurotransmitter to fuse with the terminal membrane - and this causes the neurotransmitter molecules to spill out into the synaptic cleft.

Describe what an emergent property is and how it relates to the brain

Although at first blush it seems impossible to build an acting, sentient being from neutral, ignorant parts, groups of interacting simple parts can lead to complex emergent properties - that is, characteristics of a system that do not belong to any individual component. If you divided your body into piles of all the different molecules and cells that make you up, you would have an ensemble of uninteresting (and insentient) chemical pules. But rearranging those chemicals into a particular organization, with particular relationships among the molecules, can restore the motivated, dreaming, volitional creature that your friends know and love.

What is a sensitive period? Give an example of one we discussed in class

Although brains change quite a bit in response to their interaction with the world, they are not equally plastic at all points in time - instead, they are most plastic during a window of time called the sensitive period. After this period has passed, the system becomes more difficult (but not impossible) to change. Children learning new languages is a good representation of the sensitive period. Young animals show a generalized plasticity without attentional focus. This seems to be because young animals have high levels of cholinergic transmitters but not the other inhibitory transmitters, which become available later. Therefore, young animals have the proper chemicals in their brain to react and respond to whatever environment they're placed in.

Describe two (or more) stimulation methods used to study the brain

Another powerful approach to understanding human brain function involves actively stimulating a given brain region or neural circuit and then observing the effects on cognition and behavior. One method is called transcranial magnetic stimulation (TMS), which uses powerful electromagnetic coils, held against the scalp, to generate focused magnetic field pulses that pass through the skull to activate neurons directly underneath the site of stimulation. TMS coils can be used to generate movements of the body, just as in the studies of Jasper and Penfield. However, they are also being used to study the neural circuitry responsible for a much wider range of functions from vision and hearing to planning, memory, emotion regulation, social cognition, and decision making. Some patients with depression respond to repetitive transcranial magnetic stimulation (rTMS0, multiple session of TMS. Another form of noninvasive brain stimulation, developed more recently, is called transcranial direct current stimulation (tDCS). This technique involves applying two electrodes to the scalp, each about half the size of a credit card. Once they are attached, a small device passes a weak, constant electrical current across the two electrodes so that the current passes through the scalp and the underlying brain regions. Neyrons under the positively charged cathode tend to be inhibited by this kind of stimulation, whereas neurons under the negatively charged anode tend to become excited. Although the currents are weak, even 20 minutes of tDCS can produce measurable changes in a variety of functions, depending on the site and polarity of stimulation: movement, perception, attention, memory, emotion regulation, impulsivity, and even deception. As with all the other approaches, stimulation studies have their own caveats. One of the most important is that the effects of the stimulation may spread well beyond the target site into other regions that are physically adjacent or strongly connected to one another. For example, we know that applying TMS to one hemisphere causes effects not only at the site of stimulation, but also at the same site in the opposite hemisphere via connections that cross from one side of the brain to the other. TMS of movement-controlling areas in the brain may also spread via long descending pathways to neurons several feet away, down in the spinal cord. So when we observe an effect from brain stimulation, we still need to clarify whether this is a direct effect from the area being stimulated or a secondary effect from stimulation spreading to areas that can be quite distant from the area originally targeted.

What is a multistable percept?

As another example of the illusory nature of vision, consider a multistable percept. This is an ambiguous stimulus that can be perceived in more than one way and that typically flips back and forth between the different options. Your retina is receiving the same information on its photoreceptors, but your brain is not just a passive recorder: instead it actively process input to "see". There is more than one way for the visual system to interpret the stimulus, and so it flips back and forth between the possibilities.

Describe what is meant by homeostasis and which brain region contributes to it. How is this brain region also associated with the release of hormones?

As we enter the forebrain, the nervous system takes on quite a different structure than other parts. Here we find few direct inputs or outputs to the body or the outside world. Instead, the neurons of the forebrain can mostly be considered interneurons, whose vast and elaborate circuitry is aded on to the simpler circuits. Two main structures of the diencephalon, which lies just forward of the midbrain circuits that we discussed in the section on the brainstem. These structures are the hypothalamus and the thalamus. All living organisms have survival needs (energy supplies, too little or too much water, temperature, etc.). Brains that allow the body's internal parameters to wander too far from the ideal range do not allow the body to survive to reproduce. After millions of generations of experience, the brains of today's creatures have gotten very good at maintaining homeostasis (the process of keeping the body's internal parameters in balance). The neurons that drive homeostasis can be found in the hypothalamus. Hypothalamic neurons are responsible for the homeostatic control signals we sometimes call "basic drives": including hunger, thirst, sexual arousal, temperature regulation, and sleep. These drives serve to maintain the body's balance of energy intake against energy consumption, water intake against dehydration, etc. Neurons of the hypothalamus cluster into distinct groups: the hypothalamic nuclei. Each hypothalamic nucleus has a distinct function, and many relate to a specific drive. For example, one nucleus coordinates feeding; another regulates satiety; etc. Since many drives wax and wane according to the time of day or night, one hypothalamic nucleus acts as a circadian clock to stimulate or inhibit the other nuclei. To maintain homeostasis, the neurons of the hypothalamus need input about the internal state of the body. They obtain this information from many sources: visceral inputs via the spinal cord, hormonal inputs from other body organs, even direct measurements of the chemistry of the bloodstream. They integrate the information from all of these sources and compare the results against the ideal homeostatic set points. The set points themselves can be changed when necessary. When the internal environment deviates too far from the set points the hypothalamus coordinates the necessary compensatory mechanisms. These fall into three categories: autonomic responses, endocrine responses, and behavioral responses. Hypothalamic neurons send outputs via the thalamus to the cerebral cortex, which has the computational power to elaborate basic drives into goals and plans of action. Furthermore, the hypothalamus is considered the master control gland of the body's hormone-secreting systems (which are collectively known as the neuroendocrine system). It sends control signals down a thin extension to the pituitary gland, which in turn releases many kinds of hormonal signals into other parts of the body. One example of a pituitary hormone is growth hormone, which regulates tissue growth throughout the body. Thyroid-stimulating hormone directs the thyroid in controlling the body's overall metabolic rate. Prolactin regulates lactation. Oxytocin facilitates maternal bonding, lactation, and social bonding. Antidiuretic hormone directs the kidneys to retain rather than excrete water. These kinds of hormonal responses are essential components of homeostasis. By itself, the hypothalamus cannot produce the behavior needed to maintain homeostasis. The cerebral cortex, however, is readily capable of performing all the necessary steps, just as soon as it receives a motivational signal to begin (from the hypothalamus). The cerebral cortex is a large and complicated place, however, and it is the job of the thalamus to direct signals to their correct locations in the cerebral cortex.

Describe adaptive coding and how it can result in changes to sensory/motor representations in the brain

Brains appear to employ adaptive coding, which means that they allocate more or less neural activity to any given function depending on the needs of the organism. This is true not only of sensory representation, but also of motor representation. In one experiment, monkeys were trained on two different tasks. The first task required the monkeys to retrieve small objects via skilled, fine use of the digits. The second was a key turning task, which required more wrist and forearm use. Then the researchers mapped out ow much of the monkeys' motor cortex was devoted to moving each body part. After training on the first task, the cortical representation for digits progressively usurped more territory whereas the wrist and forearm representation shrank. In contrast, if the monkeys trained on the key-turning task, the amount of neural territory devoted to the wrist and forearm expanded. By devoting more resources to novel tasks, brains can optimize their circuitry based on the goals in front of them

How does experience contribute to the refinement of connections in the brain? Give an example.

Brains reflect the environment to which they are exposed. Beyond reflecting the environment, brains require the environment to correctly develop. Instead of hardwiring everything, a more flexible and efficient strategy is to build a rough draft of the general circuitry required and let world experience refine it. Example is circadian rhythm in a cave, fluctuating between 21-27 hours. Another example is when kittens are raised with artificial strabismus (the two eyes do not look to the same point in space), the activity from the two eyes is not correlated, as it would be in a normal kitten. As a result, cells in visual cortex involved in binocular vision do not develop, and the strabismic kittens lack stereo vision. The development of normal visual circuits depends on normal visual activity. It is experience dependent. Genetic instructions have general rather than specific roles in the detailed assembly of cortical connections. That is, neuronal networks require interaction with the world for their proper development. The roles of genetic instructions are simply to guide neurons into the right general areas and to provide them with general mechanisms for adjusting their connections with other neurons. Neurons and their processes chronically fight for resources to survive, striving to find useful niches in the circuitry of a brain. If they cannot find a role in the larger society of the nervous system, they retract. Deprived of the growth factors that sustain them,, they ultimately remove themselves from the conversation altogether, dying out. There is competition between neurons. Ocular dominance columns are alternating stripes in the visual cortex that represent cells responding to signals from either the left or the right eye. During development, axons carrying visual information from the thalamus initially branch widely in the cortex and then segregate into eye-specific patches based on patters of correlated activity. This segregation is activity dependent: if all incoming activity is b locked by an injection of tetrodotoxin in the retinas, the axons in the cortex remain overlapped. Under normal circumstances, both eyes carry the same level of activity. But shutting one eye of an animal leads to an expansion of the territory occupied by fibers from the open eye. Inputs from the strong eye are retained and strengthened, whereas the inputs from the shut eye are weakened and eventually decay.

Describe how information from the left and right visual fields falls on the retina, how it organizes itself across the optic chiasm, and where it is represented in the brain.

Electrical pulses are sent directly into the retinal ganglion cells. From there, the signals move on toward the brain via the axons of the retinal ganglion cells, which converge to form the optic nerve. There can be mo photoreceptors at the point where the optic nerve leaves the eye, so this is known as the blind spot. Each of your retinas is divided into two halves by an imaginary line running vertically through the eye and located at the boundary between the right and left visual fields. The half closes to your nose is called the nasal hemiretina, and the half furthest from your nose is called the temporal hemiretina. The optic nerve conducts all of the information from your retina but keeps track of where in the retina the information originated. As you can see in the figure, the optic nerves from the left and the right eye come together at the optic chiasm, where half the fibers from your right eye and half the fibers from the left eye cross over. Specifically, those signals from the right eye that carry information from the right visual field (the right nasal hemiretina) cross over (where they will be processed in the left hemisphere), whereas those fibers from the left eye that carry information about the left visual field (the left nasal hemiretina) cross over (where they will be processed in the right hemisphere).Information from the temporal hemiretinas remains uncrossed and projects to the ipsilateral side of the brain because that information originated in the opposite (contralateral) visual field.

What is neuromodulation? When does it happen? What is an example of a neurotransmitter system which contributes to this?

For plasticity to be achieved, actions must have relevance to the animal. This ability to allow changes to occur only when something important happens is called gating. One way the brain tell if something is significant is through neuromodulatory systems: widely broadcast neural systems that correlate with reward, punishment, and alertness. Neuromodulators are diffusely released chemical signals that can gate plasticity such that changes take place only at the appropriate times, instead of each time activity passes through the network. Reorganization of parts of the cortex only occurs when paired with the release of particular neuromodulators. One important neuromodulator is acetylcholine. Neurons that release acetylcholine are called cholinergic, and these neurons exist mostly in the basal forebrain. Practicing a task is not sufficient to change the brain in the absence of the plasticity-enhancing powers of the cholinergic neurons.

Describe the difference between sparse and population coding.

Generally, there are two strategies for how the brain can encode information in visual cortex: sparse coding and population coding. Say you were displaying one of two visual objects, either Obama's face or a Tesla. In sparse coding, a small number of neurons would become active in response to a specific visual stimulus - say, a small cluster of cells for Obama and a completely different cluster of cells for the Tesla. In population coding, most neurons in ventral visual cortex would provide some response when shown either stimulus, but they would fire to different degrees. Face recognition seems to be highly specific to a small number of neurons. The same sparse coding has been found with hands, bodies, and letter strings as well. Though, for other stimuli - say, houses, cityscapes, or the general shape of an object, population coding seems to be in effect: many neurons are involved at varying levels of response rather than a few at binary response. The more familiar the stimuli, the sharper the representation of individual neurons, the sparser the encoding, and the more clustered the neurons become that represent the object.

Describe the major functions of astrocytes, microglia, oligodendrocytes, and Schwann cells

Glial cells play several roles, providing ways to speed up the signaling from neurons, regulating the concentrations of extracellular chemicals, and determining the extent to which networks of neurons can modify their connections. Oligodendrocytes are large cells whose main function is to wrap a layer of "insulation" around axons - a process known as myelination - similar to the way that a copper wire is wrapped in rubber. The consequence of myelination is the speeding up of electrical signaling by neurons. A single oligodendrocyte wraps the axons of up to 50 different neurons. Oligodendrocytes are found only in the central nervous system; the function of myelination is accomplished in the peripheral nervous system by Schwann cells. Schwann cells are quite similar to oligodendrocytes, except a Schwann cell wraps myelin around only a single axon. Myelin sheaths are not continuous along the length of an axon, but come in short segments, and the gaps between segments are called Nodes of Ranvier. Astrocytes provide physical structural support, but also perform critical functions in maintaining the balance of chemicals outside the neurons, the repair of injury in the central nervous system, the contribution of nutrients, the regulation of local blood flow to a region, and the release of chemical signals. Microglia make up 20% of the glial cell population and are the front line of immune defense in the central nervous system: they are constantly on the move, searching for any infectious agents that might damage normal neural tissue. When they detect a foreign body, they consume and destroy it to prevent disease and inflammation.

Describe hemineglect and simultagnosia. What kind of damage might result in these deficits?

Hemineglect is a disorder in which a person will disregard one half of the world. This is typically caused by brain damage (usually a stroke) to the right parietal lobe, which causes total neglect of everything on the left side of the person. There is nothing wrong with a person's visual system - instead, the problem is purely one of placing his attention anywhere in the left side of the world. Simultagnosia is an inability to recognize multiple elements in a scene and therefore the visual field as a whole. This is due to the loss of attentional steering that steals away their ability to comprehend the big picture of a visual scene. This is a symptom of Balint's syndrome, a disorder caused by damage to the parietal lobes on both sides. Their attentional systems are not functioning correctly.

What are cranial nerves? How are they similar to/different from spinal nerves?

Humans have 12 pairs of cranial nerves, which are sometimes numbered with Roman numerals. The cranial nerves transmit sensory and motor information between the brain and the periphery, similar in some ways to the peripheral nerves that connect to the spinal cord. All of the cranial nerves emerge from the brainstem, except for cranial nerves I and II (which emerge from the cerebrum itself).

What is the difference between gray and white matter?

If we take a cross-section through a spinal cord, we see a small central canal, surrounded by a butterfly-shaped structure made of gray matter, which is itself surrounded by an oval of white matter. As throughout the rest of the brain, the central gray matter is home to the cell bodies of neurons and their local connections, whereas the surrounding white matter is made up of the electrically insulated, long-distance connections between neurons. The overall size of the cord depends on the body segment. If a body segment contains a limb or part of a limb, it will need a larger cord with more gray matter to handle the extra sensory and motor information and more white matter to handle the extra communication with the distant neurons in the brain. The neurons of the gray matter are stacked in layers, or laminae, from ventral to dorsal. Sensory input enters the cord from the dorsal side, whereas motor output exits the cord from the ventral side. Hence, as you might expect, the neurons in the dorsal layers are mostly sensory neurons, whereas the neurons in the ventral layers (also called the ventral horns) are mostly motor neurons. The cell bodies of peripheral sensory neurons live just outside the spinal cord, in the dorsal root ganglion. incoming peripheral signals pass these cell bodies on the way to the spinal cord.

Where does our perception of the world arise from?

In reality, perception is nothing like a movie camera or computer display. Instead, perception is an extraordinarily sophisticated construction of the brain. Sensory machinery is confronted at every moment with a barrage of information, and it is the task of the nervous system to reduce that amount of information to a single, coherent percept, or mental representation of the thing being perceived.

What do we mean by remapping of the brain?

In the sensory and motor areas of the cortex, neighboring populations of neurons generally represent neighboring parts of the body - that is, the hand is represented near the forearm, which is represented near the elbow, and the upper arm, and so on. This map of the body is known as the homunculus. Upon dealing with changes, the brain circuitry adjusts itself to fit the body it is dealing with. The rapidity with which this happens suggests that there does not need to be a large-scale rewiring of these areas, but instead, that there are connections already in place that are merely unmaksed by these changes to sensory input. This flexible matching to the body plan allows the brain to optimize its allocation of neural resources. The brain deploys its space and resources according to the signals that come in. Thus, the visual cortex of the congenitally blind becomes tuned to tactile and auditory input.

What do we mean when we say a neuron is "defined by its connections"?

In the social life of neurons, you are who you know. Within the vast network of the brain, the role of any given neuron depends in large part on its inputs and outputs. For example, if a neuron sends direct output to the muscles surrounding the eye, it can be inferred to play a role in controlling eye movements. If that neuron's inputs come from motion-sensing visual regions of the brain, we have a hint that this neuron could help to aim the eye at any sudden movements that might occur in our visual surroundings. In contrast, if its inputs come from auditory regions of the brain, this might instead suggest that the neuron plays a role in aiming our eyes to spot the sources of sounds that might occur around us. A wide variety of methods are available for our use in tracing the connections to and from a given neuron or a given region of the brain. Some involve injecting a tracer substance into the region. Certain kinds of tracer substances are taken up by the neurons and transported along the input or output tracts of neurons until they reach the final input or output terminals of the neurons themselves. A recent technique called diffusion tensor imaging has enabled us to map out connection pathways in living human beings noninvasively. This technique uses a magnetic resonance imaging scanner to create detailed maps of the directions of water diffusion within living tissue. In brains, the connection fibers (axons) between distant regions of neurons tend to bundle together into tracts, traveling in parallel from region to region like the lanes on a major highway. Water molecules, like the cars on the highway, tend to travel more easily along the tracts than across the,. By following the water molecules as they diffuse through the brain, we can create maps showing the most likely routes of the tracts themselves.

Identify three (or more) indirect methods used when conducting correlational brain research and describe what each of them measures (what are you looking at when you use this method?)

Indirect methods can detect the metabolic or neurochemical products of brain activity rather than the activity itself. At the forefront of these approaches are neuroimaging techniques, which revolutionized the study of human brain function when they emerged in the 1980s and 1990s. Positron emission tomography involves injecting small amount of radioactively labeled chemical compounds into the body and then mapping out their distribution within the brain. A wide variety of substances can be labeled, ranging from water or glucose to specially tailored compounds that bind only to a single type of chemical receptor within the brain. magnetic resonance imaging (MRI) lets us view the structure of the brain without exposing the individual to radiation and has become widely used both in clinical medicine and in research. Functional magnetic resonance imaging (fMRI) uses a specific type of rapidly acquired MRI scan to generate whole-brain maps of blood flow and blood oxygenation within the brain. As neurons increase or decrease their activity levels, the changes register as changes in blood flow and oxygenation. Since these changes are quite localized, they can be used to generate maps of the neural activity that accompanies various forms of human cognition or behavior. A variety of other MRI-based neuroimaging techniques also exist, including magnetic resonance spectroscopy (which can detect subtle changes in the concentrations of certain substances in brain tissue), arterial spin labeling (another method for measuring blood flow in the brain as an indirect measure of neural activity), voxel-based morphometry (which can measure subtle differences in the shape or thickness of brain structures), and diffusion tensor imaging (which can map the pathways of connection tracts within the brain). Important to remember that correlation does not equal causation. A neuroimaging study may find an area whose activity correlates with the unpleasant painfulness of a hot probe applied to the hand. Does this mean that this is a "pain unpleasantness" brain region? What if the region were simply involved in suppressing the urge to move the painful hand away from the probe - an urge that would grow stronger with increasing pain, thus producing an apparent representation of painfulness? A more reliable approach is to back up the findings of our correlational studies with the results of causational studies, which involve actively altering brain activity and observing the effects on behavior.

Describe two (or more) noninvasive methods used when conducting correlational brain research

Less invasive approaches include electroencephalography, used since the 1920s to record electrical signals on the scalp that are generated by oscillating electrical activity in nearby brain regions. Magnetoencephalography, used since the 1980s, records the even fainter magnetic fields that accompany this electrical activity.

Identify the difference between a sagittal, axial (horizontal), and frontal (coronal) brain slice

Neuroscientists often view the nervous system in planes, or slices: a microscope section, a computerized tomography scan, or an MRI series. An axial slice divides the body along its long axis, into rostral and caudal. A sagittal slice divides the body into left and right. A midsagittal slice is a slice through the exact midline of the body or nervous system. A frontal or coronal slice divides the body into dorsal and ventral.

Describe what neurotransmitters are and give some examples of the neurotransmitters we discussed in class.

Neurotransmission: how cells of the nervous system communicate across small gulfs of space to each other or to targets such as the muscle cells of the heart through chemical transmission. The released chemicals are called neurotransmitters. The neurotransmitter is released by the presynaptic cell and, by diffusing from its point of release, is felt as a change of chemical concentration at the postsynaptic target. The synaptic cleft - the little space between the pre and postsynaptic cells - allows the concentration of neurotransmitter to rise and decay rapidly. Just inside the membrane of a presynaptic cell, the neurotransmitter molecules are packaged inside small spherical packages called synaptic vesicles. The release of the neurotransmitter into the extracellular space occurs when the vesicle fuses with the outer membrane and the molecules spill out into the cleft. Acetylcholine is an excitatory neurotransmitter in the peripheral nervous system, causing muscle contractions when released at the junction between the nervous system and the muscular system. Monoamines include dopamine, epinephrine, norepinephrine (all known as catecholamines), serotonin, and melatonin. Dopamine serves as the critical information-carrying molecule in the brain's reward systems and is the target of drugs of addiction such as cocaine and amphetamines. Amino acids, the building blocks of proteins, are a category of neurotransmitters. The amino acid neurotransmitter glutamate is the most common excitatory transmitter in the central nervous system. Aspartate is another excitatory amino acid neurotransmitter, and GABA and glycine are common inhibitory neurotransmitters. There are also peptide neurotransmitters, which are strings of amino acids, such as cholecystokinin, somatostatin, and neuropeptide Y. Retrograde neurotransmitters cross the synapse backwards, like nitric oxide and carbon monoxide.

What are neurotrophins and why are they important?

Neurotrophins are protein factors, secreted by the neuron's target, that allow the survival, development, and function of neurons. neurotrophins are the currency over which the neurons and synapses compete for real estate; they are what drive neurons to make connections, and the neurotrophins stabilize those connections. Essentially, the rule is that those who are successful at getting these life-preserving chemicals - which promote growth and survival, guide axons, and stimulate the growth of new synaptic connections - live. Neurotrophins work in at least two ways. one is allowing a cell to differentiate into its next stage of development. The other way, at least early in the development of the organism, is by preventing a cell from initiating suicide by apoptosis.

How are neurotransmitters removed from the synaptic cleft?

Occurs by one of three mechanisms: degradation, in which the neurotransmitter molecule is broken apart by other molecules; diffusion, in which the neurotransmitter moves out of the synapse, down its chemical concentration gradient; or reuptake, in which specialized protein transporters in the membrane will selectively pull the neurotransmitter back inside the cell, presynaptically, postsynaptically, or often, into neighboring cells. Reuptake is the most common for small neurotransmitters.

How can lesions studies be used to understand the brain? What are some of the limitations of these studies?

One of the oldest approaches to mapping out brain-behavior relationships involves studying the effects of brain lesions: areas damaged as a result of disease or other injury. A wide variety of events can cause localized damage to a part of the brain's circuitry. Traumatic brain injuries from blows to the head, accidents, or wounds from bullets or other weapons can physically destroy a small region of the brain. Stroke, meaning either bleeding or blockage of the bloody supply into a region of the brain, can also destroy brain tissue within a restricted region. Surgery, performed to remove a tumor or correct other abnormalities, often involves removing a part of the brain's structure. Infections from viruses or other microbes can selectively damage certain parts of the brain while sparing others. In each of these cases, the loss of or damage to specific pathways within the brain often results in specific effects on cognition and behavior, which can be studied experimentally. One of the oldest and most famous lesion studies was reported by the French neurologist Paul Broca in the 1860s, whose patient Tan had lost the ability to speak and say anything other than his name. At autopsy, his brain proved to have a lesion in a specific region of the left frontal lobe - a region that has been known ever since as "Broca's area" which is linked to the production of language. Lesion studies have identified areas of the brain with crucial roles in vision, hearing, movement, balance, touch sensation, memory of life events, learning of motor skills, comprehension of language, perception of motion and shape, problem solving, judgment, and decision making. In the 21st century, lesions are typically mapped out in detail using MRI rather than autopsy, which allows us to draw links between brain lesions and their behavioral effects in living human beings. Today, large-group lesion studies are helping us pinpoint neural pathways involved in addiction, fear, sadness, pleasure, empathy, the knowledge of social conventions, and our ability to understand the thoughts and intentions of other people. When combined with the detailed anatomical maps of neuroimaging and other correlational studies, lesion studies can help to provide evidence for a causal role between a given set of neural circuitry and a specific form of human cognition or behavior. There are at least three important caveats to lesion studies, however. Lesions themselves are rarely kind enough to map neatly onto just one specific brain structure or circuit, while sparing its neighbors. More commonly, lesions are large, ragged injuries that sprawl across parts of two or three structures or damage part of one structure while leaving another part intact. When, for example, a patient with such a lesion shows a deficit in, say, the recollection of personal memories, it can be difficult to say exactly which of the several partially damaged brain structures is most crucial for the lost function. Conversely, if a patient with such a lesion does not show an obvious deficit in memory recollection, we might falsely conclude that the damaged structure is not involved in this kind of memory. In fact, however, the structure could have had an important role in this kind of memory, but the lesion may have spared just enough tissue to allow it to remain intact. Lastly, in lesion studies, the exact nature of the deficit itself must be assessed carefully or the wrong conclusion can arise. This problem is nicely encapsulated in the old joke about the scientist who trains a frog to jump on command and then removes its legs and tells it to jump. When the frog remains immobile, he writes a paper announcing a momentous discovery: that frogs who lose their legs become deaf. Similar lapses in deductive reasoning can easily occur in lesion studies if the types of cognition we are studying are not yet well understood.

What is the relationship between the mind and the brain?

Our thoughts and perceptions and feelings are all very odd. Our conscious sense of ourselves provides no extra insight into these matters, but only amplified the foreignness of our internal experience. We have no access to the actions of our nervous system associated with our thoughts. Complicating things further, thoughts are private, and distinct thoughts move about with one body and attend the operation of a particular brain. All empirical evidence available today supports the idea that unthinking physical processes in our nervous systems generate our thoughts. Evidence suggests that the mind is what the brain generates. These approaches assume that our experiences do result from the operation of mindless biological parts.

Describe how the cornea, pupil, and lens contribute to the process of getting light onto the retina.

Photons enter the eye through a translucent membrane known as the cornea. Light passes through the cornea and is restricted by a ring of colored muscle fibers known as the iris, which controls the amount of light that can enter the eye. The light passes through a hole in the middle of the iris known as the pupil. From there, the light shines through a lens that will focus the image on the retina, which is at the back of the eye.

What is the difference between pruning and apoptosis?

Plasticity from world experience also involved a good deal of pruning (retraction of axonal branches) and cell death. Cells can die in one of two ways: necrosis (in an uncontrolled fashion) or apoptosis (in a deliberate, controlled fashion). The controlled process of apoptosis avoids collateral damage to neighbors, and it is a common sculpting mechanism in embryonic development. Massive die-off of neurons is standard operating procedure: neurons die because of failure to compete for chemicals provided by targets.

Identify two different types (or more) of photoreceptors and what their specialties are.

Rods and cones. Rods are more numerous, with 90 million cells, compared with only 4.5 million cones. Rods are highly sensitive to light and therefore ideal for vision in dim environments. however, they are broadly receptive to a wide range of light frequencies. Because they do not respond selectively to a particular frequency of light, they are not more responsive to one color than to another, and therefore simply detect degrees of light and dark. Cones, by contrast, are 10 to 100 times less sensitive to light than rods. They are best suited for vision in bright environments (i.e. during daylight). Cones come in three types, each of which detects a different distribution of light frequencies that peaks around red, blue, and green. Eventually, the different activity of these three types of cones in response to objects of different colors will be encoded as color by the brain. Cones are more concentrated in your central vision, a region known as the fovea, whereas there are more rods in the periphery. Cones are more sensitive to the fine details of the stimulus than the rods are. This is for two reasons. First, the fovea looks like a little indentation on the surface of the retina. This is because all those overlying layers of cells are pulled aside and the retinal ganglion cells are literally smaller in this region, to allow light more direct access to the photoreceptors. If this didn't happen, vision would be like looking through several layers of curtains to try to see something; the image would be distorted. The second reason has to do with how the photoreceptors are connected to the bipolar and retinal ganglion cells. Each cone is connected to its own bipolar cell and then to its own retinal ganglion cell. In contrast, many rods connect to a single retinal ganglion cell. For information coming from the cones, this means that when a retinal ganglion cell is activated, the light that caused that activation can come from only one place on the retina. For the information coming from the rods, the stimulus that activates the retinal ganglion cell could come from any one of many (nearby) places. Because of this, the cones have high spatial resolution and the rods have low spatial resolution

Be familiar with and able to discuss directions and orientations in the brain using the following terms: rostral, caudal, dorsal, ventral, anterior, posterior, superior, inferior, medial, lateral, ipsilateral, and contralateral.

Rostral means toward the mouth, or the front end. Caudal means toward the tail end. Dorsal means toward the top (or back). Ventral means toward the belly, or bottom end. Anterior and posterior also mean toward the front or the back, respectively; superior and inferior mean toward the top or the bottom, respectively. Medial means toward the middle; lateral means toward the side. Ipsilateral means "on the same side"; contralateral means "on the opposite side". On a body extensions such as a limb, distal means toward the far (distant) end of the limb, whereas proximal means toward the point where the limb attaches to the body.

How can we classify neurons based on their functions? How can we classify neurons based on their shape?

Sensory neurons are those that directly respond to signals from the outside environment - for example, light, sound waves, pressure, or odors. Motor neurons have direct output to muscles or glands; they are the final step for signals to exit the nervous system and effect change in the body or environment. Afferent neuron is an incoming (sensory) neuron, and efferent neurons are outgoing (motor) neurons. In mammals the vast majority of neurons are interneurons between the sensation of a signal at the one end and the action at the other end. Multipolar neurons are those with multiple dendrites: these are the most common class. Bipolar neurons are composed of a single dendrite on one end and a single axon on the other; these are often found in sensory neurons such as the retina and inner ear. Monopolar neurons have only a single extension that leaves the soma and branches in two directions. One end of a monopolar neuron receives the information and the other end serves for output. This type of neuron is typically found in sensory neurons that signal touch and pain.

Identify the two components of the peripheral nervous system. How are they different?

Sensory neurons have receptors in the skin, muscles, and joints, and through these they convey a multitude of different kinds of sensory input to the body: touch, vibration, pain, temperature, fatigue, itch, stretch, and position. Other sensory nerves extend into the visceral organs of the body: heart, lungs, stomach, intestines, pancreas, kidneys, bladder, uterus, and blood vessels. They are sensitive not only to mechanical stresses such as pain or injury, but also to inflammation, fatigue, and temperature. Motor neurons extend to the muscles of the body, making contact at a specialized structure called the neuromuscular junction. Electrical activity in the motor neuron causes a release of signaling chemicals called neurotransmitters at the neuromuscular junction, and this in turn stimulates the muscle fiber to contract. The body has two major compartmentsL the soma, including muscles, skin and bones, and the viscera, containing the internal organs. Other output neurons send signals to the visceral organs of the body. These visceral output signals regulate the activities of the body's internal world: heart rate, respiration, blood pressure, temperature regulation, movements of the stomach and intestinal tract, secretion of digestive enzymes, voiding of the bladder and bowels, and sexual organ functions. The division between the external and the internal world is reflected in the nervous system itself. The peripheral nervous system has two components: the somatic nervous system and the autonomic nervous system. The peripheral nervous system includes four kinds of neurons for input and output to these compartments: somatic afferent or somatosensory neurons (input), somatic efferent or motor neurons (output), visceral afferent or visceral sensory neurons (input), and visceral efferent or autonomic neurons (output). The somatic nervous system includes the sensory input and motor outputs for guiding voluntary body movements in the external world. When you raise your arm, kick a ball, or withdraw your hand from a hot plate, you are using the somatic nervous system. in contrast, the autonomic nervous system regulates the body's internal world. This process usually goes on automatically.

What happens when you suffer damage to the cerebellum?

Shaping the raw motor activity of reflexes and central pattern generators into smooth, efficient movements is a complicated process. A human (or other animals) need proper steering and smooth movements to navigate their environments. All of these functions require adding on a new kind of circuitry, and lots of it. This circuitry lies in the cerebellum. The cerebellum contains an enormous amount of neurons. All these neurons are densely packed into larger folds or lobules, which in turn are packed into larger lobes. This arrangement fits as many neurons into as small a space as possible, allowing them to communicate efficiently. In the cerebellum, inputs come from dedicated nuclei in the brainstem and connect to small excitatory and inhibitory interneurons in the lower part of the sheet, called the granule cell layer. These interneurons send their output signals to the upper part of the sheet, called the molecular layer. Sandwiched between these two layers lie the giant output neurons, named Purkinje cells. Purkinje cells have an intricate branchwork of input connections that gather information from the molecular layer above them. They integrate this information and send their output back to specialized output nuclei in the brainstem, which pass the information back to the spinal cord and ahead to the cerebral cortex and the rest of the brain. Damage to the cerebellum interferes with the smooth, efficient movements of body parts to their targets in the surrounding environment. Movements become jerky and clumsy. They overshoot or undershoot their targets, occur too early or too late, or are too strong or too weak. maintaining upright balance becomes difficult or impossible. Learning new motor responses also becomes more difficult. Scientists debate what the cerebellum's exact role in coordinating movements in the environment is. One possibility is that the cerebellum calculates a forward model of upcoming movements, making predictions about the expected sensory outcomes of motor actions and uses these predictions to refine outgoing motor commands.

What is the "language of the brain"? Describe what is meant by transduction.

Signals from the outside world - say, a beam of light, a sound, a small, a touch - are brought into your nervous system by different kinds of sensory receptors. This process of transforming an event from the outside world into electrochemical signals inside your nervous system is called sensory transduction. For mammals, this is usually accomplished through pressure-sensitive receptors on the skin, taste buds on the tongue, photoreceptors in the eyes, hair cells in the inner ear, stretch receptors in the muscle, and so on.

Describe the difference between simple and complex cells.

Simple cells respond to a line at a preferred orientation and particular location in the receptive field, whereas complex cells respond to a line of the preferred orientation at any location in the receptive field.

Describe the movement of Na and K ions across the membrane during the action potential. What is the refractory period?

Sodium (Na+) and potassium (K+) play key roles in making an action potential. When a cell is at rest, there is a high concentration of Na+ on the outside of the cell and a much lower concentration on the inside; this is exactly the opposite for K+ ions. When the membrane potential rises beyond a certain threshold, it triggers the opening of voltage-gated ion channels, in this case voltage gated Na+ channels - ion channels that selectively pass Na+ and are opened only at particular voltages across the membrane. When these channels open, Na+ ions suddenly find a way into the cell. These ions are driven n by both the concentration gradient (there are many more on the outside than on the inside) and the electrical gradient (the inside of the cell is more negatively charged than the outside, attracting the more positively charged Na+ ions into the cell). Why doesn't the axon become permanently depolarized and stay there? Because voltage-gated K+ channels are not far behind in their action. The influx of Na+ depolarizes the membrane further, which triggers the opening of the K+ channels. Now, K+ ions flow down their concentration gradient (that is, there are more on the inside than on the outside, so they will tend to flow out). Because the K+ ions are positive and because they are rushing out of the cell, the inside becomes more negative - that is, it repolarizes. This return to a negative voltage shuts the voltage-gated Na+ channels and ends the swing in voltage. Why don't action potentials travel in both directions? Because there is a short refractory period after an action potential, during which the Na+ channels are more resistant to opening. As a result, the action potential cannot move back to a location where it has already occurred, but can only travel forward.

Describe the chemoaffinity hypothesis and how this is related to reflexive behavior.

Sperry imagined that each incoming axon might be matched by a particular molecule expressed by each destination cell in the tectum. Later, on realizing that the genome could not possibly code for that many different address molecules, he proposed that gradients of a smaller number of molecules (some repulsive and some attractive) might do the trick, the idea being that each incoming axon will be tuned for a particular combination of concentrations.

Describe two (or more) invasive methods used when conducting correlational brain research

Such as recording the electrical activity of neurons via microelectrodes implanted directly in the brain during brain surgery. Other similarly invasive measures include the use of tiny microdialysis probes, which are capable of sampling the concentrations of chemical neurotransmitters directly from brain tissue, or voltammetry probes, which can detect neurotransmitter concentrations via minute fluctuations in electrical potential within the probes.

Identify the two components of the autonomic nervous system. What is the function of each?

The autonomic nervous system is itself divided into two subsystems with opposite functions: the sympathetic nervous system and the parasympathetic nervous system. These subsystems allow the internal world of the body to operate in two basic models. The sympathetic nervous system puts the body in the mode of reacting to threats or opportunities in the external world: feeding, fighting, fleeing, or sexual activity. In this mode, the heartbeat quickens, respiration increases, blood pressure increases, and circulation shifts from the digestive organs to the muscles, while the movements of the digestive tract itself slow down or come to a halt. This "fight-or-flight" response system prepares the body to deal with urgent matters in the external world. in the absence of urgent matters, priorities shift from fight-or-flight to "rest-and-regenerate" - and this latter mode is controlled by the parasympathetic nervous system. In this state, the heart rate slows, respiration decreases, blood pressure falls, muscle tone relaxes, and blood flow shifts to the stomach and digestive organs. The movements of the digestive tract increase as the body rebuilds its stores of energy, protein, and other nutrients.

Identify the brain regions which comprise the basal ganglia. What kind of activity is the basal ganglia involved in?

The basal ganglia are a set of closely interconnected gray matter structures beneath the white matter of the cerebral cortex. They play an important role in initiating and maintaining activity in the cerebral cortex, particularly in the motor control areas of the frontal lobes, which must often be driven by an organism's internal goals and needs. For example, the basal ganglia are involved in a diverse set of functions: limb movements, eye movements, planning and goal setting, motivation, and reward. The outermost structure is called the striatum. It consists of a comet-shape structure called the caudate nucleus and a round structure called the putamen, sitting within the "C" of the caudate. These two nuclei actually begin as a single structure, but as the brain develops, they become separated by the internal capsule: a massive tract of white matter heading from the cerebral cortex down to the spinal cord, brainstem, cerebellum, and thalamus. By the end of the fetal brain development process, the caudate nucleus and the putamen are connected by only a few thing stripes of gray matter: "striae". The ventral striatum contains a structure known as the nucleus accumbens - an important player in reward and addiction. Underneath the putamen lies another ovoid structure called the globus pallidus, a critical area for regulating voluntary movement. Other nearby structures work closely with the basal ganglia, even if they are not always considered under that umbrella term. Continubing inward from the globus pallidus, under the thalamus, we find the subthalamic nucleus. Below the subthalamic nucleus, we find the midbrain's substantia nigra. These areas are well connected to the basal ganglia, and they participate in the same functions. The neurons of the basal ganglia are densely interconnected with the cerebral cortex, especially with the frontal cortex. Cortical neurons send connections down to the striatum, which in turn sends connections further inward to the internal and external globus pallidus, sometimes indirectly through the subthalamic nucleus. From here, the circuit continues on to the motor nuclei of the thalamus, which connect back to the original site of the cerebral cortex, forming a complete loop. Different loops or channels serve different regions of the cerebral cortex, which means that they have different functions.

What does it mean when we say the brain is plastic?

The brain is a dynamic system, constantly modifying its own circuitry to match the demands of the environment and the goals of the animal. This ability to physically change, and to hold that change, is known as plasticity - just like the material we call plastic, which can be molded and retain its new shape. Plasticity is the basis of learning and memory. The brain has tremendous flexibility, can reconfigure based on experience, can find itself within any body plan, and will figure out how to configure itself to control it optimally.

Describe how behaviors might be shaped through natural selection. Are all adaptations beneficial?

The brain is an evolved biological organ. As such, its products - our thoughts, actions, emotions, moods, fears, etc. - are shaped by evolutionary pressures. As the biologist E.O. Wilson writes, "The essence of the argument, then, is that the brain exists because it promotes the survival and multiplication of the genes that direct its assembly. The human mind is a device for survival and reproduction, and reason is just one of its various techniques." The surprising character of this observation derives from the fact that what we do think, don't think, and possibly can't think are all constructions of a long, undirected evolutionary process. Some of these constructions may have arisen in response to survival pressure; that is, they are psychological adaptations - mechanisms that on average enhanced the reproductive success of those creatures that possessed them. Others may have simply arisen as neutral changes and come along for the ride. The outcome is that our possible thoughts and actions - the full reach of our cognition - need only to have served the reproductive success of our progenitors. our possible thoughts and actions do not necessarily equip us with a mental apparatus appropriate to have the right intuitions about the world - or even about our own brain. Many aspects of neural function are adaptations that were advantageous, given the survival demands placed on our ancestors. Our psychology is no exception to this: is is also an adaptation. it is a construction that made our ancestors reproductively successful and is not simply a picture of the physical world "out there".

Describe the three major problems the brain is designed to solve. What are some of the biases and weakness in our thinking?

The brain is the end result of millions of generations of careful optimization toward solving three very old, very fundamental, and very specific problems. The first is homeostasis: keeping the body fed, watered, and generally within a happy range of survival parameters. The second is agonistic behavior: defending its own survival interests against other organisms, fending off challenges from predators and rivals, and chasing down prey that made plans other than being eaten. The third is reproduction: making sure that it leaves behind other organisms similar to itself since brains that skip this last task tend to go out of circulation rather quickly. The brain is prone to an extensive set of biases and pitfalls that lead us to draw erroneous conclusions from our observations of the world. Worse yet, we tend to cling to our mistaken beliefs with a confidence that far outstrips the weight of evidence supporting them. The anchoring bias describes the human tendency to become overly influenced by a single observation, usually the first observation (the "anchor"), so that it drowns out or even distorts subsequent pieces of information to make them more consistent with the anchor. A bad first impression at a job interview, an inflated price for a house on the real estate market, or a mistaken initial diagnosis in an emergency room all tend to take on a life of their own, becoming hard to erase even when new information comes to light. Confirmation bias is the tendency to seek out or emphasize information that fits with our existing beliefs, while ignoring or discounting information that contradicts our beliefs. Confirmation bias is widespread in human thinking: reinforcing our prejudices about the people around us, shoring up our political and philosophical convictions, feeding our paranoid fantasies, etc. In trying to understand itself, the brain must contend not only with anchoring and confirmation, but also with the availability heuristic (where scenarios feel more likely when they are most easily recalled), the affect heuristic (where the brain substitutes the easy question "How do I feel about it?" for the harder question "What do I think about it?"), illusory correlation (the tendency to perceive a relationship between events that are not actually connected), belief bias (in which valid arguments with hard-to-believe conclusions are rejected), and many more that arise from applying a survival-oriented brain to problems outside its usual scope of operations.

Localize and describe the general function of the pons and the medulla

The brainstem, which is the most posterior region of the brain, acts as a point of communication between the spinal cord and the most anterior structures of the nervous system. It is composed of three structures: the medulla oblongata, pons, and midbrain. The brainstem's most caudal structure is the medulla oblongata. Ahead of it, the brainstem becomes riddled with the additional white matter tracts of the pons or "bridge" which provides connections to the elaborate circuitry of the cerebellum (little brain") at the same level. Ahead of these two structures lies the midbrain (or mesencephalon) and beyond it the rest of the brain. Extending out from the brainstem are the cranial nerves. The medulla oblongata and pons form the hindbrain. The medulla oblongata regulates involuntary functions that are essential to life, including breathing, heart rate, and blood pressure. The pons relays signals between the cerebellum and the cerebrum (the cerebrum is the anteriormost structure of the central nervous system, consisting of the cerebral cortex, basal ganglia, hippocampus, and amygdala. it originates from the telencephalon of the developing embryo). The pons is involved in arousal, sleep, breathing, swallowing, bladder control, eye movement, facial expressions, hearing, equilibrium, and posture. In many ways, the hindbrain resembles the spinal cord in structure and function. For example, the hindbrain has incoming sensory neurons and outgoing motor neurons that form peripheral nerves. The hindbrain, too, has a central gray matter with different columns of neurons interacting with the inside and outside worlds: somatic sensory, visceral sensory, visceral motor, and somatic motor neurons. However, the hindbrain has many important sensory features that the spinal cord lacks. the hindbrain has many important motor features that the spinal cord lacks. Brainstem nuclei handle these new sensory, motor, somatic, and visceral functional requirements. Simple brainstem reflex arcs can handle simple, local responses. Hindbrain circuits also act as central pattern generators for the rhythmical movements of the head and upper body. With such heavy responsibilities, the medulla oblongata is essential to survival.

Describe the difference between the central and peripheral nervous system

The central nervous system consists of the brain and the spinal cord. The spinal cord has input and output connections to the rest of the body via the peripheral nervous system. The peripheral nervous system connects not only to the skin and muscles, but also to the internal organs of the body. The developing vertebrate brain itself contains three main bulges or zones of expansion: the forebrain (prosencephalon), the midbrain (mesencephalon), and the hindbrain (rhombencephalon). A human embryo will undergo further subdivisions: the forebrain divides into the telencephalon and diencephalon, the hindbrain divides into the metencephalon and myelencephalon. These structures, in turn, become further subdivided throughout growth. Remember that no neuron is an island. All neurons connect to other neurons through circuits, and almost all of these circuits are reciprocal: when neuron A sends output to neuron B, the odds are that neuron B also sends output back to neuron A. Second, remember that the role of a neuron in the nervous system as a whole depends largely on the neuron's inputs and outputs. Knowing who sends input to a neuron and who receives its output can tell you a lot about what that neuron's role is in the nervous system. Third, remember that when the brain refines one of its functions over evolutionary time scales, it often does so by inserting an additional layer of neurons between the existing inputs and outputs. These additional layers can help to modulate the existing circuit, steering its activity more finely, in context with the circumstances at hand.

Identify the four major lobes of the brain, as well as some functions associated with them. What do we call the bumps and grooves on the brain's surface? What are some major landmarks which are useful in describing the lobes of the cortex?

The cerebral cortex is critical for all of the most elaborate forms of human cognition: speaking a sentence, reading the words on a page, planning goals for the future, turning those goals into action, recognizing and using tools, imagining the future and past, etc. The cerebral cortex consists of a layered, outer sheet of gray matter surrounding an inner white matter. As in other parts of the nervous system, the gray matter is composed mostly of the cell bodies of neurons and their local connections, and the white matter is composed of long-distance connection fibers linking neurons that are distant from one another. On the surface, the rounded convolutions of the cerebral cortex are called gyri (singular, gyrus) and the grooves between gyri are called sulci (singular, sulcus). As with the cerebellum, this crumpled pattern of gyri and sulci allows the brain to fit a large sheet of cerebral cortex into a small space while minimizing the distance between any two neurons. A large midsagittal sulcus (also known as the longitudinal fissure) divides the cerebral cortex into left and right hemispheres, which have a lateral and a medial wall. On the medial wall, you can see the large bridge of white matter connections between the two hemispheres: the corpus callosum. The corpus callosum allows the left and right hemispheres to communicate with one another . Each hemisphere is composed of a frontal lobe, temporal lobe, parietal lobe, and occipital lobe. A large lateral sulcus runs along the side of each hemisphere of the cerebral cortex; below it lies the temporal lobe. Above it, a vertical central sulcus lies between the frontal lobe and the more posterior parietal lobe. Behind the parietal and temporal lobes, at the back of the cerebral cortex, lies the occipital lobe. Broadly speaking, the division between the front and back of the cerebral cortex is the central sulcus. In rough terms, everything in front of the central sulcus does various forms of motor planning and action, whereas everything behind and below the central sulcus does various forms of sensory processing. Just in front of the central sulcus lies the precentral gyrus, which is home to the primary motor cortex: a long strip of areas that controls movements of individual body parts. In front of this gyrus are areas involved in planning movements. In front of those areas is the prefrontal cortex, which assembles more elaborate sequences of movement and behavior and is a major player in cognition and goal planning. The prefrontal cortex has a superior, middle, and inferior frontal gyrus on its lateral side. The medial prefrontal cortex lies along the medial wall of the frontal lobe. The underside of the prefrontal cortex, above the orbits of the eyes, is called the orbitofrontal cortex. It plays an imporatnt role in setting priorities and determinging how valuable an action or a resource might be, given current needs. The olfactory cortex, which is important in the sense of smell, also lies in this area. Just behind the central sulcus lies the postcentral gyrus, which is home to the primary somatosensory cortex (S1): another strip of areas that handles sensory input from the skin, muscles, and joints of individual body parts. Behind it, the rest of the parietal lobe is divided into the inferior and superior parietal lobules. The dividing line between these lobules is the intraparietal sulcus, in which a large area of cerebral cortex is hidden. Superior parts of the parietal lobe play a key role in locating objects in space, like a more elaborate version of the midbrain's superior and inferior colliculi. This is useful for planning where to make movements in space. Inferior parts of the parietal lobe play a role in organizing stimuli according to their form rather than their location. This is useful for planning what kind of movements to make. The final part of the parietal lobe lies on the medial wall and is called the precuneus. It is one of the most active regions of the brain, even when we are at rest. It is active when we are imagining scenes and when we are navigating: thinking of destinations and finding directions to them. Behind the parietal lobes lie the gyri of the occipital lobe. The occipital lobe is devoted to processing visual input and contains many different subregions for mapping out the various features of visual stimuli: position, orientation, shape, color, motion, etc. The primary visual cortex lies on the medial wall of the occipital lobe, mostly tucked away inside the deep calcarine sulcus. On the medial wall lies the visceral motor cortex of the cingulate gyrus, which wraps like a belt around the hemisphere-spanning bridge of the corpus callosum. The cingulate gyris is involved in many different functions. Below the lateral sulcus lies the temporal lobe, with a superior, middle, and inferior temporal gyrus on its lateral side. The superior temporal cortex handles auditory information, with the primary auditory cortex (A1) tucked just inside the posterior part of the lateral sulcus. The underside of the temporal lobe has two more gyri: the fusiform gyrus and parahippocampal gyrus. These areas are associated with a ventral visual pathway that handles the identification, categorization, and evaluation of visual inputs: faces, houses, cars, etc. Hidden away within the depths of the lateral sulcus lies a large area of cerebral cortex known as the insula. The insula is the visceral sensory part of the cerebral cortex. It represents the state of the internal organs and registers internal bodily states like pain, fatigue, hunger, etc.

What happens to dendritic processes in an enriched environment?

The dendritic processes expanded and grew. The environment altered the brain structure, and this in turn correlated with changes in the animal's capacity for learning and memory. The rats raised in enriched environments performed better at behavioral tasks and were found at autopsy to have lush, extensively branched dendritic trees. By contrast, the rats raised in the deprived environments were poor learners and had abnormally shrunken neurons.

What is the dorsal stream specialized for?

The dorsal stream relates less to what an object is and instead processes where it is in space. The dorsal stream in part deals with the detection of motion. To catch or intercept a moving object, the visual system does not need an explicit representation of position, or even velocity or acceleration. This counterintuitive finding merely reinforces that we have little intuitive access to the mechanisms of the visual cortex that underlie our abilities. The dorsal stream is also involved in attention. The key to attention is that it is selective: it improves perception of stimuli that are attended to, and it interferes with the processing of those that are not. Attention can be spatial. At any moment, attention involves particular places in space. The dorsal stream is critical for guiding and adjusting the spotlight of attention.

How many ventricles do we have? What is their function?

The four ventricles (cavities) in your brain are filled with cerebrospinal fluid, not neurons. Two of these, the lateral ventricles, lie at the center of each hemisphere of the cerebral cortex, inside the white matter. These connect to the third ventricle, which lies along the midline of the brain, between the left and right thalamus. This connects to the fourth ventricle, a small triangular structure tucked between the brainstem and the cerebellum. The ventricles constantly produce cerebrospinal fluid, which circulates through the ventricles and over the surface of the brain and spinal cord. The fluid protects the brain from injury and helps to maintain a stable chemical environment for the neurons.

Identify and describe the major structural components of a neuron.

The human brain contains almost 100 billion neurons. Neurons are, in most ways, like all the other cells in your body: they have a membrane, nucleus, and specialized organelles and they produce, traffic, and secrete chemicals. Neurons have proteins that are inserted into their membranes, and these proteins allow the cell to interact with its outside environment. They can transmit electrical signals quickly over long distances. Neurons have four zones of importance. The first consists of dendrites, which are long, branching extensions from the cell body. Dendritic trees can take on many shapes and sizes. Dendrites are specialized for collecting information from thousands of tiny chemical signals that they receive all along their extent. By responding to chemical messages along their intricate branching patterns, dendrites collect a great deal of information and pass it to the second zone of importance: the soma or cell body. The key feature of the soma is the cell's nucleus, which is the control center of the cell that regulates cell activity, as well as gene expression. Emerging from the soma is the single, long slender process of the axon, or nerve fiber, which is the third zone of importance. The axon is an extension that reaches long distances beyond the soma, and it is essentially a cable to conduct signals rapidly across long distances. There is only one axon coming from a neuron. Axons tend to be constant in diameter all along their length. Axons tend to be much longer than dendrites. A typical axon will branch robustly at its end, typically splitting into about 10,000 axon terminals. The terminals are identifiable as small swellings at the end tips and, as we will see, they contain packages of chemicals that can be released into the space between cells. The terminals, therefore, are optimized for the output of signals. Axon terminals are typically found in close proximity to the dendrites and somas of other cells, and such junctions are called synapses. The main location of signal transmission, the synapse links an axon to other neurons (in the CNS) or to a neuron, muscle, or gland (in the periphery). Synapses can sometimes exist along the axon themselves, in which case they are called en passant synapses.

Where are sensory and motor peripheral nerve roots relative to the spinal cord?

The human nervous system has a segmental organization. The segments are easiest to see near the spinal column. Here, the body segments are apparent in the skeleton itself: the line of vertebrae that begins with the cervical spine (within the neck), continues down the thoracic spine (within the ribcage, another segmented structure), continues farther down the lumbar spine (between the ribcage and the pelvis), and ends in humans with the sacral spine. The peripheral nerve roots emerge from the spinal cord on either side, near the junction of each vertebra with its neighbor. Hence, every segment of the spinal cord has its own set of peripheral nerve roots on the left and on the right. Near the spinal cord, inputs and outputs are kept separate. All sensory input, somatic and visceral, enters the spinal cord through the dorsal nerve root at the back of the spinal cord. All motor output, somatic and autonomic, exits the spinal cord through the ventral nerve root at the front of the spinal cord. The segmental organization of the somatic nervous system can also be observed on the outside of the body. Each pair of sensory nerve roots handles input from a narrow stripe on the body surface. The stripes are arranged in a series, from head to tail end, as if the skin were cut up into narrow sections. These stripes are called dermatomes. Each dermatome corresponds to a different spinal segment and is numbered accordingly. The motor side of the somatic nervous system is also organized into segments. In this case, the segmental "stripes" lie within the musculature rather than the skin and are therefore called myotomes rather than dermatomes. The neat, segmental pattern of the myotomes and dermatomes is not perfectly preserved at all points in the peripheral nervous system. Sensory and motor neurons take complicated routes from the spinal cord to their final destinations, joining and rejoining neurons from the other spinal levels as they reshuffle themselves into peripheral nerve bundles. The autonomic nervous system is also organized into segments. In fact, the sympathetic and parasympathetic systems exist in completely separate segmental regions. All sympathetic outputs come exclusively from the middle levels of the spinal cord: the thoracic segments and the neighboring, uppermost lumbar segments. All parasympathetic outputs come from either the tail-end segments of the sacral spinal cord or the head-end segments that lie above the spinal cord altogether, in the brainstem.

Identify some of the main structures of the limbic system. What kind of activity is the limbic system involved in?

The internal environment must interface with the external environment at some point in the nervous system. At every level of the central nervous system, we can find regions where the sensory inputs form both internal and external environments converge to help guide control of the internal environment. These areas are sometimes considered as forming their own system, central to motivation and emotion. They are known as the limbic system. What the limbic system consists of is not always agreed upon. These are some of the most agreed-on structures whose circuits bridge the gap between the brain's internal-environmental sensory inputs and motor outputs. These structures have continuously proven themselves critical in the regulation of motivation and emotion. The hypothalamus plays a key role in homeostasis and in motivation. Certain parts of the midbrain, such as the periaqueductal gray matter, also link together visceral and somatic functions to produce simple kinds of motivated and emotional behavior. Also in the midbrain, substantia nigra neurons contain dopamine, a neurotransmitter that is central to motivation and reward. Neurons of the raphe nuclei contain serotonin, a neurotransmitter that is also important for emotion and the regulation of internal states. In addition, two important limbic structures lie in the medial temporal lobes. The first of these is the amygdala, which is similar to the hypothalamus in its outputs: it, too, can directly drive the internal states of the body through autonomic mechanisms and hormonal signals. It also sends outputs to the cerebral cortex to drive motivated behaviors, prioritization, goal setting, and action planning. however, its inputs are different from those of the hypothalamus. Rather than drawing on the inside world, the amygdala obtains input directly from the external-world senses of vision, hearing, and smell. The amygdala generates emotions and motivations based on the external sensory inputs of vision, hearing, and smell. The hippocampus is another critically important site for memory and learning. A long, thin structure whose fanciful name means "seahorse", it lies on the medial temporal lobes just behind the amygdala. It is traditionally considered a part of the limbic system, although its role in emotion and motivation is indirect. The hippocampus plays an important role in spatial navigation and episodic memory: memory for past personal experiences that occurred at a specific time and place, as opposed to memory for facts. It also seems to be crucial for imagining future or hypothetical scenes. It also has a major connection pathway via a loop called the fornix to a pair of nuclei in the hypothalamus, called the mamillary bodies. This circuit may be useful for linking the body's current needs to the organism's knowledge of places and past events. Parts of the cerebral cortex are sometimes considered limbic cortex. Limbic cortex forms a ring that starts with the visceral sensory cortex of the insula. The anterior part of the insula is next to the orbitofrontal cortex, which plays a visceral motor role in generating internal bodily states, or somatic markers, based on sensory input from the internal and external environment. From here, the ring continues on to the medial wall and the anterior cingulate cortex, which also performs visceral motor functions. It follows the cingulate gyrus over the corpus callosum to the posterior cingulate cortex, which plays a role in familiarity and emotional memory. It then gradually passes to the underside of the medial temporal lobe, whose functions mirror the navigation, memory, and emotional functions of the adjacent hippocampus and amygdala.

Describe how photoreceptors, bipolar cells, and retinal ganglion cells contribute to sending signals about a light stimulus to the rest of the brain

The retina is a layered structure, composed of five layers of cells. From the side closest to the lens to the side furthest from the lens, those cells are the retinal ganglion cells, which pass information from the eye to the brain; amacrine cells, which allow communication between different parts of the retina; bipolar cells (a type of bipolar neuron), which carry information from the photoreceptors to the retinal ganglion cells; horizontal cells, which also allow communication between adjacent parts of the retina; and finally, the photoreceptors. Light passes through all of those cells, in that order, when it enters the eye. Photoreceptors capture the photons of light and convert the light into neurochemical activity through a biochemical process known as phototransduction. In phototransduction, light strikes a pigment molecule, such as rhodopsin, within the photoreceptor, causing it to break into pieces. These pieces act on proteins in the cell to change the resting membrane potential and, thereby, change the neurotransmitter signal the photoreceptor is releasing. With time, an enzyme puts the pigment molecule back together, and the cell is ready to signal again. The information that results from this process flows out of the eye to the brain through those same cells, but in the reverse sequence of the process described above.

Describe the center-surround structure of retinal ganglion cells.

The signals from the photoreceptors are relayed through the layers of cells int he retina and then reach the retinal ganglion cells. The pathway from the retina to the cortex is organized such that each retinal ganglion cell responds to stimulation only in a specific location of the visual scene. The region of visual space in which a stimulus will modulate the activity of a particular neuron is called the receptive field. Retinal ganglion cells have tiny receptive fields that cover visual space, much like you could use many small tiles to completely cover a floor. Retinal ganglion cells have a center-surround structure: a small point of light in the center of the receptive field will maximally activate the cell, whereas a ring of light in the surround (the disk around the center) will inhibit the firing of the cell (on-center cell). When both the center and the surround are stimulated - say by a large patch of light - the excitation and inhibition cancel out and the neuron responds little. Other retinal ganglion cells do exactly the opposite, responding to light in the surround but not the center (off-center cells), For both on and off center cells, note that a uniform surface of light does little to activate them; instead, these cells are optimized for detecting differences in light levels from one area to the next - that is, edges. Because of the center-surround structure, neighboring neurons can achieve contrast enhancement, that is, the amplification of a difference between the lightness of two surfaces.

Describe the reflex arc which underlies the knee-jerk reflex

The simplest kind of circuit for connecting inputs to outputs is called a reflex arc. In this kind of circuit, a sensory neuron makes an excitatory connection to a motor neuron so that when the sensory neuron is stimulated, it activates the motor neuron in return. This kind of reflex arc is useful in helping muscles compensate for additional load. If a sensory neuron detects that the muscle is being stretched, it stimulates the appropriate motor neuron to contract the muscle. The familiar "knee-jerk" reflex (properly called the patellar tendon reflex) is a result of suddenly stretching the body of the quadriceps muscle after tapping the attached tendon with the reflex hammer. The quadriceps makes a powerful, automatic contraction in response to this unexpected extra load. Reflex arcs are just as important for coordinating the activity of the sympathetic and parasympathetic nervous systems: raising the hair follicles in response to cold, producing tears in response to eye irritation, and contracting the blood vessels when standing up so as not to faint from loss of consciousness. A reflex involving a direct connection between a sensory and a motor neuron is sometimes called a monosynaptic reflex, since the entire circuit involves only one synapse, or connection between neurons. However, these kinds of circuits are rare. Most reflexes are polysynaptic reflexes - that is, they involve more than one synapse, because an interneuron lies between the incoming sensory neuron and the outgoing motor neuron in the circuit. Polysynaptic reflexes allow for more flexibility in the response than monosynaptic reflexes. For example, imagine you need to contract the biceps muscle of our arm. The problem is that this will stretch the triceps muscle on the other side of the arm. As we saw above, the triceps will automatically compensate by fighting against the stretch. Without some way of turning off the triceps stretch reflex, you cannot bend your arm. But what if we add an inhibitory interneuron (a neuron that transmits inhibitory signals between other neurons) that connects the biceps motor neuron to the triceps motor neuron? Now the triceps motor neuron has information about the contraction of the biceps and can use this information to override the stretch reflex.

Recognize the Nodes of Ranvier and describe how they, along with myelin, contribute to the propagation of an action potential along an axon.

The small gaps left between the myelin sheaths are known as nodes of Ranvier, and it is at these points that ions from outside the cell can most easily flow in and out. In the stretches of myelin-insulated axon, it is difficult for ions to move across the membrane, and the consequence of this is extraordinary: the action potential "leaps" directly from node to node instead of moving smoothly, as it does along an unmyelinated axon. This noncontinuous skipping of the spike is known as saltatory conduction. The action potential is regenerated at each node, but not at the insulated stretches in between. Saltatory conduction vastly increases the travel speed of the action potential and cuts down on energy expenditure.

Describe temporal and spatial summation and how they contribute to the firing of an action potential.

The small voltage changes collected in the dendrites (EPSPs and IPSPs) travel along the dendritic membrane to the cell body, where all the branches come together. Although the postsynaptic potentials are small, they can add up with one another in two ways. First, signals that arrive at the soma at the same time (or even close to the same time) will add up when they reach the soma - this is known as temporal summation. Second, signals that arrive on different branches of the dendrites will converge at the soma - this is known as spatial summation. As a result of both kinds of summation, the soma has the opportunity to integrate signals flowing into disparate parts of the dendrites. If the number of excitatory potentials overwhelms the number of inhibitory potentials, this can drive the voltage of cell toward more positive values, making it increasingly depolarized. If the cell voltage reaches a threshold, typically about -60 mV, something special happnes: an action potential is generated at the axon hillock, the part of the axon that connect to the soma. The axon hillock is the most excitable part of the neuron and therefore the location where spikes are initiated.

Describe the function of the thalamus

The thalamus plays a central role in brain function by acting as a relay station to the cerebral cortex, conveying incoming sensory information to the appropriate cortical areas. It also relays motor signals to the cerebral cortex from other motor control structures like the cerebellum and basal ganglia. In addition, the thalamus acts as a relay station between distant areas of the cerebral cortex itself, communicating information from one area to another. Thalamic neurons cluster into a large number of separate thalamic nuclei, which serve different regions and therefore play different roles. Further, the thalamic nuclei may play an important role in synchronizing neural activity between distant regions, enabling these regions to work together. The thalamus and the cerebral cortex are tightly interconnected. Each thalamic nucleus serves a different section of the cerebral cortex. For example, the lateral geniculate nucleus relays information from the light-sensitive neurons (or photoreceptors) of the retina to the neurons of the primary visual cortex (V1), where the first stages of visual information processing in the cortex take place. Thalamic nuclei play all sorts of role, auditory, motor control, etc. Some thalamic nuclei are dedicated to serving association areas of the cerebral cortex. The association areas of the cerebral cortex are neither purely sensory nor purely motor areas. These areas integrate sensory and motor functions and are important for more complex forms of sensory processing and motor planning. Additional thalamic nuclei convey information about motivations and drives to the cerebral cortex. Other types of thalamic nuclei called intralaminar nuclei, provide a more diffuse input to large swaths of the cerebral cortex as a whole. Since they connect to so many areas with such diverse functions, these nuclei are probably not involved in any single type of sensory or motor function. The reticular nucleus is one final an very important structure of the thalamus. It consists of a thin sheet of neurons that wraps around the entire surface of the thalamus. Unlike all other thalamic nuclei, it has no connections to the cerebral cortex and few inputs from any other outside brain structure. Instead, almost all of the input to the reticular nucleus originates within the thalamus itself. Its neurons, all of which are inhibitory, connect only to other nuclei of the thalamus. Each neuron not only inhibits some of the neurons of a thalamic nucleus, but also inhibits its own neighbors. The effect of this is like changing a babble of uncoordinated neural chatter into a respectful conversation, where other neurons grow silent when one of their neighbors is speaking.

What is the ventral stream specialized for?

The ventral stream deciphers what objects are - in other words, how to identify and categorize them. The receptive fields of IT neurons are much larger than those found in early visual cortex, which means they can respond to relevant stimuli almost anywhere in the visual field and gives them the property that they are not focused on where exactly an object is - instead they are focused on what it is. In other words, changes to the object itself (such as a change in shape) will change the firing rate of IT neurons, but a change in the position or size of the object will not. Neurons in early visual areas faithfully encode simple properties of objects. As processing moves in a hierarchy toward the anterior part of the inferotemporal cortex, neurons have larger receptive field and encode an increasingly abstract form of the stimulus - that is, local characteristics become less relevant.

Identify different patterns of reorganization which can occur in the optic tectum of tadpoles following removal of a portion of the tectum, removal of a portion of the eye, or the insertion of a new eye.

There are two possibilities that could explain what happens when the brain's available resources change: first, the system might leave out the parts of the map corresponding tho the missing tissue or, second, the brain might make the same map of the body on a smaller piece of real estate. In frogs, nerves from the eye travel directly to the optic tectum (roughly analogous to the visual cortex in mammals). There the nerves plug in retinotopically - that is, nerve fibers from the top of the eye connect to the top of the tectum, the left part of the eye to the left part of the tectum, etc. Each fiber coming from the eye appears to have a preassigned address where it plugs into the target. To understand the principles of plasticity, researchers removed half of the optic tectum during development, before the optic nerves had arrived. A full retinotopic map developed on the smaller target area. The map was compressed in size, but otherwise arranged normally. Researchers transplanted a third eye in a tadpole, and resulted in two sets of optic nerves sharing the same target area of tectum. The two eyes shared the territory in alternating stripes, each with its full retinotopic mapping. The retinal fibers utilized whatever target area was available.

What is an EPSP? What is an IPSP? What kind of changes in the membrane potential (depolarization/hyperpolarization) are associated with each?

Think of ionotropic receptors after the neurotransmitters bind and cause the flow of ions. Because there are different concentrations of ions inside and outside the cell, there is a voltage difference (also known as a potential difference) across the membrane. Normally, the outside of the cell is more positive than the inside, giving a resting membrane potential of about -70 millivolts (mV). Depending on the charge of the ions and in which direction they flow, the movement of ions across the membrane can make this potential difference smaller or larger. When positive ions, such as sodium, flow through a receptor into the cell (slightly reducing the difference between inside and outside), this is known as an excitatory postsynaptic potential (EPSP). Conversely, if neurotransmitter binding causes the potential difference in voltage between the inside and outside of the cell to grow larger (that is, the inside becomes more negative), this change in voltage is known as an inhibitory postsynaptic potential (IPSP). This can occur by allowing positively charged ions (potassium) to flow out of the cell or by allowing negatively charged ions (chloride) to flow into the cell. Typical postsynaptic potentials are tiny changes in voltage, and last only a few milliseconds. Keep in mind that it is not the neurotransmitter molecule itself that is excitatory or inhibitory - it is the action of the receptor that determines the effect.

Identify two major classes of receptors and major properties associated with each

When the neurotransmitter molecules are released into the synaptic cleft, they exert their effects by binding to receptors, specialized proteins in the membrane. Receptors can often be located presynaptically or on neighboring cells, but we'll concentrate on the overwhelmingly most common type: postsynaptic receptors. There are two main ways in which typical neurotransmitters transmit a signal to another cell: either by causing direct flow of ions into or out of the cell (ionotropic receptors) or by causing more indirect changes inside the cell by a cascade of signals (metabotropic receptors). Ionotropic receptors: there are different concentrations of ions inside and outside the cells: thus, if you were to poke a hole in a membrane, ions would tend to flow in or out. An ionotropic receptor is essentially a sophisticated way of opening a temporary pore in the membrane. In its closed state, the receptor protein blocks the flow of ions; when it is opened, or gated, by the right type of neurotransmitter, the protein changes its shape and provides a pore in the membrane. Many ionotropic receptors allow only a particular type of ion to pass through; thus a receptor that binds the neurotransmitter GABA tends to selectively pass chloride ions, whereas a receptor that binds acetylcholine may selectively pass sodium ions. Metabotropic receptors are also known as "second-messenger-coupled" receptors. Consider a family of such receptors called G-coupled protein receptors. G-proteins are associated with the inside face of the postsynaptic membrane, and their function is to relay information from neurotransmitter receptors to other proteins inside the cell. These in turn relay, amplufy, and transform the signal. Because so many receptor types are G-protein coupled, this allows the cell to develop sophisticated signaling cascades that integrate several signals from the outside. The second messengers triggered by metabotropic receptors can serve many different functions, modulating the activity of neighboring ion channels, activating or deactivating enzymes within the cell, or changing which genes are expressed within the cell. The effects of metabotropic receptors tend to operate on a much slower time scale than ionotropic receptors.

Identify the two major types of cells in the brain

neurons and glia?

Identify the location of the superior and inferior colliculi as well as the functions they contribute to.

the midbrain's local inputs and outputs come mostly from the eyes: visual signals from the retina, motor signals to control eye movements, light entry via the iris, and image focus via the lens. To make use of a visual image, the animal must determine where objects are in space. A midbrain area called the superior colliculus is involved in locating visual stimuli in space and uses this information to direct complex movements, such as turning the eyes to point toward the target. This area can also use visual stimuli to guide movements of other parts including the head, the arm, the tongue (in frogs), or even the whole body. Just below the superior colliculus, the inferior colliculus performs parallel functions using auditory rather than visual inputs. These areas are large, important players in motor control in many species such as fish, amphibians, reptiles, and birds. In mammals, many of the functions of the superior colliculus and the inferior colliculus have been transferred to the cerebral cortex.