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Bio.590-9.CNS
Integrative Physiology Ch. 9 - The Central Nervous System
| Question | Answer |
|---|---|
| How is it that combinations of neurons linked together into chains or networks collectively process emergent properties not found in any single neuron, e.g., thoughts, memories, etc.? | We do not yet have an answer to this question. The field of computational neuroscience, along with other scientific disciplines, are investigating this |
| One reason computers can’t currently accurately model brain function | Computers lack plasticity, the ability to change circuit connections and function in response to sensory input and past experience |
| Affective behaviors | Behaviors linked to feeling and emotions |
| Cognitive behaviors | Behaviors linked to thinking |
| Do paramecium have integrating centers or brain function of any kind? | Paramecium are simple, single-celled organisms that can carry out the basic tasks of life: find food, finding a mate, etc. But they have no brain or integrating center. |
| The first multicellular animals to develop neurons | Members of the phylum Cnidaria, the jellyfish and sea anemones. Their nervous system is a *nerve net* composed of sensory neurons, connective interneurons, and motor neurons that innervate muscles and glands |
| Is the nervous system of a jellyfish like the nervous system of a human? | No, it lacks an integrating center. The neurons are diffuse, there is no “brain” |
| In _____ we see the beginnings of a nervous system as we know it in higher animals | Primitive flatworms |
| Structure of the nervous system in a primitive flatworm | A rudimentary brain consists of a cluster of nerve cell bodies concentrated in the head (*cephalic*) region. Two large nerves called *nerve cords* come off the primitive brain and lead to a nerve network throughout the body |
| One step more advanced nervous system than the flatworm exists in the | Segmented worms, or annelids, such as the earthworm |
| Structure of the nervous system in the segmented worms (annelids), e.g., earthworm | Unlike the flatworms, clusters of cell bodies aren’t restricted to the head region, but also occur in fused pairs called ganglia, along a nerve cord. These ganglia allow reflexes to occur without input from the brain (like spinal reflexes) |
| Why are eyes, smell, taste, etc. located at the head? | Because in most animals the head is the part of the body that first contacts the environment as the animal moves. Thus, as brains evolved they became associated with specialized cephalic receptors such as the eyes for vision, etc. |
| Which animal has the most sophisticated brain development among the invertebrates? | The octopus (a cephalopod mollusk) which happens to have the most sophisticated behavior |
| The most dramatic change in brain development occurring in vertebrates (compared to invertebrates) | Changes of the forebrain region, which includes the *cerebrum* and the diencephalon (hypothalamus, etc.). |
| Significance of the cerebrum in various vertebrates | In fish it’s a small bulge dedicated to processing olfactory information. In birds and rodents it’s more developed. In humans it’s the largest part of the brain and it is what makes us human |
| Cerebellum | The region of the *hindbrain* devoted to coordinating movement and balance |
| The basic, overarching pattern of the CNS structure in all vertebrates | The CNS consists of layers of neural tissue surrounding a fluid-filled central cavity lined with epithelium |
| Neural plate | In the very early embryo cells that will become the nervous system lie in a flattened region called the neural plate. As development proceeds neural plate cells along the edge migrate toward the midline. |
| Neural tube | By about day 23 of human development, the neural plate cells have fused with each other, creating a neural tube. *Neural crest cells* now lie dorsal to the tube which will become the PNS |
| Development of the CNS from neural tube | Lumen of the neural tube remains hollow and becomes the central cavity of the CNS. Cells lining the neural tube either differentiates into epithelial ependyma or remains as neural stem cells. Outer layers become glia & neurons of the CNS |
| By the 4th week of human development, the anterior portion of the neural tube has begun to specialize into the three regions of the brain: | (1) Forebrain, (2) midbrain, and (3) hindbrain. Note: as development proceeds after this point, the growth of the cerebrum will outpace that of the other regions |
| The tube posterior to the hindbrain will become… | …the spinal cord |
| By week 6, the CNS has formed the seven major divisions that are present as birth: | (1) the cerebrum, (2) the diencephalon, (3) the midbrain, (4) the cerebellum, (5) the pons, (6) the medulla oblongata, and (7) the spinal cord |
| In which regions of the brain are the seven divisions of the brain located? | The cerebrum and diencephalon are located in the forebrain. The cerebellum, pons, and medulla oblongata are divisions of the hindbrain. |
| Ventricles of the brain | By week 6 the central cavity (lumen) of the neural tube enlarges into the hollow ventricles of the brain. There are two lateral ventricles (the first and the second), and two descending ventricles (the third and fourth) |
| The central canal of the spinal cord | The central cavity of the neural tube also becomes the central canal of the spinal cord |
| Gray matter of the brain | Consists of unmyelinated nerve cell bodies, dendrites and axon terminals. They’re assembled in an organized fashion in both the brain and spinal cord. They form layers in some parts and clusters (nuclei) in others |
| White matter of the brain | Made up mostly of myelinated axons and contain very few cell bodies. Its pale color comes from the myelin sheaths that surround the axons. |
| Tracts | Bundles of axons that connect different regions of the CNS (i.e., they’re the equivalent to nerves of the PNS) |
| The consistency of the brain? Why? | Soft and jellylike because, although individual neurons and glial cells have highly organized internal cytoskeletons that maintain cell shape and orientation, neural tissue has minimal matrix |
| Because neural tissue lacks a matrix, it has to… | …depend on external protection from trauma |
| What external support and protection does neural tissue get, if not from matrix? | An outer casing of bone, three layers of connective tissue membrane, and fluid between the membranes |
| What encases the brain and spinal cord? | The brain is encased in the skull (AKA cranium), the spinal cord runs through a canal in the vertebral column |
| Vertebrae | The bones, stacked upon disks of connective tissue, which make up the vertebral column. |
| How do nerves of the PNS enter and leave the spinal cord? | By passing through notches between the stacked vertebrae |
| The meninges – what is their function? | Three layers of membrane between the bones and tissues of the CNS. They help stabilize the neural tissue and protect it from bruising against the bones of the skeleton. |
| Starting from the bones and moving toward the neural tissue, the three membranes of the meninges are: | (1) the dura mater, (2) the arachnoid membrane, and (3) the pia mater |
| Dura mater | The thickest of the meninges. It’s associated with the veins that drain the blood from the brain through vessels or cavities called *sinuses*. |
| Arachnoid membrane | Loosely tied to the inner membrane, leaving a *subarachnoid space* between the two layers. |
| Pia mater | The inner membrane; it’s a thin membrane that adheres to the surface of the brain and spinal cord. Arteries that supply blood to the brain are associated with this layer |
| The internal volume of the cranium (excluding cells) is comprised of | Blood, cerebrospinal fluid, and interstitial fluid |
| Where is the interstitial and cerebrospinal fluid found? | Interstitial fluid lies within the pia mater. Cerebrospinal fluid is found in the ventricles and in the subarachnoid space |
| How do the cerebrospinal and interstitial fluid compartments communicate with each other? | Across leaky junctions of the pial membrane and the ependymal layer lining the ventricles |
| Cerebrospinal fluid (CSF) | A salty solution that is continuously secreted by the choroid complex. |
| Choroid plexus | It’s a specialized region on the walls of the ventricles that secrete CSF. It’s similar to kidney tissue and consists of capillaries and transporting epithelium derived from the ependyma. It pumps sodium/other solutes from plasma into ventricles |
| As a result of pumping solutes into the CSF… | …water is also drawn into the ventricles |
| From the ventricles, CSF flows into… | …the subarachnoid space |
| Recap: subarachnoid space | The space between the pia mater and the arachnoid membrane, filled with CSF. As a result, the entire brain and spinal cord is surrounded by fluid |
| What eventually happens to the CSF after flowing around the neural tissue? | It’s finally absorbed back into the blood by *arachnoid villi* on the arachnoid membrane in the cranium |
| How often in the CSF replenished in the nervous system? | The rate of fluid flow is sufficient to replenish the entire volume of CSF about three times per day |
| Roughly, what are the purposes of CSF? | Physical protection and chemical protection |
| CSF: physical protection | The buoyancy of CSF reduces weight of brain 30-fold, decreasing pressure on blood vessels/nerves. The fluid also provides protective padding: it’s minimally compressible, cushioning the brain during trauma |
| CSF: chemical protection | CSF exchanges solutes with the interstitial fluid of the CNS and provides a route by which wastes can be removed |
| Lumbar puncture | AKA spinal tap, the withdrawing of fluid from the subarachnoid space between vertebrae at the lower end of the spinal cord. The presence of proteins or blood cells in the CSF indicates an infection |
| Blood brain barrier | Not a literal barrier; it refers to the highly selective permeability of brain capillaries that shelter the brain from toxins and from fluctuations in hormones, ions, and neuroactive substances, e.g., neurotransmitters, in the blood |
| What makes brain capillaries so much less permeable than other capillaries? | In most capillaries, leaky cell-cell junctions and pores allow free exchange of solutes between the plasma and interstitial fluid. In brain capillaries, endothelial cells form TIGHT JUNCTIONS which prevent such movement |
| How do astrocyte foot projections play a role in the BBB (blood-brain barrier)? | Their “foot processes” which attach to the capillaries support them as well as secrete paracrines that promote tight junction formation |
| If tight junctions prevent movement between the capillaries and interstitial fluid, how does material travel to the neurons? | Only material that can diffuse through the various channels on the capillary endothelium (transcellular transport). If it can’t pass through any of the channels, it can’t cross the blood-brain barrier (unless lipophilic) |
| What kind of transport occurs across the BBB? | Nutrients is moved into the interstitial fluid; wastes are moved into the plasma |
| Parkinson’s Disease | Neurological disorder in which brain levels of dopamine are too low because dopaminergic neurons are either damaged or dead. Dopamine injections are ineffective because it can’t cross the BBB |
| If dopamine can’t be injected to treat Parkinson’s, how is it treated? | A precursor L-dopa can be transported across the BBB via an amino acid transporter into the interstitial fluid where it’s catalyzed to dopamine. Problem? Only 5% is absorbed into brain, remainder causes bad side effects |
| Do ALL materials have to pass through channels to pass the BBB? | No, lipophilic materials can diffuse through the membranes |
| Are ALL blood vessels in the brain protected by the BBB? | No, the hypothalamic-hypophyseal portal system requires that hormones be able to pass through. Another region that lacks a BBB is the vomiting center in the medulla oblongata which monitors the blood for harmful substances |
| Special metabolic requirements of neural tissue | Neurons require a constant supply of oxygen and glucose to make ATP for active transport of ions and neurotransmitters. O2 passes freely across the BBB and membrane transporters uptake glucose. |
| Because of its high demand for oxygen, the brain receives about __% of the blood pumped by the heart | 15% |
| If blood flow to the brain is interrupted, how long does it take for brain damage to occur? Why? | Only a few minutes. Because the brain needs both O2 and glucose |
| How much of the body’s glucose consumption occurs in the brain? | About half |
| How can diabetes affect negatively affect the uptake of glucose in the brain? | After a sustained period of hyperglycemia, cells of the BBB down-regulate glucose transporters. When normal glucose levels are finally restored, the patient may suffer the symptoms of hypoglycemia, and may die |
| Paralysis | The loss of the ability to voluntarily control muscles. E.g., can be caused if the spinal cord is severed. |
| The spinal cord is divided into four regions: | Cervical, thoracic, lumbar, and sacral |
| Each segment of the spinal regions gives rise to a bilateral pair of: | Spinal nerves |
| Just before a spinal nerve joins the spinal cord, it divides into two branches called: | Roots |
| What are the two roots called and what are their functions? | The dorsal root is specialized to carry incoming sensory information. The ventral root carries information from the CNS to muscles and glands |
| Dorsal root ganglia | Swellings found on the dorsal roots just before they enter the cord. They contain cell bodies of sensory neurons. |
| Describe the relative positions of the white and gray matter when viewing a cross section of the spinal cord | Gray matter appears as the butterfly-shaped core and the white matter appears as the surrounding rim |
| Dorsal horns | Sensory fibers from the dorsal roots synapse with interneurons in the dorsal horns of the gray matter. The dorsal horn cell bodies are organized into two distinct nuclei, one for somatic information and one for visceral information |
| Ventral horns | Ventral horns of the gray matter contain cell bodies of motor neurons that carry efferent signals to muscles and glands. They’re organized into somatic motor and autonomic nuclei. Efferent neurons leave spinal cord via ventral root |
| The white matter of the spinal cord is the biological equivalent of… | …fiber-optic cables that telephone companies use to carry our communication systems |
| Overall structure and function of white matter in the spinal cord | White matter can be divided into columns composed of tracts of axons that transfer information up and down the cord |
| Ascending tracts | The portion of the white matter of the spinal cord which takes sensory information to the brain. They occupy the dorsal and external lateral portions of the spinal cord |
| Descending tracts | The portion of the white matter of the spinal cord which carries mostly efferent (motor) signals from the brain to the cord. They occupy the ventral and interior lateral portions of the white matter. |
| Propriospinal tracts | The portion of the white matter of the spinal cord which remains within the cord |
| Can the spinal cord function as an integrating center? | Yes, for simple *spinal reflexes*, with signals passing from a sensory neuron through the gray matter to an efferent neuron |
| What affect does the spinal cord have on information being sent through it to or from the CNS? | Often interneurons of the gray matter will modify information as it passes through them |
| Summary -- the brain stem consists of the: | Pons, medulla oblongata, and midbrain, reticular formation |
| Summary -- the cerebellum consists of the: | Cerebellum |
| Summary -- the diencephalon consists of the: | Thalamus, hypothalamus, pituitary, pineal gland |
| Summary -- the cerebrum consists of the: | Cerebral cortex, basal ganglia, and limbic system (amygdala and hippocampus) |
| The oldest and most primitive region of the brain | Brain stem |
| Cranial nerves | 11 of the 12 cranial nerves branch off the brain stem, similar to the spinal nerves along the spinal cord. Cranial nerves carry sensory and motor information for the head and neck |
| Examples of two cranial nerves | Olfactory nerve (sensory nerve receiving information from the nose) and vagus nerve (mixed nerve that’s sensory as well as efferents to many internal organs, muscles, and glands |
| Reticular formation | Characterized by diffuse, discrete groups of nerve cell bodies located throughout the brain stem. Involved in arousal, sleep, muscle tone, stretch reflexes, breathing, blood pressure, pain modulation |
| Describe the ventricle in the brain stem | A diamond-shaped ventricle, the fourth ventricle, which runs through the interior of the brain stem and connects to the central canal of the spinal cord. |
| Medulla oblongata | AKA “medulla” is the transition from the spinal cord to the brain. Its white matter includes ascending somatosensory tracts and descending corticospinal tracts |
| Somatosensory tracts | White matter that brings sensory information to the brain |
| Corticospinal tracts | White matter that conveys information from the cerebrum to the spinal cord |
| Pyramids | About 90% of corticospinal tracts cross the midline to the opposite side of the body in a region of the medulla known as the pyramids. |
| As a result of the crossover that occurs in the pyramids of the medulla… | …each side of the brain controls opposite sides of the body. |
| Gray matter of the medulla | Includes nuclei that control many involuntary functions, such as blood pressure, breathing, swallowing, and vomiting |
| The pons | A bulbous protrusion on the ventral side of the brain stem above the medulla and below the midbrain. Its primary function is as a relay station for information transfer between the cerebellum and cerebrum. Also coordinates breathing |
| Midbrain | AKA mesencephalon – it’s a relatively small area that lies between the lower brain stem and the diencephalon. Its primary function is control of eye movement, but it also relays signals for auditory and visual reflexes |
| Cerebellum | Processes sensory information and coordinates the execution of movement. Sensory input comes from somatic receptors in the periphery of the body and from receptors for equilibrium and balance located in the inner ear |
| Diencephalon | Lies between the brain stem and cerebrum. Composed of: the thalamus, hypothalamus, pituitary, and pineal glands |
| Thalamus | Many small nuclei that occupy the diencephalon. The thalamus receives sensory fibers from the optic tract, ears, and spinal cord and motor information from the cerebellum. It projects the info to the cerebrum where it’s processes |
| Why is the thalamus often described as a relay station? | Because almost all sensory information from lower parts of the CNS passes through it. |
| Can the thalamus act as an integrating center? | Like the spinal cord, it can modify information passing through it, making it an integrating center as well as a relay station |
| Hypothalamus | Lies beneath the thalamus. It is the center for homeostasis and contains centers for various behavioral drives e.g., hunger and thirst. Output from the hypothalamus drives many functions of the autonomic system and endocrine functions |
| From where does the hypothalamus receive input? | Multiple sources including the cerebrum, the reticular formation, and various sensory receptors. |
| Where does the hypothalamus output travel? | First to the thalamus and then eventually to multiple effector pathways. Note: don’t forget the hypothalamus interacts with the anterior pituitary through the hypothalamic-hypophyseal portal system |
| Posterior pituitary | It’s a downgrowth of the hypothalamus and secretes neurohormones that are synthesized in the hypothalamic nuclei. It is not a “true” endocrine gland like the anterior pituitary |
| Pineal gland | A gland that secretes the hormone melatonin |
| The neurons of the adrenal medulla are activated by what part of the brain? | Hypothalamus |
| The largest and most distinctive part of the human brain | Cerebrum |
| Corpus callosum | The two hemispheres of the cerebrum are connected primarily at the corpus callosum, a distinct structure formed by axons passing from one side of the brain to the other |
| Each cerebral hemisphere is divided into four lobes: | Frontal, parietal, temporal, and occipital |
| The lobes of the brains are named for… | …the bones of the skull under which they’re located |
| The folds of the cerebrum | Composed of grooves (sulci, or singular: sulcus) and dividing convolutions (gyri, or singular: gyrus) |
| The cause and significance of the sulci and gyri | Cause: the cerebrum grows faster than the surrounding cranium causing the tissue to fold back on itself to fit into a smaller volume. Significance: the degree of folding is directly related to the level of processing of which the brain is capable |
| Surface appearance of the brain: rodents vs. humans | Rodents have brains with relatively smooth surfaces, humans are very convoluted; so much that, if inflated to a smooth surface, it would appear three times larger |
| Three major regions of cerebral gray matter | The cerebral cortex, the basal ganglia, and the limbic system |
| Cerebral cortex | The outer layer of the cerebrum, only a few millimeters thick. Neurons of the cerebral cortex are arranged in anatomically distinct vertical columns and horizontal layers. It’s within these layers that higher brain functions arise |
| Basal ganglia | AKA basal nuclei, are involved in the control of movement. Note: the term “ganglia” is usually preferred to be used for structures outside the CNS, but basal “ganglia” is used a lot in clinical practice |
| Limbic system | Surrounds the brain stem and probably represents the most primitive region of the cerebrum. It acts as the link between higher cognitive functions, such as reasoning, and more primitive responses, such as fear |
| The major areas of the limbic system and their basic functions | Amygdala and singulate gyrus: linked to emotion and memory; and the hippocampus: associated with learning and memory |
| White matter in the cerebrum | Found mostly in the interior. Bundles of fibers allow different regions of the cortex to communicate with one another and transfer information from one hemisphere to the other, primarily through the corpus callosum |
| How many axons are passing through the average corpus callosum | Estimated to be 200 million |
| Where does information entering and leaving the cerebrum pass through? | The thalamus (with the exception of olfactory information, which goes directly from olfactory receptors to the cerebrum) |
| What makes the brain more complex than a simple reflex pathway? | It has the ability to generate information and output signals in the ABSENCE of external input |
| Review: outline a simple neural reflex pathway | Sensory input -> afferent pathway -> integration -> efferent pathway -> response |
| Outline a complex neural pathway (includes cognition) | The sensory system, cognitive system, and behavioral state system all initiate responses. Subsequently, information about the physiological or behavioral responses created by motor output feeds back to the above systems |
| Sensory system | Monitors the internal and external environments and initiates reflex responses. |
| Cognitive system | Resides in the cerebral cortex and is able to initiate voluntary responses. |
| Behavioral state system | Resides in the brain and governs sleep-wake cycles and other intrinsic behaviors |
| Examining the cerebral cortex from a functional viewpoint, it can be divided into three specializations: | (1) sensory areas, (2) motor areas, and (3) association areas |
| Sensory areas of the cerebral cortex | (Also called sensory fields), which receive sensory input and translate it into perception (awareness) |
| Motor areas of the cerebral cortex | Direct skeletal muscle movement |
| Association areas of the cerebral cortex | (AKA association cortices) which integrate information from sensory and motor areas and can direct voluntary behaviors |
| Are the three functional areas of the cerebral cortex localized to particular lobes in the brain? | No, for one thing, functional specialization is not symmetrical across the cerebral cortex, hence the term “cerebral lateralization” or “cerebral dominance” AKA commonly called left brain-right brain dominance |
| Cerebral lateralization | AKA cerebral dominance AKA left brain-right brain dominance: language and verbal skills tend to be concentrated on the left side of the brain, with spatial skills concentrated on the right side. |
| Right-handed vs. left-handed people | The left brain is the dominant hemisphere for right-handed people, the right brain is the dominant hemisphere for left-handed people |
| Example of plasticity in the brain: losing a finger | If someone loses a finger, the regions of the motor and sensory cortex previously devoted to controlling that finger are taken over by adjacent regions of the cortex |
| Five sensory areas of the cerebral cortex that process information received from ascending pathways | Primary somatic sensory cortex, visual cortex, auditory cortex, olfactory cortex, and gustatory cortex |
| Primary somatic sensory cortex | (AKA somatosensory cortex) located in the parietal lobe, it is the termination point of pathways from the skin, musculoskeletal system, and viscera. Information processed: touch, temperature, pain, itch, and body position |
| Damage to the somatosensory cortex results in… | …reduced sensitivity of the skin on the opposite side of the body because sensory fibers cross to the opposite side of the midline as they ascend through the spine or medulla |
| Visual cortex | Located in the occipital lobe, receives information from the eyes |
| Auditory cortex | Located in the temporal lobe, receives information from the ears |
| Olfactory cortex | A small region in the temporal lobe, receives input from chemoreceptors in the nose |
| Gustatory cortex | Deep in the brain near the edge of the frontal lobe, receives sensory information from the taste buds. |
| Where is all of the aggregated sensory information transformed into perception? | Neural pathways extend from sensory areas to appropriate association areas, which integrate somatic, visual, auditory, and other stimuli into perception, the brain’s interpretation of sensory stimuli |
| Often the perception of the stimulus in the brain is different from the actual stimulus. Examples? | Light waves of different frequencies are perceived as “colors”; pressure waves hitting the inner ear are perceives as “sound”; and chemicals binding to chemoreceptors are perceived as “taste” or “smell” |
| Motor output from the CNS can be divided into three major types (and brief definition): | (1) skeletal muscle movement, controlled by the somatic motor division; (2) neuroendocrine signals, via hypothalamus and adrenal medulla; (3) visceral responses, actions of smooth muscle, endocrine & exocrine glands |
| Where is simple, stimulus-response skeletal muscle movement processed in the CNS? | Simple stimulus-response pathways, e.g., knee-jerk reflex, are processed in the spinal cord/brain stem – note: they can be modified or overridden by input from the cognitive system |
| Where are voluntary movements initiated in the CNS? | By the cognitive system and originate in the primary motor cortex and motor association area in the frontal lobes of the cerebrum |
| Where do the primary motor cortex and motor association area receive their inputs? | From sensory areas as well as from the cerebellum and basal ganglia. Remember: since information is sent through the pyramidal cells they crossover; damage to one side of the brain causes paralysis on the opposite side of the body |
| Neuroendocrine and visceral responses are coordinated primarily in… | …the hypothalamus and medulla. |
| The autonomic life functions we need such as breathing and blood pressure is mainly controlled by… | …the brain stem |
| Body temperature regulation, eating, and control of body osmolarity, among others, is controlled by… | …the hypothalamus, via neural, hormonal, or behavioral responses |
| Where are neurons of the behavioral system found? | Parts of the reticular formation in the brain stem, the hypothalamus, and the limbic system |
| The diffuse modulatory systems | Originate in the reticular formation and project their axons to large areas of the brain. |
| The four diffuse modulatory systems, classified according to the neurotransmitter they secrete: | Noradrenergic (norepinephrine), serotonergic (serotonin), dopaminergic (dopamine), and cholinergic (acetylcholine). Note: the noradrenergic and serotonergic systems seem to be highly connected to depression |
| The diffuse modulatory systems regulate brain function by influencing: | Attention, motivation, wakefulness, memory, motor control, mood, and metabolic homeostasis |
| Consciousness | The body’s state of arousal or awareness of self and environment. The reticular activating system plays a large role in controlling consciousness. |
| Reticular activating system | A diffuse collection of neurons in the reticular formation |
| Physiologically, what distinguishes being awake from various stages of sleep? | The pattern of electrical activity created by cortical neurons. The measurement of brain activity is recorded by a procedure known as electroencephalography (EEG) |
| Electroencephalography (EEG) | Surface electrodes placed on or in the scalp detect depolarizations of the cortical neurons in the region just under the electrode |
| The electrical activity of cortical neurons while awake and while sleeping | Awake: many neurons are firing but not in a coordinated fashion. Presumably the desynchronization of electrical activity in waking states is produced by ascending signals from the reticular formation. Sleep: synchronized waves |
| Frequency and amplitude of the synchronized waves as a function of state of arousal | As a person’s state of arousal decreases, the frequency of the wave decreases and the amplitude increases |
| Sleep | An easily reversible state of inactivity characterized by lack of interaction with the external environment |
| Why do we need sleep? | Various theories: conserve energy, avoid predators, allow body to repair itself, enhance immune response, and to process memories |
| Is sleep a passive or active state? | Neuronal activity in ascending tracts from the brain stem to the cerebral cortex is required for sleep. Also, the sleeping brain consumes just as much oxygen as the “awake” brain, thus, it’s an active state |
| Stages of sleep | There are 4 stages marked by patterns on EEG readings. The two main stages: slow-wave sleep (AKA deep sleep or non-REM sleep, stage 4) and REM (rapid eye movement) sleep (stage 1) |
| Slow-wave sleep (deep sleep) | Apparent on EEG by delta waves: high-amplitude, low-frequency waves of long duration that sweep across the cerebral cortex. During this phase sleepers adjust body position without conscious commands from brain |
| REM sleep | EEG pattern is closer to that of an awake person, with low-amplitude, high-frequency waves. Brain activity inhibits motor neurons to skeletal muscles, paralyzing them, with the exceptions of eye muscles and breathing muscles |
| Why does body temperature decrease during sleep | Control of homeostatic functions is depressed and body temperature falls toward ambient temperature |
| Which period does most dreaming take place? | REM sleep; the eyes move as if following the actions of the dream. |
| The cycles in a typical eight-hour sleep | Hour 1 & 2: wakefulness -> deep sleep -> REM -> deep sleep. Then the remainder of the hours: alternating between stages 1 and 2, with a little bit of stage 3 during hour 4 |
| Historical test to determine what causes sleepiness | CSF from sleep-deprived dogs could be injected into alert dogs to induce sleep |
| Sleep-inducing factors that have been discovered. Curiously…? | Interleukin-1, interferon, serotonin, and tumor necrosis factor. Curiously these also enhance immune response, leading to the hypothesis that the purpose of sleep is to enhance the immune response |
| Why do we need sleep more when we are sick? | Secretion of immune enhancing proteins |
| Which stage of sleep does sleep walking occur? | Stage 4! |
| Circadian rhythms | Sleep-wake rhythms that follow a 24-hour light-dark cycle. |
| What happens if organisms are placed in the dark or light constantly? | The circadian rhythm persists, apparently cued by an internal clock |
| Suprachiasmatic nucleus | A nucleus of the hypothalamus; it is the “internal clock” of organisms. The clock’s cycling is based upon a complex feedback loop of alternating gene expression |
| Simplified overview of the workings of the suprachiasmatic nucleus | Specific genes turn on protein synthesis -> they accumulate -> they turn off genes -> they’re degraded -> genes back on -> repeat |
| Hormones linked to the circadian rhythm – super interesting! | Cortisol and melatonin. Note: melatonin (secreted by the pineal gland) actually appears to feedback to the suprachiasmatic nucleus, hence it’s perceived ability to “reset” circadian rhythms! |
| How does caffeine work? | Caffeine is an antagonist of adenosine receptors. Adenosine has the function of suppressing neurons that promote wakefulness. If inhibited, wakefulness ensues |
| The center of emotion in the human brain | The limbic system, in particular the amygdala |
| Overall pathway of emotion in the brain | Sensory stimuli feeds into the cerebral cortex where they’re perceived and integrated in the association areas; then to the limbic system which creates emotion; then to the hypothalamus/brain stem initiating responses |
| Awareness of emotion | Occurs due to feedback to the cortex from the limbic system which creates awareness of emotion |
| Motivation | Internal signals that shape voluntary behaviors, e.g., eating, drinking, sex, curiosity, etc. Some of these behaviors are linked to survival while others (e.g., curiosity) are linked to emotions |
| Drives | Motivational states that have three properties in common: (1) they create increase CNS arousal or alertness; (2) they create goal-oriented behavior; and (3) they’re capable of coordinating disparate behaviors to achieve that goal |
| How do motivated behaviors work in parallel with autonomic and endocrine responses in the body? | Example: eat salty popcorn -> body osmolarity increases/endocrine center releases hormone that increases water retention by the kidneys -> thirst center of hypothalamus initiates a drive to seek something to drink |
| Examples of motivated behaviors that can be activated by internal stimuli that may not even be obvious to the person in whom they’re occurring | Eating, curiosity, sex drive, etc. |
| Satiety | A reached level of satisfaction. Note: many motivated behaviors stop after reaching satiety, but may continue despite feeling satiated (e.g., eating so that you don’t hurt someone’s feelings) |
| Pleasure | A physiological state accompanied by increased activity of the neurotransmitter dopamine in certain parts of the brain |
| Why are drugs like cocaine and nicotine addictive? | They increase the effectiveness of dopamine in the brain, thereby increasing the pleasurable sensations perceived by the brain |
| Moods | Similar to motivation but are longer lasting, relatively stable subjective feelings related to one’s sense of well-being |
| Depression | A mood disorder characterized by sleep and appetite disturbances, alterations of mood and libido, etc. which may seriously alter a person’s ability to function professionally and interpersonally |
| Causes of major depression – roughly | A combination of genetic factors, the serotonergic and noradrenergic diffuse modulatory systems, trophic factors such as brain-derived neurotrophic factor (BDNF), and stress |
| Brain-derived neurotrophic factor (BDNF) | A secreted protein that helps support the survival and growth of neurons. It’s active in the hippocampus, cortex, and basal forebrain, areas vital to learning, memory, and higher thinking. Note: exercise increases BDNF secretion |
| Learning can be classified into two broad types: | Associative and nonassociative |
| Associative learning | Occurs when two stimuli are associated with each other, e.g., Pavlov’s famous experiment. |
| Review: Pavlov’s experiment | He simultaneously presented a dog with food while ringing a bell. After a given time, the dogs associated the bell with a meal and begun to salivate upon hearing the bell. |
| Nonassociative learning | Change in behavior that occurs after repeated exposure to a single stimulus. This includes habituation and sensitization, two adaptive behaviors that allow us to filter out background stimuli |
| Habituation | Decreased response to an irrelevant stimulus that is repeated over and over. E.g., a sudden loud noise may be startling at first, but then lose its significance over time |
| Sensitization | The opposite of habituation. Exposure to a noxious or intense stimulus causes an enhanced response upon subsequent exposure. E.g., becoming ill when eating a particular food may cause you to avoid that food in the future |
| Memory. What are the different types? | The ability to retain and recall information. There are four different types: short-term, long-term, reflexive, and declarative; they all take place through different pathways as observed via MRI and PET scans |
| Memory traces | Memories are stored throughout the cerebral cortex in pathways known as memory traces. Some components of memories are stored in the sensory cortices where they’re processed, e.g., pictures stored in the visual cortex |
| Parallel processing | Leaning a task or recalling an already learned task may involve multiple brain circuits that work in parallel (i.e., parallel processing). It helps provide backup in case one of the circuits is damaged. |
| What else does parallel processing help with? | It’s believed to be the means by which specific memories are generalized, allowing new information to be matched to stored information. E.g., if you’ve never seen a volleyball, you’ll still recognize it as a “ball” |
| The inability to remember newly acquired information (i.e., the inability to store it into long-term memory) is a defect known as | Anterograde amnesia |
| The removal of what structure in the brain leads to anterograde amnesia | Hippocampus |
| Short-term memory | When a stimulus comes into the CNS it first goes into short-term memory, a limited storage area that can hold only about 7 to 12 pieces of information at a time. They will disappear unless repetition is used to make them more permanent |
| Working memory | A special form of short-term memory processed in the prefrontal lobes. It allows us to collect facts from short-term memory and long-term memory and connect them in logical order to solve problems or plan actions |
| Prefrontal cortex | The region of the cerebral cortex responsible for keeping track of bits of information long enough to put them to use in a task that takes place after the information has been acquired. It can link short term with long term memories |
| Long-term memory | Storage area that holds vast amounts of information. |
| Consolidation | Processing of information that converts short-term into long-term memory. It can take varying amounts of time, from seconds to minutes. Information passes through many intermediate levels of memory during this time |
| Physiological changes during consolidation | Synaptic connections of circuits involved in learning change. In some cases, new synapses form, in other cases the effectiveness of existing synapses are altered through long term potentiation or depression |
| Two types of long-term memory that are consolidated and stored via different pathways | Reflexive (implicit) memory and declarative (explicit) memory |
| Reflexive memory (AKA procedural memory) | Autonomic – it doesn’t require conscious processes for either creation or recall. It involves the amygdala and cerebellum. It’s acquired slowly through repetition. E.g., motor skills, procedures, and rules |
| Declarative memory | Requires conscious attention for its recall. Creation of declarative memories depends on higher cognitive skills: inference, comparison, and evaluation. Neuronal pathways are in temporal lobe |
| Declarative memories deal with | Knowledge about ourselves and the world around us that can be reported or described verbally |
| Do declarative memories always remain as declarative memories? | No, they can be transferred to reflexive memory with repetition. E.g., an NFL quarterback’s ability to throw a football with precise accuracy can be executed without conscious thought (i.e., muscle memory) |
| Main causes of memory loss in younger people | Trauma |
| Alzheimer’s disease | Progressive neurodegenerative disease of cognitive impairment. Examined brain tissue contains extracellular plaques made of beta-amyloid protein and intracellular tangles of tau, a protein associated with microtubules |
| Cause of Alzheimer’s | Unknown; theories include: oxidative stress and chronic inflammation. |
| Treatment for Alzheimer’s | There’s no cure, but acetylcholine agonists or acetylcholinesterase inhibitors slow the progression (because they increase the effectiveness of the neurotransmitter) |
| The most complex and elaborate cognitive behavior | Language |
| Where are the centers for language ability found in most people? | Left hemisphere of the cerebrum, even in most left-handed people |
| The ability to communicate through speech has been divided into two processes: | The combination of different sounds to form words (vocalization) and the combination of words into grammatically correct and meaningful sentences |
| The integration of spoken language in the human brain involves two regions in the cerebral cortex: | Wernicke’s area in the temporal lobe and Broca’s area in the frontal lobe close to the motor cortex |
| Input into the language areas comes from: | Either the visual cortex (reading) or the auditory cortex (listening) |
| Sensory input pathway: | First goes to Wernicke’s area, then to Broca’s area. After integration and processing, output from Broca’s area to motor cortex initiates spoken word to writing |
| Damage to Wernicke’s area results in | The inability to understand any spoken or visual information. The person’s own speech is hence nonsense because they’re unaware of their own errors. This condition is known as **receptive aphasia** |
| Damage to Broca’s area results in | The ability to understand spoken and written information, but the inability to speak or write in normal syntax. The response to a question will be a string of appropriate words in improper order. This condition is known as **expressive aphasia** |
| Mechanical forms of aphasia occur as a result of… | …damage to the motor cortex. These patients are unable to physically shape the sounds that make up words, or they’re unable to coordinate the muscles in their arm required for writing |
| Schizophrenia | The cause has both genetic and environmental components, but not known. Treated by influencing neurotransmitter release. |
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