Chapter 8 Notes
Chapter 8 Notes BIOL 3160
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This 11 page Class Notes was uploaded by Olivia Addis on Friday February 19, 2016. The Class Notes belongs to BIOL 3160 at Clemson University taught by Dr. Tamara McNutt-Scott in Fall 2015. Since its upload, it has received 22 views. For similar materials see Human Physiology in Biological Sciences at Clemson University.
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Date Created: 02/19/16
Chapter 8: Central Nervous System The Central Nervous System is made up of the brain and spinal cord. o CNS serves many functions: o sensory neurons brings information to the CNS o motor neurons take a decision away from the CNS and innervate muscles and glands o interneurons within the CNS associate a specific motor response to a specific sensory stimuli in order to maintain homeostasis. o During development the ectoderm, which is one of three embryonic tissue layers, becomes the neural tube after a groove deepens. o The anterior portion, the forebrain, develops into the brain, and the rest of the neural tube will continue to become modified to become the rest of the CNS The neural tube will remain hollow, the cavities in the tube are then called ventricles. cavity in spinal cord called the central canal Filled with cerebrospinal fluid, which is formed by the choroid plexuses located in the ventricles. o CNS is comprised of gray and white matter o Brain The brain is 33.5 lbs., and receives about 15% of the total blood flow to the body per minute because of the large number of metabolic functions that the brain does, requiring more blood to perform. It is involved with learning and memory to benefit survival by allowing behavior to change based on past experiences. Forms basis of consciousness through perceptions, emotions, and selfawareness. Holds neural stem cells that can develop into neurons and glial cells. Development of neural stem cells into neurons is called neurogenesis, which occurs in two locations: the subventricular zone in the lateral ventricles, which includes a thin layer of ependymal cells that aids in neurogenesis then sends them somewhere else, and the subgranular zone of the hippocampus. Brain creations are not a singular event, but will involve multiple areas of the brain. Cerebrum Makes up about 80% of the mass of the brain and its primary tasks are higher brain functions. It consists of a right and left cerebral hemisphere, functionally connected by the corpus callosum. Comprised of 5 Lobes: o Frontal – voluntary motor control of muscles, higher intellectual processes o Parietal – somatesthetic interpretation, understanding speech and forming words to express thoughts and emotions, interpretation of textures and shapes o Temporal – Interpretation of auditory sensations, stores auditory and visual experiences o Occipital – Integration of movements in focusing the eye, correlation of images with previous experiences or stimuli, conscious perception of vision. o Insula – Memory; sensory (mostly pain) and visceral integration Cerebral cortex is the outer layer of the cerebrum, which is made up of generally 24 mm of gray matter and underlying white matter. o The cerebral cortex is characterized by having convolutions, gyri and sulci, which help to increase surface area without increasing the volume. o It is the most complex integrating center of the nervous system sensory information processed into meaningful, perceptual “image”. Lissencephaly: smooth brain (no convolutions) leads to difficulty swallowing and basic functions; severe mental retardation so those with lissencephaly generally don’t live past about 10. o Cortex is mapped to regions of the body, which is referred to as somatotopy. Size doesn’t determine the area of the cerebral cortex. Highest densities represent largest areas in sensory cortex (postcentral gyrus) Greater motor innervation represents larger areas in motor cortex (precentreal gyrus) Ex: hands and face have a high density of sensory receptors and motor innervation. Electroencephalogram o Synaptic potentials released into extracellular space and can summate to create electrical currents that can be measured by placing electrodes on the scalp, which is an EEG. o Deviations from normal EEG patterns are used to diagnose epilepsy and other abnormal mental states. These are viewed as abnormal discharges of a cerebral neuron. Electric storm within a short circuit, occurs at a small spot within brain – focus – causes waves of electrical activity to spread throughout the brain. o In class video of a seizure, it showed that the woman seizing stopped breathing, observed loss of vocalization, and a loss of motor control. Absence of EEG signifies brain death. o Normally four types of EEG Patterns: Alpha waves – in parietal and occipital regions while a person is awake and relaxed with the eyes closed. Beta waves – in frontal lobe; evoked activity, produced by visual and mental activity Theta waves – in temporal and occipital lobes; common in newborns and sleeping adults, increase in awake during tasks that require attention or severe emotional distress can be a warning for nervous breakdown Delta waves – cerebral cortex, normal, common during sleep and in infants. If present in an awake adult, they indicate brain damage. Sleep o The function of sleep is known; however, we know that it provides a homeostatic function, while also consolidating dreams and providing the glymphatic system. o Glymphatic system – glial + lymphatic makes a “mental janitor” because during sleep, the interstitial space in the brain increases in volume, and glial cells move throughout and cleans out some space flushing of tissues. o Electroencephalogram (EEG) patterns change with sleep. o REM sleep – rapid eye movement; when dreams occur EEG characterized by theta wave; number of eye movements, HR, and respiration rate will all increase. o NonREM (NREM) sleep – time of sleep outside of the REM phase, resting phase Aids neural plasticity required for learning, which is the brain’s ability to adapt to meet the needs of the organism. o Cycles descend through the 4 (14) stages of NREM, then ascend back through the 4 stages (41) to get to REM sleep, followed by (14) stages of NREM. This cycle lasts about 90 minutes and will typically occur 45 times in one night, and will usually wake up from REM sleep. o Limbic system activated to mediate fear and anxiety, which are often emotions involved in dreaming. Basal Nuclei o The basal nuclei are masses of gray matter deep within the white matter of the cerebrum. o They play an important role in movement and posture as well as complex aspects of behavior, which is the control of voluntary behavior. o The prominent basal nuclei is the corpus striatum, which components are: caudate and lentiform (putamen and globus pallidus) nuclei. o Substantia Nigra (SN) in the midbrain and the subthalamic nuclei in the diencephalon are functionally associated with basal nuclei. o Parkinson’s Disease is characterized by problems with movement because of the dopaminereleasing cells in SN. o Motor Circuit: o The motor cortex sends excitatory signals (glutamate) to basal nuclei (primarily putamen). o Putamen in basal nuclei sends inhibitory (GABA) signals to other basal nuclei areas. o Globus pallidus and substantia nigra send inhibitory signals to the thalamus. o Thalamus then sends excitatory signals to motor cortex. The excitation of some and inhibition of others allows for intended movements and inhibiting unintended movements. Cerebral/Hemispheric Lateralization o Cerebral hemispheres have anatomic, chemical, and functional specializations. o The info entering the brain will decussate (cross over) at the corpus callosum so that the right side of the brain controls the left side of the body. o Communication through the corpus callosum allows the hemispheres to work together for the “total” body function. Patients with epilepsy will have the corpus callosum cut in half to alleviate symptoms – split brain procedures. o Experimentation like splitbrain procedures has found that each hemisphere is better at some tasks than the other cerebral dominance. o Cerebral dominance is the handedness of an individual; therefore, if one is right handed, then they are left hemisphere dominant. o Hemispheres complement each other with their individual strengths, but one is not subordinate to the other. There is specialization of function in one hemisphere cerebral lateralization Left: language and analytical ability, ex – recognize face Right: visuospatial ability, ex – recognize face is unhappy It has been speculated that creative ability may be related to interaction of info between hemispheres. Language o A complex code including listening, seeing, reading, and speaking with each aspect of language dealt with by different regions, but typically located in the left hemisphere of the brain. o Knowledge of how language works is gained through the study of people with aphasias, which are speech and language disorders, caused by damage to the brain from injury or stroke. o There is potential that the development of language mechanisms can be in either hemisphere because assignment is flexible in early years, but plasticity decreases with age. o Broca’s Area: inferior frontal lobe, directs muscles involved with speech; preparation to speak Broca’s aphasia results in slow speech and poorly articulated. Understanding is there, it is just hard to respond. o Wernicke’s Area: superior temporal gyrus, understanding written and spoken language Wernicke’s aphasia observes language comprehension destroyed – “word salad” – what comes out of their mouth does not make sense. o Concept of words begins in Wernicke’s area Broca’s area motor cortex, which controls musculature of speech To understand words, visual cortex and auditory context send information to Wernicke’s area. PET Scans Increased blood flow to specific lobes of brain during various languagebased activities. o Ex: generating words Broca’s; hearing words Wernicke’s; speaking words motor cortex Limbic System and Emotion The hypothalamus and limbic system are important brain regions for neural element of emotional o Components of the Limbic system include: cingulate gyrus, amygdala, hippocampus, septal nuclei. Limbic system is the center for emotional drives, but was derived very early in the course of vertebrate evolution, for which it was mostly used for olfaction. o Little control over emotions because there are few synaptic connections between the cerebral cortex and the structures of the limbic system. o Drives the limbic system plays a role in include: aggression, fear, feeding and satiety (feeling full), goaloriented behavior (reward/punishment), and sexual behavior/drive. Papez Circuit: closed circuit that info flows from limbic system to the thalamus and the hypothalamus; any memory must pass through this circuit. o Hippocampal/mamillothalamic tract, which is also known as the fornix o Function – consolidation of memories. Papez circuit between limbic system and hypothalamus and thalamus shows how they cooperate together for the neural basis of emotional states. Learning and Memory Learning is the acquisition and storage of info as a consequence of experience. o Likelihood of particular behavior, when presented with a specific stimulus o Rewards/punishments are important in learning because by rewarding a behavior, the experience will enhance that behavior. Memory is relativelypermanent storage of information learned from previous experiences. o Not by one structure, but many different process work together. o Memories are stored and retrieved in different ways to suit the different needs. Memory Storage and retrieval of memories involves multiple different regions of the brain. o Knowledge of these areas comes from different amnesias (loss of memory) due to damage to different areas. This suggests that the many different systems that function in information storage are available in the brain. Memory can be either shortterm, or working memory and longterm memory. o Shortterm, working memory is retaining information for a short time, like seconds to minutes. New information is not automatically permanent, and can be susceptible to modification at the molecular level. Therefore, protein synthesis and new RNA is required to make a memory stable. Memory consolidation requires the activation of genes, the production of new proteins, and the formation of new synapses. The prefrontal lobe helps to store information differently depending on its type. o Longterm memory allows memories to be stored for days all the way up to years. It depends on the synthesis of mRNA and protein for memory consolidation, converting short term memories to longterm, which is a function of the hippocampus and amygdala (neural + limbic). Longterm memory can be classified as nondeclarative and declarative. Nondeclarative, or implicit memory, is memory of simple skills such as tying shoe laces. Declarative, or explicit memory, is the retention and recall of conscious experiences that can be put into words. o Can be either semantic (memory of facts) or episodic (memory of events). o People with amnesia have impaired declarative memory. Hippocampus is important in memory in its role in functions such as NREM sleep and how it is needed for consolidation and acquisition of new information. Emotions effect memory formation by either strengthening or hindering – the amygdala (component of limbic system) improves memory with emotional aspect (especially fear). o Stress will hinder memory formation because it will reduce the ability of the hippocampus to form memories because the hippocampus and amygdala have receptors for stress hormones and can be preoccupied with stress to be used to help form memories. Synaptic Changes in Memory Shortterm memory will involve the establishment of recurrent/reverberating circuits, which means that the neurons will be in a circular path, synapsing with each other. Consolidation of memories requires permanent changes to the chemical structure of neurons and their synapses, by means of protein synthesis. o Longterm potentiation (LTP) is a type of synaptic learning because with higher frequency of signals, there will be an increased excitability of the neuron using glutamate to enhance this. These are lasting changes that ultimately will increase sensitivity of a neuron to a particular stimulus. LTP induces dendritic spines to enlarge and change shape. Summary of the process of LTP on the neurons (Image from Slide 16 is helpful): High frequency of action potentials in presynaptic cell release glutamate into the synaptic cleft Glutamate will bind to both the AMPA receptor and the NMDA receptor, which has Mg blocking its pore + + When glutamate binds to AMPA, its Na channel is opened so that Na , which causes a depolarization of the PM The depolarization moves Mg out of the pore so that the pore in the NMDA receptor is now open 2+ Ca moves into the cell and activates second messenger systems The longlasting effects are an increase in glutamate release by the presynaptic neuron and glutamate receptors in the postsynaptic neuron and thus sensitivity of the postsynaptic neuron to stimuli. Extra Facts about LTP: Low frequency action potentials will lead to Longterm depression (LTD), which is the opposite effect of LTP. Because the depolarization of the AMPA receptor is required for the NMDA receptor to be active by moving Mg , this process is referred to as depolarizationinduced suppression of inhibition, which is because the process is suppressing inhibition and enhancing the postsynaptic neurons ability to bind glutamate. o A big part of this process is the release of endocannabinoids, which are a type of lipid NT used as retrograde messengers. In this case the post synaptic neuron releases nitric oxide (NO), which will promote LTP by increasing the amount of glutamate released. Lower calcium levels are going to lead to activation of phosphatases that dephosphorylate AMPA receptors and it then cannot depolarize the cell; the NMDA receptors will remain blocked and LTP will not occur. Neural Stem Cells Neural stem cells are found in the subgranular zone of the hippocampus. o This suggests that neurogenesis (development of neural stem cells into neurons) may be involved in learning in memory. Diencephalon The diencephalon is made up of the thalamus, hypothalamus, and epithalamus around the third ventricle and surrounded by the cerebral hemispheres. o thalamus relay center for the sensory information (except for olfaction) that comes through the cerebrum promotes a state of alertness and causes arousal from sleep in response to any sufficiently strong sensory stimulus important role in understanding where things come from (pathway) somatopy (mapping of pathways to cerebral cortex) o epithalamus – pineal gland , which secretes melatonin and regulates circadian rhythms o hypothalamus – collection of nuclei involved in homeostatic processes, and is involved in the Autonomic Nervous System Processes – emotion, biological clock, thirst, hunger, HR Works with medulla to evoke visceral response to various emotional states Works with limbic system to regulate emotion. Brainstem Includes the midbrain, pons, and medulla, and involved in programming automatic behaviors for survival and provide a pathway between centers higher and lower than the brainstem. o midbrain cerebral peduncles – housing the ascending (sensory) and descending (motor) tracts corpora quadrigemina (tectal plate) – visual and auditory reflexes red nucleus – motor coordination; works by maintaining connections with the cerebrum and cerebellum substantia nigra – movement, mood, reward, addiction; can release dompamine When the dopaminergic cells degenerate, it leads to Parkinson’s disease. o pons – modifies what the medulla sets passage way for the sensory and motor tracts several nuclei of the cranial nerves (CNs) and many originate in the pons house the autonomic respiratory centers that work with the medulla to regulate breathing centers in the pons include pneumotaxic and apneustic o medulla – sets the pace all ascending and descending tracts between spinal cord and brain pass through this region This is the main site of decussation, which is where the tracts cross over because the left side of the brain controls the right side of the body and vice versa. the nuclei located in the medullar are important for motor control houses vital centers – vasomotor center (for the ANS), cardiac control center, and the respiratory center (rhythmicity center sets the rate and depth of breathing) Cerebellum – hindbrain The second largest brain structure behind the cerebellum. Proprioceptors (sensory receptors found in muscle and joints) sends sensory information to the cerebellum, and then the cerebellum will work with the basal nuclei and motor cortex to coordinate movement. Needed for motor learning and coordinating movement of different joints in movement. Required for proper timing and force required for limb movements o It will use purkinje cells to inhibit motor areas that aren’t need to contract what is needed and inhibit contraction of unnecessary movements. Current research suggests that the cerebellum may have other functions besides motor. Ataxia refers to disorders of the cerebellum resulting in disorders of gait, balance, eye movements, and swallowing. – lack of muscle coordination during movements. o Shizophrenia – individual interprets reality abnormally – cognitive dysmetria – general discoordination of sensorimotor and mental processes. o Autism – developmental problems that affect a child’s ability to communicate and interact with others; individuals tend to have smaller/abnormal areas in vermis, which is the most central part of the cerebellum. Reticular Formation and RAS: located in the brain stem The reticular formation is an interconnected group of neurons that constitutes an arousal system. o Reticular Activating System (RAS) promotes wakefulness when activated and sleep when inhibited. On = awake; Off = sleep accomplished by excitatory and inhibitory neurotransmitters, that work together to flip the switch on or off. o Many drugs act on the RAS, promoting sleep or wakefulness. o Narcolepsy – Lateral hypothalamic area (LHA) neurons are lost, which function in releasing polypeptide neurotransmitters that promote arousal. Hypothesis for Sleep Wake Cycles: o Brainstem nuclei that are part of the RAS During waking, aminergic neurons (release norepinephrine and serotonin) dominate and during REM sleep, cholinergic neurons (release acetylcholine) are dominant. o Hypothalamus with circadian and homeostatic centers – hypothalamic neurons project to RAS and influence sleepwake cycles in regards to biological clock aligned with circadian rhythm. inc. GABA (inhibitory molecule) dec. histamine dec. activation of thalamus NREM sleep dec. GABA inc. histamine inc. activation of thalamus waking Antihistamines will put you to sleep. Spinal Cord Tracts Spinal Cord: gray matter inside and white matter outside, unlike the brain. Ascending tracts are sensory and descending tracts are motor. o Ascending – info from cutaneous, proprioceptors, and visceral receptors. Decussate either in the medulla or spinal cord. o Descending arises from primary motor cortex. Not all nerve fibers decussate in the medulla; some decussate in the spinal cord, and some do not decussate at all. o The initiation of a skeletal muscle event does not involve just activation of the motor area of the cerebral cortex. Ex: thalamus, cerebellum, basal nuclei, etc. play important roles. Cranial and Spinal Nerves The peripheral nervous system (PNS) consists of nerves (collection of axons) and their associated ganglia (collections of cell bodies) outside of the CNS. A reflex arc is a neural pathway involving a sensory neuron and a motor neuron. One or more association neurons also may be involved in some reflexes. o Sensory receptor Sensory neuron Interneuron (CNS) Motor Neuron Reflex Contraction of a Muscle
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