Class Note for ECOL 182R at UA 2
Class Note for ECOL 182R at UA 2
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Date Created: 02/06/15
ECOL 182 Spring 2008 Lecture 6 Nervous system and brain Dr Regis Ferriere Department of Ecology amp Evolutionary Biology University of Arizona What are the key questions and key terms What cells are unique to nervous systems xneurons glia How do neurons generate and conduct signals membrane potential action potential How do neurons communicate With one another synapses neurotransmitter summing potentials How is the nervous system organized CentralPeripheral AfferentEfferent How are complex functions controlled by the brain xlocalization lateralization limbic system What types of cells do we find in nervous systems Neurons are the functional units of nervous systems Neurons are excitable generate and propagate electric signals called action potentials Signals code for information received by or delivered to external or internal environment Different functional types of neurons Sensory neurons transduce information from environment Afferent neurons carry information into nervous system lnterneurons integrate and process information Efferent neurons carry commands to organs What types of cells do we find in nervous systems B Specialized neurons A Generalized neuronal anatomy Cell body Cerebellum W Dendrites r39 Cell body Axon Retina Cerebral cortex 0 Anatomy of neurons LIFESeFigured43Part2 WWWWMWM l r xVery diverse But several common features VCell body contains nucleus and most organelles dendrites receive electric signals axon conducts action potentials away to other cells Axon What types of cells do we find in nervous systems A Myelinproducing Schwann cells Site and direction of myelin growth Nodes of Flanvier Nucleus of Schwann cell 8 Mitochondria Axon Glial cells glia are much more numerous than neurons Do not transmit electric signals Physically support and orient neurons supply neurons with nutrients insulate axons updated How do neurons generate and conduct signals A Na K pump ATPase B Na K channels OUtSide 0f 39quot Outside of cell 9 O Voltagegated Sodium Na 0 o 0 K channel 0 Na channel 0 potassium pump 0 0 0 O o o l 39 39 J 0 0 o 55 P o 0 Closed K 0 Na 0 o 0 Inside of cell 0 O o 0 Open 0 Inside of cell Electric current across membranes is carried by m Major ions involved Na K Ca2 Cl39 Ion pumps amp ion channels generate membrane potentials K pump moves Wm creates a K gradient across the membrane Gradient makes 5 move from inside to outside through K channels leaving negative charges behind hence resting potential Voltagegated channels VGC open and close in response to electric signals updated How are action potentials generated 2 5 tr a Outside omen V ijjl o o u 39 39 Voltagegated Na voltaqeqated channels open in response to electric signal received quotj39 ztsgazztjn quotW F if by membrane WWquot I Aclivation gale I Inactivation gale I xm moves in causing 39 depolarization membrane potential becomes less negative Positive feedback even more 4 Na VGC open action potential Egg 39 ane potential mV E Undershoot is fired Na VGC close and K VGC 390 I i39 39ng390uc39o open membrane IS now hyperpolarized undershooting resting potential 9 Figure 4111Parl 3 MTVrlrst ercf Mmcvhymn4m v u pdated How do action potentials travel Voltedgated channels have refractory period foroes direction of signal propagation Action potentials travel along axons to axon terminals without loss of signal Electrical sllrrlulus Point A Osmlloscope screen jLPoint A updated How do neurons communicate Communication occurs at synapses Chemical synapses are most common type Arrival of action potential causes release of neurotransmitter Contained in vesicles that fuse under action of Ca2 with presynaptic membrane hence release diffusion potential through synaptic cleft Acetylcholine in motor neurons Neurotransmitter can bind to quot receptors on postsvnaptic Presynaptic cell Motor neu ro n Muscle libe Elm A Acetylcholine molecules in vesicle Synaptic cleftlxitv a 1 n 39 quot 6quot 22331 N membrane a I I Postsynap cce ThlS causes chemicallygated channels to 9m hence depolarization and firing action potential updated How do neurons communicate Signals received by a neuron are integrated by summation If sum above threshold the neuron fires an action potential What is summed up Electric signals from other neurons senders as interpreted by synapses with receiver cell Excitatory imam Excitatory synapses respond to neurotransmitter by depolarization Inhibitory synapses respond to neurotransmitter by hyperpolarization Action B potential I o How is the sum taken ON h Axon hillock Ewo39 Axon hillock sensitive to spatially amps preshqu inputs from different synapses and 393 temporally repeated inputs on same synapse distributed signals If sum exceeds threshold axon hillock fires action potential 60 llllll 1123412123 Synapse number Resting potential Milliseconds 89 Figure 4415 39 How is the neural network organized The power of the nervous system as an information processor results from the organization of neurons into networks Morpholodical ordanization xCentral nervous system CNS brain and spinal cord Spinal cord communicates information between brain and rest of body can issue commands to body without input from brain xPeripheral nervous system PNS cranial and spinal nerves How is the neural network organized Functional orqanization Two main components Neural Neural ariarents efferents depending on direction of mfg information flow and whether we re aware of CONSC OUS VOLUNTARY the information gt gt UNCONSCIOUS AUTONOMIC from to a peripheral Glands smooth Efferent component 13212 iiili mquot from CNS to peripheral parts of body LIFE Be Figure 461 m mncrmwsmoanmmmm r m How does the human brain develop Brain forms from 3 swellings at anterior end of neural tube xhindbrain midbrain forebrain Forebrain develops into cerebral hemispheres telencephalon underlying thalamus and hypothalamus diencephalon Midbrain and hindbrain develops into brain stem Vcerebellum LATERAL VIEWS DORSAL VIEWS 25 days Forebrain 7 Neural tube Midbrain Hindbrain D g 1 a O O 0 gr u 100 days Adult brain Cerebral hemisphere Thalamus Hypothalamus Cerebrum Pnuitary How is our behavior controlled A Central sulcus E Central Primary somalor Primary motor cortex sulcus sensory cortex ariea lobe Frontal lohe Occipital 39 lobe Passively viewing wards Listening to words Primary visual Olfactory area bulb Temporal lobe Cerebellum Face Spinal cord recognition Speaking words Generating words LIFE Be gure 465 Pan 1 Different functions can be linked to different regions of the brain functional deoqraphv of the brain Cerebral hemispheres divided into temporal lobes process auditory information frontal lobes many motor functions parietal lobes many sensory receptors occipital lobes process visual information Cerebral cortex layers of neurons covering cerebral hemispheres 7 LIFEBeFi uI485Pan2 mummwmmwmr How are our emotions controlled Cerebral hemispheres Hypothaamus Pituitary Amygdala Spinal cord Emotions as well as instincts and Iohvsioloqical drives controlled by limbic system at the core of the forebrain VAmygdala controls fear responses Hippocampus necessary for memory Limbic system is evolutionarily very ancient What happens when we sleep Sleep and dreaming are reflected in electrical patterns in cerebral cortex Electrical patterns detected by electrodes on scalp and recorded as chanqes in voltaqe between electrodes through time Awake Awake 39 NonREM HEM Stage t Stage 1 Stage2 W 33992 1 Stage 3 WWW Stage 3 Stage 4 31899 4 WWW REM WWW 5 76 7 Time hours Time seconds What happens when we sleep In humans five patterns correspond to five stages of sleep that we go through in repeated sequences 1 stage of rapideye movement REM sleep preceded by J4 nonREM stages including 2 that are deep restorative Each sequence of 5 stages lasts 1h302h Dreams during REM stage Inhibitory commands from brain almost completely paralyze skeletal muscles No acting out of dreams We still know very little about the function of sleep How do we learn memorize things Learning modification of behavior by experience Memory ability to retain what is learned xSome learning and memory processes have been localized to specific brain areas Different types of memory shortterm longterm xShortterm memories 1015 min are transferred to long term memory xReinforcement a factor hippocampus involved Learning leading to longterm memory must involve long lastinq svnaotic chanqes xLongterm potentiation highfrequency stimulation that makes svnabses more sensitive to future stimulations xLongterm depression continuous small stimulation reduces responsiveness How did nervous system and brain evolve A S eeeeeee ne B Earthworm Cerebral hemisphere l l Olfactory lobe am stern Nervous system vary in size and complexity In animal species with increasingly complex sensory and behavioral abilities information is increasingly centralized Brains vary in size and complexity In vertebrate species of similar size brains can show immense differences Suggested readings Kempermann G and F H Gage 1999 New nerve cells for the adult brain Scientific American May Up until recently it was thought that the adult human brain could not produce new nerve cells and that there was a steady loss of nerve cells from childhood into old age Now we know that new neurons do arise in the adult brain and this knowledge could lead to treatments for CNS injury and neurodegenerative diseases Tsien J 2000 Building a brainier mouse Scientific American April By genetically engineering a neurotransmitter receptor that is involved in producing long lasting synaptic changes scientists have produced a mouse with enhanced learning and memory Siegel J 2003 Why we sleep Scientific American November A discussion of the evolutionary basis and theories of the physiological function of sleep Treffert D A and Christensen D D 2005 Inside the mind of a savant Scientific American December The memory capacity of savants is almost unbelievable Do they give us insight as to the cognitive functions and capacities of the human brain Logothetis N K 1999 Vision A window on consciousness Scientific American November The incredible advances in our knowledge of the cellular and molecular mechanisms of brain functions have contributed little insight into the question of consciousness Studies of visual perception are enabling scientists to generate new ideas about how our brains produce conscious experience
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