LS2 Week 6 Notes
LS2 Week 6 Notes Life Sciences 2
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This page Class Notes was uploaded by Jenna Kovsky on Friday November 6, 2015. The Class Notes belongs to Life Sciences 2 at University of California - Los Angeles taught by Dr. Cooper/Dr. Esdin in Fall 2015. Since its upload, it has received 33 views. For similar materials see Cells, Tissues, and Organs in Biology at University of California - Los Angeles.
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Date Created: 11/06/15
11215 O O O O O O 0000 0 Lecture 16 Central Nervous Svstem Classification of neurons based on what they do afferent send info the the CNS receive information interneurons processing neurons eg making sense of what prof is saying efferent send information out from the CNS eg moving your hand Classification based on structure multipolar lots of dendrites one axon most common type of neuron mostly motor neurons and interneurons in brain bipolar only two extensions from the cell body ears nose and eyes sensory neurons receive hearing olfactory and visual info unipolar one branch short single process branch later divides into two sensory neurons eg touch refers to extensions of the cell body Synapse the junction formed between two neurons together neurons form a network always made of lots of neurons allows communication to continue between neurons presynaptic neuron sends signal postsynaptic neuron receives signal axosomatic axon synapses on cell body axodendritic axon synapses on dendrites Electricity movement of electrons along a wire electrophysiology electricity within our bodies 0 O O 0 never free alone electrons would wreak havoc in the cell plasma membranewire ionelectrons charged atom lost or gained electrons electricity in us caused by movement of ions across the membrane through ion channels diffusion the movement of ions from an area of high concentration to an area of low concentration without the expenditure of energy 0 O ac on O 0000 O passive processes of membrane transport need driving force always there need permeability not always there because channels allowing movement to occur are not always open potential ability to move the electrical activity of voltage is a way to quantify the ions a change in voltage over a change in time 225 mph takes 002 sec to think about wiggling your toe and actually do it threshold 50 to 55 mV critical point at which slow change in voltage becomes a rapid change resting membrane potential about 70 mV peak potential about 30 mV O O slight fluctuation in electrical activities graded potential in cell body and dendrites large change in electrical activities action potential in axon hillock and axon o Membrane potential 0 O Extracellular Fluid ECF Na provides positive charge Cl provides negative Intracellular Fluid ICF K provides positive charge Anions large proteins provide negative charges across the cell are the same no difference between inside and outno charge this is how most cells in our body non excitable cells are membrane has a potential when the charge is different inside eg 5 than outside eg 5 I positive charges will be attracted to membrane because the negative charges are on the other side only care about net charges on each side of the membrane membrane function wrespect to electricity charge separator that leads to potential for positives to run to the negatives inside the cell is predominantly negative compared to the outside sodium and potassium are slightly permeable through the membrane at rest driving force is huge I Na ECF 150mM ICF 15mM sodium always wants to move into the cell I K ECF 5mM ICF 140mM equilibrium equal concentration on both sides should NEVER happen in neurons because we would lose the driving force we just want mechanisms for diffusion to occur 0 What happens at Rest O passive Sodium Leak Channels always open I sodium enters the cell I narrower than K leak channel passive Potassium Leak Channels always open I potassium leaves the cell I wider than Na leak channel these channels have very limited permeability to prevent equilibrium at rest there is more K permeability than Na permeability NalK Pump requires ATP maintains the ion gradients to prevent equilibrium I every 1 ATP 3 Na ions leave cell 2 K ions enter cell I maintains the concentration gradient 0 Giant Squid Axon O O everything we know about action potentials came from squid Hodgkin and Huxley in the 60s studied the squid s neurons because they re very large 0 depolarization cell becoming more positive from K coming in o hyperpolarization cell becomes less positive when K leaves 0 dynamic state temporary o repolarization coming back to rest from either depolarization or hyperpolarization 11415 Lecture 17 Action Potentials and Central Nervous System ACTION POTENTIAL 0 there is always movement of ions across the membrane this movementjust doesn t have an effect at rest action potential facilitates communication Divergence axon terminals branch out to stimulate more than one neuron Convergence a lot of neurons are synapsing on one neuron Action Potential 0 membrane depolarizes repolarizes then hyperpolarizes o 2 major voltage gated channels voltage change triggers them to openclose I voltagegated sodium channel VGSC o integral protein embedded in membrane 0 most proteins in our body have two state activeinactive onoff 0 but sodium channels have 3 states open closed and inac va on 0 closed but capable of opening at resting potential 70 mV 0 open activated from threshold 55mV to peak potential 30mV huge permeability since gradient is so great o lnactivated closed and not capable of opening from peak 30mV to resting potential 70mV activation gate open but channel blocked by inactivation gate 0 order always goes closedgtopengtinactivatedgtclosed etc I voltagegated potassium channel VGPC o typical protein onoff 0 closed at resting potential delayed opening triggered at threshold remains closed to peak potential 70mV to 30mV 0 open from peak potential through after hyperpolarization 30mV to 80mV 0 slow to open and slow to close 0 Steps of the Action Potential At axon hillock 0 At rest both VGSC and VGKC are closed 0 threshold is reachedgtVGSC triggered to open I at this point slow depolarization become fast depolarization because the sodium channels open and sodium floods in I Threshold voltage needed to open the VGSC 0 sodium ions flow through VGSC causing membrane depolarization voltage becomes positive I VGKC is still closed 0 membrane reaches 30mVgtVGSC inactivate blocking flow of sodium ions I VGKC finally opengtpotassium ions flow out o membrane hyperpolarizesbecause VGKC don t close til 80mV I refractory period when the VGSC are in the inactivated state 0 both voltage gated channels are closed 0 membrane comes back to resting potential influx coming in efflux leaving Rising Phase caused by Na influx Falling Phase caused by K efflux TTX Tetrodotoxin from puffer fish blocks VGSC preventing the nervous system from communicating o NovocaineLidocaine similar to TTX small concentration to keep local to inhibit pain receptors 0 Propagation of Action Potential 0 myelin a lipid sheath speeds up the spreading of the action potential come from glial cells nervous system helper cells I oligodendrocytes produce myelin in CNS I schwann cells produce myelin in PNS o Saltatory Conduction action potential jumps from node to node I VGSC are not scattered all over axon instead they are clustered at the Nodes of Ranvier because it s too thick where the myelin is I at one node action potential is being generated a lot of positive is coming into the axon I positive charges repel each other and push some to the next node which will cause that node to start depolarizing I adjacent node brought to threshold by local current flow 0 Action Potential is unidirectional it only flows from the cell body towards the axon terminals 0 when positive charges repel each other some flow back up the axon but the previous node does not depolarize because the VGSC are inactive prevents back propagation o At the Axon Terminals o where neurotransmitters are found 0 as action potential reaches axon terminals 0 Voltagegated Calcium channel calcium is positively charged but does not depolarize instead acts as a messenger o VGCC open due to action potential Ca flows in and bind to vesicles that contain neurotransmitters and bring them to the membrane to fuse with it and excrete the neurotransmitters NT exocytosis NT flow into synaptic cleft and bind to receptors on postsynaptic neuron receptors are ligandgated channels that open when bound to NT NT is not there permanently get reabsorbed or turned into waste the NT binding to receptors on postsynaptic membrane causes a graded potential OOOO o EPSP small depolarization graded potential excitatory postsynaptic potential with positive ion 0 IPSP if negative ion Cl inhibitory postsynaptic potential leads away from threshold hyperpolarizes o membrane is always summing the lPSPs and EPSPs CENTRAL NERVOUS SYSTEM 0 Neural Pathway 0 skin receptors sense pain feed info to sensory neurons unipolar neurons partially in CNS partially in PNS information sent to spinal cord relays info to interneuron multipolar entirely in CNS interneuron synapses on motor neuron multipolar partially in CNS partially in PNS 0 motor neuron synapses on effector muscle 0 Organization of Nervous System 0000 0 Central I Brain I Spinal Cord 0 Peripheral I Afferent Division sensing info from all over the body getting to CNS 0 sensory stimuli from sensory receptors o visceral stimuli from organs I Efferent Division sending info from CNS to the body 0 Somatic Voluntary goes to skeletal muscles 0 Autonomic Involuntary goes to organs particularly cardiac and smooth muscles 0 Sympathetic Fight or Flight I increase in activity in vital organs decrease in nonvital eg digestive I shifts blood flow 0 Parasympathetic Rest and Digest I body housekeeping 0 never under influence of both at the same time 11615 Lecture 18 The Bra o The Brain is an organ has multiple tissue types in it o Neurons excitable cells 0 Glial cells for support I oligodendrocytes I Schwann cells I astrocytes star shape most abundant link neurons to other cells ensure neurons get proper nutrients I microglial cells cleaning crew remove unwanted materials or debris found near neurons I ependymal produce a fluid cerebrospinal fluid or CSF that bathes the brain surrounding it 0 101 glial cells to neurons in the brain Average size of a human brain 13501400g but size doesn t determine intelligence the synapsescommunication does 0 function and connections of the brain determine learning experiences not the size Cerebrospinal Fluid CSF weighs about 50 grams so brain is floating in our skull 0 acts as shock absorber if we hit our heads 0 produced by groups of cells and blood vessels collectively known as choroid plexus o transports nutrients Ventricles cavities inside the brain that are filled with CSF o 2 with C shape lateral ventricles where CSF is produced I lined with ependymal cells third ventricle and fourth ventricle produce CSF and circulate CSF Inter ventricular foramen connects lateral ventricle to third ventricle after fourth ventricle CSF goes through central canal and then to surround the brain Phrenology 0 early 1800s 0 scientists believed that the brain was made of 27 organs and each had a unique function that influenced our personalities o Franz Joseph Gall psychologist who developed this theory 0 believed you could feel bumps on the skull that indicated Korbinian Brodmann neuroscientist that accurately mapped out the brain in the 1800s 0 based on patients and case studies based on people with brain damage 0 52 areas of the brain now 356 The brain has a right hemisphere and a left hemisphere the brain is contralateral left side of the brain controls the right side of the body and right side of the brain controls the left side of the body Lobes of the Brain each has multiple functions 0 Frontal somatic movement skeletal muscle movement I primary motor cortex responsible for initiating skeletal muscle movement executing movement 0 homunculus means little man for mapping the motor cortex by what part of it enables you to move what part of your body and the size of each represented body part indicates the uses of the O O 0 body parthow many neurons are dedicated to the movement of that body part I premotor cortex where movement is planned I prefrontal association cortex complex tasks and cognitive function higherorder cortex complex thought I Broca s Area for speech initiationdevelopment of words Parietal sense of touch sensation I somatosensory cortex conscious awareness of general somatic senses precisely localizes the received stimulus spatial discrimination pain 0 sensation is also mapped by a homunculus hand for example has large area dedicated to it I Wernicke s area overlaps in temporal lobe for speech comprehension Temporal hearing I primary auditory cortex hearing I visual association area for facial recognition I also olfaction sense of smell Occipital vision I visual cortex 0 Major structures of the brain 0 Thalamus relay center area that all sensations except smell go through the thalamus and from there to the temporal parietal or occipital lobe also plays a role in motor control Hypothalamus below thalamus regulatory center homeostasis such as temperature control thirst urine output food intake satiation sensor tells you when you re full also has an endocrine role and regulates sleepwake cycle also involved in formation of memory works as a receptor and as a control center Cerebellum small brain motor control coordination and planning of skilled voluntary muscle movement and maintenance of balance ipsilateral right side controls right side of body and left side controls left side of body Brain Stem gateway to the brain control centers for digestive respiratory and cardiovascular vital centers equilibrium and posture integration of inputs from spinal cord 0 Brain Damage 0 0 What can happen I Trauma most common injury to the head I Stroke cerebrovascular accident blood vessels that supply brain rupture or get blocked I Seizure poorly understood brain starts to fire uncontrollably Where I Language Areas speech is the only area that is only located on one hemisphere the left every other function is bilateral Wernicke s aphasia damage to Wernicke s area causes inability to make sense of what they are saying words come out normally but do not make sense Broca s aphasia damage to Broca s area causes inability to speak but can still understand I Right parietal lobe contralateral neglect syndrome trauma to right parietal lobe causes loss of interest in the left side eg only shave right side of the face only eat food on the right side of the plate etc I Split Brain patient when the corpus callosum is severed corpus callosum fibers connecting the two hemispheres procedure done in patients with VERY severe seizures right and left hemispheres cannot communicate eg if you give them an object that they can touch but cannot see 0 if they use left hand they cannot say what the object is o if they use right hand they can verbalize bc right hand controlled by left hemisphere where speech is located
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