Cognitive Neuroscience Week 2 Notes
Cognitive Neuroscience Week 2 Notes PSYC 3122
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This 19 page Class Notes was uploaded by Freddi Marsillo on Thursday September 8, 2016. The Class Notes belongs to PSYC 3122 at George Washington University taught by Dr. Shomstein in Fall 2016. Since its upload, it has received 9 views. For similar materials see Cognitive Neuroscience in Psychology at George Washington University.
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Date Created: 09/08/16
Cognitive Neuroscience Week 2 9/8/16 3:31 PM Cellular and Molecular Basis • Understanding the whole by understanding the parts • Santiago Ramon y Cajal Cajal’s Neuron Doctrine • Individual cells (neurons) with small gaps • Connectional specificity o Connections not random but specific pathways/circuits • Dynamic polarization o Parts of neurons take in information o Parts send information Building Blocks Neurons • Like other cells but some specific properties Glia • Non-neural cells playing supportive function Neurons 100-1,000 billion neurons in the brain • Each makes ~1000 connections (on average) What do neurons do with all that information? • Collect input • Process/decide in some way • Produce output • Transmit information over a distance (big toe to spinal cord) Postsynaptic versus presynaptic neurons • Presynaptic – neuron that sends info to another neuron • Postsynaptic – the neuron that receives the information o Once that neuron has the information, it then becomes the presynaptic neuron Neuron: Soma Soma • Cell body • Metabolic machinery o Nucleus, ribosomes, mitochondria, Golgi apparatus o Enclosed in membrane, suspended in cytoplasmic fluid Neuron: Dendrites Dendrites (afferent) • Receive input from neurons at synapses (postsynaptic) • Treelike – may be large arbors (Purkinje) or small (thalamus) • Spiny endings Neuron: Axons Axons (efferent) • Before synapse (presynaptic) • Communicates output of neuron • Originates at axon hillock • Insulated with myelin sheaths • Ends at presynaptic terminal button • Release neurotransmitters Variants of Neurons: Morphology Invertebrate • Unipolar – one process • Bipolar – most common o Sensory systems • Multipolar o Common ▯ One axon and many dendrites ▯ Spinal motor neurons, stellate pyramidal Glia = “nerve glue” • There are ten times more glia in the brain than neurons • Brain volume • Support systems for neurons o Guide growth o Remove metabolic waste o Grow and maintain myelin sheaths Central Nervous System (CNS) – different types of Glia • Astrocytes • Microglia • Oligodendrocytes Astrocytes • Surround neuron • Contact with vasculature at end-feet • Form blood-brain barrier – they protect neurons from any type of bleeding that can occur from the blood vessels – brain is protected from blood o Dopamine cannot cross but L-dopa, precursor, can o Blood-brain barrier is very selective in what it lets pass into brain Microglia • Assist in repair o Proliferate (multiply rapidly) in damaged region • Phagocytic function – remove waste Oligodendrocytes • Produce myelin • Wrap sheath concentrically • Oligo in CNS o Multiple at once (~50) • Schwann in periphery o Single axon • Interruption at nodes of Ranvier o Generate axon potentials Neuronal Signaling • Communication between neurons • Input contact at dendrites (or cell body) o Synapse at terminals • Output from axon terminals • Long and local distance circuits of networks How it works – the overview • Neurons receive chemical or electrical signal • Signals change membrane of postsynaptic neuron • Changes in flow of electrical currents • Neuron integrates signals • Triggers spike or action potential • Travels down axon • Releases neurotransmitter Neural Membranes • Bilayer of lipids does not dissolve • Barrier to chemicals - ions, proteins, and molecules – that are floating in the extracellular space (outside the cell) and intracellular space (inside the cell) • Bilayer is permeable – some things can pass through Neural Membranes • Resting potential o Voltage differences (-70mV) across membrane Membranes 2 Ion channels • Non-gated: passive (more potassium K+) than sodium (Na+ or Cl-) – selective permeability • Gated: opened/closed by stimuli (electrical, chemical, or physical) Active transporter pumps • Move ions across membrane • Little energy (adenosine triphosphate) pump • Change ionic gradients Concentration of Ions Ionic (chemical) gradient • More Na+ outside, more K+ inside • Membrane is more permeable to K+ • Some K+ escapes to the outside Electrical gradient • As K+ escapes out, the inside of the cell becomes more negative • As the inside becomes more negative, it is harder for K+ to escape • The struggle continues until electrochemical equilibrium is achieved Resting Potential • Electrical current ionic (charged atoms = ions) o Na+, K+, Cl-; also some large charged proteins in solution • Electrochemical equilibrium o More Na+ outside and K+ inside o Membrane more permeable to K+ o K+ tries to move out o Electrical gradient develops ▯ + move out and so remaining – attracts positives o Electrical and ionic concentration in opposition but balance Brief Review • Presynaptic, postsynaptic, soma, axon, dendrites, afferent (accepting), efferent (entering), membrane, bilayer, myelin, astrocytes • Potential differences across membrane, extracellular and intracellular charges, ionic gradient, electrical gradient • Voltages inside and outside of cells can be measured Electrical Conduction • Record potentials of membranes • Pass current to neuron o Can depolarize/make more positive intracell as current flows out • Record difference between inside and outside cell Conduction • Conductors o Cytoplasm and extracellular fluid • Insulators o Membranes with variable resistances o Myelin is a great insulator Active/passive currents • Synapse activated o Electrical currents generated o Flows in local region • Passive currents across postsynaptic membrane through dendrites and soma • If current is strong, ▯ action potential • If not, passive flow and decrement (reduction) in current (bad for long distance communications) Action Potential Long distance communication • Regenerative electrical signals Action potential • Rapid depolarization and repolarization of membrane in local area • If sufficient potential, cross threshold • All or none once crossed threshold So, what happens? • Voltage gated ion channels open when membrane is depolarized • Opens and lets some Na+ in, further depolarizes • Lets in more Na+ etc. THEN • Open voltage = gated K+ channels • Repolarizes • Overshoots resting as repolarizes (hyperpolarizes) • Refractory period Diagram of an Action Potential Saltatory Conduction • Need speed for conduction o Motor coordination • Myelin wrapped o Squeezes out cytoplasm, concentric wrap • Action potentials appear at nodes of Ranvier and regenerated • Transmission 120m/sec (football field in 1s) Saltatory Conduction (leap/hop) Synaptic transmission – Electrical • Very rapid transduction • No synaptic cleft (membranes are actually touching) • Accomplished via gap junctions • Useful for rapid conduction (some sensory neurons) Synaptic transmission – Chemical • Ca2+ flows in • Small vesicles with neurotransmitter fuse with membrane • Release transmitter into cleft • Binds with protein receptor molecules Neurotransmitters • Synthesized by presynaptic neuron • Transported to axon terminal • Stored in vesicles • Binds with postsynaptic neuron • At cleft o Active reuptake o Enzymatic breakdown o Diffusion Neurotransmitters (continued) • Excitatory o Ach o Dopamine o Catecholamine o Glutamate o Histamine o Serotonin • Inhibitory o GABA o Glycine Parkinson’s disease – insufficient dopamine ADD/ADHD – insufficient levels Sleep – low histamine low vigilance Sexual response (too much, too little) Antidepressants MDMA (ecstasy) increases levels of neurotransmitters Einstein’s Brain • Unusual Sylvian fissure Larger and thicker parietal lobe Form is derived from function Fine neuronatomy/microscopic • Anatomy of cell Gross neuroanatomy • Ensembles of cells • Columns • Lobes • Brain Interest is not just in structure but how it supports function Terminology *Dorsal means top – it also means superior *Ventral means bottom – it also means inferior *Rostral means towards the front *Caudal means toward the back *Superior – top; inferior – bottom *Anterior – front; posterior – back *Sagittal – straightforward; middle of the brain Revealing the brain • Dura • Gyri • Sulci • Tracts: bundles of axons • Gray matter o Cell bodies of neurons and glia • White matter o Myelin surrounding axons Microanatomy and Histology – Confocal Microscope Astrocyte: Group of astrocytes: Analysis of neurons And their connections • Short-range and long-range • Cortico-cortico • Corticofugal (to periphery) Staining • Microscopy • Fluorescent strains • Reveal cell types, laminar projections • Tract tracing o Retrograde ▯ Diffuses up axon to cell body (e.g., horseradish peroxidase, HRP) o Anterograde tracing ▯ Diffuses down from the cell body to the axon terminal Can stain selectively • Purkinje cells • Nissl substance for organelles • Mitochondria Cytoarchitectonics Brodmann maps Subdivisions of the Central Nervous System (CNS) Cortex = the bark of the brain • Increase surface area: gyri and sulci • Reduce axonal distance • Multiple layers o But only 3 mm thick o Neurons o Dendrites o Some axons Cortical Lobes • 4 lobes: frontal, parietal, temporal, and occipital • Central sulcus: frontal/parietal • Lateral Sylvian fissure: temporal from frontal and parietal • Parieto-occipital sulcus: occipital from parietal and temporal • Corpus callosum; longitudinal fissure (“hard body”) – divides the lobes Ventricular System • Lateral ventricle • Interventricular foramen • Third ventricle • Cerebral aqueduct • Fourth ventricle Penfield – Subdural electrode recording and stimulation in humans Motor Cortex • Frontal lobe • Motor cortex – Betz cell Somatosensory – parietal • Touch, pain, temperature, limb proprioception Auditory cortex • Lateral view of the left hemisphere Visual Cortex • Based on cell morphology • Naming: o Brodmann number (e.g. 17) o Anatomical name: calcarine o Cyto: striate o Functional: primary visual corex (V1) o Areas 18 o Area 19 Limbic System The Limbic System: for emotion (Papez circuit) Surrounds brain stem; older cortex • Mesocortex o Cingulate, hypothalamus, hippocampus, and amygdala • Emotional processing • Learning • Memory The Basal Ganglia Subcortical neuronal groups • Globus pallidus • Caudate nucleus • Putamen Connects with motor regions to monitor motor behavior The Basal Ganglia Diencephalon Thalamus • Gateway to the cortex: modalities make synaptic relay • LGN = visual; MGN = auditory • Ventral posterior nuclei = somatosensory • Receives input from basal ganglia, cerebellum, medial temporal lobe Hypothalamus • Endocrine regulation • Vasopressin (kidneys); oxytocin (arousal); circadian rhythms Midbrain • Reticular formation: sensory-motor – arousal, respiration, cardiac modulation, pain, muscle • Red nucleus: motor coordination • Pineal gland – endocrine system (wake/sleep, seasonal functions) • Superior and Inferior Coliculi – visuomotor functions, auditory relay • Substantia nigra Pons and Medulla • Pons: auditory and vestibular functions • Medulla: sensory motor functions, vestibular, motor control of face/mouth/throat/respiratory system/heart Cerebellum Posture, walking, coordinated movement (projections) Contains 11 billion cells 9/8/16 3:31 PM 9/8/16 3:31 PM
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