Cognitive neuroscience

Cognitive neuroscience H2. Introducing the brain Structure and function of theneuron; 3 components ●Cell body ●Dendrites ●Axon

●Neuron: cell that makes up nervous system + supports cognitive function

Cell body ●Containsnucleus→ contains genetic code for proteinsynthesis Dendrites ●Branch from cell body ●Enable communication with other neurons ●Receive info from neurons close by ●Number and structure varies with place in the brain (type of neuron) Axon ●Each neuron has 1 axon (may be divided into branches →collaterals ●Sends info to other neurons ●Transmits an action potential Synapse; Pre- postsynaptic ●Disc-shaped, at the terminal of an axon ●Small gap between neurons, in whichneurotransmitters(chemicalsignals) are released ●Two neurons forming the synapse

○Presynaptic: before synapse

○Postsynaptic: after synapse

○Reflects direction of info flow ●Some synapses signal electrically not chemically Axon hillock ●Start of an axon

●Electrical current is large enough: action potential initiated

Action potential

●Presynaptic neuron is active: action potential sent through axon

●When reaches axon terminal, neurotransmitters released intosynaptic cleft Neurotransmitters ●Bind to receptors on dendrites or cell body of postsynaptic neuron ●Create asynaptic potential→ conducted passively(without creating action potential) through dendrites of postsynaptic neuron ●Passive current strong enough at beginning of axon in postsynaptic neuron → action potential triggered in this neuron Passive/active conduction ●Passive conduction→ short range. Electrical signalimpeded by resistance of surrounding matter ●Active conduction→ long range, between neurons byaction potentials Cell membrane ●Barrier for certain chemicals ●Protein molecules act as gatekeepers; allow certain chemicals in/out under certain conditions 1 / 4

Chemicals going in/out membrane + balance

●Charged sodium ion: Na+

●Charged potassium ions:K+

●Balance between these in/outside membrane: normally at resting potential of -70mV across membrane (inside negative relative to outside) Important for generation of an action potential ●Voltage gated ion channels: only found in axons, so only axon can produce an action potential Sequence of events in generating action potential 1.Strong enough passive current across axon membrane: opens sodium (Na+) channels 2.Sodium enters cell, celldepolarizes→ becomes lessnegative on inside ○At -50mV: membrane becomes penetrable → charge on inside momentarily reverses → sudden depolarization + following repolarization in membrane = action potential 3.Negative potential of cell restored via potassium flowing out and sodium not flowing back in 4.Brief period of hyperpolarization → inside more negative than when at rest: more difficult for axon to depolarize + prevents AP from travelling backwards How AP moves progressively down the axon ●AP in one part of axon opens adjacent Na+ channels, so it can move from cell body to axon terminal ●Goes faster if axon is myelinated Myelin ●Fat substance around axon of some cells (mostly those that carry motor signals) ●Blocks normal Na+/K+ transfer, so AP jumps via passive conduction down axon where there’s no myelin (nodes of Ranvier)

●Destruction of myelin: MS

Protein receptors in membrane of postsynaptic neurons ●They bind to neurotransmitters ●Many set up a localised flow of Na+, K+ or chloride → creates the synaptic potential Neurotransmitters inhibitory & excitatory effects on postsynaptic neuron ●Inhibitory effects→ makes it less likely to fire ○Achieved by making inside of neuron more negative than normal → harder to depolarize ●Excitatory effects→ makes it more likely to fire ○Synaptic potentials are then passively conducted How neurons code info ●Size AP doesn’t vary, the number of AP’s per second does ●This ‘spiking rate’ (rate of responding) depends on info the neuron is carrying ○Some may have high spiking rate in some situations: during speech, but not others (during vision) ●Neurons responding to similar type of info often grouped together → specialization of brain regions Type of info a neuron carries ●Depends on input/output it receives/sends to other neurons ●Input/output determines function of a region Gray + white matter

●Gray matter: neural cell bodies

●White matter: axons and support cells (glia)

●Folded sheet of grey matter: cerebral cortex

●Center of brain, grey matter subcortex: basal ganglia, limbic system, diencephalon Association tracts + Commissures + Projection tracts ●Association tracts: white matter tracts project betweendifferent cortical regions in same hemisphere 2 / 4

●Commissures: white matter tracts project between different cortical regions in different hemispheres

○Most important commissure:corpus callosum

●projection tracts: white matter tracts project betweencortical and subcortical structures Ventricles ●Hollow chambers filled withcerebrospinal fluid CSF ○Non-cognitive functions: carries waste metabolites, transfers messenger signals, provides protective cushion for brain Brain evolution ●Adding additional structures onto older ones

• ventricles

●2 lateral ventricles: in each hemisphere

●One around subcortical structures ●One in brainstem (hindbrain) Directions for navigating the brain ●Anterior(rostral) → towards the front ●Posterior(caudal) → towards the back ●Superior(dorsal) → towards the top ●Inferior(ventral) → towards the bottom ●Lateral(medial) → outer part ●Medial→ in/toward the middle Central nervous system Coronal cross-section ●Slice in vertical plane through both hemispheres ●Brain appears round Sagittal section ●Slice in vertical plane through one of hemispheres

●When sagittal section is between hemispheres: calledmidlineormedial section

Axial section ●In horizontal plane Cerebral cortex ●Two folded sheets of grey matter; L/R hemisphere 3 / 4

●High surface area to volume ratio; efficient packaging ●3mm thick + has different layers; reflect grouping of different cell types

●6 main cortical layers:neocortex(new cortex)

Lateral surface cortex - 4 lobes per hemisphere ●Frontal, parietal, temporal, occipital lobes Insula ●Island of cortex beneath temporal lobe

• different ways to divide regions of cerebral cortex

●Regions divided by pattern of gyri and sulci ○Same pattern in everyone ●Regions divided by cytoarchitecture ○Broadman’s areas: 52 areas (BA1-BA52), based in distributionof cell types across cortical layers ●Regions divided by function ○Only for primary sensory and motor areas ○Higher cortical regions harder to ascribe unique functions to Subcortex ●Collection of grey matter beneath cortical surface ●Divided in different systems Basal ganglia ●Large round mass in each hemisphere ●Regulates motor activity, programming / termination of action ●Learning of rewards, skills, habits ●Disordershypokinetic(poverty of movement) orhyperkinetic(excess of movement) - Parkinson - Huntingtons Basal ganglia main structures ●Caudate nucleus(tail-like structure) ●Putamen(lie more laterally) ●Globus pallidus(lie more medially) Limbic system ●Region of subcortex involved in relating organism to its present and past environment ●Involved in detection/expression of emotional responses ●Include; amygdala, hippocampus, cingulate cortex, mammillary bodies Amygdala ●Detection of fearful or threatening stimuli Cingulate gyrus ●Detection of emotional and cognitive conflicts Hippocampus ●For learning and memory Mammillary bodies ●2 small round projections(uitsteeksels) implicated in memory Olfactory bulbs ●Under frontal lobes ●By connections to limbic system → importance of smell for stimuli and ●Influence on mood and memory Diencephalon, 2 main structures ●Thalamus + hypothalamus

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