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Lecture

The Brain.doc

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Department
Psychology
Course
PS101
Professor
Kris Gerhardt
Semester
Fall

Description
2 The Brain • 3-4 lbs. or 1.5-3.5% of body weight • Consumes 20% of oxygen • 100 Billion neurons – Each connected to 2 000 to 10 000 others (5,000 on average) • Are we born with all the neurons we will ever have? NO • Erikson and neurogenesis – the creation of new neurons • Distinct areas in the brain – Nuclei – Nerve pathways 3 Intro to the Neuron • Basic building block of the nervous system • 100 billion neurons x ~5000 connections – 1cubic mm = 100 000 neurons & 1 million synapses • Continually active (they don’t stop, if they do they are “dead”) – Generate electrical activity ~ 20 watts – Nerve impulse • 10pt font - period is 1000um – Typical neuron is 10um – 4 A Neuron (refer to figure in “The Brain – Figures” document) 1 • Dendrites - • Cell Body • Axon – the entire tail • Axon Terminals • Terminal Buttons • Myelin Sheath – fat layer that surrounds the axon to keep the signal inside & speed up the signal by conducting the electricity • Receptive Zone • Dendrites and the cell body - Signals come in through the dendrites/cell body and leave through the axon terminals. 6 Types of Neurons 1 • Afferent (sensory) – From body to brain (Central Nervous System) – Reminder: A with finger, fingers pointing up which means signal is sent from the body UP to the brain • Interneurons – Connections • Efferent (motor) – From brain (Central Nervous System) to body • For every 1 afferent, you have 10 efferents. For every 10 efferents, 200 interneurons. 1 9 The Action Potential • The Neuron as a battery • Voltage – The potential difference between the positive and negative charges at the different poles • Ions – Sodium (Na+), Potassium (K+), large Organic (Org-) – Not evenly distributed in and out of cell – Therefore, more negative charge inside cell • Cell Membrane is semi-permeable (lets little things through, but the big things go through ion channels) – Ion channels (like doors on a cell) 10 Transmission of AP (-50mv firing threshold: reaction starts, -70mv resting: more negative outside than inside) • AP begins at the top of the axon – Ion channels open – Na+ flows into cell – Depolarization occurs – Na+ continues until the inside of the cell is more positive than the outside – (-40mv ion channels close, too positive) • K+ leaving cell throughout – Hyperpolarization occurs – Refractory period • Cell can generate another AP in response to stimulation 11 Action Potentials • Triggered by the net graded potential at the axonhillock (trigger zone) • • Do not degrade • • Travel long distances • • All-or-none • • Must reach threshold potentia o fire 12 Action Potential con’t • Process is propagated down the length of the axon – Nerve impulse reaches the end of the axon in the same form as it started • All or none law • Terminal buttons • Neurotransmitters • Synapse – space between the neurons 13 Synaptic Transmission • If the neurotransmitter doesn’t bind, no effect on Post Synaptic membrane • If it does bind…. – 1. Increases permeability 2 • Excitatory signal – decrease threshold (up towards 0, ex: from -70 to -50) – 2. Decreases permeability • Inhibitory signal – increase threshold (down away from, ex: from -50 to -70) 15 Overview of how neurotransmitte rs work When the vesicle reaches the synapses, either: Reuptake (go back into original neuron) and enzyme destruction decreases the activity at that synapses. Binding on the other neuron increases activity. 16 Excitatory & Inhibitory Signals • 1 EPSP is insufficient to depolarize to threshold – Temporal summation – one • May take 20-100 to reach threshold – Spatial summation – many • IPSP • Some synapses generate only IPSP or EPSP • An IPSP counteracts an EPSP • Graded potentials – cell body and dendrites 17 Neurotransmitte rs • Dopamine (makes us feel good) – anti-psychotic drugs • Serotonin – Depression; Prozak • Norepinephrine • Acetylcholine – Nicotine • GABA (stops signals) – Inhibitory neurotransmitter 18 General Summary • We have looked at the very lowest level of brain function – Narrowed down to tiny neurons that continually fire – And how they fire • But is this where behaviour takes place? • Where are memories stored? It is believed to be in the synapses. • How are emotions generated? 19 Getting Info about the Brain • EEG – used to measure where brain activity is happening approximately • Brain Damage / Surgery • Single Cell Recordings • Deliberate Lesions • CT scan • PET Scans • MRI • fMRI • *****Imaging Technique Summary***** • 20 The Human Central Nervous System 1 • 3 Brainstem • The Forebrain • Limbic System
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