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Chapter 3

Chapter 3 - The Biological Bases of Behaviour.docx

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York University
PSYC 1010
Jennifer Steeves

The Biological Basis of Behaviour Cell Types in the Brain 1. Glia – Support cells; constantly replacing themselves; ~1 trillion glial cells  Provide Insulation – increase speed of neurons  Provide nutrients  Keep toxic substances out (blood-brain barrier)  Clean-up and repair Key Parts of the neuron • Soma – Cell Body; one per neuron; normal cell regulation functions; axon hillock sums inputs • Dendrites – Branching structures that receive signals from other cells; dendritic tree • Axon – Fibre that carries signals away from soma to other cells • Myelin Sheath – Insulating material that encases some axons • Terminal Buttons – Small knobs at ends of axons that release neurotransmitters at synapse The neural impulse • Resting Potential - Neuron’s stable, negative charge when inactive • Action Potential – Voltage spike that travels along axon • Absolute Refractory Period – Brief time after action potential before another action potential can occur • All-or-None Law – A neuron either fires or doesn’t fire Saltatory Conduction • Myelin Sheaths – Glia wrap around axon • Nodes of Ranvier – Gaps between glia • Action potential jumps between nodes Myelinization • Myelin – Mostly fat; fat is white; white matter contains myelinated axons • Not all neurons are covered in myelin at birth; develops in diff regions at diff times • Simpler areas (sensory & motor) become myelinated first • Can continue till ~age 20 in areas involved in abstract thinking Multiple Sclerosis • Decay of myelin sheaths; axons are exposed and break down • Impaired sensation of movement • May be an autoimmune disorder Axon Hillock • “Little hill” at the junction of the cell body and the beginning of the axon • Gathers information from dendrites Postsynaptic Potentials • Postsynaptic – on the dendrites (or sometimes the cell body) of the receiving neuron • Potential – voltage difference • Excitatory Post-Synaptic Potentials – “Yes” votes • Inhibitory Post-Synaptic Potentials – “No” votes Drug Actions • Drugs can act at any stage of synaptic transmission • Agonists – drugs that increase the effectiveness of synaptic transmission • Antagonists – drugs that decrease the effectiveness of synaptic transmission Neurotransmitters and behaviour • Acetylcholine – Released by neurons that control skeletal muscles • Serotonin – Involved in regulation of sleep; abnormal levels linked in depression and obsessive-compulsive disorder • Dopamine – Abnormal levels linked to schizophrenia; dopamine circuits activated by cocaine and amphetamines • Norepinephrine – Abnormal levels linked to depression; contributes to modulation of mood and arousal • 6ABA – Inhibitory transmitter that contributes to regulation of anxiety • Endorphins – Opiate-like chemicals involved in modulation of pain • Glutamate – Excitatory transmitter linked to memory process of long-term potentiation Synaptic Transmission Inactivation or removal (drifting away) of neurotransmitter Organization of the Nervous System Peripheral Nervous System 1. Somatic Nervous System – Nerves to voluntary muscles, and sensory receptors  Afferent (incoming) nerves  Efferent (outgoing) nerves 2. Autonomic Nervous System – Nerves to heart, blood vessels, smooth muscles, and glands  Sympathetic Division – Mobilizes bodily resources (Fight/Flight)  Parasympathetic Division – Conserves bodily resources (Rest & Digest)  Somatic System • Sensory Neurons  Input from body to Central Nervous System • Motor Neurons  Output from Central Nervous System to control muscle movements • Interneurons  Sensory-motor relay within the Central Nervous System • Both voluntary and reflex Central Nervous System 1. Brain 2. Spinal Cord • Spinal Injuries  Input can’t get in; Output can’t get out  Different level wired to different parts of the body; quadriplegic vs. paraplegic Brain and Behaviour Methods for studying the brain function • EEGs monitor the electrical activity of the brain over time, yielding line tracings called brain waves • Lesioning involves destroying a piece of the brain to learn about its function • Electrical stimulation of the brain involves sending a weak current into the brain structure to activate it • Transcranial magnetic stimulation is a new technique that permits scientists to temporarily enhance or depress activity in a specific area of the brain • CT scans and MRI scans can provide precise images of brain structure • PET scans and fMRI scans can map actual activity of the brain over time Plasticity of the brain • The anatomical structure and functional organization of the brain is somewhat malleable Hindbrain • Cerebellum – Coordinates fine muscle movement, and balance; invlved in higher cognitive tasks • Medulla – regulates unconscious functions such as breathing and circulation • Pons – involved in sleep and arousal Midbrain • Involved in locating things in space; dopamine synthesis Forebrain • Thalamus – Relay centre for cortex; distributes incoming sensory signals, except smell • Cerebrum – Handles complex mental activities, such as sensing, learning, thinking, planning  Frontal Lobes – Primary motor cortex  Prefrontal Cortex – involved in relational reasoning; working memory  Parietal Lobes – Primary somatosensory cortex  Temporal Lobes – Primary auditory cortex  Occipital Lobes – Primary Visual Cortex • Limbic System – Loosely connected network that contributes to emotion, memory & motivation  Hippocampus – Contributes to memory; memory formation  Amygdala – Involved in learning of fear responses; emotion • Hypothalamus – Regulates basic biological needs, such as hunger, thirst, and sex; autonomic NS Endocrine System • Consists of glands that secrete chemicals called hormones into the bloodstream • Governed by the hypothalamus and pituitary gland, regulates digestion, response to stress, and sexual development • Among other things, hormones regulate responses to stress, sexual development, insulin production, and metabolic rate Right Brain/Left Brain • Localization of Function; case of Phineas Gage • Each Hemisphere is divided into 4 Lobes 1. Occipital Lobe  Input from eyes via optic nerve  Contains primary visual cortex  Outputs to parietal and temporal lobes 2. Temporal Lobe  Auditory cortex gets input from the ears  Visual input from the occipital lobe  Recognition and memory; speech, face, word, and memory recognition  Outputs to limbic system, basal ganglia, and brainstem 3. Parietal Lobe  Input from touch to somatosensory cortex
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