Transcript Chapter 4
Chapter 4 Brain and Behavior Brain and Behavior Adaptive behavior is accomplished through the action of adapted brains The case of Phineas Gage – Damage to area at the front of the brain results in loss of planning abilities and “civilized behavior” The Origins of the Human Brain Brain size correlates with body size – Big animals have big brains Brain/body ratio distinguishes apes from most other animals Similarities to other animals All animals have the following organization of brain structures: – Hindbrain – Midbrain – Forebrain Different species differ in the relative sizes of these areas Cerebral Cortex Cerebrum evolved relatively recently Much more prominent in mammals – Corticalization Results in and “enormous elaboration of powers” (Dennett, 1995). Organization of the Brain The “Vertebrate Plan” All vertebrates have a similar brain organization The Human Nervous System The Human Nervous System Central Nervous System (CNS) – Brain and Spinal Cord The Human Nervous System Peripheral Nervous System (PNS) – Carry information to and from skin, organs in body, etc – Subdivided into: • Somatic Nervous System – Sensory & motor nerves to periphery • Autonomic Nervous System – Sympathetic/Parasympathetic Divisions Sympathetic and Parasympathetic Divisions of the ANS Continued on next slide Sympathetic and Parasympathetic Divisions of the ANS Neurons Basic functional unit of the nervous system The Synapse Connection between neurons Small gap between the axon terminals of one neuron and the dendrites of the next Communication between neurons results from the secretion of neurotransmitters Sensory Motor Reflex Behavior occurs solely as the result of activity at the spinal cord 2. Sensory neurons excite interneurons in the dorsal gray portion of the spinal cord 1. Flame stimulates pain receptors (sensory neurons) 3. Interneurons excite motor neurons in the ventral gray portion of the spinal cord 4. Motor nerves exit the spinal cord, excite the muscle, and initiate a movement Organization of the Spinal Cord Brain and Behavior The Reticular Formation – Responds to arousing stimulation Brain and Behavior Thalamus and Somatosensory Cortex – Homunculus (“little man”) – Representation of body on thalamus and somatosensory cortex Homunculus The greater the number of nerves in a body area, the larger its brain representation – Fingers or mouth vs. back or arm Organization of the Cerebral Cortex The Human Cortex The human cortex is much larger relative to other brain areas than is the case for other animals The Human Cortex Primary Sensory Areas – Areas that receive sensory information Association Areas – Areas that make connections between senses Humans have much more association areas than primary sensory areas Studying Brain Damage Accidents Effects of Strokes Damage influences behavior on side of the body opposite to damaged side of the brain Neurogenesis The formation of new neurons – Recent evidence suggests that adult humans can form new neurons The Cerebellum Responsible for – Coordinated motor activity – The development of conditioned associations Two Cerebral Hemispheres Lateralization of Function – Left and right hemispheres of cerebral cortex do different things Lateralization of Function Dichotic Listening Test – Present words through headphones to left and right ears simultaneously – Most people will report hearing the words presented in the right ear – Indicates the left side of the brain processes language Lateralization of Function PET Scans – Positron-emission tomography – Indicates brain activity using a radioactive form of glucose • Greater activity results in greater glucose usage – Language tasks increase activity in the left hemisphere The Split Brain Procedure The Corpus Callosum – Set of fibers connecting the two hemispheres – Epileptic activity can travel across the corpus callosum The Split Brain Procedure Cutting the corpus callosum reduces severity of epileptic seizures Results in the two hemispheres being functionally separated Testing Split Brain Patients Testing Split Brain Patients Only left hemisphere can respond verbally – Right hemisphere can use motor responses (e.g. pick up an object with the left hand Seeing with and without awareness – Right hemisphere cannot communicate its awareness Right Hemisphere Emotions Artistic ability Spatial ability Musical ability Neurotransmitters and Drugs Resting Potential Inside of neuron is negatively charged relative to the outside – More negatively charged chemicals inside than outside The Resting Potential Microelectrode Extracellular Fluid Membrane Intracellular Fluid Neurotramsitter Activity Neurotransmitter activates receptors on postsynaptic cell – May result in depolarization of cell • Cell’s charge becomes less negative • Excitatory Post-Synaptic Potential (EPSP) – May result in hyperpolarization of cell • Cell’s charge becomes more negative • Inhibitory Post-Synaptic Potential (IPSP) Action Potentials Neuron adds together EPSPs and IPSPs – If membrane is depolarized sufficiently it will generate a sudden change in the electrical state of the cell • Action Potential Ion Channels and Action Potentials Depolarization of the neuron results in the opening of sodium (Na+) ion channels – Na+ flows into cell, making it much more positively charged Potassium (K+) then flows out, making the cell much more negative All or None Principle Action potential is a complete nerve impulse Travels down the axon at the same strength Cannot be degraded Saltatory Conduction Myelin globules are divided by Nodes of Ranvier Action potential can “leap” from one node to the next – Increases the speed of the action potential 100-fold Neurotransmitter Release Neurotransmitters stored in axon terminal in vesicles Action potential arrives at axon terminals – Causes Calcium (Ca++) influx – Results in vesicles moving to wall of axon terminal and releasing neurotransmitter Neurotransmitters Multiple Neurotransmitters “Lock and Key” model – Each neurotransmitter chemical can only attach with one type of receptor Different neurotransmitters have different effects Drugs Many drugs influence neurotransmitter activity – Reduce re-uptake • Cocaine – Block receptor • Curare – Mimic neurotransmitter • Morphine