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Chapter 3

Chapter 3.docx

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Psychology 1000

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Psychology Chapter 3: Biological Foundations of Behaviour THE NEURAL BASES OF BEHAVIOUR Neurons: the basic building blocks of the nervous system. These nerve cells are linked together in circuits. A neuron has 3 main parts: 1. The cell body or soma- contains the biochemical structures needed to keep the neuron alive and a nucleus which carries the genetic information 2. Dendrites- specialized receiving units that collect messaged from neighbouring neurons and send them to the cell body 3. Axon- conducts electrical impulses away from the cell body to other neurons, muscles, or glands 4. Axon terminals They also do 2 important things: 1. Generate electricity that creates nerve impulses 2. Release chemicals that allow hem to communicate with other neurons and with muscles and glands Glial cells  Surround neurons and hold them in place  Manufacture nutrient chemicals that neurons need  Form the myelin sheath around some axons  Absorb toxins and waste materials that might damage neurons  Protect the brain from toxins Blood-brain barrier: prevents many substances, including a wide range of toxins, fro entering the brain Nerve activation involved three basic steps: 1. At rest, the neuron has an electrical resting potential due to the distribution of positively and negatively charged chemicals (ions) inside and outside the neuron 2. When stimulated, a flow of ions in and out through the cell membrane reverses the electrical charge of the resting potential, producing an action potential, or nerve impulse 3. The original distribution of ions is restored, and the neuron is again at rest Outside the neuron:  Positively charged sodium ions and negatively charged chloride ions  Positive Inside the neuron:  Negatively charged protein molecules (anions) and positively charged potassium ions  Negative Psychology Resting potential: in the electrical activity of neurons, the internal difference of the sodium ions outside the cell and the negatively charge protein ions inside the cell Action potential: a sudden reversal in the neuron’s membrane voltage, during which the membrane voltage momentarily moves from -70 millivolts (inside) to +40 millivolts Depolarization: the shift from negative to positive voltage. The reversal of the resting potential of a neuron’s cell membrane that produces the action potential Generation of Action potential  In the resting state, sodium and potassium channels are closed and the concentration of Na+ ions is 10x higher outside the neuron than in it  When the neuron is stimulated, Na+ channels open up  Attracted by the negative protein ions inside, positively charged Na+ flood into the axon, creating a state of depolarization  The interior is now positive +40MV in relation to the outside, creating the action potential  In a reflex action to restore the resting potential, sodium channels close and potassium ions flow out through their channels  This restores the negative resting potential  Eventually, excess Na+ flow out of the neuron, and the escape K+ are recovered Absolute refractory period: the recovery period as K+ ions flow out of the interior. The membrane is not excitable and cannot generate another action potential * In humans the limit is about 300 impulses All-or-none law: action potentials occur at a uniform and maximum intensity, or they do not occur at all Action potential threshold: the intensity of stimulation (excitatory minus inhibitory) needed to produce action potential Graded potentials: a change in the electrical potential of a neuron that is proportional to the intensity of the incoming stimulation, but not sufficient to produce action potential Myelin sheath: a fatty, whitish insulation layer covering axons derived from glial cells during development Nodes of Ranvier: interrupt the myelin sheath at regular intervals Unmyelinated axons, the action potential travels own the axon length like a burning fuse Myelinated axons, electrical conduction can skip from node to node Psychology Synapse: the microscopic space between neurons over which the nerve impulse is biochemically transmitted Synaptic cleft: a tiny gap between the axon terminal of one neuron and the dendrite of the next neuron Neurotransmitters: chemical substances that carry messages across the synapse to either excite or inhibit their firing Process of Chemical Communication 1. Synthesis of neurotransmitter 2. Storage in synaptic vesicles 3. Release into synaptic space 4. Binding to receptor sites 5. Deactivation through reuptake or breakdown Types of Neurotransmitters Excitatory Neurotransmitter  Depolarizes neuron’s membrane Increases liklihood of action potential Inhibitory Neurotransmitter hyperpolarizes neuron’s membrane decreases liklihood of action potential Reuptake: the transmitter molecules are reabsorbed into the presynaptic axon terminal Acetylcholine (ACh): an excitatory neurotransmitter that operates at synapses with muscles and is also the transmitter in some neural networks involving memory Dopamine: an excitatory neurotransmitter whose overactivity may underlie some of the disordered behaviours seen in schizophrenia Seratonin: a neurotransmitter that seems to underlie positive mood states; underactivity may be a factor in depression Endorphins: natural opiate-like substances that are involved in pain reduction Neuromodulators:neurotransmitter substances that are released by neurons and circulate within thenervous system to affect the sensitivity of many neurons to their natural transmitter substances Psychology THE NERVOUS SYSTEM 3 major types of neurons: 1. Sensory neurons carry input messages from the sense organs to the spinal cord and brain 2. Motor neurons transmit output impulses from the brain and spinal cord to the body’s muscles and organs 3. Interneurons link the input and output functions Nervous system has 2 subsystems: 1. Central nervous system—all the neurons in the brain and spinal cord 2. Peripheral nervous system—all the neurons that connect the central nervous system with the muscles glands, and sensory receptors, all the nerual structures outside the brain and spinal cord Peripheral Nervous System (PNS) Somatic nervous system: the branch of the perpheral nervous system that provides input from the sensory recepotrs and output to the voluntary muscles of the body Autonomic nervous system: the branch of the perpheral nervous system that stimulates the body’s involuntary muscles and internal organs Sympathetic nervous system: the branch of the autonomic nervous system that has an arousal function on the body’s internal organs, speeding up bodily processes and mobilizing the body Parasympathetic nervous system: the branch portion of the autonomic nervous system that slows down bodily processes to conserve energy and reduce appetite Homeostasis: the maintainence of of biological equilibrium, or balance, within the body Peripheral Nervous System (PNS) Autonomic system (controls Somatic system (voluntary muscle, and glands; muscle activation
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