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Chapter 2: Biological Foundations of Behavior Michael L. Farris Psychology 101 Nervous System Autonomic nervous system - The division of the nervous system that regulates the body’s inner environment (heart rate, blood pressure, digestion, pupil dilation, and electrical conductance of the skin.) Pgs. 50-51. Afferent Nerves: (advance, arrive, approach) carry sensory signals from internal organs TO the CNS (brain and spinal cord). Up. p.40. Efferent nerves (Exit, Embark, Escape p. 52) carry motor signals away from the central nervous system TO the skeletal muscles. Down. P.41. Afferent and efferent nerves are also known as sensory neurons (p. 40). 2 The Blood-Brain Barrier Blood-Brain Barrier: (Pinel, p. 55) The brain is a finely tuned electrochemical organ whose function can be severely disturbed by the introduction of certain kinds of chemicals. Fortunately, there is a mechanism that impedes the passage of many toxic substances from the blood into the brain; the blood-brain barrier. 3 The Brain Stem Brain Stem: The part of the brain on which the cerebral hemispheres rest; in general, it regulates reflex activities that are critical for survival (heart rate and respiration). The Brain Stem (particularly the medulla) regulates basic life functions (heart rate and breathing, and such reflexes as swallowing, coughing, and sneezing). P. 53. 4 Cerebral Hemispheres, Corpus Callosum The brain is composed of two sides, or hemispheres. Left Brain: Controls language, speech, writing, calculation, time sense, rhythm, and the ordering of complex movements. Right Brain: Non-verbal. Controls perceptual skills, visualization, recognition of patterns, faces, and melodies, recognition and expression of emotion, spatial skills, and simple language comprehension. The left and right hemispheres are joined together by the Corpus Callosum, a structure in the middle of the brain that enables hemispheres to share functions and information. Please see pages 54-54 in your text for more information. 5 Case Studies Studies that focus on a single case or subject. Detailed In-depth Pro: Good source of testable hypotheses. Con: not very easy to generalize to others. Humans differ; be skeptical of any biopsychological theory based on only a few case studies. P.23. Example: Lobotomy (1 primate study) 6 CNS and Cerebral Cortex Central Nervous System (CNS): The portion of the nervous system within the skull and spine. Composed of 2 divisions: Brain and Spinal Cord. Cerebral Cortex - The layer of neural tissue covering the cerebral hemispheres of humans and other mammals. Being the OUTER layer, it is most likely to be damaged by accident or surgery. Please see pages 47-50 for more information. 7 Thinking and Learning Cerebrum - The portion of the brain that sits on the brain stem; in general, it plays a role in complex adaptive processes (like learning, perception, and motivation). P.54. Cognition - Complex intellectual processes such as thought, memory, attention, and perceptual processing. p.11. 8 Comparative Psychology Comparative Psychology - The division of Biopsychology that studies the evolution, genetics, and adaptiveness of behavior, often by using the comparative method (The study of biological processes by comparison of different species). P.15. 9 Convolutions Folds on the surface of the cerebral hemispheres. Folds have increased over time greatly increased the volume of the cerebral cortex (the outermost layer of cerebral tissue). More surface area = more capacity 10 DNA, EEG, and Evolution Deoxyribonucleic acid (DNA) Double Stranded, coiled molecules of genetic material. The basic chemical material in chromosomes that carries the individual’s genetic code. (p.72). Electroencephalograph (EEG) - A measure of the general electrical activity of the brain, often recorded through the scalp. Pgs. 58-59. Evolve - To undergo gradual orderly change. P.10. 11 Myelin Myelinated Nerves carry signals 200 times FASTER than unmyelinated ones. (Axons vary in length from 0.04 inches to 1 yard.) The fastest nerve signals travel at over 250 mph. Nerve signals enter a neuron through its dendrites and rush along the axon. At the far end, called the nerve-ending, the axon has other dendrites that pass the message on to the dendrites of other neurons. Neurons that have to carry urgent signals over long distances are surrounded by thick insulation to keep the signal strong, in the same way that the cable from a TV aerial to the TV is coated with insulating plastic. In the case of neurons, the insulation is a myelin sheath—a series of long, flat cells wrapped around the axon. In people with the crippling disease multiple sclerosis, the sheaths break down, weakening the nerve signals. Pgs. 41-42. 12 Natural Selection Heritable traits that are associated with high rates of survival and reproduction are preferentially passed on to future generations. (No magic here; simply good traits get reproduced.) For example, fast horses are selected and bred by racehorse breeders, so each succeeding generation gets faster overall. The slow ones don’t get a chance to reproduce and pass on their slower genes. Nature is similar. The slow fish can’t outrun the shark, so doesn’t get to reproduce. 13 Nature/Nurture and PNS Nature-nurture issue - The debate about the relative contributions of nature (genes) and nurture (experience) to the behavioral capacities of individuals. Pgs. 72-73. Peripheral Nervous System (PNS): The division located outside the skull and spine. Composed of 2 divisions: 1. Somatic nervous system (SNS) (the part of the PNS that interacts with the external environment) 2. Autonomic nervous system (ANS), the part which participates in the regulation of the internal environment. Pgs. 47-49. 14 Lobotomy and Spinal Cord Prefrontal Lobes - The large areas, left and right, at the very front of the brain. Prefrontal Lobotomy - A surgical procedure in which the connections between the prefrontal lobes and the rest of the brain are cut as a treatment for mental illness. Spinal Cord comprises 2 different areas: 1. Gray Matter (composed largely of cell bodies and unmyelinated interneurons) 2. White Matter (composed largely of myelinated axons.) It is the myelin that gives the white matter its glossy white sheen. 15 Sympathetic and Parasympathetic Nerves Sympathetic nerves stimulate, organize, and mobilize energy resources in threatening situations. Sympathetic changes are indicative of psychological arousal. Parasympathetic nerves act to conserve energy. Parasympathetic changes are indicative of psychological relaxation (think of a parachute). Each autonomic target organ receives opposing sympathetic and parasympathetic input, and its activity is thus controlled by relative levels of sympathetic and parasympathetic activity. P.51. 16 Brain Anatomy Early brain development: 3 sections form (forebrain, midbrain, and hindbrain). Later, these grow into five major different swellings (telencephalon, diencephalons, mesencephalon (midbrain), metencephalon, and myelencephalon). ENCEPHALON means within the head. In humans, the telencephalon (right and left cerebral hemispheres) undergo the greatest growth during development. The other 4 divisions are often referred to collectively as the Brain Stem, on which the cerebral hemispheres sit. The myelencephalon is often referred to as the medulla. Again: Brain Stem = myelencephalon, metencephalon, mesencephalon, and diencephalon. 4 of 5 divisions are in the stem. 17 Brain and Spine Protectors Meninges, Ventricles, and Cerebrospinal Fluid (Pinel p. 53): The brain and spinal cord (the CNS) are the most protected organs in the body. They are encased in bone and covered by three protective membranes, the meninges. Also protecting the CNS is cerebrospinal fluid, which fills the central canal of the spinal cord and the cerebral ventricles of the brain. It also fills the subarachnoid space, which contains many large blood vessels. The cerebral ventricles are the four large internal chambers of the brain: 2 lateral ventricles, the third ventricle, and the fourth ventricle. It is believed that the ventricles are often enlarged in people with schizophrenia. 18 Neural Conduction and Synaptic Transmission Neural Conduction=Electrical (the way a nerve impulse travels along a nerve cell. Synaptic Transmission=Chemical (the way neurotransmitters travel across the synapse (gap) to communicate with another nerve cell (neuron). 19 Neural Conduction/Synaptic Transmission Nerve signals are constantly whizzing from neuron to neuron all around your body – yet no two neurons ever actually touch. Instead, there is a small gap between connecting neurons called a synapse. When a nerve signal is passed on from one neuron to the next, it is carried across the gap by special chemicals called neurotransmitters. The chemicals are released by the neuron that is sending the signal. Droplets of neurotransmitters are stored inside the nerve-ending in tiny sacs called vesicles. When a nerve signal arrives at the nerve-ending, the vesicles drift towards the synapse and spill out their contents into the gap. The neurotransmitters flood across the gap and wash up against the other nerve. Inside every nerve ending are sacs of chemical transmitters. These are released into the synapse when the nerve is activated, or “excited”, by a nerve signal. If the adjoining nerve has the right receptors (page 95), the signal will pass on. 20 Neural Conduction and Synaptic Transmission The term exocytosis (Pinel pages 94-95) refers to the process of releasing a neurotransmitter. Neurotransmitter chemicals work a bit like keys in locks. In this case, the “locks” are special receptor sites in the dendrites of the receiving neuron. These sites accept only one kind of chemical. For the nerve signal to pass on, the neurotransmitter must be the right chemical that fits, or “unlocks”, the receptor site. If the neurotransmitter fits, it changes the chemistry of the receiving nerve’s membrane (skin). This starts off the electrical charges that pass the signal along the length of the neuron. Because a receptor site responds only to one type of neurotransmitter, an active nerve will pass on the signal only to neurons that have the right receptors,21 even though it is linked to many others. Pgs.40,43-44. Excitation and Inhibition Different types of signals follow different routes through the body. If every single nerve signal were passed on by every single synapse, you would simply be overwhelmed by nerve signals. This is why at some synapses the receiving neurons react by passing on the signal, but at others they react by blocking it. This is called excitation and inhibition. 22 Neurotransmitters There are more than 40 different neurotransmitters Noradrenaline helps to control heartbeat and blood flow Dopamine works in the areas of the brain that control movement and coordination (when you’re making a tricky move on a skateboard, your nerve endings are releasing lots of dopamine, a neurotransmitter that helps muscles move more easily). Endorphins are used by the brain to control pain (they are called “endogenous opiates”—literally, opiumlike chemicals that are produced within the body; see page 100 for more information). Acetylcholine is involved in making muscles contract When you wake up in the morning, it is because certain nerves are flooding your brain with the neurotransmitter serotonin—and any nerve that is receptive gets an alarm call! 23