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Chapter 3

chapter 3 notes- biological foundations of behavior.docx

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Western University
Psychology 1000

Sept 19, 2012 Psych 1000-Chapter 3 Notes Biological Foundations of Behavior The Neural Bases of Behavior Neurons  Specialized cells: are the basic building blocks of the nervous system.  At birth, brain contains about 100 billion neurons.  3 main parts: a cell body, dendrites and an axon  cell body/soma o biochemical structures needed to keep neuron alive. Nucleus carries the genetic information that determines how the cell develops and functions.  Dendrites: o Specialized receiving units that collect messages from surrounding neurons and send them on to the cell body. Then the incoming information is combined and processed  Axon: o Conducts electrical impulses away from the cell body to other neurons, muscles, or glands. o Branches out at its end to form axon terminals o Each axon may connect with dendritic branches from numerous neuron  Function: receiving, processing and sending messages  Are supported in their functions by glial cells. o Glial cells surround neurons and hold them in place. o Manufacture nutrient chemicals that neurons need o Form the myelin sheath around some axons, and absorb toxins and waste material that might damage neurons. o Send out long fibers that guide newly divided neurons to their targeted place in the brain. o Protect the brain from toxins  Blood-brain barrier: prevents many substances/toxins from entering the brain.  The walls of the blood vessels within the brain are covered by specialized type of glial cell. The Electrical Activity of Neurons what neuron does: 1) generate electricity that creates nerve impulses 2) release chemicals that allow them to communicate with other neuron and with muscles and glands Never activation involves three basic steps: 1. at rest, the neuron has an electrical resting potential due to the +ve and –ve ions inside and outside the neuron Sept 19, 2012 2. when stimulated, a flow of ions in and out through the cell membrane reverses the electrical charge of the resting potential, producing nerve impulse 3. the original distribution of ions is restored, neuron is again at rest  Ion channel: a passageway or channel in the membrane that can open to allow ions to pass through  In the salty fluid outside the neuron are +ve charged Na+ ions and –ve charged Cl-. Inside the neuron are large –ve charged protein molecules and +ve charged K+. the high concentration of Na+ outside the cell , with the negative charged protein ions inside, results in an uneven distribution of +ve and –ve ions that makes the interior of the cell –ve compared to outside. This difference is called the neuron’s resting potential (state of polarization). -The Action Potential  A sudden reversal in the neuron’s membrane voltage from -70 millivolts (inside) to +40 millivots. This is called depolarization.  This is the action of sodium and potassium ion channels in the cell membrane.  In resting state, the neuron’s Na+ and K+ are closed, and the concentration of Na+ ions is 10 times higher outside the neuron than inside it.  When stimulated, Na+ channels open. +ve charged Na+ flood into the axon, creating a state of depolarization. Interior becomes more positive, creating action potential.  To restore the resting potential, the cell closes its sodium channels, and –ve charged K+ flow out through their channels, restoring the negative resting potential.  All-or-none law: action potentials occur at a uniform and maximum intensity, or they do not occur at all.  The –ve potential inside the axon has to be changed from -70 millivolts to about -50 millivolts (action potential threshold). Graded potentials: changes in the –ve resting potential that do not reach the -50 millivolts action potential threshold.  For a neuron to function properly, Na+ and K+ must enter and leave the membrane at the right rate -The Myelin Sheath  A fatty, whitish insulation layer derived from glial cells during development  Interrupted at regular intervals by the nodes of Ranvier, where the myelin is either extremely thin or absent.  The myelin sheath is most commonly found in the nervous systems of higher animals  Multiple sclerosis: when person’s own immune system attacks the myelin sheath. It disrupts the delicate timing of nerve impulses, resulting in jerky, uncoordinated movements and eventually paralyze. Sept 19, 2012 How Neurons Communicate: Synaptic Transmission Synapse: a functional (not physical) connection between a neuron and its target. Neurons released chemicals, and it was these chemicals that carried the message fro one neuron to the next cell in the circuit. Synaptic cleft the 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 other neurons or inhibit their firing. Five steps: 1) Synthesis: chemicals molecules are formed inside the neuron 2) Storage: chemical molecules are stored in chambers called synaptic vesicles 3) Release: when an action potential comes down the axon, these vesicles move to the surface of the axon terminal and the molecules are released into the fluid-filled space b/w the axon of the sending neuron and the membrane of the receiving neuron. 4) Binding: the molecules cross the synaptic space and bind to receptor sites- large protein molecules embedded in the receiving neuron’s cell membrane 5) Deactivation: once a neurotransmitter molecule binds to its receptor, it continues to activate or inhibit the neuron until it is deactivated  Excitation Inhibition, and Deactivation o Binding of a transmitter molecule to the receptor site produces a chemical reaction that can have one of two effects on the postsynaptic neuron: 1. reaction will depolarize (excite) the postsynaptic cell membrane by stimulating the inflow of sodium or +ve charged ions- excitatory transmitters. This stimulation may exceed the action potential threshold and cause the postsynaptic neuron to fire an action potential. o 2. Chemical reaction created by the docking of a neurotransmitter at its receptor site will hyperpolarize the postsynaptic membrane by stimulating ion channels that allow +ve charged K+ to flow out of the neuron or –ve charged ions to flow into the neuron. This makes the membrane potential even more negative-inhibitory. A given neurotransmitter can have an excitatory effect on some neurons and an inhibitory influence on others o An exquisite balance between excitatory and inhibitory processes must be maintained if the nervous system is to function properly o Deactivation occurs in two ways:  Some are deactivated by other chemicals located in the synaptic space that break them down into their chemical components.  Deactivation mechanism is reuptake, in which the transmitter molecules are reabsorbed into the presynaptic axon terminal. When the receptor molecule is vacant, the postsynaptic neuron Sept 19, 2012 returns to its former resting state, awaiting the next chemical stimulation. o Drugs may target the transmitter’s receptor, binding to the receptor in place of the neurotransmitter, or one of the steps in the synthesis or release of the neurotransmitter. Drugs can also alter synaptic transmission by influencing how the transmitter is cleared from the synaptic cleft after it has been released.  Specialized Transmitter Systems o Two widespread neurotransmitters are simple amino acids, glutamate, or glutamic acid, and gamma-aminobutyric acid, or GABA. Both are found through the central nervous system-has role in mediating virtually all behaviors.  Glutamate is excitatory and has an important role in the mechanisms involved in learning and memory. However, over- activation will induce seizure activity within the brain, especially withint he cerebral cortex  GABA is important for motor control and the control of anxiety. The symptoms of intoxication reflect the progressive inhibition of brain function within increasing GABA-induced inhibition. o Best understood neurotransmitter-acetylcholine (ACh), which is involved in memory and muscle activity. Underproduction of Ach has important factor in Alzheimer’s disease-degenerative brain disorder involving profound memory impairment. Ach is also an excitatory transmitter at the synapses where neurons activate muscle cells. o The neurotransmitter dopamine mediates motivation, reward, and feelings of pleasure; voluntary motor control; and control of thought processes. In parkinson’s disease, one group of dopamine-producing neurons degenerate and die. As dopamine is lost in the affected brain areas there is a loss of voluntary motor control. It is commonly treated with a drug (L-DOPA) that increases the amt of dopamine within the brain. Some drugs (antipsychotic drugs) attach to dopamine receptors and block dopamine from having its effects. Such blockade is effective in treating symptoms of schizophrenia-disordered thinking. o Depression involves abnormal sensitivity of serotonin, a neurotransmitter that influences mood, eating, sleep, and sexual behavior. The drug Prozac blocks the reuptake of serotonin from the synaptic space, allowing serotonin molecules to remain active and exert their mood-altering effects on depressed patients. Some other drug inhibit the activity of enzymes in the synaptic space that deactivate serotonin by breaking it down into simpler chemicals, in turn prolong serotonin activity. o Endorphins reduce pain and increase feelings of well-being. They bind to the same receptors as the ones activated by opiate drugs- opium and morphine, which produce similar psychological effects. o Most neurotransmitters have their excitatory or inhibitory effects only on specific neurons that have receptors for them. Sept 19, 2012 Neuromodulators have a more widespread and generalized influence on synaptic transmission. These substances circulate thru the brain and modulate the sensitivity of thousands, millions of neurons to their specific transmitters. They play important roles in functions such as eating, sleeping and stress. The Nervous System Sensory neurons: carry input messages from the sense organs to the spinal cord and brain Motor neurons transmit output impulses from the brain and spinal cord to the muscles and organs Interneurons linking the input and output functions, more than sensory and motor neurons, perform connective or associative functions within the nervous system. Nervous system can be broken down into interrelated subsystems: central nervous systemall the neurons in the brain and spinal cord, and the peripheral nervous system all the neurons that connect the central nervous system with the muscles, glands and sensory receptors. THE PERIPHERAL NERVOUS SYSTEM Its specialized neurons help to carry out the input and output functions that are necessary for us to sense what is going on inside and outside our bodies.  The Somatic Nervous System o Consist of sensory neurons that transmit messages from eyes, ears and other sensory receptors, and the motor neurons that send messages from the brain and spinal cord to the muscles that control our voluntary movements. o Allows you to sense and respond to your environment  The Autonomic Nervous System o Controls the glands and the smooth muscles that form the heart, the blood vessels, and the lining of the stomach and intestines involuntary functions ie) respiration, circulation and digestion. Also involved in motivation, emotional behavior and stress responses. o Subdivisions: sympathetic nervous system: activation or arousal function. It tends to act as a total unit  one situation (eg; stress) brings many more reactions o Subdivisions: parasympathetic nervous system: slows down body processes and maintains/returns to the resting state. Eg. Sympathetic nervous system speeds up heart rate; whereas parasympathetic nervous system slows it down maintaining homeostasis. Sept 19, 2012 THE CENTRAL NERVOUS SYSTEM Contains spinal cord, which connects most parts of the peripheral nervous system with the brain, and the brain itself.  The Spinal Cord o 40-45 cm long, 2.5 cm in diameter. Protected by the vertebrae (bones of the spine) o simple stimulus-response sequeneces—spinal reflexes can be triggered at the level of the spinal cord w/o any involvement of the brain. This is good because you don’t have to wait for the brain to tell you what to do, that will take longer time. Spinal reflexes reduce reaction time.  The Brain o Requires 20% of oxygen intake in resting state. It never rests. The rate of energy metabolism is relatively constant day and night.  Unlocking the Secrets of the Brain o Neuropsychological tests  To measure verbal and non-verbal behaviors that are known to be affected by particular types of brain damage.  Trail making test o Destruction and Stimulation Techniques  Research can produce brain damage under carefully controlled conditions specific nervous tissue is destroyed with electricity, with cold or heat, or with chemicals.  Also surgically remove a portion of the brain. o Electrical Recording  Electrodes “eavesdrop” electrical conversations in the brain.  inserting small electrodes into particular areas of brain or individual neurons.  Placing large electrodes on the scalp to measure the activity of large groups of neurons with the electroencephalogram (EEG).  Specific EEG patterns correspond to certain states of consciousness, such as wakefulness and sleep.  also detect abnormal electrical patters like in brain disorders.  Changes in the EEG that accompany such events are called event-related potentials (ERPs) o Brain Imaging  Imaging techniques that peer into the living brain.  CT scans, PET scans, and MRI. CT and MRIs are used to visualize brain structure, whereas PET and fMRI allow scientists to view brain activity  CT use X-ray technology to study brain structures. Highly focused beam of X-rays takes pics of narrow slices of the brain. Sept 19, 2012 Pinpointing where injuries have occurred helps to clarify relations b/w brain damage and psychological functioning.  PET measure brain activity, including metabolism, blood flow, and neurotransmitter activity. Inject patient with radioactive glucose into bloodstream, travels to the brain. The energy emitted by the radioactive substance is measured bye the PET. Researchers see how active particular neurons are by using the PET scan to measure the amt of radioactive glucose that accumulates in them researchers can tell by the glucose concentration pattern which parts of the brain were activated.  brain activity in relation to cognitive processes, behavior, mental illness can be studied  MRI combines features of CT and PET, used to study both brain structures and brain activity. It creates images based on how atoms in living tissue respond to a magnetic pulse delivered by the device. It distinguishes much better b/w different types of brain tissue. THE HIERARCHICAL BRAIN: STRUCTURES AND BEHAVIORAL FUNCTIONS Structures at the brain’s core govern the basic physiological functions breathing and heart rate, that keeps us alive.  more complex functions: sensing, emoting, wanting, thinking, reasoning. The crowning feature of brain development is the cerebrum, making you a unique human being. The Hindbrain Spinal cord enlarges to form the structures that compose the stalklike Brain stem. Attached to the brain stem is the other major portion of the hindbrain, the cerebellum  The brain stem: life support systems o Medulla-first structure after leaving the spinal cord. It plays an important role in body functions heart rate and respiration. They function automatically b/c of medulla. o Medulla is also a two-way thoroughfare for all the sensory and motor nerve tracts coming up from the spinal cord and descending from the brain. o The Pons lies above the medulla, serving as a bridge carrying nerve impulses b/w higher and lower levels of the nervous system. It has clusters of neurons that regulate sleep (involved in dreaming). It also contains motor neurons that control the muscles and glands of the face and the neck. It helps to control vital functions like medulla as well  The Cerebellum: Motor coordination centre o Attached to the rear of the brain stem directly above the pons o Concerned primarily with muscular movement coordination, as well as certain types of learning and memory. Sept 19, 2012 o Specific motor movements’ timing and coordination depend on the cerebellum. It regulates complex, rapidly changing movements that require exquisite timing. o The motor control functions of the cerebellum are easily disrupted by alcohol  producing coordination difficulties jerky, uncoordinated movements.  The Midbrain o Contains clusters of sensory and motor neurons as well as many sensory and motor fibre tracts that connect higher and lower portions of the nervous system. o Sensory portion contains important relay centers for the visual and auditory systems. o Motor neurons control eye movements.  The reticular formation: The brain’s gatekeeper o Acts as a sentry, both alerting higher centres of the brain that messages are coming and filter the messages. o Ascending part sends input to higher regions of the brain to alert it o Descending part through which higher brain centers can either admit or block out sensory input. o Role in consciousness, sleep and attention. By deactivating neurons of the ascending reticular formation, it produces a state of unconsciousness. o Severe damage to the reticular formation can produce a permanent coma. The Forebrain Consists of 2 large cerebral hemispheres, left and right that wrap around the brain stem. The outer portion of the forebrain has a thin covering—cortex,  The thalamus: The brain’s sensory switchboard o Located above the midbrain o An important sensory relay station that organizes inputs from sense organs and leads them to the appropriate areas of the brain o Visual auditory and body senses all have major relay stations in the thalamus. . nerve tracts from the sensory receptors are sent to specific areas of the thalamus. There they synapse with neurons that send the messages on their way to the higher brain region that create our perceptions. o Malfunctioning of thalamus could cause confused thinking and disordered attention schizophrenic  The basal ganglia: Movement o Five distinct structures. Critical for voluntary motor control. o Parkinson’s disease: the neurons that supply dopamine (voluntary motor control) to the basal ganglia degenerate and die.  The hypothalamus: Biological drives Sept 19, 2012 o Consists of tiny groups of neuron cell bodies that lie at the base of the brain, above the roof of the mouth o Controls many different basic biological drives sexual behavior,
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