Week 2 Summary - Brain and Behaviour PDF

Week 2 Summary WEEK 2: Biological aspects of Psychology 1 Week Objective 1: Describe the basic structure of neurons (pp. 75-76) Neurons respond to environmental changes by means of three special features: 1. Axons are fibres that carry signals away from the neuron to points where communication occur...

Week 2 Summary WEEK 2: Biological aspects of Psychology 1 Week Objective 1: Describe the basic structure of neurons (pp. 75-76) Neurons respond to environmental changes by means of three special features: 1. Axons are fibres that carry signals away from the neuron to points where communication occurs with other neurons. Neurons generally have just one axon. 2. Dendrites are fibres that receive signals from the axons of other neurons and carry those signals to the cell body. A neuron can have many dendrites. Neurons have ‘excitable’ surface membranes on some of their fibres. 1. Synapses (or synaptic gaps) are tiny spaces between neurons. Weekly Objective 2: Describe the electrical and chemical processes involved in transmission of information between neurons (pp. 76-80) The neuron’s membrane is a semipermeable barrier that keeps positively charged molecules from freely entering the axon through the gates or channels. As a result, the membrane becomes electrically polarised, such that the inside of the cell is more negatively charged than the outside. However, positively charged molecules are attracted to negatively charged ones, creating an electrochemical potential during which positively charged molecules are driven toward the inside of the cell. Some part of the axon membrane becomes depolarised, causing a gate (channel) to open. Positively charged ions rush into the axon, causing the neighbouring gates to open as well, and more positive ions rush in. When this sudden wave of electrochemical changes, called an action potential, shoots down an axon, the neuron is said to have ‘fired’. The neuron either fires or does not fire in an all-or-none type of signal. • • Action potentials can also occur in dendrites. Action potentials beginning in axons may go down the axon but also backward through the cell body and into some dendrites. It is suspected that this activity is connected to strengthening connections between neurons important to learning and memory. The speed of the action potential is constant as it travels down the axon. If a neuron is larger or is coated with myelin, a fatty substance, action potentials will be faster. • There is a rest between firings called a refractory period during which the neuron resets itself. After it repolarises, the neuron can fire again. Synapses and Communication between Neurons Usually communication between neurons occurs at the synapse. The axon of one cell delivers signals across the synapse to dendrites of another neuron which then transmit the signals to the cell body. Axons can also signal to other axons or the cell body of another neuron. In addition, dendrites of one cell can send signals to dendrites of other neurons. Neurotransmitters Neurotransmitters are chemicals that carry signals across the synapse to the postsynaptic cell. When an axon potential reaches the end of an axon, neurotransmitters, which are usually stored in bags, called vesicles at the ends of axons, are released. Neurotransmitters bind to proteins called neural receptors (or simply receptors) on the postsynaptic cell. Neurotransmitters only bind to their own specific receptors in a lock-and-key type of fit. Each neurotransmitter can bind to several different receptor types and can have different effects depending on the type of receptor to which it binds. Excitatory and Inhibitory Signals When a receiving or postsynaptic cell is reached by a neurotransmitter, a change called a postsynaptic potential makes the cell either more or less likely to fire again. A depolarised membrane will cause an excitatory postsynaptic potential (EPSP) and the neuron will be likely to fire an action potential. A hyperpolarised membrane will cause an inhibitory postsynaptic potential (IPSP) and the neuron will be less likely to fire. Postsynaptic potentials alone fade as they spread across the postsynaptic neuron. It is the combined impact of the many EPSPs and IPSPs at the junction of the axon and cell body that determines whether or not an action potential will occur. Weekly Objective 3: Explain how the major neurotransmitters can affect thoughts and behaviour (pp. 80-85) Neurons in the brain and spinal cord are organised into groups called neural networks Neurons within a network communicate with each other. Networks send signals to each other and smaller networks are organised into larger ones. It is the activity of groups of neurons firing in various combinations that underlies different patterns of thought and behaviour. Sensory systems (or senses) provide input about the environment via the five senses. Motor systems direct the response to the environment by influencing the muscles and other organs. The nervous system has two major divisions. The central nervous system (CNS) processes information and is encased in bone. The CNS is made up of the brain and spinal cord. The peripheral nervous system (PNS) runs throughout the rest of the body and relays information to and from the CNS. The Peripheral Nervous System: Keeping in touch with the world The peripheral nervous system has two components, each of which performs both sensory and motor functions. 1. The Somatic Nervous System. The somatic nervous system carries information from the senses to the CNS and sends movement instructions back to the muscles that move the skeleton. Sensory neurons bring information into the brain. Motor neurons carry information from the brain to direct motion. 2. The Autonomic Nervous System. The autonomic nervous system carries messages back and forth between the CNS and the body’s organs and glands. It has two divisions. The sympathetic nervous system mobilises the body for action through the fight-or-flight syndrome. The parasympathetic nervous system does the opposite: it slows organ and gland activity to conserve the body’s energy. The Central Nervous System: Making sense of the world The central nervous system (CNS) is made up of groups of neuronal cell bodies called nuclei and the fibre tracts (or pathways) of axons that connect them. The Spinal Cord The spinal cord carries messages to and from the brain. Reflexes are quick, involuntary muscular responses that are initiated on the basis of incoming sensory information that occur in the spinal cord without instruction from the brain. The brain is informed of each reflex after it occurs. The spinal is an example of a feedback system, a process in which information about an action’s results are conveyed back to the source of the action so that further adjustments to the activity can be made. In the spinal cord sensory neurons are afferent neurons and carry information toward the brain. Motor cord neurons are efferent neurons and carry information away from the brain. Major Neurotransmitters (pp. 109-112) Table 1. Major Neurotransmitters and How They Affect Behavior Neurotransmitter Involved in Potential Effect on Behavior Neurotransmitter Involved in Potential Effect on Behavior Acetylcholine Muscle action, memory Increased arousal, enhanced cognition Beta-endorphin Pain, pleasure Decreased anxiety, decreased tension Dopamine Mood, sleep, learning Increased pleasure, suppressed appetite Gamma-aminobutyric acid (GABA) Brain function, sleep Decreased anxiety, decreased tension Glutamate Memory, learning Increased learning, enhanced memory Norepinephrine Heart, intestines, alertness Increased arousal, suppressed appetite Serotonin Mood, sleep Modulated mood, suppressed appetite