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Chapter 3

PSYCH 1100E Chapter 3: Biological Foundations of Behaviour

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Psychology 1000
Mark Cole

Chapter 3: Biological Foundations of Behaviour Neuroscience:  Studies the connection between the brain, the mind, and behaviour  Only relatively recently the brain was considered important for thought, feeling, personality CHAPTER 3: Learning Objectives – The Nervous System Understanding of neural communication:  Structure of the neuron  Electrical transmission and the action potential  Chemical transmission and neurotransmitters Differentiate different levels of the nervous system  Peripheral nervous system o Somatic nervous system o Autonomic nervous system  Sympathetic nervous system  Parasympathetic nervous system  Central nervous system o Spinal cord o Brain BRAIN CELLS  Neurons transmit information  Interneurons connect neurons together  Glial cells outnumber neurons 10:1, and support neurons by: o Protecting brain from toxins o Forming blood-brain barrier o Getting rid of neuron waste o Creating myelin TYPES OF NEURONS  Afferent neurons (sensory)—relay information from the senses to the brain and spinal cord.  Efferent neurons (motor)—send information from the central nervous system to the glands and muscles, enabling the body to move.  Interneurons—carry information between neurons in the Central Nervous System. PARTS OF A NEURON  Axon transmits information to as many as 50,000 other neurons  Axon terminals are at the end of axons and form synapses with other neurons  Myelin sheath, made of fatty substance produced by glial cells, acts as insulator so impulses are sent more efficiently. o Not completely formed at birth. o Filling in of myelin helps account for cognitive abilities, improved movement o Multiple sclerosis is a disease where the immune system attacks and destroys the myelin… results in uncoordinated movement, paralysis  Dendrites are branches that extend from the cell body and receive most of the information from other neurons NEURONAL TRANSMISSION  Neurons generate electricity and release chemicals.  In the neuron’s resting state, the resting potential, we call the neuron polarized. Its resting potential’s charge is 70 mv.  Graded potentials happen as a result of the negative charge of the neuron changing, but not enough to set off an action potential.  An action potential is a neural impulse: the neuron becomes active, it fires. o The threshold for a neuron firing at action potential is -55 mv.  Synapses are subject to the all-or-nothing law: the neuron either fires or it doesn’t; it cannot half-fire. HOW THE ACTION POTENTIAL OCCURS  The permeability of the cell membrane increases  This process allows IONS (electrically charged atoms or molecules) to easily move into and out of the axon  Inside the axon, there are normally more negative than positive ions. When at rest (not firing), a neuron carries a negative electrical potential (or charge) relative to the fluid outside the cell. This slight negative charge is the neuron’s resting potential.  Depolarization: When a neuron is sufficiently stimulated by an incoming signal, ion channels open in the cell membrane, allowing positive sodium ions to go INTO the axon. o When polarized, the charge of the neuron is -70 o When depolarized, the charge of the neuron is +40 o This inflow of positive ions causes the membrane potential (charge) to change to a positive value  This sudden and brief reversal is called the action potential  After the action potential, the potassium ions are pumped back out and sodium comes back in. The neuron is ready again for action potential.  Absolute refractory period: recovery period when K+ flows out of the membrane. The membrane is not excitable at this time. DISCRIMINATING STIMULI  If neurons fire in the same way, how do we discern between dim light and strong light?  What changes is the rate of firing (frequency) and the number of neurons firing. SUMMARY OF ELECTRICAL TRANSMISSION  Neuron generates electrical impulse  Action potential caused by changes in concentration of negative and positive ions  Electrical impulse travels down myelin-covered axon until it reaches the axon terminals SYNAPSES  Synapse: the junction where the axon of a sending neuron communicates with a receiving neuron across the synaptic cleft  Presynaptic neurons send messages; postsynaptic receive them  Lock-and-key effect: Receptor sites have specialized spaces where only certain neurotransmitters fit. EFFECTS OF NEUROTRANSMITTERS  Excitatory neurotransmitters increase likelihood of action potential  Inhibitory neurotransmitters decrease likelihood of action potential (make the neuron more negative inside rather than depolarizing to positive)  Excitatory postsynaptic potential (EPSP) is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell. Makes the neuron more likely to fire. DEACTIVATION OF NEUROTRANSMITTERS  Breakdown: Chemical breakdown of neurotransmitters into chemical components  Reuptake: Neurotransmitters taken back into presynaptic neuron to be used after their excitatory or inhibitory effect TYPES OF NEUROTRANSMITTERS Acetylcholine (ACh) Serotonin  Memory  Mood disorders  Muscle activity  Depression (low)  Low ACh related to Alzheimer’s Dopamine Endorphins  Parkinson’s disease (low)  Painkiller  Schizophrenia (high)  Natural “high”  Mood  Motor control DRUGS  Bind to receptors and imitate neurotransmitters o Opium binds to endorphin receptors, you feel a high o Antidepressants bind to serotonin receptors, imitate serotonin “CUSTOM DESIGNED NEURONS”  Relevant to stem cell research  Stem cells are “starter cells” from fetuses; they can become anything  Stem cells can be put in the brain and they will become the cells around them  This can help treat Parkinson’s o Stem cells become neurons that produce dopamine, which is needed with Parkinson’s o Brains are very receptive to transplant, unlike heart/lung transplants o Treatment takes many years to develop, take effect, gain approval THE NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM SOMATIC NERVOUS SYSTEM  Sensory neurons send messages from senses to brain  Motor neurons control our movement, voluntary actions  Consists of things of which we are constantly aware and over which we have control AUTONOMIC NERVOUS SYSTEM  Involuntary functions – blood vessels, heart, things we’re not aware of  Sympathetic nervous system: Arouses or increases function (e.g: dilates pupil, accelerates heart) o Takes over during “fight or flight,” or under stress  Parasympathetic, contrastingly, slows things down to regain equilibrium o Homeostasis: a state of balance CENTRAL NERVOUS SYSTEM SPINAL CORD  Connects brain with the rest of the body  Neurons in spinal cord are protected by vertebrae  Interneurons connect sensory neurons to motor neurons o Spinal reflex: behaviour that occurs with no input from the brain at all. (E.g: Touch a hot stove, nerve impulses connect with interneurons and then motor neu
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