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PSYCH 101 Unit III Neuropsychology

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University of Waterloo
Richard Ennis

PSYCH 101 Unit III:  Neuropsychology  The 2 Requirements for Interacting with the Environment: • There are two requirements for interacting with the environment: 1. Sense and perception (afferent):  We must be able to observe the information from the external world and somehow bring it into our own minds  The act of being able to detect and observe this information is an AFFERANT process 2. Response (efferent):  After the information from the outside world is detected/observed, we also need to be able to respond to it in order to survive  This act of response to the information by the external world is an EFFERENT process Diagram of a Neuron: • The above is a neuron, otherwise known as a brain cell • It has 3 important biological parts: 1. Cell Body: keeps the cell alive (i.e. its support center) 2. Dendrites: involved in bringing information (afferent process) into the cell body 3. Axon: involved in the passing of messages (efferent process) from the cell body to other neurons, muscles, or glands Types of Neurons: • Sensory Neurons (2-3 million present) o Carry messages in from body’s sensory receptors to the central nervous system for processing o This is an afferent process, since it is bringing the information from the outside world inward to the brain • Motor Neurons (2-3 million present) o Carry instructions out of the central nervous system to the body’s muscles/glands o This is an efferent process, since it is bringing the information out of the brain and towards the muscles/glands to elicit a response • Interneurons (10-100 billion present) o Reside in the brain and within the spinal cord, acting to process information between sensory and motor neurons o These neurons are within the central nervous system and act as a link to interact with other neurons The Brain’s Numbers & Connections: • The brain has 100 billion neurons • 100 trillion connects are present between neurons • 621, 000m in length if all the connected neurons were laid end-to-end • Neurons in the brain ultimately connect with one another to form many networks o The brain learns by modifying certain connections in response to feedback, allowing very specific skills to develop Galvani’s Experiment: Proving the Electrical Component of Nerve Impulses • Galvani proposed a theory that neurons communicate with one another and to other parts of the body through the use of electrical impulses • His experiment used a dead frog and an electrode was attached to its leg • When he ran electricity through the electrode, the electricity went through the frog’s leg and made it jump • His theory was correct, but why did it occur? o When electricity stimulates a neuron, if it is strong enough, it will depolarize the neuron and cause action potential (i.e. a neural impulse) o The depolarization produces another action potential further down along the axon, causing gates of the neighbouring region to open  Charged ions of sodium and potassium rush in and are pumped out by membrane pumps of the cell o As the action potential continues down the axon, the first section is now recharged o Direction of the action potential is directed toward the axon terminal Loewi’s Experiment: Proving the Chemical Component of Nerve Impulses • Loewi puts an electrical stimulator to the heart that is immersed in distilled water o Naturally the heart begins to beat at this point • But then he takes the distilled water in the first heart’s container, which is now electrically charged, and pours it on a second heart in a different container • The second heart surprisingly began to beat, illustrating that there was something in the water that could influence the heart to beat o i.e. a neurotransmitter, a substance that could carry out the transmission of neuron signals • The experiment essentially proved that a direct current of electricity wasn’t the sole cause of the heart’s beating, but rather it was the water that was acting as a medium (transmitter) carrying the electricity to allow the heart to beat Finally, the Hodgkin-Huxley Model: The Electrical-Chemical Model • This theory married both the electrical and chemical models together • It argues that an electrical process is within the neuron, but when neurons pass messages from one another that electric signal is mediated by a chemical process o The chemical process is through the neuron’s use of neurotransmitters • Neurons are separated by synaptic gaps, which is where neurotransmitters travel through to go to the receptor of a receiving neuron to communicate their carried electrical signal towards The Synapse & Neurotransmitters: • Synapse: o A junction between the axon tip of the sending neuron and the dendrite of a receiving neuron • Neurotransmitters: o Chemicals used to send signals across the synapse o They are released by the sending neuron and stimulate the receptor sites on the receiving neuron, telling it whether or not to fire the next action potential o Neurotransmitters are all different and uniquely fit into the receptor site of the receiving neuron’s dendrites  When the match is found it will bind on  When a firing threshold is achieved, where a certain number of neurotransmitters from another neuron bind onto the receptors of the receiving neuron, it will exhibit an action potential How do Neurotransmitters Activate Receptors: • There are many different neurotransmitter molecules each with a shape/key that is specifically designed to bind onto a specific receiving neuron • If the key fits onto the receptor site of the receiving neuron, they the site is opened • Agonist and Antagonist molecules are ones that almost fit the receptor of the receiving neuron o Agonist molecules mimic neurotransmitters and fill the receptor site AND activates it on the receiving neuron o Antagonist molecules, by contrast, fill the receptor on the receiving neuron and acts to block the receptor site so that the neurotransmitter cannot bind (does not activate the receptor though) What Happens After Synaptic Transmission? • One of three possibilities may occur: 1. Neurotransmitter is decomposed by a specific enzyme 2. Reuptake  Reuptake ends the transmission of the signal since the chemical is taken back up by the sending neuron to be used again 3. Continues binding Examples of Neurotransmitters: • Acetylcholine (ACh): o Involved in muscle action, learning, and memory o In Alzheimer’s disease, neurons that use ACh are deteriorated • Dopamine: o Influences movement, learning, attention, and emotion (typically to make a person feel good) o Fluctuates within normal levels when not engaged in activities that would otherwise make us feel good, but if it’s too high or too low then…  Oversupply = schizophrenia  Undersupply = Parkinson’s Disease (treated with L-DOPA) • Serotonin: o Influences mood, hunger, sleep, and arousal o Undersupply = depression • Epinephrine & Norepinephrine: o Antagonistic transmitters that influence alertness, arousal, and mood o Same chemical used in endocrine system (adrenaline and noradrenaline) • Endorphin: o Body’s natural pain-killer o Also involved with emotions in limbic system (e.g. pain, pleasure, tension, etc.) Neurotransmitters & Addiction: • Cocaine and amphetamine: o Stimulants that increase release of norepinephrine and block reuptake of dopamine o Perceived as pleasurable and associated behaviours are reinforced • Opiates (opium, morphine, heroine, codeine) o Agonists that mimic endorphins by attaching to their binding sites o Blocks pain, but also transmit pleasure • Alcohol o A depressant that decreases neural activity throughout the brain, especially the frontal lobe of the brain Neurology of Addiction: • Brain maintains homeostasis o Increases or decreases neurotransmitters to compensate effect of addictive substance • Body then requires increased dosage to experience the same effect o Unoccupied sites create craving/dependence • Brain “learns” to anticipate consumption o Makes “pre-emptive” adjustment allowing an overdose to possibly occur The Peripheral Nervous System: • Nervous system  Peripheral or Central o The peripheral system can then be split into autonomic or somatic  Autonomic controls self-regulated actions of internal organs/glands • It does so by using the sympathetic nervous system (arousal) • Or the parasympathetic nervous system (calming)  Somatic controls voluntary movements of skeletal muscles Further Readings from Textbook From Module 4: Neural and Hormonal Systems The Endocrine System: • Refers to the set of glands that produce chemical messengers called hormones • Holistically, the body uses a feedback system: brain  pituitary  other glands  hormones  body and brain o Illustrates an intimate connection between the brain and the endocrine system, whereby the brain directs the endocrine system, but then the endocrine system in turn affects the nervous system • The endocrine system includes: o Hypothalamus – brain region that controls pituitary gland o Pituitary gland – secretes many different hormones, some of which affect other glands o Thyroid gland – influences metabolism o Parathyroids – regulates the level of calcium in blood o Adrenal glands – triggers fight or flight response o Pancreas – regulates sugar in the blood level o Testis (male) –secretes male sex hormones o Ovary (female) – secretes female sex hormones From Module 5: Tools of Discovery & Older Brain Structures Tools to Monitor Activities in the Brain: • Electroencephalogram (EEG): o Records the
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