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Today in class • Notes • Writing assignment • Vocabulary Activity • Reminder – quiz tomorrow • Reminder – candy neuron tomorrow – bring candy 1 Neurons and Neuronal Communication: The Structure of a Neuron There are billions of neurons (nerve cells) throughout the body. 2 Action potential: a neural impulse that travels down an axon like a wave Just as “the wave” can flow to the right in a stadium even though the people only move up and down, a wave moves down an axon although it is only made up of ion exchanges moving in and out. 3 When does the cell send the action potential?... when it reaches a threshold The neuron receives signals from other neurons; some are telling it to fire and some are telling it not to fire. When the threshold is reached, the action potential starts moving. Like a gun, it either fires or it doesn’t; more stimulation does nothing. This is known as the “all-ornone” response. How neurons communicate (with each other): The action potential travels down the axon from the cell body to the terminal branches. The signal is transmitted to another cell. However, the message must find a way to cross a gap between cells. This gap is also called the synapse. The threshold is reached when excitatory (“Fire!”) signals outweigh the inhibitory (“Don’t fire!”) signals by a certain amount. 4 The Synapse The synapse is a junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The synapse is also known as the “synaptic junction” or “synaptic gap.” 5 Neurotransmitters Neurotransmitters are chemicals used to send a signal across the synaptic gap. 6 Reuptake: Recycling Neurotransmitters [NTs] Reuptake: After the neurotransmitters stimulate the receptors on the receiving neuron, the chemicals are taken back up into the sending neuron to be used again. 7 Neural Communication: Seeing all the Steps Together 8 Roles of Different Neurotransmitters Some Neurotransmitters and Their Functions Neurotransmitter Function Problems Caused by Imbalances Serotonin Affects mood, hunger, sleep, and arousal Undersupply linked to depression; some antidepressant drugs raise serotonin levels Dopamine Influences movement, learning, attention, and emotion Oversupply linked to schizophrenia; undersupply linked to tremors and decreased mobility in Parkinson’s disease and ADHD Acetylcholine (ACh) Enables muscle action, learning, and memory ACh-producing neurons deteriorate as Alzheimer’s disease progresses Norepinephrine Helps control alertness and arousal Undersupply can depress mood and cause ADHD-like attention problems GABA (gammaaminobutyric acid A major inhibitory neurotransmitter Undersupply linked to seizures, tremors, and insomnia Glutamate A major excitatory neurotransmitter; involved in memory Oversupply can overstimulate the brain, producing migraines or seizures; this is why some people avoid MSG (monosodium glutamate) in food 9 Serotonin pathways Networks of neurons that communicate with serotonin help regulate mood. Dopamine pathways Networks of neurons that communicate with dopamine are involved in focusing attention and controlling movement. 10 Hearing the message How Neurotransmitters Activate Receptors When the key fits, the site is opened. 11 Keys that almost fit: Agonist and Antagonist Molecules An agonist molecule fills the receptor site and activates it, acting like the neurotransmitter. An antagonist molecule fills the lock so that the neurotransmitter cannot get in and activate the receptor site. 12 Recap The Structure of the Neuron • Basic Building block of the nervous system • Consist of cells specialized for rapidly Part communicating Function information DENDRITES RECEIVE INFORMATION FROM ADJOINING NEURONS SOMA (CELL BODY) RECEIVES AND STORES INFORMATION WITHIN THE CELL NUCLEUS GOVERNS AND DIRECTS ACTION OF THE CELL AXON TRANSMITS NEURAL IMPULSE DOWN LENGTH OF CELL TERMINAL BUTTONS BRANCHING AT END OF AXON; CONTAINS NEUROTRANSMITTERS 13 TYPES OF NEURONS • Sensory neurons – bring information from outside world to your brain • Motor neurons – transmit responses from brain to muscles and glands • Interneurons – Connect neurons to other neurons – Join sensory and motor neurons in spinal cord 14 Synapses • What are synapses – part of the structure of the Neuron • What is the purpose of synapses? –They are the chemical (neurotransmitter) connections between ALL neurons So can you describe the structure of the Neuron? No, not yet. 15 Next Question… • What is the purpose of Glial cells? – Fact – most numerous cells within the nervous system – Fact – Like glue – holding neurons together – Fact – assist and support activity of neurons – Fact – forms the myelin sheath (covering of the axon) –The myelin sheath – what is the myelin sheath? 16 Myelin Sheath • Fatty, protective covering on neuron axons • Forms over time, usually by age of 12 • Nodes of Ranvier (gaps in myelin sheath) – neural impulse may jump from node to node • Fact – Multiple sclerosis (MS) – a condition that occurs from the destruction of myelin sheath 17 How Neurons Communicate • Ions involved: sodium, potassium, and chloride • Resting potential – neuron not activated; cell has slightly negative charge • Depolarization – stimulation leads sodium to enter cell; electrical charge now changed from negative to positive • Action Potential – neuron fires down length of axon; called a neural impulse 18 Importance of Neurotransmitters • Synapse is tiny gap between one neuron and the next • At synapse, the impulse changes from electrical to chemical • Neurotransmitters are these chemical messengers across synapse • Chemicals from adjacent neurons may either excit or inhibit cell firing List 5 Neurotransmitters and explain what they do. 19 Can you do the following? Do you need your outline to do it? Take out a sheet of paper and do it. • 1. Describe the structure of a neuron. • 2. Describe the process by which an action potential is triggered. • 3. Describe how nerve cells communicate, and discuss the importance of neurotransmitters for human behavior. 20