Neurons and Synapses - Google Docs.pdf
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†eurons and Synapses‬ N â€Nervous system is a network of neurons that run throughout your brain and body.‬ â€â€¬ â€nerves—collections of neurons—carry signals to and from your brain,‬ â€relating perceptions, thoughts, and feelings into actions.‬ â€â€¬ â€Spina...
†eurons and Synapses‬ N â€Nervous system is a network of neurons that run throughout your brain and body.‬ â€â€¬ â€nerves—collections of neurons—carry signals to and from your brain,‬ â€relating perceptions, thoughts, and feelings into actions.‬ â€â€¬ â€Spinal cord: major bundle of nerves that connects your body to your brain‬ â€â€¬ â€The nervous system also allows us to have some important behaviors such as‬ â€reflexes without requiring the brain at all‬ â€Neuron Fundamentals‬ â€â€¬ â€Neuron = Nerve cell in the brain & nervous system‬ â€â—‹â€¬ â€Sensory neuron: Carry messages from sensory organs to CNS. Carry‬ â€information from within your body and the outside world to your brain‬ â€â—‹â€¬ â€Interneuron: Carry messages from one set of neurons to another. They‬ â€interpret, store, and retrieve information about the world, allowing you to‬ â€make informed decision before you act‬ â€â—‹â€¬ â€Motor neuron: Carry messages from CNS to muscles and glands‬ â€Divisions of the Nervous System‬ â€â€¬ â€The central nervous system consists of the brain and spinal cord. The peripheral‬ â€nervous system has two divisions: the somatic nervous system and the autonomic‬ â€nervous system.‬ â€â€¬ â€Somatic nervous system is related to voluntary commands-or commands that we‬ â€choose to do‬ â€â—‹â€¬ â€not only senses the body, but also controls your conscious body movements‬ â€â—‹â€¬ â€includes your skeletal muscles.‬ â€â€¬ â€Autonomic nervous system is related to involuntary commands, those largely not in‬ â€your control‬ â€â—‹â€¬ â€maintains the operations of the inside of your body-for example, your‬ â€heart-and is mostly outside of your conscious control.‬ â€â—‹â€¬ i†ncludes your organs, blood vessels, and glands, which are‬ â€hormone-secreting organs‬ â€â—‹â€¬ â€branches into the sympathetic and parasympathetic nervous systems‬ â€â€¬ â€sympathetic branch ensures that your body provides essential‬ â€resources needed for the fight-or-flight response,‬ â€â€¬ â€To make fight-or-flight possible, your body redirects energy‬ â€from processes that are not essential in the moment, such as‬ â€digestion and sexual reproduction.‬ â€â€¬ â€acts on blood vessels, organs, and glands in ways that prepare‬ â€the body for action, especially in life-threatening situations‬ â€â€¬ â€The parasympathetic nervous system acts on blood vessels, organs,‬ â€and glands in a way that returns the body to a resting state by both‬ â€counteracting and complementing the actions of the sympathetic‬ â€system.‬ â€â€¬ â€The restorative function of the rest-and-digest response allows‬ â€you to regenerate the energy that your body needs when it is‬ â€safe to do so. Eating is one important restorative activity.‬ â€â€¬ â€"Emotional eating" is their attempt to regulate stress by‬ â€engaging the parasympathetic nervous system's anti-stress‬ â€response.‬ â€â€¬ â€Although often working in opposition to each other, the sympathetic‬ â€and parasympathetic nervous systems work together to prepare the‬ â€body for the challenges that the brain sees lying ahead.‬ â€The Structure of Neurons‬ â€â€¬ â€Cell Body: The cell body collects neural impulses, contains the nucleus, and provides‬ â€life-sustaining functions for the cell‬ â€â€¬ â€Dendrites : receive chemical messages‬ â€from other neurons.‬ â€â€¬ â€The axon: transports electrical impulses‬ â€called action potentials to the terminal‬ â€branches, where they are converted into‬ â€chemical messages that are sent to‬ â€other neurons.‬ â€â€¬ â€Myelin: is a layer of fatty tissue that‬ â€covers and insulates the axon to ensure‬ â€electrical messages are kept intact and‬ â€travel quickly.‬ â€â—‹â€¬ â€Degradation of myelin, called demyelination, is a central characteristic of‬ â€neurodegenerative diseases‬ â€â—‹â€¬ â€Shrinks with aging‬ â€â—‹â€¬ â€Glia: cells that make up the myelin. Insulate, support, and nourish the neuron.‬ â€â€¬ â€Serve as cellular glue‬ â€â€¬ â€contribute to information processing during childhood development‬ â€and into adulthood‬ â€â€¬ â€Are essential for brain development, providing a scaffold along which‬ â€axons grow and guiding them to their correct location in the nervous‬ â€system‬ â€â€¬ â€Aid in the formation of neural networks: cluster of cells that work‬ â€together as a functional unit‬ â€â€¬ â€Terminal branches: convert electrical signals into chemical messages that they then‬ â€send to other neurons.‬ â€Action Potential and How Nerves Fire Them‬ â€â€¬ â€Neurons are bathed in extracellular fluid composed of positively and negatively‬ â€charged particles or ions (sodium (NA+), chloride (Cl-), potassium (k+), and calcium‬ â€(CA2+))‬ â€â€¬ â€The membrane that separates the intracellular (inside the cell) and extracellular‬ â€(outside the cell) fluids is selective, which means that only certain ions can pass‬ â€through the membrane to the inside of a neuron‬ â€â€¬ â€Normally, at resting potential, positively charged ions are outside the cell so the‬ â€intracellular fluid is relatively positive compared to the negative intracellular‬ â€environment‬ â€â—‹â€¬ â€A neuron cannot fire an action potential as long as this resting potential is‬ â€strongly negatively polarized‬ â€â€¬ â€If a neuron is stimulated sufficiently to pass its voltage threshold, an action potential‬ â€fires‬ â€â—‹â€¬ â€When other neurons sufficiently stimulate a neuron’s dendrites ion changes‬ â€open allowing positively charged sodium (Na + ) ions into the neuron. As‬ â€these positively charged ions flood into the neuron, they set off a chain‬ â€reaction as they spread down the axon, causing more channels to open.‬ â€1)‬ â€Depolarization: occurs when the voltage of a‬ â€neuron becomes less negatively polarized and‬ â€moves toward and past a critical voltage threshold‬ â€to fire an action potential.‬ â€a)‬ â€positive ions flowing into the axon.‬ â€2)‬ â€Voltage threshold: the critical voltage(around -50‬ â€millivolts) that the neuron must reach to fire an‬ â€action potential. The neuron's voltage then surges‬ â€rapidly and becomes positive as it passes zero.‬ â€3)‬ â€Repolarization: occurs as the neuron returns to its‬ â€resting state voltage‬ a†)‬ â€positive ions flowing out of the axon.‬ â€4)‬ â€Refractory period: is the time required before a neuron is able to fire its next action‬ â€potential‬ â€a)‬ â€during which it is difficult or impossible to get a neuron to fire an action‬ â€potential again‬ â€Neuron Signals‬ â€One of two kinds: Excitatory or Inhibitory‬ â€â€¬ â€excitatory messages: move the voltage of the neuron closer to its threshold.‬ â€â€¬ â€inhibitory messages: move it farther away from its voltage threshold.‬ â€â—‹â€¬ â€If the excitatory (positive/+) messages outweigh the inhibitory (negative/-)‬ â€messages enough to reach the voltage threshold, then the neuron fires an‬ â€action potential‬ â€â—‹â€¬ â€If the neuron receives many inhibitory (negative/-) signals, it is much less‬ â€likely to reach the threshold necessary for firing.‬ â€Neurotransmission: How Neurons Communicate‬ â€Synapse: The gap where a sending neuron communicates with the‬ â€dendrites or the cell body of the receiving neuron‬ â€â€¬ â€The process of neurotransmission allows the electrical‬ â€message to bridge the synaptic gap by converting the‬ â€electrical signal into a chemical one, thus allowing neurons‬ â€to transmit their signals to one another.‬ â€â€¬ â€Electrical-to-chemical translation is critical for‬ â€communication between neurons-from the sending‬ â€presynaptic neuron's terminals to the receiving postsynaptic‬ â€target neuron's dendrites‬ â€â€¬ â€Without making anatomical contact, the terminal branches‬ â€release chemical messengers called neurotransmitters ,‬ â€across the synaptic gap toward the target, receiving neuron‬ â€â€¬ â€On the surface of target neurons are receptors that recognize and bind with‬ â€â€¬ â€specific neurotransmitters.‬ â€â€¬ â€Each neurotransmitter has specific receptors that‬ â€selectively recognize it.‬ â€â€¬ â€'Thus, each receptor is like a lock with a key-a‬ â€neurotransmitter-that will open it. Once the‬ â€neurotransmitter binds to its receptor ion‬ â€â€¬ â€channels open hereby inducing changes in on flow‬ â€across the target‬ â€â€¬ â€neurons cell membrane. As a result an electronic‬ â€signal is generated in the target neuron‬ â€Receptor Response to Neurotransmitters‬ â€â€¬ R †eceptors targeted by neurotransmitters produce excitatory or inhibitory electrical‬ â€signals in the target neuron‬ â€â€¬ â€Ions enter the receptor, moving the target neuron closer to or farther from its action‬ â€potential threshold‬ â€â€¬ â€The receptor's response, not the neurotransmitter itself, determines whether the‬ â€signal is excitatory or inhibitory‬ â€Neurotransmitter Inactivation‬ â€â€¬ â€Inactivation of neurotransmitters in the synapse is crucial after signal generation‬ â€â€¬ â€Prevents constant stimulation and maintains neuronal balance‬ â€â€¬ â€Mechanisms for neurotransmitter removal:‬ â€â—‹â€¬ â€a) Diffusion: Neurotransmitters drift out of the synapse into extracellular‬ â€space‬ â€â—‹â€¬ â€b) Degradation: Chemical reactions break down neurotransmitters in the‬ â€synapse‬ â€â—‹â€¬ â€c) Reuptake: Presynaptic terminals reabsorb neurotransmitters‬ â€Antidepressants and Neurotransmitter Function‬ â€â€¬ â€Some antidepressants prevent neurotransmitter reuptake‬ â€â€¬ â€Selective Serotonin Reuptake Inhibitors (SSRIs) keep neurotransmitters in the‬ â€synapse longer‬ â€â€¬ â€Can be helpful for depression but may cause side effects like upset stomach or‬ â€insomnia‬ â€Class of neurotransmitters‬ â€â€¬ â€Amino acids: such as glutamate and gamma-aminobutyric acid (GABA), are the‬ â€brain’s most abundant neurotransmitters‬ â€â€¬ M †onoamines: are important for fight-or-flight response activation‬ â€â€¬ â€Acetylcholine: can behave as both an inhibitory and an excitatory signal. It supports‬ â€heart and skeletal muscle, and cognitive function.‬