Neurons and Synapses - Google Docs.pdf

‭ eurons and Synapses‬ N ‭Nervous system is a network of neurons that run throughout your brain and body.‬ ‭‬ ‭nerves—collections of neurons—carry signals to and from your brain,‬ ‭relating perceptions, thoughts, and feelings into actions.‬ ‭‬ ‭Spina...

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