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Internal Coordination Maintenance
- Monitors internal and external environment
- Determines appropriate responses
- Sends signals muscles and glands to respond
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Central Nervous System
Brain and Spinal Cord
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Peripheral Nervous System
Nerves throughout the body that carry input to/from the brain and spinal cord
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Sensory Division in Peripheral Nervous System
Carries information from sense organs to Central Nervous System
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Motor Division in Peripheral Nervous System
Sends information from central nervous system to muscles and glands
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Somatic Nervous System
Carries information to skeletal muscles
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Autonomic Nervous System
Carries information to glands, cardiac muscles, and smooth muscle
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Sympathetic Nervous System
fight or flight in autonomic nervous system
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Parasympathetic Nervous System
Rest and digest in autonomic nervous system
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Neurons
Excitable, conduct electrical signals, communicate with other neurons through chemical means, and typically has cell body (soma), dendrites, axon
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Glia
Not usually excitable, maintains homeostasis, support neurons, and form myelin.
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Cell Body (Soma)
Includes nucleus and most other organelles; integrates all incoming info
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Dendrites
Receive signals from other neurons or environments
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Axon
Conducts electrical signal
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Axon Terminal
Releases chemical signal (neurotransmitter) to communicate with other neurons, muscles, or glands
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Microglia
Protect neurons by scavenging infections agents, damaged neurons, etc
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Astrocytes
Anchor neurons to their blood supply; scavenge excess ions; recycle neurotransmitters; convert glucose to lactate to feed neurons
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Oligodendrocytes/Schwann Cells
Wrap around axons to form myelin
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Ependymal Cells
Line ventricles of brain and produce cerebospinal fluid
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Electrical Potential in Neurons
- Uneven distribution of ions across plasma membrane because of phospholipid bilayer
- Membrane potential is usually around -70 mV (compared to ~1.5 V in AAA battery); negative indicates that the inside of the cell has more negative charge that the extracellular fluid
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Resting Membrane Potential
- Some ions can leak across the membrane through channels
- But the Na+/K+ pump pumps Na+ back out and K* back in
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Incoming Information Can Alter Membrane Potential of Dendrites
- Neurotransmitter binds to Na+ channel and opens it
- This might take membrane from -70 mV to -50 mV
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Action Potential
- When the voltage changes, it can spread to axon and trigger action potential (conduction of electrical signal down axon)
- The action potential is merely a sequence of the opening and closing of several types of ion channels that repeats down the axon
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Axon Hillock
Where the action potential begins
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Myelin
Oligodendrocytes in CNS and Schwann cells in PNS wrap around dendrite to insulate them
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Function of Myelin
- Myelin allows action potential to travel faster
- Loss of myelin causes one of several diseases (including multiple sclerosis)
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Acetylcholine
Released by motor neurons
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Amino Acids
- Glutamate: excitatory neurotransmitter
- GABA: inhibitory neurotransmitter
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Monoamines
- Dopamine: reward, movement
- Norepinephrine: attention, sympathetic NS
- Serotonin: mood, apetite, sleep, memory, intestinal contractions
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Neuropeptides
- Substance P: Pain
- Endorphins: analgesia and addiction
- Neuropeptide Y: hunger
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Depolarization
Some activated receptors (like glutamate receptors) bring membrane potential closer to action potential threshold (called depolarization of excitatory postsynaptic potential)
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Hyperpolarization (IPSP)
Some activated receptors (like GABA receptors bring membrane potential farther from action potential threshold (called hyperpolarization or inhibitory postsynaptic potential)
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Too Much Neurotransmitter Problems
Epilepsy, traumatic brain injury, huntington's disease, AIDS dementia complex, neuropathic pain, parkinson's disease, ALS, Rett syndrome, Alzheimer's, Tourettes, drug addictions, multiple sclerosis, depression, glaucoma
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Too Little Neurotransmitter Problems
Parkinson's, Depression, anxiety, obesity, anorexia, bulimia, chronic pain, migraines, ADHD, restless leg syndrome, alzheimer's
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Neurotransmitter Release is Tightly Regulated
- Some diffuses away from synapse
- Some are broken down by enzymes in synapse (MAO, COMT)
- Some taken back up into presynaptic cell to be recycled
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Integration
In reality, most neurons receive input from tons of presynaptic neurons
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