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Neurons and Synapses - Chapter 7 Nervous System

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Neurons and Synapses - Chapter 7 Nervous System Neurons and Synapses - Chapter 7 Nervous System 1. Nerve Tissue: Neurons and Glial cells 2. Neurons: Conduct electrical potentials = nerve impulse. Neurons are the functional units of nervous system. a. Dendrite Cell body axon axon terminal b. Dendrites and cell bodies receive membrane potential and conduct graded potential c. Axon hillock is conical beginning of axon and acts as trigger zone to initiate an action potential. d. Axons conduct action potentials and release neurotransmitters. 3. Glial Cells – non-conducting cells that nourish, anchor and support neurons 4. Describe 3 kinds of neurons. a. Afferent neuron – brings in information to CNS form sensory receptors. (1) b. Efferent neuron – carries information to Effectors = muscles, glands, other neurons. (10) c. Interneurons connect neurons within CNS, process information. (200,000) 5. Fig 7.5 depicts Glial Cells are non-conducting cells and have 4 kinds: a. Astrocytes have many appendages, anchor neurons, and form blood brain barrier. Astrocytes pick glucose from blood capillaries and break it into lactate. Lactate is used by neurons as source of energy. Astrocytes also remove neurotransmitter Glutamate from synapses and break it into glutamine. b. Oligodendrocytes form myelin sheath around axons in CNS and Schwann cells make neurilemma and myelin sheath in PNS. c. Microglial cells are phagocytes d. Ependymal cells line ventricles in brain and central canal in spinal cord and cover tufts of blood capillaries to form Choroid Plexus which secretes cerebrospinal fluid. 6. What is Axonal Transport? Describe its 2 types. It is movement of substances inside axon of neuron. It has 2 types: a. Slow Axonal transport moves things by cytoplasmic streaming. b. Fast Axonal Transport: Motor Molecules use ATP to move vesicles or other organelles over microtubules or microfilaments. Dynein and Kinesin are 2 types of motor molecules used in axonal transport. 7. Neuronal Growth takes place in embryo by developing axons to particular targets from Stem Cells. The cells can develop in presence of certain chemicals attached on surface of glial cells. These chemicals are Neurokines. 8. Describe functional specialization of different region in multipolar neuron. Fig 7.24 9. Important terms: Fig 7.2 axon hillock = trigger zone is the joint of axon to cell body– it generate electrical signals; blood brain barrier, neurotransmitter, synapse. 10. Short Answer: Describe spatial summation of graded potentials (fig7.33) in cell body of neuron and its role in initiating action potential. 2 or more separate sub-threshold graded potentials occurring simultaneously add together in cell body and reach threshold to stimulate an action potential. 11. Role of Na+-K+ pump in developing and maintenance of resting potential. By using 1 ATP the pump delivers 3 Na+ outside and brings in 2 K+. Therefore more + ions are present outside and more negative ions are present inside. Some K+ and Na+ leak to the opposite side due to diffusion, therefore Na+ - K+ continues to maintain resting potential at – 70mV. 12. Learn to define terms depolarization, resting potential = polarization, repolarization and hyperpolarization. 13. In unmyelinated fibers propagation of impulse is continuous but in myelinated nerve fibers due to presence of myelin ions can enter or exit nerve fiber at nodes of Ranvier. Therefore, depolarization jumps from one node to next and gets quiet faster. This propagation is called Saltatory conduction. 14. Multiple Sclerosis is the degeneration of myelin sheath of nerve fibers inside CNS by the attack of own antibodies. Therefore, it is an autoimmune disorder and affects 400,000 Americans each year, young to middle age and women get it 2 more than men. 15. Important terms include: action potential, absolute refractory period, all or none, action potential and graded potential, threshold stimulus, hyperpolarized, saltatory conduction, summation, chemical (ligand) gated and voltage gated channels. 16. Draw a nerve fiber showing Na+, K+ and Cl- ions in it and around it. Show the membrane potential. 17. Short Answer: Draw a graphic representation of a graded potential or an action potential versus time. Draw Zero line and mention which parts show resting potential, depolarization, repolarization, and hyperpolarization. 18. Short Answer: List the differences between graded and action potentials. Graded Potentials Action Potentials 1. A potential with variable amplitude and duration 1. All or None potential of small duration 2. Decremental – decreases over distance 2. Maintained over distance 3. No threshold 3. Has threshold – cannot occur below it 4. No refractory period 4. Has a refractory period – cannot occur during this period 5. Synaptic, dendritic and cell body potentials are 5. Axonal potential is action potential and starts at axon graded potentials hillock 19. Short Answer: Compare continuous and saltatory conduction. 20. Excitatory Post Synaptic Potential (ESPS) brings postsynaptic membrane closer to threshold stimulus (from – 70mV to – 60mV) 21. Inhibitory Post Synaptic Potential (ISPS) either hyperpolarizes the postsynaptic membrane or stabilizes it at resting potential so that it does not respond to normal stimulation. ( from – 70mV to – 80mV or stabilizes it at – 70mV) 22. Electrical synapses have membranes connected by gap junctions and depolarizing ions directly pass from one cell to another. Most commonly found in cardiac and smooth muscles but rare in nervous system. 23. Fig 7.23 depicts storage and release of neurotransmitter into synaptic cleft. Neurotransmitter binds to receptor proteins of postsynaptic membrane and ligand gated channels of Na+ open. Entry of Na+ ions depolarizes the postsynaptic membrane towards threshold stimulus. It results in action potential. Neurotransmitter is removed from the synapse by an enzyme. Acetylcholine is degraded by Acetylcholinesterase enzyme into acetate and choline. Monoamine oxidase enzyme breaks dopamine / norepinephrine / epinephrine. 24. Table 7.7 lists the various kinds of neurotransmitter s and neuromodulators. 25. Acetylcholine receptors also have binding sites for nicotine or muscarinine (a fungus poison). Nicotinic Ach receptors are found within the brain, autonomic ganglia and skeletal muscles. Nicotinic Ach receptors produce EPSP. Muscarinic Ach receptors are present in smooth muscles, cardiac muscles and certain glands. These produce IPSP. Alzheimer’s disease is caused due to degeneration of neurons associated with acetylcholine. 26. Catecholamines have a 6 carbon ring with 2 adjacent –OH groups and an amino group. Important catecholamines include Dopamine, norepinephrine and epinephrine. All are formed from amino acid tyrosine and result in Excitatory Post Synaptic Potentials (EPSP). These are released by neurons of brain stem or hypothalamus, fewer in # but have branches everywhere in the brain. These neurotransmitters play major role in states of consciousness, mood, motivation, directed attention, movement, blood pressure regulation, and hormone release. 27. GABA (gamma amino butyric acid) is an inhibitor and results in IPSP (Inhibitory Post Synaptic Potential). GABA makes the post synaptic membrane permeable to Cl- ions and makes the membrane hyperpolarized. The receptor for GABA has binding sites for many other chemicals including drugs like Xanax and Valium which inhibit synapses and reduce anxiety and induce sleep. These receptors also have binding sites for Ethanol = ethyl alcohol and steroids. 28. Gas neurotransmitters include Nitric oxide and Carbon monoxide. These gases are not released by vesicles nor bind to receptor proteins in synapse. These are released by some cells and diffuse to neighboring cells and bind to and activate the enzyme for changing GTP to cyclic-GMP, the 2nd messenger. Nitric oxide plays a wide role in different processes learning, development, drug tolerance and penile erection (drugs like Viagra and Cialis inhibit the enzyme used to breakdown nitric oxide). 29. Adrenergic neurons produce norepinephrine or epinephrine = adrenalin). Beta-adrenergic receptors act by stimulating G proteins and producing c-AMP. Alpha-adrenergic receptors can inhibit by presynaptic stimulation the release of norepinephrine or by post synaptic inhibition or stimulation of K+ channels. Cholinergic (neurons produce acetylcholine). 30. Important terms include: convergence (occurs from sensory receptor to CNS), divergence (occurs from CNS to effectors like muscles or glands), catecholamine, dopamine, GABA, EPSP, IPSP. 31. Important questions include: a. Contrast the mechanism of excitatory and inhibitory synapses. b. Discuss differences between neurotransmitters and neuromodulators. Hint: In general neurotransmitters affect the ion channels directly but neuromodulators act via G protein and 2nd messengers. 32. Blood – Brain Barrier: 3 meninges Dura mater, arachnoid and pia mater form the barrier between blood and brain. No blood vessels directly enter brain. Exchange is done like this. Choroid plexus of 3rd and 4th ventricles secrete cerebrospinal fluid. CSF moves in ventricles of brain and central canal of spinal cord. It moves to subarachnoid space through foramina in 4th ventricle. The fluid of subarachnoid space goes to venous sinus in dura mater through arachnoid granulations. 33. #1 most used drug Caffeine. # 2 most used drug is alcohol. # 3 most used drug is nicotine. Nictotine binds tightly with many receptors including Acetylcholine releasing neuromuscular junctions, receptors releasing catecholamines and many others in brain. It is a strong stimulant and highly addictive. .
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