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APHY 201 Exam 2a
Ch. 7 The Nervous System - Neurons and Synapses
| Question | Answer |
|---|---|
| what is the term for a multipolar neuron located entirely within the CNS? | interneuron (these are multipolar) |
| what is the term for a neuron that transmits impulses from a sensory receptor into the CNS? | sensory (afferent) neuron (these are (pseudo)unipolar) |
| what is the term for a neuron that transmits impulses from the CNS to an effector organ (ex., a muscle)? | motor (efferent) neuron (these are multipolar) |
| what is the term for a cablelike collection of many axons in the PNS? may be mixed (both sensory and motor) | nerve |
| what is the term for a nerve that stimulates contraction of skeletal muscles | somatic |
| what is the term for a nerve that stimulates or inhibits contraction of smooth muscle and cardiac muscle and that stimulates glandular secretion | autonomic motor nerve |
| what is the term for a grouping of neuron cell bodies located in the PNS? | ganglion (pl. ganglia) |
| what is the term for a grouping of neuron cell bodies within the CNS? | nucleus (pl. nuclei) |
| what is the term for a grouping of axons that interconnect regions of the CNS | tract aka fasciculus |
| what are the 4 general functions of neurons? | 1. respond to stimuli (whether chemical or physical) 2. conduct electrochemical impulses (across the fluid membrane) 3. release chemical regulators via exocytosis 4. enable perception of sensory stimuli, learning, memory, and control of muscles and glands |
| what is another name for the soma (cell body) of a neuron? | perikaryon (it's Greek to me!) |
| a neuron soma contains organelles including Nissl bodies. what do these do? | like a condensed rough ER, these synthesize proteins, including those essential for synaptic transmission |
| a group of cell bodies clusters in the CNS. what is this group called? | nuclei |
| a group of cell bodies clusters in the PNS. what is this group called? | ganglion |
| what part of a neuron receives impulses and conducts a graded impulse, or LOCAL POTENTIAL, toward the cell body? | dendrites, where (together with the cell body) ligand-gated Na+ channels are located |
| what part of the neuron conducts action potentials away from the cell body? | axon |
| on a neuron, what are the 2 types of gated sodium channels and where are they, respectively? | ligand-gated Na+ channels are where cell body and dendrites are; at the axon hillock and along the nodes of Ranvier there are voltage-gated Na+ channels |
| what is an axon collateral? | a branch structure off of / a continuation of an axon |
| where are action potentials generated? | axon hillock |
| which is deeper on an axon in the PNS, the neurilemma or myelin sheath? | the myelin sheath is deeper, closer to the nerve itself than the neurilemma. the neurilemma contains the cell nucleus |
| a neuron's axon's terminals are relatively far from the soma but still need organelles and proteins moved to them, such as fresh mitochondria, neurotransmitter enzymes, and membrane proteins. what's this process called? | axonal transport (fast and slow components) |
| what are the 2 components of axonal transport and what direction(s) do they move in? | fast and slow components. fast components move vesicles in both directions; slow components move microfilaments, microtubules, and proteins only in an anterograde direction, and is the reason why damaged nerves take so long to heal |
| the two directions axon transport can move in are anterograde and retrograde. which use kinesin and dynein? why? | anterograde transport uses kinesin (toward plus end), while retrograde transport uses dynein (toward minus end). this is due to microtubule polarity |
| which direction of axonal transport recycles wastes from the axon terminal? | retrograde; waste recycling takes spent mitochondria, old membrane pieces, and degraded proteins back to the perikaryon where lysosomes can recycle them |
| what are the 2 terms for neurons located completely within the CNS and that integrate functions of the nervous system? | association neurons aka interneurons |
| which neurons are responsible for reflexes? | somatic motor neurons, these also are under voluntary control of skeletal muscles |
| which neurons innervate involuntary targets? | autonomic (SNS and PSNS) motor neurons innervate smooth muscle, cardiac muscle, and glands |
| which type of neuron structurally looks like a T that forms two longer processes? | pseudounipolar |
| which neurons are found in the retina of the eye? | bipolar neurons, which have processes on either end of the cell body |
| which neurons are the most common type of neuron structurally? | multipolar neurons, having several dendrites and one axon |
| most nerves (PNS axons) are both sensory/motor and are called mixed nerves. what are the remaining nerves' classification? | some of the cranial nerves have sensory fibers only, and are considered part of the PNS because they branch out to the rest of the body, connecting the brain/-stem to the head, neck and organs |
| what are the cells that are nonconducting but support neurons? | neuroglia |
| what are neurolemmocytes? | Schwann cells. these insulate PNS nerve axons via myelin sheaths |
| what are ganglionic gliocytes? | satellite cells. these support cell bodies within the sensory and autonomic ganglia of the PNS |
| what are the 4 neuroglia types in the CNS? | oligodendrocytes, microglia, astrocytes, ependymal cells |
| which cells form myelin sheaths around the axons of CNS neurons, producing "white matter" of the CNS? | oligodendrocytes |
| which cells migrate around CNS tissue and phagocytize foreign/pathogenic and degenerated material/debris | microglia - immune cells |
| which cells interact metabolically with neurons and modify/regulate the extracellular environment of the neurons | astrocytes, which also cover capillaries of the CNS to induce the BBB |
| which cells line the ventricles and the central canal of the spinal cord? these cover tufts of capillaries to form choroid plexuses--strucutres that secrete cerebrospinal fluid | ependymal cells |
| Schwann cell, myelin sheath, and neurilemma are all just different parts of one single cell undergoing a mechanical wrapping process. explain | Schwann cell wraps layers of highly compacted, fatty inner core called the myelin sheath, and the living, bulging outer crust is called the neurilemma where the nucleus has space to live |
| true or false, for nonmyelinated axons, the Schwann cell lacks the multiple wrappings of myelin, but still has the neurilemma | true |
| true or false, in the CNS, the oligodendrocyte produces a myelin sheath and a neurilemma | false, no neurilemma |
| in what demyelinating disease do the T cells of the immune system attack the myelin sheaths of the PNS, producing rapid onset of symptoms including muscle weakness? | Guillain-Barre syndrome |
| in what demyelinating disease do T lymphocytes go on an autoimmune attack, causing lymphocytes and monocyte-derived macrophages to enter the brain BBB and target the myelin sheaths, causing demyelination? | multiple sclerosis, which is usually environmentally triggered on a genetically susceptible individual, and women 20-40 are more likely to contract this |
| what regeneration tube is formed by Schwann cells when an axon in the PNS is cut? | band of Bunger (aka regeneration tube), which responds to growth factors that stimulate the growth of axon sprouts within the tube, and the new axon may eventually reconnect to the effector |
| 1. death receptors form that promote apoptosis 2. inhibitory proteins in the myelin sheath 3. glial scars formed by astrocytes 4. myelin debris (proteins like Nogo) and the glial scar (rich in CSPGs) actively collapse advancing axon growth cones | |
| true or false, injury in the CNS stimulates growth of axon collaterals | true, but central axons have a much more limited ability to regenerate these than peripheral axons |
| what are the proteins called that are produced predominantly by oligodendrocytes, and that inhibit axon regeneration in the CNS? | Nogo proteins |
| neurotrophins are survival and GF proteins that prevent apoptosis and promote neuronal growth in the fetal brain. what is their role in adults? | neurotrophins aid in the maintenance of sympathetic ganglia and the regeneraion of sensory neurons |
| what is the most abundant glial cell? | astrocytes, which with their perivascular feet associate with blood capillaries and axon terminals, influencing interactions between neurons and neurons/blood |
| what are some important substances that astrocytes pick up from/to neurons? | astrocytes get glucose from the blood and store it as lactate for the neurons; astrocytes also pick up glutamate after it's been used in the synaptic cleft and convert this to glutamine--can then be recycled for neuron use |
| astrocytes function as a clean-up crew for neurons. what 8 functions do they carry out? | 1. take up K+ 2. take up NTs ex.) glutamate 3. end feet convert glucose into lactate 4. store glycogen 5. help form synapses in CNS 6. regulate neurogenesis in adult 7. form BBB 8. release gliotransmitters (glutamate, ATP, adenosine, D-serine) |
| what gliotransmitters help stimulate/inhibit neuronal activity and what do they do? | glutamate accelerates speed and intensity of conversation between neurons |
| why does the neuron benefit from the astrocytes' lactate? | neurons can then save glucose or generating NADPH, which supplies the antioxidant reduced glutathione, which fights free radicals produced by normal neuronal activity |
| what is the good version of cross-talk, between neurons and glia? | neuron-glia crosstalk is when astrocytes are excited by changes in intracellular Ca2+ concentration and release gliotransmitters (does not equal action potentials) |
| how is a Ca2+ wave created in neural activity? | when some neurons are active, they release ATP, which increases the Ca2+ of adjacent astrocytes, which creates a Ca2+ wave |
| what can a rise in Ca2+ cause the astrocyte to release? | prostaglandin E2 from end-feet on a blood capillary, increasing blood flow |
| paracellular movement is blocked in the blood brain barrier. what type of junctions join adjacent capillary cells? | tight junctions that are made of specialized proteins like claudins and occludins |
| which selective processes are those which allow substances to be moved into the brain? | very selective, TRANSCELLULAR processes such as diffusion through endothelial cells, active transport, and bulk transport (also req. ATP) |
| astrocytes' end-feet that wrap brain capillaries; their secretions signal ion channel production, endothelia to produce & maintain tight junction proteins, etc. what are the secretions that help astrocytes form a proper barrier? | glial-derived neurotrophic factor (GDNF), transforming growth factor-beta (TGF-beta), and basic fibroblast growth factor (bFGF) |
| by secreting glial-derived neurotrophic factor, astrocytes influence production of what 2 groups of things? | ion channels, and enzymes that can destroy toxic substances |
| what 3 things establish neurons' resting potential of -70mV? | 1. fixed anions (large negative molecules inside the cell) 2. Na+/K+ pumps maintain inside to be more negative 3. permeability of the membrane to positively charged, inorganic ions like K+ |
| what the term for the ability for neurons and muscle cells to change their membrane potentials? | excitability or irritability |
| what causes neuron or muscle cell irritability? | changes in the permeability to certain ions, which follow their *electrochemical gradient* |
| what is the term for the combination of concentration gradient and attraction to opposite charges, that ions follow? | electrochemical gradient |
| which NTs open channels permeable to Na+? | acetylcholine and glutamate (exciting the cell) |
| which NT(s) open channels permeable to Cl-? | GABA and glycine (inhibiting the cell) |
| ACh binds to what kind of receptors on the muscle membrane? | nicotinic |
| what 5 factors cause membrane changes in the permeability to certain ions? | 1. voltage changes 2. ligands/ chemical messengers 3. physical deformation (mechanically gated channels) 4. intracellular second messengers like cAMP or Ca2+, or kinases 5. time-dependent inactivation |
| what is the term for when the membrane potential inside the cell decreases (becomes more negative than resting potential)? | hyperpolarization |
| what kind of tool can record changes of the voltage inside and outside the cell? | oscilloscope |
| hyperpolarization can occur when what 2 ions do what? | when positive ions leave the cell (usually K+) or negative ions (Cl-) enter the cell. |
| between depolarization and hyperpolarization, which is excitatory and which is inhibitory? | depolarization is excitatory and hyperpolarization is inhibitory |
| what are the 2 types of K+ channels? | K+ leakage channels that are always open and voltage-gated K+ channels that are closed at resting potential but open after Na+ channels, to repolarize the cell |
| what type(s) of ion channels does Na+ have? | Na+ has only voltage-gated channels that are closed at rest but that flicker open every so often, allowing Na+ to leak into the cell; the membrane is less permeable to Na+ at rest |
| what is the all-or-nothing threshold number in mV required to alter the physical shape of the voltage-gated Na+ channels? | -55mV. in neurons, the NT glutamate is what opens sodium gates (EPSPs), and in skel. muscle, ACh causes a massive localized depolarization called an end-plate potential. touch/hearing physically opens mechanically-gated channels letting Na+ or Ca+ rush in |
| at what number of mV do voltage-gated K+ channels open? why do they do this (to accomplish what?)? | at around +30mV, voltage-gated K+ channels open, and K+ rushes out of the cell to repolarize toward the potassium equilibrium potential of -90mV (though it settles for -70mV ultimately after hyperpolarization) |
| what is the positive feedback loop that happens for action potentials? | an AP drives rapid cell depolarization: an initial stimulus opens a few voltage-gated sodium channels, letting positively charged Na+ ions in. This depolarizes further, which triggers even more Na channels to open; this chain reaction peaks the signal |
| what is the negative feedback loop that happens after depolarizations in an action potential? | at +30mV, Na+ channels (inactivation gates) and K+ ones open |
| in a term called hyperpolarization, repolarization actually overshoots resting potential and gets down to -85mV. why doesn't it reach K+ equilibrium potential (-90mV)? | because voltage-gated K+ channels CLOSE as the membrane potential falls |
| what are the steps of ion gate activity during action gate potential? (be able to put them in order). | 1. ligand-gated Na open 2. voltage-gated Na (activation) open 3. voltage-gated Na (inactivation) close while voltage-gated K open 4. voltage-gated Na close (activation) as inactivation reopen (allows relative refractory period) 5. voltage-gated K close |
| true or false, the size of the stimulus affects the size/amplitude of the action potential | false, no matter the size of the stimulus, the action potential will always reach +30mV if the -55mV threshold is reached |
| true or false, the all-or-none law includes the fact that the size of the stimulus will not affect operation times of its gates | true |
| what is another name for action potentials? (think about how they look on a graph, all with the same amplitude--hint: Snoopy's cousin) | spike potentials |
| how does the brain code for intensity, i.e., how light or heavy a touch is? | a stronger stimulus will make action potentials occur more frequently, not higher in amplitude on the graph |
| true or false, Na+ channels are inactive during the absolute refractory period due to the inactivation gate ball stoppers being closed, and yet the activation gates are still in the open position | true |
| opening which gates starts an action potential? | opening the Na+ activation gates starts an action potential |
| which period of the action potential is happening when K+ channels are still open and the Na+ activation gates are closed and fully reset | relative refractory period (only a very strong stimulus can overcome this because positive K+ ions leaking out are working against reaching threshold again) |
| importantly, what do the refractory periods guarantee? | this way, each action potential remains a separate, all-or-none event and there's no bleeding of one AP into another |
| when you look at the graph of an action potential, which section indicates the relative refractory period? | when the line dips under the resting membrane potential |
| true or false, the cable properties of neurons show that the neuron has a high ability to conduct charges through its cytoplasm | false, this ability is poor due to high internal resistance (organelles, proteins...) as well as because there is leakage of charges through the membrane--neurons don't depend on cable properties to move an impulse down the length of an axon |
| local potentials are decremental, while the action potential of one location serves as the depolarization stimulus for the next region of the axon. what does it mean that local potentials are decremental? | their electrical strength gradually decreases as they travel away from the point of origin |
| what is the term for the rapid propagation of action potentials along myelinated axons, where the electrical signal appears to "jump" from one uninsulated gap (Node of Ranvier) to the next? | saltatory conduction |
| does the action potential conduction speed increase or decreese with the increased diameter of the neuron? | increase (reduced resistance to the spread of charges via cable properties) |
| what 2 factors increase action potential speed? | increased diameter of the neuron; myelination (e.g., an unmyelinated axon speed is very slow because it can't "jump" across) |
| sensory muscle nerves have a diameter of 12 to 22 micrometers. what is the conduction velocity in m/sec that they have? | 70 to 120 m/sec |
| autonomic fibers to smooth and cardiac muscles have a diameter of 0.3 to 1.3 micrometers. what is the conduction velocity in m/sec that they have? | 0.7 to 2.2 m/sec |
| a synapse is the functional connection between a neuron and the cell it's signaling. what is this in the CNS? the PNS? | CNS: another neuron; PNS: a muscle or gland-- these synapses are often called MYONEURAL or NEUROMUSCULAR junctions |
| a presynaptic neuron can signal the dendrite, cell body, or axon of a second neuron. what are the 3 types of synapses based on this fact? | there are axodendritic* (most are these), axosomatic, and axoaxonic synapses |
| true or false, all synapses are electrical | false, although electrical synapses are fast and direct, most are actually chemical |
| think of a chemical text like sending a text to a neighbor, while an electrical synapse is a physical, direct connection like cutting a doorway straight through the wall to their room. what are some places electrical synapses occur? | in smooth and cardiac muscle, between some neurons of the brain, and between glial cells |
| when cells are next to each other and function via electrical synapse, they are joined by what kind of junction? | gap junctions |
| regarding electrical synapses, what happens when the cells around a synapse are stimulated? | the connections between cells are highly regulated: stimulation causes enzymes to de/phosphorylate CONNEXIN proteins to open or close the channels |
| what is the term for the tip of each axon terminal branch? | terminal boutons (French for button), which are packed with tiny membrane sacks called synaptic vesicles, loaded with NTs waiting for the command to fire |
| what is the term for the structure that keeps pre- and post-synaptic clefts held together? | CAMs (cell adhesion molecules), they keep the presynaptic bouton perfectly aligned and anchored right up against the postsynaptic target |
| what specific type of channels open to stimulate the fusing of synaptic vesicles to the plasma membrane and exocytosis of neurotransmitter? | voltage-gated Ca2+channels |
| true or false, a greater frequency of action potentials results in more stimulation of the POST-synaptic neuron. | true |
| what is the name of the type of protein that sereves as a Ca2+ sensor when Ca2+ enters the cell? | synaptotagmin |
| what is the role of SNARE proteins? | vesicles containing NTs are docked at the plasma membrane by 3 SNARE proteins. the Ca2+ synaptotagmin complex displaces part of SNARE, and the vesicle fuses, forming a pore to release the neurotransmitter |
| what are 2 toxins mentioned in your slides that digests SNARE protein(s)? | tetanus and botulinum |
| the tetanus toxin digests a SNARE protein which reduces inhibitory neurotransmitter release. what symptoms result? | spastic paralysis and lockjaw |
| the botulinum toxin digests a different SNARE protein than tetanus; this protein reduces excitatory NT release, leading to what symptom? | flaccid paralysis |
| what are the 2 actions of NTs at a chemical synapse? | 1. acting as a ligand, the NT diffuses across the synapse to bind to a specific receptor protein, resulting in chemically regulated ion channels aka ligand-gated ion channels 2. graded potentials occur (EPSPs or IPSPs) |
| what is the term for the event of a graded depolarization caused by opening Na+ or Ca2+ channels? | EPSP--excitatory postsynaptic potential |
| what is the term for the event of a graded hyperpolarization causes by opening K+ or Cl- channels? | IPSP--inhibitory postsynaptic potential |
| true or false, ACh is always an excitatory neurotransmitter | false, it can also be inhibitory |
| ACh is an NT that directly opens ion channels when it binds to its receptor. when is it excitatory and when is it inhibitory? | excitatory in some areas of the CNS, in some autonomic motor neurons, and in all somatic neurons; inhibitory in some autonomic motor neurons |
| what are the 2 types of ACh receptors? | nicotinic and muscarinic |
| nicotinic ACh receptors can be stimulated by nicotine. where are these receptors found? | found on the motor end plate of skeletal muscle cells, in autonomic ganglia, and in some parts of the CNS |
| muscarinic ACh receptors can be stimulated by muscarine from poisonous mushrooms. where are these receptors found? | found in CNS and plasma membrane of smooth and cardiac muscles and glands innervated by autonomic motor neurons |
| what are agonists and antagonists with respect to acetylcholine receptors? know the examples | agonists can stimulate a receptor ion channel (nicotine for nicotinic ACh receptors and muscarine for muscarinic ACh receptors); antagonists inhibit a receptor (atropine against muscarinic receptors, curare against nicotinic receptors) |
| what are the 2 ways/channels that a chemically regulated ion channel can be opened when an NT binds to a receptor? | ligand-gated channels (direct, ionotropic) and G-protein coupled channels (indirect, metabotropic) |
| when the nicotinic ACh receptor on skeletal muscle binds, the channel opens instantly, allowing which ion to rush into the muscle to trigger a contraction? | sodium |
| when the vagus nerve releases ACh, it binds to the muscarinic ACh receptors at the heart, and allows which ion's channels open? | potassium |
| which receptors are ligand-gated channels with 2 receptor sites for 2 AChs? | nicotinic ACh receptors |
| binding of 2 acetylcholine molecules to a nicotinic ACh receptors opens a channel that allows passage of what 2 cations? | both Na+ and K+ (the nicotinic ACh receptor is a non-specific cation channel)--allows Na+ to rush in and K+ to rush out at the exact same time through the exact same doorway, though Na+ wins the race and more Na+ flows in that K+ out |
| what is the stimulus for opening of ionic gates--for action potential? for EPSP? | depolarization for action potential; ACh or other excitatory neurotransmitter for EPSP |
| what is the conduction distance--for APs? for EPSPs? | regenerated over length of axon for APs; 1-2mm (localized potential) for EPSP |
| is there positive feedback occurring--for APs? for EPSPs? | for APs yes, for EPSPs no |
| is there summation occurring--for APs? for EPSPs? | no for APs (all-or-none event), yes for EPSPs that produce graded depolarizations |
| is there a refractory period for APs? for EPSPs? | yes for APs, no for EPSPs |
| what 3 types of chemical receptors interact with ion channels via G-protein coupled channels? | muscarinic ACh receptors, dopamine receptors and norepinephrine receptors |
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