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176 Cards in this Set
- Front
- Back
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How many neurons are in the brain? |
100 billion |
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How many neurons are in the spinal cord? |
100 million |
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What are the components of peripheral nervous system? |
nerves, ganglia, enteric plexuses, sensory receptors |
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What is a nerve? |
A bundle of hundreds to thousands of axons plus connective tissue and blood vessels. Outside of the brain and spinal cord. |
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How many cranial nerves and spinal nerves are there? |
12 pairs cranial, 31 pairs spinal |
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What are ganglia? |
small masses of nervous tissue. consist primarily of neuron cell bodies, located outside of brain and spinal cord. |
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What are enteric plexuses? |
Extensive networks of neurons. located in walls of organs of GI tract. regulate the digestive system. |
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What is a sensory receptor? |
A structure of the nervous system that monitors changes in the ext. and int. env't. |
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What is the somatic nervous system? |
Consists of sensory neurons that convey information from somatic receptors int he head, body wall, limbs & special senses to CNS. And motor neurons that conduct impulses from the CNS to skeletal muscles = voluntary. |
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What is the autonomic nervous system. |
Conveys information from autonomic sensory receptors, primarily in visceral organs such as stomach and lungs to CNS + motor neurons that conduct nerve impulses from CNS to smooth muscle, cardiac muscle and glands = involuntary. |
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What is the sympathetic division? |
Of the ANS. helps support exercise of emergency actions, "fight-or-flight" response. |
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What is the parasympathetic division? |
Of the ANS. "rest-and-digest". |
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What are the three functions of the nervous system? |
Sensory, integrative and motor function. |
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What is sensory function? |
Sensory receptors detect internal stimuli (increase in blood pressure), ext. stimuli (raindrop landing on arm). carries information to brain & SC through cranial and spinal nerves. |
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What is integrative function? |
Nervous system proceses sensory info by analyzing it and making decisions/appropriate responses. |
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What is motor function? |
Motor response from activated effectors in response to sensory information. muscle contractions and gland secretions. |
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How many more neuroglia are there compared to neurons? |
25x more. |
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Do neurons undergo mitotic divisions? |
No |
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Do neuroglia undergo mitotic divisions? |
Yes |
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What is electrical excitability? |
The ability to respond to a stimulus and convert it into an action potential. |
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What is an action potential? |
A nerve impulse. An electrical signal that propagates along the surface of the membrane of a neuron. |
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How does an action potential begin? |
Ions move between IF and inside of neuron through ion channels. |
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How long are neurons? |
<1mm to as long as your leg or longer. |
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How fast do nerve impulses travel? |
0.5 to 130 meters per second. |
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What are the three parts of the neuron? |
cell body, dendrites, axon |
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What are Nissl bodies? |
prominent clusters of rough ER in the cell body. |
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What do Nissl bodies do? |
Synthesize new proteins to replace cell components, as material for growth of neurons, and to regenerate damaged axons in PNS. |
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What are dendrites? |
Receiving or input portion. plasma membranes contain receptor sites for binding chemical messengers. short, tapering, highly branched. cytoplasm contains Nissl bodies, mitochondria, other organelles. |
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What is the axon? |
propagates nerve impulses tward another neuron, muscle fibre or gland cell. contain mitochondria, microtubules, neurofibrils. no ER = no protein synthesis. |
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What is the axon hillock? |
cone-shaped elevation where axon joins to cell body |
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What is the initial segment and trigger zone? |
Initial segment is the part of axon closest to axon hillock where nerve impulses arise at trigger zone. |
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What are axon collaterals? |
Side branches of the axon, usually at a right angle. End in axon terminals. |
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WhaT is a synapse? |
Site of communication betwen two neurons or between neuron and effector cell. |
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What is synaptic end bulb? |
Tips of some axon terminals. bulb-shaped. or string of swollen bumps. |
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What are synaptic vesicles? |
Store neurotransmitters. tiny membrane-enclosed sacs. |
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How many neurotransmitter types will a neuron contain? |
Two or three. |
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What is the range of neuron diameter? |
5 micrometers to 135 micrometers. |
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How do neurons differ in shape? |
Some lack an axon, some have very short axons, pattern varies. |
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What is a multipolar neuron? |
Usually have several dendrites and one axon. these are most neurons in brain and spinal cord. all motor neurons. |
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What is a bipolar neuron? |
One main dendrite and one axon. Retina of eye, inner ear, olfactory area of brain. |
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What is a unipolar neuron? |
Dendrites and one axon fused together =continuous process from cell body. pseudounipolar because begin in embryo as bipolar but dendrites and axon fuse together during development. |
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Where is the triggerzone for unipolar neurons? |
At the junction of dendrites and the axon. Impulses propagate toward synaptic end bulbs. |
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Where are the cell bodies of unipolar neurons located? |
In the ganglia of spinal and cranial nerves. |
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Describe neuroglia. |
Make up half volume of CNS. Fill spaces made by damaged or injured neurons. |
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Which neuroglia are found in CNS? |
astrocytes, oligodendrocytes, microglia, ependymal |
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Which neuroglia are found in PNS? |
schwann cells and satellite cells. |
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What are astrocytes? |
Star-shaped. largest. most numerous. processes make contact with blood capillaries, neurons, pia mater. |
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What are the functions of astrocytes (5)? |
contain microfilaments that give them considerable strength = support neurons. processes around capillaries isolate neurons of CNS from potentially harmful substances in blood by secreting chemicas that maintain blood-brain barrier. in embryo, secrete chemicals that help regulate growth, migration and interconnection among neurons in brain. help maintain chemical environment for generation of nerve impulses (ex. regualte conc. of K+). may play role in learning and memory - influence formation of neural synapses. |
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What are oligodendrocytes? |
smaller and fewer processes. Responsible for forming and maintaining myelin sheath. |
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What is the myelin sheath? |
multilayered lipid and protein covering around some axons. insulates them. increases speed of nerve impulse conduction. |
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What are microglia? |
Small cells. slender processes with many spinelike projections. function as phagocytes. remove cellular debris from normal development and phagocytize microbes and damaged nervous tissue. |
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What are ependymal cells? |
cuboidal to columnar. single layer. microvilli and cilia. line ventricles of brain and central canal. produce, monitor, assist in circulation of cerebrospinal fluid, form barrier. |
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What are Schwann cells? |
encircle PNS axons. form myelin sheath. single cell myelinates single axon or encloses 20+ unmyelinated axons. participate in axon regenration. |
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What are satellite cells? |
flat cells. surround cell bodies of neurons of PNS ganglia. provide structural support, regulate exchnage of materials between cell bodies and IF. |
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What is myelination? |
Sheath electrically insultes axon and increases speed of nerve impulse conduction. |
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What are nodes of Ranvier? |
gaps in myelin sheath. |
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What is a nucleus? |
A cluster of neuronal cell bodies in the CNS. |
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What is the difference between white and gray matter? |
white = primarily myelinated, gray = neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, neuroglia. Nissl bodies = gray. - blood vessels present in both - gray on inside of spinal cord, more on outside of brain + cerebrum and cerebellum |
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What makes an electrical signal possible in neurons? |
existence of resting membrane potential and presence of specific ion channels. |
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What is a membrane potential? |
An electrical potential difference (voltage) across membrane |
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What is the resting membrane potential? |
voltage in excitable cells. exists because of a small buildup of negative ions in the cytosol along inside of the membrane + equal buildup of positive ions in ECF along outside of membrane. forms potential energy. typical voltage is -70mV. |
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What is the electrochemical gradient? |
A concentration difference plus an electrical difference. ions move from high to low concentration, charged ions move towards opposite charge. |
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What are the four types of ion channels? |
leak channels, ligand-gated channels, mechanically gated channels, voltage-gated channels |
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What are leak channels? |
randomly alternate between open and closed. many more K+ channels than Na+ channels. K+ are leakier. in nearly all cells, dendrites, cell bodies and axons. |
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What are ligand-gated channels? |
Open and close in response to binding of chemical stimulus (ligand, ex. neurotransmitters, hormones and ions). |
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What is an example of a ligand-gated channel? |
ACh opens cation channels Na+ and Ca2+ to diffuse inward and K+ to diffuse outward. ligand-gated channels located in dendrites of sensory neurons (ex pain receptors) + in dendrites and cell bodies of interneurons and motor neurons. |
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What is a mechanically gated channel? |
opens or closes in response to mechanical stimulation in form of vibration (ex. sound wave), touch, pressure, tissue stretching. force distorts channel from resting position, opens gate. |
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What is an example of a mechanically gated channel? |
Auditory receptors in ears, stretching monitor receptors in internal organs, touch and pressure receptors in skin |
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What is a voltage-gated channel? |
Opens in response to change in membrane potential (voltage). participate in generation and conduction of action potentials in axons of all types of neurons. |
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What is polarization? |
When a cell exhibits a membrane potential it is polarized = most body cells. |
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What is the range of membrane potentials in body cells? |
+5mV to -100mV. |
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What are the three factors that cause a resting membrane potential? |
Unequal distribution of ions in ECf and cytosol; inability of most anions to leave the cell; electrogenic nature of Na+/K+ ATPases. |
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Explain the unequal distribution of ions in the CF and cytosol. |
ECF is rich in Na+ and Cl-. In cytosol the main cation is K+, dominant anions are phosphates attached to molecules (3Phs in ATP, AA in proteins). PM has more K+ leak channels than Na+ leak channels, so the number of K+ ions that diffuse out is greater than Na+ than diffuse in. more K+ exits, inside of membrane becomes increasingly negative. |
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Explain the inability o fmost anions to leave the cell. |
Anions cannot follow K+ out of cell because they are attached to nondiffusible molecules (ATP and proteins). |
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Explain the electrogenic nature of Na+/K+ ATPases. |
Membrane permeability to Na+ is low because of fewer sodium leak channels. ATPases help maintain resting membrane potential by pumping out Na+ as fast as it leaks in, and brings in K+ (which then leaks out). Pumps remove more positive charges than bring in, they are electrogenic = contribute to negativity of resting membrane potential = small contribution = -3mV of total -70. |
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What is a graded potential? |
A small deviation from the membrane potential. Makes membrane either more or less polarized. occurs when mechanical or ligand channel opens or closes due to stimulus. occur mainly in dendrites and cell bodies (where those channels are). size of grade = variation in amplitude = dependent on strength of stimulus = depends on how many gates are open and for how long |
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What is a hyperpolarizing graded potential? |
When response makes memrane more polarized (inside more negative) |
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What is a depolarizing graded potential? |
When response makes membrane less polarized (inside less negative). |
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What is decremental conduction? |
graded potentials die out as they spread along the membrane. |
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Why are graded potentials only useful for short-distance communication? |
Because they die out within a few mm of their point of origin. |
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What is summation? |
the process by which graded potentials are added together. |
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What is an action potential? |
a sequence of rapidly occurring events taht decrease and reverse the membrane potential and then eventually restore it to the resting state |
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What is the depolarizing phase? |
When the negative membrane potential becomes less negative, reaches zero, then becomes positive. Na+ channels open rapidly due to stimulus, inflow of Na+ changes membrane potential from -55mV to +30mV. channel is open for a few ten-thousandsth of a second, 20,000 Na+ flow in, concentration hardly changes because of millions of Na+ in ECF, sodium-potassium pump bails out the 20,000 Na+ during action potential. |
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What is the repolarizing phase? |
Membrane potential is restored to the resting state of -70mV. inactivation gates close, voltage-gated Na+ channel in inactivated state. threshold-level depolarization opens voltage-gated K+ channels, slowly, Na+ inflow slows due to closing inactivation gate, K+ outflow accelerated, membrane potential changes from +30mV to -70mV. Na+ channels revert to rresting state. |
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What is the after-hyperpolarizing phase? |
following repolarizing phase. membrane potential temporarily becomes more negative than resting level. K+ channels stay open to cause this phase, membrane potential negativity increase to about -90mV. voltage-gated channels close, back to -70mV. K+ channels do not have inactivated state, just closed/resting and open/activated. |
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What happens during an action potential?
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Two types of voltage-gated channels open and then close. First, Na+ channels allow Na+ into cell, causing depolarizing. Then K+ channels open, K+ flow out, producing repolarizing phase. After-hyperpolarizing phase occurs when K+ channels remain open after previous phase ends. |
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What is a threshold? |
about -55mV in many neurons. The point at which an action potential occurs in axon, when depolarization reaches a certain level. |
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What is the all-or-none principle? |
an action potential either occurs completely or not at all. |
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What is a refractory period?` |
period of time after an action potential begins - excitable cell cannot generate another action potential in response to normal threshold stimulus. Does not occur in graded potentials. |
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What is an absolute refractory period? |
Even a very strong stimulus cannot initiate second action potential. Na+channels must return to resting state, not just inactivation. |
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How do refractory periods differ in large vs small diameter axons? |
large = large surface area = brief absolute refractory period of 0.4msec, so up to 1000 impulses/second are possible. small = absolute refractory periods as long as 4msc, so transmit max 250 impulses/sec. |
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What is the relative refractory period? |
Period of time during which a second action potential can be initiated but only by larger-than-normal stimulus. when voltage-gated K+ channels are still open, but after Na+ channels have returned to resting state. |
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What is propagation? |
Mode of conduction where action potential keeps its stretch as it spreads along the membrane (in contrast to graded potential which is decremental). Depends on positive feedback. |
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Does the same action potential propagate down the entire axon? |
No, it is regenerated over and over. |
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Which direction does the action potential propagate? |
From trigger zone to axon terminals. Can't go back toward cell body because any part that has undergone action potential is now in refractory period. |
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What are the two types of propagation? |
continuous conduction and saltatory conduction |
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What is continuous conduction? |
involves step-by-step depolarization and repolarization of each adjacent segment of PM. ions flow through voltage-gated channels in each adjacent segment of membrane. AP propagates only a short distance in a few ms. |
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What is saltatory conduction? |
myelinated axons. same amount of time as continuous, would get much further. occurs because of uneven distribution of voltage-gated channels - few are in regions where myelin sheath covers axolemma, but at nodes of Ranvier there are many voltage-gated channels, so current carried by Na+ and K+ flows across membrane mainly at nodes. |
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Why does a larger-diameter axon propagate faster than smaller ones? |
Because of their surface area |
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How is stimulus intensity encoded? |
intensity depends on the frequency of action potentials - how often they are generated at a trigger zone. light touch generates a low frequency of action potentials. firmer pressure elicits action potentials along axon at higher frequency. + number of sensory neurons recruited by stimulus. |
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Compare graded potentials and action potentials |
propagation of action potentials permits communication over long distances, graded only short-distance (not propagated). |
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What is the origin of GPs vs APs |
GPs: mainly in dendrites and cell body |
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Types of channels in GPs vs APs |
GPs: ligand-gated or mechanically gated |
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Conduction in GPs vs APs |
GPs: decremental, short distances |
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Amplitude of GPs vs APs |
GPs: depending on strength of stimulus, less than 1mV to >50mV |
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Duration of GPs vs APs |
GPs: usually longer, several milliseconds to several minutes |
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Polarity of GPs vs APs |
GPs: hyperpolarizing or depolarizing |
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Refractory period in GPs vs APs |
GPs: Not present, summation can occur |
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What is the presynaptic neuron? |
A nerve cell that carries a nerve impulse toward a synapse. |
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What is a postsynaptic cell? |
A cell that receives a signal. could be postsynaptic neuron or an effector |
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What are gap junctions? |
structures between the plasma memranes of adjacent neurons. electrical synapse where action potentials conduct. each gap junction contains ~100 tubular connexons - tunnels to connect sytosol of two cells directly. |
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Where are gap junctions found? |
visceral smooth muscle, cardiac muscle, developing embryo, brain. |
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What are the advantages of electrical synapses? |
1. faster communication - AP passes directly from presynaptic to postsynaptic cell. chemical synapses take longer and delay communication. 2. synchronization - electrical synapses synchronize activity of group of neurons or muscle fibres. important in heart, viscera; heartbeat, moving food |
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What is a synaptic cleft? |
space of 20-50nm that is filled with IF. chemical synapse passed through from presynaptic to postsynaptic neurons. nerve impulse cannot conduct across it, so neurotransmitters are released. |
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What is postsynaptic potential? |
When postsynaptic receptors received neurotransmitter across synaptic cleft. a type of graded potential. |
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What is the first step when a chemical synapse transmits a signal? |
Nerve impulse arrives at a synaptic end bulb of persynaptic axon. |
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What is the second step when a chemical synapse transmits a signal? |
Depolarizing phase. voltage-gated Ca2+ channels open in synaptic end bulbs. Ca2+ more concentrated in ECF, so Ca2+ flows inward.
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What is the thirdq step when a chemical synapse transmits a signal? |
increase in Ca2+ inside presynaptic neuron = signal = exocytosis of synaptic vesicles. vesicle membranes merge with plasma membrane, neurotransmitter molecules within vesicle released into synaptic cleft. synaptic vesicles contain 2000+ molecules of neurotransmitter |
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What is the fourth step when a chemical synapse transmits a signal? |
neurotransmitter molecules diffuse across synaptic cleft, bind to receptors in postsynaptic neuron. |
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What is the fifth step when a chemical synapse transmits a signal? |
neurotransmitter molecules binding to receptors opens ligand-gated channels, particular ions flow across PM |
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What is the sixth step when a chemical synapse transmits a signal? |
voltage changes as ions flow through channels = postsynaptic potential. might be depolarizing or hyperpolarizing. |
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What is the seventh step when a chemical synapse transmits a signal? |
when depolarizing postsynaptic potential reaches threshold, action potential triggered. |
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what is an excitatory postsynaptic potential? |
a depolarizing postsynaptic potential. doesn't initiate a nerve impulse, does cause postsynaptic cell to become excitable, and is more likely to reach threshold. |
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what is an inhibitory postsynaptic potential? |
a neurotransmitter that causes hyperpolarization of postsynaptic is inhibitory = generation of AP is more difficult because membrane potential is even more negative = farther from threshold
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How and why is the neurotransmitter removed from the synaptic cleft? |
has to be removed because it would otherwise influence postsynaptic neuron, muscle or gland indefinitely. removed in three ways: diffusion away from synaptic cleft to out of reach of receptors; enzymatic degradation, some are inactivated, ie AChase breaks down ACh in synaptic cleft; uptake by cells, many are transported back to neuron that released them.
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What is spatial summation? |
summation of postsynaptic potentials in response to stimuli that occur at different locations in the membrane of a postsynaptic cell at the same time. ex: buildup of neurotransmitter released simultaneously by several presynaptic end bulbs. |
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What is temporal summation? |
summation of postsynaptic potentials in response to stimuli that occur at the same location in the membrane of postsynaptic cell but at different times. |
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When multiple excitatory and inhibitory effects at any given time are summed, what is the effect on the postsynaptic neuron? (3) |
EPSP: total excitatory effects are greater than total inhibitory effects, but less than threshold level = EPSP does not reach threshold. subsequent stimuli might more easily generate a nerve impulse because neuron is partially depolarized. |
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What are the small molecule neurotransmitters? |
acetylcholine, amino acids, biogenic amines, ATP & other purines, nitric oxide and carbon monoxide. |
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What is acetlycholine? |
released by many PNS neurons and some CNS neurons. excitatory at some synapses, ex. NMJ, binding of ACh to ionotropic receptors opens cation channels. |
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How is ACh inactivated? |
AChE inactivates ACh by splitting it into acetate and choline fragments. |
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What are amino acids? |
some are neurotransmitters in CNS, glutamate and aspartate are excitatory. powerful. half of synapses in brain communicate via glutamate, opens cation channels, mainly Na+ ions produce EPSP. |
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How is glutamate inactivated? |
reuptake. glutamate transporters actively transport glutamate back into synaptic end bulbs and neighbouring neuroglia. |
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What is glycine? |
important AA, inhibitory neurotransmitter. opens Cl- channels at ionotropic receptors. half of inhibitory synapses in spinal cord use glycine, rest use GABA. |
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What are biogenic amines? |
certain AAs that are modified and decarboxylated, such as norepinephrine, epi, dopamine, serotonin. most bind to metabotropic receptors. may cause either excitation or inhibition. |
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What is norpepinephrine? |
Biogenic amine. plays role in arousal - awaking from deep sleep, dreaming, regulating mood. hormone. released from adrenal medulla to blood. |
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What is epinephrine? |
biogenic amine. used as neurotransmitter by small number of neurons in the brain. |
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What are catecholamines? |
norepi, epi, and dopa. an amino group (--NH2) and two adjacent hydroxyls. synthesized from amino acid tyrosine. |
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how are catecholamines inactivated? |
reuptake into synaptic end bulbs. then either recycled into synaptic vesicles or destroyed by enzymes.
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What is serotonin? |
5-hydroxytryptamine (5-HT). concentrated in neurons in part of brain called raphe nucleus. involved in sensory perception, temp regulation, mood control, appetite, induction of sleep. |
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What is nitric oxide? |
excitatory neurotransmitter secreted in brain, spinal cord, adrenal glands and nerves to penis. contains single N atom, unlike N2O (laughing gas, nitrous oxide). catalyzed by NOS from AA arginine. >2% of neurons in brain produce NO. not synthesized in advance or packaged into synaptic vesicles. forme don demand and acts immediately. |
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What is nitric oxide action brief? |
it's a free radical. exists for <ten seconds then combines with oxygen and water to form inactive nitrates. |
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Why does NO diffuse from cells that produce to neighbouring cells? What does it do there? |
It's lipid-soluble so can diffuse through PM. it activates a second messenger called cyclic GMP. |
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What's an example of synthetic NO? |
viagra - alleviates erectile dysfunction by enhancing effect of NO. |
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What role does NO play? |
possibly a role in memory and learning. produced by phagocyotic cells to kill microbes and tumour cells. |
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What are neuropeptides? |
3 to 40 amino acids linked by peptide bonds = neuropeptides. Bind to metabotropic receptors. excitatory or inhibitory. formed in neuron cell body, packaged into vesicles, transported to axon terminals. also act as hormones that regulate phsyiological responses elsewher ein the body. |
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What is a neural circuit? |
A functional group of neurons that processes specific type of information. |
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What is a simple series circuit |
presynaptic neuron stimulates a single postsynaptic neuron, stimulates another, etc. rare. |
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What is a diverging circuit? |
single presynaptic neuron synapses with several postsynaptic neurons. ex. small number of neurons in brain stimulate much larger number of neurons in spinal cord. also sensory signals relay sensory impulses to several regions of the brain. |
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What is a converging circuit? |
Several presynaptic neurons synapse with single postsynaptic neuron. more effective stimulation or inhibition of postsynaptic neuron. ex. single motor neuron synapses with skeletal muscles fibres at NMJ. receives input from several pathways from different brain regions. |
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What is a reverberating circuit? |
stimulation of presynaptic cell causes postsynaptic cell to transmit a series of nerve impulses. impulses sent back through circuit again and again. ex. breathing, coordinated muscle activity, waking up, short-term memory. |
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What is a parallel after-discharge circuit? |
Single presynaptic cell stimulates group of neurons, each of which synapses with a common post-synaptic cell. differing number between first and last, imposing various synaptic delays = EPSPs and IPSPs in last neuron. if input is excitatory, postsynaptic neuron then can send out a stream of impulses in quick succession. ex. mathematical calculations. |
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What is plasticity? |
capability to change based on experience. sprouting of new dendrites, synthesis of new proteins, changes in synaptic contacts with other neurons. |
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What drives plasticity? |
Both chemical and electrical signals. |
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What is neurogensis? |
birth of new neurons from undifferentiated stem cells. occurs in some animals such as songbirds. in humans, thought to not occur, but happens in hippocampus - crucial to learning. |
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Why doesn't neurogenesis occur in other regions of brain and SC? |
1. inhibitory influences from neuroglia, partic. oligodendrocytes, 2) absence of growth-stimulating cues that were present during fetal development. |
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What happens when an axon is damaged in the CNS? |
astrocytes proliferate rapidly, scar tissue formed that might act as physical barrier to regeneration. injury to brain or spinal cord is usually permanent. |
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What happens to damaged neurons in the PNS? |
axons and dendrites may undergo repair if cell body is intact, if Schwann cells are functional, if scar tissue doesn't form too quickly. most nerves in PNS are covered with neurolemma, which makes it more likely for nerve to be repaired, ie. in an upper limb. |
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What happens to damaged axons in PNS? |
changes usually occur both in cell body and distal site to injury. changes might also occur in proximal portion of axon to site of injury. |
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What are the steps to repair damaged axon in PNS? |
24 to 48 hours after injury to process of peripheral neuron, Nissl bodies break up into fine granular masses = chromatolysis. - 3 to 5 days later, part of axon distal to damaged region becomes slightly swollen, breaks up into fragments; myelin sheath deteriorates, neurolemma remains = Wallerian degeneration. - Schwann cells on either side of injury multiply (mitosis), might form regeneration tube. - regeneration tube guides growth of new axon from proximal area across injured area into distal area previously occupied by the original axon. - during first few days after damage, buds of regenerating axons begin to invade tube - find their way into distal tubes, grow toward receptors and effectors. |
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When can new axons not grow in PNS? |
If site of injury gap is too large or if gap becomes filled with collagen. |
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How fast do axons grow? |
1.5mm per day across damaged area. |
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What is multiple sclerosis? |
Disease. causes progressive destruction of myelin sheaths surrounding neurons in CNS. |
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How many people are afflicted by MS and whom? |
350,000 people in US, 2 millions worldwide. appears between ages of 20 to 40, affects females twice as often as males. most common in whites, less in blacks, rare in Asians. |
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What are scleroses? |
hardened scares or plaques. |
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How can MS be seen/diagnosed? |
MRI studies of the brain would show numerous plaques in white matter of brain and spinal cord. |
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What is the most common form of MS? |
relapsing-remitting MS. usually appears in early adulthood. |
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What are the first symptoms of relapsing-remitting MS? |
feeling of heaviness or weakness in muscles, abnormal sensations, double vision. attack is followed by period of remission, symptoms temporarily disappear. attacks might come back every year or two. progressive loss of function, interspersed with remission periods. |
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What causes MS? |
genetic susceptibility and possibly some environmental factor such as herpes. |
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What do beta interferon injections do? |
treatment lengthens time between relapses, decreases severity of relapses, and slows formation of new lesions in some cases. not all MS patients can tolerate it. |
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What is epilepsy? |
short, recurrent attacks of motor, sensory, psychological malfunction. almost never impacts intelligence. |
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What percent of population is afflicted with epileptic seizures? |
1% |
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How are seizures initiated? |
abnormal, synchronous electrical discharges from millions of neurons in mullions of neurons in the brain, perhaps from abnormal reverberating circuits. discharges stimulate many neurons in send nerve impulses over conduction pathways = light, noise, smells sensed when eyes, ears and nose haven;t been stimulated. skeletal muscles contract involuntarily. |
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What is a partial seizure vs. generalized? |
partial begins in small area on one side of brain, produce milder symptoms. generalized involve larger areas on both sides of brain and loss of consciousness. |
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What causes epilepsy? |
most common: brain damage at birth. also, metabolic disturbances (hypoglycemia, hypocalcemia, uremia, hypoxia), infections (encephalitis or meningitis); toxins (alcohol, tranquilizers, hallucinogens); vascular disturbances (hemorrhage, hypotension); head injuries; tumors and abscesses of brain. fevers under age of two. |
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How can seizures be eliminated or alleviated? |
antiepileptic drugs: phenytoin, carbamazepine, valproate sodium. implantable device can stimulate vagus nerve. or surgery in very severe cases. |
