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A&P 2
(2) Membrane potentials and Synapse
| Question | Answer |
|---|---|
| what are the 3 types of membrane potentials | resting, graded, action |
| what is resting membrane potential | a charge gradient (difference) between the inside and outside of a neuron while the neuron is at rest |
| what is the greater concentration inside of cells | K+ ions and negatively charged proteins |
| what is the greater concentration outside of cells | Na+ and Ca++ |
| what happens in a resting membrane potential at rest | passive K+ ion channels are open and allow K+ to easily diffuse out of the neuron, leaving non-diffusible negatively charged proteins inside the neuron |
| what generates a positive charge outside the neuron compared to an overall negative charge inside the neuron in resting membrane potential | the loss of positive ions outside and the remaining negative proteins inside |
| true or false: in resting membrane potential, there are fewer Na+ ion channels so it lows in at a much slower rate than K+ leaves | true |
| true or false: neurons are 25% more permeable "leaky" to K than Na | true |
| in resting membrane potential, when inflowing Na+ ions replace some of the lost positive K+ ions, it makes | an overall positive charge outside the neuron, and a negative charge inside |
| in resting membrane potential, what happens where there is an overall positive charge outside the neuron, and a negative charge inside | minimal ion movement and resting potential is establishes |
| what is the voltage when resting potential is established | -70mV |
| what is the charge difference maintained by | sodium potassium pumps |
| what do sodium potassium pumps do | actively transport Na back out of cell and K back into cell |
| what are graded potentials | occur on a neuron anytime it is stimulated (chemically/mechanically) |
| depolarization | neuron gets less negative |
| what are graded potentials | occur on a neuron anytime it is stimulated (chemically/mechanically) |
| depolarization | neuron gets less negative |
| what are the basics of graded potentials | smaller changes in voltage, confided to a small region, decay as they travel (short distances signals) |
| hyperpolarization | neuron gets more negative |
| what determines how far graded potentials travel | strength of stimulus |
| smaller stimulus opens... | few gated ion channels, can only travel short distance |
| stronger stimulus opens... | more gated ion channels, can travel a longer distance |
| what are graded potentials associated with | dendrites and cell bodies, receptive endings of sensory neurons, and muscle cells |
| graded potential that is depolarizing brings neuron... | closer to generating an actinon potential |
| graded potential that is hyperpolarizing... | inhibits neuron from generating an action potential |
| what are the basics of action potentials | do not decay as they travel (long distance signals), only on axons, large change in voltage, fast depolarization and repolarization of an axon |
| how do action potentials begin | when stimulus is strong enough to cause enough chemically/mechanically gated Na+ ion channels to pen, resulting in an influx of Na+ that depolarizes the neuron and brings axon hillock to a threshold of -55mV |
| what happens when an action potential reaches threshold | voltage gated Na+ channels open on axon hillock, and incoming Na+ causes depolarization to +30mV |
| true or false: there is a positive feedback mechanisms that spreads depolarization down the axon | true |
| how does repolarization happen | at +30mV, volage gated Na+ channels close, and voltage gated k+ channels open, allowing K+ to leave the neuron. the loss of positive ions allows inside to become more negative |
| true or false: K+ channels open fast | false |
| what causes hyperpolarization in an action potential | voltage gated K+ channels are slow, allowing excess K+ to leave neuron slightly until the channels close |
| at the end of an action potential, how is the original ion distribution reestablished | sodium-potassium pumps |
| what is an action potential | fast depolarization and repolarization of an area on the axon |
| true or false: the propagation (spreading) of an action potential is an impulse | true |
| what ensures one-way flow of an action potential on the axon | refractory periods |
| what is the absolute refractory period | period of time when a new action potential CANNOT be generated |
| when does the absolute refractory period begin | opening of voltage gated Na+ channels and continues until channels close and voltage gated K+ channels open and the neuron is part way repolarized |
| what do absolute refractory periods do | keeps impulse moving forward and determines how many impulses can be generated per second |
| what is the relative refractory period | period of time when a new action potential can be generated if stimulus is strong enough (even less negative that -55mV) |
| when is the relative refractory period | follows the absolute refractory period, continues until neuron has returned to resting membrane potential |
| where is saltatory conduction | on neurons with "A" and "B" fibers, action potentials can only be generated at the nodes of Ranvier |
| true or false: action potentials jump from node to node | true |
| true or false: because of saltatory conduction, speed of impulse transmission is much faster on myelinated processes | true |
| what reduces a membranes permeability to Na+ | alcohol, sedatives, anesthetics |
| what is a electrical synapse | an action potential spreads from one cell to another via a gap junction |
| what is electrical synapse associated with | smooth and cardiac muscle |
| what is chemical synapse | a junction between 2 neurons |
| what does chemical synapse include | axon terminal of a presynaptic neuron and the dendrite, cell body, or axon hillock of a postsynaptic neuron |
| what is released ono the synaptic cleft by terminal knobs belonging to the presynaptic neuron | neurotransmitter |
| how does neurotransmitter release into the synapse | when action potential reaches terminal knob, voltage gated Ca channels open, and Ca enters and activates enzyme that induces synaptic vesicles to fuse to cell membrane and release their neurotransmitter via exocytosis |
| if a neurotransmitter is ionotropic... | it will bind to ion channel linked receptor to directly open ion channel |
| if neuron transmitter is metabotropic... | it will bind to G protein linked receptor to indirectly open ion channel |
| what are the ways neurotransmitters can be removed | some will diffuse away, some may be degraded to an enzyme (acetyl cholinesterase), some may be actively pumped back into terminal knob by reuptake pumps (norepinephrine and serotonin) |
| what blocks reuptake of a neurotransmitter | some drugs (Prozac) |
| neurotransmitters are categorized as excitatory or inhibitory based on | whether they depolarize or hyperpolarize a postsynaptic neuron |
| excitatory neurotransmitters | cause depolarization of postsynaptic neuron by opening chemically gated Na+ ion channels. generate excitatory post synaptic potentials (EPSP's) |
| what are the 2 types of excitatory neurotransmitters | acetylcholine (ACH) and glutamate (glutamic acid) |
| what is the most common neurotransmitter in the whole body | acetylcholine (ACH) |
| what is glutamate (glutamic acid) | most common neurotransmitter in brain |
| inhibitory neurotramstters | cause hyperpolarization of postsynaptic neuron by opening chemically gated K+ and/or Cl- ion channels. generate inhibitory post synaptic potentials (IPSP's) |
| what are the 2 types of inhibitory neurotransmittes | GABA and Glycine |
| what is GABA | most common inhibitor in brain, opens chloride ion channels |
| what does brain rely on GABA for | to prevent too many stimuli (alcohol and drugs interfere with GABA) |
| what is glycine | primary inhibitory in spinal cord |
| what is summation | requires thousand of impulses reaching terminal knobs of axon to generate enough transmitter to bind to enough receptors to reach threshold membrane potential and trigger an action potential |
| what is spatial summation | many terminal knobs all contribute neurotransmitters to the same postsynaptic neuron |
| what is temporal summation | few terminal knobs repeatedly release neurotransmitters into same synapse until there's enough to generate a threshold membrane potential |
| what is convergence | more presynaptic neurons that postsynaptic neurons, allows control over number of impulses generated on the postsynaptic neuron |
| what is divergence | fewer presynaptic neurons than postsynaptic neurons, allows impulses to spread out into more than one pathway |
Created by:
katiew0