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A&P Lec Chap 12 Pt.2
A&P Lecture WK 7 Chap 12 Nervous Tissue Pt. 2
| Term | Definition |
|---|---|
| Unmyelinated axons have | - voltage-gated channels along their entire length |
| unmyelinated axon action potential at trigger zone causes Na+ to enter axon and | diffuse into adjacent regions - Depolarization opens voltage-gated channels - Opening of channels results in a new action potential which then allows Na+ diffusion to excite membrane immediately distal to that - Continuous conduction occurs |
| continuous conduction: | Chain-reaction continues down axon Like a wave of falling dominoes |
| Action potentials can only be generated at the | nodes, where voltage-gated ion channels are concentrated - Electrical signal must spread passively between nodes - Signal passes very quickly, but strength decreases - When signal reaches next node it can still depolarize the membrane to threshold |
| at the nodes after the signal reaches the next node to start depolarization | - Voltage gated Na+ channels open and a new, full-strength action potential occurs - Action potential seems to “jump” from node to node - Moves faster through “insulated” segments covered w myelin - Slows down when it reaches bare axon of the nodes |
| Synapse: | point where an axon terminal meets the next cell (another neuron, gland cell, muscle cell) - Where the neuron communicates with one another - Signal is received from the upstream neuron |
| For neuron-to-neuron synapses: | Action potential arrives at end of axon of presynaptic neuron Presynaptic neuron releases neurotransmitter The postsynaptic neuron responds to it |
| Neurotransmitters are released at chemical synapses: There are also electrical synapses which occur | between some neurons, neuroglia, cardiac, & single-unit smooth muscle Gap junctions join adjacent cells; electrical signals spread directly from cell to cell |
| advantages and disadvantages of electrical synapses | Advantage—much faster; no delay for release, diffusion, and binding of neurotransmitter Disadvantage—cannot integrate information |
| More than 100 neurotransmitters have been identified, most falling into these major chemical categories: | acetylcholine, amino acids, monoamines, purines, gases, neuropeptides |
| Acetylcholine: | formed from acetic acid and choline - helps with muscle contraction |
| Synapses are variable in their modes of action | - Some neurotransmitters are excitatory, others inhibitory - sometimes a transmitter’s effect differs depending on type of receptor on postsynaptic cell |
| It is important not only to stimulate a postsynaptic cell but also to turn off the stimulus | Neurotransmitter stays bound to receptor for about 1 ms - If the presynaptic cell continues to release neurotransmitter, one molecule is quickly replaced by another and the postsynaptic cell continues to be stimulated |
| To end the signal: | Presynaptic cell stops releasing neurotransmitter Neurotransmitter already in synapse is cleared in various ways |
| Neurotransmitter degradation: | enzyme in synaptic cleft breaks down neurotransmitter Example: acetylcholinesterase (AChE) breaks ACh down into choline and acetate |
| Reuptake: | neurotransmitter or its breakdown products reabsorbed into axon terminal Example: choline from ACh recycled to make new ACh |
| Amino acids and monoamines also reabsorbed, degraded in axon terminal by | enzyme monoamine oxidase (MAO) |
| monoamine oxidase (MAO): | target of some antidepressant drugs |
| Diffusion: | neurotransmitter or its breakdown products simply away from synapse into nearby ECF |
| Neural integration: | ability to process, store, recall info and use it to make decisions - decision making (allowed by chemical synapses) - complex integration - Brain cells are incredibly well connected |
| Trade off: | chemical transmission involves a synaptic delay that makes information travel slower than it would if there was no synapse |
| Two types of postsynaptic potentials produced by neurotransmitters: | Excitatory postsynaptic potential (EPSP) and Inhibitory postsynaptic potential (IPSP) |
| Excitatory postsynaptic potential (EPSP): | voltage change from the RMP toward threshold An EPSP usually results from flowing into the cell |
| Inhibitory postsynaptic potential (IPSP): | voltage becomes more negative than it is at rest An IPSP can result from C1- entry or K+ exit from cell |
| A neurotransmitter might excite some cells and inhibit others, depending on the type of receptors in the postsynaptic membrane: | ACh excites skeletal muscle but inhibits cardiac muscle due to the expression of different types of ACh receptors on the different types of muscle cells |
| Summation: | process of adding up postsynaptic potentials & responding to net effect - Occurs in trigger zone - incoming nerve fibers may produce EPSPs or IPSPs - neuron’s response depends on if net input is excitatory or inhibitory - help make decisions |
| Two ways EPSPs can be added to reach threshold: | Temporal summation and spatial summation |
| Temporal summation: | - Adding puppies continuously, one after another in quick succession - a single synapse generates EPSPs so quickly that each is generated before previous one fades - adds up over time to a threshold voltage that triggers an action potential |
| Spatial summation: | - Puppies shown all at the same time, to easily conduct a signal - EPSPs from several different synapses add up to threshold at an axon hillock - Simultaneous input from multiple presynaptic neurons required for the postsynaptic neuron to fire |
| An example of facilitation: | a process in which one neuron enhances the effect of another |
| Memory trace (engram): | pathway of synapses through the brain; physical basis of memory Along this pathway, new synapses are created or existing synapses modified to make transmission easier |
| Synaptic plasticity: | ability of synapses to change |
| Synaptic potentiation: | process of making transmission easier |
| Three kinds of memory: | Immediate memory, short-term memory, and long-term memory Correlated with different modes of synaptic potentiation that last from a few seconds to a lifetime |
| unmyelinated axons compared to myelinated axons have to | take continuous steps to work rather than larger steps like green light myelinated axons |
| Presynaptic neuron | is the neuron that is the upstream neuron which sends the signal |
| Postsynaptic neuron: | is the neuron downstream underneath that receives the signal |
| To even get the signal, | Calcium enters the end terminal causes the neurotransmitter to be released |
| -Some receptors are ligand-gated ion channels; | lock & key channels that are direct cause the neurotransmitter bind and open the gate |
| through intracellular second messengers - | signal that zaps the secondary messenger which the secondary messenger does the action - neurotransmitter binds to receptor and secondary messenger opens the gate |
| in summation, Action potential must reach | potential at axon hillock or there won’t be any signal conduction |
| Excitatory synapses | excite the cell closer to the threshold Sodium (Na+) flowing into cell |
| Inhibitory synapses | hyperpolarizes the cell, making it further away from the threshold Potassium (K+) flowing out of cell There to temper the static of super excited nervous system - helps balance signals and to not send nonsense signals |
Created by:
Katepop10