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Biology anatomy/physiology > Synaptic Transmissions > Flashcards

Synaptic Transmissions Flashcards

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1
Q

What is a refractory period?

A
  • during an impulse, the portion of the axon actively conducting the action potential is not able to respond to another threshold stimulus of normal strength.
  • refractory period limits number of action potentials generated per second
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2
Q

What is the absolute refractory period?

A
  • time when threshold stimulus cannot ternate another action potential
  • voltage-gated Na+ channels are briefly unresponsive
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3
Q

What is the relative refractory period?

A
  • time when only high-intensity stimulus can generate another action potential
  • re-polarization is not complete and membrane is re-establishing resting potential
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4
Q

What causes the variation in the speed of impulse conduction?

A
  • myelination of an axon
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5
Q

what does myelin consist of?

A
  • is rich in lipids and prevents water and water-soluble substances (such as ions) from crossing membrane; acts as electrical insulator
  • ions can cross membrane only thru gaps in myelin sheath, “Nodes of Ranvier”
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6
Q

What is saltatory conduction?

A
  • myelinated axons transmit impulses thru saltatory conduction, in which action potentials “jump” from node to node down the axon
  • saltatory conduction is much faster than impulse conduction in unmyelinated axons
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7
Q

how does axon diameter affect conduction speed?

A
  • thick axons transmit faster than thin axons
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8
Q

What are synapses?

A
  • connections where neurons communicate

- they are able to communicate chemical directions to one another

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9
Q

What is the presynaptic neuron?

A
  • referring to the neuron releasing neurotransmitter at a synapse on the “sending side of a synapse
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10
Q

What is the postsynaptic neuron?

A
  • referring to the neuron or other type of cell on the “receiving” side of a synapse
  • could also be a muscle or glandular cell
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11
Q

What is synaptic transmission?

A
  • the mechanism by which the impulse in the presynaptic neuron signals the postsynaptic cell
  • as a result of synaptic transmission, the presynaptic neuron stimulates or inhibits a postsynaptic cell
  • is a one-way process carried out by neurotransmitters
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12
Q

how does an impulse continue from one neuron to another?

A
  • it has to cross the synaptic cleft
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13
Q

What happens when an impulse reaches the synaptic knob at the end of an axon?

A
  • the synaptic vesicles release a neurotransmitter that diffuses across the synaptic cleft
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14
Q

What is the structure of a synaptic knob?

A
  • is the transmissive segment of a neuron
  • the synaptic knob contains vesicles filled with neurotransmitter
  • upon stimulation, they are released into the synaptic cleft and bind with NT-specific ligand-gated channels on the postsynaptic membrane
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15
Q

What happens when action potential reaches the synaptic knob of the presynaptic axon?

A
  • the presynaptic axon contains large numbers of NT-containing synaptic vesicles
  • When the AP reaches this region, folate-gated calcium channels open and result in an influx of calcium
  • this triggers the release of the NTs by exocytosis
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16
Q

What happens when neurotransmitters (NTs) diffuse across the synaptic cleft?

A
  • the NTs diffuse across the cleft and then bind to NT-specific receptors present on the postsynaptic membrane
  • this binding triggers the opening of ligand-gated ion channels
  • this causes either depolarization or hyperpolatization of the postsynaptic membrane
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17
Q

What happens to NTs that are left within the synaptic cleft?

A
  • they are either broken dow or taken back up into the synaptic knob
  • enzymes within the extracellular fluid break down the NTs to be taken back up to the synaptic knob
18
Q

What drives neural communication between cells?

A
  • is driven by changes in membrane permeability to ions
  • neurons receive input from multiple different types of stimuli
  • the summation of graded potentials and the unidirectional propagation of APs are due primarily to changes in Na+ and K+ membrane permeability
  • all of this ultimately results in the release of NTs
19
Q

Describe synaptic transmission

A
  • is the process by which an impulse in a presynaptic neuron transfers info to a postsynaptic cell
  • involves a chemical NT, released by the presynaptic cell that binds to receptors on the postsynaptic cell
  • this binding causes chemically-gated ion channels to open in the postsynaptic cell, creating a synaptic potential in that cell
20
Q

what are the effects of NTs?

A
  • they vary

- some open to ion channels and others close ion channels

21
Q

What are synaptic potentials?

A
  • local potentials resulting from changes in chemically gated ion channels
22
Q

What are excitatory neurotransmitters?

A
  • increase permeability to Na+ ions

- bring membrane closer to threshold; increase likelihood of generating impulses

23
Q

What are inhibitory neurotransmitters?

A
  • move membrane farther from threshold

- decrease likelihood of generating impulses

24
Q

What is an excitatory postsynaptic potential? (EPSPs)

A
  • membrane change in which neurotransmitter opens Na+ channels
  • de-polarizes membrane of postsynaptic neuron as Na+ enters axon
  • action potential in postsynaptic neuron becomes MORE likely
25
Q

What is inhibitory postsynaptic potential? (IPSPs)

A
  • membrane change in which neurotransmitter opens K+ channels
  • hyper-polarizes membrane of postsynaptic neuron as K+ leaves axon
  • action potential of post-synaptic neurons becomes LESS likely
26
Q

What is summation?

A
  • a process where EPSPs and IPSPs are added together

- summation of all inputs usually occurs at the trigger zone (axon hillock)

27
Q

What does net excitatory effect lead to?

A
  • greater probability of an action potential
28
Q

What does net inhibitory effect lead to?

A
  • effect does not generate action potentials
29
Q

What does acetylcholine do?

A
  • stimulates skeletal muscle contraction
  • used in CNS to control skeletal muscle actions
  • used in PNS to stimulate skeletal muscle contraction at neuromuscular junctions; may excite or inhibit at autonomic nervous system synapses
30
Q

What types of proteins can neurotransmitters be?

A
  • monoamines
  • amino acids
  • peptides
31
Q

Where are NTs produced?

A
  • in rough endoplasmic reticulum

- or cytoplasm

32
Q

How are NTs released when it reaches the synaptic knob of the axon?

A
  • by exocytosis
33
Q

What are the events that lead to neurotransmitter release?

A
  • action potential passes along an axon and over the surface of its synaptic knob
  • synaptic knob membrane becomes more permeable to calcium ions, and they diffuse inward
  • in the presence of calcium ions, synaptic vesicles fuse to synaptic knob membrane
  • synaptic vesicles release their NTs by exocytosis into the synaptic cleft
  • synaptic vesicle membrane becomes part of the cell membrane
  • the added membrane provides material for endocytotic vesicles
34
Q

What is vesicle trafficking?

A
  • process of membrane recycling
  • synaptic vesicle becomes part of cell membrane as it releases NT
  • endocytosis returns membrane to cytoplasm; forms new vesicles
35
Q

What are neuronal pools?

A
  • groups of interneurons that make synaptic connections with each other and are located completely with the CNS
  • interneurons work together to perform a common function
  • each pool receives input from other neurons
  • each pool generates output to other neurons
  • pools may affect other pools or peripheral effectors
36
Q

What is convergence?

A
  • one neuron receives input from several neurons
  • incoming impulses often represent info from different types of sensory receptors
  • allows nerve system to collect, process, and respond to info
  • makes it possible for a neuron to sum impulses from different sources
37
Q

What is divergence?

A
  • one neuron sends impulses to several neurons via branching of its axon
  • can amplify an impulse
  • impulse from a single neuron in CNS may activate several motor units in a skeletal muscle
  • impulse from a sensory receptor may reach different regions of the CNS for processing
38
Q

What happens during the absolute refractory period?

A
  • the axon’s voltage-gated sodium channels are temporarily not responsive at all, and the axon cannot be stimulated
39
Q

What does the refractory period ensure?

A
  • that an action potential is conducted in only one direction
  • down the axon because the area upstream from where the action potential has just occurred is still in the refractory period from the previous action potential
40
Q

What are the events leading to impulse conduction?

A
  • nerve cell maintains resting membrane potential by diffusion of Na+ and K+ down their concentration gradients as the cell pumps them up the gradients
  • neurons receive stimulation causing local potential changes which many sum to reach threshold
  • if threshold is reached, sodium channels in the trigger zone of the axon open
  • sodium ions diffuse inwards, depolarizing the membrane
  • potassium channels in the membrane open
  • potassium ions diffuse outward, re-polarizing the membrane
  • the resulting action potential causes an electric current that stimulates adjacent portions of the membrane
  • the action potential propagates along the length of the axon

Biology anatomy/physiology (27 decks)

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