Cells Cellular Physiology part 2 Flashcards Preview

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Flashcards in Cells Cellular Physiology part 2 Deck (73):
1

Synapses are

the connections between a neuron and its target cells

2

Target cells include:

~Another neuron
~Muscle cells (skeletal or smooth)
~Glandular tissue

3

Two forms of synapses

~Chemical synapses
~Electrotonic (ephaptic) synapses

4

Chemical synapses

~electrical activity releases a chemical substance (a neurotransmitter)
~neurotransmitter diffuses across the physical space (synaptic gap) to bind to chemical receptors to produce electrical changes on the target changes on the target cell
~this junction is electrical- chemical- electrical

5

where do neurotransmitters diffuse across?

synaptic gap

6

in a chemical synapse, what chemical substance is released?

neurotransmitter

7

What is another name for electrotonic synapse?

Ephaptic synapses

8

Electrotonic synapse

~physical connection between two cells
~low resistance electrical junction directly between cells

9

Which is more common in the human nervous system: chemical or electrotonic synapses?

Chemical synapses

10

Presynaptic membrane

~characterized by the presence of synaptic vesicles containing neurotransmitters
~characterized by several types of proteins in the membrane including transmitter specific transport proteins and voltage-gated Ca++ channels

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Synaptic gap

~between the pre and post synaptic gap membranes
~presynaptic vesicles release transmitters into the synaptic cleft or gap (20-30 um)
~the transmitter molecules then diffuse across the synaptic gap

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Postsynaptic membrane

~contains stereospecific neurotransmitter specific receptor proteins, which matches the shape of the transmitter- lock and key mechanism
~has 2 types of receptors
~has ligand-gated ionic channels (Na+, Cl-, or K+ channels most common)
~degredative enzymes that can break down the transmitter that is in the synaptic gap

13

what are the two types of receptors in the postsynaptic membrane?

~metabotropic receptor
~ionotropic receptor

14

Transmitter Release in presynaptic events

~is triggered when action potentials enter synaptic terminal or bouton
~depolarization of pre-synaptic terminal triggers the opening of voltage-gated Ca++ channels which produce a 100 fold increase in intracellular Ca++ concentration
~Ca++ bind to proteins found on synaptic vesicles and vesicles fuse with membrane of the terminals
~fusion of the transmitter vesicle with the pre-synaptic membrane release neurotransmitter into the synaptic gap

15

Why is the nervous system "green" or conservative?

it recycles!

16

Synaptic Vesicles (recycling- quickly)

~vesicles merge with the pre-synaptic membranes and release transmitter under influence of intracellular Ca++
~Under conditions of very rapid transmitter release, the empty vesicle may pinch right off
~will quickly refill with transmitter and put back into the quick release pool of transmitter
*there is a storage pool (a reserve of transmitters) for when there is a high level of activity demand

17

Synaptic Vesicles (recycling- membrane)

~more commonly, vesicle merge with membrane and becomes part of the pre-synaptic membrane
~when newly releasing vesicles attach to the presynaptic membrane, ,the area of membrane that represents the previous vesicle is pushed out the synaptic release area
~this process is repeated by other vesicles merging with the membrane so the membrane is continued to be pushed away from the synaptic release area
~vesicle will pinch off the membrane to be refilled with neurotransmitters
~is then recycled into either the storage or the active release pools of vesicles

18

transmitter pools can be ____ or ____ release pools

quick or slow release

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Types of transmitters

~Amino acids
~Amines
~Peptides

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Amino Acids

~small, synthesized, and packaged in synaptic vesicles

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Amines

~small, synthesized, and packages into synaptic vesicles

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Peptides

~large, synthesized, and packaged in dense-core vesicles

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Amino acid transmitters (4)

~Glycine
~Glutamate
~Aspartate
~GABA

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what does GABA stand for?

Gamma- amino butyric acid

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Glycine (inhibitory/ excitatory)

Inhibitory

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Glutamate (inhibitory/ excitatory)

Excitatory

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Aspartate (inhibitory/ excitatory)

Excitatory

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GABA (inhibitory/ excitatory)

Inhibitory

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Amine transmitters (3)

~Acetylcholine (ACh)
~Catecholamine
~Indole amines
*can be excitatory or inhibitory depending upon receptor types

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Types of Catecholamine (3)

~Dopamine (DA)
~Norepinephrine (NE)
~Epinephrine

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Types of Indole Amines (2)

~Serotonin (5-HT)
~Histamine

32

Types of polypeptides/ proteins (3+)

~Dynorphin
~Enkephalin
~Substance P
~Many others
*may be excitatory or inhibitory and is determined by the postsynaptic receptor to which it binds

33

Post-synaptic receptor (details)

~the neurotransmitter binds in a stereospecific (lock and key) mechanism to its post synaptic receptor
~the receptor is specific to its own transmitter
~there are multiple types of receptors specific to each transmitter
~post-synaptic response is dependent on neurotransmitter and transmitter receptor type

34

Ionotropic receptor

~the classic ligand-gated channel
~binding of transmitter to receptor produces opening of ionic channels

35

Metabotropic receptor

~binding of transmitter to receptor produced activation of membrane protein complex (G-proteins)

36

G-proteins

~once activated, the G-protein will break into sub-units
~these G-protein subunits then can activate a 2nd massager system such as the cyclic AMP
~the subunit activates the enzyme adenylyl cyclase which metabolizes ATP into cyclic AMP using the energy from ATP to drive the reaction

37

Cyclic AMP

~can have a number of actions including opening ionic channels, activating cascades of enzymes that can change the metabolic activity of the cell or active the nucleus to change the expression of the genome of the post-synaptic cell

38

Binding to receptor opens Na+ channels

~when binding a neurotransmitter to its receptor, the Na+ enters the cell and produces depolarization
~takes the membranes potential closer to threshold
~easier to excite these post-synaptic potentials (called excitatory post-synaptic potentials or EPSPs)

39

Binding to receptor opens K+ or Cl- channels

~Opening the K+ or Cl- channels allows K+ to leave the cell or Cl- to enter the neuron, either of which produces an increase in negative charge in the neuron (hyperpolarization)
~takes the membrane potential farther from threshold so would be inhibitory (inhibitory post-synaptic potential or IPSP)

40

EPSP

~are small (250-500 microvolts) compared to the changes needed to reach threshold which requires a 15 mV
~must add to one another or summate to reach threshold

41

what two things are required to reach threshold?

spatial summation and temporal summation (two forms of EPSP)

42

Spatial summation

when multiple synaptic inputs are arriving at the same time to the same area of dendrite

43

Temporal summation

when multiple action potentials arriving in rapid succession along one input again to the same area of dendrite

44

Axon hillock are

at the base of the axon where the it attaches onto the cells soma and is the most sensitive area

45

Closer EPSP generated to axon hillock is (harder or easier) to excite

easier

46

EPSP are local potentials and decay with

distance travels

47

threshold is reached at __ mV

15 mV

48

When it comes to integration of input within the neuron to produce its output action potential, the rules of excitability are:

~closer synapses are to axon hillock, the more influence they have
~the more synapses from a specific source, the more influence it has
~the higher the activity along a particular input, the more influence it will have
*this is how a neuron will integrate its various inputs

49

inhabitation dominates in the CNS (it comes from:)

~domination comes from both the high number of inhibitory synapses in the CNS and the power of IPSP

50

EPSP and IPSP (talking about threshold)

~so that 60 EPSP is needed to reach threshold
~ 1 IPSP can negate the effects of 1 EPSP
~ if there was 60 EPSP and 1 IPSP, would be equal to 59 EPSP and threshold would not be met (all or none action potential)

51

Removal of transmitter

~to stop synaptic action, we have to get rid of the transmitter from the synaptic gap

52

3 ways to get rid of transmitter molecules

~diffusion away from gap- transmitter like any molecules diffuse down its concentration gradient
~reuptake of transmitter presynaptically (and by glial cell) by transmitter specific reuptake transporter proteins- these are the same proteins that allow for vesicles to retake up transmitter that is now in the pre-synaptic cytoplasm
~enzyme destruction- breaking down the transmitter into its component parts which are not active against the neurotransmitter receptors

53

_____ is the most common site for action of neutrally active drugs

synapse

54

Drugs can act at the neurotransmitter receptor site by 3 ways:

~Agonist
~Antagonist
~increase affinity of binding of transmitter to its receptor

55

Agonist

drugs which mimic transmitters actions at the receptors
*also called mimetics

56

Antagonist

drug will block the action of transmitter at the receptor
*also called receptor blocker

57

Actions of neutrally active drugs

~act presynaptically as precursors of the synaptic transmitter to provide more substrate for the synthesis of new transmitter
~can block the reuptake of transmitter back into presynaptic bouton leaving it to act in the gap
~post-synaptically, drugs can block the action of enzymes, which break down the transmitter and leaving the transmitter active in the gap

58

drugs can act in the following ways:

~blockers decrease transmitter action
~agonists mimic transmitter action
~increased affinity of receptor for transmitter, transmitter precursor and receptor uptake, and enzyme blockers increase transmitter action

59

Agonists (6)

~Acetylcholine
~Norepinehrine
~Dopamine
~Serotonin
~GABA
~Enkephalin

60

Antagonists (7)

~Acetylcholine
~Norepinephrine
~Dopamine
~Enkephalins
~Serotonin
~Glutamate
~GABA

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Reuptake inhibitors (3)

~Serotonin
~Serotonin and Norepinephrine
~Norepinephrine and Dopamine

62

Increased receptor affinity (1)

~GABA

63

Enzyme inhibitor (2)

~Acetylcholine
~Norepinephrine and Dopamine

64

Neuroplasticity

~used to describe the changes in neural networks connections as a results of neural activity
~the rewiring of nervous system as a result of experience or learning

65

Synaptogenesis

~the formation of new synapses
~occurs throughout life bur there are critical (sensitive) periods when there are burst of synaptogenesis occurring

66

Synaptogenesis (steps general)

~synapse before activation
~synapse after activation: beginning to grow dendritic spines
~after continued activation, now synapses begin organizing
~formation of new synapses after repeated activation

67

what's the first step of synaptogenesis?

~an axon terminal approaches the area of post-synaptic membrane
~the post-synaptic receptors in the area of the membrane not inn contact with an axonal ending are intracellular and not on the membrane

68

After an axon terminal approaches the area of post-synaptic membrane, what is the next step in synaptogenesis?

~there is a release of neuromodulators
~they stimulate post-synaptic cells to express their receptors to the membrane surface
~will continue with the initial activation of postsynaptic neuron

69

What happens during the initial activation of post-synaptic neurons during synaptogenesis?

~further stimulates additional release of neuromodulators
~stimulate further development of membrane receptors

70

After activation of post-synaptic neurons, what is the next step in synaptogenesis?

~repeated activation of the new synapse will produce the development of dendritic spines

71

After the development of dendritic spines, what is the next step in synaptogenesis?

~continues with additional spine development
~spines further stimulate new synaptic contact

72

Critical period of synaptogenesis

~there is considerable early synaptic development after birth
~this exuberant growth of connections provide a proliferation of possible pathways that can be used for the development of wide variety of skills that children are developing
~this development requires sensory input and activity during that critical period for normal development

73

Synaptic Pruning

~this exuberant growth of connections early in development produced a great overgrowth of connections- more than needed for normal development
~those connections that were reinforced and further developed during normal development remain but others that were not during development did not survive- were "pruned"
~see a decline in connections during adolescence
~regular activity required to stimulate genetic expression of synaptic elements and neurotropic factors which form and maintain synapses