Action Potentials and Synaptic Transmission

Question 1

what are key factors of AP

Answer 1

Self-propagating biochemical disturbance that generates an electric field or dipole
Successive APs can only be triggered following a brief recovery period, and finally
Absolute and relative refractory periods
All-or-none response
Naturally travel only in one (forward) direction

Question 2

Describe an action potential generation

Answer 2

a neuron is depolarized to threshold
sodium ion channels open in response to changes in membrane potential (changes in voltage) (voltage gated ion channels)
since more positively charged sodium ions are outside the cell and inside the cell is more negative, opening of the channel allows sodium to rush in due to influence of diffusion and electrostatic forces
influx depolarizes the cell causing more voltage sodium channels to open leading to more depolarization (rising phase of an action potential)
potassium channels open and allow it to rush out along with potassium leak channels
signal moves down axon

Question 3

what is the rising phase of an AP

Answer 3

the rapid change in membrane potential
when the influx of sodium causes depolarization in turn causing more voltage gated sodium ion channels to open leading to more depolarization

Question 4

how does an ap come to an end?

Answer 4

once neuron membrane potential reaches its peak, voltage gated sodium channels begin closing
potassium moving out of a cell through potassium gated ion channels and leak channels helps repolarize the cell (back to resting membrane potential)
sodium potassium pump also helps to restore mp

Question 5

how does an AP move down an axon

Answer 5

once depolarization occurs at one segment causes voltage gated sodium ion channels to open regenerating the ap in the next segment of the axon

Question 6

lipid rich material that wraps around axons making propagation of ap down the axon faster and more efficient

Answer 6

myelin

Question 7

How does myelin help propagations of ap go faster?

Answer 7

prevents current from leaking out of the axon
increases speed of propagation interruped by nodes of Ranvier (gaps in myelin)
these nodes are rich in voltage gated sodium channels causing inrushing of sodium and regeneration of AP (happens at each node) propelling the AP down the axon

Question 8

saltatory conduction

Answer 8

regeneration of ap at nodes of ranvier and slowing at the myelinated regions between them (internodes) causes AP to appear as if its jumping down the axon

Question 9

what is meant by all or none of an AP

Answer 9

refractory period makes rate of ap firing related to intensity of stimulation
AP don’t vary in size based on intensity of a stimulus, they either fire or they don’t
when they fire they’re consistent amplitude/size

Question 10

more intense stimuli will cause ______ frequency firing of AP

Answer 10

more

Question 11

why does a more intense stimuli will cause more frequency firing of AP?

Answer 11

they’re able to overcome relative refractory period in neurons

Question 12

what happens after a RP depolarizes a receptor

Answer 12

connected axon can generate an AP
or after a receptor send NT across a synapse, the post-synaptic neuron will be triggered and if it is EXCITED postsynaptic potential (EPSP), the voltage change from the EPSP will start the AP

Question 13

what are ligand-gated channels

Answer 13

alter their permeability as a function of the binding of chemicals/ligands to specific receptors as in the binding of a neurotransmitter to a post-synaptic cell
protein channel that allows an ion to pass through the membrane in response to the binding of a chemical messenger, like a neurotransmitter

Question 14

what are mechanically or thermally gated channels

Answer 14

mechanically - open and close in response to mechanical vibration or pressure, such as sound waves or the pressure of touch
thermally - activated by temperature, voltage, pH, lipids, and agonists. usally calcium or magnesium channels

Question 15

how long to voltage gated ion channels open for

Answer 15

10 milliseconds

Question 16

where does voltage gated channel open at?

Answer 16

axon hillock

Question 17

depolarization activates what

Answer 17

voltage gated potassium channels

Question 18

gives rising phase

Answer 18

depolarization, influx of sodium

Question 19

gives falling phase

Answer 19

repolarize, potassium leaving the cell

Question 20

which channel stays open longer

Answer 20

potassium causing a prolonged outward K+ current

Question 21

what is resting potential in mv

Answer 21

-70

Question 22

how are ionic balances restored

Answer 22

sodium potassium pump

Question 23

what is absolute refractory period

Answer 23

time period after the threshold was reached (that caused the AP) until the sodium inactivation mechanism is reset which takes about 2 msec

Question 24

what is relative refractory period

Answer 24

after the sodium inactivation mechanism is reset and while there is still an outward potassium current
An AP can be generated but only by a stimulus that is stronger than what is usually required to reach threshold for an AP

Question 25

are AP travelling in one direction?

Answer 25

yes, The node or place that was just activated is still in a refractory period, but the node in the other direction is ready to fire so the AP propagates in only one direction The AP is the same “full” strength at each occurrence so it does not degenerate or lose information on its way to or from the brain

Question 26

frequency of action potential firing rate

Answer 26

frequency modulated

Question 27

gentle pressure =

Answer 27

low frequency ap (slow)

Question 28

more pressure =

Answer 28

high frequency ap (faster)

Question 29

What happens at the synaptic cleft?

Answer 29

Chemical messengers carry info from one cell to another AP reaches the terminal bouton of the axon Ca++ channels are triggered and open = influx of Ca++ Triggers neurotransmitter vesicles to release NT into synaptic cleft NT finds receptors sites on the next neuron and bind to have an action

Question 30

what are NTs?

Answer 30

amines, amino acids and neuropeptides

Question 31

what are the NTs of A/V system? (CNS)

Answer 31

glutamate + aspartate + GABAergic - glycine - acetylcholine efferent (olivocochlear bundle)

Question 32

what is NT at neuromuscular jxn (nerve to muscle) and in some areas of CNS?

Answer 32

acetycholine

Question 33

what are the efferent inhibitory NT of AVS?

Answer 33

noradrenaline

Question 34

what are the efferent excitatory NT of AVS?

Answer 34

acetycholine

Question 35

what are the afferent excitatory NT of AVS

Answer 35

glutamate aspartate

Question 36

what are afferent inhibitory NT of AVS

Answer 36

GABA glycine

Question 37

What are the Five Steps in Chemical Synaptic Transmission

Answer 37

1) Synthesis of NT in presynaptic endings and in soma 2) Concentration and packaging of NT in synaptic vesicles 3) Release of NT into synaptic cleft 4) Binding of NT to receptor molecules in postsynaptic membranes 5) Termination of NT action by uptake, degradation or diffusion

Question 38

How does termination of NT occur?

Answer 38

NT may diffuse away but this is slow at most synpases NT is absorbed by the presynaptic ending or nearby glial cells or by the postsynaptic process at some synapses, enzymes degrade the free NT reabsorbed NT can by recycled for use again

Question 39

describe fast transmission

Answer 39

uses transmitter-gated (ligand-gated) ion channels independent ap reached terminal bouton calcium goes in and causes vesicles to move to cell membrane and open and dump NT out they will bind to receptor sites on next cell and the bounding opened the channel chem ligand channel opening sodium in potassium out and causes postsynaptic in next cell

Question 40

describe slow transmission

Answer 40

usually involves a second messenger after binding of the NT to postsynaptic receptors caused some chemical to be the messenger using helper system here not as fast as the first one so the channels are slower at opening electrical change reaches terminal bouton stronger stimulus dumped NT at bottom but opens more vesicles and dumps it out on the sides binds to sites and causes second messenger to open ion channels

Question 41

destinations of AP’s going from neuron to the next is the ascending info

Answer 41

goes to CNS: spinal cord, brainstem, cerebrum, cerebellum, etc

Question 42

antagonist

Answer 42

person who is blocking you, barrier, the problem curare beta-blocker

Question 43

agonist

Answer 43

the activator el dopa - to mimic dopamine

Question 44

How does curare work

Answer 44

A molecule can bind to a receptor and prevents it from receiving a NT paralyzes by blocking

Question 45

What is the resting potential of a cell?

Answer 45

-65-70mV cell at rest is more neg inside than outside, and it is ready to be activated and receive information

Question 46

Define depolarization?

Answer 46

going from negative towards positive polarizing = negative

Question 47

What is a receptor potential?

Answer 47

bioelectrical change in a receptor as a part of sensory transduction to code a stimulus (touch, vision, etcl.) into an electrical signal the CNS can take some stimulus and code it into bioelectrical activity

Question 48

What is an action potential?

Answer 48

all or none, bioelectrical change that is self propagating in a forward direction to carry info from receptor sites to CNS or from A to B

Question 49

What is the sodium potassium pump?

Answer 49

maintains resting membrane potential active pump that maintains balance of sodium and potassium for resting membrane potential and to reset it after there has been a receptor or active membrane potential puts 3 sodium out and 2 potassium in extracellular is high and sodium out and potassium in is low

Question 50

What is a synapse?

Answer 50

method of comm from one cell to another using a nt across a synaptic cleft

Question 51

what is a neurotransmitter

Answer 51

chemical or ligand used for synaptic transmission

Question 52

step by step of sensory transduction Start with a stimulus and receptor What happens at the receptor? What triggers the AP? How does the AP travel? What happens at the terminal bouton? What happens at the synaptic cleft? What happens in the post-synaptic neuron?

Answer 52

at receptor sit at resting and stimulated by some force (mechanical, thermo, photo, etc.) volt change from a receptor causes AP AP travels in a self propagating, forward by soltatory conduction (jumping from node to node) if myelinated prep for synaptic vesicles with NT to be dumped out onto SC NT goes to next cell at synaptic cleft NT at the next cell causes either EPSP or IPSP

Question 53

if there's enough change or threshold is reached

Answer 53

an AP is activated