Things To Know For King

Front 1

how is a nerve impulse AP generated?

Back 1

an AP consists of a rapid transient depolarization of the neuronal membrane to near ENa it is generated by rapid and sequential changes in the relative permeability of membrane to Na and K

Front 2

capacitance

Back 2

transient signals do not spread as far as long-lasting signals. the prolongation of the signal by capacitance does help temporal summation of signals

Front 3

regenerative signals, why needed?

Back 3

needed for long-distance propagation of excitation

Front 4

pharmacological blockers

Back 4

TTX blocks Na current from extracellular side

Front 5

what is potential difference?

Back 5

the measure of work that is needed to move a unit of positive charge from one point to the other

Front 6

what is 1 volt?

Back 6

the energy needed to move 1 coulomb a distance of 1 meter against a force of 1 newton

Front 7

what is current?

Back 7

the net movement of positive charge per unit time

Front 8

what is an ampere?

Back 8

represents the movement of 1 coulomb of charge per second

Front 9

capacitor

Back 9

consists of two conducting platse separated by an insulating layer. it can store charges of the opposite sign

Front 10

the memrbane potential is...

Back 10

as the relative potential difference between inside and outside of a cell

Front 11

ion flux equals..

Back 11

(electrical driving force plus chemical driving force) x (membrane conductance)

Front 12

function of Na K pump

Back 12

prevents the ion gradient from running down and moves Na and K against their E/C gradients so 3 Na out and 2 K in

Front 13

permeability?

Back 13

the ease that an ion can pass through a memrane

Front 14

what is input resistance?

Back 14

depends on the number of resting ion channels and the size of the cell

Front 15

selectivity of channel by dehydration

Back 15

each ion has water surrounding aand the water has to be shed before the ion can go through the pore. Na ions are smaller than K ions so they grab onto water tigther therefore the dehydration energy is much higher

Front 16

visual transduction takes place where

Back 16

photoreceptor cells in retina

Front 17

rods

Back 17

dim light vision, high sensitivity, can detect individual photons, slow response kinetics

Front 18

cones

Back 18

bright-light/color vision fast response

Front 19

human retina has how many rod and cone types?

Back 19

1 rode and 3 cone types

Front 20

where does phototransduction take place

Back 20

on the outer segment

Front 21

electrical response to light....

Back 21

light produces a membrane hyperpolarization in rods and cones

Front 22

in dark photoreceptor is..

Back 22

depolarized at about -40mV cGMP gated non selective cation channel (Na and Ca) open leading to steady release of glutamate

Front 23

bright light does what to channels

Back 23

closes all light-sensitive channels that are normally open in darkness so it stop all dark current

Front 24

when rhodopsin is activated b y photon absorption this leads to what

Back 24

G protein transducin is activated (GDP-GTP)

Front 25

tranducin does what

Back 25

donates its GTP to a PDE which hydrolyzes cGMP leading to channel closure

Front 26

how many cGMP gated channels open in darkness?

Back 26

only 1 to a few percent on the outer segment open in darkness

Front 27

properties of cGMP gated channel

Back 27

directly gated by cGMP, nonselective among mono and divalent cations, shows no desensitization to its ligand

Front 28

cGMP in the photoreceptor production

Back 28

produced by the enzyme guanylyl cyclase and this keeps sodiumm channels open

Front 29

rhodopsin

Back 29

receptor protein with a prebound agonist called retinal. the absorption of light causes a change in the conformation of retinal so that it activates opsin which changes the wavelengths absorbed by the rhodopsin

Front 30

bleaching of rhodopsin stimulates what

Back 30

G-protein called transducin exchanges GDP for GTP

Front 31

in bright sunlight rods do what

Back 31

cGMP levels fall to the point where the response to light becomes saturated and additional light causes no more hyperpolarization

Front 32

deactivation of Rhodopsin

Back 32

Rho decays naturally over 1 min to speed this up Rh can be phosphorylated and deactivated by Rh kinases

Front 33

what prevents cGMP overproduction?

Back 33

presence of calcium-- activates calmodulin which acts directly on channel, activates GCP which acts on GC, by activating recoverin

Front 34

in light what happens to calcium levels?

Back 34

calcium levels drop bc light causes hyperpolarization. which then alows

Front 35

On bilpolar cell

Back 35

depolarizes with light in receptive field

Front 36

off bipolar cell

Back 36

depolarizes with no light in receptive field

Front 37

the pathway for visual information to exit the eye is....

Back 37

from photoreceptors to bipolar cells to ganglion cells

Front 38

ganglion cells do what

Back 38

fire action potentials in response to light

Front 39

horizontal cells

Back 39

receive input from the photoreceptors and project neurites laterally ro influence surrounding bipolar cells and photoreceptors

Front 40

amacrine cells receive input from

Back 40

bipolar cells and project laterally to influence surrounding ganglion cells bp cells and other amacrine cells

Front 41

what is the source of output from the retina?

Back 41

ganglion cells because no other retinal cell type projects an axon trhough the optic nerve

Front 42

dark adaptation:

Back 42

getting used to the dark, sensitivit to light actualy increases a millionfold or more

Front 43

what happens during adaptation

Back 43

your pupils dilate which allows more light to enter the eye

Front 44

calcium has what kind of effect on cGMP

Back 44

inhibits enzyme guanylyl cylcase that synthesizes cGMP

Front 45

Where does olfactory transduction take place

Back 45

in the cilia of olfactory receptor neurons in the olfactory epilthellium. tight junctions prevent odorant molecules from penetrating any deeper into the olfactory epithelium

Front 46

what is the olfactory epithelium?

Back 46

small thin sheet of cells high up in the nasal cavity `

Front 47

olfactory receptors neurons:

Back 47

turn over continuously which is necessary in order to compensate for physical and chemical abuseare neurons, cycle lasts 4-8 weeks

Front 48

olfactory transduction pathway:

Back 48

odorants --> bind to membrane odorant receptor proteins --> Golf stimulation--> activation of AC III--> cAMP--> binding of cAMP to specific cation channel causing Ca and Na to enter cell depolarizing it

Hint 48

calcium influx leads to opening of a Cl- channel which further amplifies odorant signal further depolarizes cell because Cl- rushes out of cell

Front 49

upon odorant binding what hapens to the ORN

Back 49

becomes depolarized and sends APs via ORN axons to the olfactory bulb in the brain

Front 50

there are how many OR genes in mouse and humans?

Back 50

in mouse 1000 and in humans about 300

Front 51

each ORN will express how many OR

Back 51

only a single OR

Front 52

how is the olfactory epithelium arranged?

Back 52

it is divided into 4 different zones and in each zone a specific set of OR genes are expressed by the ORNs with no overlap between zones

Front 53

chemical amplification

Back 53

second messengery pathways in which enzymatic cascades produce large numbers of intermediate products thereby increasing a thousandfold the effect of one activated receptor molecule

Front 54

odors are detected how and where

Back 54

in a patch of about 100,000 olfactory receptor neurons whose axons project though a thin portion of the frontal skull (cribriform plate) to the olfactory bulb

Front 55

cilia of olfactory receptors

Back 55

extend into the nasal cavity where they life in a layer of mucus that is replaced every 10 min

Front 56

where do new ORNs arise from?

Back 56

a layer of basal cells in the epithelium

Front 57

visual pigment molecules consist of two moieties:

Back 57

protein known as opsin and a chromophore, 11-cis retinal (vitamin A aldehyde)

Front 58

what is the absorption characteristics of rhodopsin

Back 58

blue-green light at about 500nm is absorbed mroe efficiently

Front 59

what happens when a photon is absorbed by rhodopsin?

Back 59

retinal undergoes a photoisomerization and changes from 11-cis to all-trans

Front 60

in the dark when cGMP gated channels are open what is happening to calcium?

Back 60

it continually flows into the photoreceptor. calcium is extruded by ion pumps and exchangers in the outer segment. under conditions of steady illumination channels close and calcium entry is reduced meanwhile it is still being actively extruded thus the intracellular concentration falls

Front 61

actions of calcium in photoreceptors

Back 61

reduces the affinity of channels to cGMP through calmodulin, inhibits GC, and activates PDE

Front 62

phosphorylation of rhodopsin mediated by what

Back 62

recoverin, a calcium binding molecule

Front 63

how do you get amplification through cGMP cascade?

Back 63

a single active rhodopsin catalyzes the exchange of many molecules of GDP for GTP thereby liberating hundres of G protein subunits of transducin and secondly each transducin activates a molecule of PDE that can hydrolyze a large number of cGMP molecules

Front 64

non activated rhodopsin is in what conformation

Back 64

11-cis retinal

Front 65

how does rhodopsin get activated

Back 65

starts with the absorption of light which causes it to change to the all-trans configuration which causes opsin to undergo a conformational change

Front 66

activated rhodopsin does what

Back 66

causes transducin to exchange GDP for GTP and become active

Front 67

ganglion cells

Back 67

output of the retina is conveyed by ganglion cells; ganglion cells transmit information as trains of action potentials