Neurons

Front 1

What is a neuron is a______ cell capable of __________ and____________ electrical signals. They vary in __________ and ___________. All use the same basic mechanisms to send signals.

Back 1

nerve, generating, transmitting, structure, properties

Front 2

neurons generate ______________ or ___________

Back 2

action potentials, passive potentials

Front 3

Neurons communicate with other neurons or cells via......

Back 3

electrical or chemical synaptic connections

Front 4

Neurons have lots of structural......

Back 4

diversity

Front 5

action potentials travel towards the cell body in ________ and away from the cell body in_______

Back 5

dendrites, axon

Front 6

axon hillock

Back 6

The axon hillock is located where the axon meets the cell body (soma) and controls the firing of the neuron. If the total strength of the signal exceeds the threshold limit of the axon hillock, the structure will fire a signal down the axon.

Front 7

neuron classification based on function: 3 types

Back 7

-Efferent neuron: neuron conducting impulses outwards from the brain or spinal cord (bipolar)

-Sensory neuron: neuron conducting impulses inwards to the brain or spinal cord (unipolar)

-Interneuron: A nerve cell found entirely within the central nervous system that acts as a link between sensory neurons and motor neurons.

Front 8

neuron classification based on structure: 3 types

Back 8

-Multipolar neurons

-Unipolar neurons

-Bipolar neurons

Front 9

Unipolar Neurons

Back 9

single axon that extends from the cell body in either direction. Dendrites are found at the peripheral process of the axon. The axon terminals are at the central process They are often sensory cells. Integration takes place where the dendrites meet the axon.

Front 10

Multipolar Neurons

Back 10

A neuron with one axon and three or more dendrites.

Front 11

Bipolar neurons

Back 11

-rare
-have only one axon and one dendrite attached to cell body

Front 12

The four neural zones are

Back 12

-Signal reception
-Signal integration
-Signal conduction
-Signal transmission

Front 13

Signal Reception: where and what happens

Back 13

-Takes place at dendrites and the cell body (Soma)
-The incoming signal is received and converted to a change in membrane potential

Front 14

Signal Integration: where and what happens

Back 14

-Takes place at axon hillock except in unipolar happens where dendrites meet axon
-summation of inhibitory postsynaptic potentials (IPSPs) and excitatory postsynaptic potentials (EPSPs) from numerous synaptic inputs on the dendrites or cell body occur. If the summated membrane potential reaches the triggering threshold, an action potential propagates through the rest of the axon
-Triggering is due to positive feedback between highly crowded voltage gated sodium channels which are present at critical density at the axon hillock but not in the soma

Front 15

Signal Conduction: where and what happens

Back 15

-Takes place at the axon which may be wrapped in a myelin sheath
-The action potential travels down the axon toward the axon terminals

Front 16

Signal Transmission: where and what happens

Back 16

-Take place at the axon terminals
-neurotransmitter is released at the axon terminals into the synapse and the neurotransmitter transmits signal to the target cell.

Front 17

Neurons like all cells have a resting ___________. Neurons are___________ which means they can rapidly change their_____________. Changes in __________ act as _____________ signals.

Back 17

membrane potential, excitable, membrane potential, membrane potential, electrical.

Front 18

How to measure the voltage of a neuron

Back 18

-use microelectrodes to measure the voltage between outside and inside
-use a conducting fluid like KCl in the microelectrode
-reference electrode is placed in the bathing medium
-potentiometer will measure the potential

Front 19

The three factors that contribute to membrane potential are:

Back 19

1. distribution of ions across the plasma membrane
2. the relative permeability of the membrane to these ions
3. the charges of the ions

Front 20

what is the origin of the resting membrane potential in a typical vertebrate neuron?

Back 20

- negatively charged proteins
-In a resting neuron 10x more K+ channels are open then Na+ or Cl- channels
-Outside of the cell is more positive relative to the inside of the cell
-K+ has highest permeability due to leak channels
- Na+ and Cl- may have leakage channels too

Front 21

Goldman equation

Back 21

-predicts membrane potential using multiple ions
-see notes

Front 22

changes in channel permeability create....

Back 22

electrical signals

Front 23

mechanically gated ion channels

Back 23

in sensory neurons and open in response to pressure or stretch

Front 24

chemically gated ion channels

Back 24

respond to ligands

Front 25

Voltage gated ion channels

Back 25

respond to changes in membrane potential

Front 26

Two types of electrical signals are

Back 26

graded potentials and action potentials

Front 27

Graded potentials vs Action Potentials

Back 27

-GP: vary in magnitude AP: always the same magnitude for a given cell type

-GP: vary in duration AP: always the same duration for a given cell type

-GP decay with distance AP can be transmitted long distances

-GP occur in dendrites and cell bodies AP occur in axons

-GP caused by opening and closing many kinds of ion channels AP caused by opening and closing of voltage gated channels

Front 28

passive conduction

Back 28

signal is limited by properties of the nerve and is reduced over distance

Front 29

Active conduction (ie active potentials)

Back 29

signal travels along nerve with no loss of amplitude

Front 30

Action potential only occurs when....

Back 30

the membrane potential at axon hillock reaches threshold

Front 31

The three phases of action potentials are

Back 31

-depolarization
-repolarization
-hyperpolarization

Front 32

Absolute refractory period is when

Back 32

the neuron is incapable of generating a new AP (from depolarization until repolarization when cell enters relative refractory period)

Front 33

Relative refractory period is when

Back 33

it becomes more difficult to produce to a new action potential (from repolarization until back to resting membrane potential)

Front 34

Voltage gated channels have positive feedback

Back 34

a influx of Na+ causes a increase in local depolarization and there for increases the number of voltage gated sodium channels that are open.

Front 35

In an action potential_______ channels open first causing the__________. The _________ channels open slower and cause the_______________. The ________ channels then close. The ______ channels close more slowly and this causes the __________

Back 35

Na+, depolarization, K+, repolarization, Na+, K+, relative refractory period.

Front 36

Voltage gated sodium channels have 3 states:

Back 36

closed, open, inactive

Front 37

Voltage gated sodium channels
Closed to open stage

Back 37

-depolarization is necessary to open channels
-acts to activate itself in a regenerative cycle
-more Na+ influx depolarizes the membrane which opens more channels which depolarizes the membrane more

Front 38

Voltage gated sodium channels
open to inactive

Back 38

-depolarization is necessary to inactivate channel
-once the channel is open it will then also switch the the inactive state and cannot be opened again

Front 39

Voltage gated sodium channels
inactive to closed

Back 39

-channel will not switch back to the closed state until the membrane has repolarized
-once in closed state it can then be reopened

Front 40

Voltage gated sodium channels
have two types of gates

Back 40

- a activation gate that is voltage dependent
-a inactivation gate that is time dependent

Front 41

Voltage gated sodium channels
steps

Back 41

1. cell at resting potential, activation gate closed, inactivation gate closed
2. suprathreshold depolarizing graded potential cause activation gates to open
3.sodium enters, more depolarization so more sodium channels open...
4.inactivation gate closes as cell reaches +30 mV so no more sodium entry
5. overtime in response to repolarization of the cell results in gates returning to original state

Front 42

Voltage gated K+ channels (delayed rectifying K+ channels) have 2 states:

Back 42

closed and open

Front 43

Voltage gated K+ channels
closed to open

Back 43

-strong depolarization is needed to open the channel
-hyperpolarizes the cell ( K+ leaves cell)
-brings membrane back towards nernst potential of K+

Front 44

Voltage gated K+ channels
Open to closed

Back 44

-will close when membrane becomes hyperpolarized
- works to shut itself down

Front 45

Voltage gated channels step by step

Back 45

see flagged in notes

Front 46

action potentials are all or none

Back 46

occurs or does not occur; identical without degradation

Front 47

action potentials are self propagating

Back 47

a AP triggers the next AP in adjacent areas of the axonal membrane

Front 48

APs have electronic current....

Back 48

spread between channels

Front 49

AP cycle

Back 49

ion entry> electronic current spread > triggering AP

Front 50

Threshold

Back 50

-most neurons -50mV (ie a 10-15 mV depolarization from resting potential)
-is all of none, The amplitude of AP is the same all along nerve and is independent of stimulus strength
-threshold reflects the need to trigger the opening the voltage gated sodium channels by depolarizing

Front 51

Rising Phase of AP

Back 51

-sodium channels open
-Na+ flows into cell
-depolarizes cell
-more sodium channels open= a regenerative response, regenerative opening of sodium channels drives MP towards a peak of the Nernst eq potential for Na+

Front 52

Peak of AP

Back 52

-during the AP the MP goes towards the Nernst eq potential for Na+
-Na+ permeability is now dominant and there for membrane potential goes towards Ena+
-usually falls short of Ena+, there is less driving force of Na+ and channels begin to inactivate rapidly after becoming active

Front 53

Fall of AP

Back 53

-MP falls back towards rest because sodium channels become inactive and delayed K+ channels open

Front 54

inactivating sodium channels

Back 54

-v-gated sodium channels do into inactive state 1-2msec after opening
-inactivated=cannot reopen
-membrane potential now determined mostly by K+ and membrane starts to repolarize

Front 55

Delayed K+ channels open

Back 55

-open 1-2 msec after threshold depolarization
-K+ flows out of cell and speeds up repolarization process
-causes hyperpolarization after AP
-open K+ makes K+ permeability higher then at rest
-hyperpolarization caused K+ channels to close
-membrane then settles back to rest by Na+/K+ ATPase

Front 56

Repolarization of AP

Back 56

-v-gated channels Na+ and K+ now closed
-membrane goes back to resting state
-only leak channels open now and they again set membrane potential

Front 57

in unidirectional signals the ________ starts at the _________ and travels towards the ______________. Upstream Na+ channels are in the __________ which prevents backward ___________and___________ of APs. The relatively refractory period also contributes by requiring a very _______stimulus to cause a AP.

Back 57

stimulus, axon hillock, axon terminal, absolute refractory period, transmission, summation, strong

Front 58

how does a nerve communicate the strength of a stimulus

Back 58

-info is given by frequency of the AP along nerve
-stimulus strength triggers different frequencies of AP
-refractory period limits the frequency of AP
-during relative refractory period an AP can be generated but needs to be at supra threshold to overcome the hyperpolarization
-will be at decreased amplitude because fewer Na+ channels available to be opened

Front 59

action potentials are triggered by the ____________ at the ____________. They do not ________ and can travel ________ distances. They are ____ or _______ and must reach _______ to fire.

Back 59

net graded potential, axon hillock, degrade, long, all, none, threshold potential

Front 60

membrane bound receptors in cell body and dendrites________ the chemical signal to and ________ signal by changing the membrane potential

Back 60

transduce, electrical

Front 61

graded potentials vary in _________ depending on the _________ of stimulus. Eg more neurotransmitter means more ____________ will open.

Back 61

magnitude, strength, ion channels

Front 62

In a graded potential ions move down an ____________. The net movement stops when equilibrium potential is reached. This can ___________ or _____________ the cell.

Back 62

electrochemical gradient, depolarize, hyperpolarize

Front 63

Graded potentials only travel short distances. There is conduction with decrement. (decrease in strength with a increase in distance from opened ion channel). This is due to

Back 63

-leakage of charged ions across the membrane
-electrical resistance of the cytoplasm (has density, diameter, myelin)
-electrical properties of the membrane

Front 64

graded potential electrotonic spread

Back 64

positive charge spreads through the cytoplasm causing depolarization of the membrane.

Front 65

graded potentials can be

Back 65

excitatory or inhibitory

Front 66

Integration of graded signals

Back 66

-many graded potentials can be generated simultaneously
-many receptor sites
-many kinds of receptors
-temporal and spatial summation

Front 67

temporal summation

Back 67

graded potentials that occur at slightly different times can influence the net change

ex the graded potentials overlap and therefore sum

Front 68

spatial summation

Back 68

graded potentials from different sites can influence the net change
example: 3 excitatory neurons fire and each graded potential is below threshold but they arrive at the trigger zone together and sum to create a suprathreshold signal so AP generated

or 2 excitatory and 1 inhibitory fire. The inhibitory signal diminishes the excitatory signals below threshold so no AP is produced

Front 69

vertebrate neurons are myelinated
myelin is? and what does it do?

Back 69

-a insulating layer of lipid rich schwann cells wrapped around the axon
-it insulates neurons so you dont have much leakage of current and increases conduction because signal jumps between nodes instead of traveling down whole axon

Front 70

glial cells

Back 70

are supportive neural cells and cannot produce a AP ex schwann cells

Front 71

nodes of ranvier

Back 71

areas if exposed axonal membrane in between schawnn cells

Front 72

internodes

Back 72

the myelinated region of axon

Front 73

saltatory conduction

Back 73

APs leap from node to node; APs at nodes of ranvier and electrotonic current spread through internodes

Front 74

Disadvantages of large axons

Back 74

-take up lots of space so limits number of neurons that can be packed into nervous system
-large volume of cytoplasm makes then expensive to maintain and produce (lots of organelles)
-over come this by myelinating cells, allows rapid signal conduction in a compact space.

Front 75

how myelin increases conduction spead

Back 75

-inc membrane resistance because it dec current loss by leak channels, so increasing resistance inc length constent
-dec capacitance b/c it increases thickness of insulating layer which decreases time constant and therefore inc conduction speed
-nodes of ranvier are needed to boost depolarization

Front 76

capacitance

Back 76

charge needed to generate a potential difference

Front 77

5 main types of glial cells

Back 77

-schwann cells
-oligodendrocyte
-astrocyte
-microglia
-ependymal cells

Front 78

schwann cells

Back 78

form myelin in motor and sensory neurons in PNS

Front 79

oligodendrocyte

Back 79

form myelin in the CNS

Front 80

astrocyte

Back 80

transport nutrients, removes debris from CNS

Front 81

microglia

Back 81

remove debris and dead cells from CNS

Front 82

ependymal cells

Back 82

line the fluid filled cavities of the CNS

Front 83

Two ways to increase conduction speed:

Back 83

Myelin or increasing diameter of the axon

Front 84

current

Back 84

amount of charge moving past a point at a given time

Front 85

voltage

Back 85

energy carried by a unit of charge

Front 86

resistance

Back 86

force opposing the flow of electrical current

Front 87

Ohms law

Back 87

V=IR

Front 88

three resisters are

Back 88

extracellular fluid, the membrane, and cytoplasm

Front 89

capacitor

Back 89

stores electrical charge, two conducting materials ICF and ECF and a insulating material (phospholipids/myelin)

Front 90

conduction with decrement (dec in signal) is due to __________. when ICF is increasing in resistance the decrement is____________, when ECF is increasing resistance the decrement is____________. When the membrane is increasing resistance the decrement is ___________ because there are fewer leak channels.

Back 90

resistance, increasing, increasing, decreasing.