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Biology 102 > Lecture 7 - Neurons and the Nervous System > Flashcards

Lecture 7 - Neurons and the Nervous System Flashcards

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1
Q

Central Nervous System

A
  • brain

- spinal cord

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2
Q

Peripheral Nervous system

A
  • nerves and neurons outside of the brain and spinal cord that connect to limbs and organs

SOMATIC

  • innervative skin, joints, muscles
  • voluntary
AUTONOMIC
- innervative organs, blood vessels and glands (visceral functions)
- involuntary
- two divisions
1, sympathetic - fight or flight
2, parasympathetic - rest and digest
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3
Q

Two Cell Types in Nervous System

A

Neurons
- generate and transmit electrical signals (action potentials)

Glia

  • 90% of the cells in your brain
  • do not conduct action potentials
  • support neurons physically, immunologically and metabolically
  • importance in modulating proper neural function becoming increasingly recognized
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4
Q

Types of Glia

A
  • astrocytes
  • oligodendrocytes
  • schwann cells
  • microglia
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5
Q

astrocytes

A
  • most numerous glia
  • fill spaces between neurons
  • regulate chemical content of extracellular space (remove excess ions, recycle neurotransmitters)
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6
Q

oligodendtocytes

A
  • provide wrapping of insulating fatty layers around axons - myelin
  • central nervous system
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7
Q

schwann cells

A
  • provide myelin for the peripheral nervous system
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8
Q

microglia

A
  • mediate immune and inflammatory response
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9
Q

Neuron and its structure

A

100 billion in the nervous system

3 parts:

  1. dentrites
    - highly branched “tree”
    - receives input to neuron
    - short, spiny stubby
  2. soma
    - cell body of the neuron
    - contains nucleus and other organelles
  3. axon
    - few branches (collaterals)
    - sends output from neuron
    - long, smooth

information flows from dendtrites through cell body to axon

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10
Q

Axon

A
  • typically only one from the soma of neuron
  • a few collaterals branch out

-where the action potential occurs

  • serves as a “telegraph wire” to send info over long distances
  • can be less than 1 mm or up to a meter
  • nerve= bundle of axons

axon hillock - beginning near soma, integrates information and initiates action potential

axo terminals - end, forms synapse

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11
Q

Synapse

A

Where the axon of one neuron meets the dendrite of another

  • presynaptic side = axon
  • postsynaptic side = dendrite

synaptic cleft
- space in between axon and dendrite
~25 nm wide

electrical signal of the AP is converted to a chemical signal

  • neurotransmitters
  • bind to receptors on postsynaptic dendrite

a given neuron in the brain can have 1,000 synapses

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12
Q

How a signal is transmitted…

A
  1. information received in dendrites (neurotransmitters bind to receptors)
  2. integrated in axon hillock (ions flow from dendrites to hillock, aggregated, if enough, will induce AP)
  3. transmitted down long axon in form of action potential
  4. converted to chemical signal at axon terminal int he form of neurotransmitter release
  5. neurotransmitter can cross synapse to bind to receptors on another dendrite and start cycle over
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13
Q

How does an action potential work?

A
  • based upon movements of ions

arise due to propagation of electrical charge down axon
electrical charge is created by charged ions

Membrane of axon

  • divides charge to create a resting membrane potential
  • allows selective flow of ions to generate the action potential
  • reliable conduction of action potential down axon
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14
Q

Monitoring Voltage of inside of the cell

A
  • movement of ions across the membrane results in a change in voltage
  • value is expressed in terms of the inside of the neuron relative to the outside solution
  • measured by voltmeter
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15
Q

Distribution of K+ ions

A

high concentration inside

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16
Q

Distribution of Na+ ions

A

high outside

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17
Q

Sodium Potassium Pump

A
  • uses ATP to pump ions against their concentration gradients
  • create a large driving force for ion flow
  • pumps Na+ outside of cell (keeps extracellular Na+ high)
  • pumps K+ in (keeps intracellular K+ high)
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18
Q

Potassium and Na+/K+ pump

A

potassium wants to rush out
+ charge leaving
inside of cells becomes more negatively charged
negative voltage inside

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19
Q

Sodium and the Na+/K+ pump

A

sodium wants to rush in
+ entering
inside of cell becomes more positively charged
positive voltage inside

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20
Q

Importance of distribution of charges

A
  1. equilibrium potential

2. membrane potential

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21
Q

equilibrium potential

A
  • takes one ion into account
  • the voltage of the cell that would result from that one ion moving freely across the membrane achieving equilibrium
  • specific potential for each ion - each ion has its own equlibrium potential (might be different fo Na+ and K+)
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22
Q

membrane potential

A
  • the actual value of the voltage inside the cell compared to the outside of the cell
  • take into account all ions
  • also dependent on permeability (which ions can cross the membrane at that point in time)
  • voltage across neural membrane at any moment
  • inside relative to outside
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23
Q

Nernst Equation

A

used to calculate the equilibrium potential

E = 61.6 log (outside/inside)

  • increasing outside conc of a positive ion will make the eq more positive
  • increasing the inside conc of a positive ion will make the eq potential more negative
24
Q

Equilibrium potential is specific to…

A
  • each ion

- what the voltage of the cell would go to if a channel for that ion and that ion only was opened

25
Q

two factors in membrane potential

A

1.Equilibrium potential of each ion

  1. how permeable the membrane is to each ion compared to the others
    - if an ion cannot flow across the membrane, it cannot be creating a charge difference (voltage)
    - the more permeable the membrane is to an ion, the close the membrane potential will be close to that ion’s equilibrium potential

*resting membrane potential = the membrane potential when no gated channels have been signaled to open

26
Q

Resting membrane potential

A

Vm = resting membrane potential

  • at rest, cell membrane is impermeable to most ions
  • except POTASSIUM LEAK CHANNELS
  • always allow K+ to flow across membarne more readily than other ions
  • therefore, at rest, membrane potential of the cells is close to the equilibrium potential for K+
27
Q

Expected resting membrane potential

A
  • at rest, the membrane potential of the cell is close to the equilibrium potential for K+
  • constant (weak) flow of K+ out of cell makes inside negative

Vm = -65mv

28
Q

Significance of ion gradients

A
  • they are used to create electrical signals in the neuron

ion channels:

  • selective for specific ions
  • gated: open/close in response to particular stimuli

Two kinds:

  • voltage gated
  • ligand gated
29
Q

Voltage gated ion channels

A
  • open in response to a change in voltage across plasma membrane in axon
  • in AXON
30
Q

ligand gated ion channels

A
  • open in response to a specific molecule (such as a neurotransmitter) binding
  • in DENDRITES
31
Q

How movements of ions change voltage in cells

A

Depolarization
- change in the cell’s membrane potential, making it more POSITIVE

Hyperpolarization
- change in the cell’s membrane potential, making it more negative

32
Q

action potential

A

“robust and fast electrical signal that neurons use to convey information”

  • change in membrane voltage that propagates down the axon
  • generated by actions of voltage-gated Na+ and K+ channels in the plasma membrane of the axon
33
Q

properties of the action potential

A
  • resting potential
  • rising phase
  • falling phase
  • undershoot
34
Q

Resting potential

A
  • Greater permeability to Potassium K+
  • leak channels always open
  • Vm = -65mv
  • voltage gated sodium channels and voltage gated - potessium chanels both closed
35
Q

threshold

A
  • depolarization above threshold (-50mv) initiates rising phase
  • threshold = membrane potential at which voltage gated sodium channels open
  • initial depolarization due to signals from dendrites
  • initiated at Axon hillock
36
Q

Rising phase

A
  • once the threshold is reahed, voltage-gated sodium channels open briefly (voltage gated potassium channels still closed)
  • sodium influx
  • rapid depolarization
  • membrane potential gets close to the na+ equilibrium potential of +56mv
  • rises to ~40mv
37
Q

falling phase

A
  • voltage gated Na+ channels close
  • voltage gated K+ channels open
  • K+ ions rush out of the cell
  • hyperpolarization
38
Q

undershoot

A
  • membrane very permeable to potassium since K+ channels are open
  • therefore membrane potential gets close to the K+ equilibrium potential of -80mv
  • extra hyperpolarization until v-gated K+ channels close
39
Q

refractory period

A
  • na+ channels close based on time (after ~1-2ms of being open) regardless of the voltage around them
  • once Na+ channels close they cannot open again for ~1-2 ms (inactivation)
  • that reagion of the axon CANNOT fire another action potential during this time
40
Q

propagation of action potential

A
  • action potential is initiated when depolarizing signal (from dendrites) brings Na+ channels at axon hillock past threshold
  • sodium influx in axon hillock leads some Na+ ions to diffuse to adjoining area
  • depolarizes that adjoining area past threshold, opening those Na+ channels
  • action propagates down length of axon
  • refractory period prevents the signal from propagating backwards
41
Q

Tetrodotoxin

How does it effect action potential?

A

(TTX)

  • selective sodium channel blocker
  • potent toxin
  • causes muscle paralysis, including breathing
42
Q

Importance of Myelin

A
  • provides insulation - increases conduction velocity
  • like wrapping a leaky hose in duct tape
  • regularly spaced gaps in myelin sheath
  • nodes of ranvier
  • voltage gated ion channels are clustered here
  • action potential at node recharges the depolarizing current
  • saltatory conduction
43
Q

Multiple Sclerosis

A
  • demylenating disease
  • autoimmune disease where body produces antibodies to myelin
  • muscle weakness
  • can also experience symptoms such as vision problems, speech problems, pain, fatigue, dizziness, changes in mood
44
Q

Action potential and neurotransmitters

A
  • action potential signals the release mof neurotransmitters into synaptic celft
  • axon terminal contains vesicles filled with neurotransmitters
  • when action potential arrives at the axon terminal, depolarization triggers the opening of voltage gated calcium channels (Ca++ flows into axon terminal)
  • increased Ca++ triggers vesicles to fuse with presynaptic membrane and release neurotransmitter
45
Q

neurotransmitters

A
  • small molecules stored in synaptic vesicles
  • released from presynaptic neuron into the synaptic cleft
  • bind to specialized receptors on the postsynaptic neuron
  • many drugs mimic the actions of neurotransmitters while others block the receptors that bind them, preventing their action

ex:

  • serotonin
  • dopamine
  • glutamine
  • GABA
  • aetylcholine
46
Q

excitatory receptor

A
  • depolarization
  • potitive ion in
  • or negative ion out
  • move membrane potential towards threshold
  • make the postsynaptic cell more likely to fire an action potential
47
Q

inhibitory receptor

A
  • hyperpolarization
  • negative ion in
  • or positive ion out
  • move membrane potential away from threshold
  • male postsynaptic cell less likely to fire an action potential
48
Q

Summation of information

A
  • neuron integrates and sums all of the information from dendrites
  • summation takes place in the axon hillock
  • summation must depolarize to reach threshold (-50mv)
  • one output for all this input = action potential
49
Q

How action potentials differ/do not differ

A

alter

  1. frequency
  2. pattern

DO NOT differ in:

  1. size
  2. duration

“all-or-none” to cross threshold value

50
Q

Neurotransmitters and their receptors

A
  • released into synaptic cleft
  • bind to receptors of postsynaptic cell
  • on dendrite
  • ligand-gated ion channels
  • open in response to neurotransmitters binding
  • allow influx of specific ions that cause depolarization of hyperpolarization

NOT an action potential, NOT voltage gated

can be

  1. excitatory
  2. inhibitory
51
Q

Depolarization spread to axon hillock

A
  • NO voltage gated ion channels in dendrite
  • no action potential in dendrite
  • depolarizations from the neurotransmitter receptors travel to the axon hillock
  • inputs from many synapses on the neuron’s many dendrite branches sum together
  • hillock integrates and sums the information from many inputs
  • if sum of depolarization is enough to cross threshols, will induce action potential in axon
52
Q

Summary of Neuron Information Flow

A
  1. Dendrites
    - ligand gated ion channels
    - neurotransmitter binds
    - depolarization or hyperpolarization
    - no action potential
  2. Axon Hillock
    - voltage changes from dendrites are summed
    - if depolarization reaches threshold (-40mv) action potential is initiated
  3. Axon
    - Voltage gatd ion channels
    - Action potential
    - Rising Phase: Na+ in
    - Falling phase: K+ out
  4. Synapse
    - voltage gated Ca++ chanels
    - Ca++ in causes neurotransmitter release into synaptic cleft
53
Q

Membrane Potential of Potassium

A

-75 mv

54
Q

Membrane potential of Sodium

A

+56 mv

55
Q

What would happen if you depolarized the middle of an axon?

What would happen if you depolarized each end?

A
  • AP would go in both directions (no refractory period)

- would cancel each other out

56
Q

Saltatory Conduction

A

Process of jumping from node to node while propagating a signal

57
Q

Node of Ranvier

A
  • regularly spaced gaps in myelin sheath
  • voltage-gated ion channels clustered there
  • action potential re-charges the depolarizing current

Biology 102 (15 decks)

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