Lecture 3: Nerve cells

Question 1

What types of cells comprise nervous system?

Answer 1

neurons and glia

Question 2

What kind of synapses is in majority in the brain?

Answer 2

chemical synapses

Question 3

Camillo Golgi

Answer 3

invented silver-based stain -> stained nerve cells with silver salts

Question 4

Santiago Ramon y Cajal

Answer 4

used staining technique to study tissues

Question 5

Golgi stain

Answer 5

stains random tissue slice -> allow a view of only occasional cells, selection process unknownn; ORANGE

Question 6

nissl stain

Answer 6

stains DNA in cell body = so you can only see cell bodies; PURPLE

Question 7

HRP stain

Answer 7

injection enables retrograde transportation through brain tissue to see neuronal projections

Question 8

soma

Answer 8

cell body of neuron (nucleus, ribosomes, mitochondria); genetic + metabolic processes

Question 9

dendrite

Answer 9

neuron entrence
afferent
carry information to soma

Question 10

axon

Answer 10

neuron exit
efferent
carry information from soma

Question 11

What are dendritic spines? What is their main function?

Answer 11

lined with specidic synaptic receptors at which dendrite receives information from other neurons => increase dendritic surface area enabling receiving more information

Question 12

cell membrane

Answer 12

skin of cell, most chemicals cannot cross membrane, but protein channels in membrane permit controlled flow of water, oxygen, sodium, potassium, calcium, chloride and other imporant chemicals

Question 13

nucleus

Answer 13

with DNA - contains chromosomes, codes for proteins

Question 14

mitochondria

Answer 14

power plants; help with construction of high energy molecules - metabolic activities

Question 15

ribosomes

Answer 15

translate genetic material into proteins; synthesis of new protein molecules

Question 16

endoplasmic reticulum

Answer 16

rNA goes there to be transalted into proteins in ribosomes

Question 17

Golgi complex

Answer 17

post office

Question 18

length constant

Answer 18

index of how far depolarization can spread down dendrite or axon
the longer -> the more likely it is that EPSP generated at distant synapses will depolarize membrane at axon hillock

Question 19

on what depends length constant?

Answer 19

• internal resistance: resistance to current flowing longitudinally down the dendrite
  -membrane resistance: resistance to current flowing across membrane

Question 20

passive dendrites

Answer 20

similar to cable, passive and inexcitable membranes = in spinal motor neurons

Question 21

excitable dendrites

Answer 21

majority! with voltage-gated sodium, calcium and potassium channels; add current to boost synaptic signal towards the soma

Question 22

How are proteins released?

Answer 22

1) they must be packed -> translation, transcription, Golgi system

2) they must be shipped -> transported along axons using specialized transport system - packed into vesicle

3) then they are uptaken into membrane

4) enzyme

5) exocytosis -> as neurotransmitters, they are released - by fusion of vesicle with the membrane - into synaptic cleft

Question 23

cell membrane

Answer 23

forms double-layer of phospholipids
heads - hydrophilic = like water
tails - hydrophobic = dislike water
protection, fatty substances can wiggle through membrane, but mostly forms impermeable layer
there are proteins embedded into the membrane

Question 24

what are membrane proteins involved in neurotransmission?

Answer 24

1) channels
2) gated channels
3) pumps

Question 25

channels in membrane

Answer 25

work through diffusion down concentration gradient permeability depends on number of channels -> usually, permeable to one or two types of ions

Question 26

gated channels in membrane

Answer 26

can open or close conformation -> change shape depend on voltage or chemical stimulus permeable to selective number of ions

Question 27

pumps in membrane

Answer 27

active transport require energy (ATP)

Question 28

neurons can be classified by structure into...

Answer 28

1) multipolar - multiple dendrites and axons 2) bipolar - with 2 poles 3) pseudounipolar

Question 29

neurons can be classfied by location/connectivity into...

Answer 29

1) projection neurons - typically myelinated 2) interneurons - typically smaller, shorter dendrites and axons, within local network, often not myelinated ---------------------------------------------------- 3) motor neurons -> extending outside nervous system to non-nervous targets 4) sensory neurons -> extending into nervous system from skin

Question 30

What is main fuel in the system?

Answer 30

glucose! can pass through blood-brain barier; brain consumes a lot of oxygen due to glucose consumptin can be synthesized in the liver from starch/amylum (primarily)

Question 31

What are types of glia cells?

Answer 31

astrocytes, oligodendrocytes, Schwann cells, microglia, radial glia

Question 32

In the cerebral cortex, there is more neurons or glia cells?

Answer 32

glia cells!

Question 33

astrocytes

Answer 33

star-shaped; wrap around synapses, functions: give brain structure, help synchronize closely related neurons enabling their axons to send messages in waves; maintain tight junctions in blood-brain barrier

Question 34

oligodendrocytes

Answer 34

in the brain and spinal cord = make myelin sheeth; can wrap around many cells

Question 35

Schwann cells

Answer 35

make myelin sheeth in periphery; you need multiple cells to cover one projection neuron

Question 36

microglia

Answer 36

smallest, inflammation causes them to grow and eat inflammation, part of immune system

Question 37

radial glia

Answer 37

guide migration of neurons during embryonic development, when embryo grows up, they differentiate into neurons, astrocytes and oligodendrocytes

Question 38

nodes of Ranvier

Answer 38

gaps along myelin sheeth

Question 39

Is new cell formation possible?

Answer 39

yes - but only in hippocampus and olfactory bulb

Question 40

Is it possible to regenerate axon?

Answer 40

Yes! If only axon gets damaged, regeneration is possible. However, death of soma has major consequences

Question 41

What does neuron eat? (nourishment)

Answer 41

almost fullly dependent on glucose! why? because it can cross blood-brain barrier in large quantities to use glucose, body requires vitamin B1

Question 42

what substances can passively cross blood-brain barrier?

Answer 42

lipophilic, hydrophobic substances, small molecules (CO2, O2), vitamines A and D

Question 43

how does water crosss blood-brain barrier?

Answer 43

through special protein channels

Question 44

what substances need active transport to cross blood-brain barrier?

Answer 44

glucose and amino acids; larger molecules; nutrients

Question 45

membrane potential

Answer 45

when at rest, membrane maintains electrical potential which is slightly negative inside in respect to outside = resting potential = -70mV

Question 46

how to record membrane potential?

Answer 46

with the use of oscillioscope one electrode should be put into bath, the other one in the axon

Question 47

why resting potential (-70mv) is needed?

Answer 47

to enable neuron to respond rapidly

Question 48

sodium potassium pump

Answer 48

pumps 3 sodium atoms outside pumps 2 potassium atoms inside net exchange results in more negative inside than outside

Question 49

what forces ions encounter?

Answer 49

1) electrical gradient 2) chemical gradient -> sum of the two determines whether specific ions will diffuse in or out (net diffusion)

Question 50

what happens when neuron is stimulated?

Answer 50

that depends whether stimulation is negative (hyperpolarization) or positive (depolarization) in case of hyperpolarization, inside gets even more negative in case of depolarization, inside gets more positive -> if threshold is reached, action potential can be obtained and neuron can fire

Question 51

EPSP -> excitatory post-synaptic potentials

Answer 51

Na channels in membrane open positive charge flows inside the cell depolarization

Question 52

IPSP -> inhibitory post-synaptic potentials

Answer 52

Cl channels in membrane open negative charge flows inside the cell hyperpolarization

Question 53

what is shunting inhibition?

Answer 53

inward movement of negatively charged chlorine ions, preventing the current flowing through soma to axon hillock

Question 54

What happens with action potentials at axon hillock?

Answer 54

voltage-dependent Na channels in axon hillock undergo a change - open when certain level of voltage passes through them -> massive influx of Na enables action potential (when threshold is reached)

Question 55

How action potential is terminated?

Answer 55

K channels open -> there is K efflux causing hyperpolarization moreover, Na channels get deactivatied

Question 56

refractory period

Answer 56

occurs right after action potential absolute: neuron cannot fire, +/- 1 ms relative: larger than usual stimulation can cause firing, +/- 2-4 ms

Question 57

what does all-or-none law mean?

Answer 57

all action potentials are the same = have equal amplitude, shape, duration, propagation speed etc. however, larger stimulation leads to more action potentials

Question 58

what is main difference between graded potentials vs action potentials?

Answer 58

graded potentials get smaller and smaller over the distance action potentials are always the same across distance

Question 59

why action potentials are always the same across distance?

Answer 59

due to meylin sheeth -> at each node of Ranvier, action potentials get renewed

Question 60

ACTION POTENTIALS SUMMARY

Answer 60

1) voltage dependent Na and K channels in axon 2) cause initiation/termination action potential 3) when crossing treshold = all or none principle 4) amplitude and speed independent of stimulus strength 5) refractory period

Question 61

electrical synapses

Answer 61

allow direct transfer of ioninc current from one cell to the next seperated by gap junctions very fast transmission common in mammalian CNS = useful in situations requiring synchronization of neurons

Question 62

chemical synapses

Answer 62

more common type seperated by synaptic cleft neurotransmitters are released from presynaptic side to bind to postsynaptic receptors in the membrane

Question 63

what happens at electrochemical synapses?

Answer 63

1) transmitter is synthesized and stored in vesicle 2) action potential invades presynaptic terminal 3) depolarization causes opening of voltage-gated Ca channels 4) influx of Ca through channels 5) Ca causes vesicles to fuse with presynaptic membrane 6) transmitter is released into synaptic cleft (exocytosis) 7) transmitter binds to receptor molecules 8) opening/closing of postsynaptic channels 9) postsynaptic current causes excitatory/inhibitory postsynaptic potential which travels further down postsynaptic cell 10) removal of neurotransmitter by glial uptake or enzymatic degradation 11) retrieval of vesicular membrane from plasma membrane

Question 64

neuromuscular junction (motor nerves x muscles)

Answer 64

synaptic junction outside CNS single action potential causes exocytosis of 200 synaptic vesicles -> evolved to be fail-safe: needs to work every time due to huge size of EPSP

Question 65

CNS synapses

Answer 65

low EPSP -> single vesicle is released in response to action potential -> more neurons perform sophisticated computations and require many EPSP produced together to produce significant depolarization

Question 66

spatial summation in CNS

Answer 66

adding together EPSP generated simultaneously at many different synapses of dendrite

Question 67

temporal summation in CNS

Answer 67

adding together EPSP generated at the same synapse as they occur in rapid succession

Question 68

what types of synapses can be found in CNS?

Answer 68

1) assymetrical = pre and post synaptic membranes are not equally thickened, depolarization! excitatory 2) symmetrical thickening of two membranes, hyperpolarization! inhibitory ----------------------------------------------------- -> axodendritic = axon x dendrite -> axosomatic = axon x soma -> axoaxonic = axon x axon -> dendodenritic = dendrite x dendrite

Question 69

What are types of neurotransmitters?

Answer 69

amino acids, amines, peptides

Question 70

amino acids

Answer 70

examples: GABA, glutamate, glycine

Question 71

amines

Answer 71

examples: acetylcholine, dopamine, epinephrine, histamine, norepinephrine, serotonin

Question 72

How are amino acids and amines synthesized?

Answer 72

both types of neurotransmitters are transported to axon terminal where they locally direct transmitter synthesis their transporters are special proteins embedded in vesicle membrane

Question 73

peptides

Answer 73

large molecules chains of amino acids stored and released from secretory granules

Question 74

How are peptides synthesized?

Answer 74

they are formed via connecting amino acids by ribosomes of cell body long peptides are then split in Golgi apparatus secretory granules bud off from Golgi apparatus and carry them to axon terminals

Question 75

what types of neurotransmitter receptors are present in postsynaptic membranes?

Answer 75

transmitter gated ion channels g-protein-coupled receptors

Question 76

transmitter gated ion channels

Answer 76

membrane-spanning proteins forming pore (closed when neurotransmitter is absent) -> when neurotransmitter binds, they undergo conformational change may be permeable to Na (depolarization) or Cl (hyperpolarization)

Question 77

g-protein-coupled receptors

Answer 77

slower, long lasting postsynaptic action upon binding of neurotransmitter, tehy activate small proteins (g proteins) which are free to move along intracellular face of postsynaptic membrane -> activated g proteins activate effector proteins

Question 78

metabotropic messengers

Answer 78

g proteins can trigger widespread metabolic effects

Question 79

How neurotransmitters are cleared from synaptic cleft?

Answer 79

1) simple diffusion = through extracellular fluid, away from synapse 2) amino acids + amines => diffusion is aided by reuptake into postsynaptic axon terminal -> then neurotransmitters are reloaded into synaptic vesicles or degraded 3) neurotransmitters may be destroyed in the synaptic cleft itself

Question 80

Why is it important to remove neurotransmitter from the cleft?

Answer 80

example: acetylcholine high concentrations of acetylchline lead to desensitization (transmitter-gated channels close) - failure of neuronal transmission

Question 81

What are effects of drugs on nervous system?

Answer 81

That depends whether drugs are antagonists or agonists. Antagonists are called inhbitors because they inhibit normal function of specific proteins involved in synaptic transmission/ Agonists are mimicking actions of neurotransmitters

Question 82

What are modulators?

Answer 82

synapses with g-protein coupled neurotransmitter receptors that are NOT directly associated with ion channels synaptic activation does not evoke EPSP or IPSP but instead modifies their effectiveness!