Lecture 3

Question 1

What processes take place in the cell nucleus?

Answer 1

Genetic and metabolic

Question 2

What kinds of neurites are there?

Answer 2

Entrance (carry information to the soma) = dendrites
Exit neurites (carry information away from the soma) = axon

Question 3

What is in the soma?

Answer 3

membrane (encasing of the whole cell), nucleus (with DNA in it that codes for proteins), mitochondria, ribosomes (genetic material is translated into proteins), endoplasmatic reticulum, golgi complex (molecules like proteins are packaged, “stamped with an address” and sent off to another place in the cell)

Question 4

Dendritic spines

Answer 4

Structures on the dendrites, onto which other neurons can synapse

Question 5

Along what are packaged proteins transported from the soma to the axon terminal?

Answer 5

Microtubulin of the axon by the kinesin

Question 6

What can happen with the proteins in the axon terminal?

Answer 6

1. Taken up into the membrane
2. Catalyze chemical reactions if it’s an enzyme
3. If it’s a neurotransmitter protein it’s kept in a vesicle and then after stimulus, it might be released

Question 7

Axon per cell

Answer 7

1, but it might branch enabling contact with many neurons

Question 8

Membrane proteins involved in neurotransmission

Answer 8

Channel, gated channel, pump

Question 9

Classification of neurons by location

Answer 9

Projection neuron, interneuron, other (motor, sensory neurons)

Question 10

Classification of neurons by structure

Answer 10

multipolar, bipolar, pseudo-unipolar

Question 11

Neurons use it as fuel

Answer 11

Glucose (it can pass through the blood-brain barrier, can be synthesized by the liver)

Question 12

Types of glial cells

Answer 12

Astrocytes, Oligodendrocytes, Schwann-cells, microglia

Question 13

Astrocytes functions

Answer 13

-Give the brain structure
-Important role in blood-brain barrier (assist in making the vessels that go into your brain really impermeable) - Play an important role in maintaining the tight junctions between the cells that make up the blood vessels
-‘Covers’ the synapse, clears excess neurotransmitters

Question 14

Oligodendrocyte function

Answer 14

Makes myelin - extensions that roll around axons, can service multiple cells,

Question 15

Schwann cell function

Answer 15

Make myelin - multiple Schwann cells are needed to cover one projection axon

Question 16

Microglia function

Answer 16

Inflammation makes them change shape, and become big. They eat dead material. They are part of the immune system

Question 17

Regeneration of neurons

Answer 17

If soma is damaged –> no regeneration
If the axon gets damaged –> regeneration

Question 18

Axon regeneration

Answer 18

The part still attached to the soma may sprout. Myelin sheets that were around it originally, retract, stay where they are and mark where the new axon should go. After the axon sprouts and grows out, the myelin sheath starts forming around it again.

Question 19

Blood-brain barrier

Answer 19

The border between blood and brain fluid is more selective in letting things through. Blood vessels are even more selectively permeable in the brain. Passive transport can occur for lipids and for small molecules (e.g. oxygen, CO2). Active transport occurs for bigger molecules like glucose, amino-acids (nutrients).

Question 20

Function of blood-brain barrier

Answer 20

Maintain the composition of the brain fluid (keep it constant).

Question 21

General function of glial cells

Answer 21

-Formation of myelin
-Insulation of the nerve fiber
-Removing dead neurons and waste
-Uptake and release of neurotransmitters/ions from the synaptic cleft
-Forming tight-junctions
-Guiding migration of neurons (radial glia)

Question 22

Resting potential

Answer 22

-70 mV

Question 23

Neurons get charged

Answer 23

Because of the protein pumps that pump ions: 3 Na+ is pumped out, 2 K+ gets pumped in - Sodium-potassium pump

Question 24

Ions encounter 2 forces

Answer 24

1. Electrical gradient
2. Chemical gradient

–> The sum of the 2 forces determines whether an ion will diffuse in or out

Question 25

Cl- concentration

Answer 25

Lower inside than outside. When Cl- channel opens, Cl- flows in –> Bigger concentration gradient

Question 26

Graded potentials

Answer 26

EPSPs: chemical stimulus in the synapse (neurotransmitter) –> Na+ channels open in the postsynaptic terminal –> Positive charge (Na+ ions) flow in, diffuse along membrane –> local depolarization of the cell-membrane
IPSPs: neurotransmitter is released in the synaptic cleft –> CL- channels–> negative charge flows in –> membrane hyperpolarizes locally

Question 27

Graded potentials move along the cell …

Answer 27

Passively, current fades away over distance. (because of outward leakage of K+ ions and diffusion of charge over increasingly large surface)

Question 28

What neurons have only graded potentials?

Answer 28

Some local neurons (interneurons)

Question 29

Action potential

Answer 29

When depolarization reaches a certain threshold (firing threshold)–> action potential

Question 30

Molecular basis of action potential

Answer 30

Voltage-dependent Na+ channels in axon hillock (closed at resting potential) –> Open when the membrane locally depolarizes to a certain threshold level–> Massive influx of Na+ –> action potential is triggered

Question 31

Why can action potentials only happen in the axon?

Answer 31

Because voltage-gated channels can only be found there

Question 32

Termination of action potential

Answer 32

2 slower processes:
1. Opening of voltage-dependent K+ channels (also open because of depolarization, but with a delay) –> K+ flows out –> cell becomes hyperpolarized
2. Inactivation of voltage-dependent Na+ channels

Question 33

Refractory period

Answer 33

Right after the action potential, the cell can’t fire for about 1 ms. Cells have to be stimulated stronger during 2-4 ms after action potential to fire again

Question 34

All or none law

Answer 34

All action potentials of cell are equal (in amplitude, duration, propagation speed, shape)

Question 35

Larger stimulation leads to…

Answer 35

More action potentials

Question 36

Saltatory conduction

Answer 36

Under the myelin: passive conduction
At the nodes of Ranvier active conduction (because there are voltage-dependent Na+ channels.) Action potential is refreshed/renewed at each node of Ranvier.

Question 37

Types of synapses

Answer 37

Electrical
Chemical

Question 38

Electrical synapses

Answer 38

Gap junctions between the presynaptic and the postsynaptic terminal, through which ions float from one cell to the other (current, electrical propagation from one to the other cell)

Question 39

Chemical synapses

Answer 39

Most synapses are chemical

Question 40

How electrochemical synapses work

Answer 40

There are neurotransmitters in the vesicles at the presynaptic terminal. Action potential comes down –> Depolarization of presynaptic terminal –> Opening of voltage-gated Ca2+ channels –> Influx of Ca2+ into the terminal –> Ca2+ through a chemical reaction that requires it leads to the fusion of the vesicles with the cell membrane –> neurotransmitter is released and passively diffused into the synaptic cleft–> Neurotransmitter finds the neurotransmitter receptor at the postsynaptic terminal –> receptors open when the neurotransmitter binds to it –> leads to graded potentials in the postsynaptic cell

Question 41

Glial cells in the synaptic cleft

Answer 41

Each synapse is surrounded by them (astrocytes mostly), they take up neurotransmitters hovering around in the cleft to remove them from the area –> cleaner situation in the cleft

Question 42

Removal of neurotransmitters from the cleft

Answer 42

Glial cells
Enzymatic degradation

Question 43

Types of synapses by function

Answer 43

Excitatory- Type 1; asymmetrical (pre and postsynaptic membrane are not equally thickened); influx Na+, Ca+
Inhibitory- Type 2 ; symmetrical, Influx Cl-

Question 44

Types of synapses by connection

Answer 44

Axodendritic
Axosomatic
Axoaxonic
Dendrodentritic