1: Physiology - Neurons, excitation and inhibition in the CNS

Question 1

What is the start of an axon called?

Answer 1

Hillock

Question 2

How are materials like mitochondria, proteins etc. transported along a nerve axon?

Answer 2

Axonal transport

Question 3

What are the names of axonal transport which move materials

a) towards the presynaptic terminal
b) towards the cell body?

Answer 3

a) Anterograde axonal transport

b) Retrograde axonal transport

Question 4

How do viruses travel within nerves?

Answer 4

(Retrograde) axonal transport

Question 5

What is a synapse?

Answer 5

Point of chemical/electrical communication between nerve cells

Question 6

What is a neurite?

Answer 6

A structure which projects from a nerve cell body

so an axon or a dendrite

Question 7

unipolar, multipolar neurons

Question 8

What is meant when describing an axon by its Golgi type?

Answer 8

Golgi type I axons are long

Golgi type II axons are short

Question 9

What is the membrane potential of

a) sodium
b) potassium?

Answer 9

a) +60 mV

b) -90mV

Question 10

In general, what is the threshold potential of a neuron?

Answer 10

The membrane potential required for Na+ channels to open

Question 11

Which channels open to cause the upstroke of an action potential in neurons?

Answer 11

Na+

Question 12

What channels open to cause the downstroke of an action potential?

Answer 12

K+ channels

Question 13

What overcompensations are caused by the opening of

a) sodium
b) potassium?

Answer 13

a) Overshoot

b) Undershoot

i.e the membrane hyperpolarises before returning to normal

Question 14

What is the difference between the conduction of action potentials and passive signals through nerve axons?

Answer 14

Action potentials have a fixed amplitude all the way along so they can travel long distances

Passive signals decay in amplitude and can therefore only travel short distances

Question 15

How far can action potentials travel in the body compared to passive signals?

Answer 15

Much further than passive signals

Question 16

Revise ohm’s law (V=IR)

Resistance of axon is constant

Current leaks as you go along the axon

So the further along the axon you go, the greater the decrease in action potential

Question 17

from what I can tell…

decreasing resistance INCREASES length constant because the action potential can travel further before decaying to 37% (specific number because it matches to exponential function)

look at ratio specifically

Question 18

r_m/r_i

Question 19

How does conduction velocity change with an increasing length constant?

Answer 19

The greater the length constant, the greater the distance the current can spread without decaying

So the greater the conduction velocity

Question 20

How does insulating a nerve axon with myelin increase the conduction velocity?

Answer 20

Insulation INCREASES membrane resistance while internal resistance remains unchanged

So the ratio rm/ri INCREASES

So length constant INCREASES

So conduction velocity increases

Question 21

Which glial cells insulate nerve axons in the

a) CNS
b) PNS?

Answer 21

a) Oligodendrocytes

b) Schwann cells

Question 22

What is a Node of Ranvier?

Answer 22

Gap between Schwann cells (found only in the PNS)

Question 23

What is saltatory conduction?

Answer 23

The jumping of an action potential between Nodes of Ranvier

Question 24

Saltatory conduction occurs only in (myelinated / unmyelinated) neurons.

Answer 24

myelinated PNS neurons only

because they have Nodes of Ranvier

Question 25

How does myelination change the conduction velocity?

Answer 25

Myelination increases conduction velocity

Question 26

Which type of disease slows down or stops nerve conduction?

Answer 26

Demyelinating disorders

Question 27

Which demyelinating disorders affect the

a) CNS
b) PNS?

Answer 27

a) MS

b) Guilain-Barre syndrome

Question 28

What is the name of the space between pre-synaptic and post-synaptic neurons?

Answer 28

Synaptic cleft

Question 29

In terms of a synapse, what is a vesicle?

Answer 29

Structure which contains neurotransmitter

Question 30

What is a membrane differentiation?

Answer 30

Area between a vesicle and neurotransmitter receptor

small as possible to make neurotransmission quick

Question 31

How do glial cells affect neurotransmission?

Answer 31

Hoover up neurotransmitters from the synaptic cleft

Question 32

Describe

a) axodendritic
b) axosomatic
c) axoaxonic

synapses.

Answer 32

a) Synapse found between the AXON of one neuron and the DENDRITE of another

b) AXON “ BODY

c) AXON “ AXON

Question 33

What are the three morphological types of synapse?

Answer 33

a) Axodendritic

b) Axosomatic

c) Axoaxonic

Question 34

What are the two functional types of synapse?

Answer 34

Excitatory and inhibitory

Question 35

Which neurotransmitters are usually found at

a) excitatory synapses
b) inhibitory synapses?

Answer 35

a) Glutamate

b) GABA, glycine

Question 36

Which named action potentials are generated by

a) excitatory synapses
b) inhibitory synapses?

Answer 36

a) Excitatory post-synaptic potential

b) Inhibitory post-synaptic potential

Question 37

In terms of changes in membrane potential, what happens at

a) excitatory synapses
b) inhibitory synapses?

Answer 37

a) Depolarisation (opening Na+ channels)

b) Hyperpolarisation (opening Cl- channels)

Question 38

Many neurons receive more than one, i.e a sum of synapses.

How does this determine whether an output will be excitatory or inhibitory?

Answer 38

Summation

so if you get two excitatory post-synaptic potentials and one inhibitory, the net result will be excitation and vice versa

Question 39

Action potentials can be summated to affect the overall output.

What other variable determines the output of a neuron?

Answer 39

Frequency

i,e if excitatory potentials are firing off quicker than inhibitory potentials, the output will be excitation and vice versa

Question 40

What two types of summation change whether a neuron’s output is excitatory or inhibitory?

Answer 40

Spatial, i.e how many of each type a neuron is receiving

Temporal, i.e how often a neuron is receiving potentials of each kind