Neurons: Design Principle

Question 1

Different neuron types have different ?

Answer 1

Number of processes extending from the soma, reflecting evolutionary and functional differences

Question 2

What are some types of neurons ?

Answer 2

• Unipolar
• Bipolar (Information conveying)
• Multipolar

Question 3

Neurons are just like other cells, but ?

Answer 3

With ‘specialisation’ for rapid communication

Question 4

What are two particular specialisations that neurons have ?

Answer 4

• Morphological features

- An electrically excitable membrane

Question 5

The contents of a neuron are contained within?

Answer 5

A plasma membrane

Question 6

This plasma membrane is a lipid bilayer structure which forms a hydrophobic barrier. This is comprised of ?

Answer 6

Amphipathic lipids –eg.phospholipids - and proteins (~20% of membrane composition)

Question 7

Is this plasma membrane stable ?

Answer 7

It is stable but fluid structure, where phosphate head groups face the aqueous environment and fatty acid tails face each other

Question 8

What does this plasma membrane act as ?

Answer 8

The membrane acts as a barrier to water-soluble ions and charged molecules

Question 9

What is the only way that they can cross the plasma membrane ?

Answer 9

Via membrane-spanning proteins

Question 10

The cytoplasm is the contents of the inside of the cell. What can this be sub-divided into ?

Answer 10

1. Cytosol
   Aqueous component of the cytoplasm
2. Everything else:
   Cytoskeleton, membranous organelles and vacuolar apparatus (Golgi, tubules, vesicles, lysosomes, endoplasmic reticulum).

Question 11

The cytoskeleton determines?

Answer 11

Cell shape

Question 12

What are three main components of cytoskeleton?

Answer 12

• Microtubules: long scaffolds involved in cell stability and transport mechanisms; dynamic
• Neurofilaments: bones of the cytoskeleton and structural support for axons – shorter; numerous and stable
• Actin: much shorter and concentrated at peripheral structures – for example, synapses where they can influence function; dynamic

Question 13

Explain the processes of active transport for transporting proteins and organelles ?

Answer 13

SLOW: Cytoskeletal elements (e.g.actin), enzymes and some proteins move anterogradely at 0.2-2.5 mm/day. Involves mechanisms including microtubule slipping.
FAST: Membranous organelles (vesicles, mitochondria etc.) are moved both anterogradely and retrogradely at >400mm/day requiring ATP and molecular motors on microtubules

Question 14

Name some transport proteins and explain ?

Answer 14

Ion channel:
Allows the passive flow of ions through the membrane
Ion pump:
Moves ions across the membrane against a concentration gradient
Other transporters:
Facilitates transfer of molecules across the membrane

Question 15

What special proteins allows passive diffusion of ions ?

Answer 15

Ion channels

Question 16

What is ion flow determined by?

Answer 16

Electrochemical driving forces

Question 17

What are leakage channels ?

Answer 17

Some channels which are open all the time

Question 18

Most channels are gated, meaning ?

Answer 18

They can be opened or closed

Question 19

How is Gating achieved ?

Answer 19

By a conformational change in the structure of the protein

Question 20

What is transport protein that uses energy to move ions across the membrane ?

Answer 20

Ion pumps

Question 21

In Ion pumps, ions do not flow freely but ?

Answer 21

Can be actively transported against their electrochemical gradient and used to establish a high concentration of ions on one side of the membrane

Question 22

Name some signalling proteins and explain ?

Answer 22

Receptors:
- Binds a signalling molecule and initiates a neuronal response
G Proteins:
- Initiates a cascade of biochemical reactions triggering a neuronal response when triggered by a signalling molecule
Other enzymes:
- Catalyses biochemical reactions associated with signalling

Question 23

Name some binding proteins and explain ?

Answer 23

Adhesion proteins:
- Anchor the neuron to other cells
Cytoskeletal binding proteins:
- Anchor the cell membrane to the internal cytoskeleton

Question 24

Explain how Glial cells are similar to neurons in a number of ways:

Answer 24

1. Electrical potential across their membrane which can be varied
2. Respond to various chemicals
3. Some have a similar structure with a cell body and neurite branches

Question 25

What is a difference between Glial cells and neurons ?

Answer 25

They do not show active electrical responses (an ‘action potential’) like those exhibited by neurons

Question 26

What are the four main classes of Glial Cells ?

Answer 26

1. Microglia
2. Oligodendrocytes
3. Schwann Cells
4. Astrocytes

Question 27

What are Microglia ?

Answer 27

They are small and mobile with a defensive function, consuming cellular debris

Question 28

What do both Oligodendrocytes and Schwann Cells generate ?

Answer 28

Myelin, the insulating material that allows rapid conduction of electrical signals

Question 29

What do single oligodendrocytes do to axons compared to Schwann Cells ?

Answer 29

Single oligodendrocytes wrap many axons, Schwann Cells wrap only one

Question 30

Is Myelin continuous ?

Answer 30

Myelin is not continuous but separated by unmyelinated gaps, called nodes of Ranvier

Question 31

In nodes of Ranvier, the density of Na+ channels is much higher which means ?

Answer 31

That the nodes are more easily excited

Question 32

What does this high density mean for the nerve impulses?

Answer 32

That they can travel much more quickly in myelinated axons because it jumps between nodes - a process called saltatory conduction

Question 33

What is the number of myelin layers proportional to ?

Answer 33

The axon diameter and small axons do not have myelin at all

Question 34

What is the shape of Astrocytes ?

Answer 34

Star-shaped glia: they are probably present in similar numbers to neurons in the brain

Question 35

Where do Astrocytes have an important role at ?

Answer 35

They have a much more important role in brain function

Question 36

What kind of roles fo Astrocytes have ?

Answer 36

Homeostatic and buffering roles

Question 37

Astrocytes have large numbers of thin processes that ?

Answer 37

Enfold brain blood vessels and ensheath synapses meaning they can control extracellular ions, neurotransmitter etc,. particularly at their end feet structures

Question 38

What is one role of the Astrocytes ?

Answer 38

One role is K+ buffering allowing the excitability of neurons to be modulated

Question 39

What can Astrocytes also regulate ?

Answer 39

Astrocytes also regulate neurotransmitter concentrations in the brain. For example, high-affinity transporters located in the astrocytes plasma membranes rapidly clear the neurotransmitter glutamate from the synaptic cleft; similar effects occur through degradation of dopamine, serotonin and others, and help to mop up toxic oxygen free radicals

Question 40

Through their associations with blood vessels, astrocytes also roles in ?

Answer 40

Mopping up macromolecules that might otherwise cross the blood-brain barrier