Neurons: Design Principle Flashcards
Different neuron types have different ?
Number of processes extending from the soma, reflecting evolutionary and functional differences
What are some types of neurons ?
- Unipolar
- Bipolar (Information conveying)
- Multipolar
Neurons are just like other cells, but ?
With ‘specialisation’ for rapid communication
What are two particular specialisations that neurons have ?
- Morphological features
- An electrically excitable membrane
The contents of a neuron are contained within?
A plasma membrane
This plasma membrane is a lipid bilayer structure which forms a hydrophobic barrier. This is comprised of ?
Amphipathic lipids –eg.phospholipids - and proteins (~20% of membrane composition)
Is this plasma membrane stable ?
It is stable but fluid structure, where phosphate head groups face the aqueous environment and fatty acid tails face each other
What does this plasma membrane act as ?
The membrane acts as a barrier to water-soluble ions and charged molecules
What is the only way that they can cross the plasma membrane ?
Via membrane-spanning proteins
The cytoplasm is the contents of the inside of the cell. What can this be sub-divided into ?
- Cytosol
Aqueous component of the cytoplasm - Everything else:
Cytoskeleton, membranous organelles and vacuolar apparatus (Golgi, tubules, vesicles, lysosomes, endoplasmic reticulum).
The cytoskeleton determines?
Cell shape
What are three main components of cytoskeleton?
- 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
Explain the processes of active transport for transporting proteins and organelles ?
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
Name some transport proteins and explain ?
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
What special proteins allows passive diffusion of ions ?
Ion channels
What is ion flow determined by?
Electrochemical driving forces
What are leakage channels ?
Some channels which are open all the time
Most channels are gated, meaning ?
They can be opened or closed
How is Gating achieved ?
By a conformational change in the structure of the protein
What is transport protein that uses energy to move ions across the membrane ?
Ion pumps
In Ion pumps, ions do not flow freely but ?
Can be actively transported against their electrochemical gradient and used to establish a high concentration of ions on one side of the membrane
Name some signalling proteins and explain ?
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
Name some binding proteins and explain ?
Adhesion proteins:
- Anchor the neuron to other cells
Cytoskeletal binding proteins:
- Anchor the cell membrane to the internal cytoskeleton
Explain how Glial cells are similar to neurons in a number of ways:
- Electrical potential across their membrane which can be varied
- Respond to various chemicals
- Some have a similar structure with a cell body and neurite branches
What is a difference between Glial cells and neurons ?
They do not show active electrical responses (an ‘action potential’) like those exhibited by neurons
What are the four main classes of Glial Cells ?
- Microglia
- Oligodendrocytes
- Schwann Cells
- Astrocytes
What are Microglia ?
They are small and mobile with a defensive function, consuming cellular debris
What do both Oligodendrocytes and Schwann Cells generate ?
Myelin, the insulating material that allows rapid conduction of electrical signals
What do single oligodendrocytes do to axons compared to Schwann Cells ?
Single oligodendrocytes wrap many axons, Schwann Cells wrap only one
Is Myelin continuous ?
Myelin is not continuous but separated by unmyelinated gaps, called nodes of Ranvier
In nodes of Ranvier, the density of Na+ channels is much higher which means ?
That the nodes are more easily excited
What does this high density mean for the nerve impulses?
That they can travel much more quickly in myelinated axons because it jumps between nodes - a process called saltatory conduction
What is the number of myelin layers proportional to ?
The axon diameter and small axons do not have myelin at all
What is the shape of Astrocytes ?
Star-shaped glia: they are probably present in similar numbers to neurons in the brain
Where do Astrocytes have an important role at ?
They have a much more important role in brain function
What kind of roles fo Astrocytes have ?
Homeostatic and buffering roles
Astrocytes have large numbers of thin processes that ?
Enfold brain blood vessels and ensheath synapses meaning they can control extracellular ions, neurotransmitter etc,. particularly at their end feet structures
What is one role of the Astrocytes ?
One role is K+ buffering allowing the excitability of neurons to be modulated
What can Astrocytes also regulate ?
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
Through their associations with blood vessels, astrocytes also roles in ?
Mopping up macromolecules that might otherwise cross the blood-brain barrier
