Lecture 2- Neurons and glia Flashcards
What is the role of neurons?
• Neuron is a key cell • 10 to the 11 neurons in human central nervous system •Neurons responsible for all “interesting phenomena? • Consciousness, self awareness, memory, emotion,planning • Control skeletal muscle, viscera and glands • Provide sensory input
What do glia mainly do?
-support neurons
What are some ways in which we can classify neurons?
- by function (excitatory vs inhibitory) - by neurotransmitter (gluatamate, GABA, cholinergic etc.) - by projection (projection neurons vs interneurons) -by shape (basket cells, chandelier cells) -by system (motor, sensory, autonomic) -all are valid approaches and there are many more ways of classifying neurons
What are the classes of neurons and the associated neurotransmitters?
- Cholinergic (Acetylcholine) 2. Glutamatergic etc. (Glutamate, GABA etc.) 3. Noradrenergic etc. (Noradrenaline, 5-HT etc.) 4. Peptidergic (Endorphins, SP, etc.) 5. Purinergic (ATP and adenosine)
What is neuronal morphology like?
-very variable -dendrites= inputs -axon= outputs -cell body is the energy powerhouse supplying the rest of the neuron -variety of standard shapes -morphologically highly specialised
What is a neuron?
- a protein producing cell - uses specialised proteins for all sorts of things - larger nucleus than most other cells as their DNA is unwrapped and accessible (Nissl bodies= rough ER, and free ribosomoes= these are so big that they actually stain!) -proteins are required for ion channels, receptors and the cytoskeleton
What is the importance of the cell membrane in a neuron?
-neuronal cell membrane is specialised for electrical activity -all cells have some sort of e difference across their membranes but neurons put theirs to work -the membrane can carry graded potentials and action potentials -requires energy expenditure to set up and maintain potential differences (ATPases drive ion flux)
What is a graded potential?
-passive electrotonic spread of current = local signal
What is an action potential?
-propagates long distances and requires specialised voltage-sensitive ion channels
What are the characteristics of dendrites?
-increase surface area for synaptic input -up to 10 000 inputs on a large neuron -lack major organelles -they increase the surface area of the membrane, means of harvesting information = the more surface area= the more info it can receive -in brain lot of neurons will have 10s of inputs -they lack features, it is the membrane that is important
What are the characteristics of an axon?
-over a metre long -carries AP -AP can be generated in cell body (axon hillock) or at tip of axon (for sensory neurons= dorsal root ganglia)
What is the volume distribution of neural components in a neuron?
-high proportion of total cell volume is in axons and dendrites -random damage often involves axon not the cell body -20 um diameter of the cell body and 30cm axon
How are neurons packed in the CNS?
-incredibly tightly, like a pack of tangled spaghetti
What does the shape of a neuron depend on?
- the complex shape depends on cytoskeleton
What are the 3 main components of the cytoskeleton?
- actin - intermediate filaments - microtubules - same classes of components as in any cell but neurons made it a crucial and specific part of the cell
What are the characteristics of actin?
-dynamic assembly/ disassembly allows shape changes and movement (e.g. spines and growth cones) -actin forms filaments from globular subfilaments and can disassemble just as quickly -the little bump on left= spines= input (excitatory) -actin forms growth cone= the growth cone can go on its own, axons are pulled by it to grow -grows spines even in the space of hours
What are the characteristics of microtubules?
-dynamic (rapid assembly/disassembly) -made of protein tubulin -have microtubule associated proteins (MAPs) -used for shifting things, like a railway
What are the characteristics of intermediate filaments?
-permanent (much more), not dynamic protein filaments -neurofilaments are the major type present in neurons -in all processes -play a crucial role in establishing the basic shape of the cell
How does axon transport work?
-have a long axon that needs nutrients etc. from the cell body so need a way of transporting these -microtubules are basis for axoplasmic transport -transports material from cell body to axon and dendrites and vice versa -moves membrane bound components by fast transport (400mm (40cm)/day)) and soluble material by slow transport (4mm/day) -fast transport is microtubule dependent and uses kinesin
What is the retrograde axonal transport?
-have to get the material back from the axon to the cell body fro recycling etc. -damaged organelles brought back to cell body for recycling by retrograde axonal transport -samples of the local environment also brought back -some viruses (herpes, chicken pox) and bacteria (tetanus) exploit the retrograde transport
What are the characteristics of the axon terminal?
-the axon terminal is where a signal passes from neuron to the target cell -the point of transmission is a specialised structure, the synapse -the information that the cell body is generating can be passed on= this is happening at the end of the axons -when AP reaches the terminal it starts a mechanism by which the information is passed on -via the synapse
What are the possible target cells for neurons?
-the target cell can be another neuron or an effector cell (muscle or secretory cell) -targets are a variety of cells -neuro-neuronal synapse/ neuromuscular synapse
What does a synapse (EM view, axo-dendritic) look like?
-the synaptic cleft is about 20nm

What are the characteristics of synaptic vesicles and the synaptic density?
- vesicles contain neurotransmitter
- the presynaptic density contains the elements necessary to dock and exocytose the vesicle
- the postsynaptic density contains receptors that respond to the neurotransmitter
- mainly supplied by axonal transport
- the binding of the neurotransmitter to receptor gets the response

