Lecture 2 Flashcards
How is the membrane specialised for electrical activity?
- Potential difference across membrane.
- Requires energy expenditure to set up and maintain potential differences (ATPases drive ion flux)
- Membrane carries graded potentials, action potentials, i.e. passive spread of electrical current when you depolarise an electrical current.
What is the difference between graded potential and action potentials?
Graded potential- results from the passive electrical property of the neuronal membrane. Graded potential must occur for action potential to occur.
- Depending on the stimulus, can be depolarisation or hyper polarising.
- Amplitude is proportional to the strength of the stimulus.
- Ligand gated, mechano-sensitive cytoplasmic signalling molecules.
Action potential-propogates long distances and is an orchestrated response to depolarisation stimuli and involve a coordinated activity of voltage gated ion channels.
- Action potentials always load to depolarisation of membrane and reversal membrane potential.
- Amplitude is all or nothing, strength is coded in frequencies.
- voltage gated Na+ and K+.
Why is does the neurone have a large pale nucleus, Nissl bodies.
because DNA is unravelled so its always accessible for protein production. The nerve cell requires A LOT of protein production in order to function.
Why does the dendrites lack in major organelles?
because the membrane is the most important part. It can have up to 10,000 synaptic inputs.
Where can an action potential be generated in an action potential?
it can be generated in the cell body (axon hillock) or at the tip of axon (for sensory neuron)
What are three components that the cytoskeleton is made of?
- actin
2 intermediate filaments
3.microtubules
it is the same classes of components as in any cell, but shows specific features in neurons.
What is the function of actin in a neuronal cell?
Actin can form filaments from reservoir of globular subunits from the cytoskeleton quickly. This dynamic assembly/disassembly allows shape changes and movement (e.g. spines and growth cones).
What are growth cones?
Growth cones pull the axon so it can elongate the axon. It is powered by actin.
What are microtubules used for?
They are used to shift things around and used sort of like a railway. They are made of protein tubulin and are dynamic (rapidly assembly/disassembly). They also have microtubules associated proteins (MAPs)
What is the function of intermediate filaments? and what is an important subclass?
They are not dynamic like the other two but mainly invoked in shape and maintaining structure. They are a permanent structure. An important subclass is neurofilaments.
How do neurons transport molecules up and down the cell?
The neuron transports molecules via axon transport. Microtubules are the basis for axoplasmic transport. Moves membrane bound components by fast transport (400mm/day) , soluble material by slow transport (4mm/day).
Fast transport is microtubule dependent and uses kinesin
Axon transport is balanced by retrograde axonal transport. Damaged organelles are brought back to cell body for recycling by retrograde axonal transport.
Samples of the local environment also brought back. The cell body can then make decision based on environment but….
Some viruses (herpes, chicken pox) and bacteria (tetanus) exploit this retrograde transport.
What is the release of neurotransmitters initiated?
An action potential triggers voltage gated Ca++ channels to open. This influx of Ca++ causes vesicles to under go exocytosis.
There are elements in the presynaptic density that contains the elements necessary to dock and exocytose the vesicles.
How is the action of neurotransmitter terminated once it has reached the receptors? or How is the effects of neurotransmitters limited post-synaptically?
The post-synaptic effects is limited by:
- diffusion of transmitter out of the cleft
- destruction of transmitter by specialised enzymes
- re-uptake of the neurotransmitter by the axon, target cell or glial cell.
Why is it that when you stop breathing, the effects are the worst on the brain?
The neuronal energy budget is very demanding. Most of a rat’s cerebral cortex’s energy is used for information transfer processes and the synapses.
The brain is only 2% of the body’s mass but consumes 20% of oxygen, 25% of glucose.
Very sensitive to loss of blood flow (O2 (4 minutes) and glucose (15 minutes)) as few energy reserves.
Glucose is the main energy supply for the brain.
Explain the activity-dependent vasodilation in CNS
If a neuron ‘thinks’ it demands more blood. Local activity in CNS leads to local increase in blood flow (increases glucose and O2 availability).
This forms the basis for MRI and PET functional imaging.
MRI detects changes in local oxyhaemoglobin, seen as the Blood/Oxygen Level Dependant (BOLD) signal.
