How Nerves Work Flashcards
What is the function of dendrites?
Receive information from its surrounding environment
What are afferent neurones?
Sensory neurones of the peripheral nervous system that detect information.
What are interneurones?
Neurones of the central nervous system that receive information from afferent neurones and decide what to do.
What are efferent neurones?
Motor neurones that receive instruction from interneurones and send a signal to an effector to carry out a response.
What are Astrocytes?
Glia cells that maintain the environment for neurones.
They also surround blood vessels and forth blood brain barrier.
What are Oligodendrocytes?
Glial cells that form myelin sheaths around neurones of the central nervous system.
What are Microglia?
Glia cells that are phagocytic hoovers and mop up infection surrounding neurones.
What are the 4 different lobes of the Cerebrum?
Frontal lobe
Temporal lobe
Parietal lobe
Occipital lobe
What 3 structures make up the Brainstem?
Midbrain
Pons
Medulla Oblongata
What 2 structures make up the Diencephalon?
Thalamus
Hypothalamus
What is the resting membrane potential?
The voltage difference across a cell membrane when it is in its resting state.
What creates the Resting membrane potential within a cell?
Leaky potassium channels.
K+ moves down conc. gradient which creates an electrical gradient which is exactly equal and opposite to the conc. gradient.
What are some different types of graded potential?
Generator potential - at sensory receptors
Postsynaptic potential - at synapses
Endplate potential - at neuromuscular junctions
Pacemaker potential - in pacemaker tissues
What is the role of a graded potential?
Determines when an action potential is fired.
What are some properties of Graded potentials?
Decremental - membrane potential gets smaller as you travel along axon as leaky channels open.
Local- can only be used over short distances due to being decremental.
Graded - the stronger the stimulus, the more channels get opened, the bigger the current flow and therefore the bigger the potential fired.
How can graded potentials be both excitatory or inhibitory?
Firing an action potential requires the graded potential to reach to a threshold (-55mV). The graded potential can either hyper-polarise or depolarise depending on which ion channels are open/closed.
How are postsynaptic potentials hyper-polarised?
Cl- or More K+ are opened so either Cl- flows in creating a fast IPSP, or K+ leaks out creating a slow IPSP.
This takes them away from threshold so it is inhibitory.
GABA and glycine do this.
How are postsynaptic potentials depolarised?
Transmitters open channels permeable to Na+ and K+ but more Na+ gets out than K+ so causes a depolarisation. This causes a fast EPSP.
Blocking K+ channels can also cause a depolarisation but it is only a slow EPSP.
How are postsynaptic potentials produced?
A neurotransmitter opening or closing ion channels - ligand gated ion channels.
How are action potentials produced?
Depolarisation of the membrane potential opening ion channels - voltage gated ion channels.
What is meant by graded potentials can summate?
They can add to each other so threshold is produced quicker. The effects of more than one stimulus are added together.
What is integration?
Looking at all the inputs whether they are synapses or stimuli and deciding whether to fire an action potential or not.
Describe the main stages of an action potential?
RMP sits at -70mV
Graded potential fired, reaches threshold of -55mV
Sudden massive depolarisation as Na+ channels open and action potential is fired, overshoots to +30mV.
Rapid depolarisation to a little below RMP.
Name some toxins that block the voltage gated Na+ channels to prevent action potentials form being fired?
Local anaesthetics
Tetrodotoxin - pufferfish
Saxitoxin - shellfish.
What are some properties of action potentials?
They have a threshold They are all or none Mediated by voltage gated channels. Stimulus depends on firing frequency. Self-propagating Have a refractory period Travel slowly.
What is the function of the refractory period?
The local current flow also spreads back when the signal fires along the axon but refractory prevents another AP being fired, keeps it going in right direction.
Why do large axons increase conduction velocity?
Large axons decrease axial resistance - the depolarisation can reach further, need less Na+ channels which take time to open.
What cells in the peripheral nervous system form myelin?
Schwann cells.
How does myelin increase the conduction velocity?
Increased resistance of the membrane allows AP to spread like a local current without much decrement. Insulates the axon.
What are the stages of AP at a NMJ causing muscle contraction?
1- Motor neurone reaches end of axon.
2- Ca2+ enters via voltage gated channels
3- Acetylcholine is released and diffuses across synapse.
4- Na+ channel are opened by Acetylcholine binding. Na+ enters.
5-Na+ channels evoke an endplate potential.
6-Adjacent membrane depolarised to threshold
7-Voltage gated Na+ channels open firing a new AP, ACh is removed by Acetylcholinesterase.
