Topic 6B - Nervous Coordination Flashcards
(76 cards)
Describe the structure of a typical neurone that explains how they are adapted to carry electrochemical signals (electrical impulses)
Myelinated neurone = myelin sheath, which is a fatty, insulating layer made up of Schwann cells (provide protection) to stop electrical impulses being carried to other nearby neurones along the axon.
Long dendrons into dendrites to cell body, connected to other neurones.
Presence of Nodes of Ranvier aid in saltarary Conduction
Many neurones have voltage - gated channels, meaning
they only open when surrounding membrane depolarises
resting potential
more relatively negative inside cell (due to more positive ions on the outside) - membrane POLARISED (-70mV); potential difference across membrane; when neurone the not stimulated
does maintaining the resting potential require ATP?
- side task to think why resting potential is so important
Yes, the sodium - potassium pump is a carrier protein that requires ATP from respiration to release energy
SOPI
3 sodium out, 2 potassium in
- results in more sodium ions outside than the amount inside (potassium only 2), overall bigger + charge outside
Where is acetylcholinesterase stored in a neuromuscular junction?
(clefts) in postsynaptic membrane
What are differences between a cholinergic synapse and a neuromuscular junction?
seneca…
role of Pacinian corpuscle
Pacinian corpuscle is a sensory receptor and its role is to convert pressure into an electrical impulse.
List the TWO features of sensory reception shown by the Pacinian corpuscle.
It is specific to one type of stimulus.
It establishes a generator potential.
Desc. how the membrane of the axon maintains resting potential / polarised
- hydrolysis of ATP (resp.) used for energy by sodium potassium pump to actively transport (3 sodium out, 2 potassium in). Results in more positive charge/ more sodium outside…
- so allows then little facilitated diff. of Na + into axon via voltage-gated sodium ion channels [link to how lots of these are closed anyway at resting] > Only open when big enough voltage.
- facilitated diff: membrane more permeable to k+ ions as many voltage-gated potassium ion channels are open & more leave axon down electrochemical gradient : less positive than outside
Desc. how action potentials work.
- an action potential occurs when a neurone sends an e. impulse down an axon, away from cell body.
- note generator potentials are caused by stimulus and become action potential when threshold men
it’s all about sodium ions first and then potassium
- think Sadie Pearson
- Voltage-gated sodium in channels open due to stimulus, permeability to sodium increases & Na + enters INTO axon (facilitated) down electrochemical gradient… inside starts to become more positive.
- Depolarising
If potential diff/ generator p. = threshold =MORE NA+ ION CHANNELS OPEN, more diffuse in via facilitated - Repolarising
(around 30mV) sodium ions calm down and start to close… voltage-gated POTASSIUM ions start to open - more permeable to K+ and leave (facilitated) neurone down electrochem. gradient - Hyperpolarisation
Voltage-gated potassium ion channels are slow to close!, too many K + ions diffuse out - Resting potential
Channels reset and Na/k pump returns polarised membrane
The refractory period occurs after action potential (around hyperpolarisation where ion channels need to be reset).
Why is it needed?
- time delay between the action potentials to limit frequency - organism might be overwhelmed
- so the a. potentials can pass along as discrete impulses (no overlap) to distinguish stimulus & where it came from
- so a. potentials can be unidirectional (if both directions, the threshold wouldn’t be reached)
Threshold may not be met due to…
weak Stimulus so not enough Na + moving into sensory neurone or due to inhibitory neurotransmitters
Desc. waves of depolarisation
- example of positive feedbade
where a wave of an action potential is carried away from the cell body, along the axon, leaving behind a refractory period > unidirectial (messages don’t clash)
1. sodium ions enter neurone at start and some diffuse sideways.
2. Voltage-gated Na + channels in next section open, causing more Na + facilitatedly diffuse in… = wave along neurone
Desc. all or nothing principle
When threshold is not reached = failed initiation, no action p. fired.
Also encompasses how bigger / stronger stimuli don’t fire bigger a. potentials, but instead more frequent
Speed of conduction of electrical impulses across axon depends on Which 3 factors?
- myelin sheath
- axon diameter
- temp
How myelination impacts conduction:
1. why does depolarisation only happen at Nodes of Ranvier (if myelinated axon)?
2. desc. saltatory conduction
- Sodium ions can’t diffuse through insulating lipid layer, sodium ion channels conc. around nodes of ranvier
- In myelinated neurone, depolarisation at nodes. The neurone cytoplasm contains enough electrical charge to depolarise the next node!
Impulse jumps to nodes and so is much faster than non- myelinated
Desc. how the axon diameter impacts speed of conduction
Large axon (more space for cytoplasm erc) = less resistance to flow of ions in cyto, compared to small one. Wave of depolarisation can occur quicker
(proportional relationship)
How temp impacts speed of conduction
* watch vid on
- how would above optimum impact speed
^ kinetic energy = ^ rate of conduction and nerve impulse AND ^ activity of resp. enzymes = ^ ATP for active transport of ions (e.g. to more quickly return membrane to polarised?)
Maybe ions have more energy too.
- denature (enzymes and ion channels), decrease speed
COLD BLOODED ANIMALS MOST AFFECTED in terms of rate of nervous system as suffer if environment too hot / cold
why do so many SER need to be in pre-synaptic neurone (cholinergic synapse)
to make proteins like enzyme acetylcholinesterase and to finish synthesis of acetylcholine!
Why are neurotransmitters unidirectional?
vesicles containing them only exist in pre synaptic neurone (so high conc. on one side), and complementary receptors for them only exist on the post synaptic neurone
synapse
junction between 2 nerve cells
neurotransmitters
Chemically transfer as potential across synaptic cleft
