Unit 6: Nervous coordination Flashcards
What is the value of the resting potential inside the axon?
-70mV
What is the resting potential
the potential difference across the membrane of an axon when an impulse isn’t being transmitted
Which ions are in a polarised neurone?
more sodium ions outside the axon and more potassium ions inside the axon
How is the resting potential maintain
- membrane is differentially permeable
more permeable to the loss of K+ than intake of Na+ - Na/K pump actively transports 3 Na+ out and 2 K+ in against their diffusion gradients ensuring that an electrochemical gradient is maintained
What is a respiratory inhibitor
prevents production of ATP so Na/K pump cant function and conc of these ions will eventually reach equilibrium and the potential difference will be 0
What causes an action potential
when a receptor is stimulates above its threshold
What happens during delolarisation
increase in permeability of the axon to Na+
Na voltage gated channels open and Na+ diffuses down a conc gradient into axon and value increases to +40mV
What happens during repolarisation
Na channels close
K voltage gated channels open and K+ diffuse out of axon making it less + e
How does the Na/K pump restore the resting potential?
actively removes Na+ which have entered and returns K+ back into axon
What happens during hyper polarisation
membrane pitential becomes more negative bc K+ diffuses out slowly
What is the refractory period?
period after the formation of an action potential when a neurone cant generate another action potential
resulting in discrete impulses
ensures that impulse travels in one direction
What is the all or nothing principle
a stimulus must be above a certain threshold level for an impulse to be generated
a strong stimulus above threshold will result in a greater frequency of impulses than a weak stimulus
amplitide of impulses always remain the same
How does temperature affect the speed of conductance?
increase in temperature will increase speed of transmission up to a particular temperature
provides more KE for the diffusion of ions inside and out the axon
How does a temperature above optimum affect speed of concordance
denaturation of enzymes and proteins in the plasma membrane would stop the transmission
How does axon diameter affect speed of conductance
greater the diameter the faster less resistance
How does myelination affect speed of conductance?
myelinated neurones increase speed as action potential jumps from one gap (node of ranvier) to another to the next
depolarisation only occurs at the nodes > saltatory conduction
in non myelinated neurones depolarisation occurs along the whole membrane of the axon slowing down transmission
Why does the synaptic knob contain many mitochondria
to provide ATP for the synthesis of the neurotransmitter
What happens during synaptic transmission
- action potential reaches synaptic knob causing depolatisation of PreSM
- stimulated Ca2+ to open in PreSM and diffuse into synaptic knob
- cause vesicles to fuse with preSM and break open
- neurotransmitter acetylcholine is released and diffuses across synaptic cleft
- acetylcholine attatches to specific receptor on postSM
- stimulates entry of Na+ leading to depolarisation of postSM and transmission of an impulse
How is acetylcholine broken down then resynthesised
- broken down in postSM by enzyme acetylcholinesterase making acetyl and choline
- acetyl and choline is taken up into the synaptic knob by active transport and is resynthesised
What is spatial summation?
two or more impulses from different synaptic knobs arrive simultaneously at different regions on the same neurone
mores likely to reach threshold as there are more knobs
What is temporal summation?
two or more impulses arrive at the same place on the axon within a short period of time
more likely to reach threshold than if one impulse arrived
how do synapse give an inhibitory effect on the postSM?
by stimulating influx of negative Cl- ions and by stimulating removal of K+ causing a more -ve charge in the axon
its more difficult to reach threshold than
What is the neuromuscular junction?
The synaptic connection between a neuron and muscle fibre
Many drugs act on the neuromuscular junctions
How do drugs work by mimicking?
drugs have a similar structure to a normal transmitter and have the same effect they bind to receptors and transmission is faster
How do drugs work by blocking?
drugs have a similar structure in a normal transmitter, but do not produce the same effect
They fit into the receptors and prevent the normal transmitter from entering this stop the transmitter from having its effect so transmission is stopped
How do drugs work by preventing?
prevent the release of the transmitter substance from the preSM so that transmission is stopped
How do drugs work by inhibiting?
The inhibit the action of enzymes which hydrolyse neurotransmitters therefore more transmitter is present so transmission is enhanced
What are cholinergic neurones
neurones possessing acetylcholine
