signalling in the nervous system Flashcards
why is there a Resting membrane potential (RMP)
it Arises due to a difference in charge (due to
ions) between the inside and outside of the
neuron at rest
• More +ve ions outside cell / more –ve ions
inside cell
• Measured in relation to outside, therefore RMP
is a –ve value
• Typical RMP of neurons -60mV to -70mV
voltage-gated
opened / closed depending on
membrane potential
ligand-gated
opened in response to binding /
activation by neurotransmitter or drug
Equilibrium potential:
membrane potential where No
ions entering cell =
No
ions leaving cell (no net gain or loss of ions)
principal features of the action potential
an action potential is very brief but dramatic change in membrane potential.
depolarisation, repolarisation , hyperpolarisation
what is depolarisation related to
increased permeability to Na+ ions . fast opening of voltage gated Na channels
repolarisation and hyperpolarisation due to
increased permeability of potassium ions .
slow opening of voltage gated K channels
voltage gated sodium channel drugs in medicine
lidocaine = sodium channel antagonist
positive charge can travel where?
along axon
out of axon via membrane
destination of current depends on
- axon diameter 2. number of open pores /channels in membrane
Saltatory conduction
Action potential ‘jumps’ from node to node in the myelinated axon. increasing the conduction velocity of action potentials
Synaptic transmission
Chemical transmission between excitable cells.
- Action potential enters presynaptic terminal
- calcium ion entry through votage gated calcium channels
- docking of synaptic vesicles containing neurotransmitters
- neurotransmitters released -exocytosis
- neurotransmitter bids to and activates receptorson post synaptic membrane
- ions sodium and chloride ions enter the cell
- causes depolarisation(excitation) or hyperpolarisation (inhibition)
Excitatory postsynaptic
potential (EPSP)
An EPSP brings the post-synaptic membrane closer to threshold
(depolarisation), therefore increasing the probability of the postsynaptic
cell producing an action potential
Inhibitory postsynaptic
potential (IPSP)
An IPSP moves the post-synaptic membrane further away from threshold
(hyperpolarisation), therefore reducing the probability of the postsynaptic
cell producing an action potential
temporal summation
frequency of firing
spatial summation
firing at multiple sites.
mechanism of eliciting an action potential in a neuron with input from multiple presynaptic cells
what is botulism
it affects the neuromuscular junction .
clostridium bacteria produces botulinum toxin and it disrupts exocytosis preventing ACh release .
Causes skeletal muscle weakness and paralysis of the diaphragm
how does myasthenia gravis affect the neuromuscular junction
it is an inflammatory disease
antibodies bind to ACh receptors in the post synaptic membrane at motor end plate.
Causes severe muscle weakness , particularly affects
- eyelids, eyes, face, throat , limb muscles
