Bioelectricity Flashcards
2 main cations that create bioelectricity of a neuron
Na+ and K+
how is membrane potential created
- high Na+ conc (135-145mM) and low K+ conc (3.5-5mM) outside cell and low Na+ conc (12mM) and high K+ conc (150mM) inside cell created charge difference between two sides of membrane
typical RMP for living neurons
-70mV
ion channels at RMP
most Na+ channels are closed; Some K+ channels are open
how is RMP maintained?
Na+/K+ pump (ATPase) shifts 3 Na+ out and 2 K+ in
ion channels
large proteins that form within the lipid bilayer to enable charge movement. highly selective
changes in membrane potential
resting, depolarised, repolarised/hyperpolarised
ion channels at depolarised RMP
Na+ channels open, Positive charges move IN, depolarised (less negative)
ion channels at repolarised RMP
K+ channels open, Positive charges move OUT, charge moves towards RMP
ion channels at hyperpolarised RMP
K+ channels open, Positive charges move OUT, charge moves past RMP
threshold potential
-59mV, minimum local potential that triggers an action potential, cell is depolarised
action potential
+30mV, temporary maximum depolarisation propagates along the axon without losing amplitude, cell is depolarised then repolarised
steps of action potential propagation
- stimulus triggers stimulus-gated Na+ channels to open and allow inward Na+ diffusion. This causes the membrane to depolarise
- as the threshold potential is reached, voltage-gated Na+ channels open
- as more Na+ enters the cell through voltage-gated Na+ channels, the membrane depolarises even further
- the magnitude of the AP peaks at +30mV when voltage-gated Na+ channels close
- repolarisation begins when voltage-gated K+ channels open, alloowing outward diffusion of K+
- after a brief period of hyperpolarisation, the resting potential is restored by the Na+/K+ pump and the return of ion channels to their resting state
conduction of AP down axons
relies on spread of depolarising electrical signal along the axon to activate the next set of voltage-gated Na+ channels
refractory period
time during which another AP cannot be passed down the same nerve, affects frequency of APs
how to improve conduction speed
myelin (insulation) of axon using schwann cells to allow saltatory conduction - ‘jumping’ between nodes between schwann cells
2 types of synapse and features
- electrical synapse - physical gap linked by gap junctions, very fast
- chemical synapse - physical gap linked by a chemical transmitter, slower than electrical but still fast
neurotransmitter at nerve to muscle synapse
ACh
features of pre-synaptic neuron
- Axon Terminal or Bouton
- Contains vesicles
- Contains cytoskeleton
- Contains mitochondria
- Must have voltage gated Ca2+ channels
features of post-synaptic neuron
- Must contain neurotransmitter receptors
- These allow Na+ or Ca2+ entry to depolarise the post synaptic cell
- Often appears as a thick post synaptic membrane called the post synaptic density PSD
process of synaptic transmission
- Action potential propagates down the axon – to the pre-synaptic bouton
- Pre-synaptic bouton is depolarised – voltage gated Ca2+ channels open
- Ca2+ ions TRIGGER the release of the neurotransmitter from the vesicles
- Neurotransmitter is released INTO the synaptic cleft
- Neurotransmitter binds to its SPECIFIC receptors on the POST SYNAPSE
- Na+ channels open – LOCAL depolarisation of post synaptic cell
- Net depolarisation followed by repolarisation – called the EXCITATORY POST SYNAPTIC POTENTIAL – or EPSP
how is a synapse switched off?
if excess transmitter is released into the cleft, it must be removed by
- degradation - enzymic
- reuptake into bouton
- reuptake into glia
removal requires ATP - mitochondria in bouton
Na+ concentration inside and outside neurons
12mM (inside) and 142mM (outside)
Types of Neurotransmitters
Acetylcholine
Glutamate
GABA
Norepinephrine / Noradrenaline
release of classic neurotransmitter
A classical neurotransmitter is released from vesicles from within the pre-synaptic bouton in response to Ca2+ influx
effect of methamphetamine on neurotransmitter
- Increases levels of noradrenaline, dopamine, serotonin.
- Stimulates fight, flight, fright response
- Stimulates reward centres, highly addictive
- Highly Neurotoxic
excitatory neurotransmitters function and examples
- cause depolarisation
- cause EPSPs
- Acetylcholine – at the nerve-muscle (somatic) and nerve-gland (autonomic) synapses, stimulus-gated Na+ channels
- Glutamate – at all excitatory synapses in the brain, stimulus-gated Na+ channels (and Ca2+ channels)
inhibitory neurotransmitters function and example
- cause hyperpolarisation
- cause IPSPs
- GABA – gamma amino butyric acid
diverging network description and functions
- Information from eg a single sensory organ may DIVERGE to arrive at different brain regions
- Provides opportunity to amplify signals as well as control points
converging network description and function
- Information from different brain regions may CONVERGE on a Single Motorneurone that excites a single muscle group
- Provides redundancy (in electronics) as well as control points
time frame of AP
concentration of K+ inside and outside cells
150mM inside and 4mM outside
