nervous transmission Flashcards
(Nerve Action Potentials)
action potentials
nerve impulses
(Nerve Action Potentials)
what requires a membrane potential
electrical charge differences across cell membrane
(like a battery)
(Nerve Action Potentials)
what is an ion channel
allows ions to move by diffusion
(Nerve Action Potentials)
what is the resting membrane potential?
70mv
(The Resting Membrane Potential)
what is the elements that can leak?
cytosol high in K+
interstitial fluid high in Na+
(sodium-potassium pumps)
(The Resting Membrane Potential)
what gets let through easily and what gets leaked poorly?
potassium can leak easy
sodium leaks poorly
(The Resting Membrane Potential)
what does RMP depend on?
relative leakage channel numbers
name some action potentials (AP)
series of active events
channels actively open and close
(active potential)
what is the required voltage threshold that is needed to reach
- 55 mv
(action potential)
what is the stimulus
any event bringing membrane to threshold
(action potential)
after the arrival of a stimulus
what is the depolarizing phase?
membrane potential rises and becomes positive
(action potential)
after the arrival of a stimulus
what is the repolarizing phase?
potential restored to resting value
may overshoot = hyperpolarizing phase
then recovery to rest
(action potential events)
what could happen if the stimulus is not strong enough to reach threshold
Na+ channels open
K+ channels then open
sodium/potassium pump
(action potential events)
what happens when the Na+ channel opens?
Na+ ions enter the cell from the extracellular fluid
depolarization (positive membrane potential)
(action potential events)
what happens when K+ channels open?
K+ leave the cell
repolarization (negative membrane potential)
(action potential events)
what happens with the sodium/potassium pump
restores original ion concentration
how can coffee effect nervous transmission
stimulant
lowering the threshold level of the nerve
increasing the possibility for a stimulant to result in a nerve potential
how can alcohol effect nerve transmission
acts as a depressant
increases threshold
decreases the possibility of a stimulus to result in a nerve action potential
how can local anaesthetics effect nerve transmission
generation of nerve action potentials can be prevented by local anaesthetics (novocaine, xylocaine)
these drugs prevent the opening of sodium-gated channels in the nerve cell membrane (pain messages are not carried from the site of injury back to the CNS)
what keeps the nerve impulses going in the right direction
refractory period
in terms of conduction of nerve impulses what is a unmyelinated fibre?
its the continuous conduction
what happens to nerve impulses with myelin
saltatory conduction
can only be triggered at nodes of Ranvier
what happens with synaptic transmission
triggered by voltage change of the action potential
what is the name for sending neuron?
presynaptic
what is the name of the receiving neuron?
postsynaptic
what does neurotransmitter mean?
a chemical that carries signal across the synaptic cleft
name the three presynaptic events
action potential arrives at the presynaptic end bulb
opens voltage-gated Ca+ channels
Neurotransmitter (NT) released into cleft
what happens when the voltage-gated Ca+ channels open?
Ca+ flows into the cell from synaptic cleft
increased Ca+ concentration in the presynaptic cell
exocytosis of synaptic vesicles
name the four postsynaptic events
NT binding at postsynaptic receptors
chemical trigger of ion channels
may depolarise or hyperpolarise postsynaptic cell membrane
if threshold reached at axon hillock
how does neurotransmitter get removed from synaptic transmission?
diffusion
destroyed by enzymes in cleft
transported back into the presynaptic cell
destroyed by neuroglia
(Neurotransmitters)
Acetylcholine (Ach)
common in PNS
may be stimulatory or inhibitory
(Neurotransmitters)
amino acids
glutamate
aspartate
gamma-aminobutyric acid (GABA)
glycine
(Neurotransmitters)
Modified amino acids
norepinephrine (NE), dopamine (DA), serotonin (5-HT)
(Neurotransmitters)
Neuropeptides
endorphins
name some chemicals that affect synaptic transmission
botulinum toxin
curare
nerve agents
what is botulinum toxin
inhibits the release of acetylcholine
inhibits muscle contraction (paralysis)
what is curare
competes for acetylcholine receptor sites on muscle cell
muscle relaxant (used in surgical procedures
what is nerve agents
inactivates acetylcholinesterase
leads to tetanus (paralysis)
