excitable cells Flashcards
what determines the condition velocity
- degree of myelination
- axon diameter
- temperature
dendrites
receive an input
axon
transfer input
output zone
release neurotransmitters
what determines the membrane potential
- concentration of ions, at rest more na+ outside and more K+ inside
- permeability of membrane
- activity of the pumps
what is the neurone resting potential
-30mV to -90mV
resting potential
- K+ leaks out of K+ channels
- Na+ leaks in at the same time
- this charge will reach equilibrium and stop movement
- membrane is more permeable to K+ so move positive goes out
- Na+/K+ pump maintain gradient, 3Na+ out for 2K+ in
graded potential
- there is a stimulus to the membrane
- dissipates through the neurone
- it does not have the capacity to reach threshold to trigger an action potential
- spreads by passive current flow
- are dependent on strength and duration of trigger event
action potential
- continues to be generated down the axon
- Na+ channels open so sodium comes in making it more positive
- once threshold is reaches sodium gates close
- potassium channels then open so potassium moves out
- leads to repolarisation
stages of action potential
depolarisation > repolarisation> hyperpolarisation
what is the purpose of the refractory period
- so action potential is propagated in one direction
- inactivation gates can’t be opened by another stimulus
- activation gates once blocked can be opened by another stimulus
types of refractory periods
- absolute refractory period
- relative refractory period
synaptic transmission stages
- action potential down axon reaches axon terminal
- depolarises the presynaptic terminal
- opens voltage gated calcium channels
- signals neurotransmitter vesicles
- vesicles move to down membrane
- released via exocytosis
- attach at the post synaptic membrane
- neurotransmitter removed
what happens to the calcium channels when neurotransmitters are released
- voltage dependent calcium channels open
- influx aids the formation of the docking complex’s
what happens at the neuromuscular junction
- calcium comes in
- neurotransmitter released
- binds to receptor
- neurotransmitter is always Ach
- causes potential
- triggers release of calcium from cytoplasmic reticulum
- neurotransmitter eliminated in the synaptic cleft
excitary event
opens sodium channels, increase membrane potential
- depolarising post synaptic potential
inhibitory event
opens chloride channels or opens potassium channels
- hyperpolarising post synaptic potential
spatial summation
potentials from different dendrites receiving different potentials at the same time
temporal summation
receive signals close together in time (only 1)
excitatory synapses
- promote action potential
- open sodium channels
- close the chloride and potassium channel
- upregulate number of receptors on post synaptic membrane
inhibitory synapses
- opening of chloride ion channels
- opening potassium channels
- close of sodium channels
- activation of receptor enzymes
is acetylcholine excitatory or inhibitory
- can be both excitatory and inhibitory
- excitatory in skeletal muscles
- inhibitory in heart
- depends on the receptors
how does an action potential start
- exitatory post synaptic potential rises high enough
- begins where the initial segment of axon where the axon leave the neuronalsome
how do neurotransmitters work
- synthesis and stored in the neurone
- released from the presynaptic ending of the neurone in response to stimulus
- binding and recognition when neurotransmitter bind to post synaptic target cells
