Physiology notes
Saltatory conduction in axons
Myelinisation makes the action potentials jump from one node of Ranvier
to another (skips the myelin sheath). Only the nods have Na+ channels.
Demyelinating diseases reduce or block conduction when current leaks out
of the previously insulated regions between the nodes.
Modulation of cell excitability: hypo- and hyperkalemia
Nernst equation is for each ion, such as potassium.
Normokalemia: subthreshold graded potential does not fire an action
potential.
A suprathreshold stimulus will fire an action potential.
Hyperkalemia (depolarizes cell): increased blood K+ concentration,
brings membrane closer to threshold. Stimulus that would normally be
subthreshold can trigger an action potential now. Resting membrane
potential: -70 -65. kidney disfunction
Hypokalamia (hyperpolarizes cell): decreased blood K+ concentration,
hyperpolarizes the membrane and makes the neuron less likely to fire an
action potential (with a stimulus normally above threshold). Resting
membrane potential: -70 -80. excessive sweating
Nernst equation
Communication in the nervous system
Presynaptic terminal to postsynaptic cell membrane majority: chemical
synapses neurocrine molecules secreted (Gaba, NE, glutamate) act
on neurocrine receptors.
Neurotransmitter release: action potential depolarizes axon terminal
calcium channels open calcium triggers exocytosis of synaptic vesicle
contents neurotransmitter diffuses across the synaptic cleft and binds
with receptors.
Neurotransmitter termination: neurotransmitters can be returned to
axon terminals or transported into glial cells enzymes inactivate
neurotransmitters can diffuse out of synaptic cleft.
Strength of stimulus
Higher stimulus more neurotransmitters released.
Modulation of synaptic signalling
Multiple axon terminals on neuron. The summation of several subthreshold
signals results in an action potential. Synaptic inhibition:
Global inhibition: all targets inhibited equally. Excitatory and
inhibitory presynaptic neurons fire summed signals are below
threshold no action potential initiated. No response occurs in any
target cell.
Local inhibition (at terminal): an inhibitory neuron synapses on one
of the presynaptic neurons and selectively inhibits one target.
Excitatory neuron fires action potential generated inhibitory
neuron fires, blocking neurotransmitters release at one synapse.
Saltatory conduction in axons
Myelinisation makes the action potentials jump from one node of Ranvier
to another (skips the myelin sheath). Only the nods have Na+ channels.
Demyelinating diseases reduce or block conduction when current leaks out
of the previously insulated regions between the nodes.
Modulation of cell excitability: hypo- and hyperkalemia
Nernst equation is for each ion, such as potassium.
Normokalemia: subthreshold graded potential does not fire an action
potential.
A suprathreshold stimulus will fire an action potential.
Hyperkalemia (depolarizes cell): increased blood K+ concentration,
brings membrane closer to threshold. Stimulus that would normally be
subthreshold can trigger an action potential now. Resting membrane
potential: -70 -65. kidney disfunction
Hypokalamia (hyperpolarizes cell): decreased blood K+ concentration,
hyperpolarizes the membrane and makes the neuron less likely to fire an
action potential (with a stimulus normally above threshold). Resting
membrane potential: -70 -80. excessive sweating
Nernst equation
Communication in the nervous system
Presynaptic terminal to postsynaptic cell membrane majority: chemical
synapses neurocrine molecules secreted (Gaba, NE, glutamate) act
on neurocrine receptors.
Neurotransmitter release: action potential depolarizes axon terminal
calcium channels open calcium triggers exocytosis of synaptic vesicle
contents neurotransmitter diffuses across the synaptic cleft and binds
with receptors.
Neurotransmitter termination: neurotransmitters can be returned to
axon terminals or transported into glial cells enzymes inactivate
neurotransmitters can diffuse out of synaptic cleft.
Strength of stimulus
Higher stimulus more neurotransmitters released.
Modulation of synaptic signalling
Multiple axon terminals on neuron. The summation of several subthreshold
signals results in an action potential. Synaptic inhibition:
Global inhibition: all targets inhibited equally. Excitatory and
inhibitory presynaptic neurons fire summed signals are below
threshold no action potential initiated. No response occurs in any
target cell.
Local inhibition (at terminal): an inhibitory neuron synapses on one
of the presynaptic neurons and selectively inhibits one target.
Excitatory neuron fires action potential generated inhibitory
neuron fires, blocking neurotransmitters release at one synapse.
