1. a stimulus starts a rapid change in voltage. 

 2. depolarization is caused by a the opening of sodium channels causing an influx of Na+ ions.
threshold is reached.

 3. repolarization results from Na+ channel closing and a large efflux of K+ ions from activated K+ channels.

 4. hyperpolarization is caused by the efflux of potassium ions and closing of the potassium channels.

​ 5. the resting state is established when the membrane potential returns to the voltage before the stimulus. 

its all about the Na+ and K+ ions...

neurotransmitter function: direct vs indirect effects

the synapse

 current = a measurement of ions crossing the membrane. the resistance of the membrane slows down ion exchange which causes the  current to be weak. 

 nicotinic vs muscarinic cholinergic receptors 

a chemical synapse is a gap between two neurons where a nerve impulse is relayed 
chemically in the form of neurotransmitters. 
chemical synapses are found at junctions between two neurons and between neurons and non-neuronal cells such as muscles (neuromuscular junction) or glands (neuroglandular junction). 

​all nicotinic receptors are ionotropic (ligand-gated ion channels)
nicotinic receptors respond to drugs such as nicotine, an agonist. 

cholinergic synapses release acelylcholine

types of
​propagation

propagation of an action potential

temporal vs spatial summation
a single excitatory post synaptic potential (ESPS)  (0.5mv)won't provide enough stimulation to reach threshold generating an action potential but individual ESPSs can combine to reach threshold. This can occur 2 ways...

spatial summation = multiple presynaptic neurons release enough neurotransmitter to reach threshold
temporal summation = one presynaptic neuron releases neurotransmitter many times over a period of time to reach threshold

nicotinic receptors are found at cholinergic synapses in the CNS, at parasympathetic and sympathetic autonomic ganglia, and at the neuromuscular junction.

refractory
​ period

an ionotropic receptor is a membrane protein that responds to ligand binding by allowing ions to move across the membrane through an open ion channel.

speaking of neuromodulation...
presynaptic inhibition by GABA

cholinergic synapses are the most common, found at:
NMJ
CNS synapses
PNS neuron/neuron synapses
NMJ/NGJ in ANS parasympathetic division

neurotransmitter imbalances

muscarinic receptors are metabotropic
(g-protein coupled receptors)
which trigger a series of intracellular events using second messengers. 

   biogenic amines  

nodes are 1-2 mm apart 

axon diameter vs propagation speed

 amino acids 

 nicotinic                         muscarinic  

 the adrenal medulla is the core of the adrenal gland. it participates in the flight or fight response by secreting epinephrine (adrenaline) and norepinephrine (noradrenaline)

the nerve  impulse

 current =
​a measurement of ions crossing the membrane 

other neurotransmitters and their functions 

cell membrane potential relies on:
1. the ECF and ICF have different composition of ions
ECF has high Na+ and Cl-
ICF has high K+ and negatively charged proteins
2. plasma membranes are selectively permeable
ions must move across via ion channels

some channels are more "accessible" than others
ex: outgoing K+ channels are "leakier" than incoming Na+ channels
proteins can not cross the membrane which contributes to cell's (-) charge  

saltatory 
​propagation along a myelinated axon travels 18-120 m/sec
(40-270 mph)

speeds:
type A - 120 m/sec
type B - 40 m/sec
type C - 1 m/sec  

adrenergic receptors (adrenoceptors) are metabotropic. they bind catecholamines such as
norepinephrine/noradrenaline and
epinephrine/adrenaline. 

and back to
​resting potential...

electrical synapses are 
electrical and mechanical connections between two neurons ​found at a gap junction. 
An electrical synapse has channel proteins between pre/postsynaptic neurons connecting the two neurons so the electrical signal can travel straight over the synapse.

muscarinic receptors are found at cholinergic synapses in the CNS and at postganglionic parasympathetic nerve terminals. 

neuropeptides

excitatory neurotransmitters initiate a post synaptic action potential by causing depolarization of the post synaptic cell producing an
EPSP = excitatory postsynaptic potential.
inhibitory neurotransmitters cause the post synaptic cell to hyperpolarize therefore suppressing an action potential producing an
IPSP = inhibitory post synaptic potential.
remember...
it is NOT the neurotransmitter that determines how the post synaptic cell will respond but rather the post synaptic receptor of that neurotransmitter. 

vs 
presynaptic facilitation by serotonin 

continu0us
​propagation along
an unmyelinated axon travels
​1 meter/sec (2 mph)

voltage is the measurement of potential energy generated by separate charges

​measured in millivolts (mv)

when a cell is at its resting potential of -70mv, it is said to be polarized.

a shift to this resting potential towards a less - potential by the movement of Na+ ions into the cell = depolarization

restoring the normal resting potential after depolarization is called 

​repolarization

an increase in the negativity of the resting potential = hyperpolarization

think threshold

in a
​nutshell...

                     adrenergic receptors