voltage is the measurement of potential energy generated by separate charges

​measured in millivolts (mv)

  resting membrane potential

vs 
presynaptic facilitation by serotonin 

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

  da da da daaaa.....action potentials!

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

in a
​nutshell...

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

graded potentials are localized, are proportional to the intensity of the stimulus and diminish as the distance from the site of stimulation increases. they may initiate a specific function in a cell such as triggering an gland cell to release its hormone via exocytosis.

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  

nodes are 1-2 mm apart 

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.

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

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

speaking of neuromodulation...
presynaptic inhibition by GABA

 current =
​a measurement of ions crossing the membrane 

neuropeptides

 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. 

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

                     adrenergic receptors                   

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. 

  changing the membrane 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

types of
​propagation

cholinergic synapses release acelylcholine

 equilibrium occurs when concentration gradient = electrical gradient

 nicotinic                         muscarinic  

other neurotransmitters and their functions 

neurotransmitter imbalances

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

the synapse

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.

 nicotinic vs muscarinic cholinergic receptors 

propagation of an action potential

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). 

gated ion channels can be:
1. ligand-gated channels
2. voltage-gated channels
3. mechanically-gated

the nerve  impulse

electrochemical gradients
​ determine
how an ion moves across a membrane.
there is a:
1. chemical gradient =  the difference in solute concentration across the membrane
2. electrical gradient = difference in charge across the membrane 

membrane potential = a gradient that causes ions to passively move in a one direction.
1. (+) ions are attracted to the (-) side of the membrane 
2. (-) ions are attracted to the (+) side of the membrane

    electrochemical gradients

think threshold

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

 amino acids 

 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)

a graded potential is a change in the membrane potential of a cell that remains localized. depolarization occurs in all directions from the site of where the stimulus was applied. 

axon diameter vs propagation speed

and back to
​resting potential...

neurotransmitter function: direct vs indirect effects

 sodium/potassium pumps are driven by the hydrolysis of ATP.

these pumps move sodium and potassium ions in opposite directions against their  concentration gradients to balance the movement of these ions in/out of the cell through their channels. One cycle pumps 3 sodium ions out of the cell and 2 potassium ions into the cell. 

   biogenic amines  

    but first...some background

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

      membrane potential

refractory
​ period

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

 K+ (potassium) is a positively charged ion. ​With an intracellular concentration of 120 mM and an extracellular concentration of 4 mM, it shows an equilibrium potential of -90 mV which means that K+ will reach electrochemical equilibrium when the cell is 90 mV lower than its environment.

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

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